Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 01 Jun 2017, at 02:26, Bruce Kellett wrote:


On 1/06/2017 4:43 am, Bruno Marchal wrote:

On 31 May 2017, at 04:01, Bruce Kellett wrote:

On 30/05/2017 9:35 pm, Bruno Marchal wrote:

On 30 May 2017, at 11:28, Telmo Menezes wrote:


I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What  
does
mind supervene on? Perhaps it is true that every single coupling  
with

the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that  
such
certainties come from a strong belief in emergentism (which I  
cannot

disprove, but find problematic).


It is impossible to recohere the past, FAPP.

But only FAPP. To make the blue T-rex interfereing with the red-T- 
rex, we must erase the trace of particle interaction between the  
T-rex in its whole light-cone, and this without forgetting the  
particles "swallowed" by the black-holes, etc. It is just  
completely impossible, but to derive from that the unicity of the  
past, is, it seems to me (and you if I understood well) is invalid.


I think the recoherence of paths that have completely decohered is  
more than just FAPP impossible, I think it is impossible in  
principle. One major problem with recoherence in general is that  
information leaks from the paths at the speed of light (as well as  
less slowly for other interactions). Since this vital information  
goes out along the light cone, it can never be recaptured and  
returned to the original interaction.


In QM + special relativity OK. (note that to me QM + special  
relativity => no collapse (and even the Many dreams, but we have  
agreed to disagree on this if I remember well).


Reasoning in QM without SR is not very profitable. Besides, QM + SR  
does not particularly imply MWI -- it is perfectly possible to have  
a consistent collapse model of QM+SR. I know you don't agree because  
of the non-locality implied by EPR, but this non-locality is not  
removed in MWI, regardless of what you might say.


I don't see it, and the mast time we discuss this, we conclude on some  
vocabulary problem. When there is no collapse, measurement tells to  
people light separated in which branch theiy belongs, but to exploits  
that information, they need to come into contact.







Consequently, indispensable phase information is lost *in  
principle*, so the recoherence is, in general, impossible.


OK. (I was reasoning in naive classical QM)

Of course, with carefully constructed systems, where the loss of  
information along the light cone is prevented, recoherence is  
possible in special circumstances, but not in general.


From this, the uniqueness of the past of any decoherent history is  
assured. So deriving the unicity (if I understand this use of the  
word) is by no means invalid -- it is proved.


In QM + SR. OK.

Even if one encounters one of those rare situations in which  
recoherence is achieved, that still does not invalidate the  
uniqueness of the past history -- recoherence, if it occurs,  
simply means that no new branches are formed at that point, so the  
decoherent history remains unique.


OK. That might suggest that we identify our indistinguishible past  
in arithmetic, if we assume mechanism. I use the Y = II principle,  
or the "quantum" linearity of the tensor product "@": we have that   
a @ (b + c) = (a @ b) + (a @ c).


That makes sense.


Linearity is the heart of QM. It is linearity that allows  
superpositions, and leads to all the "quantum weirdness".


I agree. Both "linearities" (the quantum evolution, and the tensor  
products).









FWIW, you
are expressing my own understanding of the situation: there can  
be no
superposition of red and green screens or dinosaurs, or dead  
and live cats,
because there can be no quantum superposition of macroscopic  
objects.
Superpositions of wave functions are only possible for systems  
isolated from
interaction with their environment, which is why quantum  
computers are so
fricking hard to make: keeping aggregates of particles isolated  
from
interactions with the surrounding environment is exponentially  
more

difficult as the system grows in size.


The main question for me is this: can two branches hold different
observer states, if they differ only by things that are not
observable?


I would say no, intuitively. I would even say "no" just for the  
things not observed, even when observable.


I previously answered Telmo's question in the affirmative, viz.,  
two fully decohered branches will hold different observer states,  
even if the differences are not observed or observable. So if some  
trivial physical event happens to your body, such as the decay of  
a K 40 nucleus in your foot, this would not be noticeable, or even  
particularly observable even if you were looking for it. But such  
an event causes at least two branches to form every instant -- one  
in which the decay has occurred, and one in which it has

Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 31 May 2017, at 20:21, David Nyman wrote:




On 31 May 2017 18:39, "Bruno Marchal"  wrote:

On 30 May 2017, at 17:00, David Nyman wrote:




On 30 May 2017 at 14:48, Bruno Marchal  wrote:

On 30 May 2017, at 14:10, Telmo Menezes wrote:

On Tue, May 30, 2017 at 1:35 PM, Bruno Marchal   
wrote:






Right, I agree with you and Pierz on this. My point was more on what
you address below.


What if the substitution level turns out to be at a higher level than
quantum? E.g. at the level of the neurons and their connections and
activations levels?

That would enlarge the uncertainty spectrum on the realities we can  
access without losing anything subjective.


​A point against, I assume.


Not sure. Perhaps.






​
It would help the doctor to build the artificial brain.

​A point in favour.


Yes. Modulo it helps also the charlatans, the hackers, etc. But  
that's part of the price. In the long run, 99% of the treatment of  
information might consist in cryptography. Some amount of first  
person privacy is needed to get consistent extensions.






​
It could also make more difficult to justify the smallness of  
Planck constant, and to explain why the quantum seems more  
obviously present in the micro-states,


​Against?



Problematical for the Mechanist.

I would favor the identification of the substitution level with the  
lower classical physical state up to the "quantum isolation".  I  
think this could be proved. It is the level of the molecules, and  
their most probable histories.  The quantum fuzziness is how our  
self-description relatively to the more proable histories appears  
for the average Löbian number.






​
Decoherence would be easier to fight against,

​OK
​
and quantum computing would be more easy to be realized.

​How, if the substitution is above the quantum boundary?


Then physics is deflected from the mechanist self-reference. Put it  
bluntly: computationalism is refuted or we are in a malevolent  
Bostromian simulation (or other number conspiracies. May be, if the  
Riemann hypothesis is false, ...


Of course, it can depend to what you consider to need to survive.  
The level of substitution is defined, not for the survival, but for  
the perfect survival. Above that level, you will continue to  
survive, but
-either you will be aware of a defect, from a permanent headache to  
anything you can imagine, or not.

- Or there will be a defect (observable by a third person, or not).

Exemple: the first classical teleported human, who said after the  
experience : "it is a total success,  it is a total success,  it is  
a total success,  it is a total success,  it is a total success,  it  
is a total success,  it is a total success,  it is a total success,   
it is a total success,  it is a total success,  it is a total  
success,  it is a total success,  it is a total success,  it is a  
total success,  it is a total success,  it is a total success,  ...


And continue to say so in an asylum. Did he survived?

Above the level, you lost things. Obviously, with a digital  
*electronical* neural net, you would lost the experience of  
cannabis, alcohol, salvia, tobacco, until you find the apps on the  
net, emulating the chemical level information. Neurology is  
fundamentals, including the swarm neural play, but each neuron is a  
complex chemical factory, and cells communicates mainly by  
molecules, even when they get the cable (neurons).






​
This ​makes me think that the quantum level is boundary of the  
substitution level.


​I don't follow all of the above. Do you mean a boundary above  
which, or below which, a plausible substitution might be made?


By high level, I mean a vulgar approximation of the brain/body could  
be made, with few mega on the disk.


By low level, I mean an ultra-precise description of a big  
generalized brain, like the brain + a part of the environment  
described by the quantum superstring with 10^100 decimals. You will  
need a big disk.


Normally the relative substitution level determine the boundaries  
between the classical boolean mind and the quantum observable.


But with QM without collapse, the level is not a question of micro/ 
macro, but of independence between computations, in sense which can  
be described by using the modal logics.


In the math part, the level is in the choice of the box, the  
beweisbar provability predicate. The theology is invariant for all  
the sound (mechanical, or weakenings) extensions. But no machines  
can rationally justifies any substitution level, and it is a bit  
like a private matter.


If the brain exploits the quantum weirdness, it means that we can  
extracts information from the statistical measure on all  
computations below our substitution. That possibility is independent  
of the level, and the whole of the apparent matter exploits this,  
and should entirely emerge from this ...


Here I agree with Bohr, if you define the Macroscopic by the Boolean  
laws of thought level, where th

Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 1/06/2017 8:21 pm, Bruno Marchal wrote:

On 31 May 2017, at 09:15, Bruce Kellett wrote:

On 31/05/2017 4:40 pm, Pierz wrote:


>> On 5/30/2017 7:30 PM, Pierz wrote:
>>> Thanks for these clarifications Bruce. I find your
explanations to be very lucid and helpful - they also confirm my
own understanding. IIRC, you weren't a particular fan of MWI
when I last conversed with you on this list. I wonder if you'd
care to comment on my original argument on this thread - which
has of course now been swamped by the usual brawls. Does not a
single history + the physical insignificance of the notion of a
current moment mean that there is also only a single possible
future?
>> I don't see how that follows.  In the usual model of forking
in the future direction every current moment has a single
history, but multiple futures.


Multiple futures = MWI, surely.


Not necessarily. If you insist on Schrödinger determinism, then yes, 
by reification of the wave function. But if the wave function is only 
epistemological, then there is only one probabilistic future.


How could an epistemological wave interfere all by itself? It seems 
simpler to say that the wave is real, but that the local, one branch, 
perception is epistemological.


I think you misunderstand this use of the word "epistemological". When 
it is said that the wave function is merely epistemological, what is 
meant that it is merely a calculational device: the wave function 
encapsulates our knowledge of the system of interest, and tells us how 
to calculate the probabilities of various outcomes. In other words, it 
is not a 'real' wave in space-time.



When I say a single history, I mean that from the Big Bang forward, 
the universe only followed one branch.


And that can lead into the future, only one probabilistic future.


>>
>>> And if the future is predetermined in this way, isn't this a
serious issue for single universe models of QM? How can the
outcome of quantum events be both inevitable and random?
>> Having a single future isn't the same as being determined.  A
single future in which situation A is sometimes followed by B
and sometimes by C is still random.


It depends on perspective. It's true that from 1p, it looks random. 
But from 3p, it is static and always the same, and in this sense 
determined.


Not true, the 3p view of the future is still just a single 
probabilistic world line. It is only the bird view, from outside 
space and time, that gives the appearance that there are multiply 
existing futures. Neither we from the 1p perspective, or from outside 
ourselves in the 3p perspective, can we ever see any of the other 
branches predicted by MWI.


Yes, like in WM-duplication.


No, that is a serious mistake. Unitary evolution of the wave function is 
not at all like the person duplication experiments. The main difference 
is that the duplicates of the Helsinki man are never in a pure quantum 
state. The teleportation to W or M is of separate classical entities, 
There is no superposition principle for duplicated persons.


The guy in Helsinki can predict that his first person future will be 
unique, even if he knows that in the "bird" picture, that outside the 
teleportation/duplication boxes, there will be two versions of him.


That is not the "bird" picture, that is merely the objective 3p picture 
of the ordinary classical world. The bird picture is solely to do with 
the pure state that is preserved in the unitary evolution pure state of 
the wave function.


This is where the problems with MWI really show up. When you have a 
quantum event with, say, two possible outcomes with equal probabilities, 
such as measuring the polarization of an unpolarized photon, the initial 
probability is 0.5 for each polarization. But after the measurement, the 
probability for the observed result (horizontal or transverse as 
observed) is unity -- because the result has been observed, it is now 
certain. So how did the probability suddenly change from 0.5 to 1.0?


In the classical case, such as the duplicates of the H-man going to W or 
W, there is no problem. The system is already in a mixed state, so the 
change in probability is simply the result of getting additional 
information. Just as in the toss of the fair coin, heads and tails are 
equally likely, but the jump of the probability for 0.5 to 1.0 on 
observing the result is purely a classical epistemological effect. This 
is not true for the quantum pure state. In order for the change in 
probability to be understood epistemologically, the pure state has to be 
reduced to a mixed state (a process that is not necessary in the 
classical examples). In quantum mechanics, this change is brought about 
by the unitary processes of decoherence, and the non-unitary trace over 
the environmental degrees of freedom. This is an essential difference 
between classical and quantum physics, and the necessity for this 
no

Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 31 May 2017, at 09:15, Bruce Kellett wrote:


On 31/05/2017 4:40 pm, Pierz wrote:

On Wednesday, May 31, 2017 at 3:28:18 PM UTC+10, Brent wrote:
Sorry.  Something funny with my verizon account.

Brent

On 5/30/2017 8:09 PM, Pierz Newton-John wrote:
> Brent, are you replying from a mobile? I’m still receiving your  
replies, as others are, on my private email. That’s what happens to  
me when I try to reply using my iPhone. The "reply to all" button  
is missing. I’ll reply to your remarks on the list if you post it  
there...

>
>
>> On 31 May 2017, at 1:05 pm, Brent Meeker   
wrote:

>>
>>
>>
>> On 5/30/2017 7:30 PM, Pierz wrote:
>>> Thanks for these clarifications Bruce. I find your explanations  
to be very lucid and helpful - they also confirm my own  
understanding. IIRC, you weren't a particular fan of MWI when I  
last conversed with you on this list. I wonder if you'd care to  
comment on my original argument on this thread - which has of  
course now been swamped by the usual brawls. Does not a single  
history + the physical insignificance of the notion of a current  
moment mean that there is also only a single possible future?
>> I don't see how that follows.  In the usual model of forking in  
the future direction every current moment has a single history, but  
multiple futures.


Multiple futures = MWI, surely.


Not necessarily. If you insist on Schrödinger determinism, then yes,  
by reification of the wave function. But if the wave function is  
only epistemological, then there is only one probabilistic future.


How could an epistemological wave interfere all by itself? It seems  
simpler to say that the wave is real, but that the local, one branch,  
perception is epistemological.






When I say a single history, I mean that from the Big Bang forward,  
the universe only followed one branch.


And that can lead into the future, only one probabilistic future.


>>
>>> And if the future is predetermined in this way, isn't this a  
serious issue for single universe models of QM? How can the outcome  
of quantum events be both inevitable and random?
>> Having a single future isn't the same as being determined.  A  
single future in which situation A is sometimes followed by B and  
sometimes by C is still random.


It depends on perspective. It's true that from 1p, it looks random.  
But from 3p, it is static and always the same, and in this sense  
determined.


Not true, the 3p view of the future is still just a single  
probabilistic world line. It is only the bird view, from outside  
space and time, that gives the appearance that there are multiply  
existing futures. Neither we from the 1p perspective, or from  
outside ourselves in the 3p perspective, can we ever see any of the  
other branches predicted by MWI.


Yes, like in WM-duplication. The guy in Helsinki can predict that his  
first person future will be unique, even if he knows that in the  
"bird" picture, that outside the teleportation/duplication boxes,  
there will be two versions of him.






The question is, what determined (from the 3p view) that the  
universe followed that particular path and not any of the others?


Why do you reject out of hand that the universe might be  
probabilistic?  It is possible 'nothing' determined which path from  
the possibilities was actually followed. All that is known are the  
probabilities for each path. We do not know that the other paths are  
followed, either 1p or 3p.


In QM, we do have evidences that many path are taken all together. if  
only the two slits.



Bruno




My assumption here is that "now" does not exist from the 3p POV and  
therefore the physical structure (whether it branches or not) of  
the past and the future is the same.


That can certainly be the case, whether there are existing  
alternative branches or not.


Bruce

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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 1/06/2017 6:28 am, David Nyman wrote:
On 31 May 2017 at 04:55, Bruce Kellett > wrote:


On 31/05/2017 12:30 pm, Pierz wrote:

Thanks for these clarifications Bruce. I find your explanations
to be very lucid and helpful - they also confirm my own
understanding.


Thank you for the kind comments, I try my best to be clear.


IIRC, you weren't a particular fan of MWI when I last conversed
with you on this list.


That is indeed the case. I have several reasons to be dubious
about MWI. Firstly, it amounts to reifying a complex valued
function that resides in configuration space -- I am not sure that
this is a well-defined procedure. Secondly, MWI doesn't really do
what it claims to do, which is to provide a resolution of the
measurement problem in QM. MWI doesn't provide any explanation of
the transition from a pure state to the mixed state that is
required for experiments to give definite results. At the crucial
point, MWI simply says "then a miracle happens!" To be more
explicit, deterministic evolution of the wave function by the
Schrödinger equation gives a full account of decoherence, and the
dissemination of the coherence phases into the environment. This
reduces the off-diagonal elements of the density matrix so that
the diagonal elements become *almost* orthogonal, but unitary
evolution can't go the whole way. The only way one can reduce the
pure state to a mixture is to trace over the environmental degrees
of freedom, which is to say that the residual phase information is
simply thrown away. This trace operation is non-unitary, and there
is no warrant for it in the SE itself, so it is, in the final
analysis, just an appeal to magic.


Bruce, is it perhaps finally an appeal to observation per se? IOW what 
you say is of course objectively the case, but perhaps in some way the 
​residual phase information isn't relevant (i.e. can be 'traced over') 
in the synthesis of the 'observer-observation' relation. If so, this 
relation could perhaps resolve the 'eternalist' pure state (which 
after all continues simply to be 'there' in the MWI conception) 
subjectively into what would give the 'instrumental' appearance, in 
effect, of the probability density characteristic of a mixture?


It is often argued that the density matrix is diagonalized FAPP, and 
FAPP is all that is required. Unfortunately, I don't think that that 
really works. Even though the individual off-diagonal elements might be 
arbitrarily small, there are a very large number of them (increasing as 
further environmental degrees of freedom are included). The end result 
is that the original superposition is still intact and no 'split' has in 
fact occurred -- the situation is still completely reversible. The 
problem I point to is that there is nothing in the unitary mathematics 
corresponding to "ignoring inessential degrees of freedom". That is what 
the partial trace does, but that has to be imposed by hand, it is not 
automatic, and suffers from all the old difficulties of the Heisenberg 
cut -- it is arbitrary.


Then there wouldn't seem to me to be a necessary idea of 'collapse' 
involved, except in a purely epistemological sense. The term 
'subjective' here is more in the sense of some fundamental 
compositional principle of observer-hood than a restriction to 
out-and-out 'waking consciousness'. I'm not sure if this has any 
necessary connection  to Lockwood's idea of a 'consciousness basis'. 
Of course quite clearly any of this would be highly speculative, but 
I'm wondering if it could make any sense in principle? I'd value your 
opinion.


I think that something like this was what Everett had in mind when 
called this idea the "relative state model". I think he saw the observer 
as complete in every branch, so that


 |psi> = (|1> + \2>)|me>|environment> --> (|1>|me_1> + 
|2>|me_2>)|environment>

  --> |1>|me_1>|environment_1> + |2>|me_2>|environment_2>

and he then considered the two parts of the development to be complete 
in themselves, so we found ourselves in one or the other branch. Everett 
had no particular commitment to the existence of the other branches -- 
it was DeWitt who developed the idea of many worlds. The trouble here, 
as is well known, is that the above is still a pure state, and we 
require a reduction to a mixed state in order to be able to consider one 
or other branch on its own. The 'collapse' can be regarded as 
epistemological, but we will still need the mixed state.




Thirdly, the non-observed branches in MWI play no essential role
in the theory, so Occam would say that they are inessential
entities that should be discarded. If one is simply going to
discard them, and they play no observable role, why invoke these
other branches in the first place?


I wonder if you'd care to comment on my original argument on this

Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 1/06/2017 4:43 am, Bruno Marchal wrote:

On 31 May 2017, at 04:01, Bruce Kellett wrote:

On 30/05/2017 9:35 pm, Bruno Marchal wrote:

On 30 May 2017, at 11:28, Telmo Menezes wrote:


I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What does
mind supervene on? Perhaps it is true that every single coupling with
the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that such
certainties come from a strong belief in emergentism (which I cannot
disprove, but find problematic).


It is impossible to recohere the past, FAPP.

But only FAPP. To make the blue T-rex interfereing with the 
red-T-rex, we must erase the trace of particle interaction between 
the T-rex in its whole light-cone, and this without forgetting the 
particles "swallowed" by the black-holes, etc. It is just completely 
impossible, but to derive from that the unicity of the past, is, it 
seems to me (and you if I understood well) is invalid.


I think the recoherence of paths that have completely decohered is 
more than just FAPP impossible, I think it is impossible in 
principle. One major problem with recoherence in general is that 
information leaks from the paths at the speed of light (as well as 
less slowly for other interactions). Since this vital information 
goes out along the light cone, it can never be recaptured and 
returned to the original interaction.


In QM + special relativity OK. (note that to me QM + special 
relativity => no collapse (and even the Many dreams, but we have 
agreed to disagree on this if I remember well).


Reasoning in QM without SR is not very profitable. Besides, QM + SR does 
not particularly imply MWI -- it is perfectly possible to have a 
consistent collapse model of QM+SR. I know you don't agree because of 
the non-locality implied by EPR, but this non-locality is not removed in 
MWI, regardless of what you might say.


Consequently, indispensable phase information is lost *in principle*, 
so the recoherence is, in general, impossible.


OK. (I was reasoning in naive classical QM)

Of course, with carefully constructed systems, where the loss of 
information along the light cone is prevented, recoherence is 
possible in special circumstances, but not in general.


From this, the uniqueness of the past of any decoherent history is 
assured. So deriving the unicity (if I understand this use of the 
word) is by no means invalid -- it is proved.


In QM + SR. OK.

Even if one encounters one of those rare situations in which 
recoherence is achieved, that still does not invalidate the 
uniqueness of the past history -- recoherence, if it occurs, simply 
means that no new branches are formed at that point, so the 
decoherent history remains unique.


OK. That might suggest that we identify our indistinguishible past in 
arithmetic, if we assume mechanism. I use the Y = II principle, or the 
"quantum" linearity of the tensor product "@": we have that  a @ (b + 
c) = (a @ b) + (a @ c).


That makes sense.


Linearity is the heart of QM. It is linearity that allows 
superpositions, and leads to all the "quantum weirdness".





FWIW, you
are expressing my own understanding of the situation: there can be no
superposition of red and green screens or dinosaurs, or dead and 
live cats,

because there can be no quantum superposition of macroscopic objects.
Superpositions of wave functions are only possible for systems 
isolated from
interaction with their environment, which is why quantum computers 
are so

fricking hard to make: keeping aggregates of particles isolated from
interactions with the surrounding environment is exponentially more
difficult as the system grows in size.


The main question for me is this: can two branches hold different
observer states, if they differ only by things that are not
observable?


I would say no, intuitively. I would even say "no" just for the 
things not observed, even when observable.


I previously answered Telmo's question in the affirmative, viz., two 
fully decohered branches will hold different observer states, even if 
the differences are not observed or observable. So if some trivial 
physical event happens to your body, such as the decay of a K 40 
nucleus in your foot, this would not be noticeable, or even 
particularly observable even if you were looking for it. But such an 
event causes at least two branches to form every instant -- one in 
which the decay has occurred, and one in which it has not. And since 
this is a beta decay, a neutrino is lost along the light cone in 
every case of decay. Perfect recombination of the branches is, then, 
according to the above argument, not possible. You might object that 
this decay in my toe did not alter my conscious state -- that is 
correct, but there are now two copies of the Moscow man as in step 3,


My mistake here - I misremembered step 3.  Moscow is a target, not the 
origin. I should have said two co

Re: A thought on MWI and its alternative(s)

[David Nyman]

On 31 May 2017 at 04:55, Bruce Kellett  wrote:

> On 31/05/2017 12:30 pm, Pierz wrote:
>
> Thanks for these clarifications Bruce. I find your explanations to be very
> lucid and helpful - they also confirm my own understanding.
>
>
> Thank you for the kind comments, I try my best to be clear.
>
> IIRC, you weren't a particular fan of MWI when I last conversed with you
> on this list.
>
>
> That is indeed the case. I have several reasons to be dubious about MWI.
> Firstly, it amounts to reifying a complex valued function that resides in
> configuration space -- I am not sure that this is a well-defined procedure.
> Secondly, MWI doesn't really do what it claims to do, which is to provide a
> resolution of the measurement problem in QM. MWI doesn't provide any
> explanation of the transition from a pure state to the mixed state that is
> required for experiments to give definite results. At the crucial point,
> MWI simply says "then a miracle happens!" To be more explicit,
> deterministic evolution of the wave function by the Schrödinger equation
> gives a full account of decoherence, and the dissemination of the coherence
> phases into the environment. This reduces the off-diagonal elements of the
> density matrix so that the diagonal elements become *almost* orthogonal,
> but unitary evolution can't go the whole way. The only way one can reduce
> the pure state to a mixture is to trace over the environmental degrees of
> freedom, which is to say that the residual phase information is simply
> thrown away. This trace operation is non-unitary, and there is no warrant
> for it in the SE itself, so it is, in the final analysis, just an appeal to
> magic.
>

Bruce, is it perhaps finally an appeal to observation per se? IOW what you
say is of course objectively the case, but perhaps in some way the
​residual phase information isn't relevant (i.e. can be 'traced over') in
the synthesis of the 'observer-observation' relation. If so, this relation
could perhaps resolve the 'eternalist' pure state (which after all
continues simply to be 'there' in the MWI conception) subjectively into
what would give the 'instrumental' appearance, in effect, of the
probability density characteristic of a mixture? Then there wouldn't seem
to me to be a necessary idea of 'collapse' involved, except in a purely
epistemological sense. The term 'subjective' here is more in the sense of
some fundamental compositional principle of observer-hood than a
restriction to out-and-out 'waking consciousness'. I'm not sure if this has
any necessary connection  to Lockwood's idea of a 'consciousness basis'. Of
course quite clearly any of this would be highly speculative, but I'm
wondering if it could make any sense in principle? I'd value your opinion.


Thirdly, the non-observed branches in MWI play no essential role in the
> theory, so Occam would say that they are inessential entities that should
> be discarded. If one is simply going to discard them, and they play no
> observable role, why invoke these other branches in the first place?
>
> I wonder if you'd care to comment on my original argument on this thread -
> which has of course now been swamped by the usual brawls. Does not a single
> history + the physical insignificance of the notion of a current moment
> mean that there is also only a single possible future?
>
>
> We will only experience a single future, but what that future is, is
> indeterminate at the present instant.
>
> And if the future is predetermined in this way, isn't this a serious issue
> for single universe models of QM? How can the outcome of quantum events be
> both inevitable and random?
>
>
> I don't see that there is only a single possible future. The block
> universe notion only requires indeterminate time ordering for spacelike
> separated events. The future along and inside one's future light cone is in
> the future for all observers, so need not be determined by some other
> observer having already seen what happens. The block universe only
> constrains the future only in very limited sense -- it is only for
> spacelike separations that simultaneity is ambiguous, timelike separations
> are not so constrained.
>
> Quantum non-locality is another matter, however, and there are growing
> indications that quantum entanglement and the associated non-locality might
> prove to be of fundamental significance for physics -- such as the
> possibility that space-time itself might emerge from quantum entanglements.
>

​Yes, I'm reading Wallace's Emergent Multiverse at the moment on this
topic, amongst others. ​Here's some rank speculation in the MWI vein from
the observational perspective: Let's say that entanglement does indeed turn
out to be very fundamental in the genesis of what we call 'worlds' in the
first place. Mightn't it then be the case that observers - who themselves
by assumption supervene on a very narrowly-constrained physics - thereby
can't help but find themselves observing the equally tightly-constrained
co

Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 31 May 2017, at 04:01, Bruce Kellett wrote:


On 30/05/2017 9:35 pm, Bruno Marchal wrote:

On 30 May 2017, at 11:28, Telmo Menezes wrote:


I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What  
does
mind supervene on? Perhaps it is true that every single coupling  
with

the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that such
certainties come from a strong belief in emergentism (which I cannot
disprove, but find problematic).


It is impossible to recohere the past, FAPP.

But only FAPP. To make the blue T-rex interfereing with the red-T- 
rex, we must erase the trace of particle interaction between the T- 
rex in its whole light-cone, and this without forgetting the  
particles "swallowed" by the black-holes, etc. It is just  
completely impossible, but to derive from that the unicity of the  
past, is, it seems to me (and you if I understood well) is invalid.


I think the recoherence of paths that have completely decohered is  
more than just FAPP impossible, I think it is impossible in  
principle. One major problem with recoherence in general is that  
information leaks from the paths at the speed of light (as well as  
less slowly for other interactions). Since this vital information  
goes out along the light cone, it can never be recaptured and  
returned to the original interaction.


In QM + special relativity OK. (note that to me QM + special  
relativity => no collapse (and even the Many dreams, but we have  
agreed to disagree on this if I remember well).




Consequently, indispensable phase information is lost *in  
principle*, so the recoherence is, in general, impossible.


OK. (I was reasoning in naive classical QM)


Of course, with carefully constructed systems, where the loss of  
information along the light cone is prevented, recoherence is  
possible in special circumstances, but not in general.


From this, the uniqueness of the past of any decoherent history is  
assured. So deriving the unicity (if I understand this use of the  
word) is by no means invalid -- it is proved.


In QM + SR. OK.



Even if one encounters one of those rare situations in which  
recoherence is achieved, that still does not invalidate the  
uniqueness of the past history -- recoherence, if it occurs, simply  
means that no new branches are formed at that point, so the  
decoherent history remains unique.



OK. That might suggest that we identify our indistinguishible past in  
arithmetic, if we assume mechanism. I use the Y = II principle, or the  
"quantum" linearity of the tensor product "@": we have that  a @ (b +  
c) = (a @ b) + (a @ c).


That makes sense.








FWIW, you
are expressing my own understanding of the situation: there can  
be no
superposition of red and green screens or dinosaurs, or dead and  
live cats,
because there can be no quantum superposition of macroscopic  
objects.
Superpositions of wave functions are only possible for systems  
isolated from
interaction with their environment, which is why quantum  
computers are so
fricking hard to make: keeping aggregates of particles isolated  
from

interactions with the surrounding environment is exponentially more
difficult as the system grows in size.


The main question for me is this: can two branches hold different
observer states, if they differ only by things that are not
observable?


I would say no, intuitively. I would even say "no" just for the  
things not observed, even when observable.


I previously answered Telmo's question in the affirmative, viz., two  
fully decohered branches will hold different observer states, even  
if the differences are not observed or observable. So if some  
trivial physical event happens to your body, such as the decay of a  
K 40 nucleus in your foot, this would not be noticeable, or even  
particularly observable even if you were looking for it. But such an  
event causes at least two branches to form every instant -- one in  
which the decay has occurred, and one in which it has not. And since  
this is a beta decay, a neutrino is lost along the light cone in  
every case of decay.  Perfect recombination of the branches is,  
then, according to the above argument, not possible. You might  
object that this decay in my toe did not alter my conscious state --  
that is correct, but there are now two copies of the Moscow man as  
in step 3,


But those state difference are accessible to the observers, and  
indeed, only this makes the analogy with step 3 working. With  
computationalism, the two identical states at the correct susbt-level,  
if never distinguishable, will not add ways to the probabilities (that  
would entail that a computer with double cable would have a higher  
probability). The measure remains on the first person view, which  
eventually needs the self-referential definition. usually I just say  
that if in step 3 you add a reconsitution box

Re: A thought on MWI and its alternative(s)

[David Nyman]

On 31 May 2017 18:39, "Bruno Marchal"  wrote:


On 30 May 2017, at 17:00, David Nyman wrote:



On 30 May 2017 at 14:48, Bruno Marchal  wrote:

>
> On 30 May 2017, at 14:10, Telmo Menezes wrote:
>
> On Tue, May 30, 2017 at 1:35 PM, Bruno Marchal  wrote:
>>
>
>
> 
>
>>
>>
>> Right, I agree with you and Pierz on this. My point was more on what
>> you address below.
>>
>>
>> What if the substitution level turns out to be at a higher level than
>> quantum? E.g. at the level of the neurons and their connections and
>> activations levels?
>>
>
> That would enlarge the uncertainty spectrum on the realities we can access
> without losing anything subjective.
>

​A point against, I assume.


Not sure. Perhaps.





​

> It would help the doctor to build the artificial brain.


​A point in favour.


Yes. Modulo it helps also the charlatans, the hackers, etc. But that's part
of the price. In the long run, 99% of the treatment of information might
consist in cryptography. Some amount of first person privacy is needed to
get consistent extensions.




​

> It could also make more difficult to justify the smallness of Planck
> constant, and to explain why the quantum seems more obviously present in
> the micro-states,


​Against?



Problematical for the Mechanist.

I would favor the identification of the substitution level with the lower
classical physical state up to the "quantum isolation".  I think this could
be proved. It is the level of the molecules, and their most probable
histories.  The quantum fuzziness is how our self-description relatively to
the more proable histories appears for the average Löbian number.




​

> Decoherence would be easier to fight against,


​OK
​

> and quantum computing would be more easy to be realized.


​How, if the substitution is above the quantum boundary?


Then physics is deflected from the mechanist self-reference. Put it
bluntly: computationalism is refuted or we are in a malevolent Bostromian
simulation (or other number conspiracies. May be, if the Riemann hypothesis
is false, ...

Of course, it can depend to what you consider to need to survive. The level
of substitution is defined, not for the survival, but for the perfect
survival. Above that level, you will continue to survive, but
-either you will be aware of a defect, from a permanent headache to
anything you can imagine, or not.
- Or there will be a defect (observable by a third person, or not).

Exemple: the first classical teleported human, who said after the
experience : "it is a total success,  it is a total success,  it is a total
success,  it is a total success,  it is a total success,  it is a total
success,  it is a total success,  it is a total success,  it is a total
success,  it is a total success,  it is a total success,  it is a total
success,  it is a total success,  it is a total success,  it is a total
success,  it is a total success,  ...

And continue to say so in an asylum. Did he survived?

Above the level, you lost things. Obviously, with a digital *electronical*
neural net, you would lost the experience of cannabis, alcohol, salvia,
tobacco, until you find the apps on the net, emulating the chemical level
information. Neurology is fundamentals, including the swarm neural play,
but each neuron is a complex chemical factory, and cells communicates
mainly by molecules, even when they get the cable (neurons).




​

> This
> ​
> makes me think that the quantum level is boundary of the substitution
> level.


​I don't follow all of the above. Do you mean a boundary above which, or
below which, a plausible substitution might be made?


By high level, I mean a vulgar approximation of the brain/body could be
made, with few mega on the disk.

By low level, I mean an ultra-precise description of a big generalized
brain, like the brain + a part of the environment described by the quantum
superstring with 10^100 decimals. You will need a big disk.

Normally the relative substitution level determine the boundaries between
the classical boolean mind and the quantum observable.

But with QM without collapse, the level is not a question of micro/macro,
but of independence between computations, in sense which can be described
by using the modal logics.

In the math part, the level is in the choice of the box, the beweisbar
provability predicate. The theology is invariant for all the sound
(mechanical, or weakenings) extensions. But no machines can rationally
justifies any substitution level, and it is a bit like a private matter.

If the brain exploits the quantum weirdness, it means that we can extracts
information from the statistical measure on all computations below our
substitution. That possibility is independent of the level, and the whole
of the apparent matter exploits this, and should entirely emerge from this
...

Here I agree with Bohr, if you define the Macroscopic by the Boolean laws
of thought level, where the quantum theory is made. We can see only the
border of the mind, and that does not obey 

Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 30 May 2017, at 17:00, David Nyman wrote:




On 30 May 2017 at 14:48, Bruno Marchal  wrote:

On 30 May 2017, at 14:10, Telmo Menezes wrote:

On Tue, May 30, 2017 at 1:35 PM, Bruno Marchal   
wrote:






Right, I agree with you and Pierz on this. My point was more on what
you address below.


What if the substitution level turns out to be at a higher level than
quantum? E.g. at the level of the neurons and their connections and
activations levels?

That would enlarge the uncertainty spectrum on the realities we can  
access without losing anything subjective.


​A point against, I assume.


Not sure. Perhaps.






​
It would help the doctor to build the artificial brain.

​A point in favour.


Yes. Modulo it helps also the charlatans, the hackers, etc. But that's  
part of the price. In the long run, 99% of the treatment of  
information might consist in cryptography. Some amount of first person  
privacy is needed to get consistent extensions.






​
It could also make more difficult to justify the smallness of Planck  
constant, and to explain why the quantum seems more obviously  
present in the micro-states,


​Against?



Problematical for the Mechanist.

I would favor the identification of the substitution level with the  
lower classical physical state up to the "quantum isolation".  I think  
this could be proved. It is the level of the molecules, and their most  
probable histories.  The quantum fuzziness is how our self-description  
relatively to the more proable histories appears for the average  
Löbian number.






​
Decoherence would be easier to fight against,

​OK
​
and quantum computing would be more easy to be realized.

​How, if the substitution is above the quantum boundary?


Then physics is deflected from the mechanist self-reference. Put it  
bluntly: computationalism is refuted or we are in a malevolent  
Bostromian simulation (or other number conspiracies. May be, if the  
Riemann hypothesis is false, ...


Of course, it can depend to what you consider to need to survive. The  
level of substitution is defined, not for the survival, but for the  
perfect survival. Above that level, you will continue to survive, but
-either you will be aware of a defect, from a permanent headache to  
anything you can imagine, or not.

- Or there will be a defect (observable by a third person, or not).

Exemple: the first classical teleported human, who said after the  
experience : "it is a total success,  it is a total success,  it is a  
total success,  it is a total success,  it is a total success,  it is  
a total success,  it is a total success,  it is a total success,  it  
is a total success,  it is a total success,  it is a total success,   
it is a total success,  it is a total success,  it is a total  
success,  it is a total success,  it is a total success,  ...


And continue to say so in an asylum. Did he survived?

Above the level, you lost things. Obviously, with a digital  
*electronical* neural net, you would lost the experience of cannabis,  
alcohol, salvia, tobacco, until you find the apps on the net,  
emulating the chemical level information. Neurology is fundamentals,  
including the swarm neural play, but each neuron is a complex chemical  
factory, and cells communicates mainly by molecules, even when they  
get the cable (neurons).






​
This ​makes me think that the quantum level is boundary of the  
substitution level.


​I don't follow all of the above. Do you mean a boundary above  
which, or below which, a plausible substitution might be made?


By high level, I mean a vulgar approximation of the brain/body could  
be made, with few mega on the disk.


By low level, I mean an ultra-precise description of a big generalized  
brain, like the brain + a part of the environment described by the  
quantum superstring with 10^100 decimals. You will need a big disk.


Normally the relative substitution level determine the boundaries  
between the classical boolean mind and the quantum observable.


But with QM without collapse, the level is not a question of micro/ 
macro, but of independence between computations, in sense which can be  
described by using the modal logics.


In the math part, the level is in the choice of the box, the beweisbar  
provability predicate. The theology is invariant for all the sound  
(mechanical, or weakenings) extensions. But no machines can rationally  
justifies any substitution level, and it is a bit like a private matter.


If the brain exploits the quantum weirdness, it means that we can  
extracts information from the statistical measure on all computations  
below our substitution. That possibility is independent of the level,  
and the whole of the apparent matter exploits this, and should  
entirely emerge from this ...


Here I agree with Bohr, if you define the Macroscopic by the Boolean  
laws of thought level, where the quantum theory is made. We can see  
only the border of the mind, and that does not obey to classica

Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 31/05/2017 4:40 pm, Pierz wrote:

On Wednesday, May 31, 2017 at 3:28:18 PM UTC+10, Brent wrote:

Sorry.  Something funny with my verizon account.

Brent

On 5/30/2017 8:09 PM, Pierz Newton-John wrote:
> Brent, are you replying from a mobile? I’m still receiving your
replies, as others are, on my private email. That’s what happens
to me when I try to reply using my iPhone. The "reply to all"
button is missing. I’ll reply to your remarks on the list if you
post it there...
>
>
>> On 31 May 2017, at 1:05 pm, Brent Meeker > wrote:
>>
>>
>>
>> On 5/30/2017 7:30 PM, Pierz wrote:
>>> Thanks for these clarifications Bruce. I find your
explanations to be very lucid and helpful - they also confirm my
own understanding. IIRC, you weren't a particular fan of MWI when
I last conversed with you on this list. I wonder if you'd care to
comment on my original argument on this thread - which has of
course now been swamped by the usual brawls. Does not a single
history + the physical insignificance of the notion of a current
moment mean that there is also only a single possible future?
>> I don't see how that follows.  In the usual model of forking in
the future direction every current moment has a single history,
but multiple futures.


Multiple futures = MWI, surely.


Not necessarily. If you insist on Schrödinger determinism, then yes, by 
reification of the wave function. But if the wave function is only 
epistemological, then there is only one probabilistic future.


When I say a single history, I mean that from the Big Bang forward, 
the universe only followed one branch.


And that can lead into the future, only one probabilistic future.


>>
>>> And if the future is predetermined in this way, isn't this a
serious issue for single universe models of QM? How can the
outcome of quantum events be both inevitable and random?
>> Having a single future isn't the same as being determined.  A
single future in which situation A is sometimes followed by B and
sometimes by C is still random.


It depends on perspective. It's true that from 1p, it looks random. 
But from 3p, it is static and always the same, and in this sense 
determined.


Not true, the 3p view of the future is still just a single probabilistic 
world line. It is only the bird view, from outside space and time, that 
gives the appearance that there are multiply existing futures. Neither 
we from the 1p perspective, or from outside ourselves in the 3p 
perspective, can we ever see any of the other branches predicted by MWI.


The question is, what determined (from the 3p view) that the universe 
followed that particular path and not any of the others?


Why do you reject out of hand that the universe might be probabilistic?  
It is possible 'nothing' determined which path from the possibilities 
was actually followed. All that is known are the probabilities for each 
path. We do not know that the other paths are followed, either 1p or 3p.


My assumption here is that "now" does not exist from the 3p POV and 
therefore the physical structure (whether it branches or not) of the 
past and the future is the same.


That can certainly be the case, whether there are existing alternative 
branches or not.


Bruce

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Re: A thought on MWI and its alternative(s)

[Pierz]

On Wednesday, May 31, 2017 at 3:28:18 PM UTC+10, Brent wrote:
>
> Sorry.  Something funny with my verizon account. 
>
> Brent 
>
> On 5/30/2017 8:09 PM, Pierz Newton-John wrote: 
> > Brent, are you replying from a mobile? I’m still receiving your replies, 
> as others are, on my private email. That’s what happens to me when I try to 
> reply using my iPhone. The "reply to all" button is missing. I’ll reply to 
> your remarks on the list if you post it there... 
> > 
> > 
> >> On 31 May 2017, at 1:05 pm, Brent Meeker  > wrote: 
> >> 
> >> 
> >> 
> >> On 5/30/2017 7:30 PM, Pierz wrote: 
> >>> Thanks for these clarifications Bruce. I find your explanations to be 
> very lucid and helpful - they also confirm my own understanding. IIRC, you 
> weren't a particular fan of MWI when I last conversed with you on this 
> list. I wonder if you'd care to comment on my original argument on this 
> thread - which has of course now been swamped by the usual brawls. Does not 
> a single history + the physical insignificance of the notion of a current 
> moment mean that there is also only a single possible future? 
> >> I don't see how that follows.  In the usual model of forking in the 
> future direction every current moment has a single history, but multiple 
> futures. 
>

Multiple futures = MWI, surely. When I say a single history, I mean that 
from the Big Bang forward, the universe only followed one branch.
 

> >> 
> >>> And if the future is predetermined in this way, isn't this a serious 
> issue for single universe models of QM? How can the outcome of quantum 
> events be both inevitable and random? 
> >> Having a single future isn't the same as being determined.  A single 
> future in which situation A is sometimes followed by B and sometimes by C 
> is still random. 
>

It depends on perspective. It's true that from 1p, it looks random. But 
from 3p, it is static and always the same, and in this sense determined. 
The question is, what determined (from the 3p view) that the universe 
followed that particular path and not any of the others? My assumption here 
is that "now" does not exist from the 3p POV and therefore the physical 
structure (whether it branches or not) of the past and the future is the 
same.

>> 
> >> Brent 
> > 
>
>

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Re: A thought on MWI and its alternative(s)

[Brent Meeker]

Sorry.  Something funny with my verizon account.

Brent

On 5/30/2017 8:09 PM, Pierz Newton-John wrote:

Brent, are you replying from a mobile? I’m still receiving your replies, as others are, 
on my private email. That’s what happens to me when I try to reply using my iPhone. The 
"reply to all" button is missing. I’ll reply to your remarks on the list if you 
post it there...



On 31 May 2017, at 1:05 pm, Brent Meeker  wrote:



On 5/30/2017 7:30 PM, Pierz wrote:

Thanks for these clarifications Bruce. I find your explanations to be very 
lucid and helpful - they also confirm my own understanding. IIRC, you weren't a 
particular fan of MWI when I last conversed with you on this list. I wonder if 
you'd care to comment on my original argument on this thread - which has of 
course now been swamped by the usual brawls. Does not a single history + the 
physical insignificance of the notion of a current moment mean that there is 
also only a single possible future?

I don't see how that follows.  In the usual model of forking in the future 
direction every current moment has a single history, but multiple futures.


And if the future is predetermined in this way, isn't this a serious issue for 
single universe models of QM? How can the outcome of quantum events be both 
inevitable and random?

Having a single future isn't the same as being determined.  A single future in 
which situation A is sometimes followed by B and sometimes by C is still random.

Brent




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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 31/05/2017 12:30 pm, Pierz wrote:
Thanks for these clarifications Bruce. I find your explanations to be 
very lucid and helpful - they also confirm my own understanding.


Thank you for the kind comments, I try my best to be clear.

IIRC, you weren't a particular fan of MWI when I last conversed with 
you on this list.


That is indeed the case. I have several reasons to be dubious about MWI. 
Firstly, it amounts to reifying a complex valued function that resides 
in configuration space -- I am not sure that this is a well-defined 
procedure. Secondly, MWI doesn't really do what it claims to do, which 
is to provide a resolution of the measurement problem in QM. MWI doesn't 
provide any explanation of the transition from a pure state to the mixed 
state that is required for experiments to give definite results. At the 
crucial point, MWI simply says "then a miracle happens!" To be more 
explicit, deterministic evolution of the wave function by the 
Schrödinger equation gives a full account of decoherence, and the 
dissemination of the coherence phases into the environment. This reduces 
the off-diagonal elements of the density matrix so that the diagonal 
elements become *almost* orthogonal, but unitary evolution can't go the 
whole way. The only way one can reduce the pure state to a mixture is to 
trace over the environmental degrees of freedom, which is to say that 
the residual phase information is simply thrown away. This trace 
operation is non-unitary, and there is no warrant for it in the SE 
itself, so it is, in the final analysis, just an appeal to magic. 
Thirdly, the non-observed branches in MWI play no essential role in the 
theory, so Occam would say that they are inessential entities that 
should be discarded. If one is simply going to discard them, and they 
play no observable role, why invoke these other branches in the first place?


I wonder if you'd care to comment on my original argument on this 
thread - which has of course now been swamped by the usual brawls. 
Does not a single history + the physical insignificance of the notion 
of a current moment mean that there is also only a single possible future?


We will only experience a single future, but what that future is, is 
indeterminate at the present instant.


And if the future is predetermined in this way, isn't this a serious 
issue for single universe models of QM? How can the outcome of quantum 
events be both inevitable and random?


I don't see that there is only a single possible future. The block 
universe notion only requires indeterminate time ordering for spacelike 
separated events. The future along and inside one's future light cone is 
in the future for all observers, so need not be determined by some other 
observer having already seen what happens. The block universe only 
constrains the future only in very limited sense -- it is only for 
spacelike separations that simultaneity is ambiguous, timelike 
separations are not so constrained.


Quantum non-locality is another matter, however, and there are growing 
indications that quantum entanglement and the associated non-locality 
might prove to be of fundamental significance for physics -- such as the 
possibility that space-time itself might emerge from quantum entanglements.


Bruce





On Wednesday, May 31, 2017 at 12:01:23 PM UTC+10, Bruce wrote:

On 30/05/2017 9:35 pm, Bruno Marchal wrote:
> On 30 May 2017, at 11:28, Telmo Menezes wrote:
>
>> I get your point with decoherence.
>> Again, I would say that it all depends on theories of mind.
What does
>> mind supervene on? Perhaps it is true that every single
coupling with
>> the environment prevents the current observer state to become
>> compatible with other branches. But can we be sure? I feel that
such
>> certainties come from a strong belief in emergentism (which I
cannot
>> disprove, but find problematic).
>
> It is impossible to recohere the past, FAPP.
>
> But only FAPP. To make the blue T-rex interfereing with the
red-T-rex,
> we must erase the trace of particle interaction between the
T-rex in
> its whole light-cone, and this without forgetting the particles
> "swallowed" by the black-holes, etc. It is just completely
impossible,
> but to derive from that the unicity of the past, is, it seems to me
> (and you if I understood well) is invalid.

I think the recoherence of paths that have completely decohered is
more
than just FAPP impossible, I think it is impossible in principle. One
major problem with recoherence in general is that information
leaks from
the paths at the speed of light (as well as less slowly for other
interactions). Since this vital information goes out along the light
cone, it can never be recaptured and returned to the original
interaction. Consequently, indispensable phase information is lost
*in
principle*, so the recoherence is,

Re: A thought on MWI and its alternative(s)

[Pierz]

Thanks for these clarifications Bruce. I find your explanations to be very 
lucid and helpful - they also confirm my own understanding. IIRC, you 
weren't a particular fan of MWI when I last conversed with you on this 
list. I wonder if you'd care to comment on my original argument on this 
thread - which has of course now been swamped by the usual brawls. Does not 
a single history + the physical insignificance of the notion of a current 
moment mean that there is also only a single possible future? And if the 
future is predetermined in this way, isn't this a serious issue for single 
universe models of QM? How can the outcome of quantum events be both 
inevitable and random?

On Wednesday, May 31, 2017 at 12:01:23 PM UTC+10, Bruce wrote:
>
> On 30/05/2017 9:35 pm, Bruno Marchal wrote: 
> > On 30 May 2017, at 11:28, Telmo Menezes wrote: 
> > 
> >> I get your point with decoherence. 
> >> Again, I would say that it all depends on theories of mind. What does 
> >> mind supervene on? Perhaps it is true that every single coupling with 
> >> the environment prevents the current observer state to become 
> >> compatible with other branches. But can we be sure? I feel that such 
> >> certainties come from a strong belief in emergentism (which I cannot 
> >> disprove, but find problematic). 
> > 
> > It is impossible to recohere the past, FAPP. 
> > 
> > But only FAPP. To make the blue T-rex interfereing with the red-T-rex, 
> > we must erase the trace of particle interaction between the T-rex in 
> > its whole light-cone, and this without forgetting the particles 
> > "swallowed" by the black-holes, etc. It is just completely impossible, 
> > but to derive from that the unicity of the past, is, it seems to me 
> > (and you if I understood well) is invalid. 
>
> I think the recoherence of paths that have completely decohered is more 
> than just FAPP impossible, I think it is impossible in principle. One 
> major problem with recoherence in general is that information leaks from 
> the paths at the speed of light (as well as less slowly for other 
> interactions). Since this vital information goes out along the light 
> cone, it can never be recaptured and returned to the original 
> interaction. Consequently, indispensable phase information is lost *in 
> principle*, so the recoherence is, in general, impossible. Of course, 
> with carefully constructed systems, where the loss of information along 
> the light cone is prevented, recoherence is possible in special 
> circumstances, but not in general. 
>
>  From this, the uniqueness of the past of any decoherent history is 
> assured. So deriving the unicity (if I understand this use of the word) 
> is by no means invalid -- it is proved. Even if one encounters one of 
> those rare situations in which recoherence is achieved, that still does 
> not invalidate the uniqueness of the past history -- recoherence, if it 
> occurs, simply means that no new branches are formed at that point, so 
> the decoherent history remains unique. 
>
>
> >>> FWIW, you 
> >>> are expressing my own understanding of the situation: there can be no 
> >>> superposition of red and green screens or dinosaurs, or dead and 
> >>> live cats, 
> >>> because there can be no quantum superposition of macroscopic objects. 
> >>> Superpositions of wave functions are only possible for systems 
> >>> isolated from 
> >>> interaction with their environment, which is why quantum computers 
> >>> are so 
> >>> fricking hard to make: keeping aggregates of particles isolated from 
> >>> interactions with the surrounding environment is exponentially more 
> >>> difficult as the system grows in size. 
> >> 
> >> The main question for me is this: can two branches hold different 
> >> observer states, if they differ only by things that are not 
> >> observable? 
> > 
> > I would say no, intuitively. I would even say "no" just for the things 
> > not observed, even when observable. 
>
> I previously answered Telmo's question in the affirmative, viz., two 
> fully decohered branches will hold different observer states, even if 
> the differences are not observed or observable. So if some trivial 
> physical event happens to your body, such as the decay of a K 40 nucleus 
> in your foot, this would not be noticeable, or even particularly 
> observable even if you were looking for it. But such an event causes at 
> least two branches to form every instant -- one in which the decay has 
> occurred, and one in which it has not. And since this is a beta decay, a 
> neutrino is lost along the light cone in every case of decay.  Perfect 
> recombination of the branches is, then, according to the above argument, 
> not possible. You might object that this decay in my toe did not alter 
> my conscious state -- that is correct, but there are now two copies of 
> the Moscow man as in step 3, and these can evolve in different 
> directions while each remains unaware of the existence of the other. 
> They can never recomb

Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 30/05/2017 9:35 pm, Bruno Marchal wrote:

On 30 May 2017, at 11:28, Telmo Menezes wrote:


I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What does
mind supervene on? Perhaps it is true that every single coupling with
the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that such
certainties come from a strong belief in emergentism (which I cannot
disprove, but find problematic).


It is impossible to recohere the past, FAPP.

But only FAPP. To make the blue T-rex interfereing with the red-T-rex, 
we must erase the trace of particle interaction between the T-rex in 
its whole light-cone, and this without forgetting the particles 
"swallowed" by the black-holes, etc. It is just completely impossible, 
but to derive from that the unicity of the past, is, it seems to me 
(and you if I understood well) is invalid.


I think the recoherence of paths that have completely decohered is more 
than just FAPP impossible, I think it is impossible in principle. One 
major problem with recoherence in general is that information leaks from 
the paths at the speed of light (as well as less slowly for other 
interactions). Since this vital information goes out along the light 
cone, it can never be recaptured and returned to the original 
interaction. Consequently, indispensable phase information is lost *in 
principle*, so the recoherence is, in general, impossible. Of course, 
with carefully constructed systems, where the loss of information along 
the light cone is prevented, recoherence is possible in special 
circumstances, but not in general.


From this, the uniqueness of the past of any decoherent history is 
assured. So deriving the unicity (if I understand this use of the word) 
is by no means invalid -- it is proved. Even if one encounters one of 
those rare situations in which recoherence is achieved, that still does 
not invalidate the uniqueness of the past history -- recoherence, if it 
occurs, simply means that no new branches are formed at that point, so 
the decoherent history remains unique.




FWIW, you
are expressing my own understanding of the situation: there can be no
superposition of red and green screens or dinosaurs, or dead and 
live cats,

because there can be no quantum superposition of macroscopic objects.
Superpositions of wave functions are only possible for systems 
isolated from
interaction with their environment, which is why quantum computers 
are so

fricking hard to make: keeping aggregates of particles isolated from
interactions with the surrounding environment is exponentially more
difficult as the system grows in size.


The main question for me is this: can two branches hold different
observer states, if they differ only by things that are not
observable?


I would say no, intuitively. I would even say "no" just for the things 
not observed, even when observable.


I previously answered Telmo's question in the affirmative, viz., two 
fully decohered branches will hold different observer states, even if 
the differences are not observed or observable. So if some trivial 
physical event happens to your body, such as the decay of a K 40 nucleus 
in your foot, this would not be noticeable, or even particularly 
observable even if you were looking for it. But such an event causes at 
least two branches to form every instant -- one in which the decay has 
occurred, and one in which it has not. And since this is a beta decay, a 
neutrino is lost along the light cone in every case of decay.  Perfect 
recombination of the branches is, then, according to the above argument, 
not possible. You might object that this decay in my toe did not alter 
my conscious state -- that is correct, but there are now two copies of 
the Moscow man as in step 3, and these can evolve in different 
directions while each remains unaware of the existence of the other. 
They can never recombine and compare diaries!


But this has to be tempered by the fact that any interaction will 
count as an observation, making super-exponentially hard to indeed 
recover a macroscopic superposition in the past, even the very close 
past. Of course, that might change the day we succeed in building a 
fault tolerant (topological perhaps) quantum computer.


That will not help in the general case. Our future quantum computer 
might be able to delay decoherence for some useful finite time, but that 
still only retaines the superposition in the said computer, it does not 
help with recombination of decohered branches in general.


Unfortunately, the T-rex missed them. yet, if a T-rex made a solid 
topological quantum qubit, in the state 0+1, we would have a past with 
0, and a past with 1, as long as we don't look at it. I read, already 
a long time ago, some experimental evidence of temporal Bell's 
inequality going in this direction, and I think we don't even need to 
test them, as we get them with the usual Be

Re: A thought on MWI and its alternative(s)

[David Nyman]

On 30 May 2017 at 14:48, Bruno Marchal  wrote:

>
> On 30 May 2017, at 14:10, Telmo Menezes wrote:
>
> On Tue, May 30, 2017 at 1:35 PM, Bruno Marchal  wrote:
>>
>>>
>>> On 30 May 2017, at 11:28, Telmo Menezes wrote:
>>>
>>> On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:

>
>
>
> On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:
>
>>
>>
>> On 29/05/2017 11:21 pm, Telmo Menezes wrote:
>>
>>>
>>> On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
>>>  wrote:
>>>

 On 29/05/2017 10:42 pm, Telmo Menezes wrote:

>
> On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
>  wrote:
>
>>
>> On 29/05/2017 6:26 pm, Telmo Menezes wrote:
>>
>>>
>>> On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
>>>  wrote:
>>>

 I would say that there is only one history leading to our
 present
 state.
 Whether you take an MWI view or a collapse view, the wave
 function
 branches
 deterministically at every point, so if you follow your current
 twig
 back
 down to the main trunk etc, there will be a unique path.

>>>
>>> I don't think we can say we are in a specific twig. Many things
>>> about
>>> out present state are unknown/undefined. I can imagine that there
>>> are
>>> many well-defined present states that are compatible with my
>>> current
>>> subjective state.
>>>
>>
>>
>> Sure, but we are talking about wave functions, not subjective
>> states.
>>
>
> Replace "subjective" with "incomplete knowledge".
>


 Doesn't help. Of course our knowledge is incomplete, the wave
 function
 isn't
 completely known either -- but the result of specific measurements
 are
 what
 is at stake here, and they are known quantum states.

>>>
>>> In my view, what's at stake here is the possibility of latent
>>> variables having some degree of freedom leading to the same macro
>>> states (provided that there is incomplete information about these
>>> macro states, as is the case for humans).
>>>
>>
>>
>> I am still not clear about what you are trying to say. It is certainly
>> true that many internal details of your microscopic organization could
>> be changed and you wouldn't know the difference. For that matter, an
>> almost infinite number of details about the rest of the universe could
>> be different and you would still be the same. But that is not what we
>> were talking about. I understood the issue to be whether there was a
>> unique past, or whether several (or many) different paths lead to our
>> current state. The determinism of the Schrödinger equation would
>> suggest
>> that your unique state has a unique history. Variations in microscopic
>> details of with your body, or the universe, would correspond to
>> different decohered worlds with no overlap with our world. So while
>> such
>> variations are possible, they do not amount to multiple histories
>> leading to our current state. We don't need to know that state in
>> detail
>> to be able to argue the consequences of determinism.
>>
>> In fact you can perform a quantum erasure experiment, and be sure
>>> that
>>> your current state goes through at least two different shortest
>>> paths
>>> to the root, and it becomes nonsensical to say that one is the
>>> "correct" one. I don't think anyone knows how far this can go
>>> into
>>> the
>>> macroscopic world, but I don't see any reason to believe that it
>>> doesn't.
>>>
>>
>>
>> I don't understand what you think you are getting in a quantum
>> erasure
>> experiment. If the "which way" information that was gathered is
>> erased,
>> normal interference patterns are seen in the double slit
>> situation.
>> The
>> two
>> paths (through the separate slits) are in unresolved superposition
>> until
>> they hit the detector, when decoherence takes over. There are not
>> two
>> separate worlds, and your state is the result of the superposed
>> paths,
>> not
>> of either path separately. There is no ambiguity about which the
>> the
>> "correct" path -- neither is, both contribute equally.
>>
>
> I would say that the delayed choice version of the experiment makes
> it
> clear that there are two possible pasts that lead to the same
> present
>>>

Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 30 May 2017, at 14:10, Telmo Menezes wrote:

On Tue, May 30, 2017 at 1:35 PM, Bruno Marchal   
wrote:


On 30 May 2017, at 11:28, Telmo Menezes wrote:


On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:




On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:



On 29/05/2017 11:21 pm, Telmo Menezes wrote:


On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
 wrote:


On 29/05/2017 10:42 pm, Telmo Menezes wrote:


On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
 wrote:


On 29/05/2017 6:26 pm, Telmo Menezes wrote:


On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
 wrote:


I would say that there is only one history leading to our  
present

state.
Whether you take an MWI view or a collapse view, the wave  
function

branches
deterministically at every point, so if you follow your  
current

twig
back
down to the main trunk etc, there will be a unique path.


I don't think we can say we are in a specific twig. Many  
things

about
out present state are unknown/undefined. I can imagine that  
there

are
many well-defined present states that are compatible with my
current
subjective state.



Sure, but we are talking about wave functions, not subjective
states.


Replace "subjective" with "incomplete knowledge".



Doesn't help. Of course our knowledge is incomplete, the wave  
function

isn't
completely known either -- but the result of specific  
measurements are

what
is at stake here, and they are known quantum states.


In my view, what's at stake here is the possibility of latent
variables having some degree of freedom leading to the same macro
states (provided that there is incomplete information about these
macro states, as is the case for humans).



I am still not clear about what you are trying to say. It is  
certainly
true that many internal details of your microscopic organization  
could
be changed and you wouldn't know the difference. For that  
matter, an
almost infinite number of details about the rest of the universe  
could
be different and you would still be the same. But that is not  
what we
were talking about. I understood the issue to be whether there  
was a
unique past, or whether several (or many) different paths lead  
to our
current state. The determinism of the Schrödinger equation would  
suggest
that your unique state has a unique history. Variations in  
microscopic

details of with your body, or the universe, would correspond to
different decohered worlds with no overlap with our world. So  
while such

variations are possible, they do not amount to multiple histories
leading to our current state. We don't need to know that state  
in detail

to be able to argue the consequences of determinism.

In fact you can perform a quantum erasure experiment, and  
be sure

that
your current state goes through at least two different  
shortest

paths
to the root, and it becomes nonsensical to say that one is  
the
"correct" one. I don't think anyone knows how far this can  
go into

the
macroscopic world, but I don't see any reason to believe  
that it

doesn't.



I don't understand what you think you are getting in a quantum
erasure
experiment. If the "which way" information that was gathered  
is

erased,
normal interference patterns are seen in the double slit  
situation.

The
two
paths (through the separate slits) are in unresolved  
superposition

until
they hit the detector, when decoherence takes over. There  
are not

two
separate worlds, and your state is the result of the  
superposed

paths,
not
of either path separately. There is no ambiguity about which  
the the

"correct" path -- neither is, both contribute equally.


I would say that the delayed choice version of the experiment  
makes

it
clear that there are two possible pasts that lead to the same  
present

state -- they differ by one bit of information.



That is not what is implied by delayed choice quantum erasure.  
Whether

an
interference pattern is seen or not is determined by whether the
"which
way"
information is erased or not. But whether it is or not, the
interference is
only seen when coincidence measurements tell one which photons  
to

count. And
the timing information necessary for coincidence determination  
is

available
only *after* all decisions about erasure or not have been made,
whether
that
decision is made before or after the other photon of the  
entangled

pair
has
reached its detector.

"Delayed choice" is perhaps a misleading phrase in this  
context, and

it
does
not lead to an ambiguity of path -- it merely tells whether  
there was

an
intact superposition or not.


I know, this is not what I am trying to say. I'll choose  
something much

simpler:

Suppose there is a computer running in an empty room. This  
computer is

connected to a random number generator. At some point it uses the
random value to decide if it's going to show a screen that is all
green or all red. Nobody witnesses it.



If the random number generator is based on quantum randomness,  
then in
principle you w

Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Tue, May 30, 2017 at 1:55 PM, Bruce Kellett
 wrote:
> On 30/05/2017 7:28 pm, Telmo Menezes wrote:
>>
>> On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:
>>>
>>> So you are talking different
>>> languages.
>>
>> Not sure I agree. We are perhaps implicitly assuming different theories of
>> mind.
>>
>>> I don't know if Telmo is aware or not of the conventional view of
>>> decoherence - that it is a matter of the spread of information into the
>>> environment by means of physical interactions between particles. Telmo's
>>> musings about the effect of destroying memory (could it change the
>>> measure
>>> of different futures?) clearly expresses this subjectivist view.
>>
>> I get your point with decoherence.
>> Again, I would say that it all depends on theories of mind. What does
>> mind supervene on? Perhaps it is true that every single coupling with
>> the environment prevents the current observer state to become
>> compatible with other branches. But can we be sure? I feel that such
>> certainties come from a strong belief in emergentism (which I cannot
>> disprove, but find problematic).
>>
>>> FWIW, you
>>> are expressing my own understanding of the situation: there can be no
>>> superposition of red and green screens or dinosaurs, or dead and live
>>> cats,
>>> because there can be no quantum superposition of macroscopic objects.
>>> Superpositions of wave functions are only possible for systems isolated
>>> from
>>> interaction with their environment, which is why quantum computers are so
>>> fricking hard to make: keeping aggregates of particles isolated from
>>> interactions with the surrounding environment is exponentially more
>>> difficult as the system grows in size.
>>
>> The main question for me is this: can two branches hold different
>> observer states, if they differ only by things that are not
>> observable?
>
>
> Yes, but I think we should be talking about quantum mechanics here, and that
> is a well-defined physical theory that is not really concerned with any
> theory of mind.

Ok.

> There have been some interpretations of quantum mechanics
> that ascribe the mind a role in the collapse of the wave function, or some
> such; and some who re-interpret the many worlds idea as a 'many minds'
> picture; but these issues do not seem to be relevant to any discussion of
> the quantum formalism itself.
>
> In the discussions on this list, it seems that MWI is the dominant
> understanding of QM. That is fine, one can certainly talk about things in
> this way. But it should be borne in mind that MWI is actually equivalent to
> the less well known decoherent histories approach. I guess that in my
> comments earlier in this thread, I was emphasizing the decoherent histories
> understanding. In many worlds, worlds separate off when irreversible
> interactions with the environment zero out the interference terms between
> different elements in the superposition. This happens inevitably all the
> time, and measurements, or observers, play no essential role in the process.
> Each world of the MWI is thus produced by the process of decoherence acting
> on the initial quantum state. Each decoherent line then evolves on to
> produce its own set of future decoherent lines. Following through any
> particular line gives a decoherent history -- one for each world of the MWI.
>
> Since the processes of decoherence and the formation of histories or worlds
> are independent of the observer and of the mind, it is clearly possible that
> different branches  (or histories) can differ only by things that are not
> observed, or even not observable. And this is just a matter of the formalism
> of quantum mechanics -- it has nothing to do with any theory of mind. The
> only thing that I would say, though, is that your theory of mind, and your
> theory of the origin of physics, must be compatible with this understanding
> of quantum mechanics -- or else your theory of mind/physics is falsified.
>
>
> Bruce
>
> --
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Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Tue, May 30, 2017 at 1:35 PM, Bruno Marchal  wrote:
>
> On 30 May 2017, at 11:28, Telmo Menezes wrote:
>
>> On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:
>>>
>>>
>>>
>>> On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:


 On 29/05/2017 11:21 pm, Telmo Menezes wrote:
>
> On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
>  wrote:
>>
>> On 29/05/2017 10:42 pm, Telmo Menezes wrote:
>>>
>>> On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
>>>  wrote:

 On 29/05/2017 6:26 pm, Telmo Menezes wrote:
>
> On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
>  wrote:
>>
>> I would say that there is only one history leading to our present
>> state.
>> Whether you take an MWI view or a collapse view, the wave function
>> branches
>> deterministically at every point, so if you follow your current
>> twig
>> back
>> down to the main trunk etc, there will be a unique path.
>
> I don't think we can say we are in a specific twig. Many things
> about
> out present state are unknown/undefined. I can imagine that there
> are
> many well-defined present states that are compatible with my
> current
> subjective state.


 Sure, but we are talking about wave functions, not subjective
 states.
>>>
>>> Replace "subjective" with "incomplete knowledge".
>>
>>
>> Doesn't help. Of course our knowledge is incomplete, the wave function
>> isn't
>> completely known either -- but the result of specific measurements are
>> what
>> is at stake here, and they are known quantum states.
>
> In my view, what's at stake here is the possibility of latent
> variables having some degree of freedom leading to the same macro
> states (provided that there is incomplete information about these
> macro states, as is the case for humans).


 I am still not clear about what you are trying to say. It is certainly
 true that many internal details of your microscopic organization could
 be changed and you wouldn't know the difference. For that matter, an
 almost infinite number of details about the rest of the universe could
 be different and you would still be the same. But that is not what we
 were talking about. I understood the issue to be whether there was a
 unique past, or whether several (or many) different paths lead to our
 current state. The determinism of the Schrödinger equation would suggest
 that your unique state has a unique history. Variations in microscopic
 details of with your body, or the universe, would correspond to
 different decohered worlds with no overlap with our world. So while such
 variations are possible, they do not amount to multiple histories
 leading to our current state. We don't need to know that state in detail
 to be able to argue the consequences of determinism.

> In fact you can perform a quantum erasure experiment, and be sure
> that
> your current state goes through at least two different shortest
> paths
> to the root, and it becomes nonsensical to say that one is the
> "correct" one. I don't think anyone knows how far this can go into
> the
> macroscopic world, but I don't see any reason to believe that it
> doesn't.


 I don't understand what you think you are getting in a quantum
 erasure
 experiment. If the "which way" information that was gathered is
 erased,
 normal interference patterns are seen in the double slit situation.
 The
 two
 paths (through the separate slits) are in unresolved superposition
 until
 they hit the detector, when decoherence takes over. There are not
 two
 separate worlds, and your state is the result of the superposed
 paths,
 not
 of either path separately. There is no ambiguity about which the the
 "correct" path -- neither is, both contribute equally.
>>>
>>> I would say that the delayed choice version of the experiment makes
>>> it
>>> clear that there are two possible pasts that lead to the same present
>>> state -- they differ by one bit of information.
>>
>>
>> That is not what is implied by delayed choice quantum erasure. Whether
>> an
>> interference pattern is seen or not is determined by whether the
>> "which
>> way"
>> information is erased or not. But whether it is or not, the
>> interference is
>> only seen when coincidence measurements tell one which photons to
>> count. And
>> the timing information necessary for coincidence determination is
>> available
>> only *after* all decisions about erasure or not ha

Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 30/05/2017 7:28 pm, Telmo Menezes wrote:

On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:

So you are talking different
languages.

Not sure I agree. We are perhaps implicitly assuming different theories of mind.


I don't know if Telmo is aware or not of the conventional view of
decoherence - that it is a matter of the spread of information into the
environment by means of physical interactions between particles. Telmo's
musings about the effect of destroying memory (could it change the measure
of different futures?) clearly expresses this subjectivist view.

I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What does
mind supervene on? Perhaps it is true that every single coupling with
the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that such
certainties come from a strong belief in emergentism (which I cannot
disprove, but find problematic).


FWIW, you
are expressing my own understanding of the situation: there can be no
superposition of red and green screens or dinosaurs, or dead and live cats,
because there can be no quantum superposition of macroscopic objects.
Superpositions of wave functions are only possible for systems isolated from
interaction with their environment, which is why quantum computers are so
fricking hard to make: keeping aggregates of particles isolated from
interactions with the surrounding environment is exponentially more
difficult as the system grows in size.

The main question for me is this: can two branches hold different
observer states, if they differ only by things that are not
observable?


Yes, but I think we should be talking about quantum mechanics here, and 
that is a well-defined physical theory that is not really concerned with 
any theory of mind. There have been some interpretations of quantum 
mechanics that ascribe the mind a role in the collapse of the wave 
function, or some such; and some who re-interpret the many worlds idea 
as a 'many minds' picture; but these issues do not seem to be relevant 
to any discussion of the quantum formalism itself.


In the discussions on this list, it seems that MWI is the dominant 
understanding of QM. That is fine, one can certainly talk about things 
in this way. But it should be borne in mind that MWI is actually 
equivalent to the less well known decoherent histories approach. I guess 
that in my comments earlier in this thread, I was emphasizing the 
decoherent histories understanding. In many worlds, worlds separate off 
when irreversible interactions with the environment zero out the 
interference terms between different elements in the superposition. This 
happens inevitably all the time, and measurements, or observers, play no 
essential role in the process. Each world of the MWI is thus produced by 
the process of decoherence acting on the initial quantum state. Each 
decoherent line then evolves on to produce its own set of future 
decoherent lines. Following through any particular line gives a 
decoherent history -- one for each world of the MWI.


Since the processes of decoherence and the formation of histories or 
worlds are independent of the observer and of the mind, it is clearly 
possible that different branches  (or histories) can differ only by 
things that are not observed, or even not observable. And this is just a 
matter of the formalism of quantum mechanics -- it has nothing to do 
with any theory of mind. The only thing that I would say, though, is 
that your theory of mind, and your theory of the origin of physics, must 
be compatible with this understanding of quantum mechanics -- or else 
your theory of mind/physics is falsified.


Bruce

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Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 30 May 2017, at 11:28, Telmo Menezes wrote:


On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:



On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:


On 29/05/2017 11:21 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
 wrote:

On 29/05/2017 10:42 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
 wrote:

On 29/05/2017 6:26 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
 wrote:
I would say that there is only one history leading to our  
present

state.
Whether you take an MWI view or a collapse view, the wave  
function

branches
deterministically at every point, so if you follow your  
current

twig
back
down to the main trunk etc, there will be a unique path.

I don't think we can say we are in a specific twig. Many things
about
out present state are unknown/undefined. I can imagine that  
there

are
many well-defined present states that are compatible with my  
current

subjective state.


Sure, but we are talking about wave functions, not subjective  
states.

Replace "subjective" with "incomplete knowledge".


Doesn't help. Of course our knowledge is incomplete, the wave  
function

isn't
completely known either -- but the result of specific  
measurements are

what
is at stake here, and they are known quantum states.

In my view, what's at stake here is the possibility of latent
variables having some degree of freedom leading to the same macro
states (provided that there is incomplete information about these
macro states, as is the case for humans).


I am still not clear about what you are trying to say. It is  
certainly
true that many internal details of your microscopic organization  
could

be changed and you wouldn't know the difference. For that matter, an
almost infinite number of details about the rest of the universe  
could
be different and you would still be the same. But that is not what  
we

were talking about. I understood the issue to be whether there was a
unique past, or whether several (or many) different paths lead to  
our
current state. The determinism of the Schrödinger equation would  
suggest
that your unique state has a unique history. Variations in  
microscopic

details of with your body, or the universe, would correspond to
different decohered worlds with no overlap with our world. So  
while such

variations are possible, they do not amount to multiple histories
leading to our current state. We don't need to know that state in  
detail

to be able to argue the consequences of determinism.

In fact you can perform a quantum erasure experiment, and be  
sure

that
your current state goes through at least two different shortest
paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go  
into

the
macroscopic world, but I don't see any reason to believe that  
it

doesn't.


I don't understand what you think you are getting in a quantum
erasure
experiment. If the "which way" information that was gathered is
erased,
normal interference patterns are seen in the double slit  
situation.

The
two
paths (through the separate slits) are in unresolved  
superposition

until
they hit the detector, when decoherence takes over. There are  
not two

separate worlds, and your state is the result of the superposed
paths,
not
of either path separately. There is no ambiguity about which  
the the

"correct" path -- neither is, both contribute equally.
I would say that the delayed choice version of the experiment  
makes it
clear that there are two possible pasts that lead to the same  
present

state -- they differ by one bit of information.


That is not what is implied by delayed choice quantum erasure.  
Whether

an
interference pattern is seen or not is determined by whether the  
"which

way"
information is erased or not. But whether it is or not, the
interference is
only seen when coincidence measurements tell one which photons to
count. And
the timing information necessary for coincidence determination is
available
only *after* all decisions about erasure or not have been made,  
whether

that
decision is made before or after the other photon of the  
entangled pair

has
reached its detector.

"Delayed choice" is perhaps a misleading phrase in this context,  
and it

does
not lead to an ambiguity of path -- it merely tells whether  
there was

an
intact superposition or not.
I know, this is not what I am trying to say. I'll choose  
something much

simpler:

Suppose there is a computer running in an empty room. This  
computer is

connected to a random number generator. At some point it uses the
random value to decide if it's going to show a screen that is all
green or all red. Nobody witnesses it.


If the random number generator is based on quantum randomness,  
then in

principle you will get a superposition of red and green screens, but
this is like the question as to whether we see a superposition of  
live
and dead cats

Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Tue, May 30, 2017 at 3:47 AM, Pierz  wrote:
>
>
> On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:
>>
>> On 29/05/2017 11:21 pm, Telmo Menezes wrote:
>> > On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
>> >  wrote:
>> >> On 29/05/2017 10:42 pm, Telmo Menezes wrote:
>> >>> On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
>> >>>  wrote:
>>  On 29/05/2017 6:26 pm, Telmo Menezes wrote:
>> > On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
>> >  wrote:
>> >> I would say that there is only one history leading to our present
>> >> state.
>> >> Whether you take an MWI view or a collapse view, the wave function
>> >> branches
>> >> deterministically at every point, so if you follow your current
>> >> twig
>> >> back
>> >> down to the main trunk etc, there will be a unique path.
>> > I don't think we can say we are in a specific twig. Many things
>> > about
>> > out present state are unknown/undefined. I can imagine that there
>> > are
>> > many well-defined present states that are compatible with my current
>> > subjective state.
>> 
>>  Sure, but we are talking about wave functions, not subjective states.
>> >>> Replace "subjective" with "incomplete knowledge".
>> >>
>> >> Doesn't help. Of course our knowledge is incomplete, the wave function
>> >> isn't
>> >> completely known either -- but the result of specific measurements are
>> >> what
>> >> is at stake here, and they are known quantum states.
>> > In my view, what's at stake here is the possibility of latent
>> > variables having some degree of freedom leading to the same macro
>> > states (provided that there is incomplete information about these
>> > macro states, as is the case for humans).
>>
>> I am still not clear about what you are trying to say. It is certainly
>> true that many internal details of your microscopic organization could
>> be changed and you wouldn't know the difference. For that matter, an
>> almost infinite number of details about the rest of the universe could
>> be different and you would still be the same. But that is not what we
>> were talking about. I understood the issue to be whether there was a
>> unique past, or whether several (or many) different paths lead to our
>> current state. The determinism of the Schrödinger equation would suggest
>> that your unique state has a unique history. Variations in microscopic
>> details of with your body, or the universe, would correspond to
>> different decohered worlds with no overlap with our world. So while such
>> variations are possible, they do not amount to multiple histories
>> leading to our current state. We don't need to know that state in detail
>> to be able to argue the consequences of determinism.
>>
>> > In fact you can perform a quantum erasure experiment, and be sure
>> > that
>> > your current state goes through at least two different shortest
>> > paths
>> > to the root, and it becomes nonsensical to say that one is the
>> > "correct" one. I don't think anyone knows how far this can go into
>> > the
>> > macroscopic world, but I don't see any reason to believe that it
>> > doesn't.
>> 
>>  I don't understand what you think you are getting in a quantum
>>  erasure
>>  experiment. If the "which way" information that was gathered is
>>  erased,
>>  normal interference patterns are seen in the double slit situation.
>>  The
>>  two
>>  paths (through the separate slits) are in unresolved superposition
>>  until
>>  they hit the detector, when decoherence takes over. There are not two
>>  separate worlds, and your state is the result of the superposed
>>  paths,
>>  not
>>  of either path separately. There is no ambiguity about which the the
>>  "correct" path -- neither is, both contribute equally.
>> >>> I would say that the delayed choice version of the experiment makes it
>> >>> clear that there are two possible pasts that lead to the same present
>> >>> state -- they differ by one bit of information.
>> >>
>> >> That is not what is implied by delayed choice quantum erasure. Whether
>> >> an
>> >> interference pattern is seen or not is determined by whether the "which
>> >> way"
>> >> information is erased or not. But whether it is or not, the
>> >> interference is
>> >> only seen when coincidence measurements tell one which photons to
>> >> count. And
>> >> the timing information necessary for coincidence determination is
>> >> available
>> >> only *after* all decisions about erasure or not have been made, whether
>> >> that
>> >> decision is made before or after the other photon of the entangled pair
>> >> has
>> >> reached its detector.
>> >>
>> >> "Delayed choice" is perhaps a misleading phrase in this context, and it
>> >> does
>> >> not lead to an ambiguity of path -- it merely tells whether there was
>> >> an
>> >> intact superposition or not.
>> > I know, this is not what I am t

Re: A thought on MWI and its alternative(s)

[Pierz]

On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:
>
> On 29/05/2017 11:21 pm, Telmo Menezes wrote: 
> > On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett 
> > > wrote: 
> >> On 29/05/2017 10:42 pm, Telmo Menezes wrote: 
> >>> On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett 
> >>> > wrote: 
>  On 29/05/2017 6:26 pm, Telmo Menezes wrote: 
> > On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett 
> > > wrote: 
> >> I would say that there is only one history leading to our present 
> >> state. 
> >> Whether you take an MWI view or a collapse view, the wave function 
> >> branches 
> >> deterministically at every point, so if you follow your current 
> twig 
> >> back 
> >> down to the main trunk etc, there will be a unique path. 
> > I don't think we can say we are in a specific twig. Many things 
> about 
> > out present state are unknown/undefined. I can imagine that there 
> are 
> > many well-defined present states that are compatible with my current 
> > subjective state. 
>  
>  Sure, but we are talking about wave functions, not subjective states. 
> >>> Replace "subjective" with "incomplete knowledge". 
> >> 
> >> Doesn't help. Of course our knowledge is incomplete, the wave function 
> isn't 
> >> completely known either -- but the result of specific measurements are 
> what 
> >> is at stake here, and they are known quantum states. 
> > In my view, what's at stake here is the possibility of latent 
> > variables having some degree of freedom leading to the same macro 
> > states (provided that there is incomplete information about these 
> > macro states, as is the case for humans). 
>
> I am still not clear about what you are trying to say. It is certainly 
> true that many internal details of your microscopic organization could 
> be changed and you wouldn't know the difference. For that matter, an 
> almost infinite number of details about the rest of the universe could 
> be different and you would still be the same. But that is not what we 
> were talking about. I understood the issue to be whether there was a 
> unique past, or whether several (or many) different paths lead to our 
> current state. The determinism of the Schrödinger equation would suggest 
> that your unique state has a unique history. Variations in microscopic 
> details of with your body, or the universe, would correspond to 
> different decohered worlds with no overlap with our world. So while such 
> variations are possible, they do not amount to multiple histories 
> leading to our current state. We don't need to know that state in detail 
> to be able to argue the consequences of determinism. 
>
> > In fact you can perform a quantum erasure experiment, and be sure 
> that 
> > your current state goes through at least two different shortest 
> paths 
> > to the root, and it becomes nonsensical to say that one is the 
> > "correct" one. I don't think anyone knows how far this can go into 
> the 
> > macroscopic world, but I don't see any reason to believe that it 
> > doesn't. 
>  
>  I don't understand what you think you are getting in a quantum 
> erasure 
>  experiment. If the "which way" information that was gathered is 
> erased, 
>  normal interference patterns are seen in the double slit situation. 
> The 
>  two 
>  paths (through the separate slits) are in unresolved superposition 
> until 
>  they hit the detector, when decoherence takes over. There are not two 
>  separate worlds, and your state is the result of the superposed 
> paths, 
>  not 
>  of either path separately. There is no ambiguity about which the the 
>  "correct" path -- neither is, both contribute equally. 
> >>> I would say that the delayed choice version of the experiment makes it 
> >>> clear that there are two possible pasts that lead to the same present 
> >>> state -- they differ by one bit of information. 
> >> 
> >> That is not what is implied by delayed choice quantum erasure. Whether 
> an 
> >> interference pattern is seen or not is determined by whether the "which 
> way" 
> >> information is erased or not. But whether it is or not, the 
> interference is 
> >> only seen when coincidence measurements tell one which photons to 
> count. And 
> >> the timing information necessary for coincidence determination is 
> available 
> >> only *after* all decisions about erasure or not have been made, whether 
> that 
> >> decision is made before or after the other photon of the entangled pair 
> has 
> >> reached its detector. 
> >> 
> >> "Delayed choice" is perhaps a misleading phrase in this context, and it 
> does 
> >> not lead to an ambiguity of path -- it merely tells whether there was 
> an 
> >> intact superposition or not. 
> > I know, this is not what I am trying to say. I'll choose something much 
> simpler: 
> > 
> > Suppose there is a computer running in an empty room. This computer is 
> > connecte

Re: A thought on MWI and its alternative(s)

[Jason Resch]

Isn't this the distinction between many minds and many world's? Whether to
draw the bounds if the superposition around the conscious mind or the
environment?

Does Saibal Mitra's "changing the past by forgetting" assume and rely upon
many minds?

Jason

On May 28, 2017 7:23 AM, "Pierz"  wrote:

>
>
> On Sunday, May 28, 2017 at 10:28:52 AM UTC+10, Russell Standish wrote:
>>
>> On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:
>> > Recently I've been studying a lot of history, and I've often thought
>> about
>> > how, according to special relativity, you can translate time into space
>> and
>> > vice versa, and therefore how from a different perspective we can think
>> of
>> > the past as distant in space rather than time: my childhood being 40
>> light
>> > years away, rather than 40 years for instance. I can visualise my own
>> body
>> > as a sort of long, four dimensional tendril through spacetime, of which
>> I
>> > only ever see a three-dimensional cross-section. This is the block
>> universe
>> > idea of course. What occurred to me recently was that the past, in any
>> > physical theory I know of, is "locked down". There is only a single
>> history
>> > consistent with the present (ignoring the microscopic ambiguities of
>> > quantum interference effects), but the present is consistent with
>> multiple
>> > futures.
>>
>> This assumption is wrong. There are many histories (pasts) consistent
>> with our present. If we don't know some fact about the past (eg
>> T. Rex's colour), then pasts with different colours of T.Rexes are all
>> compatible with our present. Only when we make a measurement that
>> distinguishes between different facts about the past, do we eliminate
>> some of those pasts from the compatibility list.
>>
>> I think there's a confusion there between human ignorance and physical
> ambiguity - the same confusion expressed in the Schrödinger's Cat thought
> experiment. The resolution of that paradox lies in decoherence. The fact of
> the cat's death or survival spreads into the environment in a myriad of
> ways, whether or not we are measuring them: the cat's cooling after death,
> the shift of its weight as it falls and so on. At that point it is not in a
> superposition any more. We are merely ignorant of its state. I would argue
> the same applies to the colour of T. Rex. The past is not in a
> superposition of possible values, but we are ignorant of those values. Now
> I think it is interesting to contemplate the possibility that more than one
> macroscopic history (one with green and one with red T. Rexes) might lead
> to the same present, but I think it extremely unlikely - that would
> constitute a macroscopic quantum interference effect. I suspect only one
> possible colour is consistent with the present, even though it looks
> superficially like any colour is possible.
>
>
> There are, however, arrows of time - past and future are asymmetric,
>> the future is more uncertain than the past. But I don't see how you
>> can leverage that into support for the MWI.
>>
>>
>>
>> --
>>
>> 
>>
>> Dr Russell StandishPhone 0425 253119 (mobile)
>> Principal, High Performance Coders
>> Visiting Senior Research Fellowhpc...@hpcoders.com.au
>> Economics, Kingston University http://www.hpcoders.com.au
>> 
>>
>>
> --
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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 29/05/2017 11:21 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
 wrote:

On 29/05/2017 10:42 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
 wrote:

On 29/05/2017 6:26 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
 wrote:

I would say that there is only one history leading to our present
state.
Whether you take an MWI view or a collapse view, the wave function
branches
deterministically at every point, so if you follow your current twig
back
down to the main trunk etc, there will be a unique path.

I don't think we can say we are in a specific twig. Many things about
out present state are unknown/undefined. I can imagine that there are
many well-defined present states that are compatible with my current
subjective state.


Sure, but we are talking about wave functions, not subjective states.

Replace "subjective" with "incomplete knowledge".


Doesn't help. Of course our knowledge is incomplete, the wave function isn't
completely known either -- but the result of specific measurements are what
is at stake here, and they are known quantum states.

In my view, what's at stake here is the possibility of latent
variables having some degree of freedom leading to the same macro
states (provided that there is incomplete information about these
macro states, as is the case for humans).


I am still not clear about what you are trying to say. It is certainly 
true that many internal details of your microscopic organization could 
be changed and you wouldn't know the difference. For that matter, an 
almost infinite number of details about the rest of the universe could 
be different and you would still be the same. But that is not what we 
were talking about. I understood the issue to be whether there was a 
unique past, or whether several (or many) different paths lead to our 
current state. The determinism of the Schrödinger equation would suggest 
that your unique state has a unique history. Variations in microscopic 
details of with your body, or the universe, would correspond to 
different decohered worlds with no overlap with our world. So while such 
variations are possible, they do not amount to multiple histories 
leading to our current state. We don't need to know that state in detail 
to be able to argue the consequences of determinism.



In fact you can perform a quantum erasure experiment, and be sure that
your current state goes through at least two different shortest paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go into the
macroscopic world, but I don't see any reason to believe that it
doesn't.


I don't understand what you think you are getting in a quantum erasure
experiment. If the "which way" information that was gathered is erased,
normal interference patterns are seen in the double slit situation. The
two
paths (through the separate slits) are in unresolved superposition until
they hit the detector, when decoherence takes over. There are not two
separate worlds, and your state is the result of the superposed paths,
not
of either path separately. There is no ambiguity about which the the
"correct" path -- neither is, both contribute equally.

I would say that the delayed choice version of the experiment makes it
clear that there are two possible pasts that lead to the same present
state -- they differ by one bit of information.


That is not what is implied by delayed choice quantum erasure. Whether an
interference pattern is seen or not is determined by whether the "which way"
information is erased or not. But whether it is or not, the interference is
only seen when coincidence measurements tell one which photons to count. And
the timing information necessary for coincidence determination is available
only *after* all decisions about erasure or not have been made, whether that
decision is made before or after the other photon of the entangled pair has
reached its detector.

"Delayed choice" is perhaps a misleading phrase in this context, and it does
not lead to an ambiguity of path -- it merely tells whether there was an
intact superposition or not.

I know, this is not what I am trying to say. I'll choose something much simpler:

Suppose there is a computer running in an empty room. This computer is
connected to a random number generator. At some point it uses the
random value to decide if it's going to show a screen that is all
green or all red. Nobody witnesses it.


If the random number generator is based on quantum randomness, then in 
principle you will get a superposition of red and green screens, but 
this is like the question as to whether we see a superposition of live 
and dead cats in Schrödinger's thought experiment. Even if there is an 
underlying quantum event that would give a superposition, decoherence 
steps in and resolves the outcome into separate worlds long before we 
reach the macro level of live/dead cats o

Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
 wrote:
> On 29/05/2017 10:42 pm, Telmo Menezes wrote:
>>
>> On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
>>  wrote:
>>>
>>> On 29/05/2017 6:26 pm, Telmo Menezes wrote:

 On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
  wrote:
>
> I would say that there is only one history leading to our present
> state.
> Whether you take an MWI view or a collapse view, the wave function
> branches
> deterministically at every point, so if you follow your current twig
> back
> down to the main trunk etc, there will be a unique path.

 I don't think we can say we are in a specific twig. Many things about
 out present state are unknown/undefined. I can imagine that there are
 many well-defined present states that are compatible with my current
 subjective state.
>>>
>>>
>>> Sure, but we are talking about wave functions, not subjective states.
>>
>> Replace "subjective" with "incomplete knowledge".
>
>
> Doesn't help. Of course our knowledge is incomplete, the wave function isn't
> completely known either -- but the result of specific measurements are what
> is at stake here, and they are known quantum states.

In my view, what's at stake here is the possibility of latent
variables having some degree of freedom leading to the same macro
states (provided that there is incomplete information about these
macro states, as is the case for humans).

 In fact you can perform a quantum erasure experiment, and be sure that
 your current state goes through at least two different shortest paths
 to the root, and it becomes nonsensical to say that one is the
 "correct" one. I don't think anyone knows how far this can go into the
 macroscopic world, but I don't see any reason to believe that it
 doesn't.
>>>
>>>
>>> I don't understand what you think you are getting in a quantum erasure
>>> experiment. If the "which way" information that was gathered is erased,
>>> normal interference patterns are seen in the double slit situation. The
>>> two
>>> paths (through the separate slits) are in unresolved superposition until
>>> they hit the detector, when decoherence takes over. There are not two
>>> separate worlds, and your state is the result of the superposed paths,
>>> not
>>> of either path separately. There is no ambiguity about which the the
>>> "correct" path -- neither is, both contribute equally.
>>
>> I would say that the delayed choice version of the experiment makes it
>> clear that there are two possible pasts that lead to the same present
>> state -- they differ by one bit of information.
>
>
> That is not what is implied by delayed choice quantum erasure. Whether an
> interference pattern is seen or not is determined by whether the "which way"
> information is erased or not. But whether it is or not, the interference is
> only seen when coincidence measurements tell one which photons to count. And
> the timing information necessary for coincidence determination is available
> only *after* all decisions about erasure or not have been made, whether that
> decision is made before or after the other photon of the entangled pair has
> reached its detector.
>
> "Delayed choice" is perhaps a misleading phrase in this context, and it does
> not lead to an ambiguity of path -- it merely tells whether there was an
> intact superposition or not.

I know, this is not what I am trying to say. I'll choose something much simpler:

Suppose there is a computer running in an empty room. This computer is
connected to a random number generator. At some point it uses the
random value to decide if it's going to show a screen that is all
green or all red. Nobody witnesses it.

>
> Bruce
>
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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 29/05/2017 10:42 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
 wrote:

On 29/05/2017 6:26 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
 wrote:

I would say that there is only one history leading to our present state.
Whether you take an MWI view or a collapse view, the wave function
branches
deterministically at every point, so if you follow your current twig back
down to the main trunk etc, there will be a unique path.

I don't think we can say we are in a specific twig. Many things about
out present state are unknown/undefined. I can imagine that there are
many well-defined present states that are compatible with my current
subjective state.


Sure, but we are talking about wave functions, not subjective states.

Replace "subjective" with "incomplete knowledge".


Doesn't help. Of course our knowledge is incomplete, the wave function 
isn't completely known either -- but the result of specific measurements 
are what is at stake here, and they are known quantum states.



In fact you can perform a quantum erasure experiment, and be sure that
your current state goes through at least two different shortest paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go into the
macroscopic world, but I don't see any reason to believe that it
doesn't.


I don't understand what you think you are getting in a quantum erasure
experiment. If the "which way" information that was gathered is erased,
normal interference patterns are seen in the double slit situation. The two
paths (through the separate slits) are in unresolved superposition until
they hit the detector, when decoherence takes over. There are not two
separate worlds, and your state is the result of the superposed paths, not
of either path separately. There is no ambiguity about which the the
"correct" path -- neither is, both contribute equally.

I would say that the delayed choice version of the experiment makes it
clear that there are two possible pasts that lead to the same present
state -- they differ by one bit of information.


That is not what is implied by delayed choice quantum erasure. Whether 
an interference pattern is seen or not is determined by whether the 
"which way" information is erased or not. But whether it is or not, the 
interference is only seen when coincidence measurements tell one which 
photons to count. And the timing information necessary for coincidence 
determination is available only *after* all decisions about erasure or 
not have been made, whether that decision is made before or after the 
other photon of the entangled pair has reached its detector.


"Delayed choice" is perhaps a misleading phrase in this context, and it 
does not lead to an ambiguity of path -- it merely tells whether there 
was an intact superposition or not.


Bruce

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Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
 wrote:
> On 29/05/2017 6:26 pm, Telmo Menezes wrote:
>>
>> On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
>>  wrote:
>>>
>>> On 29/05/2017 9:45 am, Pierz wrote:
>>>
>>> WRT to this whole multi-coloured T-Rex business, there is a simpler point
>>> to
>>> be made. My original argument was in favour of MWI. Now whether, in MWI,
>>> macroscopic histories can merge is surely an interesting puzzle. But
>>> without
>>> MWI, there cannot be any ambiguity about the colour of T-Rexes. In a
>>> single
>>> universe interpretation of QM, T-Rexes were blue or they were red and
>>> they
>>> can't exist in a superposition of both. The past can't turn back into a
>>> mush
>>> of probabilities, because that would imply either that there is some "3p"
>>> significance to the concept of "now", or that the past consists of many
>>> worlds. In other words I am asserting that, sans MWI, any ambiguity about
>>> the past is a matter of ignorance, not of quantum uncertainty. Otherwise
>>> you
>>> are saying that past moments which once were well defined are somehow
>>> dissolved back into ambiguity by the passage of time. But that would be
>>> privileging the now with some kind of absolute significance, which is
>>> untenable. All nows are equal.
>>>
>>> Another way of stating my argument is that the following three
>>> propositions
>>> are mutually incompatible:
>>>
>>> There is a single history
>>> There is no objective significance to the concept of the current moment
>>> ("now")
>>> The future is objectively uncertain
>>>
>>> You can take your pick which of those propositions you reject, but it's
>>> logically impossible to support all three.
>>>
>>>
>>> I would say that there is only one history leading to our present state.
>>> Whether you take an MWI view or a collapse view, the wave function
>>> branches
>>> deterministically at every point, so if you follow your current twig back
>>> down to the main trunk etc, there will be a unique path.
>>
>> I don't think we can say we are in a specific twig. Many things about
>> out present state are unknown/undefined. I can imagine that there are
>> many well-defined present states that are compatible with my current
>> subjective state.
>
>
> Sure, but we are talking about wave functions, not subjective states.

Replace "subjective" with "incomplete knowledge".

>> In fact you can perform a quantum erasure experiment, and be sure that
>> your current state goes through at least two different shortest paths
>> to the root, and it becomes nonsensical to say that one is the
>> "correct" one. I don't think anyone knows how far this can go into the
>> macroscopic world, but I don't see any reason to believe that it
>> doesn't.
>
>
> I don't understand what you think you are getting in a quantum erasure
> experiment. If the "which way" information that was gathered is erased,
> normal interference patterns are seen in the double slit situation. The two
> paths (through the separate slits) are in unresolved superposition until
> they hit the detector, when decoherence takes over. There are not two
> separate worlds, and your state is the result of the superposed paths, not
> of either path separately. There is no ambiguity about which the the
> "correct" path -- neither is, both contribute equally.

I would say that the delayed choice version of the experiment makes it
clear that there are two possible pasts that lead to the same present
state -- they differ by one bit of information.

> Bruce
>
>
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Fwd: A thought on MWI and its alternative(s)

[David Nyman]

-- Forwarded message --
From: David Nyman 
Date: 26 May 2017 at 19:36
Subject: Re: A thought on MWI and its alternative(s)
To: meekerdb , Bruno Marchal <
bruno.fernand.marc...@gmail.com>




On 26 May 2017 18:49, "Brent Meeker"  wrote:



On 5/26/2017 4:40 AM, David Nyman wrote:

> ​Forgive me for hijacking your topic for my own ends ;)​ But as is
> currently being discussed in other threads, truth has another sense which
> is most often obscured for methodological reasons and then most typically
> subsiding thereafter into complete invisibility. Brent's remarks above will
> serve as a quite typical example. This truth is what we might call
> perceptual, or the primary indubitability of perceptibility itself, to
> which Descartes notoriously referred. So truth by concordance, to which you
> refer above, is in the first instance "accessible" only in terms of its
> *primary truth for a subject* with whose perceptual spectrum it is
> coterminous. You might wish to quibble about the necessity of appropriating
> a concept of truth to these ends. But what is the indispensable
> characteristic of truth if it isn't indubitability? Yes, of course,
> subsidiary truth-notions then depend on concordances or "correspondences
> with the facts" as Tarski points out. But what are these "facts" if not in
> the first instance (and it is indeed this first instance we seek to bring
> back into the light) perceptual ones? And how could we conceive of applying
> the criterion of correspondence if the provenance of the putative "facts"
> to be correlated was already itself in doubt? I think you will see what I
> mean. For me, what has been particularly helpful in Bruno's introduction of
> the modal logics in the elementary analysis of subjectivity has been the
> rigorous rehabilitation of the indispensable (but nonetheless gone missing)
> notion of a specifically first-personal or perceptual truth. Paradoxical as
> it may seem (although consistent with our experience) it is a truth that
> cannot be proven, but only guessed at or wagered on, from any but its
> uniquely first-personal point of view. Nonetheless it is this conception of
> truth that perhaps may ultimately permit us to escape the stark
> not-even-wrongness of alternative formulations of the mind-body problem.
>

I agree that "facts" ground in first-person perceptions.  But not that they
are indubitable.


Brent, can we finally either agree or disagree on the distinction I have
repeatedly made every effort to make explicit? I am perfectly clear that
any inference whatsoever made *on the basis of* perceptual facts may be
mistaken, possibly in every respect. Descartes, of course, was equally
explicit about this, as I recently reminded you, as is Bruno, which is why
he says that Bp&p is a "bet" on a reality. Therefore *that is not my
point*. What is my point is the fact that no inference whatsoever of this
kind can even get started failing the presence of a perceptual fact, a
point also not lost on Descartes. That's all he really meant to convey in
the cogito, despite subsequent attempts to obliterate this pithy
encapsulation in a snowstorm of grammatical obfuscation. Hence this primary
fact is by its very definition indubitable, on pain of incoherence.

  We are familiar with optical illusions and other misperceptions.


As you say, we are all indeed familiar with that, which is why I was at
pains yet again to make clear the distinction. Look, I'm flattered of
course that you read me at all but your comments would be of more help to
me if you would at least take on board what I have said on repeated
occasions.

So the facts that science attempts to explain are already filtered through
intersubjective agreement, i.e. a third person view.


Well, inter-subjective agreement is properly a 1p-plural view. A 3p view is
a hypothetical idealisation of this. IOW it adopts a hypothetical view from
nowhere, which is its Achilles' heel when we forget that it thereby
implicitly appropriates a 1p interpretative perspective. The 1p-plural view
is what we accept as evidence of the relative probability of veridicality
of our perceptions. Consequently, the observables of physics are
inescapably 1p-plural phenomena.

That's why Bruno's computationalism needs to explain the appearance of the
physical world - in order that there be "facts" and not just dreams.


Yes that's exactly what it needs to explain. No one would claim it
currently fully achieves this, though it's notable that a quantum-like
logic - a consequence of the infinity of continuations - is a prediction of
the theory, as opposed to an a posteriori observation. But is there
something in particular that would lead you to believe that it cannot?

David



Brent

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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 29/05/2017 6:26 pm, Telmo Menezes wrote:

On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
 wrote:

On 29/05/2017 9:45 am, Pierz wrote:

WRT to this whole multi-coloured T-Rex business, there is a simpler point to
be made. My original argument was in favour of MWI. Now whether, in MWI,
macroscopic histories can merge is surely an interesting puzzle. But without
MWI, there cannot be any ambiguity about the colour of T-Rexes. In a single
universe interpretation of QM, T-Rexes were blue or they were red and they
can't exist in a superposition of both. The past can't turn back into a mush
of probabilities, because that would imply either that there is some "3p"
significance to the concept of "now", or that the past consists of many
worlds. In other words I am asserting that, sans MWI, any ambiguity about
the past is a matter of ignorance, not of quantum uncertainty. Otherwise you
are saying that past moments which once were well defined are somehow
dissolved back into ambiguity by the passage of time. But that would be
privileging the now with some kind of absolute significance, which is
untenable. All nows are equal.

Another way of stating my argument is that the following three propositions
are mutually incompatible:

There is a single history
There is no objective significance to the concept of the current moment
("now")
The future is objectively uncertain

You can take your pick which of those propositions you reject, but it's
logically impossible to support all three.


I would say that there is only one history leading to our present state.
Whether you take an MWI view or a collapse view, the wave function branches
deterministically at every point, so if you follow your current twig back
down to the main trunk etc, there will be a unique path.

I don't think we can say we are in a specific twig. Many things about
out present state are unknown/undefined. I can imagine that there are
many well-defined present states that are compatible with my current
subjective state.


Sure, but we are talking about wave functions, not subjective states.


In fact you can perform a quantum erasure experiment, and be sure that
your current state goes through at least two different shortest paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go into the
macroscopic world, but I don't see any reason to believe that it
doesn't.


I don't understand what you think you are getting in a quantum erasure 
experiment. If the "which way" information that was gathered is erased, 
normal interference patterns are seen in the double slit situation. The 
two paths (through the separate slits) are in unresolved superposition 
until they hit the detector, when decoherence takes over. There are not 
two separate worlds, and your state is the result of the superposed 
paths, not of either path separately. There is no ambiguity about which 
the the "correct" path -- neither is, both contribute equally.


Bruce

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Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
 wrote:
> On 29/05/2017 9:45 am, Pierz wrote:
>
> WRT to this whole multi-coloured T-Rex business, there is a simpler point to
> be made. My original argument was in favour of MWI. Now whether, in MWI,
> macroscopic histories can merge is surely an interesting puzzle. But without
> MWI, there cannot be any ambiguity about the colour of T-Rexes. In a single
> universe interpretation of QM, T-Rexes were blue or they were red and they
> can't exist in a superposition of both. The past can't turn back into a mush
> of probabilities, because that would imply either that there is some "3p"
> significance to the concept of "now", or that the past consists of many
> worlds. In other words I am asserting that, sans MWI, any ambiguity about
> the past is a matter of ignorance, not of quantum uncertainty. Otherwise you
> are saying that past moments which once were well defined are somehow
> dissolved back into ambiguity by the passage of time. But that would be
> privileging the now with some kind of absolute significance, which is
> untenable. All nows are equal.
>
> Another way of stating my argument is that the following three propositions
> are mutually incompatible:
>
> There is a single history
> There is no objective significance to the concept of the current moment
> ("now")
> The future is objectively uncertain
>
> You can take your pick which of those propositions you reject, but it's
> logically impossible to support all three.
>
>
> I would say that there is only one history leading to our present state.
> Whether you take an MWI view or a collapse view, the wave function branches
> deterministically at every point, so if you follow your current twig back
> down to the main trunk etc, there will be a unique path.

I don't think we can say we are in a specific twig. Many things about
out present state are unknown/undefined. I can imagine that there are
many well-defined present states that are compatible with my current
subjective state.

In fact you can perform a quantum erasure experiment, and be sure that
your current state goes through at least two different shortest paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go into the
macroscopic world, but I don't see any reason to believe that it
doesn't.

>  If there are points
> along this path where there has been no decoherence, so the potentially
> separate worlds never form into distinct worlds (the potential branches
> recombine), then you will pass through such potential branches as though
> they were solid stems.
>
> There is another question as to whether we are in a superposition, of say
> red and green T.Rexes, but that they are in separate decohered worlds and
> the overlap function is zero FAPP, as Russell says. I don't think such a
> question has a definitive answer. Despite what some people say, viz., that
> in the QM MWI, everything that is possible happens in some branch or other,
> I don't think that the branches of the quantum tree necessarily pass through
> every point in the possibility space. Quantum evolution in the Everettian
> picture is strictly deterministic, so if some apparently possible state of
> affairs is not consistent with the initial conditions, then if will never
> appear anywhere. Given any particular imagined possibility, one cannot say
> whether it occurs in some world or other, or in no world whatsoever.
>
> Bruce
>
>
>
>
> On Monday, May 29, 2017 at 8:17:53 AM UTC+10, Russell Standish wrote:
>>
>> On Sun, May 28, 2017 at 06:37:09PM +0200, Bruno Marchal wrote:
>> >
>> > On 28 May 2017, at 14:23, Pierz wrote:
>> >
>> >
>> >
>> > >We are merely ignorant of its state. I would argue the same
>> > >applies to the colour of T. Rex. The past is not in a
>> > >superposition of possible values, but we are ignorant of those
>> > >values.
>> >
>> > For all practical purpose. But there are temporal form of Bell's
>> > inequality violation which suggest that in principle (tacking track
>> > of all the particles the T-Rex interacted with (!)) we could make
>> > measurement showing interference of "different T-rex".
>> >
>> >
>>
>> There seems to be some confusion between superposition and
>> interference. In crude terms, we do live in a superposition |green T.Rex>
>> + |blue T.Rex>. It may well be that |green T.Rex> and |blue T.Rex> are
>> orthogonal, ie =0 (at FAPP), in which case the
>> two histories do not interfere, and there is no quantum interference
>> phenomena.
>>
>>
>> --
>>
>>
>> 
>> Dr Russell StandishPhone 0425 253119 (mobile)
>> Principal, High Performance Coders
>> Visiting Senior Research Fellowhpc...@hpcoders.com.au
>> Economics, Kingston University http://www.hpcoders.com.au
>>
>> 
>
> --
> You received 

Re: A thought on MWI and its alternative(s)

[Telmo Menezes]

On Sun, May 28, 2017 at 4:24 AM, Jason Resch  wrote:
>
>
> On Saturday, May 27, 2017, Russell Standish  wrote:
>>
>> On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:
>> > Recently I've been studying a lot of history, and I've often thought
>> > about
>> > how, according to special relativity, you can translate time into space
>> > and
>> > vice versa, and therefore how from a different perspective we can think
>> > of
>> > the past as distant in space rather than time: my childhood being 40
>> > light
>> > years away, rather than 40 years for instance. I can visualise my own
>> > body
>> > as a sort of long, four dimensional tendril through spacetime, of which
>> > I
>> > only ever see a three-dimensional cross-section. This is the block
>> > universe
>> > idea of course. What occurred to me recently was that the past, in any
>> > physical theory I know of, is "locked down". There is only a single
>> > history
>> > consistent with the present (ignoring the microscopic ambiguities of
>> > quantum interference effects), but the present is consistent with
>> > multiple
>> > futures.
>>
>> This assumption is wrong. There are many histories (pasts) consistent
>> with our present. If we don't know some fact about the past (eg
>> T. Rex's colour), then pasts with different colours of T.Rexes are all
>> compatible with our present. Only when we make a measurement that
>> distinguishes between different facts about the past, do we eliminate
>> some of those pasts from the compatibility list.
>>
>> There are, however, arrows of time - past and future are asymmetric,
>> the future is more uncertain than the past. But I don't see how you
>> can leverage that into support for the MWI.
>>
>>
>
>
> I agree, there are multiple pasts compatible with our future. Some if these
> can't be ruled out with any possible measurements, like in the case if the
> quantum erasure.
>
> That entropy increases does mean there are more futures than pasts.

This is an interesting point.

It goes in the direction of something that I ponder on for a while
(possibly a trivial thought for physicists): being that the moment of
the big bang is the simplest possible state conceivable, and assuming
the MWI, ISTM that the moment of the big bang is shared by all
histories, being in fact a nexus between all possible worlds.

A crazier idea is this: can you increase your freedom in relation to
the past (in the sense of admitting more branches) by destroying
memories?

Regarding more futures than pasts: the idea makes sense, but I would
say only at a statistical physics level. That is to say, what we call
"progress" as human beings can be seen as an increase in complexity.
People that think about complex systems tend to like this idea that
life is a phenomenon that happens "at the edge of chaos", which is to
say, there is some entropic "sweet spot" where it thrives. This
suggests to me that, although the number of possible states increases
with the arrow of time, at some point the complexity will go down. In
other words: the far future is increasingly boring...

> Regarding special relatively and collapse, I think the point is that two
> observers in different reference frames can have different presents. Two
> humans walking past each other on the sidewalk may have presents that
> include the Andromeda Galaxy hours apart in time. (See "Andromeda Paradox").
> So if something on Earth collspses the wave everywhere and instantly (in the
> present) which present is it collapsed in?
>
> I think this even more clearly shows the incompatibility between collapse
> theories and special relatively, beyond just pointing to the FTL influences
> as violations; this shows now we have to somehow use an objective reference
> frame which relatively tells us does not exist. And this leads to collapse
> events happening in different times/places for different observers, even
> ones walking past each other on a sidewalk.
>
> Jason
>
>
>
>>
>>
>> --
>>
>>
>> 
>> Dr Russell StandishPhone 0425 253119 (mobile)
>> Principal, High Performance Coders
>> Visiting Senior Research Fellowhpco...@hpcoders.com.au
>> Economics, Kingston University http://www.hpcoders.com.au
>>
>> 
>>
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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 29/05/2017 3:33 pm, Pierz wrote:
Russell, do you believe that Schrödinger's cat is in a superposition 
of dead and alive before we open the box?


That depends a little on your point of view. For the 'bird' view from 
outside the wave function, all superpositions exist timelessly, so the 
cat is both dead in one world and alive in another, but these worlds are 
both part of the same universal wave function, so there is still a 
superposition.


But in the 'frog' view from within, we only ever experience just one 
branch, so the superposition has been reduced as far as we are 
concerned. In fact, from our perspective, there is never a superposition 
of live and dead cats because decoherence will have reduced the decayed 
and non-decayed radioactive atom to separate worlds long before the 
canister of cyanide is crushed. The cat is alive in one such world, and 
dead in the other, and we, as decohered observers, are in one world or 
the other, not in any superposition.


For the case of the colour of T. Rex, even if both red and yellow are 
possible colours, the split between the worlds in which such different 
evolutionary trees are possible would have occurred long before either 
T. Rex or we appeared on the evolutionary stage. So again, no 
superposition in any effective sense.


Bruce




On Monday, May 29, 2017 at 3:26:49 PM UTC+10, Bruce wrote:

On 29/05/2017 2:52 pm, Russell Standish wrote:
> On Mon, May 29, 2017 at 11:26:18AM +1000, Bruce Kellett wrote:
>> There is another question as to whether we are in a superposition,
>> of say red and green T.Rexes, but that they are in separate
>> decohered worlds and the overlap function is zero FAPP, as Russell
>> says. I don't think such a question has a definitive answer.
Despite
>> what some people say, viz., that in the QM MWI, everything that is
>> possible happens in some branch or other, I don't think that the
>> branches of the quantum tree necessarily pass through every
point in
>> the possibility space. Quantum evolution in the Everettian picture
>> is strictly deterministic, so if some apparently possible state of
>> affairs is not consistent with the initial conditions, then if
will
>> never appear anywhere. Given any particular imagined possibility,
>> one cannot say whether it occurs in some world or other, or in no
>> world whatsoever.
>>
> It is true that you have laid bare an unstated assumption - that
the
> two different coloured T. Rexes are compatible with the universe's
> initial conditions, as we know them. Obviously, if it possible to
> deduce the colour of T. Rexes from first principles without
making any
> further measurements, then we don't live in such a
superposition. But I
> still think that if it requires a measurement (no matter how
indirect)
> to determine the fact of colour, than we do live in a
superposition.

I don't think that follows. If the initial conditions are such
that only
red T. Rexes can evolve, it would still require a colour
measurement to
determine that colour. There would be no superposition of different
coloured T. Rexes, with or without any necessary measurement. The
point,
I think, is that colour, in the sense that we are using that concept
here, is really a classical property that does not necessarily
exist in
superpositions.

Bruce

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Re: A thought on MWI and its alternative(s)

[Pierz]

Russell, do you believe that Schrödinger's cat is in a superposition of 
dead and alive before we open the box?

On Monday, May 29, 2017 at 3:26:49 PM UTC+10, Bruce wrote:
>
> On 29/05/2017 2:52 pm, Russell Standish wrote: 
> > On Mon, May 29, 2017 at 11:26:18AM +1000, Bruce Kellett wrote: 
> >> There is another question as to whether we are in a superposition, 
> >> of say red and green T.Rexes, but that they are in separate 
> >> decohered worlds and the overlap function is zero FAPP, as Russell 
> >> says. I don't think such a question has a definitive answer. Despite 
> >> what some people say, viz., that in the QM MWI, everything that is 
> >> possible happens in some branch or other, I don't think that the 
> >> branches of the quantum tree necessarily pass through every point in 
> >> the possibility space. Quantum evolution in the Everettian picture 
> >> is strictly deterministic, so if some apparently possible state of 
> >> affairs is not consistent with the initial conditions, then if will 
> >> never appear anywhere. Given any particular imagined possibility, 
> >> one cannot say whether it occurs in some world or other, or in no 
> >> world whatsoever. 
> >> 
> > It is true that you have laid bare an unstated assumption - that the 
> > two different coloured T. Rexes are compatible with the universe's 
> > initial conditions, as we know them. Obviously, if it possible to 
> > deduce the colour of T. Rexes from first principles without making any 
> > further measurements, then we don't live in such a superposition. But I 
> > still think that if it requires a measurement (no matter how indirect) 
> > to determine the fact of colour, than we do live in a superposition. 
>
> I don't think that follows. If the initial conditions are such that only 
> red T. Rexes can evolve, it would still require a colour measurement to 
> determine that colour. There would be no superposition of different 
> coloured T. Rexes, with or without any necessary measurement. The point, 
> I think, is that colour, in the sense that we are using that concept 
> here, is really a classical property that does not necessarily exist in 
> superpositions. 
>
> Bruce 
>

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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 29/05/2017 2:52 pm, Russell Standish wrote:

On Mon, May 29, 2017 at 11:26:18AM +1000, Bruce Kellett wrote:

There is another question as to whether we are in a superposition,
of say red and green T.Rexes, but that they are in separate
decohered worlds and the overlap function is zero FAPP, as Russell
says. I don't think such a question has a definitive answer. Despite
what some people say, viz., that in the QM MWI, everything that is
possible happens in some branch or other, I don't think that the
branches of the quantum tree necessarily pass through every point in
the possibility space. Quantum evolution in the Everettian picture
is strictly deterministic, so if some apparently possible state of
affairs is not consistent with the initial conditions, then if will
never appear anywhere. Given any particular imagined possibility,
one cannot say whether it occurs in some world or other, or in no
world whatsoever.


It is true that you have laid bare an unstated assumption - that the
two different coloured T. Rexes are compatible with the universe's
initial conditions, as we know them. Obviously, if it possible to
deduce the colour of T. Rexes from first principles without making any
further measurements, then we don't live in such a superposition. But I
still think that if it requires a measurement (no matter how indirect)
to determine the fact of colour, than we do live in a superposition.


I don't think that follows. If the initial conditions are such that only 
red T. Rexes can evolve, it would still require a colour measurement to 
determine that colour. There would be no superposition of different 
coloured T. Rexes, with or without any necessary measurement. The point, 
I think, is that colour, in the sense that we are using that concept 
here, is really a classical property that does not necessarily exist in 
superpositions.


Bruce

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Re: A thought on MWI and its alternative(s)

[Russell Standish]

On Mon, May 29, 2017 at 11:26:18AM +1000, Bruce Kellett wrote:
> 
> There is another question as to whether we are in a superposition,
> of say red and green T.Rexes, but that they are in separate
> decohered worlds and the overlap function is zero FAPP, as Russell
> says. I don't think such a question has a definitive answer. Despite
> what some people say, viz., that in the QM MWI, everything that is
> possible happens in some branch or other, I don't think that the
> branches of the quantum tree necessarily pass through every point in
> the possibility space. Quantum evolution in the Everettian picture
> is strictly deterministic, so if some apparently possible state of
> affairs is not consistent with the initial conditions, then if will
> never appear anywhere. Given any particular imagined possibility,
> one cannot say whether it occurs in some world or other, or in no
> world whatsoever.
> 

It is true that you have laid bare an unstated assumption - that the
two different coloured T. Rexes are compatible with the universe's
initial conditions, as we know them. Obviously, if it possible to
deduce the colour of T. Rexes from first principles without making any
further measurements, then we don't live in such a superposition. But I
still think that if it requires a measurement (no matter how indirect)
to determine the fact of colour, than we do live in a superposition.

Cheers
-- 


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: A thought on MWI and its alternative(s)

[Bruce Kellett]

On 29/05/2017 9:45 am, Pierz wrote:
WRT to this whole multi-coloured T-Rex business, there is a simpler 
point to be made. My original argument was in favour of MWI. Now 
whether, in MWI, macroscopic histories can merge is surely an 
interesting puzzle. But /without /MWI, there cannot be any ambiguity 
about the colour of T-Rexes. In a single universe interpretation of 
QM, T-Rexes were blue or they were red and they can't exist in a 
superposition of both. The past can't turn back into a mush of 
probabilities, because that would imply either that there is some "3p" 
significance to the concept of "now", or that the past consists of 
many worlds. In other words I am asserting that, /sans MWI,/ any 
ambiguity about the past is a matter of ignorance, not of quantum 
uncertainty. Otherwise you are saying that past moments which once 
were well defined are somehow dissolved back into ambiguity by the 
passage of time. But that would be privileging the now with some kind 
of absolute significance, which is untenable. All nows are equal.


Another way of stating my argument is that the following three 
propositions are mutually incompatible:


  * There is a single history
  * There is no objective significance to the concept of the current
moment ("now")
  * The future is objectively uncertain

You can take your pick which of those propositions you reject, but 
it's logically impossible to support all three.


I would say that there is only one history leading to our present state. 
Whether you take an MWI view or a collapse view, the wave function 
branches deterministically at every point, so if you follow your current 
twig back down to the main trunk etc, there will be a unique path. If 
there are points along this path where there has been no decoherence, so 
the potentially separate worlds never form into distinct worlds (the 
potential branches recombine), then you will pass through such potential 
branches as though they were solid stems.


There is another question as to whether we are in a superposition, of 
say red and green T.Rexes, but that they are in separate decohered 
worlds and the overlap function is zero FAPP, as Russell says. I don't 
think such a question has a definitive answer. Despite what some people 
say, viz., that in the QM MWI, everything that is possible happens in 
some branch or other, I don't think that the branches of the quantum 
tree necessarily pass through every point in the possibility space. 
Quantum evolution in the Everettian picture is strictly deterministic, 
so if some apparently possible state of affairs is not consistent with 
the initial conditions, then if will never appear anywhere. Given any 
particular imagined possibility, one cannot say whether it occurs in 
some world or other, or in no world whatsoever.


Bruce




On Monday, May 29, 2017 at 8:17:53 AM UTC+10, Russell Standish wrote:

On Sun, May 28, 2017 at 06:37:09PM +0200, Bruno Marchal wrote:
>
> On 28 May 2017, at 14:23, Pierz wrote:
>
>
>
> >We are merely ignorant of its state. I would argue the same
> >applies to the colour of T. Rex. The past is not in a
> >superposition of possible values, but we are ignorant of those
> >values.
>
> For all practical purpose. But there are temporal form of Bell's
> inequality violation which suggest that in principle (tacking track
> of all the particles the T-Rex interacted with (!)) we could make
> measurement showing interference of "different T-rex".
>
>

There seems to be some confusion between superposition and
interference. In crude terms, we do live in a superposition |green
T.Rex>
+ |blue T.Rex>. It may well be that |green T.Rex> and |blue T.Rex>
are
orthogonal, ie =0 (at FAPP), in which case
the
two histories do not interfere, and there is no quantum
interference phenomena.


-- 




Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellow hpc...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au



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Re: A thought on MWI and its alternative(s)

[Pierz]

WRT to this whole multi-coloured T-Rex business, there is a simpler point 
to be made. My original argument was in favour of MWI. Now whether, in MWI, 
macroscopic histories can merge is surely an interesting puzzle. But *without 
*MWI, there cannot be any ambiguity about the colour of T-Rexes. In a 
single universe interpretation of QM, T-Rexes were blue or they were red 
and they can't exist in a superposition of both. The past can't turn back 
into a mush of probabilities, because that would imply either that there is 
some "3p" significance to the concept of "now", or that the past consists 
of many worlds. In other words I am asserting that, *sans MWI,* any 
ambiguity about the past is a matter of ignorance, not of quantum 
uncertainty. Otherwise you are saying that past moments which once were 
well defined are somehow dissolved back into ambiguity by the passage of 
time. But that would be privileging the now with some kind of absolute 
significance, which is untenable. All nows are equal. 

Another way of stating my argument is that the following three propositions 
are mutually incompatible:

   - There is a single history
   - There is no objective significance to the concept of the current 
   moment ("now")
   - The future is objectively uncertain

You can take your pick which of those propositions you reject, but it's 
logically impossible to support all three. 

On Monday, May 29, 2017 at 8:17:53 AM UTC+10, Russell Standish wrote:
>
> On Sun, May 28, 2017 at 06:37:09PM +0200, Bruno Marchal wrote: 
> > 
> > On 28 May 2017, at 14:23, Pierz wrote: 
> > 
> > 
> > 
> > >We are merely ignorant of its state. I would argue the same 
> > >applies to the colour of T. Rex. The past is not in a 
> > >superposition of possible values, but we are ignorant of those 
> > >values. 
> > 
> > For all practical purpose. But there are temporal form of Bell's 
> > inequality violation which suggest that in principle (tacking track 
> > of all the particles the T-Rex interacted with (!)) we could make 
> > measurement showing interference of "different T-rex". 
> > 
> > 
>
> There seems to be some confusion between superposition and 
> interference. In crude terms, we do live in a superposition |green T.Rex> 
> + |blue T.Rex>. It may well be that |green T.Rex> and |blue T.Rex> are 
> orthogonal, ie =0 (at FAPP), in which case the 
> two histories do not interfere, and there is no quantum interference 
> phenomena. 
>
>
> -- 
>
>  
>
> Dr Russell StandishPhone 0425 253119 (mobile) 
> Principal, High Performance Coders 
> Visiting Senior Research Fellowhpc...@hpcoders.com.au 
>  
> Economics, Kingston University http://www.hpcoders.com.au 
>  
>
>

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Re: A thought on MWI and its alternative(s)

[Russell Standish]

On Sun, May 28, 2017 at 06:37:09PM +0200, Bruno Marchal wrote:
> 
> On 28 May 2017, at 14:23, Pierz wrote:
> 
> 
> 
> >We are merely ignorant of its state. I would argue the same
> >applies to the colour of T. Rex. The past is not in a
> >superposition of possible values, but we are ignorant of those
> >values.
> 
> For all practical purpose. But there are temporal form of Bell's
> inequality violation which suggest that in principle (tacking track
> of all the particles the T-Rex interacted with (!)) we could make
> measurement showing interference of "different T-rex".
> 
> 

There seems to be some confusion between superposition and
interference. In crude terms, we do live in a superposition |green T.Rex>
+ |blue T.Rex>. It may well be that |green T.Rex> and |blue T.Rex> are
orthogonal, ie =0 (at FAPP), in which case the
two histories do not interfere, and there is no quantum interference phenomena.


-- 


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: A thought on MWI and its alternative(s)

[smitra]

On 28-05-2017 04:24, Jason Resch wrote:

On Saturday, May 27, 2017, Russell Standish 
wrote:


On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:

Recently I've been studying a lot of history, and I've often

thought about

how, according to special relativity, you can translate time into

space and

vice versa, and therefore how from a different perspective we can

think of

the past as distant in space rather than time: my childhood being

40 light

years away, rather than 40 years for instance. I can visualise my

own body

as a sort of long, four dimensional tendril through spacetime, of

which I

only ever see a three-dimensional cross-section. This is the

block universe

idea of course. What occurred to me recently was that the past,

in any

physical theory I know of, is "locked down". There is only a

single history

consistent with the present (ignoring the microscopic ambiguities

of

quantum interference effects), but the present is consistent with

multiple

futures.


This assumption is wrong. There are many histories (pasts)
consistent
with our present. If we don't know some fact about the past (eg
T. Rex's colour), then pasts with different colours of T.Rexes are
all
compatible with our present. Only when we make a measurement that
distinguishes between different facts about the past, do we
eliminate
some of those pasts from the compatibility list.

There are, however, arrows of time - past and future are
asymmetric,
the future is more uncertain than the past. But I don't see how you
can leverage that into support for the MWI.


I agree, there are multiple pasts compatible with our future. Some if
these can't be ruled out with any possible measurements, like in the
case if the quantum erasure.

That entropy increases does mean there are more futures than pasts.




Jason



Unitary time evolution implies that the number of states cannot change. 
Entropy, when defined as the logarithm of the real number of states a 
closed system (or the entire universe) can really be in, does not 
increase it will always stay the same due to unitary time evolution.


Entropy as used in thermodynamics has to be defined using a coarse 
graining procedure, this will then be the logarithm of the number of 
microstates that have the same macroscopic properties as the system 
under consideration (the coarse graining is then implied by the notions 
of "macro" and "micro", as soon as you specify exactly how you draw the 
line here).


But note here that saying that there are an X number of microstates 
compatible with the macrostate of the glass of water on my table, 
doesn't mean that the glass of water can really be in any one of the X 
states.  If I were to do a  free expansion experiment where a gas 
containing N molecules  in a perfectly isolated cylinder had doubled its 
volume, then the entropy increase of N Log(2) does not mean that after 
the expansion there are really a factor of  2^N more possible states the 
gas can be in.


The unitary time evolution of the original state when the boundary is 
removed gives a one to one mapping between the initial and the final 
states, therefore after the free expansion the gas can really only be in 
exactly the same number of states. But there are then 2^N times more 
other states that will have the same macroscopic properties as the real 
states the gas really can be in. So, we have a number of fictitious 
states of (2^N - 1 ) times the original number of states that we cannot 
distinguish from the real states.


Unlike the real states, the fictitious states will most likely not 
evolve back to the original volume under time reversal. But this is not 
a property that's visible at the macroscopic scale.


One can then ask why entropy is a useful concept is it refers to the 
number of fictitious states the system can actually not be in? What do 
we make of the "equal prior probability postulate" used in statistical 
physics if it is actually not true? The reason is that one is ultimately 
doing statistics with the microscopic degrees of freedom, and in 
statistics all you need is a representative sample. Taking averages over 
a larger set will yield the same answer as computing the average over a 
more restrictive set, provided the properties you are interested in are 
statistically the same in that larger set. And mathematically it's 
easier to compute the former.



Saibal



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Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 28 May 2017, at 14:23, Pierz wrote:




On Sunday, May 28, 2017 at 10:28:52 AM UTC+10, Russell Standish wrote:
On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:
> Recently I've been studying a lot of history, and I've often  
thought about
> how, according to special relativity, you can translate time into  
space and
> vice versa, and therefore how from a different perspective we can  
think of
> the past as distant in space rather than time: my childhood being  
40 light
> years away, rather than 40 years for instance. I can visualise my  
own body
> as a sort of long, four dimensional tendril through spacetime, of  
which I
> only ever see a three-dimensional cross-section. This is the block  
universe
> idea of course. What occurred to me recently was that the past, in  
any
> physical theory I know of, is "locked down". There is only a  
single history

> consistent with the present (ignoring the microscopic ambiguities of
> quantum interference effects), but the present is consistent with  
multiple

> futures.

This assumption is wrong. There are many histories (pasts) consistent
with our present. If we don't know some fact about the past (eg
T. Rex's colour), then pasts with different colours of T.Rexes are all
compatible with our present. Only when we make a measurement that
distinguishes between different facts about the past, do we eliminate
some of those pasts from the compatibility list.

I think there's a confusion there between human ignorance and  
physical ambiguity - the same confusion expressed in the  
Schrödinger's Cat thought experiment. The resolution of that paradox  
lies in decoherence. The fact of the cat's death or survival spreads  
into the environment in a myriad of ways, whether or not we are  
measuring them: the cat's cooling after death, the shift of its  
weight as it falls and so on. At that point it is not in a  
superposition any more.


With respect to us (in our local branches). Decoherence jworks fine  
with the the many-worlds, but becomes a "magical explanation" without.  
OK?



We are merely ignorant of its state. I would argue the same applies  
to the colour of T. Rex. The past is not in a superposition of  
possible values, but we are ignorant of those values.


For all practical purpose. But there are temporal form of Bell's  
inequality violation which suggest that in principle (tacking track of  
all the particles the T-Rex interacted with (!)) we could make  
measurement showing interference of "different T-rex".





Now I think it is interesting to contemplate the possibility that  
more than one macroscopic history (one with green and one with red  
T. Rexes) might lead to the same present,


Of course, we need that, indeed.


but I think it extremely unlikely - that would constitute a  
macroscopic quantum interference effect.


But without collapse, the "unlikely" is only practical, making  
different past capable to interfere, or not. They don't need to  
interfere for existing. It is only to detect them. If you arise enough  
of your memory, you can "bactrack" up to T-rex, in principle (add the  
grain of salt).





I suspect only one possible colour is consistent with the present,  
even though it looks superficially like any colour is possible.


OK.

Bruno





There are, however, arrows of time - past and future are asymmetric,
the future is more uncertain than the past. But I don't see how you
can leverage that into support for the MWI.



--


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Principal, High Performance Coders
Visiting Senior Research Fellowhpc...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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http://iridia.ulb.ac.be/~marchal/



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Re: A thought on MWI and its alternative(s)

[Bruno Marchal]

On 28 May 2017, at 05:46, Russell Standish wrote:


On Sat, May 27, 2017 at 09:24:31PM -0500, Jason Resch wrote:


Regarding special relatively and collapse, I think the point is  
that two
observers in different reference frames can have different  
presents. Two

humans walking past each other on the sidewalk may have presents that
include the Andromeda Galaxy hours apart in time. (See "Andromeda
Paradox"). So if something on Earth collspses the wave everywhere and
instantly (in the present) which present is it collapsed in?

I think this even more clearly shows the incompatibility between  
collapse
theories and special relatively, beyond just pointing to the FTL  
influences
as violations; this shows now we have to somehow use an objective  
reference
frame which relatively tells us does not exist. And this leads to  
collapse
events happening in different times/places for different observers,  
even

ones walking past each other on a sidewalk.



Forgetting about JC's peepee for the minute, ISTM that relativity is
exclusively a 3p theory, whereas QM is both a 1pm and 3p theory. The
1p version of QM looks rather like Copenhagen, with wavefunction
collapses, and the 3p looks more like Everett, with deterministic wave
functions and many worlds.

The incompatibility between relativity and wave function collapse can
be seen as a manifestation of the incommensurate nature of the 1p/3p
distinction.


OK. And QM (without collapse) makes cosmology into 1p plural. The  
contagion of the superposition entails that we are sharing the  
"duplication boxes".


Bruno



Cheers

--


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: A thought on MWI and its alternative(s)

[Pierz]

On Sunday, May 28, 2017 at 12:24:32 PM UTC+10, Jason wrote:
>
>
>
> On Saturday, May 27, 2017, Russell Standish  > wrote:
>
>> On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:
>> > Recently I've been studying a lot of history, and I've often thought 
>> about
>> > how, according to special relativity, you can translate time into space 
>> and
>> > vice versa, and therefore how from a different perspective we can think 
>> of
>> > the past as distant in space rather than time: my childhood being 40 
>> light
>> > years away, rather than 40 years for instance. I can visualise my own 
>> body
>> > as a sort of long, four dimensional tendril through spacetime, of which 
>> I
>> > only ever see a three-dimensional cross-section. This is the block 
>> universe
>> > idea of course. What occurred to me recently was that the past, in any
>> > physical theory I know of, is "locked down". There is only a single 
>> history
>> > consistent with the present (ignoring the microscopic ambiguities of
>> > quantum interference effects), but the present is consistent with 
>> multiple
>> > futures.
>>
>> This assumption is wrong. There are many histories (pasts) consistent
>> with our present. If we don't know some fact about the past (eg
>> T. Rex's colour), then pasts with different colours of T.Rexes are all
>> compatible with our present. Only when we make a measurement that
>> distinguishes between different facts about the past, do we eliminate
>> some of those pasts from the compatibility list.
>>
>> There are, however, arrows of time - past and future are asymmetric,
>> the future is more uncertain than the past. But I don't see how you
>> can leverage that into support for the MWI.
>>
>>
>>
>
> I agree, there are multiple pasts compatible with our future. Some if 
> these can't be ruled out with any possible measurements, like in the case 
> if the quantum erasure.
>

To be truly compatible, they would need to unable to be distinguished by an 
observation even in theory - as you say like the quantum eraser. I 
acknowledged that when I said "ignoring the microscopic ambiguities of 
quantum interference effects". But that such interference effects can occur 
on a macroscopic scale, extending up to multiple dinosaur histories with 
different coloured T.Rexes - that is a huge leap. One single bit of 
physical information difference destroys quantum interference effects, so I 
seriously doubt that two universes with such different information that 
their dinosaurs are different colours could ever come to interfere with one 
another.

>
> That entropy increases does mean there are more futures than pasts.
>
> Regarding special relatively and collapse, I think the point is that two 
> observers in different reference frames can have different presents. Two 
> humans walking past each other on the sidewalk may have presents that 
> include the Andromeda Galaxy hours apart in time. (See "Andromeda 
> Paradox"). So if something on Earth collspses the wave everywhere and 
> instantly (in the present) which present is it collapsed in?
>

Well collapse really only happens at the time-space location that the 
measurement interaction occurs (if I believed in collapse!). I wouldn't say 
the collapse theories are *incompatible* with SR, because mathematically 
there is no problem - any paradox comes out in the wash. Conceptually 
though, it is certainly weird that the wave somehow "knows" to collapse 
everywhere at once, especially when "at once" doesn't have a single 
meaning, as you point out.

>
> I think this even more clearly shows the incompatibility between collapse 
> theories and special relatively, beyond just pointing to the FTL influences 
> as violations; this shows now we have to somehow use an objective reference 
> frame which relatively tells us does not exist. And this leads to collapse 
> events happening in different times/places for different observers, even 
> ones walking past each other on a sidewalk.
>
> Jason
>
>
>  
>
>>
>> --
>>
>>
>> 
>> Dr Russell StandishPhone 0425 253119 (mobile)
>> Principal, High Performance Coders
>> Visiting Senior Research Fellowhpco...@hpcoders.com.au
>> Economics, Kingston University http://www.hpcoders.com.au
>>
>> 
>>
>> --
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>> For more options, visit https://groups.google.com/d/optout.
>>
>

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Re: A thought on MWI and its alternative(s)

[Pierz]

On Sunday, May 28, 2017 at 10:28:52 AM UTC+10, Russell Standish wrote:
>
> On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote: 
> > Recently I've been studying a lot of history, and I've often thought 
> about 
> > how, according to special relativity, you can translate time into space 
> and 
> > vice versa, and therefore how from a different perspective we can think 
> of 
> > the past as distant in space rather than time: my childhood being 40 
> light 
> > years away, rather than 40 years for instance. I can visualise my own 
> body 
> > as a sort of long, four dimensional tendril through spacetime, of which 
> I 
> > only ever see a three-dimensional cross-section. This is the block 
> universe 
> > idea of course. What occurred to me recently was that the past, in any 
> > physical theory I know of, is "locked down". There is only a single 
> history 
> > consistent with the present (ignoring the microscopic ambiguities of 
> > quantum interference effects), but the present is consistent with 
> multiple 
> > futures. 
>
> This assumption is wrong. There are many histories (pasts) consistent 
> with our present. If we don't know some fact about the past (eg 
> T. Rex's colour), then pasts with different colours of T.Rexes are all 
> compatible with our present. Only when we make a measurement that 
> distinguishes between different facts about the past, do we eliminate 
> some of those pasts from the compatibility list. 
>
> I think there's a confusion there between human ignorance and physical 
ambiguity - the same confusion expressed in the Schrödinger's Cat thought 
experiment. The resolution of that paradox lies in decoherence. The fact of 
the cat's death or survival spreads into the environment in a myriad of 
ways, whether or not we are measuring them: the cat's cooling after death, 
the shift of its weight as it falls and so on. At that point it is not in a 
superposition any more. We are merely ignorant of its state. I would argue 
the same applies to the colour of T. Rex. The past is not in a 
superposition of possible values, but we are ignorant of those values. Now 
I think it is interesting to contemplate the possibility that more than one 
macroscopic history (one with green and one with red T. Rexes) might lead 
to the same present, but I think it extremely unlikely - that would 
constitute a macroscopic quantum interference effect. I suspect only one 
possible colour is consistent with the present, even though it looks 
superficially like any colour is possible.


There are, however, arrows of time - past and future are asymmetric, 
> the future is more uncertain than the past. But I don't see how you 
> can leverage that into support for the MWI. 
>
>
>
> -- 
>
>  
>
> Dr Russell StandishPhone 0425 253119 (mobile) 
> Principal, High Performance Coders 
> Visiting Senior Research Fellowhpc...@hpcoders.com.au 
>  
> Economics, Kingston University http://www.hpcoders.com.au 
>  
>
>

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Re: A thought on MWI and its alternative(s)

[David Nyman]

On 28 May 2017 4:46 a.m., "Russell Standish"  wrote:

On Sat, May 27, 2017 at 09:24:31PM -0500, Jason Resch wrote:
>
> Regarding special relatively and collapse, I think the point is that two
> observers in different reference frames can have different presents. Two
> humans walking past each other on the sidewalk may have presents that
> include the Andromeda Galaxy hours apart in time. (See "Andromeda
> Paradox"). So if something on Earth collspses the wave everywhere and
> instantly (in the present) which present is it collapsed in?
>
> I think this even more clearly shows the incompatibility between collapse
> theories and special relatively, beyond just pointing to the FTL
influences
> as violations; this shows now we have to somehow use an objective
reference
> frame which relatively tells us does not exist. And this leads to collapse
> events happening in different times/places for different observers, even
> ones walking past each other on a sidewalk.
>

Forgetting about JC's peepee for the minute, ISTM that relativity is
exclusively a 3p theory, whereas QM is both a 1pm and 3p theory. The
1p version of QM looks rather like Copenhagen, with wavefunction
collapses, and the 3p looks more like Everett, with deterministic wave
functions and many worlds.

The incompatibility between relativity and wave function collapse can
be seen as a manifestation of the incommensurate nature of the 1p/3p
distinction.


Isn't there an ineliminably 1p aspect of relativity in that here and now
can only be defined with respect to a particular point of view? But perhaps
you mean that this point of view can be described univocally in a purely 3p
manner without the equivalent of 'collapse'. There is of course no
provision in the formalism for 'counterfactual' continuations. Perhaps it's
that limitation that makes it incommensurable with a QM that can be parsed
in either way.

David


Cheers

--


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: A thought on MWI and its alternative(s)

[Russell Standish]

On Sat, May 27, 2017 at 09:24:31PM -0500, Jason Resch wrote:
> 
> Regarding special relatively and collapse, I think the point is that two
> observers in different reference frames can have different presents. Two
> humans walking past each other on the sidewalk may have presents that
> include the Andromeda Galaxy hours apart in time. (See "Andromeda
> Paradox"). So if something on Earth collspses the wave everywhere and
> instantly (in the present) which present is it collapsed in?
> 
> I think this even more clearly shows the incompatibility between collapse
> theories and special relatively, beyond just pointing to the FTL influences
> as violations; this shows now we have to somehow use an objective reference
> frame which relatively tells us does not exist. And this leads to collapse
> events happening in different times/places for different observers, even
> ones walking past each other on a sidewalk.
> 

Forgetting about JC's peepee for the minute, ISTM that relativity is
exclusively a 3p theory, whereas QM is both a 1pm and 3p theory. The
1p version of QM looks rather like Copenhagen, with wavefunction
collapses, and the 3p looks more like Everett, with deterministic wave
functions and many worlds.

The incompatibility between relativity and wave function collapse can
be seen as a manifestation of the incommensurate nature of the 1p/3p
distinction.

Cheers

-- 


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: A thought on MWI and its alternative(s)

[Jason Resch]

On Saturday, May 27, 2017, Russell Standish  wrote:

> On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:
> > Recently I've been studying a lot of history, and I've often thought
> about
> > how, according to special relativity, you can translate time into space
> and
> > vice versa, and therefore how from a different perspective we can think
> of
> > the past as distant in space rather than time: my childhood being 40
> light
> > years away, rather than 40 years for instance. I can visualise my own
> body
> > as a sort of long, four dimensional tendril through spacetime, of which I
> > only ever see a three-dimensional cross-section. This is the block
> universe
> > idea of course. What occurred to me recently was that the past, in any
> > physical theory I know of, is "locked down". There is only a single
> history
> > consistent with the present (ignoring the microscopic ambiguities of
> > quantum interference effects), but the present is consistent with
> multiple
> > futures.
>
> This assumption is wrong. There are many histories (pasts) consistent
> with our present. If we don't know some fact about the past (eg
> T. Rex's colour), then pasts with different colours of T.Rexes are all
> compatible with our present. Only when we make a measurement that
> distinguishes between different facts about the past, do we eliminate
> some of those pasts from the compatibility list.
>
> There are, however, arrows of time - past and future are asymmetric,
> the future is more uncertain than the past. But I don't see how you
> can leverage that into support for the MWI.
>
>
>

I agree, there are multiple pasts compatible with our future. Some if these
can't be ruled out with any possible measurements, like in the case if the
quantum erasure.

That entropy increases does mean there are more futures than pasts.

Regarding special relatively and collapse, I think the point is that two
observers in different reference frames can have different presents. Two
humans walking past each other on the sidewalk may have presents that
include the Andromeda Galaxy hours apart in time. (See "Andromeda
Paradox"). So if something on Earth collspses the wave everywhere and
instantly (in the present) which present is it collapsed in?

I think this even more clearly shows the incompatibility between collapse
theories and special relatively, beyond just pointing to the FTL influences
as violations; this shows now we have to somehow use an objective reference
frame which relatively tells us does not exist. And this leads to collapse
events happening in different times/places for different observers, even
ones walking past each other on a sidewalk.

Jason




>
> --
>
> 
> 
> Dr Russell StandishPhone 0425 253119 (mobile)
> Principal, High Performance Coders
> Visiting Senior Research Fellowhpco...@hpcoders.com.au
> 
> Economics, Kingston University http://www.hpcoders.com.au
> 
> 
>
> --
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Re: A thought on MWI and its alternative(s)

[Russell Standish]

On Thu, May 25, 2017 at 06:30:07PM -0700, Pierz wrote:
> Recently I've been studying a lot of history, and I've often thought about 
> how, according to special relativity, you can translate time into space and 
> vice versa, and therefore how from a different perspective we can think of 
> the past as distant in space rather than time: my childhood being 40 light 
> years away, rather than 40 years for instance. I can visualise my own body 
> as a sort of long, four dimensional tendril through spacetime, of which I 
> only ever see a three-dimensional cross-section. This is the block universe 
> idea of course. What occurred to me recently was that the past, in any 
> physical theory I know of, is "locked down". There is only a single history 
> consistent with the present (ignoring the microscopic ambiguities of 
> quantum interference effects), but the present is consistent with multiple 
> futures. 

This assumption is wrong. There are many histories (pasts) consistent
with our present. If we don't know some fact about the past (eg
T. Rex's colour), then pasts with different colours of T.Rexes are all
compatible with our present. Only when we make a measurement that
distinguishes between different facts about the past, do we eliminate
some of those pasts from the compatibility list.

There are, however, arrows of time - past and future are asymmetric,
the future is more uncertain than the past. But I don't see how you
can leverage that into support for the MWI.



-- 


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: A thought on MWI and its alternative(s)

[David Nyman]

On 26 May 2017 at 07:03, Pierz  wrote:

>
>
> On Friday, May 26, 2017 at 2:21:37 PM UTC+10, Brent wrote:
>>
>>
>>
>> On 5/25/2017 8:36 PM, Pierz Newton-John wrote:
>>
>> Is something up with Everything List - your reply is not on the site and I’m 
>> seeing this business with “reply to David 4” etc…?
>>
>>
>> On 26 May 2017, at 12:29 pm, Brent Meeker  wrote:
>>
>>
>>
>> On 5/25/2017 6:30 PM, Pierz wrote:
>>
>> Recently I've been studying a lot of history, and I've often thought about 
>> how, according to special relativity, you can translate time into space and 
>> vice versa, and therefore how from a different perspective we can think of 
>> the past as distant in space rather than time: my childhood being 40 light 
>> years away, rather than 40 years for instance. I can visualise my own body 
>> as a sort of long, four dimensional tendril through spacetime, of which I 
>> only ever see a three-dimensional cross-section. This is the block universe 
>> idea of course. What occurred to me recently was that the past, in any 
>> physical theory I know of, is "locked down". There is only a single history 
>> consistent with the present (ignoring the microscopic ambiguities of quantum 
>> interference effects
>>
>> I think that is assuming a lot.  Consider the biverse model of cosmogony - 
>> then the past "forks" just like the future.
>>
>> When I’ve asked physicists this question, I’ve been told that a single past 
>> is the general assumption. IIRC, there may be ambiguous histories very close 
>> to the Big Bang (Hawking?), but that’s not really relevant. Maybe that’s the 
>> biverse cosmology you refer to (googling it didn’t help).
>>
>>
>> In the biverse model the universe inflates into the past as well as the
>> future (as defined by us), thus maintaining time symmetry.   Here's a
>> another, more worked out version of the idea:
>>
>> Spontaneous Inflation and the Origin of the Arrow of Time
>> Sean M. Carroll
>> , Jennifer
>> Chen 
>> (Submitted on 27 Oct 2004)
>>
>> We suggest that spontaneous eternal inflation can provide a natural
>> explanation for the thermodynamic arrow of time, and discuss the underlying
>> assumptions and consequences of this view. In the absence of inflation, we
>> argue that systems coupled to gravity usually evolve asymptotically to the
>> vacuum, which is the only natural state in a thermodynamic sense. In the
>> presence of a small positive vacuum energy and an appropriate inflaton
>> field, the de Sitter vacuum is unstable to the spontaneous onset of
>> inflation at a higher energy scale. Starting from de Sitter, inflation can
>> increase the total entropy of the universe without bound, creating
>> universes similar to ours in the process.* An important consequence of
>> this picture is that inflation occurs asymptotically both forwards and
>> backwards in time, implying a universe that is (statistically)
>> time-symmetric on ultra-large scales.*
>>
>> Comments: 36 pages
>> Subjects: High Energy Physics - Theory (hep-th); Astrophysics
>> (astro-ph); General Relativity and Quantum Cosmology (gr-qc)
>> Report number: EFI-2004-33
>> Cite as: arXiv:hep-th/0410270 
>>   (or arXiv:hep-th/0410270v1  for
>> this version)
>>
>>
>> ), but the present is consistent with multiple futures. However, we know 
>> that "now" - and therefore the division into past and future - is an 
>> artifact of mind with no physical reality, a "quale". So therefore, if the 
>> past is singular, so is the future, and seen from "outside", every quantum 
>> event, whether "future" or "past" from any particular fame of reference, is 
>> in fact completely determined in its outcome, even though it is also random 
>> in the sense there is no way of explaining why it is the way it is, beyond 
>> the description provided by Born rule probabilities. Is that not weird, if 
>> not downright absurd? What is this "necessity" that dictates that this 
>> particular subset of all the possible quantum events was selected as the way 
>> things are?
>>
>> If there were such a "necessity" that would be a deterministic theory and 
>> inconsistent with the Born rule...and observation.
>>
>> Well it’s not inconsistent with observation because if such a thing were 
>> true, there’d still be no way an observer inside the system would know what 
>> the predetermined outcome was going to be. Doesn’t mean I like the idea 
>> though, obviously.
>>
>> Somehow the idea of the future being indeterminate but the past fixed seems 
>> palatable because it accords with our subjective experience, but really it 
>> is incoherent as soon as we acknowledge that the past-future distinction is 
>> not physically meaningful.
>>
>> But it is meaningful.  Entropy increases in the future direction. We 
>> remember and record the past but not the future.
>

Re: A thought on MWI and its alternative(s)

[Pierz]

On Friday, May 26, 2017 at 2:21:37 PM UTC+10, Brent wrote:
>
>
>
> On 5/25/2017 8:36 PM, Pierz Newton-John wrote:
>
> Is something up with Everything List - your reply is not on the site and I’m 
> seeing this business with “reply to David 4” etc…?
>
>
> On 26 May 2017, at 12:29 pm, Brent Meeker   
> wrote:
>
>
>
> On 5/25/2017 6:30 PM, Pierz wrote:
>
> Recently I've been studying a lot of history, and I've often thought about 
> how, according to special relativity, you can translate time into space and 
> vice versa, and therefore how from a different perspective we can think of 
> the past as distant in space rather than time: my childhood being 40 light 
> years away, rather than 40 years for instance. I can visualise my own body as 
> a sort of long, four dimensional tendril through spacetime, of which I only 
> ever see a three-dimensional cross-section. This is the block universe idea 
> of course. What occurred to me recently was that the past, in any physical 
> theory I know of, is "locked down". There is only a single history consistent 
> with the present (ignoring the microscopic ambiguities of quantum 
> interference effects
>
> I think that is assuming a lot.  Consider the biverse model of cosmogony - 
> then the past "forks" just like the future.
>
> When I’ve asked physicists this question, I’ve been told that a single past 
> is the general assumption. IIRC, there may be ambiguous histories very close 
> to the Big Bang (Hawking?), but that’s not really relevant. Maybe that’s the 
> biverse cosmology you refer to (googling it didn’t help).
>
>
> In the biverse model the universe inflates into the past as well as the 
> future (as defined by us), thus maintaining time symmetry.   Here's a 
> another, more worked out version of the idea:
>
> Spontaneous Inflation and the Origin of the Arrow of Time 
> Sean M. Carroll 
> , Jennifer 
> Chen 
> (Submitted on 27 Oct 2004)
>
> We suggest that spontaneous eternal inflation can provide a natural 
> explanation for the thermodynamic arrow of time, and discuss the underlying 
> assumptions and consequences of this view. In the absence of inflation, we 
> argue that systems coupled to gravity usually evolve asymptotically to the 
> vacuum, which is the only natural state in a thermodynamic sense. In the 
> presence of a small positive vacuum energy and an appropriate inflaton 
> field, the de Sitter vacuum is unstable to the spontaneous onset of 
> inflation at a higher energy scale. Starting from de Sitter, inflation can 
> increase the total entropy of the universe without bound, creating 
> universes similar to ours in the process.* An important consequence of 
> this picture is that inflation occurs asymptotically both forwards and 
> backwards in time, implying a universe that is (statistically) 
> time-symmetric on ultra-large scales.*
>
> Comments: 36 pages 
> Subjects: High Energy Physics - Theory (hep-th); Astrophysics (astro-ph); 
> General Relativity and Quantum Cosmology (gr-qc) 
> Report number: EFI-2004-33 
> Cite as: arXiv:hep-th/0410270  
>   (or arXiv:hep-th/0410270v1  for 
> this version) 
>
>
> ), but the present is consistent with multiple futures. However, we know that 
> "now" - and therefore the division into past and future - is an artifact of 
> mind with no physical reality, a "quale". So therefore, if the past is 
> singular, so is the future, and seen from "outside", every quantum event, 
> whether "future" or "past" from any particular fame of reference, is in fact 
> completely determined in its outcome, even though it is also random in the 
> sense there is no way of explaining why it is the way it is, beyond the 
> description provided by Born rule probabilities. Is that not weird, if not 
> downright absurd? What is this "necessity" that dictates that this particular 
> subset of all the possible quantum events was selected as the way things are?
>
> If there were such a "necessity" that would be a deterministic theory and 
> inconsistent with the Born rule...and observation.
>
> Well it’s not inconsistent with observation because if such a thing were 
> true, there’d still be no way an observer inside the system would know what 
> the predetermined outcome was going to be. Doesn’t mean I like the idea 
> though, obviously.
>
> Somehow the idea of the future being indeterminate but the past fixed seems 
> palatable because it accords with our subjective experience, but really it is 
> incoherent as soon as we acknowledge that the past-future distinction is not 
> physically meaningful.
>
> But it is meaningful.  Entropy increases in the future direction. We remember 
> and record the past but not the future.
>
> The arrow of time is physically meaningful, not the idea of “now”, which is 
> the reference point for determini

Re: A thought on MWI and its alternative(s)

[Brent Meeker]

On 5/25/2017 8:36 PM, Pierz Newton-John wrote:

Is something up with Everything List - your reply is not on the site and I’m 
seeing this business with “reply to David 4” etc…?


On 26 May 2017, at 12:29 pm, Brent Meeker  wrote:



On 5/25/2017 6:30 PM, Pierz wrote:

Recently I've been studying a lot of history, and I've often thought about how, according 
to special relativity, you can translate time into space and vice versa, and therefore 
how from a different perspective we can think of the past as distant in space rather than 
time: my childhood being 40 light years away, rather than 40 years for instance. I can 
visualise my own body as a sort of long, four dimensional tendril through spacetime, of 
which I only ever see a three-dimensional cross-section. This is the block universe idea 
of course. What occurred to me recently was that the past, in any physical theory I know 
of, is "locked down". There is only a single history consistent with the 
present (ignoring the microscopic ambiguities of quantum interference effects

I think that is assuming a lot.  Consider the biverse model of cosmogony - then the past 
"forks" just like the future.

When I’ve asked physicists this question, I’ve been told that a single past is 
the general assumption. IIRC, there may be ambiguous histories very close to 
the Big Bang (Hawking?), but that’s not really relevant. Maybe that’s the 
biverse cosmology you refer to (googling it didn’t help).


In the biverse model the universe inflates into the past as well as the 
future (as defined by us), thus maintaining time symmetry. Here's a 
another, more worked out version of the idea:



 Spontaneous Inflation and the Origin of the Arrow of Time

Sean M. Carroll 
,Jennifer 
Chen 

(Submitted on 27 Oct 2004)

   We suggest that spontaneous eternal inflation can provide a natural
   explanation for the thermodynamic arrow of time, and discuss the
   underlying assumptions and consequences of this view. In the absence
   of inflation, we argue that systems coupled to gravity usually
   evolve asymptotically to the vacuum, which is the only natural state
   in a thermodynamic sense. In the presence of a small positive vacuum
   energy and an appropriate inflaton field, the de Sitter vacuum is
   unstable to the spontaneous onset of inflation at a higher energy
   scale. Starting from de Sitter, inflation can increase the total
   entropy of the universe without bound, creating universes similar to
   ours in the process./***An important consequence of this picture is
   that inflation occurs asymptotically both forwards and backwards in
   time, implying a universe that is (statistically) time-symmetric on
   ultra-large scales.*/

Comments:   36 pages
Subjects: 	High Energy Physics - Theory (hep-th); Astrophysics 
(astro-ph); General Relativity and Quantum Cosmology (gr-qc)

Report number:  EFI-2004-33
Cite as:arXiv:hep-th/0410270 
	(orarXiv:hep-th/0410270v1 for 
this version)







), but the present is consistent with multiple futures. However, we know that "now" - and therefore the division into past and 
future - is an artifact of mind with no physical reality, a "quale". So therefore, if the past is singular, so is the future, and 
seen from "outside", every quantum event, whether "future" or "past" from any particular fame of reference, 
is in fact completely determined in its outcome, even though it is also random in the sense there is no way of explaining why it is the way 
it is, beyond the description provided by Born rule probabilities. Is that not weird, if not downright absurd? What is this 
"necessity" that dictates that this particular subset of all the possible quantum events was selected as the way things are?

If there were such a "necessity" that would be a deterministic theory and 
inconsistent with the Born rule...and observation.

Well it’s not inconsistent with observation because if such a thing were true, 
there’d still be no way an observer inside the system would know what the 
predetermined outcome was going to be. Doesn’t mean I like the idea though, 
obviously.

Somehow the idea of the future being indeterminate but the past fixed seems 
palatable because it accords with our subjective experience, but really it is 
incoherent as soon as we acknowledge that the past-future distinction is not 
physically meaningful.

But it is meaningful.  Entropy increases in the future direction. We remember 
and record the past but not the future.

The arrow of time is physically meaningful, not the idea of “now”, which is the 
reference point for determining what is future or past. No event belongs 
intrinsically to the past or future, it is a relative concept for some 
conscious observer.



Would this mean that if we could run the big bang over a

Re: A thought on MWI and its alternative(s)

[Brent Meeker]

I clicked "reply", but for some reason it only went to you.  I'll copy 
to the list.


Brent

On 5/25/2017 8:36 PM, Pierz Newton-John wrote:

Is something up with Everything List - your reply is not on the site and I’m 
seeing this business with “reply to David 4” etc…?


On 26 May 2017, at 12:29 pm, Brent Meeker  wrote:



On 5/25/2017 6:30 PM, Pierz wrote:

Recently I've been studying a lot of history, and I've often thought about how, according 
to special relativity, you can translate time into space and vice versa, and therefore 
how from a different perspective we can think of the past as distant in space rather than 
time: my childhood being 40 light years away, rather than 40 years for instance. I can 
visualise my own body as a sort of long, four dimensional tendril through spacetime, of 
which I only ever see a three-dimensional cross-section. This is the block universe idea 
of course. What occurred to me recently was that the past, in any physical theory I know 
of, is "locked down". There is only a single history consistent with the 
present (ignoring the microscopic ambiguities of quantum interference effects

I think that is assuming a lot.  Consider the biverse model of cosmogony - then the past 
"forks" just like the future.

When I’ve asked physicists this question, I’ve been told that a single past is 
the general assumption. IIRC, there may be ambiguous histories very close to 
the Big Bang (Hawking?), but that’s not really relevant. Maybe that’s the 
biverse cosmology you refer to (googling it didn’t help).


), but the present is consistent with multiple futures. However, we know that "now" - and therefore the division into past and 
future - is an artifact of mind with no physical reality, a "quale". So therefore, if the past is singular, so is the future, and 
seen from "outside", every quantum event, whether "future" or "past" from any particular fame of reference, 
is in fact completely determined in its outcome, even though it is also random in the sense there is no way of explaining why it is the way 
it is, beyond the description provided by Born rule probabilities. Is that not weird, if not downright absurd? What is this 
"necessity" that dictates that this particular subset of all the possible quantum events was selected as the way things are?

If there were such a "necessity" that would be a deterministic theory and 
inconsistent with the Born rule...and observation.

Well it’s not inconsistent with observation because if such a thing were true, 
there’d still be no way an observer inside the system would know what the 
predetermined outcome was going to be. Doesn’t mean I like the idea though, 
obviously.

Somehow the idea of the future being indeterminate but the past fixed seems 
palatable because it accords with our subjective experience, but really it is 
incoherent as soon as we acknowledge that the past-future distinction is not 
physically meaningful.

But it is meaningful.  Entropy increases in the future direction. We remember 
and record the past but not the future.

The arrow of time is physically meaningful, not the idea of “now”, which is the 
reference point for determining what is future or past. No event belongs 
intrinsically to the past or future, it is a relative concept for some 
conscious observer.



Would this mean that if we could run the big bang over again from the same 
initial conditions, it would always go exactly the same way? That is absurd, as 
it would mean there is something prebuilt as it were into the laws of physics 
that dictates that only this particular world history is permitted, for no 
reason at all.

That would be t'Hooft's superdeterminism.

I’ll look it up. But sounds daft :)

But if it could go a different way, that is equally absurd because it implies that 
variance is allowed at the level of entire universes, but not at the level of individual 
quantum events within those universes. What can resolve this paradox? Perhaps I'm 
cheating by imagining different possible universes in a universe where only one is real 
and allowed, but who can seriously countenance such a cosmology of absurdity where 
everything "just is"?

Of course if MWI is correct, then the paradox is resolved, because there is 
only a single past in the sense that there is only a single shortest path from 
any limb of a tree to its base, and there is no need for some principle of 
arbitrary necessity to dictate that all quantum events only have one possible 
outcome. For me this is a powerful argument in favour of many worlds, yet it's 
not one I've heard before. Any comments?

It's a pretty good argument...and one I've heard (and even thought of myself) 
before.  Does it really solve a problem that a collapse of the wave function 
doesn't solve?

Well I believe some experiments (currently impracticable) have been proposed to 
test it (can’t recall details but they involve undoing a series of quantum 
interactions). And of course Deutsch argues that a sufficie

A thought on MWI and its alternative(s)

[Pierz]

Recently I've been studying a lot of history, and I've often thought about 
how, according to special relativity, you can translate time into space and 
vice versa, and therefore how from a different perspective we can think of 
the past as distant in space rather than time: my childhood being 40 light 
years away, rather than 40 years for instance. I can visualise my own body 
as a sort of long, four dimensional tendril through spacetime, of which I 
only ever see a three-dimensional cross-section. This is the block universe 
idea of course. What occurred to me recently was that the past, in any 
physical theory I know of, is "locked down". There is only a single history 
consistent with the present (ignoring the microscopic ambiguities of 
quantum interference effects), but the present is consistent with multiple 
futures. However, we know that "now" - and therefore the division into past 
and future - is an artifact of mind with no physical reality, a "quale". So 
therefore, if the past is singular, so is the future, and seen from 
"outside", every quantum event, whether "future" or "past" from any 
particular fame of reference, is in fact completely determined in its 
outcome, even though it is also random in the sense there is no way of 
explaining why it is the way it is, beyond the description provided by Born 
rule probabilities. Is that not weird, if not downright absurd? What is 
this "necessity" that dictates that this particular subset of all the 
possible quantum events was selected as the way things are? Somehow the 
idea of the future being indeterminate but the past fixed seems palatable 
because it accords with our subjective experience, but really it is 
incoherent as soon as we acknowledge that the past-future distinction is 
not physically meaningful.

Would this mean that if we could run the big bang over again from the same 
initial conditions, it would always go exactly the same way? That is 
absurd, as it would mean there is something prebuilt as it were into the 
laws of physics that dictates that only this particular world history is 
permitted, for no reason at all. But if it could go a different way, that 
is equally absurd because it implies that variance is allowed at the level 
of entire universes, but not at the level of individual quantum events 
within those universes. What can resolve this paradox? Perhaps I'm cheating 
by imagining different possible universes in a universe where only one is 
real and allowed, but who can seriously countenance such a cosmology of 
absurdity where everything "just is"?

Of course if MWI is correct, then the paradox is resolved, because there is 
only a single past in the sense that there is only a single shortest path 
from any limb of a tree to its base, and there is no need for some 
principle of arbitrary necessity to dictate that all quantum events only 
have one possible outcome. For me this is a powerful argument in favour of 
many worlds, yet it's not one I've heard before. Any comments?

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