date:20220412

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread Brent Meeker




On 4/11/2022 11:30 PM, smitra wrote:

On 11-04-2022 20:40, Brent Meeker wrote:

On 4/11/2022 12:47 AM, smitra wrote:

On 11-04-2022 09:19, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 3:58 PM smitra  wrote:


On 10-04-2022 06:15, Bruce Kellett wrote:


Not relevant, since there is no enclosing reflecting boundary.


Yes there is.


Where is it then?


One can also consider an observation inside the event
horizon of a supermassive black hole. No photons escape from there.


We are not currently inside a supermassive black hole. Besides, you
knowledge of BH physics seems somewhat faulty. Inside the horizon, all
particles move towards the singularity at r = 0 (because that is the
forward direction of time). So there is no reflection off the inside
of the horizon. That is a fanciful (and wrong) idea.




The escaping Hawking radiation is so small that it doesn't contain
much
information.

And since you are attempting to promote a FAPP argument to an in
principle argument, you also have to consider that the space
environment
is not a perfect vacuum, so photons do not travel at exactly the
speed
of light. This means that in principle one can retrieve the escaping

photons


I don;t think the difference between c, the speed of light in a
vacuum, and the speed of light in outer space is a relevant
consideration -- you still are not going to catch and reverse those IR
photons.



That's all FAPP, not in principle. The laws of physics are 
reversible, it requires a rigorous argument from the fundamental 
laws of physics to demonstrate that reversing a measurement is 
impossible. Arguing from a practical situation and pointing to 
immense difficulties is a FAPP argument.


You seem to think the purpose of physics is to study the consequences
of equations.  If something is impossible to observe, I think the
purpose of physics is to explain why it's impossible.

In physics, when we try to figure out something new, one has to accept 
that there is incomplete knowledge about it and that in principle a 
large number of possibilities are in principle possible. But not all 
possibilities are equally reasonable. We all know how creationists 
invoke a "God of the gaps". In principle God could have created the 
universe not so long ago and one can always point to something science 
has not yet been able to figure out yet.


So, in practice one can always invoke a "God of the gaps" argument 
against a reasonable hypothesis. This is how Bruce is arguing here in 
opposition to the MWI. One may oppose the MWI on many reasonable 
grounds, but Bruce has the habit of invoking gaps that do not even 
exist, like that QFT is inconsistent with ordinary QM because QFT is 
manifestly local and he insist that the dynamics of QM must be 
non-local to account for Bell-type correlations. So, he is invoking a 
gap that doesn't even exists to argue his point.


Bruce has considered the QFT version of EPR.  That's the interpretation 
in which all combinations of Alice and Bob meet in the future and almost 
all combinations somehow are annihilated, leaving only those that are 
observed.


I think QFT is only an approximate theory /because/ it assumes only 
local interactions.




Then in case of observations may take the position that observations 
cannot be reversible. But since our brain can be simulated and you 
could in principle run the simulation of a quantum computer, that 
implies that observations can actually be reversible. 


Only if your quantum computer never produces an output.

So, the irreversible aspects of observations in the real world have 
nothing to do with the observations. Just like in the real world there 
is always friction which affects the motion of objects. True but 
things can also move in a perfect vacuum.


Now, in previous discussions the argument was made that you can't 
consider a simulation of observers in a quantum computer because, by 
definition, measurements must be irreversible. But that definition is 
can then be argued to be unreasonable. One can argue that even in the 
real world everything is in principle reversible. But then what about 
IR photons? Well, that doesn't stand in the way for inn principle 
reversibility either.


But then this whole argument then strayed into the unreasonable 
domain, because the physics of what happens on my brain during 
observations isn't affected by escaping IR photons and it can in 
principle be simulated to arbitrary accuracy in a fully reversible 
quantum computer.


I'm afraid you seem very inconsistent.  Earlier you insisted that an 
analysis had to include M81 and NGC215 as well as Alice, Bob, and 
instruments.  Now you, you just want to simulate the brains (and not 
include any IR photons).


Brent

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Re: aiming to complete Everett's derivation of the Born Rule

2022-04-12 Thread George Kahrimanis

On Friday, April 8, 2022 at 3:19:08 AM UTC+3 Lawrence Crowell wrote:

> This is an appeal to some sort of imperative that demands the Born Rule
> because the counterfactual lack this certainty. This is a sort of "It must
> be true" type of argument.

Thanks for the comments! I wonder though, do you agree with my criticisms
of previous proposals for deriving the Born Rule, or are you undecided? I
will challenge you (and you all) on this matter, later in this message.

First, a correction: I have not referred to *counterfactuals* (I think that
you meant "alternatives") but now that you mention them, I may have implied
one:
"If QM were not a workable theory, *we would have no direct, experimental
clue that it is a fundamental theory in physics*".
(Not the typical use of a counterfactual, which is in an "if..." clause, as
in "*If I was a rich man*...".)

What I say is not exactly
> "It must be true"
but rather
"Although I cannot be certain, it seems to be in my interests to form this
assessment now, when I decide how to act in the present situation".

If you find this argument too loose: I have pointed out that it is the same
kind of argument that a judge uses to form a decision based on the
evidence, or an engineer uses, to trust the theory of real numbers, for her
project.

My aim has been to complete *Everett's argument,* which I outline next.
Imagine that we repeat the same trial N times, and we record the ratio
{statistical "frequency") r of one among the possible outcomes
(eigenstates). Conventional QM assigns a probability R for this outcome, so
we need an explanation why r SEEMS to approach R in the long run (though we
know that in very many worlds it will not be so!). Everett noted that, for
any positive real ε (however small), the measure of all "outlier"
sequences, that is: for which r is outside
[R-ε, R+ε],
is small, with limit zero as N increases to infinity. However, *a problem
remains:* why "small measure" or "vanishing measure" have any significance
in the interpretation of QM? *My proposal answers this question,* finding
an argument about "small measure" within the reasoned assessment that QM is
a workable theory.

*Here is my challenge to you.* I ask you if you agree with either of the
following two proposals (for deriving the Born Rule in a MWI).

First, Deutsch's (1999) proposal, here in a simplified version. Imagine a
simulated tossing of a fair coin, using a qubit instead of a coin, with
which you either win or lose one dollar. If this bet has a definite, single
value to you (presumably, by some kind of intuitive averaging over possible
futures) it will necessarily be zero, for symmetry reasons. Caveat: Deutsch
points out that we do not derive probability strictly speaking. I accept
the reasoning, but not the premise: I am uncomfortable with averaging my
future selves, and there is no direct rationale why I SHOULD do so. So, *what
do you think?*

Second (and last), proposals such as Zurek's are of the following pattern
(here I reuse the previous example): I am uncertain about the outcome, and
I expect the theory to give me some clue, which will be probability -- what
else? For symmetry reasons, the probability here must be 1/2. My objection
is that there is no randomisation in MWI (no shuffling, stirring, or God
playing dice) so that the use of probability is not rationally justified.
Again* I ask for your opinion.*

Clarification. Instead of probability proper, I derive the following. With
regard to any given application, an Everettian agent may expect "with moral
certainty" (remember the judge and the engineer!) that statistical
frequency in the long run will be as close to the Born probability as one
needs it to be (in the particular application). Some people may think
"po-tah-toes, pot-eight-os", but at some level of thinking *this* is the
crucial issue. In particular, a serious consequence for decision theory
results from failing to find any rationale for probability proper!

George K.

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra

On 12-04-2022 11:32, George Kahrimanis wrote:

On Tuesday, April 12, 2022 at 10:29:07 AM UTC+3 Bruce wrote:

If the memory is reversed (whatever that might mean) then there is
no evidence that the memory ever existed. You are back into
fantasy-land.

No, there is a formal proof that an entanglement can be reversed and
nonetheless we still have a record indicating that, temporarily, an
entanglement had been in effect! I remember David Deutsch showing this
in a lecture, in 1985.

George K.

Indeed David Deutsche came up with this argument that can distinguish
between the CI and the MWI.

Saibal

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra


On 12-04-2022 09:28, Bruce Kellett wrote:

On Tue, Apr 12, 2022 at 5:08 PM smitra  wrote:


On 12-04-2022 08:52, Bruce Kellett wrote:

On Tue, Apr 12, 2022 at 4:31 PM smitra  wrote:


Now, in previous discussions the argument was made that you can't
consider a simulation of observers in a quantum computer because,

by

definition, measurements must be irreversible.


That was never the argument. The problem that was raised over the
simulation of people (and measurements) in a quantum computer was

that

measurement involves the formation of permanent records through
decoherence.


Measurement with permanent records is a red herring. One may define
measurement as an observations with a permanent record. But we can
perfectly observe things without there ever going to be permanent
records.


You are just playing with words. A scientific measurement involves the
formation of permanent records. What you think you observe might be
nothing but an illusion.

Scientific measurements are carried out in a rigorous way so that 
scientists can ahve confidence in the results. That's a separate issue 
from what the laws of physics say about the process of observation. 
There is nothing in the laws of physics that ties the act of observation 
to any requirement hat there be permanent record.




And many copies of the results so that many different
observers can check what has been done.


If no one can ever check what I have observed right now, that
doesn't
mean that I didn't make that observation. At most you can argue that
to
other observers I will be in a superposition of different
observations.


No, superpositions do not come into it. Your dreams do not put you in
a superposition.



It depends on whether the observed system was in a  superposition.


Decoherence is also necessary
to find a measurement basis that is robust against decoherence in

the

environment.


Yes, but that's irrelevant to observation.


Any measurement is made in terms of an eigenfunction and an eigenvalue
in some basis. That basis has to be determined somehow.

An obvious choice is the basis in which the observer considered as an 
algorithm, is diagonal.




QCs can never do this. A quantum computer is not adapted

to the formation of permanent records, and it goes to great

lengths to

avoid decoherence.


Decoherence and permanent records are irrelevant for observation.


Sez you, and you are wrong. They are crucial for scientific
measurements. You can change words, so that you claim to be talking
about personal observations whereas the basic discussion is about
scientific measurement, but that convinces no one.



The claim is that IF MWI is true THEN we can conclude X, Y, Z etc. we 
then don't need to argue about scientific proof, it's then enough that 
according to the MWI, all branches exist and whatever follows from that. 
If we do not assume MWI and want to do a test, then we can't make any 
such assumptions and scientific proof wih the necessary records will 
then play a more important role.



Consequently, a person simulated in a computer can

report that he has achieved all sorts of results, but he cannot
produce any evidence of this.


Unlike in criminal law. the laws of physics do not care about the
lack
of evidence.


Personal memories are not scientific
evidence.


What matters is that personal memories can form, not that it can
serve
as evidence to convince others later.


But the formation of scientific theories is crucially dependent on
verifiable evidence. Otherwise, it is just your random fantasies that
you are talking about.



It's perfectly legitimate to argue from theory, like IF MWI is true, 
THEN X, Y, Z etc., even if X, Y, Z are not good enough to prove the MWI 
due to a lack of scientific rigor associated with them like an absence 
of permanent records.



And it is doubtful if even personal memories could be
created in a quantum computer -- QCs do not produce any permanent
records before the final result is printed out, and personal

memories

are a form of (semi-)permanent record.


That's irrelevant for the formation of personal memories, if it is
later
reversed, then the memories did exist.


If the memory is reversed (whatever that might mean) then there is no
evidence that the memory ever existed. You are back into fantasy-land.



On the basis of experiments we have established that the laws of physics 
are reversible and that therefore it's possible for memories to b 
reversed. The point of this argument is to argue that observation is not 
the same as the formation of permanent records. The two things look like 
strongly associated with each other, but that's a consequence of living 
in the macroscopic world were decoherence occurs extremely fast.


If I observe something then my brain will be in a particular 
computational state. It's that state that matters. Whenever it's 
reproduced, by a brain, by a computer or whatever other device, then 
that experience of me having that experience will be

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra


On 12-04-2022 09:16, Bruce Kellett wrote:

On Tue, Apr 12, 2022 at 4:58 PM smitra  wrote:


On 12-04-2022 01:17, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 10:47 PM smitra  wrote:


On 11-04-2022 14:02, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 5:35 PM smitra  wrote:

The trouble with this is that the entanglement spreads only at

the

speed of light or less. If faster than that, then it is

npn-local.

Alice and Bob make their separate measurements at spacelike
separations. So if the entanglement resulting from Alice's

measurement

affects Bob's measurement, that that is FTL or non-local.


In the MWI Alice's measurement does not affect Bob's measurement.


That is your contention.


It's not just 'my contention"" it is implied by the rules of QM when
we
omit collapse.


But if Alice does not make a measurement, Bob
gets both up and down, 50/50. If Alice does make a measurement,

then

the Alices branch in which she got up does not have a Bob who saw
50/50 up/down. So Bob's result is clearly affected by Alice's
measurement.


No it isn't because Bob is not located in one or the other branch
before
he observes what Alice has found.


Wrong. Bob does not have to observe anything. He is automatically
split into two copies -- one in the sector in which Alice saw up, and
the other in the sector in which she saw down, when the forward light
cone from Alic'e measurement intersects his position. He does not have
to observe anything to be split in this way.

It doesn't have to happen at that moment. While decoherence is a fast 
process, if we associate Bob with the algorithm his brain is running 
then that algorithm representing Bob's mind will not split until Bob 
becomes consciously aware of Alice's results. However, this doesn't 
really matter, you can just as well let Bob split earlier when he moves 
into Alice's lightcone from her measurements. ither way, it's clear that 
Bob acquiring information about Alice's results is a local process.



Before he makes that observation,
Alice is in a superposition of both possibilities.


No, she is not. By decoherence she has definite results in both
sectors, and Bob sees her in both of these sectors since Bob splits
along with the rest of the world.



It doesn't matter, what matters is that Bob does not split before he 
comes into Alice's lightcone from her observation.



And we know that, in
general, if you are going to assume that the measurement results
exist
prior to measurement that will introduce non-local effects.


No one in this discussion is assuming that measurement results exit
prior to measurement. But I would certainly claim that measurement
results can be definite and exist before a third party becomes aware
of them. The measurement splits the observer, the device, and the rest
of the world as it becomes entangled with the result through
decoherence. Bob, if he is some distance away, is also split when the
forward light cone from the event entangles him along with everything
else. He need not be aware of this. Physics is an objective science.
It doesn't depend on what people are aware of or conscious of.



As long as the splits are assumed to happen due to decoherence after the 
observer moves into the relevant lightcone, there is not going to be an 
issue with locality.



And in each branch, Bob's result is affected by Alice's

measurement. The measurement outcomes are correlated, after all,

and

that is what correlation means -- the results are not independent.

Not

independent means that if one of the pair does not make a

measurement,

then the results for the other are different. (Counterfactuals

rear

their ugly head here.)



But because both branches objectively exist, and Bob can end up in
either one,


But he actually ends up on both of Alice's branches, carrying
different results to each branch.



That's right, but there is no issue with locality here.


he's identical in both before he observes Alice's result,
his results remains random even after Alice makes her measurement.


The point I was trying to make is a simple logical one. If Alice's and
Bob's results are truly local and independent, then there is no
correlation between them.


That's not true because they are measuring two parts of a correlated 
system. If they read the same copies of a book, there would be a 
correlation between what they read. That's of a course a trivial 
example. But it does show that locality does not imply that that there 
cannot be any correlations between space-like events.



The fact that they are correlated means that
they are not independent. If their measurements are not independent,
even at spacelike separation, then a non-local influence is implied.


The non-local effect is caused by the entangled spins. Alice and Bob 
could just as well be reading the same copies of a book.



You can't have it both ways. If local and independent then no
correlation. If there is a correlation, then they are not independent
and the measurement of

Re: W boson anomaly, new physics or new methods?

2022-04-12 Thread John Clark

On Sun, Apr 10, 2022 at 6:25 AM Lawrence Crowell <
goldenfieldquaterni...@gmail.com> wrote:

> *> A natural possible unitless gravitational coupling constant might then
> be the α_g = (M_h/M_p)^2 for H_h the mass of the Higgs boson M_h = 125GeV*
>  [...]
>

*I was wondering why you use the mass of the Higgs particle (125GeV) rather
than the value of the Higgs field that breaks electroweak symmetry and
gives mass to the W and Z bosons which is 246 GeV, I could be wrong but in
some ways it seems like a more important number.*
John K ClarkSee what's on my new list at  Extropolis


keex

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Re: W boson anomaly, new physics or new methods?

2022-04-12 Thread John Clark

On Sun, Apr 10, 2022 at 6:25 AM Lawrence Crowell <
goldenfieldquaterni...@gmail.com> wrote:

*> A natural possible unitless gravitational coupling constant might then
> be the α_g = (M_h/M_p)^2 for H_h the mass of the Higgs boson M_h = 125GeV*
>  [...]
>

*I was wondering why you use the mass of the Higgs particle (125GeV) rather
than the value of the Higgs field that breaks electroweak symmetry and
gives mass to the W and Z bosons which is 246 GeV, I could be wrong but in
some ways it seems like a more important number.*

John K ClarkSee what's on my new list at  Extropolis



>

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread John Clark

On Tue, Apr 12, 2022 at 3:29 AM Bruce Kellett  wrote:

*> A scientific measurement involves the formation of permanent records.*


Any record, permanent or otherwise, must involve a change of some sort, if
not in the thing being observed then certainly in the observer because if
there wasn't a change of some sort to the observer's brain he wouldn't
remember it. And if Hugh Everett is correct then any change is enough to
split a universe.

*> What you think you observe might be nothing but an illusion.*


That doesn't matter because a brain that remembers seeing an illusion is
different from a brain that doesn't remember seeing an illusion. And as I
said, if Hugh Everett is correct then ANY change is enough to split a
universe.

John K ClarkSee what's on my new list at  Extropolis

eh3

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread George Kahrimanis

On Monday, April 11, 2022 at 1:43:12 AM UTC+3 Bruce wrote:

> The point seems to be that the fact that some Alice/Bob pairings violate 
> QM can be known only after they pair up. For the branches that form these 
> problematic pairings not to form requires a non-local effect. That is the 
> point I am trying to get across.
>  
> On Mon, Apr 11, 2022 at 3:07 AM George Kahrimanis wrote:
>
>> A realistic version of the scenario with Bob and Alice [...]
>>
>> There have always been worries about detection inefficiencies and errors 
> in the tests of Bell inequalities. [...]
>

Thanks for the hints! I too think of splits as global; I would be curious 
though to see a CONSISTENT formalism that treats them as propagating in 
light cones, and if "new physics" would be possible.

My comment, as brief as possible: I do not think that "bad pairings" is a 
strong enough argument against a local-split theory, because they arise in 
examples with perfect precision only, which must be treated just as limits 
(we agree, I know), so "pairings of measure zero" is the right way to put 
it. Then I cannot blame a theory just because it predicts violation of 
physical laws in branches of measure zero, or practically zero.

To be more descriptive: think of just one experimenter and a local 
experiment. The pair
|1> |1>
will be "of measure zero" to her when the polarisers are parallel, in the 
limit with decreasing imprecision; not "physically impossible", strictly 
speaking. (It is "impossible" only in the ideal example directly, not in 
the limit of vanishing imprecision.)

For finding a physical difference introduced by assuming locality of 
splits, I would look elsewhere. First, in the EM radiation and the 
gravitational effect of an electron curving (up or down) in a polariser -- 
just a hunch.

George K.

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread George Kahrimanis

On Tuesday, April 12, 2022 at 10:29:07 AM UTC+3 Bruce wrote:

> If the memory is reversed (whatever that might mean) then there is no 
> evidence that the memory ever existed. You are back into fantasy-land.

No, there is a formal proof that an entanglement can be reversed and 
nonetheless we still have a record indicating that, temporarily, an 
entanglement had been in effect! I remember David Deutsch showing this in a 
lecture, in 1985.

George K.

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread Bruce Kellett

On Tue, Apr 12, 2022 at 5:08 PM smitra  wrote:

> On 12-04-2022 08:52, Bruce Kellett wrote:
> > On Tue, Apr 12, 2022 at 4:31 PM smitra  wrote:
> >
> >> Now, in previous discussions the argument was made that you can't
> >> consider a simulation of observers in a quantum computer because, by
> >> definition, measurements must be irreversible.
> >
> > That was never the argument. The problem that was raised over the
> > simulation of people (and measurements) in a quantum computer was that
> > measurement involves the formation of permanent records through
> > decoherence.
>
> Measurement with permanent records is a red herring. One may define
> measurement as an observations with a permanent record. But we can
> perfectly observe things without there ever going to be permanent
> records.
>

You are just playing with words. A scientific measurement involves the
formation of permanent records. What you think you observe might be nothing
but an illusion.


> And many copies of the results so that many different
> > observers can check what has been done.
>
> If no one can ever check what I have observed right now, that doesn't
> mean that I didn't make that observation. At most you can argue that to
> other observers I will be in a superposition of different observations.
>

No, superpositions do not come into it. Your dreams do not put you in a
superposition.

> Decoherence is also necessary
> > to find a measurement basis that is robust against decoherence in the
> > environment.
>
> Yes, but that's irrelevant to observation.
>

Any measurement is made in terms of an eigenfunction and an eigenvalue in
some basis. That basis has to be determined somehow.

QCs can never do this. A quantum computer is not adapted
> > to the formation of permanent records, and it goes to great lengths to
> > avoid decoherence.
>
> Decoherence and permanent records are irrelevant for observation.
>

Sez you, and you are wrong. They are crucial for scientific measurements.
You can change words, so that you claim to be talking about personal
observations whereas the basic discussion is about scientific measurement,
but that convinces no one.

  Consequently, a person simulated in a computer can
> > report that he has achieved all sorts of results, but he cannot
> > produce any evidence of this.
>
> Unlike in criminal law. the laws of physics do not care about the lack
> of evidence.
>
> > Personal memories are not scientific
> > evidence.
>
> What matters is that personal memories can form, not that it can serve
> as evidence to convince others later.
>

But the formation of scientific theories is crucially dependent on
verifiable evidence. Otherwise, it is just your random fantasies that you
are talking about.

> And it is doubtful if even personal memories could be
> > created in a quantum computer -- QCs do not produce any permanent
> > records before the final result is printed out, and personal memories
> > are a form of (semi-)permanent record.
> >
> That's irrelevant for the formation of personal memories, if it is later
> reversed, then the memories did exist.
>

If the memory is reversed (whatever that might mean) then there is no
evidence that the memory ever existed. You are back into fantasy-land.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread Bruce Kellett

On Tue, Apr 12, 2022 at 4:58 PM smitra  wrote:

> On 12-04-2022 01:17, Bruce Kellett wrote:
> > On Mon, Apr 11, 2022 at 10:47 PM smitra  wrote:
> >
> >> On 11-04-2022 14:02, Bruce Kellett wrote:
> >>> On Mon, Apr 11, 2022 at 5:35 PM smitra  wrote:
> >>>
> >>> The trouble with this is that the entanglement spreads only at the
> >>> speed of light or less. If faster than that, then it is npn-local.
> >>> Alice and Bob make their separate measurements at spacelike
> >>> separations. So if the entanglement resulting from Alice's
> >> measurement
> >>> affects Bob's measurement, that that is FTL or non-local.
> >>
> >> In the MWI Alice's measurement does not affect Bob's measurement.
> >
> > That is your contention.
>
> It's not just 'my contention"" it is implied by the rules of QM when we
> omit collapse.
>
> > But if Alice does not make a measurement, Bob
> > gets both up and down, 50/50. If Alice does make a measurement, then
> > the Alices branch in which she got up does not have a Bob who saw
> > 50/50 up/down. So Bob's result is clearly affected by Alice's
> > measurement.
>
> No it isn't because Bob is not located in one or the other branch before
> he observes what Alice has found.

Wrong. Bob does not have to observe anything. He is automatically split
into two copies -- one in the sector in which Alice saw up, and the other
in the sector in which she saw down, when the forward light cone from
Alic'e measurement intersects his position. He does not have to observe
anything to be split in this way.

Before he makes that observation,
> Alice is in a superposition of both possibilities.

No, she is not. By decoherence she has definite results in both sectors,
and Bob sees her in both of these sectors since Bob splits along with the
rest of the world.

And we know that, in
> general, if you are going to assume that the measurement results exist
> prior to measurement that will introduce non-local effects.
>

No one in this discussion is assuming that measurement results exit prior
to measurement. But I would certainly claim that measurement results can be
definite and exist before a third party becomes aware of them. The
measurement splits the observer, the device, and the rest of the world as
it becomes entangled with the result through decoherence. Bob, if he is
some distance away, is also split when the forward light cone from the
event entangles him along with everything else. He need not be aware of
this. Physics is an objective science. It doesn't depend on what people are
aware of or conscious of.

  And in each branch, Bob's result is affected by Alice's
> > measurement. The measurement outcomes are correlated, after all, and
> > that is what correlation means -- the results are not independent. Not
> > independent means that if one of the pair does not make a measurement,
> > then the results for the other are different. (Counterfactuals rear
> > their ugly head here.)
> >
>
> But because both branches objectively exist, and Bob can end up in
> either one,

But he actually ends up on both of Alice's branches, carrying different
results to each branch.

he's identical in both before he observes Alice's result,
> his results remains random even after Alice makes her measurement.
>

The point I was trying to make is a simple logical one. If Alice's and
Bob's results are truly local and independent, then there is no correlation
between them. The fact that they are correlated means that they are not
independent. If their measurements are not independent, even at spacelike
separation, then a non-local influence is implied. You can't have it both
ways. If local and independent then no correlation. If there is a
correlation, then they are not independent and the measurement of one party
influences the results that the other can obtain, in a non-local way.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra

On 12-04-2022 08:52, Bruce Kellett wrote:

On Tue, Apr 12, 2022 at 4:31 PM smitra wrote:

Now, in previous discussions the argument was made that you can't
consider a simulation of observers in a quantum computer because, by

definition, measurements must be irreversible.

That was never the argument. The problem that was raised over the
simulation of people (and measurements) in a quantum computer was that
measurement involves the formation of permanent records through
decoherence.

Measurement with permanent records is a red herring. One may define
measurement as an observations with a permanent record. But we can
perfectly observe things without there ever going to be permanent
records.

And many copies of the results so that many different
observers can check what has been done.

If no one can ever check what I have observed right now, that doesn't
mean that I didn't make that observation. At most you can argue that to
other observers I will be in a superposition of different observations.

Decoherence is also necessary
to find a measurement basis that is robust against decoherence in the
environment.

Yes, but that's irrelevant to observation.

QCs can never do this. A quantum computer is not adapted

to the formation of permanent records, and it goes to great lengths to
avoid decoherence.

Decoherence and permanent records are irrelevant for observation.

Consequently, a person simulated in a computer can

report that he has achieved all sorts of results, but he cannot
produce any evidence of this.

Unlike in criminal law. the laws of physics do not care about the lack
of evidence.

Personal memories are not scientific
evidence.

What matters is that personal memories can form, not that it can serve
as evidence to convince others later.

And it is doubtful if even personal memories could be
created in a quantum computer -- QCs do not produce any permanent
records before the final result is printed out, and personal memories
are a form of (semi-)permanent record.

That's irrelevant for the formation of personal memories, if it is later
reversed, then the memories did exist.

Saibal

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra


On 12-04-2022 01:17, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 10:47 PM smitra  wrote:


On 11-04-2022 14:02, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 5:35 PM smitra  wrote:

The trouble with this is that the entanglement spreads only at the
speed of light or less. If faster than that, then it is npn-local.
Alice and Bob make their separate measurements at spacelike
separations. So if the entanglement resulting from Alice's

measurement

affects Bob's measurement, that that is FTL or non-local.


In the MWI Alice's measurement does not affect Bob's measurement.


That is your contention.


It's not just 'my contention"" it is implied by the rules of QM when we 
omit collapse.



But if Alice does not make a measurement, Bob
gets both up and down, 50/50. If Alice does make a measurement, then
the Alices branch in which she got up does not have a Bob who saw
50/50 up/down. So Bob's result is clearly affected by Alice's
measurement.


No it isn't because Bob is not located in one or the other branch before 
he observes what Alice has found. Before he makes that observation, 
Alice is in a superposition of both possibilities. And we know that, in 
general, if you are going to assume that the measurement results exist 
prior to measurement that will introduce non-local effects.




Adding the other branch in which Alice got down does not
affect this result, since in that branch, Bob's result is also
affected in that he did not see 5-/50 up/down.



Bob then does end up seeing a 50/50 result for up/down, because the 
branch he'll end up with is random.





Since in the local case, Bob's measurement is independent of

Alice's,

he must see |up> and |down> with equal probability (in different
branches). By dropping the entangled part of the wave function

after

Alice's measurement, you rule out the possibility that Bob can get
|up> or |down> with equal probability after Alice's measurement

(as he

certainly can before her measurement). What is it about Alice's
measurement that changes the probabilities for Bob's result? At
spacelike separation, this can only be a non-local influence.



Bob's result is not affected by Alice's measurement because she is
in a
superposition of the two possible results.


The fact that she is in a superposition makes no essential difference.
One can always look at what happens in one branch of the
superposition.


No one can't because for Bob bith results are relevant.

 And in each branch, Bob's result is affected by Alice's

measurement. The measurement outcomes are correlated, after all, and
that is what correlation means -- the results are not independent. Not
independent means that if one of the pair does not make a measurement,
then the results for the other are different. (Counterfactuals rear
their ugly head here.)



But because both branches objectively exist, and Bob can end up in 
either one, he's identical in both before he observes Alice's result, 
his results remains random even after Alice makes her measurement.



The analysis that you give above is the standard analysis for QM

with

collapse, and that is usually regarded as a non-local effect.


No it isn't because in the analysis I gave there is no collapse. So,
as
far as Bob is concerned, Alice has not found one definite result.


Any copy of Alice that Bob meets has only one result.


The Bob she meets is identical to the Bob in another sector where her 
copy has found a different result.



The
superposition can always be analysed in terms of the separate
components. You have built a collapse into your analysis without
realizing it -- Bob sees a different wave function according to
whether Alice makes a measurement or not.


No he doesn't, Bob factors out of the superposition.


If she makes a measurement,
the non-compliant part of the original wave function collapses -- it
is not passed on to Bob. If she does not make a measurement, Bob sees
the whole original wave function.


That's not how it works. No noncompliant parts ever arise.


It might be useful here to compare the correlated case with the
picture if the particles that Alice and Bob measure are completely
independent. In the case of independent particles, there is no doubt
that both observers have a 50/50 chance of seeing up or down. When
they meet (or when their forward light cones overlap) the rules of MWI
say that each, being part of the world entangled with the other
party's measurement, splits into two -- one branch for each result
obtained by the other.


That's your Straw Man version of the MWI again. What the MWI says is to 
evolve the initial state according to the Schrödinger equation and then 
to not invoke any collapse of the wavefunction.



 The consequence is that there are four

branches: up-up, up-down, down-up, and down-down.



Yes, that's what yolu will get if you do the math in this case.


When the spins are
correlated, two of these branches do not appear; the up-up and
down-down branches do not conserve angular

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread Bruce Kellett

On Tue, Apr 12, 2022 at 4:31 PM smitra  wrote:

>
> Now, in previous discussions the argument was made that you can't
> consider a simulation of observers in a quantum computer because, by
> definition, measurements must be irreversible.

That was never the argument. The problem that was raised over the
simulation of people (and measurements) in a quantum computer was that
measurement involves the formation of permanent records through
decoherence. And many copies of the results so that many different
observers can check what has been done. Decoherence is also necessary to
find a measurement basis that is robust against decoherence in the
environment. QCs can never do this. A quantum computer is not adapted to
the formation of permanent records, and it goes to great lengths to avoid
decoherence. Consequently, a person simulated in a computer can report that
he has achieved all sorts of results, but he cannot produce any evidence of
this. Personal memories are not scientific evidence. And it is doubtful if
even personal memories could be created in a quantum computer -- QCs do not
produce any permanent records before the final result is printed out, and
personal memories are a form of (semi-)permanent record.

Bruce

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Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra

On 11-04-2022 20:40, Brent Meeker wrote:

On 4/11/2022 12:47 AM, smitra wrote:

On 11-04-2022 09:19, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 3:58 PM smitra wrote:

On 10-04-2022 06:15, Bruce Kellett wrote:

Not relevant, since there is no enclosing reflecting boundary.

Yes there is.

Where is it then?

One can also consider an observation inside the event
horizon of a supermassive black hole. No photons escape from there.

We are not currently inside a supermassive black hole. Besides, you
knowledge of BH physics seems somewhat faulty. Inside the horizon,
all

particles move towards the singularity at r = 0 (because that is the
forward direction of time). So there is no reflection off the inside
of the horizon. That is a fanciful (and wrong) idea.

The escaping Hawking radiation is so small that it doesn't contain
much
information.

And since you are attempting to promote a FAPP argument to an in
principle argument, you also have to consider that the space
environment
is not a perfect vacuum, so photons do not travel at exactly the
speed
of light. This means that in principle one can retrieve the escaping

photons

I don;t think the difference between c, the speed of light in a
vacuum, and the speed of light in outer space is a relevant
consideration -- you still are not going to catch and reverse those
IR

photons.

That's all FAPP, not in principle. The laws of physics are reversible,
it requires a rigorous argument from the fundamental laws of physics
to demonstrate that reversing a measurement is impossible. Arguing
from a practical situation and pointing to immense difficulties is a
FAPP argument.

You seem to think the purpose of physics is to study the consequences
of equations. If something is impossible to observe, I think the
purpose of physics is to explain why it's impossible.

In physics, when we try to figure out something new, one has to accept
that there is incomplete knowledge about it and that in principle a
large number of possibilities are in principle possible. But not all
possibilities are equally reasonable. We all know how creationists
invoke a "God of the gaps". In principle God could have created the
universe not so long ago and one can always point to something science
has not yet been able to figure out yet.

So, in practice one can always invoke a "God of the gaps" argument
against a reasonable hypothesis. This is how Bruce is arguing here in
opposition to the MWI. One may oppose the MWI on many reasonable
grounds, but Bruce has the habit of invoking gaps that do not even
exist, like that QFT is inconsistent with ordinary QM because QFT is
manifestly local and he insist that the dynamics of QM must be non-local
to account for Bell-type correlations. So, he is invoking a gap that
doesn't even exists to argue his point.

Then in case of observations may take the position that observations
cannot be reversible. But since our brain can be simulated and you could
in principle run the simulation of a quantum computer, that implies that
observations can actually be reversible. So, the irreversible aspects of
observations in the real world have nothing to do with the observations.
Just like in the real world there is always friction which affects the
motion of objects. True but things can also move in a perfect vacuum.

Now, in previous discussions the argument was made that you can't
consider a simulation of observers in a quantum computer because, by
definition, measurements must be irreversible. But that definition is
can then be argued to be unreasonable. One can argue that even in the
real world everything is in principle reversible. But then what about IR
photons? Well, that doesn't stand in the way for inn principle
reversibility either.

But then this whole argument then strayed into the unreasonable domain,
because the physics of what happens on my brain during observations
isn't affected by escaping IR photons and it can in principle be
simulated to arbitrary accuracy in a fully reversible quantum computer.

Saibal

Brent

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra


On 11-04-2022 20:38, Brent Meeker wrote:

On 4/11/2022 12:35 AM, smitra wrote:

On 11-04-2022 08:46, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 4:23 PM smitra  wrote:


On 10-04-2022 06:53, Bruce Kellett wrote:

On Sun, Apr 10, 2022 at 2:13 PM smitra  wrote:

The simplest way to counter your assertions is to provide a simple
counterexample. Consider the standard Alice/Bob setup, with

up/down

results coded as 1/0. According to MWI, on each trial, Alice

splits,

one copy recoding |1> and the other copy recording |0>. After N
trials, there are 2^N copies of Alice, with records consisting of

all

possible binary sequences of length N. If Bob is spacelike

separated

and independent, he also splits into 2^N copie, consisting of all
possible binary sequences of length N.

When Alice and Bob meet (or exchange trial results), each copy of

each

splits into 2^N copies, one for each copy of the other party. So

for

Alice, each copy of Aice with some binary sequence of results,

splits

into 2^N copies, one for each of Bob's sequences. Now say, for
example, that Alice and Bob both happen to have the same polarizer
setting for the 10th trial, so that for trial 10, their polarizers

are

parallel. Since there are copies of Alice for all possible results

for

trial 10, there is an Alice with result |1> for this trial, and a
different Alice with result |0>. Now each Alice splits according

to

all possible copies of Bob. So the Alice with result |1> meets a

Bob

with result |0> for the same trial. That is OK according to

quantum

mechanics. But by the rules of MWI, there is also a copy of Alice

with

result |1> who meets a Bob who recorded |1> for the 10th trial.


No, there is no such copy. MWI = QM without collapse, and it's known

that MWI yields the same predictions as QM with collapse.


You have a very unusual understanding of MWI. Look at a good textbook
on the subject, such as David Wallace's "The Emergent Multiverse". He
certainly states that there are four copies of each observer on each
trial in this situation. When a measurement of spin is made, each
observer splits, and the rest of the universe splits with them
(including the other observer when they become included in the 
forward

light cone of the event). So when Alice measures her particle, she
splits into "Alice saw up" and "Alice saw down". Bob splits in the
same way when he makes his independent measurement. When their future
light cones overlap, each independently gets caught up in the
splitting caused by the measurement made by the other. The result is
four branches (copies), namely: "up-up" up-down' "down-up" and
"down-down".  The challenge is that only the "up-down" and "down-up"
branches agree with QM when the polarizers are parallel. This is
simple logic applied to the rules of MWI, so the QM-violating "up-up"
and "down-down" branches certainly exist in strictly local MWI. The
only way you are going to get rid of them (since they are unphysical
and not observed) is by invoking a non-local interaction at the 
source

of the measurement. Bob's measurement depends non-locally on the
result of Alice's measurement (or vice versa for a different time
order).



But why not simply analyze what the evolution according to the 
Schrödinger equation would lead to? Obviously all that's going to 
happen is that the measurements o the spins will cause the 
entanglement to spread further. we started with two entangled spins 
and now we end up with the entire Bob and Alice sectors becoming part 
of this entanglement. If the polarizer are parallel then if Alice 
finds spin up there is only a "Bob finds down" in her sector. That's 
clearly what the local time evolution according the the Schrödinger 
equation predicts.


|Alice>[|up,down> - |down, up>] ---> |(Alice sees with up) ,down> - 
|Alice sees down, up>]


It's a local interaction because Alice interacts only with her spin, 
not with Bob's spin.


Peres would say there is only one spin and it is located in Hilbert
space.  That it can interact at two different locations is what
non-local means.



Yes, that's another way to look at it. The entangled spin pair has 
non-local properties, that's beyond dispute. It's just that all the 
aspects of this can be explained using only local dynamics. It's 
analogous to how using ordinary classical means you can get to nonlocal 
correlations, e.g. if Alice and Bob read copies of the same book.


I note here that Bruce has denied that the quantum mechanics involved in 
Bell-type experiments is inconsistent with QFT, because he insists that 
the dynamics must be non-local while QFT is local. That's something that 
I strongly disagree with and it's a claim that few people in the physics 
community would support.


Saibal




Brent



Then that these interactions will reproduce the usual predictions of 
QM including those that violate Bell's inequality are then not due to 
any non-local interactions. hat's not a paradox, because Bell's 
theorem showing that

Re: The Nature of Contingency: Quantum Physics as Modal Realism

2022-04-12 Thread smitra

On 11-04-2022 20:34, Brent Meeker wrote:

On 4/11/2022 12:16 AM, smitra wrote:

On 11-04-2022 08:26, Bruce Kellett wrote:

On Mon, Apr 11, 2022 at 4:12 PM smitra wrote:

On 10-04-2022 06:06, Bruce Kellett wrote:

You will have to start providing textual evidence from the writing

Jon Bell himself for some of the more outrageous claims that you

are

making.

Besides, MWI is the epitome of a deterministic theory!

I've sited the algebra of these derivations before, they make it
clear
that it doesn't apply to QM in general.

I don't recall you ever quoting John Bell. You cite secondary
sources,

but they often have their own agendas.

What matters is the math. The derivations only involve simple
clear-cut algebra.

Bell's theorem shows that QM cannot have a deterministic completion.
This is a theorem about QM, so the claim that Bell's theorem does not
apply to QM is just absurd.

Bell's theorem shows that local deterministic theories make
predictions incompatible with those of QM. The math about the bounds
on correlations applies to a class of local deterministic theories,
not to QM nor the MWI of QM.

But other places you assert that MWI is deterministic and local???

John Clark has explained this well in detail in the previous posting
here. The MWI is deterministic but it predicts multiple outcomes.

Saibal

Brent

So, when it is shown that local deterministic theores are not
compatible with QM then that leaves open the possibility that you can
have a deterministic theory that's non-local. However because the MwI
is not in the class of such deterministic theories, one cannot
conclude that MWI is non-local. Indeed that would be impossible,
because MWI is a manifestly local theory by construction.

Saibal

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