On 09-12-2017 21:18, Brent Meeker wrote:
On 12/9/2017 4:00 AM, smitra wrote:
On 09-12-2017 12:01, Bruce Kellett wrote:
On 9/12/2017 9:44 pm, smitra wrote:
On 09-12-2017 02:48, Bruce Kellett wrote:
On 9/12/2017 11:49 am, smitra wrote:
On 09-12-2017 00:03, Bruce Kellett wrote:
On 9/12/2017 4:21 am, Bruno Marchal wrote:
On 08 Dec 2017, at 00:22, Bruce Kellett wrote:
On 8/12/2017 3:31 am, Bruno Marchal wrote:
On 06 Dec 2017, at 12:19, Bruce Kellett wrote:
But as I pointed out, thermal motion gives momenta of
magnitudes such that the quantum uncertainties are negligible
compared to the thermal randomness. And thermal motions are
not coherent.
You seem to work in Bohr QM, with some dualism between the
quantum reality and the classical reality.
Not at all. The (semi-)classical world emerges from the quantum
substrate; if you cannot give an account of this, then you have
failed to explain our everyday experience. And explaining that
experience is the purpose of physics.
No problem with this, except for your usual skepticism of
Everett's program (say).
Skepticism is the scientific stance.....
You are right that this does not change anything FAPP, but our
discussion is not about practical applications, but
metaphysics.
No, we were talking about tossing a coin, we were not talking
about metaphysics. Your metaphysics has served merely to
confuse you to the extent that you do not understand even the
simplest physics.
That is ad hominem remark which I take as absence of argument.
You don't take kindly to criticism, do you Bruno?
All I said is that without collapse, shaking a box with some
coin long enough would lead to the superposition of the two coin
state. You seem to be the one confusing the local decoherence
with some collapse. The Heisenberg uncertainties are great
enough to amplify slight change of the move of the coin when
bouncing on the wall.
That is simply assertion on your part, without a shred of
argument or
justification. When one looks at the arguments, such as that put
forward by Albrecht and David (referred to by smitra), one finds
that
the emperor has no clothes!
Similarly, a shroedinger car, once alive + dead, will never
become a pure alive, or dead cat. It will only seems so for
anyone looking at the cat, in the {alive, dead} base/apparatus.
Superposition never disappear, and a coin moree or less with a
precise position, is always a superposition of a coin with more
or less precise momenta. The relation is given by the Fourier
transforms, which gives the relative accessible states/worlds.
I pointed out that for a macroscopic object such as a coin, the
uncertainty relations give uncertainties in positions and/or
momentum
far below any level of possible detection. And I gave an argument
with
an actual calculation -- not just an assertion. Uncertainties in
the
constituents of the object are uncorrelated, random, and cancel
out.
So although the superposition originating from the big bang is
intact
from the bird's point of view, it is so completely irrelevant for
everyday purposes that it is an insult to even refer to the
classicality of the world as FAPP -- it is complete. Relying on
the
charge of "FAPP" as a justification for your assertions is
nonsense.
It's not irrelevant if you don't have the information that locates
you in a sector where the uncertainties are indeed small enough.
You have to start with the complete state in the bird's view, and
then consider the sector where you have some definite information
and then project onto that subspace. If you do that, then your
coins are not at all in a precisely enough classical state but
rather in superpositions (entangled with the environment) that
lead to wildly different outcomes of coin tosses.
E.g. in the bird's view there exists exact copies of me that live
on planets that are not the same, some will have a radius of a few
millimeter larger than others. Here exact copy means exactly the
same conscious experience, which is then due to exactly the same
computational state of the brain described by some bitstring
that's exactly the same.
So, from totally different decoherent branches of the wavefunction
one can factor out some bitstring describing a conscious
experience, the reduced state of the rest of the universe in that
sector is then a superposition of a many different effectively
classical states.
If this were not true then each single conscious experience would
contain in it information about such things as the exact number
of atoms in the Earth, Sun etc. etc.
I prefer to live in the real world, so I would rather not indulge
your
fantasies.
The real world is not what you think it is. It was only when you
read about the fact that dinosaurs had once existed that the sector
you were in diverged from other sectors where dinosaurs had never
existed and some other evolutionary path of mammals led to you and
the exact same information in your brain before becoming aware of
the existence of dinosaurs.
Evidence?????
This is generically the case in a MWI setting. Of course, the MWI may
not be correct, QM may not be the ultimate foundation of the laws of
physics, but if we assume the MWI, then some observer who is aware of
precisely the information specified by some bitstring b (and nothing
more or less than specified by b), the observer should consider
him/herself to be in a superposition of all branches where b appears
in.
But what does "aware of" refer to? A brief thought that "b is true"?
When the thought passes is he no longer in that superposition? Is he
flitting from one superposition to another as he has thoughts b, c,
d... Or is it enough that he could recall these these? But what
causes the recall? What if he forgets them?
Let's step back and consider the usual formalism of quantum mechanics
involving a complete set of commuting observables. So, one assumes that
for any physical system there exists observables and you can add more
and more that commute with each other until you have some maximum
number. You can measure these observables simultaneously, the set of
eigenvalues that you find completely specifies the physical state of the
system.
Now, one can argue that an observer only ever measures his/her own state
directly. So, if I claim to have measured the spin of an electron, what
I really have observed directly is some brain processes that in turn
were triggered by signals coming into my brain that in turn were caused
by the experimental set-up for measuring the spin.
So, why not apply the formalism involving a complete set of commuting
observables directly to the brain of the observer him/herself? If we
imagine the observer to be a robot controlled by a computer that has
well defined computational states that can be specified by bitstrings,
then we can consider the complete set of commuting bitstring operators
O_k that measure the kth component of the bitstring.
My point is then that the observer is always finds him/herself in a
simultaneous eigenstate of all the O_k, so, it can always be specified
by a bitstring, simply because the observer is always measuring itself.
The bitstring thus specifies everything the observer is aware of.
If someone named John in New York has pain in his left toe then the
bistring specifies not just this pain there but also that's it's John
experiencing this pain including everything that John knows about his
own life, and all other knowledge he has right at that moment.
So, b is then what we've in this list called an "observer moment". The
bitstring will contain in it information about memories of the past.
These then refer to other observer moments that are not completely
specified. So, we have only an illusion about having evolved in time, in
reality we only ever exist in single observer movements. When we recall
having been at some place in the past, then that memory does refer to a
real event, except that it's just as much of a parallel world event as
in other MWI branches.
Just like the MWI-skeptics can argue that you can never prove the
reality of other branches, you can apply exactly the same arguments to
show that you can never prove the reality of the 1980s. The local nature
of the laws of the laws of physics means that any experiment or
observation you do can only ever involve interactions with the here and
now.
So, just like we can reasonably conclude that there exists a past and a
future based on what exists here and now, we can also reasonably
conclude that there exists other MWI branches.
Saibal
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