On 21-04-2022 22:37, Brent Meeker wrote:
On 4/21/2022 1:27 PM, smitra wrote:
On 21-04-2022 20:18, Brent Meeker wrote:
On 4/21/2022 1:32 AM, smitra wrote:
On 21-04-2022 02:53, Bruce Kellett wrote:
On Thu, Apr 21, 2022 at 10:05 AM George Kahrimanis
<gekah...@gmail.com> wrote:
On Tue, Apr 19, 2022 at 11:09 AM Brent Meeker <meeke...@gmail.com>
wrote:
The only purpose of the box in Schroedinger's thought experiment
was
to put off the observers perception. Really the thought
experiment
is over when the radioactive decay occurs. That atom has
transitioned to a different nuclear state which is entangled with
and recorded in the environment.
On Tuesday, April 19, 2022 at 4:20:49 AM UTC+3 Bruce wrote:
Yes. Schrodinger had the cat in a box to emphasize the idea that
the
cat was in a macro-superposition of alive/dead. This misled Wigner
to the extent that he thought the state collapsed only when the
box
was opened. All of this was made redundant when it was realized
that
decoherence rendered the state definite almost instantaneously.
Saibal makes the same mistake when he claims that Alice, after her
measurement, is still in a superposition until Bob sees her
result.
The idea that the superposition still exists since decoherence is
only FAPP is something of a red herring -- in MWI, Alice has
branched according to her result into up and down branches that no
longer interfere. There is no macro-superposition.
This is wrong, because inability to demonstrate interference does
not mean that there is no superposition.
Alice does not branch due to decoherence. It is true that there are
two branches where the results of Bob are different due to rapid
decoherence. But before Alice knows the result of Bob, the state of
the algorithm that represent Alice's mind will be identical in both
branches. What matters is whether or not information about Bob's
result can change Alice's subjective state. Only then can the two
branches from Alice's point of view, diverge. If this were possible,
then that means that Alice could obtain information about Bob's
result without even looking at his result. So, Alice would have
psychic abilities.
Of course she can obtain information about Bob's result without
looking at it. That's what decoherence does, spread information into
the environment so that there is a fact-of-the-matter as to the
result.
You've apparently bought into the Many Minds interpretation of MWI,
so
the cat isn't dead, the vial isn't broken, and the atom isn't decayed
until Wigner's friend looks in.
Yes, the Many Minds version of the MWI makes the most sense. The mind
as defined by the algorithm the brain is running is the same in the
different sectors.
-1- Decoherence (by a chaotic environment) turns an entangled
superposition into a non-coherent density matrix, only if we
subsequently omit the environment from the description of the
system.
(Not if we keep the environment in the description.)
FAPP is for a reason -- we automatically trace out unneeded
environmental variables.
-2- The "box" (in which Scroedinger's cat is enclosed, with the
lethal apparatus) contains also its "environment", so a quantum
descrition of this box describes the environment also. Therefore I
do not agree that decoherence INSIDE THE BOX will ruin the
superposition ASSESSED FROM OUTSIDE THE BOX. So, Wigner was right.
I
suppose that Saibal also is right, though I have not checked that
message (sorry).
Unfortunately for this idea, decoherence does not stop at the box.
In
the time that Wigner thinks about this before he opens the box,
decoherence has enveloped essentially the whole world, so Wigner
himself has decohered into either a world with a dead cat or a
world
with a live cat. He can't dissociate himself from the split that
occurs, so from his point of view outside the box, the
superposition
is long gone, and he has to deal with a simple classical state of
either a dead cat or a live cat -- no superposition remains.
The superposition does remain, it's just that it cannot be probed in
interference experiments. Before Wigner knows the result, his
subjective state of his mind is the same in both branches. It
doesn't matter that everything in his environment including the
atoms in his brain is entangled with the state after the experiment.
What matters is that Wigner cannot know the result without observing
it. The bitstring that contains all the information he is aware of,
is the same in both branches.
What if he forgets what he saw?
If he forgets, then he'll merge with the versions in the other sectors
that also forgot what he saw. What matters is the bit string that
represents everything she is aware of at a certain moment. When he
remembers again then he'll spit again.
This splitting an merging dozens of times per second. But merging
with what or whom. Is Bob merging with other Bob's who have different
memories but aren't recalling them at the moment?
Yes. In principle one has to start with a definition of Bob as an
algorithm (in practice one then assumes that such a definition exist
without one being able to specify it explicitly). When the algorithm is
run by a brain or some other machine, it will take in information and
change as a result. So, the Bob of now is not the same as the Bob of one
second later, these are different algorithms, albeit it very similar
ones.
So, what we have is a large set of algorithms. Some algorithms have a
working memory and for those algorithms it makes sense to talk about
their subjective past This is then defined by the algorithm itself. For
each algorithm there then exist a set of possible future algorithms that
are one computational step away from it. This then follows from applying
the algorithm itself to data that has yet to be processed by the
algorithm and is therefore unknown to it. This uncertainty leads to the
multiple future states.
You do realize don't you that if you take this view you've made QM
personal and epistemic so we can forget all the MWI muddle and adopt
QBism whose only problem is that what you think reality is, is
personal.
One may get to something that looks like QBism, but one cannot conclude
that reality is personal within the framework that I suggest.
Remembering is the result of consulting the memory and the memory was
in a superposition entangled with the environment. If information in
the memory is processed by the algorithm that represents the mind of
the person, then the person's mind will split again.
But then you've completely forsaken physics, which depends on
inter-subjective agreement about events.
The universe is what it is. We can try to find out how it works by doing
experiments according to rigorous protocols thst we've designed that are
good at distinguishing rival models from each other. But there is no
guarantee that the way the universe works at the fundamental level will
itself be consistent with our own protocols. It may be that at the macro
level FAPP things do work out that way, but that in principle, there is
a tension between the way we do physics in practice and how the universe
works.
Inter-subjective agreement about experiments is something that arises
FAPP when we do experiments in practice. This is not going to be
violated when doing those experiments that are needed to find the
fundamental laws of nature. But those laws may then tell us that a
multiverse exists and events in one branch may then be different from
events in another branch.
Saibal
Brent
Saibal
Brent
If not and the bitstring would have diverged across the two branches
and Wigner could then simply feel the result without having to do
any observation.
Saibal
I rephrase my conclusion. I agree with you, on the splits being
technically non-local, but this is only an artifact of describing
the dynamical evolution of the wavefunction in space-like slices
forming a time-like stack. Thus a split affects the whole slice in
which it occurs. But seen from a moving train, it would be a
different slice! Only on and inside the light cone, the split is
physically meaningful.
The split is associated with the light cone, so it is Lorentz
invariant.
Thanks to your insistence, now I see the difference between
non-local HV theories, which violate relativity, and MWI, which
does
not.
I had always made a distinction between faster-than-light
influences,
which are intrinsically local since they involve the local transfer
of
information via some medium (albeit FTL), and non-local influences,
which do not involve any FTL transfers. They are instantaneous and
non-local. So that does not violate relativity. In fact, FTL
transmission does not strictly violate relativity either --
tachyons
are perfectly consistent with relativity. All that relativity
forbids
is the acceleration of a subluminal particle to the speed of light
and
beyond. Tachyons are always superluminal, so are not forbidden. The
various no-signalling theorems demonstrate that Bell-type
correlations, while non-local, do not involve FTL signalling or
tachyons
Bruce
I am writing in a hurry, because these days are hectic. I may have
missed some important postings, sorry. I would welcome any hints
(with the name and time of posting) sent to my G-mailbox:
GeKahrim.
George K.
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