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>

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.


-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 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.


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

Thanks to your insistence, now I see the difference between
non-local HV theories, which violate relativity, and MWI, which does

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


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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