On 4/20/2022 5:53 PM, 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.
-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.
Superposition or pure wave-function is a matter of basis. We say no
superposition remains because we can only measure in a few classically
stable dimensions: alive/dead here/there ... But exactly why this is
the case is known as "the basis" problem. It's not obvious from the
Schroedinger equation, as MWI advocates are wont to pretend.
Brent
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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