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.)

-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).

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.

Thanks to your insistence, now I see the difference between non-local HV 
theories, which violate relativity, and MWI, which does not.

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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