On Thursday, September 5, 2002, at 09:34  AM, Jesse Mazer wrote:

> But even if one understands that conscious observers are not necessary 
> to "collapse the wave function," Tim's questions do not go away. One 
> could always imagine that the box in the Schroedinger's cat experiment 
> was made of some super-material that blocked interaction between the 
> inside and the outside so effectively that decoherence was completely 
> eliminated, so from the outside the cat would have to be treated as 
> being in a macroscopic superposition until the box was opened, even 
> though the cat (or a video camera inside the box) would remember 
> having been in a single definite state all along.

In fact, all formulations I have seen of the SC experiment are exactly 
as you describe: a sealed box, with the necessary condition of no 
information from inside the box, whether meows of the cat or portholes 
cut in the side of the box or video signals coming out.

Hence the "mixed state" (as it described) holds up to the time the box 
is opened. Whether or not a camera is inside recording the process. 
Whether or not other humans are also inside the box, wearing gas masks 
perhaps, observing the process. Whether or not that box is inside an 
even larger box, a la the Chinese boxes thought experiment.

>
>> > One could arrange a thought experiment involving literally
>> > a series of boxes within boxes, each being opened at, say,
>> > one minute intervals after the cyanide was released or not
>> > released. One set of observers sees the cat either alive
>> > or dead at the end of the canonical one hour period. But
>> > they are sealed inside a box. After one minute, their box
>> > is opened, and the observers in the next-larger box then
>> > see the "collapse of the wave function at the 61-minute
>> > point." After another minute, their box is opened and a
>> > new set of observer sees "the collapse of the wave
>> > function at the 62-minute point."
>>
>> > And so on. (I don't know if I'm just reinventing a thought
>> > experiment someone developed many decades ago...it seems
>> > like a natural idea.)
>
> Yes, this is similar to the "Wigner's friend" thought-experiment. The 
> physics dictionary entry on Schrodinger's cat at 
> http://physics.about.com/library/dict/bldefschrdingerscat.htm 
> describes it briefly:
>
> "Wigner's friend is a variation of the Schrądinger's cat paradox in 
> which a friend of the physicist Eugene Wigner is the first to look 
> inside the vessel. The friend will find a live or dead cat. However, 
> if Professor Wigner has both the vessel with the cat and the friend in 
> the closed room, the state of the mind of the friend (happy if there 
> is a live cat but sad if there is a dead cat) cannot be determined in 
> Bohr's interpretation of quantum mechanics until the professor has 
> looked into the room although the friend has already looked at the 
> cat. These paradoxes indicate the absurdity of the overstated roles of 
> measurement and observation in Bohr's interpretation of quantum 
> mechanics."

Thanks for the reference. It matches my own thought experiment.

(Which, aside from showing some "overstated roles" for human 
observation, also shows that this whole business of "the wave function 
being defined everywhere and then suddenly vanishing" is a deeply 
flawed notion, as we've just shown many such points of potential
"collapse." Fortunately, nothing in the "shut up and calculate" 
practical side of QM depends on "collapse of the wave function," so it 
has mainly been a side show.)

But this thread is stimulating me to refresh my memory of QM and to 
study it more deeply. (I have a bunch of the recent Zeilinger papers on 
delayed-choice and double-slit experiments, but haven't had a chance to 
read them except by skimming.)

--Tim May

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