Re: MWI, Copenhage, Randomness

From: Jesse Mazer <>
Date: Thu, 05 Sep 2002 12:34:40 -0400

Brent Meeker wrote:

>On 04-Sep-02, Tim May wrote:
> > By the way, issues of observers and measurements are
> > obviously fraught with "Chinese boxes" types of problems.
> > In the Schrodinger's Cat pedantic example, if the "cat
> > alive or cat dead" measurement is made at the end of one
> > hour by opening the sealed box, what if a video camera had
> > been also sealed inside the box, and had seen the cat
> > breathe in the cyanide gas at 10 minutes into the
> > experiment? Does this imply the "wave function collapsed"
> > at the time of the measurement by the human observers, at
> > the one hour point, or at the time the video camera
> > unambiguously recorded the cat's death?
>Alive and dead are very macroscopic operators (average of
>lots of micro-states) and so the cats interaction with it's
>environment (the box) will very quickly diagonalize the
>Alive X Dead density matrix. To introduce observers as
>having a special effect seems to introduce an aphysical

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.

> > 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 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 describes it

"Wigner's friend is a variation of the Schrödinger'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."

By the way, anyone interested in the measurement problem and interpretations
of QM might want to take a look at the book "Foundations and Interpretations
of Quantum Mechanics" by Gennaro Auletta...I haven't read it, just browsed
it (it's a bit over my head for now), but it looks like a very comprehensive
phone-book sized reference on these issues, with a lot of discussion of new
interesting experiments probing quantum weirdness. There's a brief
description and a table of contents at


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Received on Thu Sep 05 2002 - 09:36:00 PDT

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