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From: lambert@boring.uucp (Lambert Meertens)
Newsgroups: net.physics
Subject: Re: quantum mechanics and all that
Message-ID: <6746@boring.UUCP>
Date: Thu, 30-Jan-86 03:56:25 EST
Article-I.D.: boring.6746
Posted: Thu Jan 30 03:56:25 1986
Date-Received: Sat, 1-Feb-86 07:19:34 EST
References: <10137@tardis.UUCP>
Reply-To: lambert@boring.UUCP (Lambert Meertens)
Distribution: net
Organization: CWI, Amsterdam
Lines: 49
Apparently-To: rnews@mcvax

In article <10137@tardis.UUCP> tmb@tardis.UUCP writes:
> Assume I put a cat into a box, together with a device that performs an
> experiment whose two outcomes are equally likely, according to quantum
> mechanics, and one outcome of which causes a cyanide capsule to break
> within the box and the cat to die.
> ALL THAT QUANTUM MECHANICS PREDICTS is that if you make an infinite number
> of such boxes and perform the experiment with all of them then, after
> the experiment, in one half of the boxes you will find dead cats,
> in the other half you will find live cats. [...]
> Other people suggest that the cat isn't really dead until someone observed
> that it is dead, i.e. that the decision about its death isn't made until
> someone observes it. [...] This point has no relevance.

Now do the following: make two slits A and B close to each other in the box
that can be opened or closed from the inside.  Install equipment that
monitors if the cat is alive (as used in intensive care) that causes slit
A (initially open) to close, and B (initially closed) to open when the cat
dies.  After an elapsed time such that the probabilities of life vs. death
are equal, let an electron be fired to the slits.  It will pass through A
or B, with equal probabilities.

To an outside observer, to whom this devilish contraption is a black box,
this is the same as a box with two open slits to which an electron is
fired; if measurements concerning the passing of the electron are made, it
is equally likely to pass through A as through B.  If no such measurement
is made but a photographic plate is placed behind the slits, we get an
interference pattern because of self-interference of the "probability wave"
passing through the slits, i.e., the superposition of the two waves
corresponding to the two outlets.

Now it seems to me that if this Russian roulette played on a cat results in
the superposition of a live and a dead cat, then the output of the box is
likewise the superposition of an electron passing through A, and the *same*
electron passing through B.  So we should see an interference pattern here
as well.  Is this indeed what QM predicts?  (I honestly don't know; it's
not my field.  I have a gut feeling it does not, in which case I would
really like to know why not.)

This is an experiment that can be performed.  (Instead of cats, dogs can be
used, which, although not so stupid, are much more obnoxious:-)  If the
outcome shows indeed interference, then I don't see how other positions
than "Schroedinger's cat (or Meertens' dog) is in a sense both dead and
alive" can be maintained.  On the other hand, if it does not show
interference, that ambivalence would seem quite untenable to me.
-- 

     Lambert Meertens
     ...!{seismo,okstate,garfield,decvax,philabs}!lambert@mcvax.UUCP
     CWI (Centre for Mathematics and Computer Science), Amsterdam