From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Schrodingers Dog
Keywords: Cats , Quantum Merchanics, Cruelty to Animals
Date: 4 Oct 92 21:55:07 GMT

naturman@uctvax.uct.ac.za writes:

>1) Kitty cats are tangible objects.
>2) Wavefunctions are mathematical functions defined over a region of space and
>   time. They are abstract.

A quite sensible way to look at things, imho: we have no idea to what
extent anyone should reify the wave function, as has been amply
demonstrated here.

>Physicists just don't seem to understand that probability has got to do with
>knowledge. 

*Classical* probabilities do.  That what we call quantum probability
is actually an epistemic sort of thing is a hallmark of hidden variable
theories, not QM.

>Probabilities are not absolute but depend on the observer. If we
>put Schrodingers doggy in the box with a gas mask then the "alive/dead
>wavefunction" collapses for him when he sees the kitty kick the bucket or not,
>but it does not collapse for Schrodinger.

This is a reasonable interpretation, and is actually quite close to that
of John Baez: if you want to calculate a probability for something, you
don't put in any "collapse events" prior to the measurement you're actually
calculating probabilities for, no matter what that might be-- you can
"import" and "export" measurements from the unitary evolution, and
you never have to even refer to "collapse" as a process that changes
the wave function *after* a measurement, separate from unitary evolution.
If you want to calculate probability for Spot seeing Fluffy kick
the bucket before time t, you evolve the wave function without collapse
up to t.  If you want to calculate probabilities for Schrodinger getting
various results at t', you evolve the wave function up to t' without
collapse. 

That kind of viewpoint is not so unpopular with the physicists around 
here, though hotly debated.  I like it.

But how do you *know* that this is actually the correct picture?  You
seem to be justifying it by reference to probability as a function of
ignorance of hidden variables, or something similar.  That's not
necessary, and, indeed, seems to require some kind of nonlocality
to work properly.

>One of the reasons I gave up physics to become a mathematician was that I was
>sick and tired of physicists who had no understanding of basic probability
>theory but who continually bullshited about QM.

What kind of bullshit?  If they used Schrodinger's cat type arguments
to justify some kind of special role for consciousness, then I might
agree with you.  If they were merely assigning unjustified amounts of
reality to the wave function, well, I'd probably regard that as
excusable. 

>Lets face it, the argument is not about kitty cats. The real gripe is that some
>people are worried about not having free will and they think that their nonsense
>interpretations of QM will restore their lost free will.

That is, personally, NOT my intention, and I regard arguments relating
QM to free will as generally extremely bogus.  I think the vast majority
of working physicists feel the same way.  The interpretations that
assign a major role to consciousness are in the minority, and are
by no means current physics dogma or even physics fashion.

People try to interpret QM in part because of a desire to make it more
than an operational theory of how to get probabilities (I have no idea
whether this is justified or not, though it appeals to my more 
optimistic nature), in part because of a desire to make the 
operational prescriptions precise and well-defined (which I think is
a necessary and honorable goal), and sometimes because they want to
make it conform to some other philosophical agenda.  IMHO only the
latter is grounds for suspicion.
-- 
Matt McIrvin, posting nonsense again 
Newsgroups: sci.physics