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From: desj@brahms.BERKELEY.EDU (David desJardins)
Newsgroups: net.philosophy,net.physics
Subject: Re: Does the moon exist?
Message-ID: <12629@ucbvax.BERKELEY.EDU>
Date: Mon, 24-Mar-86 18:45:36 EST
Article-I.D.: ucbvax.12629
Posted: Mon Mar 24 18:45:36 1986
Date-Received: Wed, 26-Mar-86 04:13:45 EST
References: <12628@ucbvax.BERKELEY.EDU>
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Reply-To: desj@brahms.UUCP (David desJardins)
Organization: University of California, Berkeley
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Xref: watmath net.philosophy:4647 net.physics:3972

In article <12628@ucbvax.BERKELEY.EDU>
   weemba@brahms.BERKELEY.EDU (Matthew P. Wiener) writes:
>This comes from a debate in net.philosophy about whether existence is
>the same thing as following physical law.
>
>To make the debate a little more interesting, I shall pursue one standard
>view of modern physics a la John Archibald Wheeler.  In particular, I shall
>suggest that following physical law, as it is now understood, implies that
>either physical things do not exist or that a non-physical thing does.
>..........

   Rhetorical Question #1:  Is the moon physical?  Obviously yes.  (If the
moon is not physical then nothing is, and the word has no meaning!)

   Rhetorical Question #2:  Does the moon exist?  Again, obviously yes.
Einstein's question, while insightful, is obviously rhetorical.  Whatever
the word "exists" means, we had better make sure that we include the moon.

   Non-Rhetorical Question:  What is the moon?  That is, what is is that
we are referring to when we say "the moon"?  My answer has to be that it
is a quantum wavefunction (or a segment of one) in the enormous Hilbert
space we call the universe.

   So, I don't think I agree with your conclusion.  The moon is a physical
thing.  It is also a quantum wavefunction in a Hilbert space.  I do not
find these irreconcilable, as you seem to.

   In particular, when not being observed, "the moon" is no longer an
eigenfunction of our observables.  It is neither here nor there, but
somewhere in between.  Nevertheless, I still insist on calling it a
*physical* object (as you noted, all other routes lead to paradox...).
The only conclusion we can draw is that "physical" does *not* mean that
the observables of the object are fixed.
   Really, even classical uncertainty tells us this.  Observable parameters
of a physical object can only be measured (i.e. only exist) up to some
residual uncertainty.  What is so horrible about this?

   I now feel ready to answer Einstein's question with confidence.  The
moon doesn't go away when I don't look at it.  But it *does* get sort of
fuzzy!

   -- David desJardins