FOM: Reply to Davis re undecidable propositions JSHIPMAN at
Fri Dec 5 03:43:56 EST 1997

When I said that a proposition *essentially* incapable of being decided was in
a sense meaningless, and that a proposition which is *knowably* essentially
undecidable is meaningless in a stronger sense, I was referring to mathematical
propositions.  But although I was not contemplating nonmathematical examples
like Martin's, I don't think they disprove my thesis.  There are some very deep
waters here because of the philosophical status of quantum physics.  First of
all, neither of Martin's examples is *essentially* undecidable, just
practically so.  But he could have chosen an example which really was
essentially undecidable, e.g. by measuring a quantum spin and not looking at it
rather than tossing a coin.  In this case Schrodinger's cat enters the picture
and many physicists and philosophers will say that yes indeed it is meaningless
to say it was up rather than down, the wave function didn't collapse.  This
deserves an e-mail list of its own, I'll just remark here that the debate in
physics is still going on fiercely and David Deutsch's book "The Fabric of
Reality" is a good source (and a good gift at $20.97 at Shipman

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