NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/physics/21694

Internet Message Format | 1992-12-23 | 1.7 KB

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From: [e-mail] (Jack Sarfatti)
Subject: re: Dirac's question to Feynman
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Date: Wed, 23 Dec 1992 21:05:26 GMT
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When Dirac first heard Feynman lecture on his new path version of QM based
upon Dirac's paper on the Lagrangian in QM, Dirac asked "Is it unitary?"
and Feynman was not sure what unitarity was - as reported in James Gleick's
GENIUS.

The sci.physics discussion on this - which Baez would no doubt have rejected
ab initio had he had the power in a "moderated" version - has led to the
interesting apparent discovery that while strict unitarity of the time
evolution of states between irreversible measurements is sufficient to
conserve the sum of local probabilities to unity it is apparently (i.e.
tentatively) not necessary. One can formulate a weakly non-unitary
generalization of standard QM that conserves the sum of local probabilities
while permitting quantum connection communication outside the light cone
etc.  Since the whole rational for unitarity is conservation of
problability,
this may be an important discovery. I was confused at the start because in
my computations probability was conserved - I had neglected to check the
off-diagonal invariance of orthogonal inner products because I had checked
the diagonal invariance of norms. If this distinction between diagonal and
off-diagonal invariance of inner products is frame-invariant then it is
an important clue - I'm not sure about the frame invariance yet.