Aihuxv.111
net.misc
utzoo!decvax!harpo!ihnss!ihuxv!lew
Wed May  5 23:20:47 1982
The quantum coffee break
The error in Don Chan's article of April 28, as correctly pointed
out by Charles Poirer and re-iterated by myself, is that A and B
cannot both *observe* the electron. This wouldn't be so if the 
observation didn't completely localize it, but the article explicitly
makes this a condition of the observation.

This fact is the essence of the Einstein et al paradox. In this case,
over repeated trials the observations of A have perfect anti-correlation
with the observations of B ( assuming the electron doesnt escape unobserved.)
In the spin correlation case, intermediate values of correlation are
possible, depending on the relative orientations of the polarizers.

Although the quantum coffee break can be treated relativistically,
the classical treatment contains all the salient features of the paradox.
The case of a particle track in a cloud chamber is a real example
of this thought experiment. The initial spherical ( or otherwise )
wavefunction is *focused* ( repeatedly collapsed ) by its interaction
with the chamber. A relativistic (fast) particle will have a track
which obeys *classical* (non-quantum) relativity, but it is the track
itself which illustrates the quantum observation effect. For a relativistic
treatment of the two-interaction case see Sakurai - Advanced QM.


				Lew Mammel - ihuxv

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