🚀 go-pugleaf

firth@sei.cmu.edu (Robert Firth) writes:

>In article <mcirvin.713566546@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
>>[my boneheaded statement that, because operators with spacelike
>>separations commute, measurements of them "can't affect each other"]

>But that's simply not true.  In the straightforward Aspect type of
>experiment, the observables commute, but the results of the
>measurement are correlated, precisely because either measurement
>projects the total wavefunction into an eigenstate of BOTH
>observables.
>[explanation of EPR correlation deleted]

Sorry.  I didn't mean that-- I should have been more specific. 
I plead innocence by noting that I corrected the statement about
an hour later-- though the Net is much more asynchronous than EPR,
so you might not have read that yet. 

Of course such correlations can exist.  What I meant was that
no uncertainty relation or "quantum incompatibility" can exist
between the two observables.  Measuring one won't destroy an
eigenstate of the other, so you can't transmit messages faster
than c by, say, doing a string of repeated measurements for every
"1" bit at one end and watching the probabilities change at the
other end.  Mr. Sarfatti claims that there *can* be an uncertainty
relation between two commuting observables.  It's not clear how
that can happen when the measurements perform a projection.
Sarfatti's spin-flip is neither a projection nor a unitary
transformation nor some composition of the two.

>This seems to me to be the flaw in most criticisms of Mr Sarfatti's
>experiment: they assume that the wave functions are decoupled, or,
>alternatively, that a measurement of one observable cannot affect
>an observable of the "other" particle.  This is circular reasoning:
>it is precisely that assumption that leads to Bell's inequality.

Actually, most criticisms of Mr. Sarfatti's experiment (still
gedanken at this point, so far as I know) have been more
careful about language than I was, and they have nothing to
do with the locality involved in hidden variables.  They just 
assume that the evolution of the system occurs according to the
rules of quantum mechanics.  Most of them forgot to mention
the fact that measurement is nonunitary in many interpretations
of QM, a fact that Mr. Sarfatti tried to use to dispel the
"unitarity red herring"; but his spin-flip isn't what
happens in a measurement either.
 
-- 
Matt McIrvin, professional gradgrind, amateur Usenet drifter