[ExI] QT and SR

[scerir]

Stuart: 
> Could the correlation be said to move or travel 
> at any speed at all?

David Mermin wrote a very beautiful paper trying to
explain the difference between (quantum) correlations
and the difficult existence of physical "correlata". 
http://arxiv.org/abs/quant-ph/9801057

The peculiar problem here, in orthodox QM, seems to be 
that correlations have physical reality but that which 
they correlate does not. 

It seems interesting to point out that, viceversa, in MWI 
"correlata" have physical reality, but correlations do not!

It is evident that correlations do not move at any speed
at all. 

It is less evident whether or not physical "influences" 
can move at superluminal speed (or in a reversed time) 
between two space-like separated wings of an EPR set-up, 
when Alice's or Bob's measurement causes the so called 
"collapse" (or whatever) of the singlet state.

These FTL "influences" cannot be true informations (not 
because this is forbidden by SR postulates, not because it 
is impossible to know if Alice performed her measurement 
before Bob, or viceversa, when they are space-like separated) 
because the process of quantum measurement is indeterministic. 
Alice cannot "force" a specific measurement outcome, thus 
cannot she send a definite message to Bob, and viceversa. 
Shimony called it the "peaceful coexistence" between QM and SR.

It is - in principle - possible that "some" information is
transferred superluminally in the EPR experiments. Namely
an information about the spin correlation, which is
greater than expected from the local-realistic models.
But even this kind of superluminal information does not 
allow one observer to send a message to the other distant 
or space-like separated observer.