[ExI] QT and SR

scerir scerir at libero.it
Fri Sep 12 11:46:51 UTC 2008

> Perhaps one of the Everettistas could explain this to me.
> If the split starts at Alice and travels at c toward Bob,
> if Bob is space-like separated it won't ever reach him.

In the orthodox view the (usual) collapse must be instantaneous.

Carlton M. Caves has shown that the collapse must be taken
as instantaneous and that assuming the collapse takes a
non-zero time would lead to observable conflict with, e.g.,
the Stern-Gerlach experiment. See Carlton M. Caves, 
'Quantum mechanics of measurements distributed in time', 
Part-I: Phys. Rev. D33 pp.1643-1665 (1986), Part-II: 
Phys. Rev. D35 pp.1815-1830 (1987).

Regarding the collapse due to measurements of entangled
pairs the orthodox view does not say anything, at least 
to my knowledge. QM only gives pure and simple algebraic 
expressions for those correlations. Nothing more.

But if one (like Einstein, or Bohm, or many more) tries
to inject a realistic explanation (i.e. a causal behaviour 
in space-time) into the orthodox picture (by means of 'spooky 
actions', or by means of 'empty waves', etc.) strange
consequences arise (i.e. actions/passions at a distance, 
superluminal influences, non-locality of some uncontrollable 
kind, etc.). 
>From the experimental side, again, the Geneva group has shown 
(with measurements on time/energy entangled pairs, performed 
with fast rotating Franson interferometers) that realistic 
explanations (like Bohmian mechanics, or 'spooky actions') 
presuppose superluminal velocities. 

Now, that said, it seems to me that MWI is a realistic 
interpretation (I was an 'Everettista' in the early '70s!). 
It also seems to me difficult that MWI - being a realistic 
interpretation, or a realistic theory - may avoid the tragic 
destiny of all other interpretations which try to introduce 
elements of reality in QM or in measurement theory. 

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