RE: unbohrlievable

From: Reason (
Date: Mon Jan 14 2002 - 14:35:42 MST


> > Raymond Chiao and Paul Kwiat (among the very best in the field)
> > performed experiments with a couple of entangled photons (PDC
> > generated). One member of the pair (the idler) is sent to a filter
> > and to a photomultipier. The other member (the signal) is sent to
> > an interferometer (Michelson type). Now, in order to conserve
> > total energy and to fullfill the uncertainty (time, energy) relations,
> > they find that the visibility of the signal photon fringes depends
> > on the bandwith of the filter through which just the idler photon
> > goes. Thus the width of the collapsing signal photon wave packet
> > depends on that (remote, and well separated) filter.
> I don't think this description can be correct. You make it sound like
> changing the filter over here causes instantaneous observable changes
> in the interference fringes over there. Clearly this would contradict
> relativity, which you say the experiment does not do.

It doesn't break causality -- which is the important thing, not any other
old theory :) -- because you can't tell anyone about it faster than the
speed of light. Quantum entanglement of states means that you can set up any
number of situations in which doing something at point A measurably changes
something at point B instantaneously with no delay ("spooky action at a
distance" -- google that phrase). However, you can never take advantage of
that fact to break causality by transmitting actual information faster than


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