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Faster than a Speeding Light Ray
For any local readers, today there is a seminar by John Cramer on “An experimental test of nonlocal quantum communication.” Should be interesting!
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January 16th, 2007 at 7:34 pm
Is this a Bell-type experiment?
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January 17th, 2007 at 5:38 am
Greg: Is this a Bell-type experiment.
Bell-type experiment? Those are for scientific girlie-men! Cramer’s experiment is a full-bore faster-than-light, backwards-in-time, none-of-them-darn-statistics communicator.
Functionally, it amounts to the design and construction of one of science fiction writer Ursula K. Le Guin’s ansibles.
Just to mention, I personally know, like, and respect John Cramer. I went to the talk and it was good. And John and Warren Nagourney are definitely going to do the experiment.
But if it works, then it means that orthodox quantum mechanics is wrong. Since we engineers are ultra-orthodox, we think it won’t work.
The most likely failure mechanism (JMHO) has to do with the detailed quantum-mechanical description of the outgoing entangled-photon wavefront.
Namely, it is not quite clear that two rather technical constraints on the optical configuration can be satisfied simultaneously.
In brief, the Cramer/Nagourney optics must be adjusted such that simultaneously (1) slits are optically resolved, and (2) clicks are strongly correlated. It seems likely (again, JMHO) that this will prove hard to accomplish–sufficiently hard to obstruct the experimental goals—in consequence of the usual wave-particle uncertainty relations.
But like I say, they’re very good scientists, it’s a very good experiment, and they definitely ought to attempt it.
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January 17th, 2007 at 9:16 am
It is a Bell-type experiment, with a twist. If I have time this afternoon I’ll write a post describing it. I think I know what’s going to happen but I haven’t pinned it down with certainty in my mind yet.
Sadly Cramer didn’t spend any time talking about the transactional interpretation.
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January 18th, 2007 at 8:27 am
Hi Dave! The room was crowded & I didn’t see you there, otherwise I’d have said hello.
What I think will happen is pretty specific. John and Warren will begin by adjusting their optics so that the experiment’s first goal of resolving a clear two-slit diffraction pattern on the lower path is achieved. Good.
Then they’ll insert a spatial filter on the upper path, and further adjust the optical train, to achieve the experiment’s second goal of increasing the probability of two-photon coincidence. Good.
But IMHO the experiment will encounter trouble in achieving the first goals and the second goals simultaneously. Systematically optimizing these two goals will require a rather tedious advLIGO-style analysis of the propagation of quantum-entangled optical wavefronts throughout the whole optical train. This analysis will reveal that the usual mechanisms by which quantum uncertainty relations block information transfer in traditional Bell-type experiments apply also to the Cramer/Nagorney experiment.
IMHO, the required theoretical formalism for propagating quantum-entangled optical wave-fronts will itself have considerable value as a teaching tool. Also, maybe orthodox quantum theory is wrong, and the Cramer/Nagourney experiment will work! Which is why they should do this experiment.
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January 19th, 2007 at 7:38 am
Can anyone give a description of the actual experiment, or a link to one?
Some of those can be quite interesting puzzles.
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January 19th, 2007 at 10:38 am
Ralph (and anyone) I can send you a pdf of that
experiment (actually the Jensen gedanken experiment, which is the core of the Cramer experiment). But I need your email.
scerir@libero.it
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April 11th, 2007 at 3:19 pm
Seattle PI update 08 April
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