From: Hal Finney (hal@finney.org)
Date: Tue May 07 2002 - 15:15:03 MDT
Scerir forwards:
> 'A Bell Telegraph'
> Daniel O. Badagnani
> 4 pages, 2 figures
> http://arxiv.org/abs/quant-ph?0204108
> We show a device with which, apparently, information (in the form of a
> "slash-dot" code) is instantly transmitted via Bell state collapse,
> over arbitrary distance. We discuss some problems and paradoxes arising
> when this conclusion is viewed in the relativistic framework.
It's a cute title, but come on, there is no way this device can work.
The author doesn't even offer any reasons in the paper why it should work!
There are no equations at all - that should be a tip-off.
At first I thought the author was just a quack, but according to
http://cabtep5.cnea.gov.ar/particulas/daniel/pag-db.html he is actually
a physicist working on string theory and such. So now I think it is
a joke, maybe a late April Fool's effort (do they celebrate April 1 in
Argentina?) or perhaps he wants to see who can spot the error.
Basically he is taking a classic two-slit interference experiment and
trying to arrange things so that he can remotely measure which slit the
particle went through. Then he assumes that he will be able to make the
interference pattern appear or vanish depending on whether he actually
makes the remote measurement or not.
My suspicion is that the device will fail because the two photons
which are supposed to interfere (when no remote measurement occurs)
are not actually correlated in phase. In order to have interference,
there must be a simple phase relationship. In a two slit interference
this works because we send the same photon through both slits. But in
this case we aren't doing that.
We're (in effect) sending an excited atom through two slits, letting it
decay to a pair of photons, then capturing one of them on our screen.
Before the decay the two instances of the atom would be correlated.
But decay is a random process. I think the resulting photon pair,
although correlated with each other, will not be correlated to photons
that might have been emitted by an alternate version of the excited atom
in the other pipe. The decay time will be different in that alternate
"universe" and so there will be no relationship in phase.
Therefore I think that in practice there will not be any interference
in the system, whether remote observation is done or not. The decay
process will randomize the photon phase and so even though the atoms
were correlated, the photons in the two pipes will not be.
It's been a long time since I've studied this so I might be wrong.
But the fact that he doesn't write down any equations for the photons
makes me suspicious that the author knew it wouldn't work. Probably on
sci.physics you could find experts who could tell whether my explanation
is right or whether something else goes wrong.
Although the author discusses some paradoxes, he doesn't seem to mention
the most obvious one, which is that you could observe the photons after
the ones at the other end have already hit the screen. Just make the
screen end of the pipe shorter so the photons get there first. Now you
need to have had no interference, even after interference has occured.
Oops! Maybe the universe will come to an end and God will write the
whole thing off as an embarrassing mistake.
Hal
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