Re: FTL by Down-converting (Revised)

From: CSharpner (google_at_easiesttoremember.com)
Date: 10/28/04 

Date: 28 Oct 2004 14:05:36 -0700

Let me put a disclaimer here before my responses below:

I'm not a physicist, but I DID stay at a Holiday Inn last night! But
seriously, I've been reading heavily about the double-slit experiments
and soaking it all up. I'd label myself as a "Laymen's expert", but I
wouldn't attempt to compete with a real physicist. I reserve the
right to be completely misled and confused. With that in mind...

hheffner@mtaonline.net (Horace Heffner) wrote in message news:<hheffner-2710041402540001@dialups-45.palmer.mtaonline.net>...
> FTL by Down-converting (Revised)
>
> A method is proposed here to achieve faster than light (FTL) communication
> by the use of down-converters. A down-converter splits a photon into two
> photons each having half the energy of the original photon.
>
> Suppose we have a sender Alice, a receiver Bob, and an intermediary
> facilitator Charlie. Charlie uses a beam splitter to create two beams of
> laser light: L the left beam and R, the right beam. Charlie then
> down-converts the L beam to create beams L1 and L2, and similarly creates
> beams R1 and R2 from the beam R. Beams R2 and L2 are normal path or
> "signal" photons through the down-converter, while beams R1 and L1 are
> called "idler" photons. "Beam" here means a flow of individually
> detectable photons sent in very short intervals so as to provide a useful
> rate of communication. Charlie directs beams L1 and R1 to Alice and beams
> R2 and L2 to Bob. The corresponding photons arrive at both Bob and Alice
> at nearly the same time, but here assume Alice receives hers first, but
> just barely before Bob.
>
> Bob directs beams R2 and L2 such that they can create an interference
> pattern in a set of detectors arranged so it is feasible to rapidly and
> with high probability determine whether an interference pattern is present
> or not. The signal photon beams R2 and L2 can create such an interference
> pattern because they are the two paths from a beam splitter.

OK so far...

> Alice can direct her idler beams L1 and R1 at will, in a co-linear
> fashion, to opposing sides of a half silvered mirror, but at an angle of
> 45 degrees. Fig.1, which requires fixed font (e.g courrier) to view,
> shows this configuration. Half of L1 and half of R1 then goes to a
> detector DL. Similarly, half of L1 and half of R1 then goes to a detector
> DR. The beams emerging from both sides of the mirror are thus fully mixed,
> and the which-path information for all photons is lost. In this case Bob
> must see an interference pattern. If Alice then diverts her beams
> directly to detectors, the which-way information is then restored to 100
> percent available, and Bob must see a bimodal distribution.

[snipped the rest]

You're half right. Bob's interference patterns do come and go, but
he's not aware of it until Alice, classically and sub-luminally,
transmits her detected information to Bob. At that point, Bob can
make timing comparisons with his detections to determine which of his
photon detections from his two bell curves should be considered
cancelled out or not, so he can calculate an interference pattern from
his and Alice's old data.

All of these experiments that I've read about require a coincedence
counter that's connected to both sets of receptors and it's not until
AFTER information from both sets of detectors is transmitted to a
single place (and transmitted via conventional, classical, sub-luminal
speeds) that a determination can be made as to wether or not any
photon detections at Bob's place should be considered for an
inteference pattern.

Apart from that, your logic looks sound to me. I believe this FTL
comm scenario is the first thing that likely pops into most people's
minds when they learn of the double-slit experiment. It did mine, and
it obviously did yours.

Uncle Al is right about FTL.

Generally, if you find some cool method to transmit FTL such as what
you've proposed above, the next step is to figure out what you missed.
 If you can show me FTL communication, then I can, using relativity,
show you backwards in time communication. And, with backwards in time
comm, I can show you a paradox. If a theory produces a paradox, it's
DOA. :( If, on the other hand, relativity can be disproven, then
paradoxes may not be a concern, but I won't be holding my breath for
that to happen.

Relevant Pages

  • Re: FTL by Down-converting (Revised)
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