Re: Ask Dr.SETI: Faster-Than-Light Communications


Dr. H. Paul Shuch (n6tx@setileague.org)
Tue, 06 Jul 1999 07:36:57 -0400


At 12:24 PM 7/6/99 +0200, you wrote:
>>
>Let us assume that the two photons have a link which enables them to
>communicate. If we are able to GENERATE a steady stream of this
>synchronized photons, and send them as two laser beams to two different
>places, we suddenly have a FASTER-THAN-LIGHT COMMUNICATIONS DEVICE !
>

There has been a lot of speculation on this subject (much of it on the SETI
email discussion list), but so far, it's only theoretical -- no practical
demonstration of the technology to generate such coupled pairs has been
made. See the editorial at <http://www.setileague.org/editor/darcy.htm>
for further speculation.
        Perhaps, someday, this will be a useful communications mode. For now, we
stick to what tools we have.

Below is an excerpt from our discussion list:

> Doesn't sound to me as if FTL,
> action at a distance is a proven reality. But then I haven't read Nick
> Herbert's book.

The core of the page you point me to is here:

=====================

    (2) n[A+, B+] <= n[A+, C+] + n[B+, C-].

Additional inequality relations can be written by just making the appropriate
permutations of the letters A, B and C and the two signs. This is Bell's
inequality principle, and it is proved to be true if there are real (perhaps
hidden) variables to account for the measurements.

At the time Bell's result first became known, the experimental record was
reviewed to see if any known results provided evidence against locality. None
did. Thus an effort began to develop tests of Bell's inequality. A series of
experiments was conducted by Aspect ending with one in which polarizer angles
were changed while the photons were `in flight'. This was widely regarded at
the time as being a reasonably conclusive experiment confirming the
predictions of QM.

Three years later Franson published a paper showing that the timing
constraints in this experiment were not adequate to confirm that locality was
violated. Aspect measured the time delays between detections of photon pairs.
The critical time delay is that between when a polarizer angle is changed and
when this affects the statistics of detecting photon pairs. Aspect estimated
this time based on the speed of a photon and the distance between the
polarizers and the detectors. Quantum mechanics does not allow making
assumptions about where a particle is between detections. We cannot know when
a particle traverses a polarizer unless we detect the particle at the
polarizer.

Experimental tests of Bell's inequality are ongoing but none has yet fully
addressed the issue raised by Franson.

====================

Despite 25 years of trying, no-one has proven locality. Bells theorem still
stands as "proof" to some observers that reality is "non-local", or to put it
another way, that reality requires FTL interconnectedness among quantum
particles.

Nick Herberts book goes into detail describing the attempts to refute the
result of Bell's theorem, describing them and why they seem to be grasping.

Beyond this, you will have to read the book, or something similar, yourself.

John Marcus.

--------------------------------
H. Paul Shuch, Ph.D., CFII, FBIS
Executive Director, The SETI League, Inc.
433 Liberty Street, PO Box 555
Little Ferry NJ 07643 USA
voice (201) 641-1770; fax (201) 641-1771
n6tx@setileague.org www.setileague.org
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