From: "David P. Reed" <address@hidden>
To: Dewayne Hendricks <address@hidden>, Steve Schear <address@hidden>
Subject: Re: Fwd: Re: [Discuss-gnuradio] Salon article -- off topic
Date: Thu, 13 Mar 2003 06:43:16 -0800
MIME-Version: 1.0
At 05:33 AM 3/13/2003 -0800, Steve Schear wrote:
David Reed's physics is not strictly correct. He maintains that
"Photons in free space act almost exclusively as waves. Therefore,
when they cross paths they merely set up an interference pattern
for the very brief time of their interaction. No energy is
exchanged and the quantum state of each photon is unchanged after
they pass each other."
Steve, Dewayne -
I never said this. (and I wouldn't have)
Here's what I said in my mail:
Steve - of course you are right that when two photons interact with
an electron they can produce other photons with surprising
behaviors.
We see these interactions every day. That is how signals interact
inside antennas. (which are seas of electrons). That is how
signals reflect and refract. You can get frequency doubling, you
can get tropospheric tunneling, etc.
QED explains everything about radio, in theory, and it is
remarkably precise. and predictive. It's one of the most well
established parts of science.
Two photons don't create a momentary interference pattern when they
"cross paths". Unless they are the *same* identical photon, they
don't interact at all (and of course the concept of a photon
interacting with itself is a manifestation of wave-like behavior of
the probability amplitudes). If, however, the photons interact
with the same electron, which is possible, their probability
amplitudes get entangled, which can lead to interference patterns.
Take the electron away and there is no interference pattern.
I make this point only because I do know a lot of physics, and your
"quote" above makes me sound (at least to a physicist) a bit
clueless. My credibility is pretty important in this case,
especially since I'm mostly talking to folks with little or no
physics or information theory, who are sure they know how radios
work and how they interfere from the simplified little diagrams that
teach a little about amplitude modulation and stop there.
I don't participate in the gnu radio discussion list, because I just
don't have the time needed. But if there's a way to get this
corrected, I'd appreciate it.