Gene Fuller wrote:
Cecil Moore wrote:
Yes, signals traveling in opposite directions don't interfere.

This is a distinction with no technical value. Waves in the same
location are subject to the usual rules of linear superposition of the
fields. Whether you want to call this "interference" is simply a
philosophical choice.

Not so. Here's what Eugene Hecht says: "... optical
interference corresponds to the interaction of two
or more [plane] light waves yielding a resultant
irradiance that deviates from the sum of the component
irradiances."

Superposition can occur with or without interference. If
P1 and P2 are the power densities for two plane waves:

If Ptot = P1 + P2, there is no interference because the
resultant power density does not deviate from the sum of
the component power densities.

If Ptot P1 + P2, there exists interference because
the resultant irradiance does deviate from the sum of
the component power densities.

There is utterly no scientific distinction that applies to "signals
traveling in opposite directions."

Interference only occurs when coherent, collinear waves
are traveling in the same direction. When they are
traveling in opposite directions, standing waves are
the result. Let's limit our discussion to plane waves.

The mathematical results may look
special in the opposite direction case, but the same basic equations
apply in all cases.

Yes, but boundary conditions apply. The phasors of the plane
waves traveling toward each other are rotating in opposite
directions so interference is impossible. Here is a slide
show about interference which only occurs when the waves are
traveling in the same direction.

http://astro.gmu.edu/classes/a10594/...8/l08s025.html
--
73, Cecil http://www.w5dxp.com