From: matus (matus@matus1976.com)
Date: Thu Jul 03 2003 - 12:50:40 MDT
Jeff Said:
> Is a moving reflector equivalent to a
> moving emitter? What are the differences between
> these two radiation-'manifesting' processes? And what
> are the differences between the reflection(1) we
> associate with mirrors (metallic and dielectric), and
> the reflection(2) we associate with, say, the moon,
> which seems more rightly a case of absorption and
> re-emission?
>
Not being the resident expert in this area, I would still submit that
yes a moving reflector can be thought of as a moving emitter, because
the process of reflection is one of absorption and re-emission, and
there is no substantial difference between a mirror and the moon (other
than macroscopic surface properties). In the most fundamental form, the
incoming photon, intrinsic as an electromagnetic disturbance, with
opposing electric and magnetic fields oscillating over time, 'hit' an
electron, the opposing fields go from zero interaction to non-zero, and
the electron is moved to a higher energy level. (all of this I am sure
everyone knows) When the electron drops back down an energy level, it
constitutes an electric charge in motion, accelerating from zero to
non-zero, then back again to zero. This produces a changing electric
field, which simultaneously produces a changing magnetic field, and the
two fields self propagate. Since the solar sail is moving, the time in
which the electrons motion creates an electric disturbance is spread
over a larger distance, and thus its frequency must be lower. If the
emission process took place in zero time, there would be no Doppler
change, however, such an emission is impossible, as you can not have a
time-varying field without a change in time. So, a moving reflector
must reflect a photon of lower frequency.
Michael Dickey
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