Jamie Morken said:
One thing that makes linear polarization more fundamental than circular
polarization is that it gives a simpler explanation that circular
polarization can provide. Apparently there are no strong natural
sources of circular polarized light, or in other words, 99.9%+ of all
known light appears to be linearly polarized. So if you want to believe
that circularly polarized light is the fundamental type of light, then
how is the circular polarized light converted to linear polarized light
99.9%+ of the time?
It seems to me 99% of light is not polarized at all -- black body
radiators don't care, for instance. I don't know that any other primary
physical phenomena cares (radiation, emission, absorption, etc.).
Interactions with matter can do interesting things; reflections are well
known to increase polarization (hence polarized sunglasses). Reflection
is a surface thing, so it gives a reference plane to the polarization.
Surfaces in space tend to be random, so I imagine the amount of
polarization is small and averages to zero. I'm not very familiar with
astronomical sources of polarization. I just read that magnetic fields
are known to produce circular polarization. You'll see far more surfaces
(dust, objects, etc.) and volumes (dust clouds, nebulas) than intense
magnetic fields (compact objects such as planets and stars), especially in
terms of what the light goes through (e.g. translucent dust clouds).
This explains the greater incidence of linear polarization, but makes no
statement as to its fundamental nature. If you'd like to make a practical
argument, then there is a lot of linear polarization out there, and it's
somewhat easier to make a linearly polarized antenna.
As I mentioned previously, QM gives a useful reason for circular to be
fundamental-- it carries angular momentum, on the order of hbar per
photon. A sufficiently weak, linearly polarized beam will have circular
polarization, if you look at each photon. The circularity averages to
zero, since each photon is a coin flip. But there *is* a coin, and it's
either 1 or -1, never zero or sideways. If the photons were fundamentally
linearly polarized, they would carry no angular momentum on any scale,
individual or average.
If they were linearly polarized, would there be any way to tell? Is there
a quanta of tangential momentum which could be delivered which averages to
angular momentum, for an apparently circular polarized beam? I don't see
any way this would work, so it looks like circular is the winner.
Tim
), you've just proven that circular is also the fundamental type of
