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[Phys-L] Re: entropy and electricity



Fayngold, Moses wrote:

Exactly! I think, John has confused the issue by substituting the=
=20
word "photon" in my example with the word "light" in his. A single
photon is always in some definite polarization state, be it linear,
circular, or elliptical polarization. Light (an ensemble of photons)
may (if it is a pure ensemble) or may not (if it is a mixture) be in
a definite polarization state.

That is perhaps false, or at best vacuous ... depending on what
is meant by "definite" state. Either way, it is unhelpful.

By the same token, we could say that the entire universe is in
"some" state. We don't happen to know what that state is, and
therefore we attribute entropy to the present situation.

The exact same words apply to a single photon. I can easily
build an apparatus that produces photons one at a time, yet
you have not the slightest chance of predicting their polarization.
Each such photon has a spin entropy of one bit.
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