On Sun, 26 Jul 2009 12:45:36 +1000, "Peter Webb"
wrote:
This raises a couple of questions for me ....
1. The equations for black body radiation do not involve the physical nature
of the radiating body.
Don't they? The equations rely on the emissivity of a material, which is
surely a parameter that describes its physical nature. A true black body
has an emissivity of one. Anything less and the equations become
approximations, or otherwise need modification. So what do you have if
dark matter has an emissivity of zero?
As an additional complication, can DM have a temperature above 0K? I
don't know the answer to that, but if it doesn't absorb any EM, how is
energy transferred to it? By definition, a black body absorbs 100% of
the EM that hits it. Nearly by definition, DM absorbs none.
Are you claiming that a macroscopic body composed of
DM would not emit radiation as per the black body equations?
I think that describes the commonly accepted viewpoint, where DM is
assumed to consist of non-baryonic particles. There's certainly no
evidence
2. On the other side ... I have always just accepted bb radiation as a fact
of hot bodies. Now I have to think about this. I assume that the coupling
between heat and EM derived from the existence of charged particles
(electrons and atomic nuclei) in the radiating body which ultimately accept
EM waves, turn them into electric potential (physical separation of positive
and negative charges) which re-appears as thermal energy, and vice versa.
Note that this is all mediated by charged particles being accelerated by the
E component of the EM wave, or in reverse the acceleration of charged
particles causing EM waves. Thinking about it, how does this work for
neutron starts, which have no charged particles? They absorb and emit bb
radiation, right? If so, what is the physical mechanism for the exchange of
energy between an EM wave and uncharged matter?
I'm not sure of the answer here, but my first thought is that the
mechanism depends on force carriers, but is not necessarily limited to
simple charged particles.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com