Re: EM Radiation Without a Source

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding John Denker's comment:
>       ...                Instead, they just assume there was nothing but
> EM energy and let everything else be created in due course as the universe
> evolves according to the laws of physics.

I don't think " they just assume there was nothing but EM energy". I was
under the impression that the assumption made was that the universe was
in an initial thermodynamic equilibrium at an astronomically high
temperature such that the thermal energy scale kT was much hotter than
the rest energy of all the elementary particles.  Such a state
effectively has energy equally partitioned among *all* the (boson) field
degrees of freedom of the universe whose single particle excitation
energies are significantly less than the temperature. (I think things
are trickier for the fermion degrees of freedom, but they also share
prominantly in the pie of energy present and are highly excited.)
Effectively the initial state is one of approximately equal numbers of
all the various kinds of elementary particles.  So instead of there
being "nothing but EM energy" the EM contribution to the total energy is
crudely approximately 1/n where n is the total number of species (modulo
possibly a few stoichiometric coefficients that depend on species spin
or other internal degeneracies) of elementary particles in the universe.

Only *after* things cooled down enough for most of the particles (with
mass) to annihilate with their antiparticles was it cool enough for most
of the remaining particles present to be in the form of EM photons (&
maybe neutrinos).  Once the temperature dropped well below the rest
energy of a proton the great majority of the *energy* in the universe was
tied up in the rest energy of the (relatively few non-annhilated) massive
particles (i.e. nucleons), whereas the great majority of the *number* of
particles in the universe remained the photons of electromagnetism (&
presumably, lots of neutrinos as well).  This aspect of the situation
hasn't changed to this very day.

David Bowman
David_Bowman@georgetowncollege.edu