Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Plasma

> > . . . It is thought that the ionization is due to
> > gravitational interaction. . . .

On 11/25/2003 12:23 PM, Ludwik Kowalski wrote:

That is very interesting and puzzling.

It's puzzling because it's wrong.

> I would think
that partial ionization of intergalactic atoms is due
to cosmic rays, UV, etc.

Well, that correctly explains how they *get*
ionized. But then you need to explain why
they *stay* ionized. (In epidemiological
terms, this is the difference between incidence
and prevalence.)

> But conditions near the
"edges of the infinite universe" are likely to
generate a lot of surprises.

Well, there are *some* weird things that go on
in the distant reaches of the universe, but this
is not one of them.

This is just garden-variety undergrad-level thermo.

For homework, rederive the Saha equation. It's
easy if (hint!) you remember it's not supposed to
be exact, just close enough for astronomy work.
So make some simplifying approximations. For
instance (hint, hint!) take the atom to be a
two-state system, either in the ground state or
completely ionized (disregarding the various
bound-but-excited states).

It's just thermo. Stat mech. Phase space and
all that. In the ionized state it has "twice
as much" phase space as in the bound state. At
low densities the entropy term crushes everything
else.