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Leigh has presented very interesting arguments,
but I have a few questions and comments.
1. Why is the ionization channel Y + H -> p + e
ignored? Photons of appropriate energies are
emitted (1) during recombination and (2) in
nearby galaxies.
2. Energy must be added to an ideal gas during
an isothermal expansion, but Leigh does not
describe the addition of any energy during
the expansion, implying that the expansion
is adiabatic. The temperature of an ideal
gas decreases during an adiabatic expansion.
Would the decrease in temperature result in
a net decrease in degree of ionization?
Now consider what happens if the volume of the box is suddenly
doubled.
("Suddenly" means that the wall or walls of the box move faster than
any of the particles during the expansion.) The kinetic energies of
the
particles in the box, and therefore the temperature of the system,
remains constant.
3. Why is the expansion of an ideal gas important
anyway? Is Leigh saying that the degree of
ionization of intergalactic hydrogen is
affected by the expansion of the universe?
But the expansion of the universe is not
sudden, as he has defined it, and it is not
applicable in the cores of the rich galaxy
clusters he discussed in his earlier posts
on this subject.
4. Three-body recombination has a much smaller
probability than two-body recombination at
the low concentrations in intergalactic
media; therefore, its effect on the degree
of ionization should be small even in the
case of isothermal expansion.