I have been reading the popular scientific articles about Dark Matter,
and am having trouble digesting the concept. My big problem is figuring
out how it cooled off enough after the Big Bang to settle down and form
galactic halos. When normal matter was formed in the Big Bang, it was
very hot. It cooled by emitting huge amounts of EM radiation. Dark
Matter doesn't emit EM radiation. Where did the energy go? The weak
force is far too short range to provide a pathway.
It's fairly easy to postulate some form of radiation that interacts with
Dark Matter that does not interact with normal matter, but that just
leads me to another point of confusion. I don't see how this
hypothetical 'sneaky energy' could behave like the Dark Energy the
astronomers talk about. It would have to be an analog of the EM
momentum exchange that allows normal matter particles to bump into each
other and shed momentum. If Dark Matter can collapse into a galactic
halo, can it form dense aggregates. What would a solar mass of Dark
Matter look like? Would it be a perfectly clear gravitational lens?
If dark matter forms large aggregates, it seems we should be able to see
normal matter suns orbiting with dark companions, losing matter to dark
companions, and even forming composite bodies of dark matter and regular
matter. If Dark Matter does not form large aggregates, why not? If it
cooled enough to form a galactic halo, it should cool enough to form
dense bodies.
One alternative is that maybe Dark Matter didn't cool off at all.
Instead, it may have a much larger gravitational constant. That would
let it orbit faster in the galactic halo.
It's enough to make a guy chuck the whole idea, and postulate long range
variations in the law of gravity instead.
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