🚀 go-pugleaf

This thread has probably gone on long enough, but I do want to clarify my
own view on the subject of dark matter.  The hypothesis I've been trying to
defend is that the mass density of the Universe is enough to make
the Universe flat, and that this density is dominated by some unkown, 
nonbaryonic form of matter, possibly one of the new particles that the
particle physicists tell us should exist.  This is the closest thing
cosmologists have to a "standard model" of structure formation.

I'm not 100% convinced that this hypothesis is right:  It's an extraordinary
hypothesis, and as such should be supported by extraordinary evidence.
Whether you think the evidence is strong enough to justify it is up to you.
What started me posting to this thread was reading Dale's comments, which
present the impression that the hypothesis was made up by some fanciful
cosmologist without any hard evidence to support it.  This is clearly false.
I've tried to explain that the hypothesis does make definite predictions,
and is therefore testable, and that at the moment a number of tests have
already been done that support it.  Does that mean the hypothesis is right?
Of course not.  But it is at the moment the only theory around that is
based on known and accepted physical principles and explains the observations.

I also want to reiterate that the dark matter hypothesis looks considerably
less "outrageous" when you note that virtually every extension of the
standard model of particle physics predicts heavy new particles.
The suggestion that the reason for this is that the particle physicists
have rigged their theories in order to make this true so that they can
solve the dark matter problem is manifestly absurd:  The idea that there
should be a grand unified symmetry is older than the dark matter problem,
and has many strong arguments to recommend it that are independent of
cosmology.  Grand unified theories require new massive particles.  This
is an argument in favor of nonbaryonic dark matter which is completely
independent of the usual cosmological ones.

The most important point is simply this:  If you want to decide whether
or not to believe in nonbaryonic dark matter, you'd best study the evidence,
and see whether or not you find it compelling.  It's not good enough just
to say, "It sounds pretty strange to me, so I don't buy it."

-Ted