More on dark matter
Also highly recommended is Mark's post on Good Math, Bad Math, about how the dark matter hypothesis and its apparent confirmation hinge upon the use of solid math in physics. Mark offers a lucid explanation of the data, plus a video, plus some insightful comments on math:
As I always say, one of the ways to recognize a crackpot theory in physics is by the lack of math. For an example, you can look at the electric universe folks. They have a theory, and they make predictions: but because there's no math, the predictions are vague, and there's no good way of really testing them, because there's no quantifiable way of making a precise prediction - because there's no math. So they can make predictions like "the stardust experiment will get bigger particles than they expect"; but they can't tell you how big.I remember being charmed by Tom Siegfried's Strange Matters when we published it the last time I worked at NAP, because it was all about doing cosmology by interpreting numbers, but I hadn't thought very deeply about the mutual interreliance of math and physics. (When I defend math, it's usually only as far as math I can actually do -- i.e. explaining to people why algebra is critical knowledge.) This is an excellent explanation of why the really high-level math, the stuff that some of us might think is too lofty and theoretical, is actually an inalienable component of any decent explanation of the universe.