Tuesday, August 22, 2006

You Say You Want a Revolution

Maybe the odds are a bit better for Big New Physics being developed in my lifetime than I thought.

It appears "dark matter" is no longer just speculation. Here's some observational evidence that there is something out there that we can't see.

Short explanation for those who've never heard of dark matter before: for a long while, it's appeared that the galaxies and other astronomical objects we can see don't move the way we'd expect them to for the mass they appear to have, if they were just acting under the influence of gravity. So physicists speculated that either they were more massive than they look (by a lot!) or our understanding of gravity was wrong.

But there are apparently reasons to believe that if they are more massive than they look, that mass doesn't come in the form of stuff made of neutrons and protons and electrons. It seems it has to come from something that doesn't interact with normal matter by almost any means except through gravity, otherwise we'd be able to detect it. So ghostly "dark matter" was invoked. Such convenient substances have been hypothesized before, though, and eventually disproved, as in the case of luminiferous aether

Only all of the sudden it's no longer so mysterious, so speculative. It seems that some astronomers have found a couple of galactic clusters which collided, and the collision knocked the matter in them away from the gravitational center of mass. Now normally the center of mass is, you know surrounded by mass. That is to say, surrounded by matter. But here all the matter's been pushed away, and the gravity is still pulling things toward where it used it be. It's as if the Sun got knocked out of the solar system but the earth kept orbiting the point where it once was. You'd have to assume there was something else there, right?

The revolution will come when and if we ever figure out what dark matter actually is, besides all around us.

(Actually dark matter still isn't enough to completely explain the dynamics of the stars. Something else, called "dark energy" or sometimes "the cosmological constant," is invoked to explain some aspects. But that remains in the realm of speculation and controversy for now. Anyway, I'm looking forward to finally taking that general relativity class this winter, and I'm sort of glad I'll be taking it after this dark matter discovery.)

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