Scientists Seek Wimps

Of course, according to the code of the schoolyard, any kid interested in scientific matters was already a wimp, so some might be surprised by this particular search. Football team captains who read the headline would surely suggest, "Just look in the mirror, pencil-neck!"

But the reality is that 1) scientists are often not wimps, and 2) this particular search is actually for something called Weakly Interacting Massive Particles, called WIMPs for short. WIMPs are candidates for the mysterious "dark matter" that cosmologists propose as one reason galaxies don't fly apart and the universe is expanding more slowly than it ought to be.

Galaxies rotate very fast, which means all the stars in them, especially the ones on the edges, ought to go spinning out on their own. The same centrifugal force that makes all the cookie dough gather at the edge of the bowl when its being spun in a mixer should make stars light on outta here, but it doesn't. Gravity must be keeping them together, but there's not enough matter in the galaxy to have that much gravity. Therefore, one theory goes, there must be some other stuff around someplace that adds to the gravity but which otherwise is difficult to detect. Thus, "dark" matter, because it can't be seen.

An experiment on the International Space Station seems to have offered some evidence of the existence of WIMPs. WIMPs are not like other particles in one important way. They are their own antiparticle. This means that instead of having an opposite anti-matter particle around somewhere waiting to annihilate them, WIMPs are their own worst enemy. Your average electron has no problem with another electron. It won't blow up unless it meets up with an anti-electron. But WIMPs, on the other hand, wipe each other out whenever they meet.

Such destruction emits a new particle, called a positron, and the space station experiment verified positron energies in numbers that match up with what they would expect if dark matter was real. But there are lots of other things that might produce positrons, so some other experiments will be done deep down in the earth to see if WIMP interactions produce positrons like those measured by the space station. By doing the measurements deep underground, the other potential sources for positron emission will be screened out.

The experiments take a long time -- the "WI" in WIMP means the particles interact with other particles weakly, and that means those interactions are rare. Which is kind of like real-world wimps, in a way, because sometimes it's hard to get them to interact with anything else either.