The universe has no respect for personal space. Every second, trillions of particles zip right through your body, most of them with no effect. Most are the ephemeral particles known as neutrinos, which are produced in the cores of stars. But some are particles of dark matter. These particles produce no detectable energy, but they exert a gravitational pull on the normal matter around them.
There's far more dark matter in the universe than normal matter. Yet no one knows just what the particles that make up dark matter are like.
Scientists are trying to learn more about dark matter by watching them zip through special detectors buried far underground. The deep locations filter out cosmic rays and other particles that might overpower the signals produced by dark matter.
One experiment is taking place in a cavern next to a former iron mine in Minnesota. If a dark matter particle strikes an atom on one of the experiment's detectors, it should cause the atom's nucleus to rebound, producing a tiny vibration. Only a few of these vibrations would be enough to confirm dark matter, and even tell scientists what the dark-matter particle is like.
An even bigger dark-matter search is being planned for the Homestake gold mine in South Dakota. It's one of several experiments that could be built at Homestake if the federal government decides to make the site a national laboratory -- a decision that's expected sometime this year.
Script by Damond Benningfield, Copyright 2011
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