Every second of every day, trillions of particles from beyond Earth stream through your body. You don't notice them because they don't do anything -- almost all of them pass through you, and the solid Earth, and entire stars without effect. And because of that, they're hard to study -- no telescope can "catch" them.
Even so, neutrinos are important because they can tell us about the universe. Some come from the Sun, so they tell us about the Sun's inner workings. Others are produced when cosmic rays slam into atoms, so they can tell us about the birth of cosmic rays.
HALZEN: Cosmic rays were discovered in 1912. I always say in my talks that by 2012 we will know where they come from. As the time approaches I become less and less confident, but it's still a goal and there is no reason not to deliver. We will see. [:19]
That's Francis Halzen, a scientist at the University of Wisconsin and the leader of a project designed to detect neutrinos produced by cosmic rays. It's called IceCube, and it consists of thousands of light detectors buried in the ice at the South Pole -- a cubic kilometer of it.
HALZEN: You don't see neutrinos, neutrinos crash into atoms in your kilometer-cube block of ice. The ice is the detector, it stops the neutrino. The neutrino converts itself in a nuclear collision into other particles which emit light when they stream through the ice. Then we reconstruct that light pattern and we reconstruct the direction of the neutrino. Every neutrino we see has come through the Earth. Nothing else comes through the Earth. [:31]
So the neutrinos can tell scientists their source -- a subject that's still being debated. More about that tomorrow.
Script by Damond Benningfield, Copyright 2009
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