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November 24, 2012

Learning about the Big Bang isn’t easy. Cosmologists have to rely on obscure clues to probe conditions during that moment of creation almost 14 billion years ago. One of the most important is something that’s in your water: a form of hydrogen called deuterium.

Most hydrogen atoms have one proton and no neutrons. But deuterium is a heavy form of hydrogen, with both a proton and a neutron. Deuterium can occur in molecules just as normal hydrogen does. In fact, a glass of water contains not just molecules of H2O, but also trillions of molecules of H-D-O, in which one of the hydrogen atoms is deuterium.

Deuterium is valuable to scientists who study the universe’s origin because it’s one of the few elements forged in the Big Bang. And nuclear reactions in stars destroy deuterium, so the universe’s supply has dwindled over time. By looking at the space between the stars, though, astronomers can detect it and estimate how abundant it is.

This abundance reveals the conditions that prevailed just moments after the Big Bang. In particular, the more deuterium the universe has, the less dense the universe must be. That’s because in a denser universe, more nuclear reactions would have destroyed deuterium just after the Big Bang. But it turns out that a fair amount of deuterium is still around. That’s one indication that the universe will expand forever — there’s not enough matter packed tightly enough to cause the universe to pull itself back together.


Script by Ken Croswell, Copyright 2012

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