| Themes > Science > Physics > Elementary particle physics > An Introduction to Particle Physics > An Introduction to Particle Physics > Dark Matter |
We know from observing the rotation of galaxies that about 90% of the matterthey contain is invisible to us. The matter we can't see is called "missing" or"dark" matter. The amount of dark matter contained in the universe is crucialto its fate. If it is greater than a certain amount, the universe willeventually collapse. Below this, and it will keep on expanding for ever. There are many ideas about what dark matter might be, ranging from exotic newparicles to black holes. One idea says that the neutrino, an abundant fundamental particle which is thought to have zero mass, actuallyhas a tiny mass. However, neutrinos generally move about the universe quicklyand are not stuck together in clumps, as they would need to be to explain the rotation of the galaxies. The most recent explanations of dark matter therefore use a combination of "hot" matter, like neutrinos, and "cold" matterlike black holes. The true answer has yet to be found. Underground experimentson dark matter are taking place now. |
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