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History, composition and Fate of the universe

Questions about the size and age of the universe, how it began, how it has evolved, and how it will end are part of "cosmos-ology", or cosmology. In recent times, qualified acceptance of the Big Bang theory has been strengthened by evidence that the universe is constantly expanding, and observation of a universal "cosmic background" radiation. Students can do calculations of the age and expansion rate of the universe using data on galactic red shifts.  

One of the first realizations cosmologists came to was that the galaxies near us were moving so fast that they would have left the local cluster if there were not more mass than we could observe keeping them gravitationally bound. This extra mass, whose presence as been verified in other ways, is now known as non-luminous, or "dark" matter, and trying to define or characterise it is a subject central to most cosmological theories.

As observational astronomy adds to the knowledge base, exisiting theories must constantly be re-examined, and new ones are always emerging. Will the universe re-collapse in a "Big Crunch"? Will it keep expanding? Is the expansion speeding up?? Recent evidence (2001) suggests it is, but how can this idea be tested further. There's no end to cosomology in sight!