Expanding Universe

Learn about the expanding universe.

Looking back on the years of discovery and upheaval between 1915 and 1930, the Dutch astronomer Willem de Sitter rightly identified the period as perhaps the most extraordinary ever known to physical scientists. In the theories of relativity and the quantum, physicists starting with Albert Einstein had given entirely new and astounding explanations of energy, matter, gravity, even space and time. As astronomers tried to apply these new tools to cosmology, they were struck with their own revelations. As described on the previous page, Harlow Shapley's concept of the Big Galaxy was quickly followed by Edwin Hubble's proof of the existence of island universes. Stranger still, at the end of the 1920s came the realization that the universe is expanding.

The universe was born with the Big Bang as an unimaginably hot, dense point. When the universe was just 10-34 of a second or so old — that is, a hundredth of a billionth of a trillionth of a trillionth of a second in age — it experienced an incredible burst of expansion known as inflation, in which space itself expanded faster than the speed of light. During this period, the universe doubled in size at least 90 times, going from subatomic-sized to golf-ball-sized almost instantaneously.

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