U.S. Department of Energy

Pacific Northwest National Laboratory

Cosmic acceleration

An important part of scientists’ story of the origin and evolution of the Universe is the existence of two periods during which the expansion of the Universe accelerated. A primordial epoch of acceleration, called inflation, occurred during the first fraction of a second of existence. The cause of this inflation is unknown, but may have involved currently unexplored physics at ultra-high energies. A second distinct epoch of accelerated expansion began about nine billion years later and continues today. This expansion is presumed to be driven by some kind of dark energy, which could be related to Einstein’s cosmological constant, or driven by a different type of dark energy that evolves with time.

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