Inflationary universe cosmology

Article By:

Krauss, Lawrence M. School of Earth and Space Exploration and Physics Department, Arizona State University, Tempe, Arizona.

Last reviewed:March 2019

DOI:https://doi.org/10.1036/1097-8542.343650

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• Inflationary universe cosmology, published May 2014:Download PDF Get Adobe Acrobat Reader

A theory motivated by considerations from elementary particle physics and problems in standard big bang cosmology, which asserts that the early universe underwent a rapid period of exponential expansion. Inflationary theories predict that the scale of the universe increased by at least 28 orders of magnitude in an epoch starting perhaps as early as a trillionth of a trillionth of a trillionth of a second (∼10^-36) after the big bang and ending by ∼10^-32 s. The period of superluminal (faster than light) expansion, considered the "inflation" in the theories' name, in most theoretical scenarios is caused by the appearance of a nonzero constant energy density in the universe, associated with a phase transition between different ground state configurations of matter as the universe expands and cools. (An analogous phase transition is the changeover from liquid water to ice at a certain temperature and pressure threshold.) After the transition is completed, the constant energy density is converted into the energy density of a gas of fast-moving particles. At this point, inflationary scenarios match the standard big bang cosmological model (Fig. 1). See also: Big bang theory; Cosmology; Ground state; Matter (physics); Phase transitions; Universe; Water

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