The physical universe is defined as all of space and time (collectively referred to as spacetime) and their contents. Such contents comprise all of energy in its various forms, including electromagnetic radiation

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The word universe derives from the Old French word univers, which in turn derives from the Latin word universum. The Latin word was used by

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The prevailing model for the evolution of the universe is the Big Bang theory. The Big Bang model states that the earliest state of the universe was an extremely hot and dense one, and that the universe subsequently expanded and cooled. The model is based on

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Of the four fundamental interactions, gravitationis the dominant at astronomical length scales. Gravity's effects are cumulative; by contrast,

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Model of the universe based on general relativity
General relativity is the geometric theory of gravitation published by Albert Einsteinin 1915 and the current

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Historically, there have been many ideas of the cosmos (cosmologies) and its origin (cosmogonies). Theories of an impersonal universe governed by physical laws were first proposed by the Greeks and Indians. Ancient Chinese philosophy encompassed the notion of the universe

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The universe is composed almost completely of dark energy, dark matter, and ordinary matter. Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass-energy of the universe) and

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