expanding universe

expanding universe
a representation of the universe, based on the observed redshifts of distant galaxies, in which the galaxies are assumed to be receding from each other at a speed proportional to their separation as a result of the expansion of the universe. Cf. Hubble's constant, cosmological redshift.

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Current understanding of the state of the universe.

It is based on the finding that all galaxies are moving away from each other. Application of general relativity to cosmology, along with the detection of redshifted light coming from galaxies outside the Milky Way Galaxy, led to the realization in the 1920s that all galaxies are receding (see Edwin Hubble). It is unknown whether the universe will expand indefinitely (open universe) or eventually collapse (closed universe) into an extremely dense, congested state, as it began, according to the big-bang model. See also Friedmann universe.

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      dynamic state of the extragalactic realm, the discovery of which has transformed 20th-century cosmology. The development of general relativity and its application to cosmology by Albert Einstein, Wilhelm de Sitter, and other theoreticians, along with the detection of extragalactic redshift (red shift) (a shift to the longer wavelengths of light from galaxies beyond the Milky Way) by Vesto Slipher, led to the realization in the 1920s that all galaxies are receding. Edwin Hubble (Hubble, Edwin Powell) correlated these observations in mathematical form to provide evidence that the universe is expanding. The discovery of the 2.7 K background radiation in 1965 by Arno A. Penzias and Robert W. Wilson is regarded as convincing evidence that the universe originated approximately 15 billion years ago in a very dense and hot state referred to as the big bang (see big-bang model).

      Observations so far have not succeeded in determining whether the universe is open (of infinite extent in space) or closed (of finite extent) and whether the universe in the future will continue to expand indefinitely or will eventually collapse back into an extremely dense, congested state. See also cosmology.

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Universalium. 2010.

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