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The '''Big Bang Theory''' is the current dominant scientific hypothesis explaining the acceleration of matter throughout the Universe.  Big bang theories are actually a ''class'' of scientific models that describe the Universe as expanding from a very hot, dense state approximately 16.5 -- although this number has changed many times throughout recent history -- billion years ago. It was first proposed by [[Georges-Henri Lemaitre]] and evidence for the expansion was observed by [[Edwin Hubble]]<ref>Hubble, E. Proceedings of the National Academy of Sciences of the United States of America, Volume 15, Issue 3, pp. 168-173.</ref>. Later [[George Gamow]] predicted that the Big Bang would leave an observable microwave background radiation (or CMBR). This radiation was subsequently discovered by Arno Penzias and Robert Wilson at [[Bell Labs]] and found to be close to that predicted by Gamow (Gamow predicted a background radiation level equivalent to a roughly 3K black body object, and the observed level is that of a 2.725K body). Pensiaz and Wilson were awarded a Nobel Prize in 1978 for their work.

The '''Big Bang Theory''' is the current dominant scientific hypothesis explaining the acceleration of matter throughout the Universe.  Big bang theories are actually a ''class'' of scientific models that describe the Universe as expanding from a very hot, dense state approximately 16.5 -- although this number has changed many times throughout recent history -- billion years ago. It was first proposed by [[Georges-Henri Lemaitre]] and evidence for the expansion was observed by [[Edwin Hubble]]<ref>Hubble, E. Proceedings of the National Academy of Sciences of the United States of America, Volume 15, Issue 3, pp. 168-173.</ref>. Later [[George Gamow]] predicted that the Big Bang would leave an observable microwave background radiation (or CMBR). This radiation was subsequently discovered by Arno Penzias and Robert Wilson at [[Bell Labs]] and found to be close to that predicted by Gamow (Gamow predicted a background radiation level equivalent to a roughly 3K black body object, and the observed level is that of a 2.725K body). Pensiaz and Wilson were awarded a Nobel Prize in 1978 for their work.

The term "Big Bang" implies an explosion of matter into pre-existing space, but the theory actually indicates that space is dynamic and more space is constantly created in the interstices between particles as the density of the universe falls.  Big Bang theorists state that the Hubble [[redshift]] is a consequence of this stretching of the fabric of space.

The term "Big Bang" implies an explosion of matter into pre-existing space, but the theory actually indicates that space is dynamic and more space is constantly created in the interstices between particles as the density of the universe falls.  In other words, the Big Bang describes the expansion of space and time.  Big Bang theorists state that the Hubble [[redshift]] is a consequence of this stretching of the fabric of space.

Observations of distant supernovae indicate that the Universe is actually undergoing accelerated expansion<ref>Riess, A. G., et al. The Astronomical Journal, Volume 116, Issue 3, pp. 1009-1038.</ref><ref>Perlmutter, S., et al. The Astrophysical Journal, Volume 517, Issue 2, pp. 565-586.</ref> and galaxy surveys<ref>[http://www.sdss.org/dr5/ Sloan Digital Sky Survey]</ref><ref>Tegmark, M., et al. Physical Review D, vol. 74, Issue 12.</ref> and recent observations of the microwave background<ref>[http://map.gsfc.nasa.gov/ Wilkinson Microwave Anisotropy Probe]</ref><ref>See, for example, http://arxiv.org/abs/astro-ph/0603449</ref> have corroborated these claims. Conventional wisdom is that the acceleration is caused by some sort of [[dark energy]], which has not yet been directly observed.

Observations of distant supernovae indicate that the Universe is actually undergoing accelerated expansion<ref>Riess, A. G., et al. The Astronomical Journal, Volume 116, Issue 3, pp. 1009-1038.</ref><ref>Perlmutter, S., et al. The Astrophysical Journal, Volume 517, Issue 2, pp. 565-586.</ref> and galaxy surveys<ref>[http://www.sdss.org/dr5/ Sloan Digital Sky Survey]</ref><ref>Tegmark, M., et al. Physical Review D, vol. 74, Issue 12.</ref> and recent observations of the microwave background<ref>[http://map.gsfc.nasa.gov/ Wilkinson Microwave Anisotropy Probe]</ref><ref>See, for example, http://arxiv.org/abs/astro-ph/0603449</ref> have corroborated these claims. Conventional wisdom is that the acceleration is caused by some sort of [[dark energy]], which has not yet been directly observed.