Big bang theories are actually a ''class'' of scientific models that describe the Universe as expanding from a very hot, dense state approximately 13.7 billion years ago<ref>[http://map.gsfc.nasa.gov/m_uni/uni_101age.html WMAP Cosmology 101: Age of the Universe]</ref> (although this number has been revised several times throughout recent history). It was first proposed by the Catholic priest [[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 [[cosmic microwave background|microwave background radiation (or CMBR)]]. This radiation was discovered by Arno Penzias and Robert Wilson at [[Bell Labs]]; it was found to be close to that predicted by Gamow (Gamow predicted a background radiation level equivalent to a roughly 3 K black body object, and the observed level is that of a 2.725 K body). | Big bang theories are actually a ''class'' of scientific models that describe the Universe as expanding from a very hot, dense state approximately 13.7 billion years ago<ref>[http://map.gsfc.nasa.gov/m_uni/uni_101age.html WMAP Cosmology 101: Age of the Universe]</ref> (although this number has been revised several times throughout recent history). It was first proposed by the Catholic priest [[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 [[cosmic microwave background|microwave background radiation (or CMBR)]]. This radiation was discovered by Arno Penzias and Robert Wilson at [[Bell Labs]]; it was found to be close to that predicted by Gamow (Gamow predicted a background radiation level equivalent to a roughly 3 K black body object, and the observed level is that of a 2.725 K body). |