Topics: Big Bang, Physical cosmology, Cosmic microwave background radiation Pages: 23 (7627 words) Published: January 20, 2014
Big Bang
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"Big Bang theory" redirects here. For the American TV sitcom, see The Big Bang Theory. For other uses, see Big Bang (disambiguation).

According to the Big Bang model, theUniverse expanded from an extremely dense and hot state and continues to expand today. A common analogy explains that space itself is expanding, carrying galaxies with it, like spots on an inflating balloon. The graphic scheme above is an artist's concept illustrating the expansion of a portion of a flat universe. Part of a series on

Physical cosmology

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 Category: Physical cosmology
The Big Bang theory is the prevailing cosmological model for the early development of the Universe.[1] According to the theory, the Big Bang occurred approximately 13.798 ± 0.037 billion years ago,[2][3][4][5][6] which is thus considered the age of the universe.[7][8][9][10] At this time, the Universe was in an extremely hot and dense state and began expanding rapidly. After the initial expansion, the Universe cooled sufficiently to allow energy to beconverted into various subatomic particles, including protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed. The majority of atoms that were produced by the Big Bang are hydrogen, along with helium and traces of lithium. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies, and the heavier elements were synthesized either within stars or during supernovae. The Big Bang is the scientific theory that is most consistent with observations of the past and present states of the universe, and it is widely accepted within the scientific community. It offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure, and the Hubble diagram.[11] The core ideas of the Big Bang—the expansion, the early hot state, the formation of light elements, and the formation of galaxies—are derived from these and other observations. As the distance between galaxies increases today, in the past galaxies were closer together. The consequence of this is that the characteristics of the universe can be calculated in detail back in time to extreme densities and temperatures,[12][13][14] while large particle accelerators replicate such conditions, resulting in confirmation and refinement of the details of the Big Bang model. On the other hand, these accelerators can only probe so far into high energy regimes, and astronomers are prevented from seeing the absolute earliest moments in the universe by various cosmological horizons. The earliest instant of the Big Bang expansion is still an area of open investigation. The Big Bang theory does not provide any explanation for the initial conditions of the universe; rather, it describes and explains the general evolution of the universe going forward from that point on. Georges Lemaitre first proposed what became the Big Bang theory in what he called his "hypothesis of the primeval atom". Over time, scientists built on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions such as homogeneity and isotropy of space. The governing equations were first formulated by Alexander Friedmann and similar solutions were worked on by Willem de Sitter. In 1929, Edwin Hubble discovered that the distances to far away galaxies were strongly correlated with their redshifts—an idea originally...

References: XDF (2012) view - each light speck is a galaxy - some of these are as old as 13.2 billion years[26] - the universe is estimated to contain 200 billion galaxies.
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