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[[File:lighterstill.jpg]][[File:The-Universe-Beyond-the-Big-Bang-Documentary.jpg|right|frame]]

[[File:lighterstill.jpg]][[File:The-Universe-Beyond-the-Big-Bang-Documentary.jpg|right|frame]]

*[http://en.wikipedia.org/wiki/1948 1948]

*[https://en.wikipedia.org/wiki/1948 1948]

==Definition==

==Definition==

*1:  the [[cosmic]] [[explosion]] that marked the beginning of [[the universe]] according to the ''big bang'' theory  

*1:  the [[cosmic]] [[explosion]] that marked the beginning of [[the universe]] according to the ''big bang'' theory  

==Description==

==Description==

The '''Big Bang''' theory is the prevailing [[cosmological]] model that describes the early [[development]] of [[the Universe]]. According to the [[theory]], the Big Bang occurred approximately [http://en.wikipedia.org/wiki/Planck_(spacecraft)#2013_data_release 13.798 ± 0.037 billion years ago], which is thus considered the age of the universe. 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 be converted into various subatomic [[particles]], including [http://en.wikipedia.org/wiki/Proton protons], [http://en.wikipedia.org/wiki/Neutrons 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 [http://en.wikipedia.org/wiki/Hydrogen hydrogen], along with [http://en.wikipedia.org/wiki/Helium helium] and traces of [http://en.wikipedia.org/wiki/Lithium 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 [http://en.wikipedia.org/wiki/Supernova_nucleosynthesis during supernovae].

The '''Big Bang''' theory is the prevailing [[cosmological]] model that describes the early [[development]] of [[the Universe]]. According to the [[theory]], the Big Bang occurred approximately [https://en.wikipedia.org/wiki/Planck_(spacecraft)#2013_data_release 13.798 ± 0.037 billion years ago], which is thus considered the age of the universe. 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 be converted into various subatomic [[particles]], including [https://en.wikipedia.org/wiki/Proton protons], [https://en.wikipedia.org/wiki/Neutrons 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 [https://en.wikipedia.org/wiki/Hydrogen hydrogen], along with [https://en.wikipedia.org/wiki/Helium helium] and traces of [https://en.wikipedia.org/wiki/Lithium 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 [https://en.wikipedia.org/wiki/Supernova_nucleosynthesis 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 [http://en.wikipedia.org/wiki/Cosmic_microwave_background cosmic microwave background], [[large scale structure]], and the [http://en.wikipedia.org/wiki/Hubble_diagram Hubble diagram]. 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, while large [http://en.wikipedia.org/wiki/Particle_accelerator 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 [http://en.wikipedia.org/wiki/High-energy_physics high energy regimes], and astronomers are prevented from seeing the absolute earliest moments in the universe by various [http://en.wikipedia.org/wiki/Cosmological_horizons 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.

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 [https://en.wikipedia.org/wiki/Cosmic_microwave_background cosmic microwave background], [[large scale structure]], and the [https://en.wikipedia.org/wiki/Hubble_diagram Hubble diagram]. 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, while large [https://en.wikipedia.org/wiki/Particle_accelerator 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 [https://en.wikipedia.org/wiki/High-energy_physics high energy regimes], and astronomers are prevented from seeing the absolute earliest moments in the universe by various [https://en.wikipedia.org/wiki/Cosmological_horizons 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.

[http://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre Georges Lemaître] 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 [http://en.wikipedia.org/wiki/Isotropy isotropy] of space. The governing equations were first formulated by [http://en.wikipedia.org/wiki/Alexander_Friedmann Alexander Friedmann] and similar solutions were worked on by [http://en.wikipedia.org/wiki/Willem_de_Sitter Willem de Sitter]. In 1929, [http://en.wikipedia.org/wiki/Edwin_Hubble Edwin Hubble] discovered that the distances to far away galaxies were strongly correlated with their [http://en.wikipedia.org/wiki/Redshift redshifts]—an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant [[galaxies]] and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity, regardless of direction. Assuming that we are not at the center of a giant explosion, the only remaining interpretation is that all observable regions of the universe are [http://en.wikipedia.org/wiki/Metric_expansion_of_space receding from each other].

[https://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre Georges Lemaître] 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 [https://en.wikipedia.org/wiki/Isotropy isotropy] of space. The governing equations were first formulated by [https://en.wikipedia.org/wiki/Alexander_Friedmann Alexander Friedmann] and similar solutions were worked on by [https://en.wikipedia.org/wiki/Willem_de_Sitter Willem de Sitter]. In 1929, [https://en.wikipedia.org/wiki/Edwin_Hubble Edwin Hubble] discovered that the distances to far away galaxies were strongly correlated with their [https://en.wikipedia.org/wiki/Redshift redshifts]—an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant [[galaxies]] and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity, regardless of direction. Assuming that we are not at the center of a giant explosion, the only remaining interpretation is that all observable regions of the universe are [https://en.wikipedia.org/wiki/Metric_expansion_of_space receding from each other].

While the scientific community was once divided between supporters of two different expanding universe theories—the ''Big Bang'' and the [http://en.wikipedia.org/wiki/Steady_State_theory Steady State theory], observational confirmation of the Big Bang scenario came with the [[discovery]] of the [http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation cosmic microwave background radiation] in 1964, and later when its [[spectrum]] (i.e., the amount of radiation measured at each wavelength) was found to match that of thermal radiation from a [http://en.wikipedia.org/wiki/Black_body black body]. Since then, astrophysicists have incorporated observational and theoretical additions into the Big Bang model, and its [http://en.wikipedia.org/wiki/Parametrization parametrization] as the [http://en.wikipedia.org/wiki/Lambda-CDM_model Lambda-CDM model] serves as the framework for current investigations of theoretical cosmology.[http://en.wikipedia.org/wiki/Big_bang]

While the scientific community was once divided between supporters of two different expanding universe theories—the ''Big Bang'' and the [https://en.wikipedia.org/wiki/Steady_State_theory Steady State theory], observational confirmation of the Big Bang scenario came with the [[discovery]] of the [https://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation cosmic microwave background radiation] in 1964, and later when its [[spectrum]] (i.e., the amount of radiation measured at each wavelength) was found to match that of thermal radiation from a [https://en.wikipedia.org/wiki/Black_body black body]. Since then, astrophysicists have incorporated observational and theoretical additions into the Big Bang model, and its [https://en.wikipedia.org/wiki/Parametrization parametrization] as the [https://en.wikipedia.org/wiki/Lambda-CDM_model Lambda-CDM model] serves as the framework for current investigations of theoretical cosmology.[https://en.wikipedia.org/wiki/Big_bang]

==See also==

==See also==

*'''''[[The Big Bang Never Happened]]'''''

*'''''[[The Big Bang Never Happened]]'''''