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Submitted : 2011-07-31 00:00:00Word Count : 549Popularity: 0Tags:
The Big Bang model, or theory, is the prevailing cosmological theory of the early development of the universe.[1] The theory purports to explain some of the earliest events in the universe. According to the theory, the universe was once in an extremely hot and dense state that expanded rapidly (a "Big Bang"). As there is little consensus among physicists about the origins of the universe, the Big Bang theory explains only that such a rapid expansion caused the young universe to cool and resulted in its present continuously expanding state. According to recent measurements, the original state of the universe existed around 13.7 billion years ago (see age of the Universe),[2][3] to which some physicists refer as the time that the Big Bang occurred.[4][5] Physicists have attempted to establish the theory's validity through scientific evidence and observations.[6][7]
Georges Lema?tre proposed what became known as the Big Bang theory of the origin of the universe; he [link widoczny dla zalogowanych] [link widoczny dla zalogowanych] called it his "hypothesis of the primeval atom". The framework for the model relies on Albert Einstein's general relativity and on simplifying assumptions (such as homogeneity and isotropy of space). The governing equations had been formulated by Alexander Friedmann. In 1929, [link widoczny dla zalogowanych] Edwin Hubble discovered that the distances [link widoczny dla zalogowanych] to far away galaxies were generally proportional to their redshifts—an idea originally suggested by Lema?tre 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.[8]
If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures,[9][10][11] and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of this theory. On the other hand, these accelerators have limited capabilities to probe into such high energy regimes. There is little [link widoczny dla zalogowanych] evidence regarding the absolute earliest instant of the expansion. Thus, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it [link widoczny dla zalogowanych] describes and explains the general evolution of the universe going forward from that point on. The observed abundances of the light elements [link widoczny dla zalogowanych] throughout the [link widoczny dla zalogowanych] cosmos closely match the [link widoczny dla zalogowanych] calculated predictions for the formation of these elements from nuclear processes in the rapidly expanding and cooling first minutes of the universe, as logically and quantitatively detailed according to Big Bang nucleosynthesis.
Fred Hoyle is credited with coining the term Big Bang during a 1949 radio broadcast. It is popularly reported that Hoyle, who favored an alternative "steady state" cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it [link widoczny dla zalogowanych] was just a striking image meant to highlight the difference between the two models.[12][13][14] Hoyle later helped considerably in the effort to understand stellar nucleosynthesis, the nuclear pathway for building certain [link widoczny dla zalogowanych] heavier elements [link widoczny dla zalogowanych] from lighter ones. After the discovery of the cosmic microwave background radiation in 1964, and especially when its spectrum (i.e., the amount of radiation measured at each wavelength) was found to match that of thermal radiation from a black body, most scientists were fairly convinced by the evidence that some [link widoczny dla zalogowanych] version of the [link widoczny dla zalogowanych] Big Bang scenario must have occurred.
Bigbang
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