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Selasa, 24 November 2009


Big Bang Theory, currently accepted explanation of the beginning of the universe. The big bang theory proposes that the universe was once extremely compact, dense, and hot. Some original event, a cosmic explosion called the big bang, occurred about 13.7 billion years ago, and the universe has since been expanding and cooling.

Expanding Universe Experiment One way to understand the concept of an expanding universe is to draw dots, representing galaxies, on a balloon. As the balloon is inflated, each dot moves away from all the others. To a person viewing the universe from a galaxy, all other galaxies would seem to be receding. The distant galaxies appear to be moving away faster than the near ones, which demonstrates Hubble’s law. Some astronomers believe that this expansion will continue forever, whereas others think that at a certain point the universe will begin contracting.© Microsoft Corporation. All Rights Reserved.

Background Radiation
Even when all other sources of radio waves are eliminated, some static appears on the most sophisticated radios. Some of this radiation is energy left over from the big bang, the explosion that created the universe. As the map created by the Cosmic Background Explorer satellite shows, the background radiation is not entirely smooth.© Microsoft Corporation. All Rights Reserved./M. Tegmark, A. de Oliveria-Costa, M. Devlin, B. Netterfield, L. Page & E. Wollack, Astrophysical Journal, 474, L77

The theory is based on the mathematical equations, known as the field equations, of the general theory of relativity set forth in 1915 by Albert Einstein. In 1922 Russian physicist Alexander Friedmann provided a set of solutions to the field equations. These solutions have served as the framework for much of the current theoretical work on the big bang theory. American astronomer Edwin Hubble provided some of the greatest supporting evidence for the theory with his 1929 discovery that the light of distant galaxies was universally shifted toward the red end of the spectrum (see Redshift). Once “tired light” theories—that light slowly loses energy naturally, becoming more red over time—were dismissed, this shift proved that the galaxies were moving away from each other. Hubble found that galaxies farther away were moving away proportionally faster, showing that the universe is expanding uniformly. However, the universe’s initial state was still unknown.

The Evolutionary Universe
In the 1950s cosmologists (scientists who study the evolution of the universe) were considering two theories for the origin of the universe. The first, the currently accepted big bang theory, held that the universe was created from one enormous explosion. The second, known as the steady state theory, suggested that the universe had always existed. Russian-American theoretical physicist George Gamow advanced the big bang theory and its underpinnings in a 1956 Scientific American article. Gamow’s estimate of a 5-billion-year-old universe is no longer considered accurate; the universe is now thought to be significantly older.
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In the 1940s Russian-American physicist George Gamow worked out a theory that fit with Friedmann’s solutions in which the universe expanded from a hot, dense state. In 1950 British astronomer Fred Hoyle, in support of his own opposing steady-state theory, referred to Gamow’s theory as a mere “big bang,” but the name stuck. Indeed, a contest in the 1990s by Sky & Telescope magazine to find a better (perhaps more dignified) name did not produce one.

Microsoft ® Encarta ® Reference Library 2005. © 1993-2004 Microsoft Corporation. All rights reserved.

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