Big Bang Theory

                                   


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

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.

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Dark Matter in the Universe

Many astronomers believe that as much as 90 percent of the matter in the universe is dark matter (matter that does not emit light). Some scientists think dark matter may be exotic particles that do not consist of the atoms making up ordinary matter as we know it. Although dark matter currently cannot be observed directly, scientists have evidence of its existence from observations of its gravitational influence on visible bodies, such as the vast collections of stars known as galaxies. In this article from Scientific American Presents, astronomer Vera Rubin explores contemporary views on the nature of dark matter.

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