universe, totality of matter matter, anything that has mass and occupies space. Matter is sometimes called koinomatter (Gr. koinos=common) to distinguish it from antimatter, or matter composed of antiparticles .
..... Click the link for more information. and energy energy, in physics, the ability or capacity to do work or to produce change. Forms of energy include heat , light , sound , electricity , and chemical energy.
..... Click the link for more information. in existence. The study of the origin of the universe, or cosmos, is known as cosmogony, and that of its structure and evolution, cosmology cosmology, area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe .

Modern Cosmological Theories

..... Click the link for more information. . The age of the universe depends on which theory of cosmology one accepts. According to the big bang theory, favored by most scientists, the universe is between 10 and 20 billion years old. The steady-state theory holds that the universe has been in existence for all time.

Matter and Energy in the Universe

The matter in the universe is subject to various forces, but the greatest force on the cosmological scale is gravitation gravitation, the attractive force existing between any two particles of matter .

The Law of Universal Gravitation

Since the gravitational force is experienced by all matter in the universe, from the largest galaxies down to the smallest particles, it
..... Click the link for more information. . This force pulls matter together to form stars star, hot incandescent sphere of gas, held together by its own gravitation , and emitting light and other forms of electromagnetic radiation whose ultimate source is nuclear energy .
..... Click the link for more information. , which either exist alone or are part of binary star binary star or binary system, pair of stars that are held together by their mutual gravitational attraction and revolve about their common center of mass.
..... Click the link for more information. or multiple star systems, or brown dwarfs brown dwarf, in astronomy, celestial body that is larger than a planet but does not have sufficient mass to convert hydrogen into helium via nuclear fusion as stars do.
..... Click the link for more information. , which are also known as "failed stars." Gravitation also acts to group billions of stars into galaxies galaxy, large aggregation of stars , gas, and dust, typically containing billions of stars. Recognition that galaxies are independent star systems outside the Milky Way came from a study of the Andromeda Galaxy (1926–29) by Edwin P.
..... Click the link for more information. and to group galaxies into clusters and superclusters. The main source of energy in the universe is the conversion of the matter of the stars into energy through thermonuclear reactions (see nuclear energy nuclear energy, the energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity . In these processes a small amount of mass is converted to energy according to the relationship E = mc², where E
..... Click the link for more information. ). These reactions continue throughout the different stages of stellar evolution stellar evolution, life history of a star , beginning with its condensation out of the interstellar gas (see interstellar matter ) and ending, sometimes catastrophically, when the star has exhausted its nuclear fuel or can no longer adjust itself to a stable
..... Click the link for more information. (see also stellar populations stellar populations, two broadly contrasting distributions of star types that are characteristic of different parts of a galaxy . Population I stars are young, recently formed stars, whereas population II stars are old and highly evolved.
..... Click the link for more information. ) until the star has consumed all its available nuclear fuel.

The Size and Shape of the Universe

The first systematic theory of the size and shape of the universe that attempted to explain observed data was constructed by Ptolemy in the 2d cent. In this theory the solar system solar system, the sun and the surrounding planets, natural satellites , dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is by far the most massive part of the solar system, containing almost 99.9% of the system's total mass.
..... Click the link for more information. was thought to be the entire universe, with the earth at its center and the distant stars located just beyond the farthest planet. This belief was held until the 16th cent., when Copernicus advanced the idea that the sun, rather than the earth, is at the center of the system and that the stars are at very great distances compared to the planets. During the first part of the 20th cent., astronomers discovered that the sun is only one of billions of stars in the Milky Way Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky.
..... Click the link for more information. galaxy and is located far from the galactic center.

Estimates of the size of the universe have been refined as methods of measuring galactic and extragalactic distances have improved. Close stellar distances were at first found by measuring a star's trigonometric parallax parallax (pâr`əlăks)
..... Click the link for more information. . A more powerful contemporary method is to analyze the light reaching the earth from an object by means of a spectroscope; the distance of a very faint object can be estimated by comparing its apparent brightness to those of similar objects at known distances. Another method depends on the fact that the universe as a whole appears to be expanding, as indicated by red shifts (see Doppler effect Doppler effect, change in the wavelength (or frequency) of energy in the form of waves, e.g., sound or light, as a result of motion of either the source or the receiver of the waves; the effect is named for the Austrian scientist Christian Doppler, who demonstrated
..... Click the link for more information. ) in the spectral lines of distant galaxies. Hubble's law Hubble's law, in astronomy, statement that the distances between galaxies (see galaxy ) or clusters of galaxies are continuously increasing and that therefore the universe is expanding.
..... Click the link for more information. makes it possible to estimate their distances from the speed with which they are rushing away from the earth. At present the universe is believed to be at least 10 billion light-years light-year, in astronomy, unit of length equal to the distance light travels in one sidereal year . It is 9.461 × 10¹² km (about 6 million million mi). Alpha Centauri and Proxima Centauri, the stars nearest our solar system, are about 4.
..... Click the link for more information. in diameter. One problem with estimating the size of the universe is that space itself (or more properly, space-time) may be curved, as held by the general theory of relativity relativity, physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference.
..... Click the link for more information. . This curvature would affect measurements of distance based on the passage of light through space from objects as far away as 5 billion light-years or more.

Bibliography

See A. S. Eddington, The Expanding Universe (1933); J. H. Jeans, The Universe Around Us (4th ed. 1953); G. Gamow, The Creation of the Universe (1961); F. Hoyle, Man in the Universe (1966); L. B. Young, ed., Exploring the Universe (2d ed. 1971).

universe

Whole cosmic system of matter and energy of which Earth is a part. Its main constituents are the galaxies, within which are stars and stellar groupings and nebulae (see nebula). Earth's Sun is one star among the billions of stars in the Milky Way Galaxy. All atoms, subatomic particles, and everything they compose are also part of the universe. The universe is governed by four fundamental forces: the strong force, the weak force, the electromagnetic force, and gravitation. Numerous theories have been proposed for the origin and structure of the universe. See also big bang; cosmology; expanding universe; steady-state theory.

A relational DBMS from IBM that runs on the major Unix servers and Windows NT/2000. By 1997, more than a million seats had been sold. UniVerse includes its own BASIC programming environment and a variety of tools and enhancements for programming UniVerse applications. UniVerse was originally developed by Ardent Software, which was acquired by Informix and then IBM. It is part of IBM's U2 product family. See UniData.