U is for Universes
U = Universes and Dimensional Realities, Space-Time Continuums.
See also: dimensions, reality, continuums, worlds, channels.
u·ni·verse (yʹnə-vûrs´) noun
1. All matter and energy, including Earth, the galaxies and all therein, and the contents of intergalactic space, regarded as a whole.
2. a. The earth together with all its inhabitants and created things. b. The human race.
3. The sphere or realm in which something exists or takes place.
4. Logic. See universe of discourse.
5. Statistics. See population.
[Middle English, from Old French univers, from Latin ūniversum from neuter of ūniversus, whole : ūnus, one + versus past participle of vertere, to turn.]
ASTRONOMY & SPACE SCIENCE
Astronomy, science dealing with all the planets and their satellites, comets and meteors, stars and interstellar matter, star systems known as galaxies, and clusters of galaxies.
The Egyptians may have been the first to discover that the relative position of the sun among the stars changes in approximately 365 days and nights (see Ecliptic). The sun, the moon, and the planets are all seen in changing positions amid a narrow belt of stars called the zodiac. The sun and moon always cross the zodiac from west to east. However, the five bright planets-Mercury, Mars, Venus, Jupiter, and Saturn, which have a generally eastward motion-also move westward, or retrograde.
The Babylonians realized about 400 BC that the apparent motions of the sun and moon around the zodiac do not have a constant speed. The Babylonians knew the daily positions of the moon and sun for every day during the month and could predict the time of the new moon. They also calculated planetary positions with both eastward and retrograde motions.
Aristarchus of Sámos believed that the earth turns around on its axis once every 24 hours and, along with the other planets, revolves around the sun. This explanation was rejected by most Greek philosophers, who regarded the heavy earth as a motionless globe around which light objects revolve. This theory, known as the geocentric system, remained virtually unchallenged for about 2000 years.
In the 2nd century AD, Greek astronomers Hipparchus and Ptolemy used a series of circles with the earth near the center to represent the general motions of the sun, moon, and planets around the zodiac. To explain variations in the speed of the sun and moon and the retrogressions of the planets, they proposed that each of these objects revolves around a second circle, called an epicycle, centered on the circumference of the first.
The Copernican Theory
In the 16th century, the contributions of Polish astronomer Nicolaus Copernicus changed astronomy dramatically. He showed that the planetary motions can be explained by assuming a central position for the sun rather than for the earth. In 1609 Galileo made a small refracting telescope and discovered that Venus has phases like the moon’s, which indicate that Venus revolves around the sun; he also discovered four moons revolving around Jupiter, as well as the rings of Saturn.
The Newtonian Theory
Using data compiled by Danish astronomer Tycho Brahe, his German assistant, Johannes Kepler, formulated new laws of planetary motion, stating that the planets revolve around the sun in elliptical orbits at varying speeds and that their distances from the sun can be calculated from the periods of revolution. British physicist Sir Isaac Newton argued that an attractive force of gravitation exists between the sun and each of the planets, its strength varying with the masses of the sun and planets and the distances between them.
Improved telescopes have permitted examination of planetary surfaces, the discovery of many faint stars, and the measurement of stellar distances. In the 19th century, spectroscopy yielded information about the chemical composition and the motions of astronomical objects. During the 20th century, increasingly larger telescopes have revealed the structure of galaxies and clusters of galaxies. New classes of astronomical equipment have been built, sensitive to a wide range of electromagnetic radiation (see Radar Astronomy; Radio Astronomy).
The Solar System
With the use of the telescope, many new members of the solar system were discovered, including Uranus in 1781, Neptune in 1846, and Pluto in 1930. The number of known planetary satellites has grown to more than 60. Space probes have discovered rings around Jupiter and new moons of that planet, Saturn, and Uranus.
The nearest star, Alpha Centauri, is about 260,000 times farther from the earth than is the sun. The first star distances were measured in 1838. Star masses can be determined for the sun and for some pairs of stars. Of the nearest stars, about 10 percent are brighter, larger, and more massive than the sun.
In the 1960s British astronomers Jocelyn Bell and Antony Hewish discovered pulsars, which are apparently the last stage before a star’s extinction as a black hole. In 1994 the Hubble Space Telescope provided the first convincing evidence of such a black hole. Scientists estimate that it has a mass 2.5 billion to 3.5 billion times that of the sun.
In the late 18th century, Sir William Herschel decided that the sun is one of a vast cloud of stars, called the Milky Way. A ray of light, moving at a speed of about 300,000 km/sec (about 186,000 mi/sec), would require 400,000 years to cross the Milky Way. The Milky Way is a spiral galaxy containing about a million million stars. The sun is located about 30,000 light-years from the center of the Milky Way.
The Milky Way is only one of many galaxies, some as far away as several billion light-years. Quasars, discovered in the 1950s with the use of radio telescopes, are believed by most astronomers to be the energetic nuclei of very distant galaxies. A quasar 12 billion light-years distant was discovered in 1991.
American astronomer Edwin Hubble showed that the galaxies are all moving away from the Milky Way, a fact indicating that the universe is expanding, and that it originated from an extremely hot, dense state of matter by an explosion called the big bang (see Cosmology).
ASTRONOMY & SPACE SCIENCE
Cosmology, science that studies the whole universe, including theories about its origin, evolution, structure, and future. The study of the origin of the universe and of astronomical systems, such as the solar system, is often called cosmogony.
Early Cosmological Theories
The Mesopotamians believed that the earth is the center of the universe. The motion of stars was explained by Greek thinkers Aristotle and Ptolemy as rotating crystal spheres. Although Greek astronomer Aristarchus of Sámos maintained that the earth revolves around the sun, the concept of the earth as the center of the universe held until Polish astronomer Nicolaus Copernicus proposed that the planets revolve around the sun, which he believed to be the center of the universe. He explained the motion of the stars by the rotation of the earth. English mathematician and physicist Sir Isaac Newton stated general laws of motion and gravitation, which he said are valid throughout the universe.
Thousands of galaxies lie outside the Milky Way galaxy that contains the solar system. Each galaxy contains hundreds of billions of stars. Most galaxies are receding from the Milky Way at several hundred kilometers per second. American astronomer Edwin Hubble discovered that more remote galaxies have proportionally higher recession velocities (see Red Shift). The universe is expanding, carrying galaxies away from each other in all directions.
The Age of the Universe
If the rate of expansion of the universe is known, its age can be estimated. At the present time, estimates of the age of the universe range between 7 and 20 billion years. Lower estimates in this range seem to conflict with the age of the oldest stars, which are believed to be about 16 billion years old.
Static and Expanding Models of the Universe
German-American physicist Albert Einstein proposed a theory of the universe, based on general relativity, in which gravitation is equivalent to a curvature of four-dimensional space. His solution indicated that the universe was not static but must be expanding or contracting. Of various nonstatic theories, that proposed by Russian mathematician Alexander Friedmann is the currently accepted one. The fate of the Friedmann universe depends on the average density of matter in the universe. If there is relatively little matter in the universe, the gravitational attraction among the galaxies will be slight, and the universe will expand forever to an infinite extent. If the density of matter is above a critical value, the expansion will slow to a halt and reverse to contraction, ending in the total collapse of the entire universe. The fate of this collapsed universe is uncertain. One theory is that it would explode, producing a new expanding universe, which would again collapse, and so on forever.
The Steady-State Theory
British astronomers Hermann Bondi, Thomas Gold, and Sir Fred Hoyle presented an entirely different theory of the universe. They proposed that the decrease in the density of the universe caused by its expansion is balanced by the continuous creation of matter, maintaining forever the present appearance of the universe. The steady-state theory is no longer accepted by most cosmologists.
The Big Bang Theory
Russian-American physicist George Gamow proposed that the universe was created in a gigantic explosion now called the big bang. This theory provided a basis for understanding the earliest stages of the universe and its subsequent evolution. Extremely high density would cause the universe to expand rapidly. Hydrogen and helium would cool and condense into stars and galaxies. According to Gamow’s theory, radiation left over from the big bang would cool to about 3 K (about -270° C/-454° F) today. This cosmic background radiation was detected in 1965, providing what most astronomers consider to be confirmation of the big bang theory. Inflationary theory resolves difficulties in Gamow’s original theory by including recent advances in particle physics.
Evolution of the Universe
It remains unknown whether the universe will expand forever or will contract again. One approach to solving this problem is to learn the average density of matter in the universe. The mass of each galaxy multiplied by the number of galaxies is only 5 to 10 percent of Friedmann’s critical value. Multiplying galactic cluster mass by the number of clusters results in an average density near the critical value. The difference between these results suggests the presence of invisible matter, the so-called dark matter, outside the galaxies but within the clusters. Until the missing-mass phenomenon is understood, this method of determining the fate of the universe will be inconclusive.
Creation Stories, myths that explain the origin of the universe, or cosmos. Creation forms one of the principal themes of mythology throughout the world. Most creation stories assume the eternity of matter or even of the world itself. However, these myths hold that the world in its precreation state was uninhabitable and had to be organized either by the action of cosmic forces or by creator deities. Some creation myths reflect the environmental circumstances of a particular culture.
Creation mythologies explain the actual formation of the world by a variety of processes. These processes include the sacrifice of a primal being; a struggle between supernatural powers; the union or fusion of elements, particularly water and earth; the incubation of a cosmic egg; and the utterance of a divine word. In myths that credit primary creation to gods, these deities often become hazy, remote figures in later mythology; stories often recount their overthrow by their own offspring. Many mythological accounts ascribe creation to impersonal agents rather than to individual deities. Mythologies also frequently include the creation of a pantheon of related gods. Many creation myths focus on the idea that primal elements were made distinct from one another during the act of creation-for instance, the separation of light from darkness. In others, the raw material for making the world derives from a specific source, such as mud or a primordial being.
Cosmogonic myths generally culminate in the creation of humankind, after which the mythic cosmos comes to resemble the world of human experience. In mythic history, the earliest era of the world is usually the closest to perfection-a Golden Age or Garden of Eden-with later phases showing the progressive degeneration of the world as it grows distant from the original creative impulse. The earliest human beings are often thought to have been of extraordinary stature and longevity and to have been much closer to the gods than are present-day human beings.
THEOLOGY & PRACTICES
Creationism, broad range of beliefs involving an appeal to God’s miraculous intervention to explain the origin of the universe, of life, and of the different kinds of plants and animals on earth. Creationists invoke divine intervention to explain at least some of these phenomena, although they do not necessarily agree on the length of time involved in creation.
Early Views on Creation
By the first half of the 19th century, most people in the West-including the great majority of scientists-accepted creationism in some form. As paleontologists proposed evidence of the antiquity of life on earth, many Christians remained loyal to the traditional view, while others adopted one of two popular reinterpretations of the biblical account of creation. The first was the so-called Day-Age theory, which proposed the six days of biblical creation as vast geological ages rather than 24-hour periods. The second reinterpretation, known as the Gap theory, proposed an immense interval between an initial creation and the creation of the Garden of Eden in about 4000 BC.
Scientists proposed at least three competing versions of creationism: (1) simultaneous creation in one location of single pairs of animals, (2) multiple centers of creation established at various times and in different places, and (3) simultaneous creation of multiple individuals, widely distributed over the earth. All three of these views allowed for Earth’s history to extend far beyond 6000 years.
The theory of evolution was considered in the mid-1800s. In his book On the Origin of Species (1859) English naturalist Charles Darwin first acknowledged an initial act of creation but later ruled out any role for God in the origin and development of living things. Most naturalists embraced Darwin’s theory, although few shared his complete elimination of God from the process. Some attempted to create new theories blending both creationist and evolutionist ideas.
Despite the growing influence of the theory of evolution, most evangelical Christians in the United States remained skeptical of the idea. After World War I (1914-1918), American Christian fundamentalists began a movement against the idea of evolution, partly because of the popular belief that German aggression expressed a Darwinian doctrine of survival of the fittest (see Social Darwinism). Several states banned or condemned the teaching of evolution in U.S. public schools.
In 1925 the issue gained international attention during the trial and conviction of high school science teacher John T. Scopes in Dayton, Tennessee. Scopes had assisted the American Civil Liberties Union (ACLU) in contending the constitutionality of a Tennessee antievolution law. In the 1960s the Creation Research Society promoted the theory of young-earth creationism, relying on catastrophism, the doctrine that large-scale changes in the earth’s crust are explained by violent, unrepeatable geologic events, such as the biblical flood. The theory eventually became called scientific creationism or creation science.
ASTRONOMY & SPACE SCIENCE
Dark Matter, in astronomy, nonluminous material undetectable by observing electromagnetic radiation but suggested to exist by theories.
Galaxies near the Milky Way appear to rotate faster than would be expected from calculations based on the amount of visible matter in these galaxies. Up to 90 percent of the matter in a typical galaxy may be invisible. Some astronomers argue that more than 90 percent of the matter holding clusters of galaxies together is dark matter.
The inflationary theory of the big bang asserts that the early universe expanded rapidly. If this theory is correct, the mass of the universe must be more than 100 times the visible mass. This calculation indicates that more than 99 percent of the mass of the universe must arise from dark matter.
Candidates for the material that makes up dark matter include neutrinos with mass, brown dwarfs (starlike objects smaller and fainter than the sun), white dwarf stars, black holes, and unusual subatomic elementary particles.
ASTRONOMY & SPACE SCIENCE
Galaxy, group of hundreds of millions of stars orbiting around a center. There are about 50 billion galaxies in the universe. The largest known galaxy has about 13 times as many stars as the Milky Way, the galaxy that the earth is in. Besides stars and planets, galaxies contain hydrogen gas, complex molecules, and cosmic rays. Galaxies radiate visible light, radio waves, infrared radiation, ultraviolet radiation, and X rays.
Early History of the Study of Galaxies
By the mid-18th century, only three galaxies had been identified. In 1780, French astronomer Charles Messier published a list that included 32 galaxies. Thousands of galaxies were cataloged by British astronomers Sir William Herschel, Caroline Herschel, and Sir John Herschel in the early 19th century. Since 1900 galaxies have been discovered in large numbers. The spectra of all galaxies show a red shift (see Spectroscopy), interpreted by American astronomer Edwin Hubble as evidence that the universe is expanding (see Cosmology).
Classification of Galaxies
Elliptical galaxies are globular, with a bright center, old stars, little apparent gas or dust, and few new stars. Spiral galaxies are flat disks with many young stars, and much gas and dust, in long spiral arms. Irregular galaxies have large amounts of gas, dust, and young stars, but no spiral form. Their appearance probably results from gravitation from a nearby larger galaxy.
Determination of Extragalactic Distances
Astronomers estimate distances by comparing objects in another galaxy with those in the earth’s galaxy. Cepheid variables, stars that periodically vary in brightness, are especially valuable because the period of variation is related to the brightness of the star, indicating distance. The speed of stars orbiting in a galaxy depends on the galaxy’s brightness and also indicates distance.
Distribution of Galaxies
Galaxies occur in groups, which form large clusters. The earth’s galaxy is one of about 20 in the Local Group. The earth’s galaxy and the Andromeda galaxy are the two largest members. The Large, Small, and Mini Magellanic Clouds are nearby galaxies but small and faint. The Local Group is a member of the Virgo cluster, which contains thousands of galaxies. Superclusters of tens of thousands of galaxies occur in lacelike networks around large voids.
The most distant galaxies known are blue because of the hot, young stars they contain. Some, 13 billion light-years away, formed when the universe was just 10 to 20 percent of its current age. These galaxies appear to be spherical.
Rotation of Spiral Galaxies
Stars orbit spiral galaxies more quickly at increasing distances from the center. At the edges, velocities of 300 km/sec (about 185 mi/sec) have been measured. The increase in speed means that the mass of a galaxy is not centrally concentrated. Mass at large distances from the center has so little luminosity that it has been detected only by its gravitational attraction. Its exact nature is unknown.
See Also Quasar.
universe, omneity, whole
world, globe, creation, all creation
sum of things, plenum, matter and antimatter, matter
cosmos, macrocosm, microcosm
expanding universe, metagalaxy
outer space, deep space, intergalactic space
cosmogony, nebular hypothesis, planetesimal hypothesis
big bang theory, steady state theory, start
substantiality: totality of existence, plenum, world, world of nature, universe
great quantity: expanse, sheet, lake, sea, ocean, world, universe, world of, power of
whole: collectivity, system, world, globe, cosmos, universe
arrangement: cosmos, universe
generality: macrocosm, universe