unidentified flying object (UFO) Aerial object or optical phe¬ nomenon not readily explainable to the observer. Interest in UFOs increased with developments in aeronautics and astronautics after World War II. A U.S. government panel investigating sightings in the 1950s reported that 90% coincided with astronomical or meteorological phenomena or sightings of aircraft, birds, or hot gases, sometimes under unusual weather conditions. Some remained unexplained, however, and in the mid 1960s a few scientists concluded that a small percentage indi¬ cated the presence of extraterrestrial visitors. This sensational hypothesis, promoted in the press, met with prompt resistance from other scientists. A U.S. Air Force UFO study begun in 1968 firmly rejected the extrater¬ restrial hypothesis, but a large fraction of the public, and a few scientists, continued to support it. UFO reports vary widely in reliability. The unaided eye is easily fooled; radar sightings of UFOs, more reliable in some ways, may fail to distinguish physical objects from meteor trails, rain, or thermal discontinuities and are subject to radio interference. See also SETI.
Unification Church officially Holy Spirit Association for the Unification of World Christianity Religious movement founded (1954) in South Korea by Sun Myung Moon. Influenced by yin-yang prin¬ ciples and Korean shamanism, it seeks to establish divine rule on earth through the restoration of the family, based on the union of the Lord and Lady of the Second Advent (believed to be Moon and his wife, Hak Ja Han). It strives to fulfill what it asserts to be the uncompleted mission of Jesus —procreative marriage. The church has been criticized for its recruit¬ ment policies (said to include brainwashing) and business practices. Its
mass marriage ceremonies have gained press attention. Its worldwide membership is about 200,000 in more than 100 countries.
unified field theory Attempt to describe all fundamental interactions between elementary particles in terms of a single theoretical framework (a “theory of everything”) based on quantum field theory. So far, the weak force and the electromagnetic force have been successfully united in elec- troweak theory, and the strong force is described by a similar quantum field theory called quantum chromodynamics. However, attempts to unite the strong and electroweak theories in a grand unified theory have failed, as have attempts at a self-consistent quantum field theory of gravitation.
unified science or unity-of-science view In the philosophy of logical positivism, the doctrine holding that all sciences share the same lan¬ guage, laws, and method. The unity of language has been taken to mean either that all scientific statements could be restated as a set of protocol sentences describing sense-data or that all scientific terms could be defined using physics terms. The unity of law means that the laws of the various sciences must be deduced from some set of fundamental laws (e.g., those of physics). The unity of method means that the procedures for support¬ ing statements in the various sciences are basically the same. The unity- of-science movement that arose in the Vienna Circle held to those three unities, and Rudolf Carnap’s “physicalism” supported the notion that all the terms and statements of empirical science could be reduced to terms and statements in the language of physics.
uniform circular motion Motion of a particle moving at a constant speed on a circle. Though the magnitude of the velocity of such an object may be constant, the object is constantly accelerating because its direc¬ tion is constantly changing. At any given instant its direction is perpen¬ dicular to a radius of the circle drawn to the point of location of the object on the circle. The acceleration is strictly a change in direction and is a result of a force directed toward the centre of the circle. This centripetal force causes centripetal acceleration.
Uniform Resource Locator See URL
uniformitarianism Doctrine in geology that physical, chemical, and biologic processes now at work on and within the Earth have operated with general uniformity (in the same manner and with essentially the same intensity) through immensely long periods of time and are sufficient to account for all geologic change. In other words, the present is the key to the past. Although the term is no longer much used, the principle, origi¬ nated by James Hutton, is fundamental to geologic thinking and underlies the whole development of the science of geology. See also Charles Lyell.
Unilever Vyii-no-.le-vorX Either of two linked companies, Unilever PLC (based in London) and Unilever NV (based in Rotterdam). They are the holding companies for more than 500 firms worldwide that manufacture and sell soaps, foods, and other products. The modern Unilever was estab¬ lished in 1929 as an association between the British manufacturer Lever Bros, and several other European soap and margarine manufacturers. Today most Unilever sales are in household products, including soaps and detergents, margarines, cooking fats, dairy products, toiletries, and pack¬ aged and processed foods. The group also produces paper and plastic products, industrial chemicals, and animal feeds.
union See labor union
Union, Act of (May 1, 1707) Treaty that effected the union of England (and Wales) and Scotland under the name of Great Britain. The union benefited England’s need for political safeguards against a possible Jaco¬ bite restoration through Scotland, and it gave Scotland economic security by freedom of trade with England. Under the treaty, initiated by Queen Anne, the two kingdoms adopted the Protestant succession, preserved Scots law and the law courts, and agreed to uniform taxation.
Union, Act of (Jan. 1, 1801) Legislative agreement uniting Great Brit¬ ain and Ireland under the name of the United Kingdom of Great Britain and Ireland. After the unsuccessful Irish revolt of 1798, the British prime minister, William Pitt the Younger, decided that the best solution to the Irish problem was a union to strengthen the connection between the two countries. The Irish parliament resisted the proposal, which called for its abolition, but votes bought by cash or honours ensured passage of the agreement in 1800. The union remained until the recognition of the Irish Free State (excluding six of the counties of the northern province of Ulster) by the Anglo-Irish treaty concluded on Dec. 6, 1921; the union officially ended on Jan. 15, 1922.
Unicorn, detail from "The Lady and the Unicorn" tapestry, late 15th century; in the Musee de Cluny, Paris
GIRAUDON/ART RESOURCE
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1964 I Union Islands ► United Arab Emirates
Union Islands See Tokelau
Union League Association formed to inspire loyalty to the Union cause in the American Civil War. Ohio Republicans formed the first Union League of America (1862) to counteract the antiwar Copperheads. Leagues formed in other states to support the war effort and to revitalize the Repub¬ lican Party. They also acted as social organizations, and some remain as clubs in cities such as New York and Washington. After the Civil War, leagues formed in the South to promote the Republican cause among free blacks.
Union of Soviet Socialist Republics (U.S.S.R.) or Soviet Union Former republic, eastern Europe and northern and central Asia. It consisted, in its final years, of 15 soviet socialist republics that gained independence at its dissolution: Armenia, Azerbaijan, Belorussia (now Belarus), Estonia, Georgia (now Republic of Georgia), Kazakhstan, Kir¬ gizia (now Kyrgyzstan), Latvia, Lithuania, Moldavia (now Moldova), Rus¬ sia, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan. It also contained 20 autonomous soviet socialist republics: 16 within Russia, 2 within Geor¬ gia, 1 within Azerbaijan, and 1 within Uzbekistan. Capitaclass="underline" Moscow. Stretching from the Baltic and Black seas to the Pacific Ocean and encom¬ passing some 8,650,000 sq mi (22,400,000 sq km), the Soviet Union con¬ stituted the largest country on Earth, having a maximum east-west extent of about 6,800 mi (10,900 km) and a maximum north-south extent of about 2,800 mi (4,500 km). It encompassed 11 time zones and had com¬ mon boundaries with 6 European countries and 6 Asian countries. Its regions contained fertile lands, deserts, tundra, high mountains, some of the world’s longest rivers, and large inland waters, including most of the Caspian Sea. The coastline on the Arctic Ocean extended 3,000 mi (4,800 km), while that on the Pacific was 1,000 mi (1,600 km) long. The U.S.S.R. was an agricultural, mining, and industrial power. Following the Russian Revolution of 1917, four socialist republics were established on the ter¬ ritory of the former Russian Empire: the Russian Soviet Federated Social¬ ist Republic, the Transcaucasian Soviet Federated Socialist Republic, the Ukrainian Soviet Socialist Republic, and the Belorussian Soviet Socialist Republic. These four constituent republics established the Union of Soviet Socialist Republics in 1922, to which other republics subsequently were added. A power struggle begun in 1924 with the death of communist leader Vladimir Lenin ended in 1927 when Joseph Stalin gained victory. Implementation of the first of the Five-Year Plans in 1928 centralized indus¬ try and collectivized agriculture. A purge in the late 1930s resulted in the imprisonment or execution of millions of persons considered dangerous to the state (see purge trials). After World War II, with their respective allies, the U.S.S.R. and the U.S. engaged in the Cold War. In the late 1940s the U.S.S.R. helped to establish communist regimes throughout most of eastern Europe. The U.S.S.R. exploded its first atomic bomb in 1949 and its first hydrogen bomb in 1953. Following Stalin’s death, it experienced limited political and cultural liberalization under Nikita Khrushchev. It launched the first manned orbital spaceflight in 1961. Under Leonid Brezhnev liberalization was partially reversed, but in the mid-1980s Soviet leader Mikhail Gorbachev instituted the liberal policies called glas- nost and perestroika. By the end of 1990 the communist government had toppled, and a program to create a market economy had been imple¬ mented. The U.S.S.R. was officially dissolved on Dec. 25, 1991.