zero, that number which, when added to any number, leaves the latter unchanged; its symbol is 0. The introduction of zero into the decimal system was the most significant achievement in the development of a number system in which calculation with large numbers was feasible. Without it, modern astronomy, physics, and chemistry would have been unthinkable as we know them. The lack of such a symbol was one of the serious drawbacks of Greek mathematics. Its existence in the West is probably due to the Arabs, who, having obtained it from the Hindus, passed it on to European mathematicians in the latter part of the Middle Ages. The Maya of Central America and probably the Babylonians also invented zero. With the extension of the number system to negative as well as positive numbers, zero became the name for that position on the scale of integers between -1 and +1. It is used in this sense in speaking of zero degrees on the Fahrenheit and Celsius temperature scales; "absolute zero" is a term used by physicists and chemists to indicate the theoretically lowest possible temperature—a use reminiscent of zero as a symbol for nothing. Unlike other numbers, zero has certain special properties in connection with the four fundamental operations. By definition zero added to or subtracted from any number leaves the number unchanged. Any number multiplied by zero gives zero. Zero multiplied by or divided by any number (other than zero) is still zero. But division by zero is undefined; i.e., there is no number that is the value of a number divided by zero.

absolute zero, the zero point of the ideal gas temperature scale, denoted by 0 degrees on the Kelvin and Rankine temperature scales, which is equivalent to -273.15°C; and -459.67°F;. For most gases there is a linear relationship between temperature and pressure (see gas laws), i.e., gases contract indefinitely as the temperature is decreased. Theoretically, at absolute zero the volume of an ideal gas would be zero and all molecular motion would cease. In actuality, all gases condense to solids or liquids well above this point. Although absolute zero cannot be reached, temperatures within a few billionths of a degree above absolute zero have been achieved in the laboratory. At such low temperatures, gases assume nontraditional states, the Bose-Einstein and fermionic condensates. See also low-temperature physics; temperature.

Mostel, Zero, 1915-77, American actor, b. New York City as Samuel Joel Mostel. Mostel made his Broadway debut in Keep 'Em Laughing (1942). A comic actor with an expressive face, he combined a large paunch with acrobatic grace. His major stage appearances include Ulysses in Nighttown (1958 and 1974), Rhinoceros (1961; film, 1973), A Funny Thing Happened on the Way to the Forum (1962; film, 1966), and Fiddler on the Roof (1964). Mostel's other films include The Producers (1968).

Vibrational energy retained by molecules even at a temperature of absolute zero. Since temperature is a measure of the intensity of molecular motion, molecules would be expected to come to rest at absolute zero. However, if molecular motion were to cease altogether, the atoms would each have a precisely known location and velocity (zero), and the uncertainty principle states that this cannot occur, since precise values of both position and velocity of an object cannot be known simultaneously. Thus, even molecules at absolute zero must have some zero-point energy.

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Complex formerly consisting of seven buildings around a central plaza, near the southern tip of Manhattan. Its huge twin towers (completed 1970–72) were designed by Minoru Yamasaki (1912–86). At 1,368 ft (417 m) and 1,362 ft (415 m) tall, they were the world's tallest buildings until surpassed in 1973 by the Sears Tower in Chicago. The towers were notable for the relationship of their simple, light embellishment to their underlying structure. In 1993 a bomb planted by terrorists exploded in the underground garage, killing several people and injuring some 1,000. A much more massive attack occurred on Sept. 11, 2001, when first One World Trade Center and then Two World Trade Center were struck by hijacked commercial airliners that were deliberately flown into them. Shortly thereafter both of the heavily damaged towers, as well as adjacent buildings, collapsed into enormous piles of debris. The attacks claimed the lives of some 2,750 people. Thousands more were injured. See September 11 attacks.

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Temperature at which a thermodynamic system (see thermodynamics) has the lowest energy, 0 kelvin (K). It corresponds to −459.67°F (−273.15°C) and is the lowest possible temperature theoretically achievable by a system. A gas at constant pressure contracts as the temperature is decreased. A perfect gas would reach zero volume at absolute zero. However, a real gas condenses to a liquid or a solid at a temperature higher than absolute zero. At absolute zero, the system's molecular energy is minimal and none is available for transfer to other systems. The Kelvin temperature scale has absolute zero as its zero point, and its fundamental unit is the kelvin.

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orig. Samuel Joel Mostel

(born Feb. 28, 1915, New York, N.Y., U.S.—died Sept. 8, 1977, Philadelphia, Pa.) U.S. actor. He initially worked both on Broadway and in film, but after being blacklisted in Hollywood after 1955, he worked principally in theatre in New York City. He gave acclaimed performances in Ulysses in Nighttown (1958) and Rhinoceros (1961), and he had lead roles in the musicals A Funny Thing Happened on the Way to the Forum (1962) and Fiddler on the Roof (1964). His later films included Mel Brooks's The Producers (1968) and The Front (1976), a film about the blacklisting era. Mostel was also a serious painter throughout his life.

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