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.

absolute value, magnitude of a number or other mathematical expression disregarding its sign; thus, the absolute value is positive, whether the original expression is positive or negative. In symbols, if ~~pipe~;a~~pipe~; denotes the absolute value of a number a, then ~~pipe~;a~~pipe~; = a for a < 0 and ~~pipe~;a~~pipe~; = -a for a > 0. For example, ~~pipe~;7~~pipe~;= 7 since 7 < 0 and ~~pipe~;-7~~pipe~; = -(-7), or ~~pipe~;-7~~pipe~; = 7, since -7 > 0.

absolute temperature scale: see Kelvin temperature scale; temperature.

absolute pitch, the position of a tone in the musical scale determined according to its number of vibrations per second, irrespective of other tones. The term also denotes the capacity to identify any tone upon hearing it sounded alone or to sing any specified tone. Experiments have shown that this ability, a form of memory, can be acquired through practice, but in some individuals it appears to be inborn.

absolute music, term used for music dependent on its structure alone for comprehension. It is the antithesis of program music. It is not associated with extramusical ideas or with a pictorial or narrative scheme of emotions, nor does it attempt to reproduce sounds in nature. Hence it is always instrumental, although not all instrumental music is absolute. Bach's Art of Fugue is an example of absolute music.

absolute monarchy: see monarchy.

absolute magnitude: see magnitude.

absolute differential calculus: see tensor.

absolute, in philosophy, the opposite of relative. The term has acquired numerous widely variant connotations in different philosophical systems. It means unlimited, unconditioned, or free of any relation; perfect, complete, or total; permanent, inherent, or ultimate; independent, or valid without reference to a perceiving subject. In epistemology, absolute means certain or indubitable as opposed to probable or hypothetical. As a substantive, the absolute is the ultimate basis of reality, the principle underlying the universe. Theologically, it is synonymous with, or characteristic of, God. Philosophically, it may be considered as the unknowable, the thing-in-itself; as that ultimate nonrelative that is the basis of all relation; as the ultimate, all-comprehensive principle in which all differences and distinctions are merged. The concept of the absolute was present in Greek philosophy. In modern times, both realists and idealists have used the term, but it is, perhaps, most intimately connected with the idealism of G. W. Hegel.

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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Political doctrine and practice of unlimited, centralized authority and absolute sovereignty, especially as vested in a monarch. Its essence is that the ruling power is not subject to regular challenge or check by any judicial, legislative, religious, economic, or electoral agency. Though it has been used throughout history, the form that developed in early modern Europe (16th–18th century) became the prototype; Louis XIV is seen as the epitome of European absolutism. Religious authority was assumed by the monarch, who became the head of the church as well as the state, on the basis that the right to rule came from God (see divine kingship). Seealso authoritarianism, dictatorship, totalitarianism.

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