# absolute zero

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absolute zero
the temperature of -273.16°C (-459.69°F), the hypothetical point at which all molecular activity ceases.

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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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temperature at which a thermodynamic system has the lowest energy. It corresponds to −273.15 °C on the Celsius temperature scale and to −459.67 °F on the Fahrenheit temperature scale.

The notion that there is an ultimately lowest temperature was suggested by the behaviour of gases (gas) at low pressures: it was noted that gases seem to contract indefinitely as the temperature is decreased. It appeared that an “ideal gas” at constant pressure would reach zero volume at what is now called the absolute zero of temperature. Any real gas actually condenses to a liquid or a solid at some temperature higher than absolute zero; therefore, the ideal gas law is only an approximation to real gas behaviour. As such, however, it is extremely useful.

The concept of absolute zero as a limiting temperature has many thermodynamic consequences. For example, all molecular motion does not necessarily cease at absolute zero, but none is available for transfer to other systems, and it is therefore correct to say that the energy at absolute zero is minimal. (For more on this, see thermodynamics.)

Any temperature scale having absolute zero for its zero point is termed an absolute temperature scale or a thermodynamic scale. In the International System of Units, the kelvin (K) scale is the standard for all scientific temperature measurements. Its fundamental unit, the kelvin, is identical in size to the Celsius degree and is defined as 1/273.16 of the “triple point” of pure water (0.01 °C)—i.e., the temperature at which the liquid, solid, and gaseous forms of the substance can be maintained simultaneously. In effect, the interval between this triple point and absolute zero comprises 273.16 kelvins; a temperature given in degrees Celsius can be converted to degrees Kelvin by adding 273.15.

Another absolute temperature scale, once used for engineering applications in the United States, is the Rankine (°R) scale. The Rankine scale is based on the Fahrenheit (Fahrenheit temperature scale) temperature unit, which is 5/9 of the unit used in the Celsius and Kelvin scales. A temperature given in degrees Fahrenheit can be converted to degrees Rankine by adding 459.67.

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Universalium. 2010.

### Look at other dictionaries:

• Absolute zero — Absolute Ab so*lute, a. [L. absolutus, p. p. of absolvere: cf. F. absolu. See {Absolve}.] 1. Loosed from any limitation or condition; uncontrolled; unrestricted; unconditional; as, absolute authority, monarchy, sovereignty, an absolute promise or …   The Collaborative International Dictionary of English

• Absolute zero — Zero e ro, n.; pl. {Zeros}or {Zeroes}. [F. z[ e]ro, from Ar. [,c]afrun, [,c]ifrun, empty, a cipher. Cf. {Cipher}.] [1913 Webster] 1. (Arith.) A cipher; nothing; naught. [1913 Webster] 2. The point from which the graduation of a scale, as of a… …   The Collaborative International Dictionary of English

• Absolute Zero — Éditeur Eidos Interactive Développeur Domark Dat …   Wikipédia en Français

• absolute zero — the idea dates back to 1702 and its general value was guessed to within a few degrees soon thereafter, but not precisely discovered until Lord Kelvin s work in 1848. It was known by many names, e.g. infinite cold, absolute cold, natural zero of… …   Etymology dictionary

• absolute zero — ► NOUN ▪ the lowest temperature theoretically possible (zero kelvins, 273.15°C) …   English terms dictionary

• absolute zero — n a theoretical temperature characterized by complete absence of heat and equivalent to exactly 273.15°C or 459.67°F * * * the lowest possible temperature, designated as 0 on the Kelvin or Rankine scale; by definition this is equivalent to… …   Medical dictionary

• absolute zero — n [U] the lowest temperature that is believed to be possible …   Dictionary of contemporary English

• absolute zero — noun uncount 273ºC or 460ºF, the lowest temperature that is possible in theory …   Usage of the words and phrases in modern English

• absolute zero — n. the temperature at which matter has no heat and its molecules are completely still; theoretically, the lowest possible temperature: equal to about 273.16°C or about 459.69°F or 0°K …   English World dictionary

• Absolute zero — For other uses, see Absolute Zero (disambiguation). Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means. A… …   Wikipedia