Absolute zero
What is absolute zero?
How did the behavior of gases suggest the idea of absolute zero?
What is the Kelvin scale?
What is the lowest temperature that has been achieved?
Absolute zero, is the 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 behavior of gases at low pressures: it was noted that gases seem to contract indefinitely as temperature decreases. 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 behavior. 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 cease at absolute zero (molecules vibrate with what is called zero-point energy), but no energy from molecular motion (that is, heat energy) is available for transfer to other systems, and it is therefore correct to say that the energy at absolute zero is minimal.
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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 such that the Boltzmann constant is equal to 1.380649 × 10−23 joule per kelvin. The lowest temperature achieved has been 9.7 picokelvin (pK; 1 pK = 10−12 K), which was achieved in an experiment on the Chinese space station Tiangong.