Absolute zero

Absolute zero is called the lower limit for the temperature. This defines the origin of the absolute temperature scale and is than 0 K, -273.15 ° C according to laid down. The existence and the extrapolated value of absolute zero can be derived from the first law of Gay- Lussac.

After the third law of thermodynamics, absolute zero is an ideal measure, which is not attainable, but real temperatures can be realized arbitrarily close to absolute zero. With laser cooling samples could be cooled to within a few billionths of a Kelvin already.

History

Guillaume Amontons found out in 1699 that varies linearly with the volume of a quantity of gas with its temperature. Since the volume of a gas but should not be negative, he concluded that there must be an absolute zero point at which the volume of gas amount would be equal to zero. By extrapolation of its readings he estimated from the position of this zero point and came to a value of minus 248 degrees Celsius. However, this method must be considered very critical, because the legality of the volume reduction is valid only for ideal gases, but not for materials that change their state of aggregation, for example, become liquid.

William Thomson, 1st Baron Kelvin discovered in 1848 that the volume reduction is not critical to this question, but the energy loss. It is immaterial whether it is gas or solid substances. Thomson then proposed to define a new, absolute temperature scale at which the change in volume is proportional. This new temperature scale has no negative values ​​more starts at zero (which corresponds to minus 273.15 degrees Celsius, refer to properties of the Kelvin scale) and rises so that a temperature difference of one Kelvin corresponds in each case a temperature difference of one degree Celsius. This same step size was achieved by imposing that the kelvin the 273.16 - te of the thermodynamic temperature of the triple point of water - this is 0.01 ° C -. The unit for this temperature scale was initially called level A ( A for absolute ), later K ( K for Kelvin). The kelvin is no longer supplemented since 1967 by definition degrees (°).

"If now the magnetic field away suddenly, enters the thermomagnetic cooling effect. In this way obtained with alum at a temperature of 0.05K. In 1935 one is even already penetrated to 0,005 K. [ ... ] In order to assess the progress made properly, you really ought logarithmic temperature scale, as has been suggested by Lord Kelvin apply. Thereafter, a reduction of 100 K would happen to 10 K have the same meaning as [ ... ] of 1 K to 0.1 K. "

Properties

Physical systems with temperatures close to absolute zero have some special behaviors such as superfluidity and Bose -Einstein condensation. This temperature field of low temperature physics can be achieved only with special methods.

At normal pressure at the zero point are set, all elements, except for helium, which is there in a liquid or superfluid phase.

Thermodynamic statements about the zero point in relation to the entropy makes the theorem of Nernst. Perfect crystals reach the zero point for the entropy of a constant value, since the entropy is defined as multiplied by the Boltzmann constant logarithm of the number of possible states according to the statistical definition of micro- and there is only one possible implementation of the observed macrostate. At ( amorphous ) glass is available with several identical energetic realizations of a state such that the entropy of zero.