The absolute zero is the lowest Température. It is worth by convention -273,15°C or 0 K (Kelvin). But also 0 °R (on the scale Rankine) and - 459.67 °F (on the scale Fahrenheit). It is the minimal temperature asymptotically. It is theoretical and inaccessible, 450pK (0.45nK) is the record reached in 2003 at the research laboratory of the Massachusetts Institute off Technology (MIT) by a team Co-directed by the Nobel Prize of physics Wolfgang Ketterle. With 0K, a substance does not contain any more on a macroscopic scale the thermal energy (or Chaleur) necessary to the occupation of several microscopic energy levels. The particles which compose it (atoms, molecules) are all in the same state of minimal energy (fundamental state). That results by a Entropie null due to the indiscernibility of these particles in this same fundamental Energy level and in a total immobility with the traditional direction. But in fact, one knows that according to the Quantum physics, the particles always have a nonnull Quantité of movement according to the Principe of uncertainty (Heisenberg).

Indeed, while tending towards the absolute zero, the molecules of a body would have their momentum more and more precisely definite (near to zero), their positions would tend to have a residual intrinsic indetermination. But as they also tend towards the stop, their positions would also tend to being precisely defined. In fact, they tend towards a state of minimal energy, with the approaches of the absolute zero, thus respecting the quantum Principe of indetermination.

To make conversion °C towards Kelvin, one fixes at T (K) = T (°C) + 273,15.

Physics

One cannot measure temperature lower than the absolute zero; 0 K is a limiting insuperable. This limit is defined in the Third principle of thermodynamics, it corresponds to a null Entropie. The measuring unit used in physics is the Kelvin (symbol K).

This absolute temperature is theoretical and cannot thus be reached, moreover it does not exist nowhere in the Univers.

History

The state of the absolute zero was proposed for the first time by Guillaume Amontons in 1702. Amontons works on the relation between temperature and pressure in gases although it does not have at its disposal of precise thermometer. Although its results are quantitative, it establishes that the pressure of a given quantity of gas confined in a given volume increases about third when it passes from a temperature " froide" with that of the boiling of water. Its work leads it to suppose that a sufficient reduction of temperature would involve an absence of pressure.

In fact, although the absolute zero can be defined in this way, all the gases are liquefied before reaching 0 K.

In 1848, William Thomson, Lord Kelvin, proposes a scale of absolute temperature in which a reduction of the measured temperature corresponds to an equivalent reduction in the body heat studied. This concept, while being released from the constraints of the law of gases, establishes an absolute zero as being the temperature to which more no heat can be drawn from the body.

Application

The physicists discovered that certain substances develop very interesting properties when they reach this limit. Certain fluids, the stable isotopes of the Helium, lose any viscosity (it is the Superfluidité). And certain metals or alloys lose their electrical resistance (it is the Supraconductivité). Research to approach the absolute zero is thus numerous.

In practice, one reaches today easily 0,21 K while evaporating helium. Another method - called the “adiabatic demagnetization of paramagnetic substances” - makes it possible to obtain temperatures even lower, until 10^-6 K. Lastly, the atomic gas cooling bosonic until the Condensation of Bump-Einstein makes it possible to reach temperatures about 10^-9 K. It is this technique of Refroidissement of atoms per laser which was used by the researchers of MIT to reach the record of 450pK.

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