Absolute zero

Absolute zero is the lowest possible temperature. At this temperature, the internal energy level of the system is the lowest possible, so that the molecules, according to classical mechanics, lack movement; however, according to quantum mechanics, absolute zero must have a residual energy, called zero point energy, in order to fulfill the Heisenberg uncertainty principle. Absolute zero serves as the starting point for both the Kelvin scale and the Rankine scale. Thus, 0 K (or what is the same, 0 R) correspond, for definition according to international agreement, at the temperature of −273.15 °C or −459.67 °F .

According to the third law of thermodynamics, absolute zero is an unreachable limit. In September 2014, scientists from the CUORE collaboration at the Laboratori Nazionali del Gran Sasso in Italy cooled a copper vessel with a volume of one cubic meter to 0.006 kelvin (−273.144 °C) for 15 days, setting a record for the hottest temperature low recorded in the known universe over such a large contiguous volume. The difficulty in reaching such a low temperature in a cooling chamber is the fact that the molecules in the chamber, upon reaching that temperature, do not have enough energy to make it drop further.

The entropy of a pure and perfect ideal crystal would be zero. If the atoms that compose it do not form a perfect crystal, its entropy must be greater than zero, so the temperature will always be higher than absolute zero and the crystal will always have imperfections induced by the movement of its atoms, requiring a movement that compensate and, therefore, always having a residual imperfection.

It should be mentioned that at 0 K absolutely all known substances would solidify and that according to the current model of heat, molecules would lose all ability to move, vibrate or rotate.

Until now the closest temperature to absolute zero has been obtained in the laboratory by scientists at the Massachusetts Institute of Technology in June 2015. It was obtained by cooling a gas in a magnetic field to 500 nanokelvin (5 10 ⁻⁹ K) above absolute zero.

Phenomena near absolute zero

Bose-Einstein's conviction in a ruby atom. The red color indicates a high speed, and the white-blue a low speed. The image on the right is the coldest sample of the three.

When approaching absolute zero, certain phenomena can be produced in some materials, such as the Bose-Einstein condensate, or some superfluids such as helium II.

In 1924, Albert Einstein and the Indian physicist Satyendranath Bose predicted the existence of a phenomenon called the Bose-Einstein condensate. In this state, the bosons are grouped together in the same quantum state of energy. This phenomenon was confirmed in 1995, and since then many of its properties have been investigated.

At temperatures very close to absolute zero, superfluids can be formed, or even fragile molecules that do not exist at higher temperatures for study, among other phenomena.

Currently, a practical application can be found in the LHC particle accelerator at CERN. The Large Hadron Collider (LHC) reaches a temperature of 1.9 K. The experiments that will be carried out in this accelerator Particles require freezing of certain circuits to become superconducting. This is possible thanks to the combination of helium compressors fed with liquid nitrogen, which enters the circuits at approximately 80 K (−193.15 °C) to gradually drop in temperature as it passes through the circuit of the 3 compressors. The lowest temperature reached in the LHC is 1.8 K.

History

Robert Boyle was a pioneer in the idea of absolute zero.

One of the first scientists to discuss the possibility of an absolute minimum temperature was Robert Boyle. His 1665 text New Experiments and Observations touching Cold (New experiments and observations about absolute zero ), articulated the dispute known as the primum frigidum The concept was well known among naturalists at the time. Some held that this absolute minimum temperature occurred within the Earth (since it was one of the so-called four "elements"), others that within water and others that in the air, and some more recently in nitro. Although they all seemed to agree that: "There is one body or another that by its very nature is extremely cold and that through its participation all other bodies obtain that quality."

Limit for “degree of cold”

The question of whether there was a limit to the degree of cold possible, and if so, where the zero should be placed, was first addressed by the French physicist Guillaume Amontons in 1702, in connection with his improvements in the air thermometer. In his instrument, temperatures were indicated by the height to which a column of mercury was supported by a given mass of air, the volume, or "spring," which varied with the heat to which it was exposed. Therefore Amontons argued that the zero of his thermometer would be the temperature at which the volume of air in him reduced to nothing. On the scale he used, the boiling point of water was marked at +73 and the melting point of ice at 51, so the zero on his scale was equivalent to about −240 on the Celsius scale.^{[citation required]}

This approximation to the modern value of −273.15 °C of air thermometer zero was further improved in 1779 by Johann Heinrich Lambert, who observed that −270 °C could be considered absolute cold.

Values of this order for absolute zero were not, however, universally accepted at the time. Pierre-Simon Laplace and Antoine Lavoisier, in their 1780 treatise on heat, arrived at values ranging from 1,500 to 3,000 below the freezing point of water, and thought that, in any case, it must be at least less than 600 John Dalton in his Chemical Philosophy gave ten calculations of this value, eventually adopting −3000 °C as the natural zero of temperature.

Lord Kelvin's work

After James Prescott Joule had determined the mechanical equivalent of heat, Lord Kelvin approached the question from an entirely different point of view, and, in 1848, devised an absolute temperature scale, which was independent of the properties of any particular substance and was based solely on the fundamental principles of thermodynamics. Starting from the axioms of that scale, he placed its zero at − 273.15 ° C , at almost exactly the same point as the zero of the air thermometer.