Absolute zero

In 1702 Guillaume Amontons introduced the concept of absolute zero based on observations of gases. In 1810, Sir John Leslie froze water to ice artificially. The idea of absolute zero was generalised in 1848 by Lord Kelvin. In 1906, Walther Nernst stated the third law of thermodynamics.


The word cryogenics means “the production of freezing cold”; however the term is used today as a synonym for the low-temperature state. It is not well-defined at what point on the temperature scale refrigeration ends and cryogenics begins. The workers at the National Institute of Standards and Technology at Boulder, Colorado have chosen to consider the field of cryogenics as that involving temperatures below –180 °C (93.15 K). This is a logical dividing line, since the normal boiling points of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen, and normal air) lie below -180 °C while the Freon refrigerants, hydrogen sulfide, and other common refrigerants have boiling points above -180 °C.

James Dewar

His name is most widely known in connection with his work on the liquefaction of the so-called permanent gases and his researches at temperatures approaching absolute zero. His interest in this branch of physics and chemistry dates back at least as far as 1874, when he discussed the “Latent Heat of Liquid Gases” before the British Association. In 1878 he devoted a Friday evening lecture at the Royal Institution to the then recent work of Louis Paul Cailletet and Raoul Pictet, and exhibited for the first time in Great Britain the working of the Cailletet apparatus. Six years later, again at the Royal Institution, he described the researches of Zygmunt Florenty Wróblewski and Karol Olszewski, and illustrated for the first time in public the liquefaction of oxygen and air. Soon afterwards he built a machine from which the liquefied gas could be drawn off through a valve for use as a cooling agent, before using the liquid oxygen in research work related to meteorites; about the same time he also obtained oxygen in the solid state.

By 1891 he had designed and built, at the Royal Institution, machinery which yielded liquid oxygen in industrial quantities, and towards the end of that year he showed that both liquid oxygen and liquid ozone are strongly attracted by a magnet. About 1892 the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases – the Dewar flask (otherwise known as a Thermos or vacuum flask) – the invention for which he became most famous. The vacuum flask was so efficient at keeping heat out that it was found possible to preserve the liquids for comparatively long periods, making examination of their optical properties possible. Dewar did not profit from the widespread adoption of his vacuum flask – he lost a court case against Thermos concerning the patent for his invention, and while he was recognised as the inventor, because he did not patent his invention, there was no way to stop Thermos from using the design.

He next experimented with a high pressure hydrogen jet by which low temperatures were realized through the Joule–Thomson effect, and the successful results he obtained led him to build at the Royal Institution a large regenerative cooling refrigerating machine. Using this machine in 1898, liquid hydrogen was collected for the first time, solid hydrogen following in 1899. He tried to liquefy the last remaining gas, Helium, which condenses into a liquid at −272.2°C, but owing to a number of factors, including a lack of Helium with which to work, Heike Kamerlingh Onnes beat Dewar and was the first person to produce liquid helium, in 1908. Onnes would later be awarded the Nobel Prize in Physics for his research into the properties of matter at low temperatures – Dewar was nominated several times but never successful in winning the Nobel Prize.[3]

In 1905 he began to investigate the gas-absorbing powers of charcoal when cooled to low temperatures, and applied his research to the production of high vacuums, which were useful for further experiments in atomic physics. Dewar would continue his research work into the properties of elements at low temperatures, specifically low-temperature calorimetry, until the outbreak of World War I. The Royal Institution laboratories lost a number of staff to the war effort, both in fighting and scientific roles, and after the war, Dewar had little interest in re-starting the serious research work which went on before the War. Shortages of scholars necessarily compounded the problems. His research during and after the war mainly involved investigating surface tension in soap bubbles, rather than further work into the properties of matter at low temperatures.

Lord Kelvin and the Heat Death of the Universe

The heat death is a possible final state of the universe, in which it has “run down” to a state of no thermodynamic free energy to sustain motion or life. In physical terms, it has reached maximum entropy. The hypothesis of a universal heat death stems from the 1850s ideas of William Thomson, 1st Baron Kelvin who extrapolated the theory of heat views of mechanical energy loss in nature, as embodied in the first two laws of thermodynamics, to universal operation.

The idea of heat death of the universe derives from discussion of the application of the first two laws of thermodynamics to universal processes. Specifically, in 1851 William Thomson outlined the view, as based on recent experiments on the dynamical theory of heat, that “heat is not a substance, but a dynamical form of mechanical effect, we perceive that there must be an equivalence between mechanical work and heat, as between cause and effect.”

In 1852, Thomson published his “On a Universal Tendency in Nature to the Dissipation of Mechanical Energy” in which he outlined the rudiments of the second law of thermodynamics summarized by the view that mechanical motion and the energy used to create that motion will tend to dissipate or run down, naturally. The ideas in this paper, in relation to their application to the age of the sun and the dynamics of the universal operation, attracted the likes of William Rankine and Hermann von Helmholtz. The three of them were said to have exchanged ideas on this subject.[3] In 1862, Thomson published the article “On the age of the sun’s heat” in which he reiterated his fundamental beliefs in the indestructibility of energy (the first law) and the universal dissipation of energy (the second law), leading to diffusion of heat, cessation of motion, and exhaustion of potential energy through the material universe while clarifying his view of the consequences for the universe as a whole. The key paragraph is:[4]

The result would inevitably be a state of universal rest and death, if the universe were finite and left to obey existing laws. But it is impossible to conceive a limit to the extent of matter in the universe; and therefore science points rather to an endless progress, through an endless space, of action involving the transformation of potential energy into palpable motion and hence into heat, than to a single finite mechanism, running down like a clock, and stopping for ever.

In the years to follow both Thomson’s 1852 and the 1865 papers, Helmholtz and Rankine both credited Thomson with the idea, but read further into his papers by publishing views stating that Thomson argued that the universe will end in a “heat death” (Helmholtz) which will be the “end of all physical phenomena” (Rankine).

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