Editing Absolute zero (section)

==History==
[[File:Robert Boyle 0001.jpg|thumb|upright=1.05|[[Robert Boyle]] pioneered the idea of an absolute zero.]]
One of the first to discuss the possibility of an absolute minimal temperature was [[Robert Boyle]]. His 1665 ''New Experiments and Observations touching Cold'', articulated the dispute known as the ''primum frigidum''.<ref>{{Cite book |last=Stanford |first=John Frederick |author-link=John Frederick Stanford |url=https://books.google.com/books?id=8vRaAAAAMAAJ&pg=PA651 |title=The Stanford Dictionary of Anglicised Words and Phrases |year=1892}}</ref> The concept was well known among naturalists of the time. Some contended an absolute minimum temperature occurred within earth (as one of the four [[classical element]]s), others within water, others air, and some more recently within [[nitre]]. But all of them seemed to agree that, "There is some body or other that is of its own nature supremely cold and by participation of which all other bodies obtain that quality."<ref>{{Cite book |last=Boyle |first=Robert |title=New Experiments and Observations touching Cold |year=1665}}</ref>

===Limit to the "degree of cold"===
The question of whether there is a limit to the degree of coldness possible, and, if so, where the zero must be placed, was first addressed by the French physicist [[Guillaume Amontons]] in 1703, in connection with his improvements in the [[gas thermometer|air thermometer]]. His instrument indicated temperatures by the height at which a certain mass of air sustained a column of mercury—the pressure, or "spring" of the air varying with temperature. Amontons therefore argued that the zero of his thermometer would be that temperature at which the spring of the air was reduced to nothing.<ref>{{Cite journal |last=Amontons |date=18 April 1703 |title=Le thermomètre rèduit à une mesure fixe & certaine, & le moyen d'y rapporter les observations faites avec les anciens Thermométres |trans-title=The thermometer reduced to a fixed & certain measurement, & the means of relating to it observations made with old thermometers |url=https://www.biodiversitylibrary.org/item/87349#page/216/mode/1up |journal=Histoire de l'Académie Royale des Sciences, avec les Mémoires de Mathématique et de Physique pour la même Année |language=French |pages=50–56}}  Amontons described the relation between his new thermometer (which was based on the expansion and contraction of alcohol (''esprit de vin'')) and the old thermometer (which was based on air).  From p. 52:  ''" […] d'où il paroît que l'extrême froid de ce Thermométre seroit celui qui réduiroit l'air à ne soutenir aucune charge par son ressort, […] "''  ([…] whence it appears that the extreme cold of this [air] thermometer would be that which would reduce the air to supporting no load by its spring, […])  In other words, the lowest temperature which can be measured by a thermometer which is based on the expansion and contraction of air is that temperature at which the air's pressure ("spring") has decreased to zero.</ref> He used a scale that marked the boiling point of water at +73 and the melting point of ice at +{{frac|51|1|2}}, so that the zero was equivalent to about −240 on the Celsius scale.<ref name="AS2016">{{Cite EB1911|wstitle=Cold}}</ref> Amontons held that the absolute zero cannot be reached, so never attempted to compute it explicitly.<ref>{{Cite journal |last=Talbot |first=G. R. |last2=Pacey |first2=A. C. |date=1972 |title=Antecedents of thermodynamics in the work of Guillaume Amontons |journal=Centaurus |volume=16 |issue=1 |pages=20–40 |bibcode=1972Cent...16...20T |doi=10.1111/j.1600-0498.1972.tb00163.x}}</ref> The value of −240&nbsp;°C, or "431 divisions [in Fahrenheit's thermometer] below the cold of freezing water"<ref>{{Cite book |last=Martine |first=George |title=Essays Medical and Philosophical |date=1740 |publisher=A. Millar |location=London, England, UK |page=291 |chapter=Essay VI: The various degrees of heat in bodies |chapter-url=https://books.google.com/books?id=tSm2Ws6bg0oC&pg=PA291}}</ref> was published by [[George Martine (physician)|George Martine]] in 1740.

This close approximation to the modern value of −273.15&nbsp;°C<ref name="sib2115"/> for the zero of the air thermometer was further improved upon in 1779 by [[Johann Heinrich Lambert]], who observed that {{convert|-270|C|F K}} might be regarded as absolute cold.<ref>{{Cite book |last=Lambert |first=Johann Heinrich |title=Pyrometrie |year=1779 |location=Berlin, Germany |oclc=165756016}}</ref>

Values of this order for the absolute zero were not, however, universally accepted about this period. [[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 600 below. [[John Dalton]] in his ''Chemical Philosophy'' gave ten calculations of this value, and finally adopted −3,000&nbsp;°C as the natural zero of temperature.

===Charles's law===
From 1787 to 1802, it was determined by [[Jacques Charles]] (unpublished), [[John Dalton]],<ref>J. Dalton (1802), [https://books.google.com/books?id=3qdJAAAAYAAJ&pg=PA595 "Essay II. On the force of steam or vapour from water and various other liquids, both in vacuum and in air" and Essay IV.  "On the expansion of elastic fluids by heat" ], ''Memoirs of the Literary and Philosophical Society of Manchester'', vol. 8, pt. 2, pp. 550–574, 595–602.</ref> and [[Joseph Louis Gay-Lussac]]<ref>{{Citation |last=Gay-Lussac, J. L. |title=Recherches sur la dilatation des gaz et des vapeurs |work=Annales de Chimie |volume=XLIII |page=137 |year=1802 |author-link=Joseph Louis Gay-Lussac}}. [http://web.lemoyne.edu/~giunta/gaygas.html English translation (extract).]</ref> that, at constant pressure, ideal gases expanded or contracted their volume linearly ([[Charles's law]]) by about 1/273 parts per degree Celsius of temperature's change up or down, between 0° and 100°&nbsp;C. This suggested that the volume of a gas cooled at about −273&nbsp;°C would reach zero.

===Lord Kelvin's work===
After [[James Prescott Joule]] had determined the mechanical equivalent of heat, [[William Thomson, 1st Baron Kelvin|Lord Kelvin]] approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature that was independent of the properties of any particular substance and was based on [[Nicolas Léonard Sadi Carnot|Carnot]]'s theory of the Motive Power of Heat and data published by [[Henri Victor Regnault]].<ref>{{Cite journal |last=Thomson |first=William |author-link=Lord Kelvin |date=1848 |title=On an Absolute Thermometric Scale founded on Carnot's Theory of the Motive Power of Heat, and calculated from Regnault's observations. |url=https://www.biodiversitylibrary.org/item/87114#page/72/mode/2up |journal=Proceedings of the Cambridge Philosophical Society |volume=1 |pages=66–71}}</ref> It followed from the principles on which this scale was constructed that its zero was placed at −273&nbsp;°C, at almost precisely the same point as the zero of the air thermometer,<ref name="AS2016" /> where the air volume would reach "nothing". This value was not immediately accepted; values ranging from {{convert|-271.1|C}} to {{convert|-274.5|C}}, derived from laboratory measurements and observations of [[Atmospheric refraction#Astronomical refraction|astronomical refraction]], remained in use in the early 20th century.<ref>{{Citation |last=Newcomb |first=Simon |title=A Compendium of Spherical Astronomy |date=1906 |page=175 |place=New York |publisher=The Macmillan Company |oclc=64423127 |author-link=Simon Newcomb}}.</ref>

===The race to absolute zero===
{{see also|Timeline of low-temperature technology}}
[[File:Leiden - Kamerlingh Onnes Building - Commemorative plaque.jpg|thumb|upright=1.2|Commemorative plaque in Leiden]]
With a better theoretical understanding of absolute zero, scientists were eager to reach this temperature in the lab.<ref name="MyUser_YouTube_November_23_2016c">{{Cite web |title=ABSOLUTE ZERO – PBS NOVA DOCUMENTARY (full length) |url=https://www.youtube.com/watch?v=mTFRgosx4aQ&t=894s |url-status=dead |archive-url=https://web.archive.org/web/20170406015107/https://www.youtube.com/watch?v=mTFRgosx4aQ |archive-date=6 April 2017 |access-date=23 November 2016 |newspaper=YouTube}}</ref> By 1845, [[Michael Faraday]] had managed to liquefy most gases then known to exist, and reached a new record for lowest temperatures by reaching {{convert|-130|C|F K}}. Faraday believed that certain gases, such as oxygen, nitrogen, and [[hydrogen]], were permanent gases and could not be liquefied.<ref>[http://www.scienceclarified.com/Co-Di/Cryogenics.html Cryogenics]. Scienceclarified.com. Retrieved on 22 July 2012.</ref> Decades later, in 1873 Dutch theoretical scientist [[Johannes Diderik van der Waals]] demonstrated that these gases could be liquefied, but only under conditions of very high pressure and very low temperatures. In 1877, [[Louis Paul Cailletet]] in France and [[Raoul Pictet]] in Switzerland succeeded in producing the first droplets of [[liquid air]] at {{convert|-195|C|F K}}. This was followed in 1883 by the production of liquid oxygen {{convert|-218|C|F K}} by the Polish professors [[Zygmunt Wróblewski]] and [[Karol Olszewski]].

Scottish chemist and physicist [[James Dewar]] and Dutch physicist [[Heike Kamerlingh Onnes]] took on the challenge to liquefy the remaining gases, hydrogen and [[helium]]. In 1898, after 20 years of effort, Dewar was the first to liquefy hydrogen, reaching a new low-temperature record of {{convert|-252|C|F K}}. However, Kamerlingh Onnes, his rival, was the first to liquefy helium, in 1908, using several precooling stages and the [[Hampson–Linde cycle]]. He lowered the temperature to the boiling point of helium {{convert|-269|C|F K}}. By reducing the pressure of the liquid helium, he achieved an even lower temperature, near 1.5 K. These were the [[Lowest temperature recorded on Earth|coldest temperatures achieved on Earth]] at the time and his achievement earned him the [[Nobel Prize]] in 1913.<ref name="nobel">{{Cite web |title=The Nobel Prize in Physics 1913: Heike Kamerlingh Onnes |url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1913/onnes-bio.html |access-date=24 April 2012 |publisher=Nobel Media AB}}</ref> Kamerlingh Onnes would continue to study the properties of materials at temperatures near absolute zero, describing [[superconductivity]] and [[superfluids]] for the first time.