Editing Absolute zero (section)

==Very low temperatures==
[[File:Boomerang nebula.jpg|thumb|right|The rapid expansion of gases leaving the [[Boomerang Nebula]], a bi-polar, filamentary, likely proto-planetary nebula in Centaurus, has a temperature of 1&nbsp;K, the lowest observed outside of a laboratory.]]

The average temperature of the universe today is approximately {{convert|2.73|K|C F|abbr=on}}, based on measurements of [[cosmic microwave background]] radiation.<ref>{{Cite web |last=Kruszelnicki, Karl S. |date=25 September 2003 |title=Coldest Place in the Universe 1 |url=http://www.abc.net.au/science/articles/2003/09/25/947116.htm |access-date=24 September 2012 |publisher=Australian Broadcasting Corporation}}</ref><ref>{{Cite web |date=3 August 2004 |title=What's the temperature of space? |url=http://www.straightdope.com/columns/read/2172/whats-the-temperature-of-space |access-date=24 September 2012 |publisher=The Straight Dope}}</ref> Standard models of the [[future of an expanding universe|future expansion of the universe]] predict that the average temperature of the universe is decreasing over time.<ref>{{Cite journal |last=John |first=Anslyn J. |date=25 August 2021 |title=The building blocks of the universe |journal=HTS Teologiese Studies/Theological Studies |volume=77 |issue=3 |doi=10.4102/hts.v77i3.6831 |s2cid=238730757 |doi-access=free}}</ref> This temperature is calculated as the mean density of energy in space; it should not be confused with the mean [[electron temperature]] (total energy divided by particle count) which has increased over time.<ref>{{Cite news |date=10 November 2020 |title=History of temperature changes in the Universe revealed—First measurement using the Sunyaev-Zeldovich effect |url=https://www.ipmu.jp/en/20201110-CosmicThermal_History |language=en |agency=Kavli Institute for the Physics and Mathematics of the Universe}}</ref>

Absolute zero cannot be achieved, although it is possible to reach temperatures close to it through the use of [[Evaporative cooling (atomic physics)|evaporative cooling]], [[cryocooler]]s, [[dilution refrigerator]]s,<ref>{{Cite journal |last=Zu |first=H. |last2=Dai |first2=W. |last3=de Waele |first3=A. T. A. M. |year=2022 |title=Development of Dilution refrigerators – A review |journal=Cryogenics |volume=121 |doi=10.1016/j.cryogenics.2021.103390 |issn=0011-2275 |s2cid=244005391}}</ref> and [[Magnetic refrigeration#Nuclear demagnetization|nuclear adiabatic demagnetization]]. The use of [[laser cooling]] has produced temperatures of less than a billionth of a kelvin.<ref>{{Cite web |last=Catchpole, Heather |date=4 September 2008 |title=Cosmos Online – Verging on absolute zero |url=http://www.cosmosmagazine.com/features/online/2176/verging-absolute-zero |url-status=dead |archive-url=https://web.archive.org/web/20081122144155/http://www.cosmosmagazine.com/features/online/2176/verging-absolute-zero |archive-date=22 November 2008}}</ref> At very low temperatures in the vicinity of absolute zero, matter exhibits many unusual properties, including [[superconductivity]], [[superfluidity]], and [[Bose–Einstein condensate|Bose–Einstein condensation]]. To study such [[phenomena]], scientists have worked to obtain even lower temperatures.
* In November 2000, [[nuclear spin]] temperatures below {{nowrap|100 picokelvin}} were reported for an experiment at the [[Helsinki University of Technology]]'s Low Temperature Lab in [[Espoo]], [[Finland]]. However, this was the temperature of one particular [[Degrees of freedom (physics and chemistry)|degree of freedom]]—a [[quantum]] property called nuclear spin—not the overall average [[thermodynamic temperature]] for all possible degrees in freedom.<ref>{{Cite book |last=Knuuttila |first=Tauno |url=http://www.hut.fi/Yksikot/Kirjasto/Diss/2000/isbn9512252147 |title=Nuclear Magnetism and Superconductivity in Rhodium |publisher=Helsinki University of Technology |year=2000 |isbn=978-951-22-5208-4 |location=Espoo, Finland |access-date=11 February 2008 |archive-url=https://web.archive.org/web/20010428173229/http://www.hut.fi/Yksikot/Kirjasto/Diss/2000/isbn9512252147/ |archive-date=28 April 2001 |url-status=dead}}</ref><ref>{{Cite press release |title=Low Temperature World Record |date=8 December 2000 |publisher=Low Temperature Laboratory, Teknillinen Korkeakoulu |url=http://ltl.hut.fi/Low-Temp-Record.html |access-date=11 February 2008 |url-status=live |archive-url=https://web.archive.org/web/20080218053521/http://ltl.hut.fi/Low-Temp-Record.html |archive-date=18 February 2008}}</ref>
* In February 2003, the [[Boomerang Nebula]] was observed to have been releasing gases at a speed of {{Convert|500000|km/h|abbr=on}} for the last 1,500 years. This has cooled it down to approximately 1&nbsp;K, as deduced by astronomical observation, which is the lowest natural temperature ever recorded.<ref>{{Cite journal |last=Sahai |first=Raghvendra |last2=Nyman, Lars-Åke |year=1997 |title=The Boomerang Nebula: The Coldest Region of the Universe? |journal=The Astrophysical Journal |volume=487 |issue=2 |pages=L155–L159 |bibcode=1997ApJ...487L.155S |doi=10.1086/310897 |s2cid=121465475 |doi-access=free |hdl=2014/22450}}</ref>
* In November 2003, [[90377 Sedna]] was discovered and is one of the coldest known objects in the Solar System, with an average surface temperature of {{cvt|-240|C|K F|sigfig=2}},<ref>{{Cite web |title=Mysterious Sedna {{!}} Science Mission Directorate |url=https://science.nasa.gov/science-news/science-at-nasa/2004/16mar_sedna/#:~:text=NASA%27s%20new%20Spitzer%20Space%20Telescope%20also%20looked%20for,minus%20240%20degrees%20Celsius%20(minus%20400%20degrees%20Fahrenheit). |access-date=25 November 2022 |website=science.nasa.gov}}</ref> due to its extremely far orbit of 903 [[astronomical unit]]s.
* In May 2005, the [[European Space Agency]] proposed research in space to achieve [[femto-|femtokelvin]] temperatures.<ref>{{Cite web |title=Scientific Perspectives for ESA's Future Programme in Life and Physical sciences in Space |url=http://www.esf.org/fileadmin/Public_documents/Publications/Scientific_Perspectives_for_ESA_s_Future_Programme_in_Life_and_Physical_Sciences_in_Space.pdf |url-status=dead |archive-url=https://web.archive.org/web/20141006024523/http://www.esf.org/fileadmin/Public_documents/Publications/Scientific_Perspectives_for_ESA_s_Future_Programme_in_Life_and_Physical_Sciences_in_Space.pdf |archive-date=6 October 2014 |access-date=28 March 2014 |website=esf.org}}</ref>
* In May 2006, the Institute of Quantum Optics at the [[University of Hannover]] gave details of technologies and benefits of femtokelvin research in space.<ref>{{Cite web |title=Atomic Quantum Sensors in Space |url=http://www.physics.ucla.edu/quantum_to_cosmos/q2c06/Ertmer.pdf |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/http://www.physics.ucla.edu/quantum_to_cosmos/q2c06/Ertmer.pdf |archive-date=9 October 2022 |website=University of California, Los Angeles}}</ref>
* In January 2013, physicist Ulrich Schneider of the [[University of Munich]] in Germany reported to have achieved temperatures formally below absolute zero ("[[negative temperature]]") in gases. The gas is artificially forced out of equilibrium into a high potential energy state, which is, however, cold. When it then emits radiation it approaches the equilibrium, and can continue emitting despite reaching formal absolute zero; thus, the temperature is formally negative.<ref>{{Cite web |date=3 January 2013 |title=Atoms Reach Record Temperature, Colder than Absolute Zero |url=http://www.livescience.com/25959-atoms-colder-than-absolute-zero.html |website=livescience.com}}</ref>
* In September 2014, scientists in the [[CUORE]] collaboration at the [[Laboratori Nazionali del Gran Sasso]] in Italy cooled a copper vessel with a volume of one cubic meter to {{cvt|0.006|K|C F|sigfig=6}} for 15 days, setting a record for the lowest temperature in the known universe over such a large contiguous volume.<ref>{{Cite news |title=CUORE: The Coldest Heart in the Known Universe. |url=http://www.interactions.org/cms/?pid=1034217 |access-date=21 October 2014 |publisher=INFN Press Release}}</ref>
* In June 2015, experimental physicists at [[MIT]] cooled molecules in a gas of sodium potassium to a temperature of 500 nanokelvin, and it is expected to exhibit an exotic state of matter by cooling these molecules somewhat further.<ref>{{Cite web |title=MIT team creates ultracold molecules |url=https://newsoffice.mit.edu/2015/ultracold-molecules-0610 |url-status=dead |archive-url=https://web.archive.org/web/20150818112454/http://newsoffice.mit.edu/2015/ultracold-molecules-0610 |archive-date=18 August 2015 |access-date=10 June 2015 |website=Massachusetts Institute of Technology, Massachusetts, Cambridge}}</ref>
* In 2017, [[Cold Atom Laboratory]] (CAL), an experimental instrument was developed for launch to the [[International Space Station]] (ISS) in 2018.<ref>{{Cite news |date=5 September 2017 |title=Coolest science ever headed to the space station |url=https://www.science.org/content/article/coolest-science-ever-headed-space-station |access-date=24 September 2017 |work=Science {{!}} AAAS |language=en}}</ref> The instrument has created extremely cold conditions in the [[microgravity]] environment of the ISS leading to the formation of [[Bose–Einstein condensate]]s. In this space-based laboratory, temperatures as low as {{nowrap|1 picokelvin}} are projected to be achievable, and it could further the exploration of unknown [[Quantum mechanics|quantum mechanical]] phenomena and test some of the most fundamental [[laws of physics]].<ref name="NASA Cold Atom Laboratory Mission">{{Cite web |date=2017 |title=Cold Atom Laboratory Mission |url=http://coldatomlab.jpl.nasa.gov/mission/ |url-status=dead |archive-url=https://web.archive.org/web/20130329092843/http://coldatomlab.jpl.nasa.gov/mission/ |archive-date=29 March 2013 |access-date=22 December 2016 |website=Jet Propulsion Laboratory |publisher=NASA}}</ref><ref name="CALnasa">{{Cite web |date=26 September 2014 |title=Cold Atom Laboratory Creates Atomic Dance |url=http://www.nasa.gov/mission_pages/station/research/news/cold_atom_lab/ |url-status=dead |archive-url=https://web.archive.org/web/20210708201720/https://www.nasa.gov/mission_pages/station/research/news/cold_atom_lab/ |archive-date=8 July 2021 |access-date=21 May 2015 |website=NASA News}}</ref>
* The current world record for effective temperatures was set in 2021 at {{nowrap|38 picokelvin}} through matter-wave lensing of rubidium [[Bose–Einstein condensate]]s.<ref name=":0">{{Cite journal |last=Deppner |first=Christian |last2=Herr |first2=Waldemar |last3=Cornelius |first3=Merle |last4=Stromberger |first4=Peter |last5=Sternke |first5=Tammo |last6=Grzeschik |first6=Christoph |last7=Grote |first7=Alexander |last8=Rudolph |first8=Jan |last9=Herrmann |first9=Sven |last10=Krutzik |first10=Markus |last11=Wenzlawski |first11=André |date=30 August 2021 |title=Collective-Mode Enhanced Matter-Wave Optics |url=https://link.aps.org/doi/10.1103/PhysRevLett.127.100401 |journal=Physical Review Letters |language=en |volume=127 |issue=10 |pages=100401 |bibcode=2021PhRvL.127j0401D |doi=10.1103/PhysRevLett.127.100401 |issn=0031-9007 |pmid=34533345 |s2cid=237396804}}</ref>