Coldest temperature recorded on Earth

The coldest natural temperature ever recorded on Earth was −89 °C (−128°F) at the Russian Vostok Station in Antarctica July 21, 1983. [http://www.globe.gov/fsl/html/templ.cgi?archive_atmos10271999&lang=en&nav=6] Lower temperatures have been achieved artificially, including a record cold temperature of 450pK, or 4.5×10^-10K at MIT in 2003.

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Early cooling

In 1904 Dutch scientist Kamerlingh Onnes created a special lab in Leiden with the aim of producing liquid helium. In 1908 he managed to lower the temperature to less than one degree above absolute zero, to less than −272.15 °C. Only in this exceptional cold will helium liquefy, the boiling point of helium being at −268.94 °C . Onnes received a Nobel Prize for his achievement.

Onnes method relied upon depressurising the subject gases, causing them to cool. This follows from the first law of thermodynamics;

$partial\; U\; =\; partial\; Q\; -\; partial\; W$

where "U" = internal energy, "Q" = heat added to the system, "W" = work done by the system.

Consider a gas in a box of set volume. If the pressure in the box is greater than atmospheric pressure, then upon opening the box our gas will do work on the surrounding atmosphere to expand. As this expansion is adiabatic and the gas has done work

$partial\; Q\; =\; 0$

$partial\; W\; >\; 0$

Now as the internal energy has decreased so has the temperature.

Modern cooling

In September 2003, MIT announced a record cold temperature of 450pK, or 4.5×10^-10 K in a Bose-Einstein condensate of sodium atoms. This was performed by Wolfgang Ketterle and colleagues at MIT. [Leanhardt, A. "et al." (2003) "Science" 301 1513. [http://physicsweb.org/article/news/7/9/8 Physicsweb news report] ]

As of November 2000, nuclear spin temperatures below 100 pK were reported for an experiment at the Helsinki University of Technology's Low Temperature Lab. However, this was the temperature of one particular type of motion—a quantum property called nuclear spin—not the overall average thermodynamic temperature for all possible degrees of freedom. [The experimental methods and results are presented in detail in T.A. Knuuttila’s Ph.D. thesis which can be accessed from [http://www.hut.fi/Yksikot/Kirjasto/Diss/2000/isbn9512252147/ this site] . Also the university’s press release on its achievement is [http://ltl.hut.fi/Low-Temp-Record.html here] ]

The current apparatus for achieving low temperatures has two stages. The first utilizes a helium dilution refrigerator to get to temperatures of millikelvins, then the next stage uses adiabatic nuclear demagnetisation to reach picokelvins.

Notes

See also

*Absolute zero
*Timeline of low-temperature technology
*Dilution refrigerator
*Adiabatic demagnetization
* [http://ltl.tkk.fi/Low-Temp-Record.html Details of HUT experiment, including details of the cryostat]