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WonderScience fact

Absolute zero, −273.15°C, is the lowest temperature possible: the point at which a substance has given up all the heat energy it can lose. Scientists have come within 38 trillionths of a degree of it, but the laws of physics say it can never be reached exactly.

Physics

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The story behind the card

In 1848 William Thomson, later Lord Kelvin, worked out that temperature has a natural floor at about −273°C, and the kelvin scale used by scientists starts there: 0 kelvin is absolute zero. Early in the 20th century the chemist Walther Nernst showed why it cannot be reached. This became the third law of thermodynamics: no process can remove the last of a system's heat in a finite number of steps. Even at absolute zero, particles would not be perfectly still, because quantum physics leaves them a minimum jiggle called zero-point energy. Close to absolute zero, matter behaves strangely: some metals carry electricity with no resistance at all, and liquid helium flows without friction. Deep space, warmed by the afterglow of the Big Bang, sits at about 2.7 kelvin. The record of 38 trillionths of a degree was set at the University of Bremen.

Türkçe oku
Mutlak sıfır, yani −273,15°C, olabilecek en düşük sıcaklıktır: Bir maddenin verebileceği bütün ısıyı vermiş olduğu noktadır. Bilim insanları bu sınıra bir derecenin 38 trilyonda biri kadar yaklaştı; ama fizik yasalarına göre oraya tam olarak varmak imkânsızdır.

1848'de, sonradan Lord Kelvin unvanını alan William Thomson, sıcaklığın yaklaşık −273°C'de doğal bir alt sınırı olduğunu hesapladı. Bilim insanlarının kullandığı kelvin ölçeği de oradan başlar: 0 kelvin mutlak sıfırdır. 20. yüzyılın başında kimyager Walther Nernst, bu sınıra neden varılamayacağını gösterdi. Termodinamiğin üçüncü yasası denen bu ilkeye göre hiçbir işlem, sonlu sayıda adımda bir sistemin ısısını sonuna kadar çekip alamaz. Mutlak sıfırda bile parçacıklar tamamen durmaz; kuantum fiziği onlara sıfır noktası enerjisi denen en küçük bir titreşimi bırakır. Mutlak sıfıra yaklaşıldıkça madde tuhaf davranmaya başlar: Bazı metaller elektriği hiç dirençsiz iletir, sıvı helyum sürtünmesiz akar. Büyük Patlama'dan kalan ışımayla ısınan uzay boşluğunun sıcaklığı yaklaşık 2,7 kelvindir. Bir derecenin 38 trilyonda birine kadar inen rekor, Bremen Üniversitesi'ndeki araştırmacılara ait.

Sources and further reading

Background reading: Absolute zero
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