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This seems like a farce...

Quantum gas goes below absolute zero
Ultracold atoms pave way for negative-Kelvin materials.
by Zeeya Merali, Nature News 03 January 2013, DOI: 10.1038/nature.2013.12146

I have seen several recent articles like this one and I am extremely skeptical. Perhaps my skepticism is based upon an ignorance of physical principles, but I am less offended by apparent violations of the speed of light than by considering that temperatures below absolute zero could exist. I have studied under scientists who were using advanced techniques and vast amounts of energy to get small samples cooled down to a few nanokelvin. The physics seems to imply that if a sample were to reach zero, even the nuclear forces cohering the particles would cease. This was hypothesized in hushed tones, in awe and reverence. Now this article (which seems akin to scientific blasphemy) is causing an existential crisis. What is the deal with negative absolute temperature?

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    $\begingroup$ There's the subtle but all-important issue of defining "temperature". Under the most common (Boltzmann) definition, negative absolute temperatures are possible and are actually "above infinite temperature". However, using the Gibbs definition, only positive temperatures seem possible. There's an extensive Wikipedia article on the matter, as well as several questions in the Physics.SE site. $\endgroup$ – Nicolau Saker Neto Jun 25 '15 at 2:09
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    $\begingroup$ I wrote a blog post about it here: proteinsandwavefunctions.blogspot.dk/2013/01/… $\endgroup$ – Jan Jensen Jun 25 '15 at 13:25
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    $\begingroup$ I'm voting to close this question as off-topic because it belongs to Physics.SE. $\endgroup$ – Wildcat Nov 22 '15 at 16:22
  • $\begingroup$ I want to add that thermodynamics tells us that we cannot reach absolute zero. Negative temperatures doesn't violate that statement. $\endgroup$ – DSVA Nov 1 '17 at 20:54
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    $\begingroup$ Negative temperatures are very much a thing, even with applications such as lasers. Such a system is not colder than absolute zero. Quite the opposite. en.wikipedia.org/wiki/Negative_temperature $\endgroup$ – Oscar Lanzi Nov 1 '17 at 22:38
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It is a quirk in how temperature would be measured using quantum mechanics. In general thermodynamics is about "bulk" properties and ignores quantum mechanics. Resolving these sort of quirks is why it would be so wonderful to have a theory of everything that would tie all the forces together.

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