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Posts Tagged ‘thermodynamics’

Today I was greeted with the following line

Quantum Gas Temperature Drops Below Absolute Zero

This is the way the news about a quantum system that is effectively at negative temperature was reported in Wired. The thing is, negative temperatures are hotter than any finite positive temperature.

One can also check this fact in the Wikipedia entry for negative temperature. The simplest system that has an effective negative temperature is a laser: to get a negative temperature one just needs what is called a population inversion. 

In that report it was stated that

Previously absolute zero was considered to be the theoretical lower limit of temperature as temperature correlates with the average amount of energy of the substance’s particles.

The crucial mistake is the expression “Previously absolute zero was considered” which suggests that we have overturned theoretical physics knowledge on its head, because a new and revolutionary temperature below zero has been obtained! Moreover, we have measured systems with negative temperatures at least since the invention of the laser, and actually since the invention of the maser ( a laser in the microwave region).

The news is actually  well reported in Ars technica. In that article they actually explain facts correctly about how to think about negative temperatures.

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Most graduate students out there can at times feel a lot pressure to perform. Heck, that is not just graduate students. Pressure at work seems to be one of those things that most people can relate to and feel all the time. It gives rise to a lot of stress. I don’t have any good recipe for combating stress that is guaranteed, but cooking sometimes helps. Seeing as what I just wrote is not too funny, maybe I should get to the point and talk about Pressure cookers and as a bonus you get a cooking recipe (no peeking). When in doubt, pick a gadget and explain it, yes sireee. Besides, the explanations that I found on the internet about how pressure cookers work teeter on the edge of crackpottery. Not all are bad, but most don’t really say anything other than water boils at higher temperature at higher pressure which is correct, but unsatisfying. It’s like saying it just works that way.

My 3d rendition of a pressure cooker

My 3d rendition of a pressure cooker

(more…)

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