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Comment by jpdoctor | Hacker News Reader

The usual explanation of such things: T is not so important as 1/T. So negative abs temp is achieved by going through +infinity temp and coming back via -infinity temp.

Note that this is only allowed in systems which have states that are bounded in energy. The usual example is a laser: When in inversion, its absolute temperature (of the electron population) is negative.

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If you'll allow a car analogy - isn't this like saying backing up is slower than being parked?

Yes, it's a negative number in the context of a forward velocity vector, but it's a higher energy state.

No. The problem is that for historical reasons we choose the wrong scale and it's a little late to change all the books.

We choose to measure the temperature in this way

  (infinityK) ... ->- 10K ->- 1K ->- .1K ->- ... | 0K(impossible) | ... ->-.1K ->- -1K  ->- -10K ->- ... (infinityK)

Where ->- means hotter

In this scale 0K is impossible and impassable. But infinityK is possible (only one unsigned infinity) and some kind of systems when they get hotter they can pass from very "big" positive temperatures to very "big" negative temparatures.

And the negative values are hotter than the positive. For example: -.1 is hotter than -10K that is hotter than 10K that is hotter than .1K

It's (theoretically) better to measure beta=1/temperature (the usual notation is beta) In this way:

  (infinity/K) ... -<- 10/K -<- 1/K -<- .1/K -<- ... 0/K(possible) ... -<-.1/K -<- -1K  -<- -10K -<- ... (infinityK)

Where -<- means hotter

In this scale infinity/K is impossible as expected. But 0/K is possible. And the order is the correct order hotter=less_than. Using beta they are ordered more intuitively. Hotter means moving to the right in the line.

Thank you; this helped clarify things quite a bit.

isn't negative absolute temperature an oxymoron?

No. Temperature is just the relationship between entropy and energy: ∂S/∂E. This relationship can be negative.

Ok, this is at atomical level, it is possible to increase the energy of the system till you freeze the electrons? What would happen then if the particles are organized at subatomical levels?. And below that? Could it be a way to study matter properties?(in place of the cern way)

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