

So you thought absolute zero was absolute zero, huh? - opless
http://www.mpg.de/6776082/negative_absolute_temperature

======
dalke
No. Entropy is S = log of the number of microstates. Temperature is 1/T =
dS/dE. We are used to living in an open system, where only absolute zero has a
single microstate. In a closed system at the maximum amount of energy, there
is also only one microstate, so it entropy and temperature is zero. Drop the
energy slightly, more microstates are available, and dS/dE is negative,
leading to a negative temperature.

Bear in mind, it's been a long time since undergraduate level statistical
mechanics. I may have the details wrong. But this title sounds like needlessly
taunting. The actual title is simply "A temperature below absolute zero".

What's new about this work is "We have thus created the first negative
absolute temperature state for moving particles". Previous negative
temperatures were seen in things like spin-systems.

I would suggest the title "Moving particles with negative temperature".

~~~
gus_massa
I agree, the current title is bad because "absolute zero" is actually
"absolute zero". Negative temperatures are hotter than positive temperatures,
but it doesn't change the zero.

I like the proposed title or perhaps "Negative temperature in system with
moving particles".

