A Temperature Below Absolute Zero: Atoms at Negative Absolute Temperature Are the Hottest Systems

[sir pball]

6. It's more like games with the concept of "temperature"..

The world at large uses the classical concept of temperature, the average kinetic energy you mentioned. Boffins use the more rigorous and formal thermodynamic definition - the relationship between added energy and entropy of the system. Negative temperatures are paradoxical to the point of nonsense in a classical sense; in a thermodynamic sense, they simply mean that any energy added to the system will *decrease* the entropy.

http://en.wikipedia.org/wiki/Negative_temperature

We covered negative-absolutes in undergraduate thermodynamics, it's not a hard concept at all if it's explained clearly. The problem is the so-called "science journos" who don't seem to have the relatively basic education to understand what they're reporting on.