Negative absolute temperature is possible.
A Potassium-39 gas was held in a dipole trap and optical lattice to give it an 'inverted Boltzmann distribution' with limited high-energy states. It became hotter than infinite positive temperature.
https://www.mpg.de/research/negative-absolute-temperature
A Potassium-39 gas was held in a dipole trap and optical lattice to give it an 'inverted Boltzmann distribution' with limited high-energy states. It became hotter than infinite positive temperature.
https://www.mpg.de/research/negative-absolute-temperature
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