Does negative temperature really exist?

Synopsis

In 1951, the experimental measurements about negative temperature was first realized by Purcell and Pound. And later than that, theoretical concepts and hypotheses of negative temperature were proposed and discussed by many scientists. However, there still has been a debate on whether the negative temperature really exists. Generally speaking, there are two opposite theories: Gibbs entropy theory and Boltzmann entropy theory, which are against and in favor of the existence of negative temperature respectively, and a final conclusion hasn’t been drawn yet. Therefore, this problem still remains on an open question and needs to be finalized in the future. Anyway, I still believe this is an interesting topic that is worth discussing. In this presentation, we will go over the concept of negative temperature, both theoretically and experimentally, make a comparative analysis of the two different theories and also look into their effects on the Carnot cycle.