I’m a sucker for good (or bad) physics puns. And the latest viral physics paper (arXiv preprint) allows endless opportunities for them. It’s actually about a system with a negative temperature!

Negative temperature sounds pretty cool, but I have to admit, at first I didn’t think this was that big of a deal to anyone except condensed matter physicists. Sure, it could pave the way for some neat technological applications, but that’s far in the future. The idea of negative temperature itself is old news among physicists; in fact, this isn’t even the first time negative temperatures have been produced in a lab. But maybe you’re not a physicist. Maybe you’ve never heard about negative temperature. Well, you’re in luck, because in this post I’m going to explain what negative temperature means and why this experiment is actually such a hot topic. ⌐■_■

On Temperature

To understand negative temperature, we have to go all the way back to the basics. What is temperature, anyway? Even if you’re not entirely sure of the technical definition, you certainly know it by its feel. Temperature is what distinguishes a day you can walk …