Chemistry student saying hi to everyone Just read http://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146 about negative temperature. I knew I wouldn't understand a single sentence of the actual Science paper, but I took a look at the Science perspective (Lincoln D. Carr) but I didn't understand it either. So I understand nothing about physics. But as far as I know, K=0 is defined as when all energy levels (vibrational movements etc) are in their respective ground state? So as little movements as possible. Then I don't really understand how you can get negative temperature. If I understand the Perspective (http://www.sciencemag.org/content/339/6115/42.summary if you have access) correctly, at temperatures above 0, particles have a distribution where only a few are in a high-energy state. I get that. But what's crazy is that to achieve negative temperatures, they mess with the particles so that MOST are in a high-energy state. But then I really don't follow what happens next. K=0 is already as little movement as possible (as there is no excited state), so how could you get below that? How would you explain this phenomena to someone with no physic knowledge? Thanks!!!