Right now? My poison is trying to figure out how the fuck negative absolute temperature works. Seriously it's all I can think about. @.@
It means the entropy- or level of disorder- of a system begins to drop as the energy is increased. Ironically negative 'temperature' is much 'hotter' than positive temperature.
A 'cold' collection of particles occupy an uneven range of energies, with many occupying very low energies. There are not many ways of rearranging the particles and the collection appearing the same, so it's low entropy. Like a sandcastle, you can't move the grains around much without the castle looking different.
As the collection is heated the particles occupy a more even range of energies. You can rearrange the particles in many ways and they will appeare similar, so the the entropy is high. Like a pile of sand. You can rearrange the sand however much you like now.
Increase the energy even further and a disproportionate amount of particles begin occuping very high energies and the distribution of particles at different energies is no longer all nice and smoothe. It's lumpy, just like the low energy particles so we're back at the sand castle scenario.
This is called negative temperature, I guess because temperature relates enetropy and energy, and the relationship you would expect is turned on its head in this kind of example.
