Whatever you were thinking — inside of a meat locker, the dark side of the moon, a New York apartment with a chintzy landlord — we’re talking colder than that. Colder, even, than zero degrees Kelvin. If this pans out, absolute zero won’t be so absolute anymore:
[Y]ou read off the temperature of a system from a graph that plots the probabilities of its particles being found with certain energies. Normally, most particles have average or near-average energies, with only a few particles zipping around at higher energies. In theory, if the situation is reversed, with more particles having higher, rather than lower, energies, the plot would flip over and the sign of the temperature would change from a positive to a negative absolute temperature, explains Ulrich Schneider, a physicist at the Ludwig Maximilian University in Munich, Germany.
Ah. Quantum stuff. No wonder it seems odd.
Schneider and his colleagues reached such sub-absolute-zero temperatures with an ultracold quantum gas made up of potassium atoms. Using lasers and magnetic fields, they kept the individual atoms in a lattice arrangement. At positive temperatures, the atoms repel, making the configuration stable. The team then quickly adjusted the magnetic fields, causing the atoms to attract rather than repel each other. “This suddenly shifts the atoms from their most stable, lowest-energy state to the highest possible energy state, before they can react,” says Schneider. “It’s like walking through a valley, then instantly finding yourself on the mountain peak.”
This is another one of those cases where it sounds plausible enough, to the extent that anything sounds plausible after quantum effects. Then again, we thought the speed of light, another absolute, had been exceeded — for a while, anyway.
(Via this @syaffolee tweet.)