No, colder than that

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.)


  1. KingShamus »

    5 January 2013 · 7:25 am

    Is quantum physics just a way to try to subvert Einsteinian physics without a full-on revolution?

    I dunno, but it kinda sounds like it.

  2. Tatyana »

    5 January 2013 · 10:00 am

    …and, besides, my NYC (well, Brooklyn’s) building is heated as fiercely, as if we were living through Alaskan winter. The radiators are humming all day long, valves pushing up excess steam – and I have to keep the windows quarter-open to be able to breath.
    Or maybe it’s because my super is from warm and sunny Croatia…

  3. CGHill »

    5 January 2013 · 11:02 am

    Science is supposed to be self-subverting: when new data arrive, the theories are rewritten. (The guys who think they deserve a hand on the global thermostat are therefore the reactionaries.)

  4. rmtodd »

    5 January 2013 · 12:09 pm

    This isn’t really quantum stuff at all, just basic thermodynamics: basically, Boltzmann’s law says that the odds of an atom/particle/whatever being in a state of energy E is proportional to exp(-E/kT) where T is the temperature and k is a constant (called “Boltzmann’s constant”). If T is positive, that means you’re less likely to have particles in high energy states and more likely to have them in low energy states; if T is negative, the reverse happens and you’re more likely to have particles in high-energy states. This stuff is nothing new, Boltzmann law dates back to the late 19th century IIRC.

    The quantum stuff just comes in in trying to explain how you can come up with a system where most of the particles are in a high energy state instead of a low one. This isn’t terribly new either; the innards of any laser qualify, as when the laser’s ready to fire most of the atoms are in high-energy states vs. low-energy. So rather than something exotic, you’ve been having negative temperatures inside the laser diode of your CD player all this time and never even noticed.

  5. CGHill »

    5 January 2013 · 12:19 pm

    Geez. Too bad I can’t use some of that cold to cool down the CPU.

    I only vaguely remembered Boltzmann, and I didn’t make the connection to lasers. Dumb me. In this light, so to speak, I should thus consider this experiment heartening: perhaps my children’s children will have the coldest possible beer. (Not that they could drink it, exactly, but you know what I mean.)

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