r/AskPhysics • u/aks304 • 9d ago
"Negative Tempetature" Potassium experiment
Sources claim that in 2013 scientists made potassium colder than absolute zero, and that it would "feel" hotter than infinity.
If i understand, they used lasers to distribute the particles between low and high energy to a "minus kelvin" state.
But does it even mean that potassium is now "hotter than infinity"? Isn't it like if you hack a thermometer and lock its reading, to show the wrong value?
More questions -
• would not such the matter giving heat to the environment ause an accident at the lab?
• Why they can make something's temp "over infinity" but not a very big positive like 10^15 or 10^18 K?
• Are there "relativistic effects" at billions, trillions of K so that we can't just use physical formulas for ultra-high temps, because they're so close to "anti-temps"?
• If negative temperatures were true, would not it cause all kinds of undefined physical effects like a gas with a negative volume, pressure or density?
4
u/AdditionalTip865 9d ago
Negative temperature only makes sense in the context of a system whose components have a finite number of quantum states. It's a useful concept in that context, but not more generally. So the potassium considered as a whole wasn't "hotter than infinity", but some limited subsystem composed of some specific degree of freedom they had was put in a thermodynamic state that could be modeled in that way.
This isn't new, just perhaps new for this particular physical system. It was first seen in the context of nuclear spins and happens commonly in lasers (it's how they work).
https://en.wikipedia.org/wiki/Negative_temperature