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Yaver_Mbizi t1_j68ilyz wrote

Reply to comment by Varsect in In the absence of cosmic radiation, would an object placed in space eventually cool to absolute zero? by IHatrMakingUsernames

> Nevermind anything below that.

Well, it actually is possible to get below 0 K. It's pretty different to how one might imagine it, though - it's hotter than the hottest temperature, rather than colder than the coldest temperature for starters.

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AssCakesMcGee t1_j68rpdq wrote

That's not a conventional definition of temperature. A particle gaining energy but losing entropy is strange, but it's not what people think when you say 'negative temperature' since these particles are indeed, quite hot.

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Awhodothey t1_j693ug3 wrote

Yeah, because defining temperature is, in fact, not as straightforward as you might imagine.

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QuantumCakeIsALie t1_j69wxbt wrote

It's a very conventional way to define temperature in thermodynamics/physics.

Fun fact, you could create infinite energy if you could create a Carnot thermodynamical cycle that crosses + and - temperatures. That was a big issue with the concept of negative temperatures, until someone proved that it's impossible to create such a cycle to begin with.

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Putrid-Repeat t1_j6ae0nv wrote

Well it's not the layman definition of temperature but, it is the actual definition 😉

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sebzim4500 t1_j6ck159 wrote

What definition of temperature are you thinking of? The only definition I know is based on how the entropy changes with energy, which clearly makes negative temperature objects extremely hot.

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Varsect t1_j68j8hk wrote

Nature doesn't really factor in such stuff where entropy decreases (unless you're freezing stuff like crazy) and energy levels go crazy but uh, sure?

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Lyress t1_j6hjakx wrote

What do you mean nature doesn't factor that in? In what sense?

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XtremeGoose t1_j6b37o7 wrote

That's because temperature as it's classically defined has a coordinate asymptote (at 0K). The fix used in quantum thermodynamics is to talk about thermodynamic beta which is the inverse of temperature, where heat flows from a low thermodynamic beta to a higher. That fixes the coordinate issue and you can cross easily from the classically to the quantum.

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buff-equations t1_j68u129 wrote

Sounds like how a lot of computer counters work. -1? Nah that’s just 2 billion

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Chemomechanics t1_j69zwi7 wrote

As a side point, it's not. Such counters click down from 0 to the maximum count since they can't represent a negative. Temperature is different—arguably, the more fundamental parameter is the reciprocal 1/T, which is positive in most familiar systems but can in some circumstances swing below zero. This implies (very weirdly) that the temperature shoots up to ∞ and then to -∞. Again, it takes special effort to construct such a system; it won't occur around the house.

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