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whoelsebutme
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Can we obtain temperatures below absolute zero i.e. 0 Kelvin?
First Question. This negative temperature concept appears to be limited to "spin" degree of freedom systems--is this correct ? Second Question. Since a spin system with negative absolue temperature should be hotter than a positive temperature system, would you predict that the outcome of linking two quantum spin engines ( one with negative absolute temperature, and the second with positive) would be an engine with efficiency > 1 ?ZapperZ said:If you look at how "temperature" is defined within statistical mechanics, you'll see that, using the partition function methodology, there CAN be situations where you can get a negative absolute temperature. While this is not a system under equilibrium, you can still get such temperature based on an inverse population of states.
http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/neg_temperature.htmlZz.
If you mean 'more energy out than in, then the answer is a definite 'no'. That would be a perpetual motion machine. :yuck:Rade said:would be an engine with efficiency > 1 ?
Rade said:First Question. This negative temperature concept appears to be limited to "spin" degree of freedom systems--is this correct ?
Second Question. Since a spin system with negative absolue temperature should be hotter than a positive temperature system, would you predict that the outcome of linking two quantum spin engines ( one with negative absolute temperature, and the second with positive) would be an engine with efficiency > 1 ?
There's only so much energy in the universe, though. Doesn't that also imply that there's a limit to how much you can channel into heating something?lalbatros said:There is no upper bound in energy and therefore no upper bound on temperature.
There's only so much energy in the universe, though.
ZapperZ said:It doesn't have to be exclusively only for spin systems. It just happens that this would be the easiest system to illustrate.
Sure! Under certain non-equilibrium situation, you can violate the 2nd law. There's nothing here that contradicts thermodynamics since this all came out of thermodynamics predictions. However, such a system doesn't last very long, and if you calculate the Helmholtz free energy out of such a system, you'll be hard pressed to use it to do any work (a fact that most quacks tend to overlook).
Zz.
Rade said:First Question. This negative temperature concept appears to be limited to "spin" degree of freedom systems--is this correct ?
Second Question. Since a spin system with negative absolue temperature should be hotter than a positive temperature system, would you predict that the outcome of linking two quantum spin engines ( one with negative absolute temperature, and the second with positive) would be an engine with efficiency > 1 ?
lalbatros said:Let's put two systems in thermal contact.
One (A) with a positive temperature.
A second (B) with a negative temperature.
How can we predict the heat flux?
I could imagine heat going from B to A simply because the number of microstates of A+B could be higher so. Indeed, less energy in B would mean more microstates for B and eventually also for A+B.
Is it possible that heat goes from cold (B) to hot (A) ?
Is it compatible with the second law ?
Michel
Absolute zero is the lowest possible temperature on the Kelvin scale, at which point all molecular motion in a substance ceases. It is the point at which a substance has the least amount of thermal energy and cannot get any colder.
No, absolute zero is considered a theoretical concept and cannot be reached in real life. This is because it would require a substance to have zero thermal energy, which is not possible according to the laws of thermodynamics.
No, temperature cannot go below 0 Kelvin. This is because the Kelvin scale is based on the concept of absolute zero, so there is no value below 0 Kelvin.
At absolute zero, all molecular motion in a substance stops, so matter would have no kinetic energy. This would cause substances to become extremely brittle and their properties would change significantly.
Yes, there are substances that can exist at temperatures close to absolute zero, such as certain gases and supercooled liquids. These substances have very low thermal energy and can exhibit unique properties at these extreme temperatures.