Can a population inversion truly result in negative temperature?

[floped perfect]

If an atom was below zero Kelvins, or at zero Kelvins, would it be possible that the electrons would lose their energy level completely and the atom would collapse?

 

[kirovman]

If an atom was below zero Kelvins, or at zero Kelvins, would it be possible that the electrons would lose their energy level completely and the atom would collapse?

Below zero Kelvin? You are suggesting negative temperature.

That's not possible I'm afraid. You would have to take more thermal energy out of the atom than it had in it in the first place.

I read something about negative temperature in Quantum Statistics, but I think it was a model, not a reality.

 

[ZapperZ]

If an atom was below zero Kelvins, or at zero Kelvins, would it be possible that the electrons would lose their energy level completely and the atom would collapse?

The solutions to the atomic energy level are solved, in principle, at T=0K. When we say this is the GROUND STATE state energy level, we mean it.

Zz.

 

[Astronuc]

There is a reason that we call T=0 K "Absolute Zero".

Temperature is a measure of "atomic" kinetic energy.

 

[dextercioby]

That's not possible I'm afraid. You would have to take more thermal energy out of the atom than it had in it in the first place.

I read something about negative temperature in Quantum Statistics, but I think it was a model, not a reality.

It was a model describing reality... Yes,under certain conditions,you can obtain negative temperatures.

Daniel.

 

[marlon]

Below zero Kelvin? You are suggesting negative temperature.

That's not possible I'm afraid.

Yes it can be...But then again that is very exotic. For example in some spin-systems (i mean many atoms and we only look at spin spin interactions) absolute NEGATIVE temperatures can arise. These temperatures are no really negative, but they need to be looked at as bigger then infinity...


The conditions for this to occur are for example that the spin-spin relaxation time is little compared to the spin lattice relaxation time. This means that the spins mutually interact long before thermal degrees of freedom come into play...


regards
marlon

 

[misogynisticfeminist]

hey, this is really interesting. Is there a name for this phenomenon? Can i have more information or articles regarding this? Thanks alot...

 

[ohwilleke]

To even think about a subzero kelvin temperature you pretty much have to define what kelvin temperature means. The customary definition of kelvin temperature is incapable of being below zero in any possible configuration of atoms with any possible momenta.

 

[marlon]

http://boojum.hut.fi/research/magnetism/zero.html

marlon

 

[ohwilleke]

http://boojum.hut.fi/research/magnetism/zero.html

marlon

From the above link:

A rather unique property of nuclear magnets is the possibility of producing negative spin temperatures. This does not violate the laws of thermodynamics, i.e. inaccessibility of the absolute zero, because the negative side of the temperature scale is reached by a rapid magnetic field reversal. During this process the spin temperature is strictly speaking ill defined, but can be thought of evolving via infinity. In a sense, negative absolute temperatures are not colder than zero but actually hotter than infinite temperature!

 

[humanino]

Yes it can be...But then again that is very exotic. For example in some spin-systems (i mean many atoms and we only look at spin spin interactions) absolute NEGATIVE temperatures can arise. These temperatures are no really negative, but they need to be looked at as bigger then infinity...


The conditions for this to occur are for example that the spin-spin relaxation time is little compared to the spin lattice relaxation time. This means that the spins mutually interact long before thermal degrees of freedom come into play...


regards
marlon

true my dear Godfather
the right quantity to look is $$-\frac{1}{kT}$$ which remains continuous in that case. Somehow, negative temperature are "higher" than positive temperature, and in reverse order (so the highest of all is near 0 and negative) if I remember correctly. In any case, it is a very simple exercise of statistical physics

 

[kirovman]

Yes it can be...But then again that is very exotic. For example in some spin-systems (i mean many atoms and we only look at spin spin interactions) absolute NEGATIVE temperatures can arise. These temperatures are no really negative, but they need to be looked at as bigger then infinity...


The conditions for this to occur are for example that the spin-spin relaxation time is little compared to the spin lattice relaxation time. This means that the spins mutually interact long before thermal degrees of freedom come into play...


regards
marlon

Yes that's the one I saw in Quantum Statistics. Only touched on it briefly though, and I didn't bother learning it for the exam (luckily never turned up).
The lecturer was awful for teaching this material!

I'm quite interested now though, I will go back and read a bit more.

 

[Creator]

To even think about a subzero kelvin temperature you pretty much have to define what kelvin temperature means. The customary definition of kelvin temperature is incapable of being below zero in any possible configuration of atoms with any possible momenta.

True,... just depends on how you define temperature.

Before the development of the laser, population inversion was commonly referred to as a negative temperature based on standard thermodynamics.

Here's quote from an article:
"Simply adding energy by thermally agitating the medium is not sufficient (under thermodynamic equilibrium) to produce a population inversion, because heat only increases the average energy of the population, but does not increase the number of species in the excited state relative to that in the lower state. The ratio of the number of atoms at two energy levels (1 and 2) under thermodynamic equilibrium is given by the following equation:

N2/N1 = exp[- (E2 - E1) / kT]
where N(1) and N(2) are the number of atoms in level 1 and level 2, respectively, E(1) and E(2) are the energies of the two levels, k is the Boltzmann constant, and T is the temperature in kelvins. As demonstrated by the equation, at thermodynamic equilibrium, N(2) can be greater than N(1) only if the temperature is a negative number. Before the research describing maser and laser action was published, physicists referred to a population inversion as a negative temperature, which was symbolic of their view that any condition other than thermodynamic equilibrium was unlikely to be sustained..."