# Below zero Kalvin

is this possible anywhere?
i know 0 kalvin is the lowest temperature possible that we've been able to attain. but is it possible that in outerspace where there is no heat from sun, that it gets below zero kalvin?

im just curious. im not sure wether this was "proven" to be the lowest possible temp or just the lowest temp we've been able to get. because i do know that no matter how hard you try to take heat out of something, more heat will just keep going back into it at the same time

Mapes
Homework Helper
Gold Member
According to current understanding, no temperature below 0 K exists. Also, it is not possible from a practical perspective to cool an object to 0 K (the process would take an infinite amount of time). The lowest humans have achieved is less than one billionth of a Kelvin, far colder than interstellar space, which is approximately 2.7 K.

Yes, we've never been able to get to 0K. Space is at about 2.7K like Mapes says because of the Cosmic Background Radiation.

The reason we can't get to 0K is because of statistical mechanics, basically.

http://en.wikipedia.org/wiki/0K

is this possible anywhere?
i know 0 kalvin is the lowest temperature possible that we've been able to attain. but is it possible that in outerspace where there is no heat from sun, that it gets below zero kalvin?

im just curious. im not sure wether this was "proven" to be the lowest possible temp or just the lowest temp we've been able to get. because i do know that no matter how hard you try to take heat out of something, more heat will just keep going back into it at the same time
Yes, it's possible, in a Laser system, for example.

Temperature can be defined as the partial derivative of energy with respect to entropy; in a system like a Laser, there is "population inversion" so entropy *decreases* instead of increase, when energy increases, so the absolute temperature is negative.

Mapes
Homework Helper
Gold Member
As Norman Ramsey has pointed out, objects with negative temperature are not colder than absolute zero, but instead hotter than anything else. Heat energy will always flow from a inversion state to a state that is closer to equilibrium; this is the characteristic of a high temperature, not a low temperature.

Andy Resnick
As lightarrow points out, the statistical-mechanical origin of 'temperature' can lead to counterintuitive results- for example, a population inversion in a two-state system corresponds to negative temperatures.

0 K should be considered a thermodynamic limit.

'0 K' is not acheivable due to the laws of thermodynamics, and it is also not true that 'all motion ceases at 0 K' due to the zero-point energy.

ok that is confusing that -k is actually hotter than +k. there are actually mechanical tests where they created a negative temperature? and it was hotter? thats strange

mgb_phys
Homework Helper
ok that is confusing that -k is actually hotter than +k. there are actually mechanical tests where they created a negative temperature? and it was hotter? thats strange
Probably better to think of it as a mis-use of the concept of temperature.
There are areas of solid state physics where you treat an electron as having negative mass - the maths works and you get the right answer - but it's not necessarily 'real'.

o. so basically we just arent technologically advanced enough to get the right formula to acheive the real -k (if it exists)

Mapes
Homework Helper
Gold Member
o. so basically we just arent technologically advanced enough to get the right formula to acheive the real -k (if it exists)
How did you conclude that from the responses? It's not a technological barrier.

mgb_phys