# Temperature lower than 0 k

1. Nov 1, 2009

### delplace

Is it possible to obtain a temperature lower than 0 K

2. Nov 1, 2009

3. Nov 1, 2009

why ?

4. Nov 1, 2009

### Pengwuino

The temperature is related to the energy of a particle. In a simplistic explanation, a particle can't have a negative energy, thus it can't have a negative temperature. It's more complicated than that though, so hopefully someone else can bring in more detail.

5. Nov 2, 2009

### delplace

thank you, :) but you know it depends on the reference you take. For ice, you can obtain solid water with a temperature lower than 0°C; for example I have ice at -18 °C in my fridge. At O K, all particles are freezed and I read that entropy = 0 (desorder is at its minimum). But I can not understand why we are not able to obtain -300 °C

6. Nov 2, 2009

### Pengwuino

Remember, Kelvin is an absolute scale, it begins at 0. Celsius and Fahrenheit are relative scales where their 0's are at convenient temperatures and not actual absolute 0's.

7. Nov 2, 2009

### delplace

Thank you Pengwuino :-) have a nice day

8. Nov 2, 2009

### elixirnova

I would imagine this topic is getting into theoretical physics than what is known and used everyday. I sure do not know anything about it, but it is interesting to ponder.

Unfortunately without anyone being able to do it there is nothing to be known about it hah. All theory and from what other posters have said I would assume theory says it isn't possible which is what my thermodynamics class assumes.

9. Nov 2, 2009

### delplace

Well, I agree with you, but I consider that limits can hide something unknown. Science history is full of that...
0 Kelvin is the limit where all subatomic particles stop moving. Why do they stop ? To stop something you need to brake. What is the force braking e- p+... Do photons continue moving at O K. I find this subject complex.

10. Nov 2, 2009

Staff Emeritus
No, it's the limit where the particles have the minimum energy. You can't have energy less than the minimum. (That's what minimum means)

11. Nov 2, 2009

### diazona

It's a little different for photons because they're massless particles - they never stop moving, but I suppose their energy would become zero at temperature 0K. For example, if you plug T=0 into the Planck radiation law, it shows you that the intensity of radiation becomes zero for all nonzero photon frequencies.

12. Nov 2, 2009

### delplace

Sorry but I thought that energy means movement in that case; kinetic energy giving rise to pressure. Is it true ?

13. Nov 2, 2009

### Pengwuino

Edited for nonsense.

Last edited: Nov 2, 2009
14. Nov 2, 2009

### delplace

Sorry but if photons move, it means for me they have kinetic energy ! is it wrong ?

15. Nov 2, 2009

Staff Emeritus
Yes they do. A photon's kinetic energy is given by E = pc.

16. Nov 2, 2009

### delplace

ouf !

17. Nov 2, 2009

### iamthegelo

Here's another take...I learned this from Feynman (The Lectures).

0 K is not possible because it violates the uncertainty principle. At 0 K it is assumed that there is no motion, therefore we know its definite position and velocity (= 0) hence, it violates the uncertainty principle.

18. Nov 2, 2009

### delplace

true ! but what does it mean ? it is not possible to reach 0 K ? is it a limit to the uncertainty principle ?
Definitely I find this question interesting !

19. Nov 2, 2009

### fatra2

Hi there,

One of the best approach to understand the absolute temperature is to consider a "perfect gas". A gas where the particles are considered point-particle, and where they do not interact with the others in the gas.

If you retract energy from these particles, the gas will contract. If you keep on taking energy the gas will contract some more. What happens if you take all the energy from the particle, the volume of the gas will become a point in space. At this time, the temperature can be easily calculated to be 0K.

Cheers

20. Nov 2, 2009

### delplace

ok, but by lowering the temperature of your gas, you will reach a change of state : gas --> liquide and finally solid !