# What is temperature

1. Mar 7, 2009

### ark

moleculars' motion are stoped at absolute zero.
according to the relative theory, does it mean the highest tempearture in our world is the one when all the molecular's velocity is equal to light's?

2. Mar 7, 2009

### Nabeshin

First, at absolute zero molecule's motion doesn't stop. This is a common misconception, and the reasoning is quantum-mechanical and you can read it at:
http://en.wikipedia.org/wiki/Absolute_zero

As far as the second point, no there is no highest temperature. You're right, a molecule's velocity cannot exceed the speed of light, but temperature is a measure of the average kinetic energy of the molecules. According to relativity there isn't a limit on kinetic energy, so temperature can in that sense be infinite.

I seem to recall someone mentioning that due to GR, if your energy density gets too high (corresponding to too high a temperature in a sense), things collapse into a black hole so this could provide a temperature upper bound, but I'm not sure about that.

Cheers!

3. Mar 8, 2009

### ark

temperature is too difficult for me to grasp.
:(

4. Mar 8, 2009

### ark

may i say kinetic energy of a substance at absolute zero is at the lowest level that it can't transfer to any other substance.

kinetic energy is defined as E=1/2*m*v^2.
E=0 only if v=0.
molecule's motion doesn't stop at absolute zero. that means v>0, and E>0.
so, may i say absolute zero is a 'relative' lowest energy level accorrding to the zeroth law of thermodynamics.
and is it possible has the TRUE absolute zero that all molecule's motions was stopped?

5. Mar 8, 2009

### Nabeshin

I think you should read the article again. Also, if you're going to be wondering about the upper limit on temperature you should use the relativistic definition of KE:
$$E_{k}=mc^{2}(\gamma-1)$$
So you can see that there is no upper bound on kinetic energy.

6. Mar 9, 2009

### Archosaur

Except for the fact that there is a finite amount of energy in the universe.... right?

7. Mar 9, 2009

### cesiumfrog

Ignoring quantum and relativistic effects, your original post was pretty much correct.

8. Mar 9, 2009

### jobyts

The highest possible temperature, called the Planck temperature, is equal to 10^32 degrees Kelvin.

9. Mar 10, 2009

### cragar

there would haft to be an absolute temperature cause there is only so much energy in the universe to fuel it. we can't creat more energy but we can transform it.