# Lowest possible temperature

1. Oct 27, 2012

### sreerajt

Hello friends... Please answer to this question…
Lowest possible temperature is -2730C. Why?

2. Oct 27, 2012

### Drakkith

Staff Emeritus
Actually it's -273C, not -2730. The answer is simply that since temperature is the measure of an objects internal energy there simply exists a lowest point at which you cannot reduce the energy of that object any further.

3. Oct 28, 2012

### sreerajt

it was a small mistake 0C meant degree centigrade..
i heard that it stems out from Charles's law

4. Oct 29, 2012

### Staff: Mentor

You can use this law to estimate the lowest possible temperature, but its existence does not follow from gas laws, it is much more fundamental.

Thermodynamics allows to assign a negative temperature to some systems (in the kelvin scale, where 0 is the coldest possible temperature), but those are hotter than anything with a positive temperature.

5. Oct 29, 2012

### sreerajt

sorry... What? what does that last sentence says?

6. Oct 29, 2012

### FeynmanIsCool

As Drakkith stated, internal energy can only be reduced so much. -273C just happens to be that number. As to WHY it is that number cant really be answered, that's just the way nature cooked it up! I'm not sure the number has any special significance.

7. Oct 30, 2012

### Staff: Mentor

Just ignore it. It requires some knowledge about thermodynamics to understand, and I wrote it small as it is not really relevant here.

8. Oct 30, 2012

### pabloenigma

Or,more humbly,thats like what we have cooked our Centigrade system to be.It looks more natural in the more fundamental Kelvin scale,isnt it?
Infact,you will find,Kelvin had remarked,a logarithmic scale would have been better,with temperatures running from minus infinity to plus infinity.However,we didnt switch to that one because all engineering and scientific data are compiled in this one

9. Oct 30, 2012

### AbsoluteZer0

The lowest possible temperature is -273.15C or 0K. Why this is can be interpreted using the Uncertainty Principle. This principle states that you cannot know both the momentum and the position of a particle without some degree of uncertainty. Kinetic molecular theory states that all atoms have some degree of energy and are perpetually in motion. At -273.15C, absolute zero (my namesake,) the given atom or particle has no energy left and therefore is not in motion. If it is not in motion then you can find both its velocity and its position, which cannot happen according to the Uncertainty Principle.

10. Oct 30, 2012

### Drakkith

Staff Emeritus
I don't believe this is correct. At absolute zero a material is in it's ground state, which is the minimum energy it can possess. Also, it is necessary to look further into Quantum Mechanics to really see what happens to a material near absolute zero. For example electrons in a metal still have high velocities even at absolute zero thanks to Fermi Energy.

11. Oct 31, 2012

### AJ Bentley

It looks like the definition of the Kelvin is still mired in the 19th century. There's an ongoing proposal to redefine it based on Boltzmann's constant.

Maybe discussing the QM aspects is over-egging the pudding.

12. Nov 1, 2012

### Staff: Mentor

Well, that is just a re-definition of the Kelvin scale to avoid its dependence on water. A unit which depends on isotopic compositions of ocean water is... odd. It does not change the lower bound: 0 K would stay 0 K.

Only in classical physics, in QM this is not true.

13. Nov 1, 2012

### Rap

It's still tied to water, just less so. Triple point of water is 273.16 K by definition.

14. Nov 1, 2012

### Staff: Mentor

The current definition is tied to water, a redefinition by fixing the Boltzmann constant would make it independent of water.

15. Nov 1, 2012

### Rap

Yes. The triple point of water could change (probably become more accurate) but the temperature scale would not. I think its a good idea.