# Absolute zero, help

1. Mar 2, 2007

### Maxwells Demon

I've been told that heat is vibrations of the molecules.

I see two ways to reach absolute zero -273,15 C

1. you could stop all the molecules so that they wouldn't move at all.

or maybe?? 2. remove all the molecules. No molecules no vibrations no heat??

is no 2. possible?

2. Mar 2, 2007

No. You can't have a perfectly empty space because of the background radiation (or something like it) when you go deep, deep down into the nano-nanometer levels of spacetime.

Also, you cannot stop a molecule from moving. (I may be proven wrong on this a few millenia from now).

3. Mar 2, 2007

### Feldoh

I'm a lowly physics I student, but isn't that the whole theory behind 0K? At that temperature molecules cease to move?

4. Mar 2, 2007

### ZapperZ

Staff Emeritus
It is if you consider only classical thermodynamics. However, once you get to temperature range that low, quantum effects will kick in and you simply can't extrapolate all that you've known at higher temperatures down to such low temperatures. We have already seen how such things break down when certain material instead becomes a superfluid.

Zz.

5. Mar 2, 2007

### Feldoh

So, in other words we really don't know what will happen at absolute zero 100% of the time?

Last edited: Mar 2, 2007
6. Mar 3, 2007

### Maxwells Demon

All right assume that the background radiation isn't there...

Hadn't though quantum mechanically on that one, but my question is also just in theory..

Would you have 0 kelvin if you had a space with 0 molecules inside???

7. Mar 3, 2007

### ZapperZ

Staff Emeritus
It depends on the substance.

Note that for a quantum harmonic oscillator, the lowest energy state that it can occupy is $\hbar\omega/2$. So if you have molecules or solids that can be described by such harmonic oscillators, we already know that they do not stop moving, since there are no lower state than that.

Furthermore, in noble gasses, we have also seen a deviation in the specific heat measurement as you approach very low temperatures. The deBoer effect observed in such measurements can clearly be attributed to such zero-point energy, where by such quantum effects will start kicking in.

Zz.

8. Mar 3, 2007

### Maxwells Demon

Helium at -271,15 Celsius is a superfluid.. Zapper do you know anything about that? definition?

9. Mar 4, 2007

### Hootenanny

Staff Emeritus
10. Mar 4, 2007

### ObsessiveMathsFreak

In order for a substance to be at absolute zero, it's atoms but be absolutely still. However, if this were the case, we could know the position and momentum (0) of a particle exactly, which goes against quantum mechanical principles.