# Can ice go below zero degrees C?

1. ### deepthishan

38
What happens at -273 oC?

(everything under 1atm)

I know about the cooling curve but just wondering what would happen to substances at absolute zero- does the temperature keep reducing/get harder?

Also, how do gases stay in gaseous form in outer space?

2. ### abluphoton

20
nothing much, all kind of vibrations stop. all its electrons will be in the ground state. thats what happens when an object reaches absolute zero.

3. ### DaveC426913

16,081
No.

No physical substance can reach absolute zero. And even near zero, the very substance will change dramatically. Its atoms will smear out into a Bose-Einsteinian Condensate.

Gas is the default state in vacuum. Unbound Solids and liquids can only stay that way when under pressure. Remove the pressure and there's nothing to keep the individual atoms from simply floating away.

4. ### Integral

7,345
Staff Emeritus
Yes, ice can go below 0C.

Just for future reference:
It is not a good idea to ask one question in the title then ask another in the text. You will get much better threads if you just ask 1 question at a time.

Integral

5. ### DaveC426913

16,081
I suspect he meant 0 K in the title, but found he couldn't change it afterward...

6. ### chrisbaird

617
I politely disagree. All sorts of fun things happen near absolute zero: superconductivity, bose-einstein condensation, superfluidity.

7. ### Thiago

18
As some one stated, below 0ºC the ice can, below -273ºC or 0ºK it can't.

to be fair near -273 it starts doing cool things but I believe it never will reaches 0k as it will be against the Uncertainty principle.

8. ### abluphoton

20
sorry i wasn't clear, when i was explaining what all happens at 0k i meant what would happen if a substance can actually go to 0k. zero entropy concept. and also tell me one thing, if no material can go to zero then the concept of "residual entropy" purely theoretical ??

9. ### DaveC426913

16,081
Why explain what would happen in the case of something that can't happen?

You were clear; it was just wrong.

10. ### Steger

30
Residual entropy is indicative of a frustrated system which will likely have an interesting T=0 quantum phase diagram. It is true that the 3rd law of thermodynamics prevents actually achieving T=0, however, it can be shown that these quantum phases will survive into the T>0 region provided h*omega >> k*T (where omega is usually said to be something like the energy of the elementary excitations). The beauty is that the math is much easier when T=0 so you work the theory there and then know it will hold for some region T>0. That's why we care about things like residual entropy despite T=0 being unphysical

11. ### Steger

30
It's pretty common to say that absolute zero can't exist since temperature is the average kinetic energy and heisenberg's unceratinty... etc. However, the impossibility of absolute zero was known well before quantum mechanics and is simply a result of thermodynamics.

The 3rd law is often phrase in terms of entropy (often incorrectly stated as "the entropy goes to zero at T=0") however, even without residual entropy when ever there is a degenerate ground-state you're going to have a non-zero (though tiny) T=0 entropy. Thus I've always found a stronger condition for the 3rd law follows from considering the following definition of entropy:

$$S = S_0 + \int \frac{C_x}{T} dT.$$

Looking here was see that the only way the integral converges at T=0 is if the SPECIFIC HEAT goes to zero. I find this a nicer formulation of the 3rd law and it also makes the impossibility of achieving T=0 intuitive. If one imagines cooling a system by taking heat out of it we see that one would need to take out an infinite amount of energy since the specific heat goes to zero, to lower the temperature to zero. Also the closer you get the harder it gets.