Can Helium 3 & 4 really be frozen?

Sep 2019
41
4
Azores
I am slightly confused as usual, and seeking clarification?

Phase diagrams show Helium reaching absolute zero. Since absolute zero can not be attained are these phase diagrams derived on actual measurements or are they purely theoretical. Or am I missing something ref zero point energy of the Vacuum and zero point energy of atoms?

Helium becomes a super fluid when not pressurized as it approaches absolute zero. But absolute zero can never be reached due to zero point energy of the vacuum.

Also if Helium is pressurized it can be frozen, as it tends towards zero kelvin. But as you increase pressure the temperature normally increases. By pressurizing Helium are you not also increasing its energy density. ie can it truly ever reach absolute zero. Do the phase diagrams perhaps refer to the zero point energy of the atoms and equate this to zero kelvin.

Am I misunderstanding zero kelvin? ie zero point energy of the vacuum prevents absolute zero being reached. But zero point energy of atoms can be reduced to zero in pressurized helium.

Edit this link on helium isotopes is the reason for my confusion http://ltl.tkk.fi/research/theory/helium.html
 
Last edited:

topsquark

Forum Staff
Apr 2008
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On the dance floor, baby!
I am slightly confused as usual, and seeking clarification?

Phase diagrams show Helium reaching absolute zero. Since absolute zero can not be attained are these phase diagrams derived on actual measurements or are they purely theoretical. Or am I missing something ref zero point energy of the Vacuum and zero point energy of atoms?

Helium becomes a super fluid when not pressurized as it approaches absolute zero. But absolute zero can never be reached due to zero point energy of the vacuum.

Also if Helium is pressurized it can be frozen, as it tends towards zero kelvin. But as you increase pressure the temperature normally increases. By pressurizing Helium are you not also increasing its energy density. ie can it truly ever reach absolute zero. Do the phase diagrams perhaps refer to the zero point energy of the atoms and equate this to zero kelvin.

Am I misunderstanding zero kelvin? ie zero point energy of the vacuum prevents absolute zero being reached. But zero point energy of atoms can be reduced to zero in pressurized helium.
This isn't about the ZPE, it's about the Uncertainty Principle. All (or most) heat that can be described as an object's temperature makes the atoms vibrate. At 0 K this heat term is gone so by Classical Thermodynamics the vibration should stop also. But then we can not only pin down where the atom is we can also say how much momentum it has at any point in time. This is forbidden by the Uncertaintly Principle so any comment about how a material reacts at 0 K is really a limit as temperature tends to 0 K.

I'm not quite up on my Statistical Mechanics to say what happens as the temperature drops to 0 K for either fermionic or bosonic materials. For fermionic materials try a search on "fermi surface" for fermions and Bose-Einstein condensate for bosons.

-Dan
 
Jun 2016
1,198
565
England
My own thoughts (don't take as definitive).

I have never heard of frozen helium.
To create a solid, a compound has to be able to generate inter- atomic (or inter-molecular) forces
to bind the atoms together into a lattice.

For helium, the inter-atomic forces are tiny,
and also they have no asymmetry so there is no preferred direction for the forces
so there is no "guidance" toward a lattice structure.
I guess it could create a "glass" (a disordered structure) rather than a crystal (ordered structure)

Having said all that, I suspect that as the temperatures approach absolute zero,
the behaviours of materials start to go beyond the simple everyday solid/liquid descriptions.
It is possible that you start to enter the world of quantum condensates before you get to solid helium.
 
Oct 2017
578
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Glasgow
Helium becomes a superfluid at very low temperatures. It has some very strange properties.
 
Jun 2016
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565
England
I guess that a super-fluid can be regarded as an extra state of matter.
So rather than gas to liquid to solid,
helium goes from gas to liquid to super-fluid.
 

topsquark

Forum Staff
Apr 2008
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On the dance floor, baby!
Actually I believe I have heard of solid helium but only under extreme pressures. It's not easy to create. I don't know any more about the stuff, though.

-Dan
 
Sep 2019
41
4
Azores
Actually I believe I have heard of solid helium but only under extreme pressures. It's not easy to create. I don't know any more about the stuff, though.

-Dan
Thanks
Ah So! frozen pressurized Helium has been achieved then. I was thinking it might be theoretical only. Absolute zero I understand can not be achieved due to the zero point energy of the vacuum.
 
Jun 2016
1,198
565
England
Poking around on the internet led me to this site:
https://www.chemicool.com/elements/helium.html

The key point from this site is that solid helium can be made
at temperatures of about 1 Kelvin and pressures of about 25 atmospheres.
(Note that this is the triple point for Helium).

Higher pressures allow solid helium at higher temperatures,
but at "normal" pressures solid helium is impossible.
 
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Jun 2016
1,198
565
England
There is a strange philosophical issue about an object at absolute zero.
How would you know it existed?

If you illuminated it, or touched it, or in fact did anything to verify that it was in fact there,
you would unavoidably heat it up!

Maybe just a tiny fraction, but then it would not be at absolute zero any more.
 
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Oct 2017
578
297
Glasgow
There is a strange philosophical issue about an object at absolute zero.
How would you know it existed?

If you illuminated it, or touched it, or in fact did anything to verify that it was in fact there,
you would unavoidably heat it up!

Maybe just a tiny fraction, but then it would not be at absolute zero any more.
Yep. The only thing I can think of is orbital electron photoabsorption and reemission, which is fully reversible, but if you do that, the behaviour of the state you're probing is now the excited state, which is definitely not absolute zero, even if the initial and final temperatures were both at absolute zero.
 
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