I have read that Helium does not freeze at absolute zero under normal pressures.

How could this be possible given that the absolute zero is the lowest attainable temperature and at that temperature, all random movements of the atom stop?

Shouldn't the atoms just stop vibrating and solidify instantly? Why do they possess kinetic energy at absolute zero?

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    $\begingroup$ Actually nothing ever gets to 0K, so in a sense 0K is the lowest unattainable temperature, not attainable. Try reading something about superfluidity. $\endgroup$ Commented Aug 17, 2016 at 17:28
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    $\begingroup$ But how can anything exist in liquid state at 0K? The atoms just don't contain any kinetic energy! $\endgroup$
    – AmeyaS
    Commented Aug 17, 2016 at 17:32
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    $\begingroup$ The zero-point energy of helium is too high to allow freezing $\endgroup$ Commented Aug 17, 2016 at 17:32
  • $\begingroup$ Try en.wikipedia.org/wiki/Superfluid_helium-4 $\endgroup$ Commented Aug 17, 2016 at 17:35
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    $\begingroup$ Why do they possess kinetic energy at absolute zero? They must keep moving, otherwise we would know what this article says we are not able to....en.wikipedia.org/wiki/Uncertainty_principle $\endgroup$
    – user108787
    Commented Aug 17, 2016 at 17:47

4 Answers 4


You have been misled by the idea that temperature is a measure of energy. While this is approximately true at high temperatures, it is not correct at low temperatures. Temperature is actually a measure of entropy; the derivative of entropy with respect to internal energy at constant particle number and volume is inverse temperature. At very low temperatures, quantum mechanical effects become important, and even at absolute zero (0 K), the particles have energy, known as zero point motion. In helium, this zero point motion is large enough to prevent the atoms from sticking together as a solid - it remains a liquid. Above roughly 3.2 MPa Helium-3 becomes solid at high pressure. For Helium-4 it will become solid above ~2.5 MPa. http://ltl.tkk.fi/research/theory/helium.html


The key point here is the following: the contribution from the zero-point energy is seven times larger than the depth of the attractive potential between two He(4) atoms. Therefore, the zero-point energy is enough to destroy any crystalline structure of He(4) that the material would otherwise form.

A more rigorous answer can be found here in this Answer.


At $0K$ there is still zero point energy. As He is very light and inert the associated zero point motion this is enough to prevent solidification.


Kinetic energy at lower temperature does not figure out the motion of particle their may be at random in an insiginifant way not visible or difficult to account but it's not at zero


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