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Question about Helium at absolute zero

  1. Mar 13, 2013 #1
    At absolute zero, I understand that atoms have a minimum vibration (the atoms are not completely still). Because of this minimal vibration, He atoms can not freeze at absolute zero. But if enough pressure is applied, the liquid then becomes a solid. Does the pressure eliminate or reduce the minimum vibration? Is solid He colder than absolute zero?
     
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  3. Mar 13, 2013 #2

    Simon Bridge

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    Liquid helium is not at absolute zero.
    Nothing is... it is the empirical limit of zero volume on a T-V graph.
    Solids still have vibration.
    Define "enough" pressure - how much would be "enough" to solidify liquid helium?
    Bear in mind that liquid helium II is already a Bose-Einstein condensate.

    I think you need to bear in mind that simple models tend to break down in extreme situations.
     
  4. Mar 16, 2013 #3
    Right. I should have said "theoretically speaking" regarding helium at absolute zero.


    do you mean molecules/atoms?


    Also, if helium were under adequate pressure, I assumed that it could exist as a solid and I was wondering about the atoms minimum vibration under these conditions. Is the assumption wrong?
     
  5. Mar 16, 2013 #4

    Simon Bridge

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    Perhaps you should have said - "a perfect ideal gas, in the classical regime, at absolute zero" rather than specifying "helium". But all you've done is render the question meaningless as that would mean the state of zero volume.

    Liquid helium 3 and 4 does solidify under high pressures. 25-30Atmospheres.
    You can go look up the properties.
     
  6. Mar 17, 2013 #5
    I am referring specifically to helium. Helium is the one exception that will not freeze at absolute zero.
    The minimum amount of vibration of helium at absolute zero will not let helium turn into a solid (freeze), unless under a great amount of pressure.

    I am not interested in how much pressure is required to squeeze helium into a solid. Instead, I wanted to know if this pressure reduces the amount of vibration for the helium.
     
  7. Mar 17, 2013 #6

    Simon Bridge

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  8. Mar 18, 2013 #7

    DrDu

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    The state of a substance at (or near) absolute zero is not so much a question of vibrations but of minimal entropy. In superfluid He, the atoms form a quantum condensate, however at higher pressures a solid is energetically favoured.
    Analogous effects occur in metals, even at zero temperature: At normal metallic densities, the electrons in a metal behave like a gas of electrons, while at very low densities, they form a solid structure, the so-called Wigner lattice.
     
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