Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why not absolute zero?

  1. Jan 29, 2004 #1
    I hear in all sorts of experiments that scientists cool materials down to within billionths of a degree of absolute zero. What prevents us, or is there a reason scientists dont, from reaching all the way to absolute zero?
  2. jcsd
  3. Jan 29, 2004 #2
    Part of the reason is there is no perfect insulator, so there is always some heat being transfered to the substance being cooled.
  4. Jan 29, 2004 #3

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    Absolute zero is an approachable limit, like the speed of light. You can always get closer, but you can never get there. IT's called the third law of thermodynamics.

    An easy way to consider this one is: in order to cool something down, it must be put into a place that is colder. OTherwise heat wont flow out of the thing. SO: if you theoretically put an object (like a turkey) into a freezer that was at abosolute zero, heat would flow from the turkey into the freezer, and that would make the freezer have some heat and therefore it would not be at absolute zero anymore.

    There are fancier ways of cooling things (do a google on "evaporative cooling")but the same law gets in the way no matter which method you choose.
  5. Jan 29, 2004 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    Yet a third point (both the previous responses are true) is "quantum uncertainty". If the particles are known to be with the confines of the experiment then there is enough uncertainty in the momentum to keep the temperature above absolute 0.
  6. Jan 29, 2004 #5
    I believe that third law of thermodynamics and the impossibility of attainment of exactly 0K temperature.

    But there is such a thing as NEGATIVE absolute temperature(!)

    John Baez: Below Absolute Zero - What Does Negative Temperature Mean? --->

  7. Jan 30, 2004 #6
    But according to boyles law, volume would be 0 if 0 Kelvin, and thats why its impossible!
  8. Jan 30, 2004 #7
    The most fundamental reason for the inability to reach absolute zero temp. is because of something derived from quantum mechanics called 'zero point' energy, (actually Planck 'discovered' it.), meaning energy is there even at the zero point of temperature.

    When we talk of absolute zero temperature we usually 'mean' a state where there is no longer any kinetic motion of the molecules, that is, a complete stand still.
    Because zero point energy is so ubiquitous (even exists in the vacuum), then all molecules retain a minimum of that amount of energy.

    Last edited: Jan 30, 2004
  9. Jan 30, 2004 #8
    but if molecules and electrons stop moving, wouldn't the electrons be dragged into the nucleus of the atom?
  10. Jan 30, 2004 #9
    Who said anything about electrons stopping? Its the molecules (and atomic motion) that slows down kinetically at low temperature. However, they cannot stop completely due to zero point fields.

    Last edited: Jan 30, 2004
  11. Jan 31, 2004 #10
    So, which theory is generally more used to prove this: The one Artman/Chi brought up, or the one Creator brought up?
  12. Jan 31, 2004 #11
  13. Jan 31, 2004 #12
    Here is a bit more to expand on the previous:

    Analog Science Fiction & Fact Magazine/John Cramer/1995/Bose-Einstein Condensation, a New Form of Matter --->

    Here is a pretty good historical description of absolute zero temperature --->

    I would demur on one bit from this explanation.

    "we are unable to reach absolute zero itself. It is forbidden by the third law of thermodynamics."

    A statement of a law cannot prevent something from happening*. A law is a scientific summary of understanding and its correctness is exactly what is at stake when one asks about reaching absolute zero temperature. Thermodynamics was developed in the nineteenth century essentially to cover nineteenth century physical situations. It is not a foregone conclusion that it remain forever correct in the face of more advanced discoveries. But the author is correct that avoidance of reheating is a formidable practical obstacle to furthur reduction of a tiny absolute temperature.

    *remember the joke about the traffic cop that pulled over a car:
    cop: "You can't make a U-turn in the middle of that busy street."
    uncool driver: "Whadaya mean I can't? I just did!"
  14. Feb 1, 2004 #13
    Depends on which approach you prefer, thermodynamics or QED.

    Here's an interesting report of the first experimental measure of the zero pt. energy of a Bose Condensate showing it to correspond to the uncertainty in the particle momentum (as mentioned by HallsofIvy):


    I believe the first exper. evidence of molecular zero point energy in 'normal' matter was a few years after Planck's derivation of ZPE by a fellow named Mulliken (1924). Planck's discovery was a result of thermodynamic considerations as he was working to derive the correct blackbody distribution formula. Notice this was all actually prior to Heisenberg's derivation of the same using matrix mechanics.

    Last edited: Feb 1, 2004
  15. Feb 4, 2004 #14
    If you stick around with a topic long enough, some news is apt to fly in.

    Fermi-Dirac condensation? Potassium atoms instead of Rubidium atoms?

    NIST/University of Colorado Scientists Create New Form of Matter: A Fermionic Condensate --->

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Why not absolute zero?
  1. Absolute zero (Replies: 3)

  2. Absolute Zero (Replies: 18)

  3. Absolute Zero (Replies: 13)

  4. Absolute Zero (Replies: 11)

  5. Absolute Zero (Replies: 3)