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What happens to matter near absolute zero

  1. Jun 10, 2012 #1
    I'm trying to figure out why things happen to objects placed in environments near absolute zero. so let's take an ice cube. In a freezer it will remain stable, I'm guessing because the atoms that make up the ice cube will bounce off atoms in the air that are roughly similar in energy to the atoms that make up the cub. when two atoms collide energies average, the colder one will become warmer and the warmer one will become colder. now, let's put that same ice cub in outer space. it will undergo an enormous change. i'm guessing it is because there are no atoms for the ice cub to bounce off of and with no other atoms to keep it at a high energy and since objects seek their lowest energy state the ice cube will quickly seek it's lowest energy state and rapidly condense. let me know if this portrayal is accurate.
     
    Last edited: Jun 10, 2012
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  3. Jun 10, 2012 #2

    phinds

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    "environments near absolute zero" is a meaninglessly ambiguous statement.

    (1) Outer space next to the sun
    (2) intergalactic space
    (3) in a lab on earth
    (4) etc


    for ice cubes in outer space (assume intergalactic space), look up sublimation
     
  4. Jun 12, 2012 #3
    I don't think "environments near absolute zero" is meaningless, but just unquantified. As in "well, how close to absolute zero do you mean?"

    I suppose the environment best for getting arbitrarily close to absolute zero would be a hypothetical time/place in which no EM sources are visible and the CMB radiation is redshifted into oblivion. How would an ice cube behave in such an environment?

    I imagine it would start by losing heat due to black body radiation, and it would be gaining nothing back because of the null CMB. I heard in another thread that sufficiently cold gasses turn into a "Bose-Einstein condensate", but I don't know how that applies to solids.

    Phinds, do you know if there's a threshold temperature below which water ice doesn't sublime?
     
  5. Jun 12, 2012 #4
    what i mean by near absolute zero is just simply outer space, 2.7 kelvin
     
  6. Jun 12, 2012 #5

    f95toli

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    2.7K is positively balmy compared to the temperatures we can reach in the lab. Using a modern dilution fridge you can cool LARGE samples (several kg and in principle even more if you are patient) down to about 10 mK (0.001K).

    And the answer to your question is: not much. Of course the materials become more brittle, but as long as you don't put them under too much mechanical stress they will just go back to normal when you heat them up again. Glues and similar chemical tend to crack, because of the stress when you cool/heat them but that is just a mechanical effect.
     
  7. Jun 12, 2012 #6
    But are my reasons for what happens to ice at 2.7K correct?
     
  8. Jun 12, 2012 #7

    Nugatory

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    Not really. You've been talking about temperature (how fast the molecules move in the air surrounding the ice, how much the molecules in the solid ice jiggle in place) but not pressure (how many air molecules hit the surface of the ice, and how hard they hit)

    All else being the same, the ice cube will be more stable in a colder environment, as the air molecules hit the water molecules less hard, so are less likely to knock them loose.

    However, in outer space the pressure is so low that when a water molecule gets loose, there's nothing to stop it from drifting off into space - the ice cube evaporates without melting first. This is the process called "sublimation", which Phinds suggested you look up back in post #2. (Did you? If not, you're not getting full value from the time you're spending on this forum).

    So high pressures and low temperatures increase the stability of the ice cube; low pressures and high temperatures encourage it to melt or sublime. Try googling for "triple point of water" and see where that takes you.
     
  9. Jun 12, 2012 #8

    mfb

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    After some sublimation and radiation, the block of ice reaches 2.7K, where the average energy per atom is quite small - sublimation will still happen, but with a really slow rate. As space is not a perfect vacuum, it might even collect some other particles.
     
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