Can you reach absolute zero in complete empty space

  1. Ok, so I know that the laws of physics say reaching absolute zero temperature is impossible, but suppose we took a box that was perfectly insulated in completely empy space, and I took all the particles out of it to create a vacuum. Now, since there are no particles in the box, then wouldn't the temperature inside the box be absolute zero (no heat energy = no temperature, right?)? If I am wrong, what would the temperature inside the box be? Since the average temperature of the universe is only 2.73 kelvin, then it seams like there would be areas in space that are like this....
     
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,261
    Science Advisor
    Homework Helper
    Gold Member

    What does "temperature" measure?
     
  4. The concept of temperature deals with systems where the number of particles is large enough to approximate the density of states as a continuous function of energy. If you get to small number of particles, then the discrete nature of states becomes important, and temperature ceases to have any meaning.
     
  5. Simon Bridge

    Simon Bridge 15,261
    Science Advisor
    Homework Helper
    Gold Member

    I suppose one may choose to attribute a characteristic temperature to the zero-point energy in a volume, by E=kT or whatever, but it is not clear what this would mean, hence the question in post #2.

    Focussing on what temperature is should help.
     
  6. mfb

    Staff: Mentor

    Negative temperatures are hotter than every positive temperature.

    The same as the temperature of the box, about 2.7K (there is no perfect heat isolation). You don't need matter to have a temperature, radiation is sufficient.
     
  7. phinds

    phinds 9,161
    Gold Member

    In addition to the answers above, there is another issue that you might find interesting in this context. Following up on Khashishi's statement "If you get to small number of particles, then the discrete nature of states becomes important, and temperature ceases to have any meaning" --- It is my understanding that there are dust clouds that have a "temperature" of millions of degrees and yet they are a hard vacuum compared to what we can get in a vacuum chamber on earth.
     
  8. Drakkith

    Staff: Mentor

    But there aren't a small number of particles in a giant dust cloud.
     
  9. phinds

    phinds 9,161
    Gold Member

    I didn't say there aren't any particles. Reread what I said. Do you think man-made vacuum chambers evacuate every single particle?
     
  10. Simon Bridge

    Simon Bridge 15,261
    Science Advisor
    Homework Helper
    Gold Member

    Yes, but so what?
    What, in the "this" context of temperature vis-a-vis the limit of zero particle density in a fixed volume, is the interest?

    Do you mean that temperature need not decrease with the particle density?
     
  11. Drakkith

    Staff: Mentor

    You've lost me phinds. I don't know what you are getting at.
     
  12. phinds

    phinds 9,161
    Gold Member

    I was just presenting a factoid that I though the OP might find interesting because he was talking about temperature and a hard vacuum. Let me restate it

    Hm ... I don't see any way to restate it and make it any more clear that what I already said: It is my understanding that there are dust clouds that have a "temperature" of millions of degrees and yet they are a hard vacuum compared to what we can get in a vacuum chamber on earth.
     
  13. Drakkith

    Staff: Mentor

    Are you simply saying that a man made vacuum doesn't pump out all the gas? And that these clouds that are millions of degrees are more of a vacuum than what we can produce on Earth?
     
  14. phinds

    phinds 9,161
    Gold Member

    That is exactly what I am saying.
     
  15. Drakkith

    Staff: Mentor

    I thought you were getting at something with the temperature too. My mistake good sir.
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?