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

Below zero Kalvin

  1. Apr 27, 2008 #1
    is this possible anywhere?
    i know 0 kalvin is the lowest temperature possible that we've been able to attain. but is it possible that in outerspace where there is no heat from sun, that it gets below zero kalvin?

    im just curious. im not sure wether this was "proven" to be the lowest possible temp or just the lowest temp we've been able to get. because i do know that no matter how hard you try to take heat out of something, more heat will just keep going back into it at the same time
     
  2. jcsd
  3. Apr 27, 2008 #2

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    According to current understanding, no temperature below 0 K exists. Also, it is not possible from a practical perspective to cool an object to 0 K (the process would take an infinite amount of time). The lowest humans have achieved is less than one billionth of a Kelvin, far colder than interstellar space, which is approximately 2.7 K.
     
  4. Apr 27, 2008 #3
    Yes, we've never been able to get to 0K. Space is at about 2.7K like Mapes says because of the Cosmic Background Radiation.

    The reason we can't get to 0K is because of statistical mechanics, basically.

    http://en.wikipedia.org/wiki/0K
     
  5. Apr 28, 2008 #4
    Yes, it's possible, in a Laser system, for example.

    Temperature can be defined as the partial derivative of energy with respect to entropy; in a system like a Laser, there is "population inversion" so entropy *decreases* instead of increase, when energy increases, so the absolute temperature is negative.
     
  6. Apr 28, 2008 #5

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    As Norman Ramsey has pointed out, objects with negative temperature are not colder than absolute zero, but instead hotter than anything else. Heat energy will always flow from a inversion state to a state that is closer to equilibrium; this is the characteristic of a high temperature, not a low temperature.
     
  7. Apr 28, 2008 #6

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    As lightarrow points out, the statistical-mechanical origin of 'temperature' can lead to counterintuitive results- for example, a population inversion in a two-state system corresponds to negative temperatures.

    0 K should be considered a thermodynamic limit.

    '0 K' is not acheivable due to the laws of thermodynamics, and it is also not true that 'all motion ceases at 0 K' due to the zero-point energy.
     
  8. Apr 28, 2008 #7
    ok that is confusing that -k is actually hotter than +k. there are actually mechanical tests where they created a negative temperature? and it was hotter? thats strange
     
  9. Apr 28, 2008 #8

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Probably better to think of it as a mis-use of the concept of temperature.
    There are areas of solid state physics where you treat an electron as having negative mass - the maths works and you get the right answer - but it's not necessarily 'real'.
     
  10. Apr 29, 2008 #9
    o. so basically we just arent technologically advanced enough to get the right formula to acheive the real -k (if it exists)
     
  11. Apr 29, 2008 #10

    Mapes

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    How did you conclude that from the responses? It's not a technological barrier.
     
  12. Apr 29, 2008 #11

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    No I mean that negative temperature in a laser inversion isn't real it's just a convenient mathematical trick.
    It's like being overdrawn at the bank, you don't really own 10 negative dollars - it's just easier to do the sums that way.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?