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In the universe, without a heat source does it take energy to cool?

  1. Dec 18, 2008 #1
    In the universe, without a heat source does it take energy to cool?

    For example if there was no sun or gravity or other heat sources, does it take energy to cool? And cool to what temp? 0 Kelvin?

    Thanks just curious :)

  2. jcsd
  3. Dec 18, 2008 #2
    If you mean will the universe cool over time of its own accord, the answer is yes. Even with billions and billions of suns since they will exhaust their energy supplies over time. The basic temperature of the universe is currently 2.7 degrees kelvin, the temperature of the cosmic background radiation...and as our universe expands it is believed it will eventually cool to about absolute zero....and everything will come to a cold dismal end.

    If you'd like to try to cool it tonight, it would take a lot of energy.

    Some may claim global warming will slow that process down....it gets blamed for everything imaginable..
  4. Dec 18, 2008 #3
    From how I understand it heat will not simply disappear, it will only dissipate and equalize throughout all matter. If we had a closed system with a single hot object and a cloud of cold matter then after a period of time the heat would equalize between the two and they would remain at the temperature until something else changed the balance. You could think of it as a faucet (heat source) that is putting out some sort of thick gel (heat), as the gel falls out it piles up in a hill (high temperatures), but eventually spreads out to being level (equilibrium temperature). As long as you continue to put out gel there will be a hill, but if you turn it off and wait eventually it will be perfectly level.

    As far as taking heat to cool, you can only even cool a local area at the expense of heating up another area at least as much as you cooled the first down (it would take 100% efficacy to be the same). Really you can only move heat from one place to another (and in the process add more due to inefficiencies), that's why AC and refrigerators have radiators outside the area that is to be cooled.
  5. Dec 18, 2008 #4


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    Staff: Mentor

    It sounds to me like the OP is asking about objects in the universe. The answer is no, a heat input is not required to make heat flow from a hot area to a cold area.
  6. Dec 19, 2008 #5
    Thanks all!! Excellent Forum.

    So if this universe was all at a certain temperature, it would actually take energy to increase and decrease the temperature? correct.

  7. Dec 19, 2008 #6


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    Science Advisor

    ??? You got three responses, all of which said "No, not correct"!
  8. Dec 19, 2008 #7
    everything that changes takes energy..its a simple physics rule...
    if it moves then something has to move it...
    it couldnt cool unless some sort of energy was exhausted...even temperatures evening out are caused by some sort of energy(convection/conduction)..otherwise it would remain exactly the same forever..if you had a warmer spot it would stay exactly that temp..if you had a cooler spot it would stay exactly the same...the only time it could change is if some energy source moved the particles around

    so in a short answer...YES it takes energy to cool...or it could not cool
  9. Dec 19, 2008 #8


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    Homework Helper

    I believe that you are asking here about a unifrom temperature throughout the universe. That's a difficult question, and the scenario is hard to imagine in a nontrivial universe. To simplify, assume that the universe is simply an infinitely extensive fluid with uniform temperature. In order to increase or decrease the temperature of the universe uniformly as a whole, you would have to violate a few laws of physics, conservation of energy being one of them. I am assuming that, by definition, no energy can come from outside the universe. Energy can be conserved if a hot spot forms somewhere, as long as a corresponding cold spot forms somewhere else. However, this violates the second law of thermodynamics since heat would have to flow in a direction of increasing temperature.
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