1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why does everything achieves to reach equilibrium?

  1. Sep 3, 2007 #1
    I don't get this....Why does everything tries to move to settle equilibrium? I thought, to move, you need energy. Or is it like everything is compressed and setting up equilibrium is bassically being released from the compression?

  2. jcsd
  3. Sep 3, 2007 #2


    User Avatar
    Homework Helper
    Gold Member

    Systems in nature like to reach states of minimum total energy. This thing we call equilibrium is the name for a state of minimum energy.

    EDIT: I just realized that I was posting in another thread with both of you. Deja Vu!:smile:
    Last edited: Sep 3, 2007
  4. Sep 3, 2007 #3
    GO1 saves the day again! yea it is the same theroy
  5. Sep 4, 2007 #4


    User Avatar
    Science Advisor
    Homework Helper

    OK.... but energy is convserved, yes? So if one system reaches a state of miimum total energy, some other system increases its energy...

    I know what you mean, GO1 - but I'm just feeling in a nit-picking mood as to whether this "explains" why things are the way they are.

    Most mainstream physics doesn't even attempt to explain "why" - it stops at describing "what".
  6. Sep 4, 2007 #5


    User Avatar
    Science Advisor

    But that doesn't say WHY the "like to reach states of minimum total energy"!

    Look at the definition of "equilibrium" (of any kind). When something is in equilibrium, it, by definition, stays there. If it is not in equilibrium, it keeps "moving". Sooner or later it will, perhaps entirely by chance, hit an equilibrium and stay there. Eventually, everything will have stumbled upon an equilibrium.
  7. Sep 4, 2007 #6


    User Avatar
    Homework Helper
    Gold Member

    OK, what I said doesn't describe why systems tend to equilibrium, but I felt like trying anyway! I guess should have quit while I was on top.:smile:
  8. Sep 4, 2007 #7
    According to the second law of thermodynamics, entropy (or disorder) tends to increase overall. In statistical thermodynamics, entropy is shown proportional to the logarithm of accessible states of the system. (By a particular state one might mean one of all possible arrangements of quantum numbers comprising a system at a given time.) These first two sentences are equivalent to saying that the number of states available in a system tends to increase.

    If we had continually exact knowledge of a system, the entropy measured might appear not to change. However, quantum mechanics tells us that to participate in a system disturbs a system, generating randomness. It is a lot easier to view salt and pepper segregated in their respective shakers than separate them, mixed in a pile, by observation.
  9. Sep 5, 2007 #8
    but, nothing that I know of is in 'true equilibrium'---you have to go into 'reference frames' to get close, I believe.
  10. Sep 5, 2007 #9
    But why does the entropy increase? And what is entropy?(is it state of universe(increasing meaning it is expanding) and time?)
  11. Sep 6, 2007 #10
    Have you looked around the web for some explanations yet?


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

Similar Discussions: Why does everything achieves to reach equilibrium?