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!

How and why does everything in life reach equilibrium?

  1. Sep 30, 2009 #1

    In science there are so many equilibrium concepts. Pressure, electricity ,concentration.....

    Everything seems to be moving from high to low to reach equilibrium

    My questions are

    1. Why does everything try to reach equilibrium? (Extremes are generally harmful and for survival of this word equilibrium is required is that the reason)
    2. From where do the particles get energy to move from high to low and how do they know they have to move from high to low to reach equilibrium.

    Thank you very much!!
  2. jcsd
  3. Sep 30, 2009 #2
    Everything tries to reach a state where its energy (total energy, maybe thermal, electrical, potential, whatever) is minimum.

    Contrary to what you quote, particles have to *lose* energy as opposed to *get* energy to move from high to low. And as we all know, losing is easier than gaining. How they know which state has the lowest energy and where they need to go is much more involved and would involve discussions on entropy and geometry.
  4. Sep 30, 2009 #3
    Thanks tanujkush for the reply. :smile: It is afterall a natural process.
  5. Sep 30, 2009 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    If you dig the question a bit, the first answer is: we call in fact "equilibrium", the "most probable state". If you dig the question even more, the answer is that we don't really know :smile: but it is probably best to stop just before reaching this conclusion. :biggrin:

    Not always, and in all circumstances, systems try to reach "equilibrium", but most of the time they do, and that comes about because, contrary to what you seem to think, the "system" doesn't "know" anything of where it "has to go" and its interactions make it wander of eratically. Now, if you wander off eratically, chances are that you will end up in the "biggest chunk" of possibilities, and that's nothing else but the "equilibrium state".

    Consider it this way: suppose your system is 100 dice in a (big) jar. Now, if you throw the dice, and you make the sum of all outcomes, then the outcome "100" is extremely rare, because there is only ONE dice configuration that can do this (all dice must be "1"). In the same way, the outcome "600" is extremely rare, because again, only one dice configuration can do that (all dice must be "600").

    But 350 is the most probable, because it has the most different possible dice configurations that sum to 350. So the "equilibrium" sum must be somewhat around 350.

    It is only if the motions of the dice in the jar would somehow "know what to do" that you could deviate from this. Randomly thrown dice will tend to have a sum around 350, simply because there are more different configurations of them leading to that sum than to any other. So "350" corresponds to the biggest "chunk" in "configuration space" (or "possibility space of the system").

    They exchange energy with one another. Some win, some loose, and the distribution of energy over the different constituents is one of the things that will settle in "most probable" configuration.

    edit: btw, it is not in general true that "systems try to reach lowest energy". Otherwise, all water would freeze, all air would liquify etc...
  6. Sep 30, 2009 #5
    1. Everything tries to reach equilibrium because the whole thing (system ) will get higher entropy.
    2. Energy is not lost or gained, it just moves from high energy parts to low energy ones.
  7. Sep 30, 2009 #6

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    "equilibrium" has a simple definition, but in practice, is not so obvious. Living matter, for example, is maintained at far-from-equilibrium conditions. Physical structures may seem to be in equilibrium, but "how long do you want to wait"? mountains erode, continents move, orbits decay.

    Even so, since we can be very quantitative about "how long we want to wait", equilibrium is a very useful concept. To answer your specific questions:

    1) Because everything in the universe is lazy and tends to a minimum in energy.
    2) Unless there is an energy barrier present, systems to not need to aquire energy to reach a minimum- they are losing energy. And systems tend to lose energy because of (1).
  8. Oct 1, 2009 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Hum, that sounds like the beginning of a lyric :smile:


    but my love for you will always stay

    tadum dadum tadum ...


    (hum, sorry).
  9. Oct 1, 2009 #8
  10. Oct 2, 2009 #9
    Thanks for all the answers :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook