Quick Physics Question

vapid1

Given a sufficiently long time (any time before the end of eternity), can a system in equilibrium (such as a universe) ever bring itself out of equilibrium, into some state of non equilibrium?

Xaviar

I have limited knowledge, but my understanding is: not without an external force.

The tricky part here is that there isn't really any such thing as a closed system, so there will always be external forces.

And I'd hesitate to declare the universe in equilibrium in the first place.

Though, as I said, I have limited instruction on the subject.

Lemming

（･∀･)つ⑩ ( o )( o ) wrote: »

Given a sufficiently long time (any time before the end of eternity), can a system in equilibrium (such as a universe) ever bring itself out of equilibrium, into some state of non equilibrium?

Nope. In a closed system, entropy can only either remain the same or increase. If it didn't, then you could have a situation where you had, say, there are two bars that are the same temperature touching one another, and all of a sudden one of them gets warmer and one gets colder with no outside influence.

Edit: Of course, this doesn't mean there can't be a dynamic equilibrium. If you have something like air in a cube, the air molecules can still bounce around and stuff and be in equilibrium, so things can still be moving.

vapid1

But there exists a small probability that all the particles may decide to move toward one side of the cube, fucking up equilibrium?

Lemming

（･∀･)つ⑩ ( o )( o ) wrote: »

But there exists a small probability that all the particles may decide to move toward one side of the cube, fucking up equilibrium?

Pretty much no. To get closer together and more compact requires a certain amount of energy, and if all the particles have the same amount of energy, they won't be able to "group up" like that. This isn't the whole picture, however, because if you took the kinetic energy of the particles and grouped them up and gave it a higher potential energy, it could still have the same amount of overall energy, but to get that distribution requires some outside force. You would need to do some kind of work to get such a distribution, and if it is a closed system, then you can't get any more work in, and if it's at equilibrium, there's no way to extract any further work from inside the system.

Demerdar

Nope, entropy pretty much prevents that.

Also, look up Boltzmann's H-Theorem, it provides a nice discussion on equilibrium and change in entropy.

Fantasma

Who says the universe is in equilibrium?, I didn't know that, I guess that two galaxies that collided are part of the equilibrium:

http://en.wikipedia.org/wiki/Antennae_Galaxies