# Why does everything achieves to reach equilibrium?

1. Sep 3, 2007

### Skhandelwal

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?

Thx.

2. Sep 3, 2007

### G01

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!

Last edited: Sep 3, 2007
3. Sep 3, 2007

### kaisxuans

GO1 saves the day again! yea it is the same theroy

4. Sep 4, 2007

### AlephZero

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".

5. Sep 4, 2007

### HallsofIvy

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.

6. Sep 4, 2007

### G01

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.

7. Sep 4, 2007

### Loren Booda

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.

8. Sep 5, 2007

### rewebster

but, nothing that I know of is in 'true equilibrium'---you have to go into 'reference frames' to get close, I believe.

9. Sep 5, 2007

### Skhandelwal

But why does the entropy increase? And what is entropy?(is it state of universe(increasing meaning it is expanding) and time?)

10. Sep 6, 2007

### rewebster

Have you looked around the web for some explanations yet?

eg

http://www.entropylaw.com/