# Entropy and Equilibrium

1. Jun 18, 2009

### jisun.hong

I'm so confused.
So my textbook tells me that entropy of the universe is equal to zero at equilibrium.
And then later on it tells me at equilibrium the universe achieves maximum entropy.
So is it zero or max?
Thanks for the help.

2. Jun 18, 2009

### fluidistic

Maximum since entropy tends to increase. So if you have a system at equilibrium it means that its entropy remains constant, but as entropy tends to increase it means that the entropy of the system is at its maximum. It seems that your book take the whole universe as a system, so replace "system" by "universe" in my post and all is fine.

3. Jun 18, 2009

### Mapes

Could your book have said that the change in entropy (mathematically, $dS$ rather than $S$) is zero for small changes to a system in equilibrium?

4. Jun 18, 2009

### fluidistic

Good catch Mapes :) Must be this.