## Can Gravity Decrease Entropy? - A Hint

#### John Baez

So, you're wondering why gravity doesn't violate the
2nd law of thermodynamics, even though the entropy of a
gas cloud decreases as it shrinks under its own gravitational
pull? The answer is simple, but I'll just give you a hint.
We've already
seen that as it shrinks, it loses energy. The energy has to
go somewhere. Where does it go? If you figure that out, you'll
see that the total entropy is not actually decreasing - it's just
leaving the gas cloud and going somehere else!

© 2000 John Baez

baez@math.removethis.ucr.andthis.edu