[net.physics] Entropy, Gases and fluctuations.

stekas@hou2g.UUCP (J.STEKAS) (03/22/84)

Sure it's possible for all the gas in a room to find itself
in one corner - it's called a "fluctuation".  It's easy to
calculate the probability of such a fluctuation ...

Say the room has a mole of particles (10^23) and we want to find
out the probability that all the particles find themselves in a
sub-volume which amounts to 10% of the total volume.  Now the
probability for a given particle to be in that small volume
is 0.1, so the probability that ALL of them would be in that small
volume is

                                      23
                                  (10    )
                          p = 0.1


                                                       23
Now this number is not of order of magnitude 23, but 10  .  That means
10^23 zeros to the right of the decimal point!  I think that this is
about as "unlikely" as anything one can imagine, considerably less likely
than finding a Unicorn in your garage tomorrow.

                                                 Jim