Michael asked:

Re: entropy and probability in August 1999 edition (Answers 1)

It's standard physics I know that if — say you — pour out something it will tend to spread out, rather
than roll back into the cup or spell your name. An explanation of entropy as being just an expression
of the Law of Probability seems insufficient. It seems to me to be something more profound and
important as the arrow of time and entropy run in the same direction. We are born, we grow old and
die. Reversing my car backwards up the motorway does not refill the tank with petrol.

============

Suppose you have a closed container, a cube, say, with lots of little balls bouncing around in it, in all
different directions. Now suppose you squeeze the container on one side. It gets smaller, the balls
bounce around in a smaller space, right? Now suppose you suddenly release that side and the cube
pops back to its original size and shape. Do the balls stay in the quarter of the cube they were in
when you squeezed it? Why not? They spread out into the whole cube, right? Why? What is the
chance, keeping the cube the same size, that they will all suddenly fly up into one corner, all at once?
Pretty low, right? Why? What if you start with all the balls just lying on the bottom of the cube and you
start bouncing the cube. Do the balls just bounce up and down, and stay like that, bouncing up and
down? Why not? If one ball bounces a little to one side, soon all the balls will be bouncing in various
directions. Why?

All we're dealing with, in the above, are laws of probability. In a closedsystem, you get, eventually,
uniform distribution of energy and position. An open system is another thing entirely. Now, on the way
to that uniform distribution, you can get all sorts of strange effects: chaotic systems, various periodic
effects, and so forth. You might take a look at Prigogine on that. But ultimately you get uniformity. The
organization that living creatures exhibit in their bodies is obtained at the price of increasing entropy
in the form of radiated heat, mostly; and we are, locally, on earth (neglecting the rest of the galaxy,
etc., makes it an open system), in an open system with the sun supplying us with energy to maintain
our structures. But it's all running down, as far as we know at this point.

Now, why should reversing your car fill it with petrol, any more than walking backward would make
you gain weight? Come on. We're dealing with events on a micro level here. It takes energy to
reverse your car, so you supply that energy, you don't gain it. You need to do some reading in basic
physics. The only systems in which you can do anything resembling beating the system here are on
the lowest levels of structure, the quantum levels, and even there it's only temporary, or a stasis.
Even protons have a decay rate; it's verylong, but it exists. Depressing, isn't it. But that's no excuse;
depressing or not, that's reality as we know it at the beginning of the 21st century.

Steven Ravett Brown

46