Construct a simple system: take a box, a simple solid rectangular solid. Within
this box, place a gaseous substance. Heat the box, sit back, and watch. What
happens to the gas? Everyone knows that warm gases rise while cooler gases
sink; and initially, the portions of the gas closest to the walls of the box will
become heated and rise. At certain temperatures, the gas will begin to form
cylindrical rolls spaced like jelly rolls lying lengthwise in the box. On one side
of the box, the gas rises, and on the other, it sinks; the rising gases move to one
side and carry warmer gases up with them; as the gas cools, it falls on the other
side of the box. With a regularly applied temperature, a smooth box interior,
and a system completely closed with regards to the gas itself, it might be
expected that the circular motion of the moving gas should be regular and
predictable. Nature, however, is neither regular nor predictable. It turns out
that the motion of the gas is chaotic. The rolls do not simply roll around and
around in one direction like a steam-roller; they roll for a while in one direction,
and then stop and reverse directions. Then, seemingly at random, the gas reverses
direction again; these changes continue at unpredictable times, at unpredictable
speeds.