We can begin to understand the role of the distribution of energy by thinking about
a ball (the system) bouncing on a floor (the surroundings). The ball does not rise as
high after each bounce because there are inelastic losses in the materials of the ball and
floor. The kinetic energy of the ball’s overall motion is spread out into the energy of
thermal motion of its particles and those of the floor that it hits. The direction of
spontaneous change is towards a state in which the ball is at rest with all its energy
dispersed into disorderly thermal motion of molecules in the air and of the atoms of
the virtually infinite floor (Fig. 3.2).
A ball resting on a warm floor has never been observed to start bouncing. For
bouncing to begin, something rather special would need to happen. In the first place,
some of the thermal motion of the atoms in the floor would have to accumulate in a
single, small object, the ball. This accumulation requires a spontaneous localization of
energy from the myriad vibrations of the atoms of the floor into the much smaller
number of atoms that constitute the ball (Fig. 3.3). Furthermore, whereas the thermal
motion is random, for the ball to move upwards its atoms must all move in the same
direction. The localization of random, disorderly motion as concerted, ordered
motion is so unlikely that we can dismiss it as virtually impossible.1
We appear to have found the signpost of spontaneous change: we look for the
direction of change that leads to dispersal of the total energy of the isolated system. This
principle accounts for the direction of change of the bouncing ball, because its energy