is spread out as thermal motion of the atoms of the floor. The reverse process is not
spontaneous because it is highly improbable that energy will become localized,
leading to uniform motion of the ball’s atoms. A gas does not contract spontaneously
because to do so the random motion of its molecules, which spreads out the distribution
of kinetic energy throughout the container, would have to take them all into the
same region of the container, thereby localizing the energy. The opposite change,
spontaneous expansion, is a natural consequence of energy becoming more dispersed
as the gas molecules occupy a larger volume. An object does not spontaneously
become warmer than its surroundings because it is highly improbable that the jostling
of randomly vibrating atoms in the surroundings will lead to the localization of thermal
motion in the object. The opposite change, the spreading of the object’s energy
into the surroundings as thermal motion, is natural.
It may seem very puzzling that the spreading out of energy and matter can lead to
the formation of such ordered structures as crystals or proteins. Nevertheless, in due
course, we shall see that dispersal of energy and matter accounts for change in all its
forms.