The relationship of people to the environment is also conditioned by another
physical law, the second law of thermodynamics. Known popularly as the entropy law,
this law states that “entropy increases.” Entropy is the amount of energy unavailable
for work. Applied to energy processes, this law implies that no conversion from one
form of energy to another is completely efficient and that the consumption of energy is an irreversible process. Some energy is always lost during conversion, and
the rest, once used, is no longer available for further work. The second law also
implies that in the absence of new energy inputs, any closed system must eventually
use up its available energy. Since energy is necessary for life, life ceases when useful
energy flows cease.