The development of steam engines during the industrial
revolution went hand-in-hand with formulation of one of the most
powerful laws of physics. The second law of thermodynamics
provides insight into everything from the workings of
refrigeration systems and such oddities as black holes to why
time only runs forward. The second law is frequently
misunderstood, ignored or misstated to obscure its meaning.
Consequently, countless would-be inventors have expended energy
in fruitless attempts to build perpetual-motion machines, which
the second law demonstrates is not possible. The second law has
many implications that have led to its being stated in a number
of ways. Some formulations are rigorous and make reference to an
unfamiliar quantity, while others are more pragmatic.
Ultimately, they are all equivalent. One formulation states
that, in a closed system, entropy always increases. Entropy is a
thermodynamic parameter, like heat and temperature, which is
necessary to characterize the thermal properties of a s