PERPETUAL MOTION M R C HIH E S 263
inventors have never produced a perpetual motion machine, the enormous time and energy invested in building such a fabled machine has
led physicists to carefully study the nature of heat engines. (In the
same way, the fruitless search of alchemists for the philosopher's
stone, which can turn lead into gold, helped to uncover some of the basic laws of chemistry.)
For example, in the 1760s John Cox developed a clock that could
actually run forever, powered by changes in atmospheric pressure.
Changes in air pressure would drive a barometer, which would then
turn the hands of the clock. This clock actually worked and exists even
today. The clock can run forever because energy is extracted from the
outside in the form of changes in atmospheric pressure.
Perpetual motion machines like Cox's eventually led scientists to
hypothesize that such machines could run forever only if energy was
brought in to the device from the outside, that is, that total energy was
conserved. This theory eventually led to the First Law of Thermodynamics-that the total amount of matter and energy cannot be created
or destroyed. Eventually three laws of thermodynamics were postulated. The Second Law states that the total amount of entropy (disorder) always increases. (Crudely speaking, this law says that heat flows
spontaneously only from hotter to colder places.) The Third Law states
that you can never reach absolute zero.
If we compare the universe to a game and the goal of this game is
to extract energy, then the three laws can be rephrased as follows:
"You can't get something for nothing." (First Law)
"You can't break even." (Second Law)
"You can't even get out of the game." (Third Law)
(Physicists are careful to state that these laws are not necessarily
absolutely true for all time. Nevertheless, no deviation has ever been
found. Anyone trying to disprove these laws must go against centuries
of careful scientific experiments. We will discuss possible deviations
from these laws shortly.)
inventors have never produced a perpetual motion machine, the enormous time and energy invested in building such a fabled machine has
led physicists to carefully study the nature of heat engines. (In the
same way, the fruitless search of alchemists for the philosopher's
stone, which can turn lead into gold, helped to uncover some of the basic laws of chemistry.)
For example, in the 1760s John Cox developed a clock that could
actually run forever, powered by changes in atmospheric pressure.
Changes in air pressure would drive a barometer, which would then
turn the hands of the clock. This clock actually worked and exists even
today. The clock can run forever because energy is extracted from the
outside in the form of changes in atmospheric pressure.
Perpetual motion machines like Cox's eventually led scientists to
hypothesize that such machines could run forever only if energy was
brought in to the device from the outside, that is, that total energy was
conserved. This theory eventually led to the First Law of Thermodynamics-that the total amount of matter and energy cannot be created
or destroyed. Eventually three laws of thermodynamics were postulated. The Second Law states that the total amount of entropy (disorder) always increases. (Crudely speaking, this law says that heat flows
spontaneously only from hotter to colder places.) The Third Law states
that you can never reach absolute zero.
If we compare the universe to a game and the goal of this game is
to extract energy, then the three laws can be rephrased as follows:
"You can't get something for nothing." (First Law)
"You can't break even." (Second Law)
"You can't even get out of the game." (Third Law)
(Physicists are careful to state that these laws are not necessarily
absolutely true for all time. Nevertheless, no deviation has ever been
found. Anyone trying to disprove these laws must go against centuries
of careful scientific experiments. We will discuss possible deviations
from these laws shortly.)