In a series of letters exchanged between James Clerk Maxwell and Peter Trait
Maxwell suggested the possibility of a revolutionary machine
Maxwell’s machine was an isolated chamber divided into two equal parts
that contained an arbitrary gas. However, there stood in between the chamber, on
the line dividing it, what he described as a finite being, what Lord Kelvin later
described as a demon. Maxwell’s being is called a demon
because he is very cunning, and you’d understand why in a moment
The molecules of a gas are known to travel at the same speed, but this is
only the average speed. Individually, a few molecules travel fast and thereby
generate more heat while the others travel slow and generate less heat
leaving the average speed and temperature somewhere in the middle
What Maxwell’s demon does is filter the gas. It separates the faster molecules
from the slower molecules by cleverly opening and shutting the gate between
them. Eventually, there exist only high-energy molecules in one chamber
and low-energy molecules in the other. The demon has raised the temperature and
therefore the pressure of one chamber in comparison to the other. This pressure
difference can be used to push a piston or a turbine to power an engine or
create electricity. Notice that the demon has not broken the
law of conservation of energy: the energy in the isolated chamber is constant; the
demon has merely redistributed it.
Maxwell’s machine produces energy out of nothing.
However, demons don’t exist, or at least we haven’t found one yet, but what
about this machine. Look at it carefully... there’s no demon up to something sneaky, yet
the machine produces energy from….the very energy it produces? Because such a
machine works perpetually, it is called a perpetual motion machine. Coil a magnet
around the wheel’s circumference and fix two magnets adjacent to it and you can
produce AC current forever. If this revolutionary machine is so easy to
build why isn’t it ubiquitous? Isn’t unlimited, unconditional energy the dream
the technology of our utopian future? Well, there’s a catch. In fact, the
technology was realized by Nicolas Carnot, the father of thermodynamics, 200
years ago and was repudiated at that very instant.
Carnot realized that such a machine is a physical impossibility, as no system
can do work with 100% efficiency. Some usable energy, say, the fuel, is inevitably
spent on raising its internal temperature. This is unusable energy and
the measure of this unusable energy is called entropy. Entropy in a machine or
technically, an isolated system, will only increase. This is the second law of
thermodynamics and it is one of the most fundamental and indisputable laws of the
universe. Entropy is ordinarily called a measure of disorder because unusable
energy, such as the heat given off by a tirelessly working engine, is considered
disorder. On the other hand, usable energy is extracted from order. And this order
in an isolated system, due to the increase in the system’s internal
temperature, is destined to be disturbed and diminish. The perpetual motion
machine cannot be actualized because the bearings are not frictionless; they
eventually lose their mobility and come to a halt as the kinetic energy is
converted to frictional heat, however gradual the rate. Basically, disorder is
bound to be introduced. In fact, if you’re still wondering why such a machine
shouldn’t work, ask yourself - what’s wrong with this? ... On the other hand, Maxwell’s
demon cannot be actualized because it must consume energy to detect the
particles and open and close the gate. Once all of its usable energy is
converted into unusable energy through internal heating, it is rendered
unworkable. Only entropy will then reign over the chamber. The only way the demon
and the ball-bearing machine can be made to work again is if we replenish them
with more usable energy, if we restore order. This can only be achieved
externally, thereby making the system no longer isolated. For instance, say that
you are a machine whose sole objective is to clean and organize dishes. However,
because no machine can do work with full efficiency, you purge the dishes of only
90% of the germs. Eventually, as you extinguish your finite energy, entropy
in the kitchen sink increases as the remaining 10% reproduce.
To bring the quantity of germs back down to 10%, you must be replenished, which is
achieved through food, which plants would have stopped producing if the sun hadn’t
been bathing them with its light. Bear in mind that all three of those systems - you
the plant and the sun - are not fully efficient: of all the usable energy they
produce, some is destined to be dissipated as unusable heat. However, what
happens when the sun itself runs out of usable energy, after it has exhausted all
of its hydrogen and helium? Stars are the universe’s primary sources of energy , and
and once every one of them has eventually exhausted its fuel, no more energy can be
produced. Order cannot be restored externally either, because the universe
is the ultimate isolated system. It cannot extract energy from its
surroundings because nothing lies outside it. We might reduce entropy in
the kitchen, but order in the universe is finite; we can extract order from it only
at the expense of dispensing disorder into it. Therefore, entropy in the
universe, like in any isolated system, inexorably increases. It is increasing as
you’re watching this video. Why does disorder, entropy and chaos dominate the
universe? No mysterious force drives the second law of thermodynamics; it is not
an inherent feature built into the cosmos. Entropy dominates simply because
isorder is statistically more probable than order. Think about it .. there are
obviously many ways to arrange the parts to not form a sofa, but there’s only one
way to arrange them to make the sofa “correctly”. Or consider a sand castle: any
volume of sand is utter complete chaos and there are only a handful of unique
ways to arrange the trillions of grains to form a highly structured castle, but
even that will eventually be annihilated by a wave. Entropy reigns simply because
it is more probable. The instant the universe’s last star radiates its final
photons, entropy will be so indescribably high in the universe that its every
inhabitant would have already decayed and perished. An organism wouldn’t be
able to extract order from its surroundings because its surroundings
would be more disordered than the organism itself. At that point the
universe will become cold and lifeless. This is called the heat death and it is
one of the ways that physicists predict the cosmos will reach the end of its
illustrious journey. In other words, enjoy the summer while it lasts!