It often happens that scientists need to use metaphors for
explaining their point to other scientists and the general public. This is how
many mysterious fantastic creatures are born. Many of these creatures were fabricated
during the debates on the Second Law of Thermodynamics. Undoubtedly, the most
popular of all those creatures was Maxwell demon – a product of a thought
experiment created by the physicist James Clerk Maxwell, the author of the
famous Maxwell's equations that accurately describe the electromagnetic field.
Since 1871, Maxwell's demon had occupied the great minds of science. Scientists
still look for processes which would allow heat to pass from less hot bodies to
hotter bodies. Of course, all of us (or at least those of us who still remember
our physics classes) know that heat can be passed from hot to cold bodies. The
paradigm called the Second Law of Thermodynamics seemed irrefutable until it
was challenged by the existence of Maxwell’s demon.
The idea of Maxwell’s demon is very simple: imagine a sealed container,
divided into two gas-tight parts with by the wall with door that would allow
just one gas atom to pass through it. At the beginning of the experiment, the
upper part of the vessel contains gas, and at the bottom part is filled with vacuum.
The door in the middle of the wall dividing both parts is guarded by an
imaginary microscopic janitor who is vigilantly watching over molecules. The
janitor would allow fast molecules to go through the door to the bottom of the
container, while the slow molecules are left in the top half. Clearly, if such
a watchman is on duty at the door for a long time, the gas will be divided into
two parts: in the upper part of the container there would be cold gas contained
of slow molecules, and in the bottom part of the container there would be hot
gas consisting of fast molecules. This mythical janitor opening and closing the
door was nicknamed “Maxwell's demon”.
Maxwell's demon has such special powers that he can monitor every single
molecule in its movements and recognize its speed. He opens the door only to
fast or slow molecules, forcing them to move to different parts of the container.
Thus, in one part of the container the temperature and pressure are getting higher
than in the other which yields the unlimited supply of energy at no costs. In
case Maxwell's demon remains on duty forever (or several Maxwell’s demons do
shifts), the container can be turned into full-functioning “perpetuum mobile”.
Many prominent scientists argue that Maxwell's demon was merely a joke
of the great physicist. Indeed, Maxwell's demon is not effective in a container
with two molecules. In that case, all molecules might end up in just one part
of the container to begin with. However, if the number of molecules is high, the
probability of such a case is extremely small.
Maxwell’s demon keeps occupying many scientists’ minds. Not long ago, there
was an article published on that issue in one scientific journal that explains
the existence of Maxwell's demon in a form of a quantum oscillator, a laser which
separates the molecules with high energy from the low-energy molecules.
Recently, the debate on the existence or non-existence of Maxwell's
demon was enforced by the quantum entanglement theory that aims at developing
supercomputers, instant Internet and even teleporting devices. In their recent
paper Japanese physicists showed that quantum effects make information
translation into energy to be more efficient than previously thought. Although
their paper was not yet accepted for publication, its pre-print is available at
Cornell University’s archive and can be downloaded here: http://arxiv.org/abs/1207.6872.
The Japanese scientists’ major innovation is the introduction of quantum
entanglement into Maxwell’s experiment. In their extension of Maxwell’s
experiment, there were two vessels with quantum entangled particles. By
measuring the rate of only one of these particles, one can obtain information
about the other. If all the particles in the experiment are entangled in pairs,
this means that the demon will need only half of the time to recognize the
nature of the particle than in the case of classical particles. The authors
performed statistical calculations that take this into account and showed quantum
entanglement would effectively increase the performance of Maxwell’s demon.
So far, no one has proved whether Maxwell’s demon exists or whether it
is just a myth. But one thing is certain - Maxwell's demon might help scientists
to heat up the interest in further research in natural sciences!
Happy Halloween everyone!
EL and WS
Happy Halloween everyone!
EL and WS
