The universe is defined by some strange fundamental principles that help shape our world and our place in it. This is what we unintuitively understand as the laws of physics. Whatever physics entails, it has also led us to quite a number of thought experiments that physicists still ponder about today — like the second law of thermodynamics. How better do you understand it? Still having a hard time? Then, you have to think about it in terms of Maxwell’s Demons. We’d explain!
Related media: Reversing Entropy With Maxwell’s Demon
Laws Of Physics, Or Illusion?
There’s this thought experiment that was first introduced in 1871 by Scottish physicist James Clerk Maxwell in his ground-breaking book, ’Theory of Heat.’ He begins by examining the second law of thermodynamics, in what’s been dubbed the most quoted passage in all of physics. What’s relevant? His demon. Let’s say you have an even distribution of temperature and pressure in a closed system, can you force that distribution to become uneven without exerting energy?
All Maxwell wants you to do is imagine the presence of a little being (that’s his demon, who came to the scene long after). What the demon does is to observe individual molecules as they move, and tell the ones that are hot (moving at a fast pace) from the ones that are cold (moving at a slow pace). This isn’t prove that magic is real, it is just a metaphor for how advanced he believed technology would be one day for such a kind of experiment. (Are we there yet?)
In his original experiment, he used a gas-filled chamber, but for a real-world scenario, imagine a swimming pool that’s divided in two (A and B) with a wall. The temperature of both sides are even, and has roughly the same mixture of fast and slow pace molecules, but the water can’t pass through the wall except for a single molecule outlet in the wall. The demon (who often wear a scuba gear, no wonder) is always at the outlet observing all fast and slow pace molecules. Each time he gets a hot (fast pace) molecule, he places it inside ‘B,’ and a cold (slow pace) molecule inside ‘A.’
“He will thus, without expenditure of work,” as Maxwell concludes, “raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics.”
This thought experiment was used to pinpoint some flaws in the laws of the universe, and thus, might exist due to our limitation in science. Scientists back in the day didn’t have the required technology to control individual molecules, and they had, Maxwell claims, they could contradict the second law of thermodynamics, completely change our perception of matter and energy.
What if we could harness the power of heat without using any energy, would that mean that that energy is free? Not at all. Then, neither would we need fossil fuel nor solar panels nor nuclear plants; and any technology as primitive as steam engines could run forever without fuel. Its been over than a century with our technological progresses, and since Maxwell’s thought experiment.
Where art thou perpetual motion machines?
The Demon In Detail
You might have guessed, there are problems with the demon. Obviously! Here’s the catch: If this “demon” was a real device and not magical, then it would use energy to detect the individual molecules and to trigger the outlets between both sides. Specifically speaking, the demon would actually use more energy than required to even identify molecules, and to move them, than it could out of the final product.
And of course, if this thought experiment was easily debunked, it wouldn’t be common in scientific journals. Or is it? Till this date, scientists still debate about the nitty-gritty details of this demon, and there has been quite some progress in the realm of Quantum Mechanics. Maybe in the near future, who knows, we might be able to harness the power of Maxwell’s Demon and you’ll never charge your phone ever again. Huh?
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Written by: Nana Kwadwo, Sun, Apr 05, 2020.