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- Physicists created a new quantum theorem for entropy, and included is a possible exception.
The Second Law of Thermodynamics says that entropy in the universe must always increase. It's an immutable law of physics, and it's the reason you can't get free energy or perpetual motion machines. But a group of physicists may have found a way to break this law, at least in some specific circumstances.
The researchers, from Argonne National Laboratory, have developed a theoretical model where the Second Law is violated on a molecular level. Their results are published in the journal Science Direct.
The basic idea behind the discovery is the H-theorem, which says if you mix a hot thing and a cold thing, the mixture will end up somewhere in the middle. The H-theorem relies on a statistical interpretation of the way molecules move around. Because it's pretty much impossible to keep track of every single molecule, physicists just treat them as groups and use statistics to figure out how they'll behave.
The team from Argonne decided to look at the problem through the lens of quantum mechanics. They created a quantum H-theorem that is, at least theoretically, more accurate than the traditional theorem. Their new formula revealed that in some special cases, entropy might actually decrease, at least in the short term.
A few years before Boltzmann proposed his H-theorem, another physicist had an idea for a way to cheat the Second Law. James Clerk Maxwell proposed a hypothetical thought experiment: What if a small demon sat between the hot and cold things and controlled their mixing? The demon would only allow hot things to go one way and cold things to go another. Essentially, the demon could unmix the mixture.
It turns out that this doesn't actually violate the Second Law because the demon creates more entropy than it eliminates. Today, we use electricity to play this role, unmixing hot and cold things with our air conditioners and refrigerators. But the researchers' model suggests a quantum demon that could actually violate the Second Law.
This is all theoretical, of course. But if the theory pans out, quantum demons might someday power our air conditioners and refrigerators, saving you electricity and cheating the current laws of physics at the same time.
Source: Argonne National Laboratory via Futur