Maxwell's demon is an imaginary creature that allows one directional flow of particles or selectively allowing flow of particles based on their energies. It was originally proposed for breaking the second law of thermodynamics. However even if we have such a device that acts like Maxwell's demon it doesn't violate the law. Even some science writers described real world examples of Maxwell's demon. I like to discuss this matter with you.
Dear Hewa Ahmed Mustafa , you write
"... if we have such a device that acts like Maxwell's demon it doesn't violate the law".
Of course, Maxwell's demon simply does (useful) work. And it reduces the entropy in the system.
You and I are constantly doing useful work, improving the world around us. Inside us, the body does useful work, so that our organs are in order.
Sincerely yours, Dulin Mikhail.
A laser implementation of Maxwell's classical setup has been proposed and built, see e.g.
Article Photonic Maxwell’s Demon
Article Laser Maxwell's demon
When considering implications with respect to the second law of thermodynamics, please be careful about subsystem issues: if you only look at the subsystem, it might seem like you have a dS
The second law is related to the impossibility of the perpetual motion of the second kind. Many people have tried to break this but so far nobody was able to achieve this. There is a nice book about these attempts:
Capek, Vladislav, and Daniel P. Sheehan. Challenges to the second law of thermodynamics. Dordrecht: Springer, 2005.
"In this volume we will attempt to remain clear on this point; that is, while the second law might be potentially violable, it has not been violated in practice."
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