ABC2019 wrote:Exnihiloest wrote:We must also see that in practice, we don't care about the increase in the entropy of the universe. For us humans, if we succeed in making a system that locally decreases the entropy by extracting the heat energy from a single ambient thermal bath, even if it increases the entropy much more elsewhere, we will have won the Holy Grail !
uh no it doesn't work like that. The second principle FORBIDDEN to transform a thermal bath into work, that's all. No macroscopic system can do that. For a microscopic system, you can have random thermal fluctuations which seem to temporarily violate the 2nd principle, but if you try to do it statistically on a large number of systems to be macroscopic, the law of large numbers will make that on average you will not can't transform heat from a monothermal source into work, period.
"To increase entropy elsewhere", that means concretely to take heat in a hot source and to give some of it back to a colder source. There is no other solution, and there never will be.
"The second principle FORBIDDEN to transform a thermal bath into work": yes, that is precisely what is in the spotlight.
If you take what the second principle says as proof of its veracity, you are in a tautology.
I'm not saying it's wrong, I'm not saying it was bypassed (although there are some disturbing experiences), I'm saying that the theoretical impossibility of a Maxwell demon has not been demonstrated except for special cases. I hold the second principle for a weak link in classical physics (compared to that of energy conservation or the invariance of the space-time interval by change of reference frame, for example), and in particular because it is only true statistically.