I know the *base* of the story, every single system doing any kind of work leads to a certain loss of energy, basically what makes perpetual motion machines impossible, as without pumping more energy into the system, the one it already have will eventually all be exchanged in the form of friction and whatnot.
But I want to go to the *fundamentals*, why is it like that? Why is it impossible? Why can’t we imagine a hypothetical machine made with whatever unobtainium we might need that is actually, mathematically energetically perfectly efficient? *Why did heat beat us? xd*
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Fundamentally, you can’t have 100% efficient systems because you can’t 100% control what direction atoms are going.
Heat is random motion of atoms. And, since it’s random, there’s always *some* of the motion going in a direction you don’t want.
The only way to get an atom to not go anywhere you don’t want (not counting quantum weirdness) is to cool it to absolute zero, but now it has no thermal energy and you can’t do anything useful with it in a thermodynamic sense.
The second you add any energy it starts wiggling and you can’t completely control how it bounces off it’s surroundings so it’s *always* going to dump some kinetic energy into the things it interacts with, which is just heat transfer at the molecular level. And since energy is conserved and *some* of it must end up us heat, you’re never going to get 100% of it to do non-heat (i.e. anything useful).
If you *do* want heat, then you can get 100% efficiency, as others have said, because that’s the only place you can guarantee all the energy will eventually go.
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