The second law of thermodynamics is only applicable to macroscopic systems?

Question

If the second law is only applicable to "macroscopic" systems, what is included in the "microscopic"? Just elementary particles?

If a particle moves back in time, does it's antiparticle move forward? Is that why entropy is always increasing?

Answer 1

it refers to things around the Plank scale, where the quantum nature of matter becomes relevant to the uniformity of the rate of entropy.

For anything to go backwards in time, you have to assume the existence of a particle traveling faster than light, which has never been observed. Even if you were to to use an artifact like wormholes as a mechanism for anything to go back in time, we wouldn't really travel back in time in the sense that the said particle would only be walking around the block, while we're taking an alley across it.

Answer 2

Thermodynamics is all about the statistics of large ensembles of particles interacting with each other. There's no fine line, though, between large and small size-wise. It has more to do with the number of particles that interact. For example, you're *unlikely* to see the reverse of a complex chain of 5 interactions amongst the electron orbitals of a large atom, but since 5 is still pretty small, it's possible. However, you will likely never see an egg with 10^24 particles reassemble itself after being broken in the life of the universe.