I'll quote Feynman's Lectures, chapter 52 (Symmetry in Physical Laws) of volume 1:
[...] If we see the egg splattering on the sidewalk and the shell cracking open, and so on, then we will surely say, "That is irreversible, because if we run the moving picture backwards the egg will all collect together, and that is obviously ridiculous!" But if we look at the individual atoms themselves, the laws look completely reversible. [...]
I understand that the laws that govern atoms are reversible, but macroscopic things are made of atoms and macroscopic processes do not look reversible at all. How should I interpret this apparent paradox?
Is it the case that most states (combinations of positions and velocities of the atoms) of a physical system lead to an intuitive ending (e.g. egg splattering) and thus intuitive endings are more likely, but if we reverse all the velocities we would arrive at a higly unlikely state?
Or could it be that states that lead to unlikely endings (e.g. egg collecting itselt back together) are so unstable that small sources of randomness are enough to ensure that unlikely endings indeed will not happen? What kinds of randomness must be accounted for? Influences from outside the system? Would it be correct to say that quantum mechanics is a source of randomness in a closed system?