2nd law of thermodynamics question?

Question

2nd law of thermodynamics says that energy "spreads out" to try to reach equlibrium. My understanding is that it's like a gas which spreads out to fill the room it's in. Then why hasn't the universe reached a state of equilibrium? 2nd law says processes are irreversible. Does physics also say there is reversability in the universe? That's my only explanation.

Answer 1

The law applies itself on isolated systems exclusively in contact with others (or different parts of the same isolated system).Some researchers suggest that the universe is not a closed system, although the Sun and planets in our solar system are often treated as an isolated system, this is an idealization because real life isolated system do not exist but behave like this for a finite time. Regarding reversability, physics has "Loschmidt's paradox, also known as the reversibility paradox,[which] is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics. This puts the time reversal symmetry of (almost) all known low-level fundamental physical processes at odds with any attempt to infer from them the second law of thermodynamics which describes the behaviour of macroscopic systems. Both of these are well-accepted principles in physics, with sound observational and theoretical support, yet they seem to be in conflict; hence the paradox."