Originally Posted By: Finiter
in a reactor, the change is controlled one (here, it is controlled by us). Similarly, the model of expansion 'with an explosion' and 'without an explosion' are different.

Does this mean you disagree with the idea that the Universe might have expanded by several orders of magnitude in a very small fraction of a second?

(A perfectly reversible change is defined as a change that happens infinitely slowly, and where the system is always in equilibrium).

So, a perfectly reversable change is one that is never completed?
There never was nothing.