The Mystery of Time’s Arrow

But the reliance on an unexplained initial condition to explain two of the most striking features of the universe—the growth of entropy around us alongside the steady growth of structure in the universe at large—leaves Penrose and others like myself dissatisfied. Thus, if we restrict attention to the considered diagonal and define the direction of time by the growth of structure out of chaos, we obtain a story that, in its most basic features, models rather well what cosmologists observe in the universe. If we reverse the arrows on it and again take the “primordial chaos” as the birth of time, we get another “history of the universe,” different from the first but qualitatively of the same kind.

Source: nautil.us