Chapter 9: Fundamental Physics

Section 3: Irreversibility and the Second Law of Thermodynamics

Cosmology and the Second Law

In the standard big bang model it is assumed that all matter in the universe was initially in completely random thermal equilibrium. But such equilibrium implies uniformity, and from this it follows that the initial conditions for the gravitational forces in the universe must have been highly regular, resulting in simple overall expansion, rather than random expansion in some places and contraction in others. As I discuss on page 1026 I suspect that in fact the universe as a whole probably had what were ultimately very simple initial conditions, and it is just that the effective rules for the evolution of matter led to rapid randomization, whereas those for gravity did not.

From Stephen Wolfram: A New Kind of Science [citation]