The Remarkable Uniformity of the Universe

One of the remarkable features of the universe is that above a certain scale (about 10²⁴ metres) it is highly uniform in structure. However, this degree of uniformity is an embarrassment to cosmologists.

According to relativity theory, there should be no causal connection between points separated by distances greater than c multiplied by t (where c is the velocity of light and t is the age of the universe). Extrapolating this back to the Big Bang suggests that the primordial universe was partitioned into about 10⁸⁰ causally separate regions. Nevertheless, all these disconnected regions had to expand at the same rate to maintain the observed degree of uniformity! Coincidence or co-operation? Small wonder that Paul Davies comments:

It is hard to resist the impression of something - some influence capable of transcending spacetime and the confinement of relativistic causality - possessing an overview of the entire cosmos at the instant of its creation, and manipulating all the causally disconnected parts to go bang with almost exactly the same vigour at the same time, and yet not so exactly co-ordinated as to preclude the small scale, slight irregularities that eventually formed the galaxies, and us.

Davies’ reference to small-scale irregularities highlights another feature of cosmic uniformity. According to current theories, galaxy formation depends upon the existence of small initial irregularities in the Big Bang itself. These are amplified by cosmic expansion to the point where gravitation can begin the process of stellar condensation. If the initial irregularities are too large the result is the rapid and widespread formation of black holes instead of stars. If the initial irregularities are sufficiently small, the precise expansion rate of the cosmos becomes critical - too rapid and the irregularities will not be amplified enough for galaxy formation to occur; too slow and the cosmos will be closed with a lifetime too short to permit biological evolution.

Email link | Feedback | Contributed by: Dr. Christopher Southgate
Source: God, Humanity and the Cosmos  (T&T Clark, 1999)