Many-Universes Models

These are a convenient way to explain why our universe seems so special, and precisely geared to allow the possibility of life. The response is simply to postulate that there are or have been a vast number of universes. Three such strategies are to be found in the literature.

•  The first is to extend the Big Bang model to permit an endless series of expansions and contractions: the so-called cyclic Big Bang (see is the Big Bang a moment of creation?). Each passage through a singularity is supposed to randomize the physical parameters which give rise to the anthropic features. In an infinite series of closed universes there will certainly be a subset whose physical features permit the evolution of life and the function of the Weak Anthropic Principle is to remind us that only in such an atypical subclass of universes could life evolve. The main difficulty faced by this scenario is justifying the assumption that, while the singularity randomizes the laws and constants of nature, it leaves the geometry of spacetime untouched. If, as seems reasonable, passage through a singularity also affects the geometry of the universe, we should expect an open Big Bang after a finite number of cycles, thus putting an end to any hope of an infinite sequence of universes.
• A second approach would be to opt for one of the recent sophisticated variants of steady-state cosmology. For example, one may envisage an infinite chaotic universe in which ‘bubbles’ of order appear and disappear at random. Thus our universe is merely a small local departure from the steady-state conditions. However, if spacetime is truly infinite in extent, we should expect every possible stable state to appear an infinite number of times!
• The third and, currently, most popular strategy for relaxing the uniqueness of our universe is to adopt a many-worlds interpretation of quantum mechanics. Again it is sufficient to invoke the Weak Anthropic Principle to ‘explain’ our atypical cosmos.

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