Model of Anthropic Reasoning , Addressing the Dark to Ordinary Matter Coincidence ∗

If inflation occurs after the breaking of Peccei-Quinn symmetry then large values of the breaking scale F , which are forbidden in conventional axion cosmology, are permitted, provided that we inhabit a region of the Multiverse where the initial misalignment is small. Regions having approximately this initial misalignment may occupy a small volume of the Multiverse, but they contain a large fraction of potential observers. This scenario has many consequences, including a possible explanation of the approximate equality of dark and baryon matter densities. 1 Methodology and Anthropic Reasoning There are good reasons to view attempts to deduce basic laws of Matter from the existence of Mind with skepticism [1]. Above all, it seems gratuitous. Physicists have done very well indeed at understanding matter on its own terms, without reference to Mind. We have found that the governing principles take the form of abstract mathematical equations of universal validity, which refer only to entities – quantum fields – that clearly don’t have minds of their own. Working chemists and biologists for the most part are committed to the program of understanding how minds work under the assumption that it will turn out to involve complex orchestration of the building blocks that physics describes [2]; and while this program is by no means complete it hasn’t encountered any show-stopper, and it is supporting steady advances over a wide front. Computer scientists have made it plausible that the essence of mind is to be found in the operation of algorithms that in principle could be realized within radically different physical embodiments (cells, transistors, Tinkertoys) and in no way rely on the detailed structure of physical law [3]. To put it shortly, the emergence of Mind doesn’t seem to be the sort of thing we’d like to postulate and use as a ∗Solicited article for the book “Universe or Multiverse?”, ed. B. Carr, based in part on a talk at the Anthropic Workshop, Cambridge University, June 2001.