Why the universe is just so

Abstract

Some properties of the world are fixed by physics derived from mathematical symmetries, while others are selected from an ensemble of possibilities. Several successes and failures of "anthropic" reasoning in this context are reviewed in the light of recent developments in astrobiology, cosmology and unification physics. Specific issues raised include our spacetime location (including the reason for the present age of the universe), the timescale of biological evolution, the tuning of global cosmological parameters, and the origin of the Large Numbers of astrophysics and the parameters of the Standard Model. Out of the twenty parameters of the Standard Model, the basic behavior and structures of the world (nucleons, nuclei, atoms, molecules, planets, stars, galaxies) depend mainly on five of them: m e , m u , m d , α, and α G (where m proton and α QCD are taken as defined quantities). Three of these appear to be independent in the context of Grand Unified Theories (that is, not fixed by any known symmetry) and at the same time have values within a very narrow window which provides for stable nucleons and nuclei and abundant carbon. The conjecture is made that the two light quark masses and one coupling constant are ultimately determined even in the "Final Theory" by a choice from a large or continuous ensemble, and the prediction is offered that the correct unification scheme will not allow calculation of (m d − m u )/m proton from first principles alone.

Anthropic predictions: the case of the cosmological constant

“…Of course, observation of galaxies at z ∼ 4.5 means only that z max > ∼ 4.5, and Weinberg referred to (5) as "a lower bound on the anthropic upper bound on ρ v ." At present, galaxies are observed at considerably higher redshifts, up to z ∼ 10.…”

“…Examples of calculation for specific models have been given in [12,22,23]. 5 Needless to say, the details of the fundamental theory and of the inflationary dynamics are too uncertain for a definitive calculation of P prior . We shall instead rely on the following general argument [27,28].…”

“…Extensions to parameters like the electron mass or charge, which do affect life processes, is on a much shakier ground. Untill these processes are much better understood, one will have to resort to qualitative arguments, as in [1][2][3]5].…”

“…The observed values of these parameters are then determined by chance and by anthropic selection. It has been argued, at least for some of the constants, that only a narrow range of their values is consistent with the existence of life [1][2][3][4][5].…”

Three's a Crowd: On Causes, Entropy and Physical Eschatology

“…It is an objective proposal for explanation of particular low-entropy initial conditions observed in our cosmological domain, which relies on the observational selection effects, embodied in the so-called anthropic principle (for exhaustive reviews, see Barrow and Tipler 1986;Balashov 1991;Hogan 2000;Bostrom 2002). Anthropic principle(s) have been subject to much controversy in recent years, centered mainly on the alleged teleological implications of at least some of their formulations (e.g.…”