ar X iv : a st ro - p h / 99 09 29 5 v 1 1 6 Se p 19 99 Why the Universe is Just So

Some properties of the universe are fixed by physics derived from mathematical symmetries, others may have been selected from an ensemble of possibilities. Some 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, 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: me,mu,md, α, αG, three of which are independent in the context of Grand Unified Theories (that is, not related by any known symmetry). These parameters also need to be finely tuned to make stable nucleons and nuclei and abundant carbon, leading to the conjecture that the two light quark masses and one coupling constant are ultimately determined even in the “Final Theory” by a choice from a continuous ensemble, and the prediction that the correct unification scheme will not allow calculation of (md −mu)/mproton from first principles.