Published in Rev. Mod. Phys. 72, 1149, 2000.
WHY THE UNIVERSE IS JUST SO
Craig J. Hogan
Astronomy
and Physics
Departments
University of
Washington, Seattle, Washington 98195, USA
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: me, mu,
md, 
, and
G (where
mproton and
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
(md - mu) /
mproton from first principles alone.
"What really interests me is whether
God had any choice in creating the world."
(1)
-Einstein
Table of Contents
1 Einstein
is also famous for declaring that "God
does not play dice". This comment did not refer to the structure of
physical law
but to the randomness and indeterminacy inherent in quantum measurement.
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