CRA Seminar (Prof. Fred Adams, University of Michigan)

The Degree of Fine-Tuning in our Universe — and Possibly Others

Fred C. Adams, University of Michigan

https://lsa.umich.edu/astro/people/jointly-appointed-faculty/fca.html

The fundamental constants of nature must fall within a range of values
in order for the universe to develop structure and ultimately support
life. This talk considers the current constraints on these quantities
and assesses the degree of fine-tuning required for the universe to be
viable. The first step is to determine what parameters are allowed to
vary. In the realm of particle physics, we must specify the strengths
of the fundamental forces and the particle masses. The relevant
cosmological parameters include the density of the universe, the
cosmological constant, the abundance of ordinary matter, the dark
matter contribution, and the amplitude of primordial density
fluctuations. These quantities are constrained by the requirements
that the universe lives for a sufficiently long time, emerges from its
early epochs with an acceptable chemical composition, and can
successfully produce galaxies. On smaller scales, stars and planets
must be able to form and function. The stars must have sufficiently
long lifetimes and hot surface temperatures. The planets must be
large enough to maintain atmospheres, small enough to remain
non-degenerate, and contain enough particles to support a biosphere.
We also consider specific fine-tuning issues in stars, including the
triple alpha reaction that produces carbon, the case of unstable
deuterium, and the possibility of stable diprotons. For all of these
issues, the goal of this enterprise is to delineate the range of
parameter space for which universes can remain habitable.