TAP Colloquium - Dr. Fred Adams
The Degree of Fine-Tuning in our Universe
Dr. Fred Adams
Ta-You Wu Collegiate Professor of Physics
University of Michigan
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 current constraints on these quantities and assesses the degree of tuning required for the universe to be viable. In the realm of particle physics, the relevant parameters are the strengths of the fundamental forces and the particle masses. Additional astrophysical parameters include the cosmic energy density, the cosmological constant, the abundances of ordinary matter and dark matter, and the amplitude of primordial density fluctuations. These quantities are constrained by the necessity that the universe lives for a long time, emerges from its early epochs with an acceptable chemical composition, and successfully produces 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. We also consider potential fine-tuning related to 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 is to delineate the range of parameter space for which universes can remain habitable. In spite of its biophilic properties, our universe is not optimized for the emergence of life, in that the proper variations could result in more galaxies, stars, and potentially habitable planets.