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College of Arts & Sciences
Physics and Astronomy

Colloquium: "Fine-Tuning Constraints on Stellar Operations"

Thursday, November 2, 2017 - 16:00 to 17:15


Dr. Fred Adams
Ta-You Wu Collegiate Professor of Physics
College of Literature, Science, and the Arts
University of Michigan
Ann Arbor, Michigan



Motivated by the possible existence of other universes, with different values for the fundamental constants, this talk considers stars and stellar structure with different values for the fundamental constants of nature.  Focusing on the fine structure and gravitational constraints, we first enforce the following constraints:  [A] long-lived stable nuclear burning stars exist, [B] planetary surfaces are hot enough to support chemistry, [C] stellar lifetimes are long enough to allow biological evolution, [D] planets are massive enough to maintain atmospheres, [E] planets are small enough to remain non-degenerate, [F] planets are massive enough to support complex biospheres, [G] planets are less massive than stars, and [H] stars are less massive than galaxies.  The parameter space that satisfies these constraints is relatively large:  viable universes can exist when the structure constants vary by several orders of magnitude.  Next, we consider a number of other fine-tuning issues, including the triple alpha fine-tuning problem for carbon production, nucelosynthesis in universes without stable deuterium, and structure formation in universes with varying amplitudes for the primordial density fluctuations.  In all of these scenarios, the basic parameters of physics and cosmology can vary over wide ranges and still allow the universe to operate (in contrast to previous claims).

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