Multiverse Predictions for Habitability: The Number of Stars and Their Properties

Abstract

In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, any of which could falsify the multiverse scenario.

Multiverse Predictions for Habitability: Fraction of Life That Develops Intelligence

“…This is a continuation of the work initiated in [1][2][3] aimed at advancing progress on the multiverse hypothesis by connecting it to biological and geological notions of habitability to generate predictions which will be testable within the timespan of several decades. Our technique has been to use detailed criteria for what life needs to count the number of environments suitable for life in the universe, and to check how this depends on the fundamental constants of physics.…”

“…Here α is the fine structure constant, m e is the electron mass, m p is the proton mass, and below M pl is the Planck mass and λ is a dimensionless measure of the stellar mass, as in [1]. The large coefficient, while somewhat off-putting when regarded as a supposed constant independent of physics, is necessary to bridge the gap between these two extremely disparate timescales.…”

“…Because comets' velocities are orbital, they are larger than the Earth's escape velocity 2 and so the Earth's cross section is given by its geometric value σ C " πR 2 C . In contrast, the sun's escape velocity is larger than typical comet speeds, so its cross section 1 Here, and in the following, the expressions from our previous appendices [1,2] are used. Here κ is a dimensionless measure of galactic density.…”

“…To give probabilities that are compatible with our observations, this analysis must be included with some of the other factors that affect habitability as discussed in the previous papers of this series. Throughout, we will take the entropy and yellow conditions as our baseline, as detailed in [1,3], and check how extinctions hinder this already viable criterion. A more thorough analysis would run through all the previous combinations to check which are affected by extinctions, but the results of this would be much too cumbersome to report on in this paper.…”

“…Distribution of observers taking comet impact extinctions into account. The black dot denotes values in our universe, and the orange, blue, and purple lines are the hydrogen stability, stellar fusion, and galactic cooling thresholds discussed in[1]. The white line corresponds to the discontinuity where d dust " d SO x .…”