Multiverse Predictions for Habitability: Number of Potentially Habitable Planets

Abstract

How good is our universe at making habitable planets? The answer to this depends on which factors are important for life: Does a planet need to be Earth mass? Does it need to be inside the temperate zone? are systems with hot Jupiters habitable? Here, we adopt different stances on the importance of each of these criteria to determine their effects on the probabilities of measuring the observed values of several physical constants. We find that the presence of planets is a generic feature throughout the multiverse, and for the most part conditioning on their particular properties does not alter our conclusions much. We find conflict with multiverse expectations if planetary size is important and it is found to be uncorrelated with stellar mass, or the mass distribution is too steep. The existence of a temperate circumstellar zone places tight lower bounds on the fine structure constant and electron to proton mass ratio.

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 κ is a dimensionless measure of galactic density. 2 This hierarchy does not actually hold for all parameters, but the full implications of this will be explored in future work.…”

“…The radius of the inner solar system is given by the orbits of the outer planets, which is about 15 AU. The giant planets' locations are set as a small multiple of the snow line, a planets " 5.6 a snow , where the snow line was found in [2] to be a snow " 30.4 λM pl {pα 5{3 m 5{4 e m 3{4 p q. However, the injection rate, as computed in [21], is actually independent of this quantity, being given by the ratio of kinetic to gravitational energy f inj " ∆v 2 {p2 GM d {a Oort q.…”

“…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.…”

“…The coefficient has been set to match the observed value in our universe. Using expressions for the galaxy mass and radius from the appendix in [2], the extinction rate becomes…”