Planets in Other Universes: Habitability constraints on density fluctuations and galactic structure

Understand

Motivated by the possibility that different versions of the laws of physics could be realized within other universes, this paper delineates the galactic parameters that allow for habitable planets and revisits constraints on the amplitude $Q$ of the primordial density fluctuations.

• Previous work indicates that large values of $Q$ lead to galaxies so dense that planetary orbits cannot survive long enough for life to develop.
• Small values of $Q$ lead to delayed star formation, loosely bound galaxies, and compromised heavy element retention.
• This work generalizes previous treatments: [A] We consider models for the internal structure of galaxies and find the fraction of galactic real estate that allows stable, long-lived planetary orbits.