Multiverse Predictions for Habitability: The Habitability of Exotic Environments

TL;DR

This paper uses multiverse reasoning to establish bounds on the habitability of exotic environments, showing that some properties of water are incompatible with multiverse predictions and that future violations could falsify the multiverse hypothesis.

Contribution

It introduces a novel application of multiverse reasoning to constrain the habitability of various exotic environments and challenges assumptions about water's unique properties for life.

Findings

Bounds on habitability of rogue planets and waterworlds are an order of magnitude stronger in a multiverse context.

Some properties of water, like ice floating, are incompatible with the multiverse hypothesis.

Violations of these bounds could falsify the multiverse hypothesis.

Abstract

The relative abundances of exotic environments provides us with (uninformed) bounds on the habitability of those environments relative to our own, on the basis that our presence here is not too atypical. For instance, since red stars outnumber yellow stars 7 to 3, we can infer that red stars must be less than 8.1 times as habitable as yellow, as otherwise our presence around a yellow star would be a statistical outlier at the level of $5\%$. In the multiverse context, the relative abundances of exotic environments can be drastically different from those in our universe, which sometimes allows us to place much stronger bounds on their relative habitability than we would get by restricting our attention to our universe. We apply this reasoning to a variety of different exotic environments: tidally locked planets, binary star systems, icy moons, rogue planets, liquids with properties different from water, and waterworlds. We find that the bounds on the relative habitability of rogue planets and waterworlds are at least an order of magnitude stronger in a multiverse context than from our universe alone. Additionally, the belief that some of water's special properties are essential for life, such as the fact that ice floats and, with some caveats, that it acts as a universal solvent, are incompatible with the multiverse hypothesis. If any of these bounds are found to be violated in the future, the multiverse hypothesis can be falsified to a high degree of confidence.