Famed multiverse theorist, physicist Lee Smolin, in a recent essay, says he isn’t sure whether he even believes in his own multiverse hypothesis anymore, but he does give it credit for having some predictive power and experimental support:
An alternative approach, which does lead to at least a few falsifiable predictions, is cosmological natural selection, which I introduced in 1992. This is based on a cosmological scenario that is constructed to be analogous to population biology. Universes are born from “bounces” deep inside black holes, which replace their singularities, where time had been hypothesized to end, with new expanding universes. This leads to a prediction that a typical universe is one where the parameters are tuned to maximize the production of black holes. There is in fact evidence that this is true of the laws that govern our universe. Most importantly, in this theory our universe is supposed to be typical of the ensemble, which leads to several genuinely testable predictions, all of which have held up since they were first published, such as the prediction that the upper mass limit of stable neutron stars is about 1.6 solar masses.
The timeless “block universe” is also something he regards with skepticism:
Many cosmologists today believe that we live in a timeless multiverse — a universe where ours is just one of an ensemble of universes, and where time does not exist • The timeless multiverse, however, presents a lot of problems. Our laws of physics are no longer determinable from experiment and it is unclear what the connection is between fundamental and effective laws • Furthermore, theories that do not posit time to be a fundamental property fail to reproduce the space—time that we are familiar with • Many of these puzzles can be avoided if we adopt a different set of principles that postulates that there is only one universe and that time is a fundamental property of nature. This scenario also opens the way to the possibility that the laws of physics evolve in time.
Smolin’s complete essay is full of similarly challenging reflections, and can be read here.