Could our massive universe be just one of many, like a bubble in a frothy stream of cosmos-spawning stuff? It sounds like something out of a 1970s British scifi novel, but it’s become a popular explanation for the origin of our universe.
How can we test this hypothesis, when we’re stuck in just one universe? As attempts to paint our universe as an inevitable, self-contained structure falter, the multiverse camp is growing. Proponents of the multiverse idea must show that, among the rare universes that support life, ours is statistically typical. The exact dose of vacuum energy, the precise mass of our underweight Higgs boson, and other anomalies must have high odds within the subset of habitable universes. If the properties of this universe still seem atypical even in the habitable subset, then the multiverse explanation fails.
For years, the inability to calculate ratios of infinite quantities has prevented the multiverse hypothesis from making testable predictions about the properties of this universe.