Testing the Untestable

The biggest criticism of multiverse theory is that it seems unfalsifiable. If other universes are forever beyond our reach, how can we ever prove or disprove them? Some physicists argue this makes the idea philosophy, not science.

Others look for indirect support. String theory allows for an enormous number of possible universes — often called the landscape — each with its own physical constants. If that landscape is real, a multiverse follows naturally. Whether such reasoning counts as testable science is still hotly debated.