  Cosmological models that invoke a multiverse - a collection of unobservable
regions of space where conditions are very different from the region around us
- are controversial, on the grounds that unobservable phenomena shouldn't play
a crucial role in legitimate scientific theories. I argue that the way we
evaluate multiverse models is precisely the same as the way we evaluate any
other models, on the basis of abduction, Bayesian inference, and empirical
success. There is no scientifically respectable way to do cosmology without
taking into account different possibilities for what the universe might be like
outside our horizon. Multiverse theories are utterly conventionally scientific,
even if evaluating them can be difficult in practice.
