what’s scientifically testable are our mathematical theories, not necessarily their implications, and that this is quite okay. As we discussed in Chapter 6, because Einstein’s theory of general relativity has successfully predicted many things that we can observe, we also take seriously its predictions for things we can’t observe—for example, what happens inside black holes. Likewise, if we’re impressed by the successful predictions of inflation or quantum mechanics so far, then we also need to take seriously their other predictions, including the Level I and Level III multiverses.
