Does the multiverse exist? Well, multiverse models might qualify as scientific, and the Bible does not clearly rule out the possibility. In past articles, I have argued that Christians need not fear the multiverse because multiverse models appear to have a beginning and exhibit design. Nevertheless, we should exercise caution. One key criticism of multiverse models pertains to the assumptions and testable claims (or lack thereof) they make. In an article published in Scientific American, eminent cosmologist George F. R. Ellis articulates some problems that multiverse models must resolve in order to truly claim a scientific basis.1
Outer space almost certainly extends beyond what we can see. Scientists are trying to understand how our observable universe fits within this larger picture. Do these other regions have the same initial distribution of matter and energy as ours? Do the physical constants vary? Do the laws of physics take a different form? Are any of these proposed differences even permissible or likely?
These are all good questions. The only way to develop answers is to extrapolate what we know about our observable universe to infer knowledge about regions we will never see. However, of necessity, our uncertainty about those extrapolations increases at larger distances. Multiverse-model conclusions depend on the assumptions made about the proper way to extrapolate. But we will never be able to directly measure these regions to validate or falsify any of these assumptions!
More detailed knowledge about inflation, the cosmic microwave background, and a quantum theory of gravity might tell us that regions beyond the observable universe exist. Yet it seems that scientific studies will never provide any testable knowledge about the properties of those regions.
Anything that Can Happen Does Happen
Inflation virtually ensures that regions beyond our observable universe exist. It is even reasonable to argue that many universes of unlimited size exist. Usually, cosmologists couple this idea with some theoretical framework (like string theory) to argue that every conceivable combination of the physical constants and initial conditions happens somewhere in this multiverse. Such a scenario seems to readily explain the abundant and pervasive fine-tuning detected in our observable universe.
Separate from the assumption problem described earlier, Ellis points out an additional difficulty with this scenario: How do we test a model where anything and everything possible happens? For example, at least two explanations come to mind to explain why you are reading this article. One entails a 14-billion-year-old universe with fine-tuned laws of physics that result in galaxies, stars, and planets forming where one of those stars hosts a 4.5-billion-year-old planet where human life arose, one of whom is you sitting and reading this article. Another entails a quantum vacuum where an energy fluctuation arises that looks identical to the previous explanation, except none of the apparent past history actually happened. In the multiverse, no test (not even future measurements) can distinguish these two proposals. Unless we are careful, multiverse proposals undermine the very foundation of the scientific enterprise.
Ellis closes his article by asserting that multiverse models ultimately are “scientifically based philosophical speculation.” He does this not to deride multiverse models but simply to name them honestly. RTB also makes scientifically based philosophical claims that the God of the Bible is the best explanation for all that we see. It does make me wonder why one claim appears to enjoy the support of the scientific community but not the other.
If you would like to see a question about the multiverse addressed in this forum, send it to firstname.lastname@example.org.