I don’t spent a lot of time thinking about the multiverse: the possible existence of regions of the cosmos that have never been connected to ours at any time, and may never be in the future. That’s because those parallel pocket universes aren’t directly detectable, and may never be even indirectly detectable, putting them into a category that’s hard for a scientist to deal with. However, inflation — the extremely rapid expansion of the Universe in its earliest instants — almost certainly would produce those pocket universes, so I’ve reluctantly come to terms with the existence of the multiverse, on the principle that the alternative ideas are largely problematic.

Some physicists have gone a bit farther with the multiverse idea. Since our Universe has the correct physical/chemical properties to harbor life (self-evidently, since we’re here to talk about it), and those properties depend on a delicate balance of physical parameters, then maybe the multiverse can help explain what makes our pocket universe habitable. If those other pocket universes have different physical parameters, maybe the set ours has came about by a random process: no need for “fine-tuning”. However, as I argue in a new piece for the Nautilus blog, the fine-tuning problem is separate from the question of the multiverse, and philosophy won’t provide the solution to either.

We know that the universe is capable of supporting life, and that any physical parameters must be consistent with that obvious fact. Beyond that, we can’t go yet: We have no more evidence for multiverses than we have evidence for life beyond Earth—though it’s reasonable to think both exist. The uncomfortable possibility is that there are other pocket universes, but we’ll only ever know about them indirectly. That doesn’t make them any less real, just discomforting. [Read more…]