For the past week the major news coming from science was that faint gravitational waves from the earliest moments of the universe were detected by the BICEP2 observatory near the south pole. The findings, if correct, would confirm a prediction made by Einstein nearly 100 years ago in General Relativity, as well as in inflationary theory developed by Alan Guth in 1980.
"It's hard to build models of inflation that don't lead to a multiverse," says Guth, quoted from a recent Huffington Post article. Since most models of inflation lead to a multiverse, and the recent finding corroborates predictions made by inflation theory, then it seems that the multiverse just got a big boost in credibility. For years the critics were saying that the multiverse was pure speculation, tantamount to an atheistic version of god as an explanatory force. We may or may not ever have direct confirmation of another universe, but if the data holds up and is confirmed by additional tests (of which there are several pending) then the predictions made in inflation theory that other universes are likely will move it closer to physics from metaphysics.
The multiverse does offer us an explanation for many of the current puzzles in science, like why the values of the physical constants are in the life permitting range. So if we have good evidence that the multiverse is true, there goes the fine tuning argument - which I consider the only decent argument theism has. And if the fine tuning argument implodes, then theism is really going to be in trouble in the future. Take away the cosmological argument and the fine tuning argument for example, (which I think there are already good refutations for) and theism really has nothing left to stand on. There is nothing within the universe that really needs god as an explanation that isn't better served by science and philosophy.
So what's left for theism? What will the nature of apologetics look like in 2050 when we might have discovered quantum gravity and when an inflation model with multiverse predictions becomes the cosmological paradigm rendering the fine tuning argument a total dud? I wonder what debates about the existence of god will be like then.
Presumably the atheist will have a much larger arsenal of data to draw from, as has always been the case when new scientific discoveries are made. I am optimistic that within this century, theism will become the minority position in the West, because it's explanatory power will fail to compete with the rigor of naturalistic science, and because many of the social functions that religion has played will be replaced by secular alternatives.