The Sciences

Let the Universe Be the Universe

Cosmic VarianceBy Sean CarrollSep 25, 2012 3:37 PM


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My article in the Blackwell Companion to Science and Christianity, which asks "Does the Universe Need God?" (and answers "nope"), got a bit of play last week, thanks to an article by Natalie Wolchover that got picked up by Yahoo, MSNBC, HuffPo, and elsewhere. As a result, views that are pretty commonplace around here reached a somewhat different audience. I started getting more emails than usual, as well as a couple of phone calls, and some online responses. A representative sample:

  • "Sean Carroll, servant of Satan..."

  • "God has a way of bring His judgement to those who mock Him... John Lennon stated "Christianity will end, it will disappear." Lennon was shot six times after saying that... Marilyn Monroe said to Billy Graham after Graham said the Spirit of God had sent him to preach to her: "I don't need your Jesus". A week later she was found dead in her apartment."

  • "See you in hell."

  • "Maybe GOD is just a DOG that you will meet when you are walking on the Beach trying to figure out how to get sand out of your butt crack."

I admit that last one is a bit hard to interpret. The others I think are pretty straightforward. A more temperate response came from theologian William Lane Craig (a fellow Blackwell Companion contributor) on his Reasonable Faith podcast. I mentioned Craig once before, and here we can see him in action. I'm not going to attempt a point-by-point rebuttal of his comments, but I did want to highlight the two points I think are most central to what he's saying. One point he makes repeatedly -- really the foundational idea from which everything else he has to say flows -- is that a naturalist account of the form I advocate simply doesn't explain why the universe exists at all, and that in my essay I don't even try. Our old friend the Primordial Existential Question, or Why is there something rather than nothing? I have to admit I'm a bit baffled here. I suppose it's literally true that I don't offer a reason why there is something rather than nothing, but it's completely false that I ignore the question. There's a whole section of my paper, entitled "Accounting for the world," which addresses precisely this point. It's over a thousand words long. I even mention Craig by name! And he seems not to have noticed that this section was there. (Among my minor sins, I'm happy to confess that I would always check first to see if my name would appear in someone else's paper. Apparently not everyone works that way.) It would be okay -- maybe even interesting -- if he had disagreed with the argument and addressed it, but pretending that it's not there is puzzling. (The podcast is advertised as "Part One," so maybe this question will be addressed in Part Two, but I still wouldn't understand the assertion in Part One that I ignored the question.) The idea is simple, if we may boil it down to the essence: some things happen for "reasons," and some don't, and you don't get to demand that this or that thing must have a reason. Some things just are. Claims to the contrary are merely assertions, and we are as free to ignore them as you are to assert them. The second major point Craig makes is a claim that I ignored something important: namely, the Borde-Guth-Vilenkin singularity theorem. This is Craig's favorite bit of cosmology, because it can be used to argue that the universe had a beginning (rather than stretching infinitely far backwards in time), and Craig is really devoted to the idea that the universe had a beginning. As a scientist, I'm not really devoted to any particular cosmological scenario at all, so in my paper I tried to speak fairly about both "beginning cosmologies" and "eternal cosmologies." Craig quotes (misleadingly) a recent paper by Audrey Mithani and Alex Vilenkin, which concludes by saying "Did the universe have a beginning? At this point, it seems that the answer to this question is probably yes." Mithani and Vilenkin are also scientists, and are correspondingly willing to be honest about our state of ignorance: thus, "probably" yes. I personally think the answer is "probably no," but none of us actually knows. The distinction is that the scientists are willing to admit that they don't really know. The theorems in question make a simple and interesting point. Start with a classical spacetime -- "classical" in the sense that it is a definite four-dimensional Lorentzian manifold, not necessarily one that obeys Einstein's equation of general relativity. (It's like saying "start with a path of a particle, but not necessarily one that obeys Newton's Laws.") The theorem says that such a spacetime, if it has been expanding sufficiently fast forever, must have a singularity in the past. That's a good thing to know, if you're thinking about what kinds of spacetimes there are. The reason I didn't explicitly mention this technical result in my essay is that I don't think it's extremely relevant to the question. Like many technical results, its conclusions follow rigorously from the assumptions, but both the assumptions and the conclusions must be treated with care. It's easy, for example, to find examples of eternally-existing cosmologies which simply don't expand all the time. (We can argue about whether they are realistic models of the world, but that's a long and inconclusive conversation.) The definition of "singularity in the past" is not really the same as "had a beginning" -- it means that some geodesics must eventually come to an end. (Others might not.) Most importantly, I don't think that any result dealing with classical spacetimes can teach us anything definitive about the beginning of the universe. The moment of the Big Bang is, if anything is, a place where quantum gravity is supremely important. The Borde-Guth-Vilenkin results are simply not about quantum gravity. It's extremely easy to imagine eternal cosmologies based on quantum mechanics that do not correspond to simple classical spacetimes throughout their history. It's an interesting result to keep in mind, but nowhere near the end of our investigations into possible histories of the universe. None of this matters to Craig. He knows what answer he wants to get -- the universe had a beginning -- and he'll comb through the cosmology literature looking to cherry-pick quotes that bolster this conclusion. He doesn't understand the literature at a technical level, which is why he's always quoting (necessarily imprecise) popular books by Hawking and others, rather than the original papers. That's fine; we can't all be experts in everything. But when we're not experts, it's not intellectually honest to distort the words of experts to make them sound like they fit our pre-conceived narrative. That's why engagement with people like Craig is fundamentally less interesting than engagement with open-minded people who are willing to take what the universe has to offer, rather than forcing it into their favorite boxes.

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