A Universe Made for Us? Statistics and the Multiverse
Not a bicycle built for two, but a universe made for me...and you?
Posted Nov 19, 2018
In parts one and two of this four-part series, I looked at the vexed question of whether the universe was somehow – and by Someone – fine-tuned for us. There may not be a genuine, no-nonsense, unequivocal answer, but there is much to be learned by merging statistics, logic, and common sense, especially when it comes to the difference between probabilities before and after an event, and much head-scratching occasioned by the multiverse hypothesis.
For example, philosopher Niall Shanks asks us to imagine shuffling a deck of cards and then dealing them out, face down. What is the likelihood that someone could predict the entire sequence, in advance, and without any hanky-panky? The chance of getting the first card correct is 1 in 52. The chance of getting the first two cards correct is 1/52 x 1/51 = 1/2652, and so on, so that the probability of guessing the entire deck in the proper order is 1/52!. (The notation "!” in mathematics is described as “factorial,” with 52! = 52 x 51 x 50 ... x 1.) This is an unimaginably small number, something like one in ten followed by 60 zeros. And yet, it is also true that the chance of the cards having been dealt in the order that actually occurred is 100 percent. They had to come out some way, and among the near-infinite number of possibilities, one in particular actually emerged. Is that astounding? Yes, if you concern yourself with the chance of that precise outcome before it happened. But no, if you look at the post-hoc outcome, knowing that it had to be one way or another.
Alternatively, consider the probabilities before versus after a simple physical event, such as the position of a golf ball before versus after a golfer hits it. It would take a near-miracle to identify, in advance, the precise eventual location of that ball. But the outcome – wherever the ball ends up – isn’t miraculous at all, nor is it evidence of divine intervention or of the golf course having been designed so as to arrange that particular eventual placement of the ball since it had to be somewhere. Even though any one specific location is extraordinarily unlikely, it is even less likely that the ball would have disappeared entirely, or had it landed atop the flat head of a hippo. For us to marvel at the fact of our existing (in a universe that permits that existence) is comparable to a golf ball being astounded at the fact that it ended up someplace.
There are many ways to interpret what might be called the unexpectedness of our existence, none of which necessarily supports the claim that we must attribute that existence to particular pre-planning, by the cosmos and for us. Every person exists because a particular egg (one out of roughly 500 ovulated by his or her mother over the latter's lifetime) encountered a particular sperm (one out of roughly 150 million produced by his or her father in a single ejaculation). Every member of the human population – roughly 7.5 billion – can, therefore, insist that his or her existence was fore-ordained, evidence of a kind of me-thropic principle.
For a more wide-ranging example, the Chicxulub asteroid crashed into what is today Mexico’s Yucatan peninsula 66 million years ago, eventually wiping out the dinosaurs and clearing a path for the rise of mammals and eventually, us. Without that impact and the ecological niches that were opened up by the demise of those previously dominant dinosaurs, it is extremely unlikely that our species would ever have evolved. Had things proceeded differently, the prospect is vanishingly smaller yet that I would be writing this blog, or that you would be reading it.
Should we therefore see the Chicxulub impact as further evidence that our planet was fine-tuned, with my writing and your reading in mind? And that the dinosaurs’ destruction was mere collateral damage en route to the ultimate goal of creating Homo sapiens roughly 65 million years later? If so, then we are responsible for that asteroid and were it not for the universe’s goal of producing us, T. rex and company would still be around. Mazel tov! We really are important!
Physics has additional possible explanations for what masquerades as cosmic fine-tuning. Of these, one of the more intriguing (albeit difficult to grasp) is the possibility of “multiverses,” which revisits the question of probabilities before versus after an event, albeit in somewhat different guise. Here is astrophysicist Martin Rees:
"There may be many “universes” of which ours is just one. In the others, some laws and physical constants would be different. But our universe would not be just a random one. It would belong to an unusual subset that offered a habitat conducive to the emergence of complexity and consciousness. The analogy of the watchmaker would be off the mark. Instead, the cosmos may have something in common with an off-the-rack clothes shop: if the shop has a large stock, we are not surprised to find one suit that fits. Likewise, if our universe is selected from a multiverse, its seemingly designed or fine-tuned features would not be surprising.[i]."
Under the multiverse hypothesis, there is not only a potentially infinite number of universes, but the basic physical laws and constants might well vary across them. It is a radically difficult concept, but perhaps no weirder than basic quantum mechanics, which we now know to be valid. It was recently reported that there are something like two trillion galaxies in the currently known universe, which is about 20 times more than had previously been thought.[ii] Each galaxy consists of millions – in some cases, billions – of stars, many of which have their own planets. And although it appears that the fundamental physical constants hold across the known galaxies, the mere fact that there are so many (the overwhelming majority of which are not in any meaningful sense “known”) opens the possibility that our Earthly experience may be a small subset of the possible – even without introducing the prospect of multiple universes.
Niall Shanks suggests that the multiverse hypothesis “does to the anthropic universe what Copernicus’s heliocentric hypothesis did to the cosmological vision of the Earth as a fixed center of the universe.”[iii] Now, post-Copernicus (and Kepler, Galileo and others), the Earth is known to be just one planet among many, in one galaxy among many. Perhaps we’re just the occupants of one universe among many. Interestingly, even as he demoted the Earth, Copernicus himself placed the Sun in the center of the universe, just as he assumed that planetary orbits were perfect circles, an assumption that was widespread in early astronomy, based on the notion that the “heavenly bodies” are necessarily perfect, just as, in their geometry, circles are perfect. Galileo, too, assumed that planetary orbits were circular; it wasn’t until Kepler – using data from the aforementioned Tycho Brahe - that astronomers recognized they are elliptical. The cosmos, like the human body, is far from perfect. But like the human body and the bodies of all other organisms, it is good enough to have permitted us and them to exist.
In my next and final post on the question of whether the universe is anthropic, we’ll take a look at quantum weirdness, along with other weirdnesses.
David P. Barash is professor of psychology emeritus at the University of Washington. His most recent book relevant to this topic is Through a Glass Brightly: using science to see our species as we really are (2018, Oxford University Press).
[i] Martin Rees. 2001. Our Cosmic Habitat. Princeton, NJ: Princeton University Press.
[iii] Niall Shanks. 2004. God, the Devil, and Darwin. New York: Oxford University Press.