Science fiction, contingency, and the multiverse

by Matthew R. Francis 

I have a full beard, slightly pointy on the chin. I study arcane subjects. I have a cat who sits in my lap while I work. I own a black trench coat. Let’s face it: I have the hallmarks of the Evil Twin from Parallel Earth.

You know what I mean. In science fiction stories, movies, and TV shows, it’s a common trope to have a parallel reality where everything is nearly the same, down to the same people — but where the subtle differences lie in life choices, technology, or sometimes personality. In that world, your counterpart could be just like you, only…evil. TV being what it is, that evilness is often expressed visually in darker hair, taller boots, choice in pets, and (if you’re a guy) a beard. Somewhere in a parallel reality, there’s a clean-shaven version of me that plays soccer, owns a golden labrador retriever, and teaches kindergarten.

Whether evil or not, though, the premise of having such a parallel existence is to hint at might-have-beens: what if Mr. Spock, the avatar of logical thought and ethics, was actually cruel? What if transportation was based on alien technology, thanks to contact and trade decades before? The interaction between the story’s protagonists and their parallel-reality counterparts highlights the contingent nature of history. If we rewound the film of history (talk about an old-fashioned metaphor in this age!), we might not see the same story at all.

In science, we are also interested in contingency: if subtle changes to the environment affect the health of organisms (especiallly people), or the effect of present human activity on future climate. On a grander scale, we’d like to know what evolution would have made from the raw materials of the first organisms if we restarted Earth’s history at the origin of life. If the asteroid impact at the end of the Cretaceous hadn’t happened, would the non-bird dinosaurs still be around?

Or, if we replayed the history of the Universe from the moment of the Big Bang, would there be an Earth or stars at all?

Cosmologists (those scientists studying the history and contents of the entire Universe) usually turn the question around, asking what the early cosmos must have been like to produce the galaxies and their arrangement. If, for example, there were more dark matter, then we might see fewer galaxies, but those we see might be more massive. Too much dark energy — the mysterious substance that causes the Universe’s expansion to accelerate — and the Universe might be devoid of galaxies entirely, since expansion would be faster than the slow action of gravity to pull matter together. (That would be like trying to make hand-tossed pizza crust but pulling the dough apart too quickly.)

However, there’s another trickier question that can’t be answered by looking at galaxies. The Universe as we understand it is governed by four fundamental forces: gravity, electromagnetism, and the creatively named weak and strong forces. Particle physics is largely engaged in studying these forces, as well as the Higgs boson. The relative strength of the forces and the behavior of the Higgs are in many ways strange: gravity is much weaker than the other three, which are themselves delicately balanced to produce the structure of atoms and their nuclei. If this balance were different, then no atoms, no molecules, no stars, no galaxies…and no us.

That’s known as the “fine-tuning problem”, and it’s inspired a lot of nonsense from scientists, philosophers, and writers. While it’s possible to overstate the problem (there’s some wiggle-room in the parameters), getting everything just right for the Universe we see looks almost too good to be true. For that reason, some cosmologists postulated that rapid expansion after the Big Bang produced a multiverse: a set of isolated pocket universes within the total cosmos, each of which has a different set of parameters. In this scheme, the forces we have are contingent upon the structure of the entire multiverse. We happen to live in one of those pocket universes that can make stars, galaxies, planets, and penguins. Other parts of the multiverse may be completely devoid of all that; call those the Boringverses.

Which of course brings us back to Parallel Earth and the Evil Matthew Hypothesis. (Someone please write a science fiction novella with that title.) In these stories, somehow the protagonists are able to travel between the different realities, either meeting themselves or being confused with their doppelgangers. In the multiverse, there’s no obvious way to travel between pocket universes, or even to know they exist — a serious problem for those of us who care about testability of our theories. And even if the multiverse exists, the parallel universes would each be subject to their own contingencies and histories, meaning the chances of another Earth, much less another you, are basically zero.

Another possibility is that the fine-tuning problem is a failure of our ingenuity, meaning that we just haven’t figured out a theory that tells us why things are as they are. Personally, I think even if the multiverse exists (and I’ve sort of come to terms with it), we still need to understand the contingencies involved in making our cosmos what it is. It’s a complex and sometimes worrying topic, and I admit I’m not entirely happy with any of the options right now.

My dissatisfaction comes mainly because the physicists working in this area have many ideas, but little data to work with. While several theories, including some versions of string theory, predict a multiverse, there’s little agreement on how that multiverse should look or even if we can distinguish between the ideas using observations.Those of us who really want to know, rather than just make plausibility arguments, are always going to be grumpypantsed with theories containing untestable aspects. However, the situation may improve with the advent of new experiments measuring the polarization of light left over from the Universe’s early moments. While they may not give us the complete answer, they should at least help us rule out some of the alternatives.

I don’t really think I’m an evil person. My beard is more 19th-century than satanic; my cat is an attention-hungry tuxedo rather than a haughty white Angora. Give me the same genetics but a different life history — different triumphs and tragedies — and who knows what I’d be like today. The challenge in cosmology is to understand contingencies on the biggest scales, to comprehend why our Universe is the way we see it.