Multiverse Stories Are All The Rage. The Theoretical Science Behind Them Is Even Stranger

In Season 1 of Dark Matter, college physics professor Jason Dessen encounters a surprising nemesis: himself. Apple’s sci-fi series sees Dessen kidnapped and sent to an alternate reality, one where he’s a famous but lonely research lab co-founder rather than a family man stuck in a dead-end job. Dark Matter Season 2 is now underway on Apple TV, and that multiverse is expanding in surprising ways. That said, Dark Matter’s take on the multiverse is limited to universes in which the traveler was born or could have been born. And the Dessen family and Leighton and others should be grateful for this limitation. String theory co-founder Leonard Susskind believes there may be 10^500 universes out there.

If you’re having trouble wrapping your head around that number, here’s a comparison: there are “only” 10^82ish atoms in the observable universe. So, what does multiverse theory mean for those of us here in this particular universe?

A Multitude of Multiverses

Growing a universe into a multiverse has become the go-to move for pop culture franchises looking to raise their stakes. Most obviously, Marvel’s Multiverse Saga began in 2021 and is slated to close next year. But there’s a multiverse of multiverses out there: the old DC Universe created the famous Crisis on Infinite Earths, and more recently, Everything Everywhere All at Once and Spider-Man: Into the Spider-Verse won Oscars with multiverses.

It’s not a new concept — Star Trek introduced its sinister mirror universe in 1967, and parallel universes appeared in comic books and pulp sci-fi decades before that. But the multiverse is now so common that it’s a little exhausting.

Either way, how a fictional multiverse works is usually glossed over with a little talk of magic or technobabble. Dark Matter fares a bit better on this front, as the brain chemistry aspects of how superposition is managed are central to the storyline, and author Blake Crouch based much of the 2016 novel version of Dark Matter on Hugh Everett’s approach to multiverse theories.

But what do we really know in real life? While they at least know a few hard facts about their parallel universes, we can only speculate about the existence, workings, and implications of ours. Here’s what we think we maybe kinda know.

Quantumania

The multiverse, to define it beyond “different worlds with different Spider-Mans,” encompasses not just the 83 billion light-years and quadrillions of stars and planets that make up our universe, but the entirety of space, time, matter, and energy across all universes that may conceivably exist. While we’ve speculated about other universes since ancient times, contemporary arguments date back to the 1950s. And while there are many different theories, physicist Paul Halpern places most of them in two major categories that emerged from cosmology and quantum physics.

The quantum physics approach is called the many-worlds interpretation. The first cracks at MWI came from Hugh Everett and Erwin Schrödinger, but it was another physicist, David Deutsch, who really kicked things off in the 1970s. You can probably guess what Schrödinger’s presence in this paragraph means.

One of the core ideas of quantum physics is quantum superposition, where something minuscule like an electron can be in two different states at once. Schrödinger’s cat is the most famous example, but a clearer example is a spinning coin: until it lands and shows us heads or tails, it is both and neither at once. Again, Dark Matter is hyper-focused on superposition, with a fictional chemical that alters brain chemistry — in order for the mind to process superposition — is central to much of the show’s plotting.

So, if we replace coins with the fundamental building blocks of the universe, then an electron taking one quantum path might produce another universe where it took the other path. Seeing the coin land on heads doesn’t necessarily eliminate the existence of a universe where it landed on tails; it just makes the tails-verse impossible to observe from head-land.

Deutsch and other physicists have taken this argument to its metaphysical extremes, arguing that quantum computers could catch glimpses of these other universes, and even that, given an infinite number of universes, any fictional story that obeys the laws of physics could eventually become real. It’s around the time we start legitimizing Jane Austin fanfic that other physicists dismiss MWI as a ludicrous, incoherent fantasy, and since MWI generally posits that all of these worlds could never witness or interact with each other, it’s kind of a moot point anyway. But if you skip past that inconvenient detail, MWI lets shows like Dark Matter and Star Trek explain all those evil doppelgängers.

Cosmology, meanwhile, offers inflation theory, which comes from the work of Alexei Starobinsky and Alan Guth. In the 1970s and ‘80s, they argued that the universe inflated less than a second after the Big Bang, rapidly expanding to give us a universe that’s properly universe-sized. This helps explain, among other things, why the universe is pretty much the same temperature no matter where we look: it reached that uniform point before it inflated. The tiny bumps in temperature we can sometimes spot suggest the process wasn’t quite uniform; NASA has called these bumps “stretch marks.”

That’s not controversial, but according to the idea of eternal inflation, the process was much less uniform, unlike blowing up a balloon. Some distant regions of the universe may have continued to inflate, and these regions may have broken off into their own universes, like a bubble splitting in two. Those universes would also inflate, and that inflation would produce new universes, and so on forever. Physicist Paul Davies — a critic — said inflation “can best be understood by imagining that the observable universe is, relatively speaking, a tiny blob of space buried deep within a vast labyrinth of interconnected cosmic regions.” Within this labyrinth, additional Big Bangs are constantly firing off like interstellar popcorn, too far beyond the cosmological horizon to ever be observed.

If there are a quattuordecillion or two other universes out there, the differences between them wouldn’t be as simple as Futurama’s regular and cowboy universes. While MWI argues that all those split paths still obey our laws of physics, every universe in the inflationary multiverse could have radically different laws; our laws, Davies says, are more like “local bylaws.” So if you throw in some gibberish about a special portal or spaceship engine, your sci-fi story can have everything it needs to travel to another universe where everything is radically different.

Other realms of science, like string theory, offer their own confounding multiverse theories. But they all come with a huge caveat: there’s no hard evidence for the existence of other universes, nor is there any known way to observe or test for one.

Maybe, Maybe Not

The boundary between science and philosophy gets blurry here, as critics have argued that the multiverse, in any form, can be a way to cheat around the fine-tuning argument. Sentient life, given the staggering size of the universe, is rare and fragile. We’re the only example that we know of, and were the physical constants of the universe just a little different — if the force of gravity were weaker or stronger, if protons and electrons had different charges, or if carbon and oxygen weren’t as plentiful — then we wouldn’t be here. And yet here we are.

A common analogy is that life, as we understand it, requires a lot of different dials to be parked at just the right setting. That’s wildly improbable if left to random chance, and yet that’s exactly what happened. Religious philosophers and scientists have offered up theistic explanations for the state of our universe, while other theories range from “life isn’t as picky as we think” to “the universe is a simulation” and “the laws of the universe simply are what they are, and cannot be anything else.”

If there is a multiverse, our existence isn’t improbable at all. You would eventually win the lottery if you could buy infinite tickets, and multiverse theory argues that our universe won the lottery of physical constants. Our universe appears fine-tuned because we’re in a finely-tuned universe, while there is no life — or at least no carbon-based life — to observe the countless universes that aren’t friendly to it.

To critics like Davies and science writer Philip Ball, this is an unsatisfying explanation. Not every physicist and cosmologist agrees with the raw mechanics at play here — critics of MWI, for example, argue that the universes we don’t observe simply collapse out of existence. But the larger and more ironic issue is that multiverse theory has to be taken on faith. We can’t observe any evidence of other universes, and we’ll almost certainly never be able to.

That the solution to the riddle of existence might be “there are actually a gajillion wacky universes” isn’t necessarily compelling on a scientific or even emotional level; nature is no longer elegant, but a sprawling series of whimsies that tell Occam’s razor to get bent. Davies even cheekily posits a scenario where an infinite number of universes produces countless civilizations capable of simulating consciousness within computers, leading to simulated universes within real universes, some of which also produce simulated universes, and so on forever until you’re left with something like No Man’s Sky on methamphetamines.

More realistically, science writer and self-proclaimed multiverse agnostic John Horgan argues that, like God, science will never be able to definitely prove or disprove the existence of the multiverse, because the idea’s very nature as something outside of everything we can grasp puts it beyond the quantifiable realm of science. And no matter how many universes are out there, you’re still stuck with the question of why any of them are there, and we still have to wonder why we exist in this one. But Horgan does concede that the multiverse can be an interesting way of looking at our already tiny place in the cosmos, at least in the right hands.

So while explaining the nature of existence is slightly beyond our mandate as a pop culture publication, maybe these fundamental riddles explain why the fictional multiverse has become so popular. Okay, sure, it’s mostly money and Michael Keaton cameos. But in the time since science fiction emerged as a genre, we’ve taken flight and landed on the moon, built hulking mainframe computers and shrunk them down to pocket-sized marvels, and observed the tiniest particles and the furthest reaches of the one universe we’re certain about. Maybe the one thing we have left to explore is ourselves, and the multiverse gives us infinite ways to do so. Critics of the multiverse argue that scientists could use a little more philosophy in their lives, and that, ironically, is where multiverse fiction comes in.

Dark Matter streams on Apple TV.