What is the multiverse?

Physicists acknowledge the word has a poetic quality — and is sometimes used as an umbrella term to describe different concepts. The simplest answer is that our universe — all the light we can see, stretching back 13.8 billion years ago to the Big Bang — is not the only one. Instead, it’s one of many, many billions of possible universes. The concept of a multiverse is also linked to the famous but controversial “many-worlds interpretation” of quantum mechanics, which proposes that each event that could have more than one outcome — whether it’s a person’s decision to speed through a yellow light, or a card falling face down — causes reality to splinter and branch off to create new universes where alternate events happen: the card falls face up, or the person slams on the brakes. This version of a multiverse is an outgrowth of the weird nature of quantum reality, where everything is described in probabilities. “I actually try to think, when I get a parking ticket, ‘Hey, there’s another version of a parallel universe where I didn’t get ticketed,’ so I can feel a bit better. And there’s another version where my car got towed,” said Max Tegmark, a physicist at the Massachusetts Institute of Technology. But more complicated multiverses are “more fun if you’re a Hollywood writer,” Tegmark says. In some conceptions, those multiverses could not only have different history books, but also different physics, with new fundamental constants that govern how gravity works, or different masses for the fundamental particles that make up matter.

Why do some scientists think the multiverse is real?

For a long time, the multiverse was seen as the province of philosophy, not physics. Hugh Everett III, the physicist who proposed the above-mentioned many-worlds interpretation in 1957, left academia with his ideas ridiculed. “He was forced out of physics and ended up being drunk and dying young. A tragic ending. Scientists knew this is what happened when you work on the multiverse,” said Laura Mersini-Houghton, a cosmologist at the University of North Carolina at Chapel Hill. The idea of a multiverse has been resisted by many scientists because it couldn’t be measured or tested. We can’t reach these other universes even if they do exist, so what’s the point in positing them? But like so many things in physics, one of the key reasons that the idea has gained traction is because of weird discrepancies in our established reality. For example, the probability that our universe exists, and with conditions favorable to life, is vanishingly small. Mersini-Houghton points to the Boltzmann brain paradox, where the odds of a naked brain forming in space are more likely than any of our scientific explanations for how the universe developed. A multiverse — in which our universe is just one among billions — begins to make the improbable coincidence of our existence more plausible. “If we insist that we only have one universe, then of course we are limiting our options,” Mersini-Houghton said.

What are some of the theories that give rise to a multiverse?

The multiverse isn’t a theory, but a consequence of various different theories. The many-worlds interpretation, for example, is an outgrowth of quantum mechanics. Another way to spawn the multiverse builds off cosmic inflation, the theory that our universe expanded exponentially in mere moments after the Big Bang. Under “ eternal inflation ,” that exponential expansion keeps happening, creating a froth of cosmic bubbles that each hold its own universe. When different bubble universes collide, they may leave detectable fingerprints on other universes. Scientists have been searching for these signatures in the cosmic microwave background, the faint radiation glow left over from the Big Bang. String theory, which proposes that matter and energy are created by vibrating strings, also predicts the existence of a multiverse. Mersini-Houghton combines quantum mechanics and string theory to predict that our universe is just one of many. All of these ideas are fascinating, but a little hard to wrap your head around, and there’s no scientific consensus on whether any version of the multiverse is real. Still, proponents argue that as scientists gather evidence for various theories, like cosmic inflation, they strengthen the case for the multiverse. “In science, if you take seriously a theory, you’re forced to take seriously its predictions also — not only the things you like,” Tegmark said.

Which multiverse is the movie based on?

In an interview with the New York Times , “Everything Everywhere All at Once” directors Daniel Scheinert and Daniel Kwan said that they were inspired by both the many-worlds interpretation of quantum mechanics and the idea of cosmic bubble universes. But several physicists said that while they enjoyed the movie, it doesn’t really hold up to scientific scrutiny. It’s more “inspired by” than “based on” any real scientific theory. “I think they’re using this multiverse as a toy, or more to explore an existential problem in a beautiful artistic way. I don’t think they’re using it in any kind of scientific way,” said Djordje Minic, a physicist at Virginia Tech. “I’m not going to nitpick, not going to grade a movie as if it was a physics quiz,” Tegmark said. Mersini-Houghton said she was invited to a screening of the movie after the publication of her book, “ Before the Big Bang .” “As a scientist, you can’t help whenever you watch something that is mildly related to science — you are not paying attention to the artistic side,” she said. “I couldn’t help but see all the traveling to universes and all that — the science was not there.”

So we can’t jump to other universes?

Sorry, but no. There’s currently no theory of how to travel between different realities in the multiverse. The bubble universes have been theorized to collide with one another, leaving ancient scars that could be detected. But “verse jumping” isn’t currently thought to be possible — and it is particularly cataclysmic in the many-worlds interpretation. “This is a problem,” Minic said. “Once you start interacting, you are violating all sorts of things in physics and the very nature of quantum theory.”

Why should I care about the multiverse?

You mean besides the fact that it’s cool to contemplate such huge questions about the nature of reality? Tegmark, of MIT, thinks that the multiverse can make us all a bit more humble, acknowledging that we don’t know everything. The incomprehensible vastness could make some people feel small and powerless, but not Tegmark. “People can use a bit of cheering up in these trying times. It’s really quite marvelous, if you think about the history of humanity, how science has really expanded our horizons,” Tegmark said. At first, “we didn’t even realize we lived on a ball in space. But we are part of something much grander — a solar system, a galaxy cluster, probably among many other parallel universes. I find that inspiring.”

How physics inspired Oscar nominee ‘Everything Everywhere All at Once’

By Carolyn Y. Johnson

March 10, 2023 at 6:00 a.m. EST

The mind-bending idea that our universe is one among many is gaining legitimacy in physics, and is central to the plot of “Everything Everywhere All At Once.” (iStock)

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In at least one universe this Sunday evening — perhaps our own — the imaginative, absurdist, sci-fi comedy-drama “Everything Everywhere All at Once” will sweep the Oscars, shining Hollywood’s brightest spotlight on the mind-bending notion that our universe is just one in a kaleidoscopic array of others.

In the movie, a laundromat owner played by Michelle Yeoh jumps around the multiverse, flitting in and out of different parallel universes, each containing variations of her life. In one, she’s a glamorous movie star and kung fu master. In another, she has comically floppy hot-dog fingers. In yet another, she’s a sentient rock with googly eyes. It’s a fantastical plot device, but also an extended riff on a real idea in physics.

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The movie takes a lot of liberties with working theories — one physicist flatly said “the science was not there.” But the idea of a multiverse, once a fringe concept that physicists talked about in bars after conferences, has been gaining legitimacy in recent years and is firing serious scientific debate.

Questions about the multiverse quickly get philosophical, but here’s some of what scientists (think) we know.