Is The Multiverse Real? The Science Behind ‘Everything Everywhere All At Once’

Do multiverses exist? Is our universe one of many? The multiverse is a key plot device in the hit movie Everything Everywhere All At Once—in prime position to win big at the 95th Academy Awards a.k.a. the Oscars—in which a Chinese immigrant explores parallel universes where she leads completely different lives.

But does the multiverse have any basis in science?

In the movie, Michelle Yeoh’s character Evelyn Wang connects with versions of herself in parallel universes to prevent the multiverse from being destroyed. Is it far-fetched? Of course! But right now, cosmologists are trying to figure out if there’s a group of multiple universes running parallel to each other—and whether they might be habitable.

What is the multiverse?

It’s a basket of ideas from cosmologists and quantum theorists about that our universe might not be the only one and that it might share a higher structure with multiple other universes. “Some suggest that the burst of inflation in the early stages of our universe might be eternal, with individual universes crystallising out of it, each written with its own unique laws of physics,” said Geraint Lewis Professor of Astrophysics at the University of Sydney, Australia and author of “Where Did the Universe Come From? And Other Cosmic Questions.” In this cosmological explanation of the multiverse, the other universes parallel to our own—if they exist—may or may not be capable of sustaining life.

That burst of inflation in our universe is, of course, key evidence for our universe having emerged from a hot, dense point—the Big Bang. However, what happened before the Big Bang—and whether other universes were perhaps simultaneously created alongside our own—is utterly unknown.

Common misconceptions about the multiverse

There is zero evidence for other universes. So the biggest misconception about the multiverse is that it’s a bone fide theory that’s been proven. “It isn’t—it doesn’t really have a mathematical basis—it is a collection of ideas,” said Lewis. “In the cycle of science it remains at the hypothesis stage and needs to become a robust proposition before we can truly understand the consequences.”

One of Stephen Hawking’s last theories before his death in 2018 predicts the universe is finite and far simpler than many current theories about the Big Bang say. That has consequences for the multiverse paradigm. “We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes,” said Hawking.

In 2020 Nobel Laureate Sir Roger Penrose claimed that an earlier universe existed before the Big Bang and can still be observed today as a scar on the cosmic microwave background (CMB). The CMB is a faint glow of very long wavelength microwave radiation that fills our universe, which is a key part of the evidence for the Big Bang itself. A similar hypothesis to Penrose’s was put forward last year by cosmologist Laura Mersini-Houghton. Both are intriguing theories, but both are unsubstantiated. For now the multiverse remains a wonderful idea, but little more.

Can the multiverse ever be proven?

As we understand it so far, no, which is why discussion of the multiverse gets ridiculed by some scientists. But that doesn’t mean it can’t one day become a scientific theory. “We have no idea if it is testable or not,” said Lewis. “Once we have the mathematics in hand, we will have a chance of seeing if we can detect the presence of other universes … currently we have no idea which path we are on.” What science needs is a mathematical theory to test. It doesn’t yet have one.

Could it be possible to jump between parallel universes?

If they do exist then, sure, it might be possible to travel between parallel universes. Why not? “I do wonder if the potential complex geometry of all the universes means that they could be connected somehow—via wormholes and the like,” said Lewis. “That would mean inference about their existence is possible, and even travel between universes, too.”

However, thoughts about jumping between parallel universes—let alone seeing or meeting other versions of ourselves in them—is getting a little too Hollywood. After all, what if there are actually an infinite number of parallel universes and all of them are lifeless? This is an area where multiverse science is beginning to be done.

Is the multiverse hospitable to life?

Hollywood might be content to wonder what would happen in a parallel universe if someone made a different life decision. Cosmologists are more interested in pondering whether if other universes exist, they might have laws of physics different from our own. Could they still host life? That’s the central question in new work on multiverse predictions, the latest of which was published this month. “We already know that some changes to the laws of physics rapidly result in universes that are dead and sterile,” said co-author Lewis.

So are we just lucky to live in a universe that can form galaxies capable of hosting life? It’s not that simple. “There is an idea—the Rare Earth hypothesis—that even though our universe is clearly habitable, the conditions for life are vanishingly rare,” said Lewis. With colleagues, he picked apart billions of years of processing of elements in our universe, from what elements were generated in stars, how they were distributed around our universe, and the chemical reactions that took place. The results suggest that the ratio of carbon to oxygen—something determined by nuclear reactions inside stars—appears to be particularly important. So does a balance of both of those elements, though other elements appear to be less critical.

“There are those who study galactic habitability and think that life in the outer edges of galaxies is likely to be extremely rare as there simply has not been enough generation of elements for life,” said Lewis. So, if parts of our universe are uninhabitable, so will be parts of—and perhaps entire—other universes. However, if life was discovered in these so-called uninhabitable regions of our universe then suddenly everything, everywhere (all at once) would change. “If we find that life is common in lots of these environments —which itself would be a momentous story—then that would suggest that life should be possible across a swath of the multiverse,” said Lewis.

Does the multiverse theory have a future?

The use of the multiverse in Everything Everywhere All At Once has been a massive success, but the concept itself is a long way off from becoming an accepted scientific theory. “All good science starts with a (sometimes wacky) idea,” said Lewis. “But so do the paths to dead ends.”

Wishing you clear skies and wide eyes.