Is the multiverse real? The science behind “Everything, everywhere at once”

Are there multiverses? Is our universe one of many? The multiverse is a central plot device in the successful film Everything everywhere at once– in prime position to win big at the 95th Academy Awards, aka the Oscars – in which a Chinese immigrant explores parallel universes in which they lead vastly different lives.

But does the multiverse have a scientific basis?

In the film, Michelle Yeoh’s character, Evelyn Wang, bonds with versions of herself in parallel universes to prevent the multiverse from being destroyed. Is it far fetched? Naturally! But right now, cosmologists are trying to figure out if there’s a cluster of multiple universes that run parallel to each other — and if they might be habitable.

What is the multiverse?

It is a bundle of ideas from cosmologists and quantum theorists that our universe may not be the only one and that it shares a higher structure with several other universes. “Some suggest that the inflationary spurt could be perpetual in the early stages of our universe, from which individual universes crystallize, each written with their 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 able to sustain life.

This inflationary spurt in our universe is, of course, important evidence that our universe emerged from a hot, dense point – the Big Bang. However, what happened before the Big Bang – and whether other universes were created at the same time as our own – is completely unknown.

Common misconceptions about the multiverse

There is no evidence for other universes. So the biggest misconception about the multiverse is that it’s a bone-hard theory that’s been proven. “It’s not — it doesn’t really have a mathematical basis — it’s a collection of ideas,” Lewis said. “In the cycle of science, it remains in the hypothesis stage and must become a robust statement before we can truly understand the implications.”

One of Stephen Hawking’s final theories before his death in 2018 predicts that the universe is finite and much simpler than many current Big Bang theories claim. This has implications for the multiverse paradigm. “We don’t rely on a single, unique universe, but our results imply a significant reduction of the multiverse to a much smaller set of possible universes,” Hawking said.

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 an important piece of evidence for the Big Bang itself. A hypothesis similar to Penrose’s was put forward by cosmologist Laura Mersini-Houghton last year. Both are intriguing theories, but both are unfounded. For now, the multiverse remains a wonderful idea, but not much more.

Can the multiverse ever be proven?

As we have understood it so far, no, which is why the discussion of the multiverse is ridiculed by some scientists. But that doesn’t mean it can’t become a scientific theory one day. “We have no idea whether it’s testable or not,” Lewis said. “Once we have the math in our hands, we have the opportunity to see 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 have any.

Could it be possible to jump between parallel universes?

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

However, the thought of jumping back and forth between parallel universes — let alone seeing or meeting other versions of ourselves in them — is getting a little too Hollywood-y. Because what if there really are an infinite number of parallel universes and all of them are lifeless? This is an area where multiverse science is beginning to take hold.

Is the multiverse livable?

Hollywood might be content to wonder what would happen in a parallel universe if someone made a different life choice. Cosmologists are more interested in considering whether other universes, if they exist, might have different physical laws than our own. Could they still harbor 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 in the laws of physics quickly lead to dead and sterile universes,” said co-author Lewis.

So are we just lucky to live in a universe that can form galaxies that can host life? It is not so easy. “There’s an idea — the rare-earth hypothesis — that while our universe is clearly habitable, the conditions for life are infinitesimal,” Lewis said. Together with colleagues, he has dissected billions of years of processing elements in our universe, what elements were created in stars, how they were distributed in our universe, and what chemical reactions took place. The results suggest that the ratio of carbon to oxygen – something determined by nuclear reactions inside stars – appears to be particularly important. This also applies to a balance between these two elements, although other elements seem to be less critical.

“There are those who study galactic habitability and think that life on the outer edges of galaxies is probably extremely rare because there just aren’t enough elements for life,” Lewis said. So if parts of our universe are uninhabitable, so will parts – and perhaps whole – of other universes. However, if life were discovered in these so-called uninhabitable regions of our universe, then suddenly everything, everywhere (at once) would change. “If we find that life is common in many of these settings — which would be a significant story in itself — then that would suggest that life should be possible in some part of the multiverse,” Lewis said.

Does the multiverse theory have a future?

Using the Multiverse in Everything everywhere at once was a great success, but the concept itself is far from becoming an accepted scientific theory. “All good science starts with a (sometimes crazy) idea,” said Lewis. “But so are the dead-end paths.”

I wish you clear skies and big eyes.