Are there multiverses? Is our universe one of many? The multiverse is a key plot device in the hit film Everything Everywhere Simultaneously—in a prime position to win big at the 95th Academy Awards, aka the Oscars, in which a Chinese immigrant explores parallel universes where she lives completely different lives.
But does the multiverse have any basis in science?
In the film, Michelle Yeoh’s character Evelyn Wang connects with versions of herself in parallel universes to prevent the destruction of the multiverse. Is it far-fetched? Of course! But right now, cosmologists are trying to figure out whether there is a group of multiple universes running parallel to each other—and whether they might be habitable.
What is the multiverse?
It is a basket of ideas from cosmologists and quantum theorists that our universe may not be alone and that it may share a higher structure with many other universes. “Some suggest that the burst of inflation in the early stages of our universe may be eternal, with individual universes crystallizing from 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, other universes alongside our own—if they exist—may or may not be capable of sustaining life.
This burst of inflation in our universe is, of course, key evidence that our universe emerged from a hot, dense spot—the Big Bang. However, what happened before the Big Bang – and whether other universes were perhaps created simultaneously with our own – is completely unknown.
Common misconceptions about the multiverse
There is no evidence of other universes. So the biggest misconception about the multiverse is that it is a proven theory. “It’s not — it’s not really mathematically based — it’s a collection of ideas,” Lewis said. “In the science community it remains at the hypothesis stage and a strong proposal needs to be made before we can really understand the implications.”
One of Stephen Hawking’s last theories before his death in 2018 predicts that the universe is finite and much simpler than many current Big Bang theories say. This has implications for the multiverse paradigm. “We are not in a single, unique universe, but our findings suggest a significant reduction of the multiverse, to a much smaller range of possible universes,” Hawking said.
In 2020, Nobel laureate Sir Roger Penrose claimed that an older universe existed before the Big Bang and can still be observed today as a scar in 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 made last year by cosmologist Laura Mersini-Houghton. Both are interesting theories, but both are unfounded. For now the multiverse remains a great idea, but little more.
Can the multiverse ever be proven?
As we understand it so far, no, which is why the multiverse talk is ridiculed by some scientists. But that doesn’t mean it can’t one day become a scientific theory. “We have no idea if it’s controlled or not,” Lewis said. “Once we have the math in our hands, we’ll have a chance to see if we can detect the presence of other universes … for now we have no idea what path we’re on.” What science needs is a mathematical theory to test. He doesn’t have one yet.
Could it be possible to jump between parallel universes?
If they exist, then surely it might be possible to travel between parallel universes. Why not? “I wonder if the possible complex geometry of all the universes means that they could be connected in some way—via wormholes and the like,” Lewis said. “That would mean inferring their existence, even interuniverse travel, is possible.”
However, thoughts of hopping between parallel universes – let alone seeing or meeting other versions of ourselves in them – are getting a little over the top in Hollywood. After all, what if there are actually an infinite number of parallel universes and they are all lifeless? This is one area where the science of the multiverse is starting to be done.
Is the multiverse hospitable to life?
Hollywood can content itself with wondering what would happen in a parallel universe if someone made a different life decision. Cosmologists are more interested in considering whether other universes exist, might have laws of physics different from ours. Could they still host life? That’s the central question in new work on multi-recommendation predictions, the latest of which was published this month. “We already know that certain 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 capable of harboring life? It’s not that simple. “There’s an idea — the Rare Earth hypothesis — that even though our universe is clearly habitable, the conditions for life are extremely rare,” Lewis said. With colleagues, he picked out billions of years of processing elements in our universe, from the elements that formed in stars, how they are distributed in 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 is the balance of both of these elements, although other elements seem to be less critical.
“There are those who study the habitability of galaxies and believe that life in the outer edges of galaxies is likely to be extremely rare because there simply hasn’t been enough production of evidence for life,” Lewis said. Thus, if parts of our universe are uninhabited, so will parts—and perhaps wholes—of other universes. However, if life were discovered in these so-called uninhabited regions of our universe, then suddenly everything, everywhere (all at once) would change. “If we find that life is common in many of these environments — which would be a significant story in itself — then that would suggest that life should be possible in a strip of the multiverse,” Lewis said.
Does the multiverse theory have a future?
The use of the multiverse in Everything Everywhere Simultaneously it was a huge success, but the idea itself is far from being an accepted scientific theory. “All good science starts with a (sometimes outlandish) idea,” Lewis said. “But so do dead-end paths.”
I wish you clear skies and open eyes.