Multiverse Theory Explained Ahead of 'Spider-Man: No Way Home' Release

Comic book fans and moviegoers alike are eagerly awaiting the release of the next installment of the Spider-Man movie franchise, No Way Home, in December. Trailers for the film feature Tom Holland's Peter Parker and Dr. Strange, played by Benedict Cumberbatch, facing off against familiar villains from alternate Universes like Alfred Molina's Doctor Octopus.

Speculation is rife that even an alternate Spider-Man or two may even pop up from their respective Universes to lend the Marvel Cinematic Universe's version of the character a hand in defeating the multiversal bad guys.

While a popular concept in science-fiction tales for decades, the concept of a multiverse actually originates from science theory, with many researchers speculating that other universes may exist alongside our own.

There was a time when the word "universe" was used to describe everything in existence, but the more we have learned about our universe in the field of cosmology, the more we have begun to wonder if it could be part of a larger patchwork of universes.

Bouncing Branes

One idea to explain how a series of universes could grow and co-exist is the inflationary multiverse theory. This is the idea that the period of rapid inflation, more commonly called the Big Bang, that marked the beginning of our universe didn't begin or end there, but went on to inflate other universes that could be broken up and sealed off into bubbles. Each of these bubbles could possess different physical laws.

One researcher who has helped develop this idea is Massachusetts Institute of Technology (MIT) professor, Alan Guth, who says that the existence of a multiverse is simply a logical extension of the fact we have found our own universe to be undergoing inflation.

"Inflation does very much point toward the possibility of our universe not being unique but rather our universe being part of a much larger complex, which has come to be called the multiverse," Guth told an audience of MIT alumni in 2019. "A multiverse means many big bangs and our big bang was just one of many. So what is the reason for this?"

The answer to this question may lie in how the universes in a multiverse are arranged. Various physicists, including professor of physics and mathematics at Columbia University, Brian Greene, support a multiversal concept called Brane theory. This suggests that our universe and all others sit on vast membranes located in a higher dimension.

As these universes move around this brane they occasionally collide, with each other. These bumps release vast amounts of energy creating all the matter and energy in our universe. These membranes then bounce apart. The newborn universe, on its brane, evolves and eventually burns out. But some supporters of this concept suggest that the collide-and-bounce process repeats itself ad infinitum constantly creating new universes.

"As soon as I started working on this, I appreciated that time marched on—that there was no beginning of time," said Perimeter Institute for Theoretical Physics researcher Neil Turok, who authored a paper on "bouncing branes" or so-called "braneworlds" in 2007.

But even if there are multiple universes occupying a multiverse, what are the chances any of them actually contain life?

Fine-Tuned for Life?

American astrophysicist and Ta-You Wu Collegiate Professor of Physics at the University of Michigan, Fred Adams has written both papers and books that suggest the physical properties of our universe suggest that it is just one of many.

He asks if our universe is fine-tuned for life, what about other universes that could exist alongside ours in a vast multiverse—albeit with different laws of physics?

"The laws of physics are described by a collection of fundamental constants that could, in principle, take on different values"," Adams told Elsevier. "Here, the fine-tuning of the universe in the context of a multitude of alternate universes is the ultimate big-picture question. It brings together almost all of physics and astronomy."

In a paper published in Physics Reports Adams suggests that our universe has just the right parameters to support the formation of structure, stars, planets, and even biological systems that give rise to life.

The major criteria described by Adams included; mostly stable chemical elements; stars must be sufficiently hot and long-lived; galaxies with gravity strong enough to retain heavy elements, but still remain diffuse enough to allow planets to remain in orbit.

He believes that as a consequence of this there may be a multitude of 'empty' Universes where the conditions were not quite so favorable for the formation of such structures.

On the flip side of this, Adams suggests that there could be universes alongside ours with conditions even more favorable to the development of structure, and, as a consequence, life.

"The net result is that the ranges allowed for the fundamental constants are significantly larger than indicated in most previous work," he explained to Elsevier. "In fact, one can imagine a universe with combinations of the constants that allow it to be even better suited for the development of life than our own."

The big question is, of course, how could we possibly scientifically investigate the proposition of a multiverse?

Because a universe contains all the "stuff" that could possibly be seen by an astronomer in that universe, the wider multiverse may be impossible to observe, detect or probe.

This doesn't mean theorizing about the multiverse and attempting to "see" beyond the limits of our universe is a complete scientific dead end, however.

"Such research also helps us understand how our own universe works," Adams said. "We get a more in-depth perspective on the operations of our universe, with its stars and galaxies, by considering alternate scenarios where such astronomical entities have different properties or even cannot exist."

Spider-Man: No Way Home opens in theaters on December 17, 2021.