Welcome to the Multiverse

Some of today's most popular movies tell larger-than-life stories about superpowered characters, like the web-slinging Spider-Man, the godlike trickster Loki, and the sorcerer Dr. Strange. These characters are all part of the Marvel Cinematic Universe (MCU), which features dozens of heroes and villains. from Marvel comic books. Now this expansive franchise is about to get even bigger. That’s because the next phase of the MCU—including the upcoming movie Spider-Man: No Way Home (December 2021)—will explore the web of alternate realities, dimensions, and timelines known as the multiverse.

In the Marvel universe, characters—often aided by magic portals or high-tech devices—can travel to different versions of their world. Sometimes, these other realities closely resemble their own, with only minor changes. Other times they’re surreal and strange. Some alternate realities are even populated with different versions of familiar Marvel characters. By traveling between timelines in the TV show Loki, for example, the main character teams up with a female Loki, a Loki who is still a young boy, and even an alligator Loki!

Some of today’s most popular movies tell larger-than-life stories about superpowered characters. Spider-Man slings webs, Loki is a godlike trickster, and Dr. Strange is a sorcerer. These characters are all part of the Marvel Cinematic Universe (MCU). It features dozens of heroes and villains from Marvel comic books. Now this huge franchise is about to get even bigger. That’s because the MCU’s next stage will explore the multiverse. It’s a web of alternate realities, dimensions, and timelines. The new movie Spider-Man: No Way Home (December 2021) will be a part of this. 

In the MCU, characters can travel to different versions of their world. They often use magic portals or high-tech devices. Sometimes, these other realities look like their own, with only small changes. Other times, they’re dreamlike and strange. Different versions of familiar Marvel characters live in some alternate realities. For example, the main character in the TV show Loki travels between timelines. He teams up with a female Loki, a Loki who is still a young boy, and even an alligator Loki! 

As far-fetched as this sounds, the science behind Marvel’s multiverse may not be completely fictional. That’s because the concept of multiple realities takes inspiration from actual physics. “Real-world scientific theories provide an element of realism that allows our viewers to connect with the fantastical worlds and stories we tell,” says Brad Winderbaum. He’s the executive producer for What If…?, a Disney+ show about alternate-universe versions of MCU heroes. But just how accurate is the multiverse portrayed in superhero TV shows and movies?

This sounds far-fetched. But the science behind Marvel’s multiverse may not be completely made-up. The idea of multiple realities comes from actual physics. “Real-world scientific theories provide an element of realism that allows our viewers to connect with the fantastical worlds and stories we tell,” says Brad Winderbaum. He’s the executive producer for What If...? This Disney+ show is about alternate-universe versions of MCU heroes. But just how accurate is the multiverse shown in superhero TV shows and movies? 

The 2016 film Doctor Strange was one of the first Marvel movies to depict the multiverse. In it, Dr. Strange uses his mystical powers to travel between dimensions. Each universe he visits looks completely different. In Spider-Man: No Way Home, Dr. Strange will team up with Spider-Man after a magic spell gone wrong accidentally brings characters from other universes into theirs.

In real life, theoretical physicists use math to create models that show how the universe might work. Doctor Strange and Spider-Man take their multiverse ideas from a field of physics called cosmology, says Jessie Muir, a physicist at Perimeter Institute for Theoretical Physics, in Ontario, Canada. Cosmology is the study of the universe on a large scale, including how it started and how it might end.

The film Doctor Strange was released in 2016. It was one of the first Marvel movies to include the multiverse. In it, Dr. Strange uses his magical powers to travel between dimensions. He visits other universes that look completely different. In Spider-Man: No Way Home, Dr. Strange will team up with Spider-Man after a magic spell goes wrong. It accidentally brings characters from other universes into theirs.

In real life, theoretical physicists try to understand how the universe might work. They use math to create models. Doctor Strange and Spider-Man take their multiverse ideas from a field of physics called cosmology, says Jessie Muir. She’s a physicist at the Perimeter Institute for Theoretical Physics, in Ontario, Canada. Cosmology is the study of the universe on a large scale. It includes how the universe started and how it might end.  

Many cosmologists think the universe began with a period of expansion called inflation, during which all of space rapidly stretched in all directions. Eventually, says Muir, “a pocket of space could calm down and start behaving like the ordinary space that we’re used to.” As time went on, more parts of space would stabilize, forming other calm pockets. “These parts of the universe are totally disconnected from each other,” says Muir. “Even light doesn’t have time to reach one from the other. We can think of them as different universes.”

If space goes on forever, as some scientists believe, this means there could be an infinite number of these other realms, floating like bubbles in the nothingness of space (see Universe Bubbles). But this is just one scientific theory that lends support to the idea of a multiverse.

How did the universe start? Many cosmologists think it expanded during a period called inflation. All of space quickly stretched in all directions. Eventually, “a pocket of space could calm down and start behaving like the ordinary space that we’re used to,” says Muir. Over time, more parts of space would stabilize. Then other calm pockets would form. “These parts of the universe are totally disconnected from each other,” says Muir. “Even light doesn’t have time to reach one from the other. We can think of them as different universes.” 

Some scientists believe that space goes on forever. If they’re right, an endless number of these pockets could exist. They would float like bubbles in the nothingness of space (see Universe Bubbles). But this is just one scientific theory that supports the idea of a multiverse. 

The Loki TV series, released this past summer, revealed that anytime a Marvel character makes a decision, a new “branch” of reality is created for each possible outcome. To understand the science behind Marvel’s branching timelines, you need to think about the multiverse on a much smaller scale. This field of physics is called quantum theory. It describes the behavior of extremely small systems, made up of subatomic particles smaller than atoms. (Think about the movie Ant Man, where characters shrink down until they’re so small they enter the “Quantum Realm.”)

In our universe, all large-scale physical interactions are governed by forces that affect an object’s motion in predictable ways (like the pull of gravity). Consider throwing a baseball, says Muir. If we know how hard the ball was thrown, we can use that information to predict where the ball is going, how fast it’s moving, and when it will get there. But describing the behavior of electrons, subatomic particles with a negative charge, or photons, the smallest particles of light, is different—and much stranger.

The Loki TV series was released this past summer. It revealed what happens when a Marvel character makes a decision. A new “branch” of reality forms for each possible outcome. There’s science behind Marvel’s branching timelines. But to understand it, you need to think about the multiverse on a much smaller scale. This field of physics is called quantum theory. It describes the behavior of extremely small systems. Subatomic particles smaller than atoms make up these systems. (Think about the movie Ant Man. The characters shrink small enough to enter the “Quantum Realm.”)

In our universe, we know what to expect from large-scale physical interactions. The forces that affect an object’s motion are easy to predict. One example is gravity. Consider throwing a baseball, says Muir. If we know how hard the ball was thrown, we can predict the outcome. We know where the ball is going, how fast it’s moving, and when it will arrive. But what about the behavior of electrons, subatomic particles with a negative charge? Or photons, the smallest particles of light? Then things are different—and much stranger. 

In the world of quantum physics, scientists cannot predict exactly what these particles will do. They can only make predictions based on probability—the likelihood of something happening. That’s because quantum-scale objects can be in multiple states—that is, doing multiple things—at once, until observed or measured (see Dead or Alive?). Does that sound confusing? Most physicists would probably agree. “Quantum theory is perhaps the most bizarre theory of all time,” says Michio Kaku, a theoretical physicist at the City College of New York.

Some physicists explain the odd behavior that happens at the quantum level using the many-worlds interpretation. It’s the idea that random quantum events cause the universe to branch into multiple, slightly different copies. “Each universe continually branches, like a tree, creating even more new parallel universes,” says Kaku. Some physicists have even proposed that alternate realities could be interconnected in a way that might allow people to travel between them—just like Marvel characters do, says Kaku. But the likelihood of this is so small that it’s basically impossible.

In the world of quantum physics, scientists cannot predict exactly what these particles will do. They can only make predictions based on probability, or the chance of something happening. That’s because quantum-scale objects can be in multiple states at once. They’re doing multiple things, until they're observed or measured (see Dead or Alive?). Does that sound confusing? Most physicists would probably agree. “Quantum theory is perhaps the most bizarre theory of all time,” says Michio Kaku. He’s a theoretical physicist at the City College of New York.

The behavior of particles at the quantum level seems quite odd. Some physicists try to explain it with the many-worlds interpretation. This idea says that random quantum events cause the universe to branch. Multiple, slightly different copies form. “Each universe continually branches, like a tree, creating even more new parallel universes,” says Kaku. Some physicists have even suggested that alternate realities could be interconnected. That might allow people to travel between them, says Kaku. That’s just what Marvel characters do. But the chance of this happening in reality is so small that it’s basically impossible.

For physicists who are trying to untangle the twisted science of the multiverse, it’s difficult to confirm the different ideas without more data. “These hypotheses are speculative,” says Muir. “We don’t really have observable evidence to test them, or even enough information to do concrete calculations.”

Thankfully, Marvel writers don’t have to worry too much about separating fact from fiction. “First and foremost, we want to focus on telling fun and complex stories,” says Winderbaum. Many Marvel filmmakers look to science to ground their ideas, he says. And “from there, they can let their imaginations run wild.”

Physicists are trying to untangle the twisted science of the multiverse. But it’s difficult to confirm the different ideas. More data is needed. “These hypotheses are speculative,” says Muir. “We don’t really have observable evidence to test them, or even enough information to do concrete calculations.”

So it’s tricky to tell fact from fiction. Thankfully, Marvel writers don’t have to worry too much about it. “First and foremost, we want to focus on telling fun and complex stories,” says Winderbaum. Many Marvel filmmakers look to science to ground their ideas, he says. “From there, they can let their imaginations run wild.”