Before going full Doctor Strange in the Multiverse of Madness, the MCU dabbled in alternate realities with Loki and What If…? But did you know that real-life physicists also talk about the existence of a multiverse? Stephen Hawking, often credited as the smartest person on Earth, accepted the potential for other realities. In the below interview with John Oliver, the multiverse isn’t the only idea Hawking shares that sounds more like science fiction.

What pop culture calls the multiverse is referred to as the “many worlds” interpretation of quantum mechanics here on Earth. This allows for parallel realities, where every decision leads to possible outcomes. These are the branches the TVA prunes in the MCU, preserving their sacred timeline.

What physicists call the multiverse, however, is different. It suggests that our ever-inflating cosmos leaves room for pocket universes where anything could be true. The likelihood for a repeat of our own is slim. A lot went into creating our solar system and life as we know it, and any small change could lead to an unrecognizable reality.

We don’t have the ability to test either of these theories. At least not yet. Physics, like all science, is constantly pushing the boundaries of its own knowledge. As Arthur C. Clarke said, “Any sufficiently advanced technology is indistinguishable from magic.” But just because we’re not equipped to reach one of these alternate universes doesn’t mean they couldn’t make first contact.

Defender Doctor Strange holds his hand out in Multiverse of Madness
Marvel Studios

Future humans may find it hilarious that we ever considered such a thing as alternate or pocket universes as real just because we couldn’t explain a few things. Science could have it all figured out one day. In the meantime, it’s a wonderfully fun device for storytelling. Which also leads to a feedback loop. Scientists getting ideas from science fiction writers is nothing new. Perhaps some physicists out there are specifically trying to prove or disprove the mechanics of Back to the Future.

The Arrowverse certainly didn’t shy away from the multiverse. Some of the main shows even took place on different Earths. In the everything-goes chaos of DC’s Legends of Tomorrow, our heroes finally rejected the idea of fixed points in history that often wave away any questions about killing Hitler or righting similar wrongs. “Crisis on Infinite Earths” was a fun crossover event that continued the Arrowverse’s tinkering with the idea of good versus evil. Sometimes it was subtle, sometimes not so much. A planet where everyone is evil? “Been there, it sucks,” says Barry Allen while explaining multiverse theory on Supergirl.

Star Trek‘s Mirror Universe is one such alternate reality where everything is terrible. It began with The Original Series but was also covered in Deep Space Nine, Enterprise, and Discovery. The genocidal Terran Empire wears shinier uniforms and murders each other more often than in the Prime Universe. People cross between the two through various accidents and other plot devices. Transporters, shuttlecrafts, and spore drives can be so unreliable. But we got to see Spock with a goatee and Tilly with straight hair, so we can’t be mad about it.

The pop cultural multiverse isn’t just in sci-fi. Romantic comedies like Sliding Doors and About Time explore the effects of seemingly small decisions. Humans love to examine the possibility of making different choices. Even if we never get a chance to do this in real life, we can keep up the speculation through escapist fiction.

Paramount Studios

Thanks to Dr. Lisa Will for helping me understand real-life multiverse theory. She is a professor of physics and astronomy at San Diego Community College and hosts planetarium shows, both virtual and in-person at the Fleet Science Center in San Diego.

Melissa is Nerdist’s science & technology staff writer. She also moderates “science of” panels at conventions and co-hosts Star Warsologies, a podcast about science and Star Wars. Follow her on Twitter @melissatruth.