It’s a hot August day in Los Angeles, and Clifford Johnson opens the window to his study. The salty breeze wafts in, ruffling papers filled with equations and sketches on his desk. He grabs a pencil — he prefers a Blackwing — and starts scribbling furtively, careful not to wake his young son who is sleeping nearby.

If we were to score this scene, cue the Beatles:
Words are flowing out like endless rain into a paper cup
They slither wildly as they slip away across the universe

Except Johnson relies less on words. The equations, symbols and geometry that emerge from his pencil are the product of his lifelong pursuit to describe the origin and fundamental makeup of the universe.

A professor of physics and astronomy at the USC Dornsife College of Letters, Arts and Sciences, Johnson came to prominence by developing theoretical tools to describe the basic fabric of nature. He works mainly on superstring theory, quantum gravity, gauge theory and M-theory, studying objects such as black holes and Dirichlet membranes (dynamical extended objects in quantum gravity that can move, wiggle, and wrap around things), using math and physics. His work has been recognized with the National Science Foundation’s CAREER Award and the Institute of Physics’ James Clerk Maxwell Medal and Prize for outstanding contributions to theoretical physics.

But the U.K.-born theoretical physicist who spent some of his childhood living on the Caribbean island of Montserrat is comfortable leaping worlds. Take a look at his IMDb page. He’s one of the few physicists with movie credits to his name.

Many of Hollywood’s biggest sci-fi movies and TV shows — think “Avengers: Infinity War” and “Endgame” and “Star Trek: Discovery,” to name a few — are grounded in real science thanks to people like Johnson. He helped convinced Marvel to explore the meaning of Thor’s hammer being forged in the “heart of a dying star.” He advised on the time travel scenarios that became the central plot of “Avengers: Endgame.” He even has a cameo in the 2020 film “Palm Springs,” another movie for which he was a scientific advisor. Meanwhile, he regularly appears on the History Channel series “The Universe.”

As the founder of the African Summer Theory Institute, Johnson actively works to promote science in the public and increase representation in physics. In 2017, he wrote and illustrated “The Dialogues,” a nonfiction graphic novel meant to be a modern-day Socratic dialogue about the science of the universe for non-scientists.

We interrupted Johnson in between solving the mysteries of the universe and his next big Hollywood project and putting his son to bed to talk to us about black holes, parallel universes and how a glass of beer explains multiverse theory.

How do you describe your work?

Whenever I’m asked this, I often use the word “origins” — everything that we have seen so far about our universe and what everything is made of. In the last few years, I’ve focused on aspects of black holes, which in some ways contain some of the biggest clues to these origin questions. Black holes and quantum physics — putting them together in what’s called quantum gravity — is my main line of investigation these days.

How does the multiverse play into this?

That origin question is what often knocks on the door of things like the multiverse because, if you’re trying to describe this universe and you come up with a class of theories, like string theory — which I also work on to describe model universes — oftentimes, out of those same equations come alternate universes. And you ask yourself: Is there just the one that’s correct? Or maybe they’re all correct? That’s one of the ways people arrive at the multiverse idea, with equations that essentially tell you that you have choices.

What tools do you use to work on these deep, universal questions?

A Blackwing 602 pencil, because I’m constantly expressing ideas on paper, scribbling, sketching and writing equations. The language of nature seems to be mathematics. Nobody knows why, but nature is amenable to being described by the science of patterns, shapes, structures and logic. It’s not random. There’s a predictability, an organization, a structure. Ideas are cheap, and there are many cool ideas about how the universe works, but the hard work lies in testing an idea to destruction. And that takes mathematics and imagination.

What are some of the current ideas about the multiverse?

The term “multiverse” is very loosely used in public and even among some physicists. There are several distinct things that can lead you to the idea of multiple universes, and they’re not necessarily connected. I guess the only way to describe it is to tell you some of the different options.

The most famous one is due to people thinking about quantum physics, people like David Deutsch (who pioneered the field of quantum computation) and also Hugh Everett (who first proposed the many-worlds interpretation of quantum physics). Everett was trying to understand the fact that quantum physics tells you that, fundamentally, you seem to have choices in the outcome of an experiment. Not the randomness of tossing coins, but built-in, you have all these different quantum outcomes. Each of these in turn has a certain probability, but when you do a measurement, you measure only one of the outcomes. So you get to ask the question, If I chose one, what happened to all the others? For a long time, people were worried about this fundamentally probabilistic nature of our universe that emerged with quantum physics. People like Everett were thinking that maybe those choices do happen but in a different universe. It isn’t just that the universe is making these probabilistic choices — both choices were chosen, but you only live in the one where that particular choice was made. Every time there’s a quantum choice, for every microscopic system, for every molecule, there’s a huge number of universes in this quantum multiverse. I certainly can’t disprove that because the basic idea is such that these universes then don’t have anything to do with each other.

But my take on that is that it seems to be an incredibly uneconomical solution to an interpretation problem, namely the interpretation of quantum physics. To have it fit within our classical notions of how physics should be, you must invent an infinite number of these universes that you can’t interact with. That sounds to me like we’re putting something on nature that nature doesn’t do. Perhaps that’s a question best left to the philosophers.

The other multiverse idea seems to be forced on you by the physics, as we understand it so far. This has to do with the dynamic question as we start thinking about cosmology. We know now from observation that the best explanation we have for how our universe came to be involves not just the Big Bang, but also what’s called a period of inflation, where the universe is born out of a rapid expansion. You start out with a tiny patch of primordial space-time and that gets exponentially large for a fractionally small amount of time. It keeps doubling and doubling and doubling, if you like, in size until it gets up to the macroscopic scale that we live in today. After that period of inflation, you get the usual sort of Big Bang–type physics, where the universe expands over the 13.8 billion years. So, in the first few fractions of a second, there’s this inflationary period that’s essential to describing how the universe looks today. The problem with inflationary theory is that there’s no reason why it just happened to that one patch of primordial space-time.

Also, we can’t explain what turns on and off the inflationary period, so what would we learn that would be consequential to our reality?

Right. Picture a glass of beer and watch what happens as I pour beer into your glass. Some mechanism gives rise to bubbles forming, and it’s cool. You could focus on one bubble and start describing its physics. But why are you focusing on just that one bubble when there are thousands of bubbles forming all the time and doing different things? You know they’re all bubbles and you have your theory of bubbles, but you can’t predict where the other one will form and what it will do. So you must deal with the fact that if you have a mechanism that creates that one bubble, it can create many more bubbles of slightly different types in your beer glass. That’s the multiverse. Once you’ve written all the equations down and you feel good about it and it’s describing all these cool things about our universe, you go, But what’s wrong with all these other choices? This could keep happening. More universes could be generated. That’s the fundamental cosmological origin of the multiverse idea.

Now, if we were to stop right here it might not be so interesting. But the point is that this may have observational consequences. What happens if these bubbles interact with each other? These different universes might leave signatures of the existence of the others in some sort of thing that we could measure, maybe by looking in the sky at the right thing. Something about how galaxies are distributed, something about how the different periods of the universe, the first stars, the first light, may depend upon whether it’s interacting with other universes.

You can imagine universes that are slightly different — even a tiny amount of difference perhaps in the laws of physics for that universe. The makeup of fundamental particles that make everything up might be slightly different. It might be that the rules are the same but the ingredients are slightly different so you could end up with a slightly different universe. Or it could be that the ingredients are the same but the rules are slightly different.

Let’s talk about your work as a science advisor on films. What films have you worked on?

I’ve worked on several Marvel movies, and for me, it’s fascinating to think about other ways our universe could be. Another way people arrive at the multiverse idea is through time travel as it shows up in the “Avengers: Infinity War” and “Endgame” movies. People resolve the paradox of going back into the past and changing things such that when you go back, you’re no longer in the universe you began with, you’re in a new universe — the multiverse. This idea of multiple universes is beginning to show up a lot more in the “Loki” series. Actually, these multiverse ideas started entering the Marvel Cinematic Universe with the second season of the “Agent Carter” TV series, for which I was the science advisor. Later, you started seeing them show up in “Doctor Strange.”

What elements of the Marvel Cinematic Universe do you help shape?

Primarily I talk to writers and directors about plot elements and terminology. I also sometimes help the visual effects artists formulate their vocabulary of the visuals, in addition to advising the filmmakers about the different scientists they might have on screen and putting words in their mouths. I also help them with the look of things, if they’re interested. What a setting might look like, whether it be the chalkboard that a scientist is writing on or the look of the wormhole in “Thor: Ragnarok.” They don’t always take my advice, but I give it if they ask.

There are the rules of the film but then there are the laws of physics. Do you often find yourself in the middle of a story that contradicts the physics?

My job is to understand their story goals, not to help them make a physics documentary. I ask the filmmakers, “What are you trying to achieve here?” Sometimes that can help them improve the science of the story and use science that is more directly connected to the real science. I can see this fun thing they’re doing here with a bit of science, but here’s this other bit of science that they don’t know about that’s much more fun and connects to the real world that they can use instead. Oftentimes, that results in more story ideas, and even characters, that they hadn’t originally thought of because they hadn’t talked to a scientist. For me, that’s when it works best.

How do you reconcile the scientist with the science advisor on a Marvel movie?

I see my role as someone who invites more people to play in this awesome space called science. I think there’s too much of this belief that it takes a very narrow kind of person to do science. Or people saying, “I don’t have the right kind of brain for it,” I think that’s nonsense. If we think of ourselves as some sort of educated literate citizen out there in the world, we ought to be able to dabble in lots of things and one of those things should be science. It’s all part of what makes human culture so rich.

I also encourage filmmakers to broaden who’s a scientist on screen. I don’t want people to think it’s only Tony Stark or Bruce Banner. Let’s also have women and people of color, all kinds of people being the primary scientists solving problems, by use of reason, not just hitting stuff and blowing stuff up.

On the other hand, the science community must embrace the power of storytelling because, frankly, as a society, we spend a lot of our time entertaining ourselves with the moving image. It’s where our eyeballs are. So, if I’m smart and I’m trying to get people excited about some ideas, I should go to where their eyeballs are, right? People won’t suddenly go and pick up a physics book. So why not bring the physics to where they’re already looking?

We’ve talked about some of the impact you’ve had on films, but I wonder if a story has also affected the way you think about your work.

Working as a science advisor on a film is like solving a puzzle, whether it’s figuring out how to visualize something or explaining a concept to a poet, an artist or a storyteller. I feel that has a benefit to me, as well, because I’m forced to reformulate how I communicate the physics to someone who isn’t a physicist. That’s a powerful way of making sure you really understand what you’re doing. It forces you to translate it into a different language. If you haven’t found a way to translate it from your language to another, it probably means you haven’t fully understood it yet. To me, the most powerful, long-lasting physics ideas transcend the purely physics context in which you found them.