Fresh off of his critically acclaimed and crowd-pleasing movie Air, Matt Damon is feeling good. “That experience, top to bottom, was about as much fun as I’ve ever, ever had,” the Oscar winner tells VF. “That one really worked out for everybody. Sometimes it happens like that.” Damon may find himself in a similar position again this year: He plays a pivotal character in Christopher Nolan’s Oppenheimer, a historical drama about theoretical physicist (played by Cillian Murphy) who created the atomic bomb.

Damon portrays General Leslie Groves, director of the top secret Manhattan Project, who appointed Oppenheimer to develop nuclear weapons and help end World War II. Discussing his role for the first time, Damon says that while Groves and the scientist had a “wonderful working relationship,” the dynamic between them caused a lot of friction. In the film’s trailer, we see an emotionally charged Damon questioning both an official’s and Murphy’s priorities as they face the challenges of quickly assembling a team of scientists to invent an unprecedented weapon.

“Groves was a military man, and so much of that ethos is about compartmentalization and the need to know all of the stuff. And the scientists were all about sharing information so that they can get the truth right…there was this constant tension,” Damon says in a recent Zoom call. “The scientists felt it was actually necessary to be sharing all the information that they could, and the military felt we had to try to make whatever gains we could without giving away any of our secrets.”

To remain faithful to the era, Nolan ensured every aspect of the film was historically accurate. “He’s so exacting. There’s been so much work before you get there, and you can feel it when you walk on [the set]. The level of detail is really exquisite,” explains Damon. The filmmaker reproduced bomb tests without using CGI; hired real scientists as extras; filmed inside historical Manhattan Project buildings—including the home where Oppenheimer, his wife, and two children actually lived; and recreated Los Alamos, a remote site in northern New Mexico where Oppenheimer ran his secret laboratory.

“You could see over the horizon the actual testing site and where the original town was,” says Damon. “Ruth [De Jong], our production designer, basically rebuilt the town, so we had an active kind of town to work in. It reminded me of shooting [Saving] Private Ryan in the sense that [Steven] Spielberg would rebuild these areas and we had carte blanche—we could go anywhere we wanted to go. So, Chris had the flexibility to shoot as he wanted and needed to all around the town. It was fully immersive.”

Filming in the secluded desert setting was not isolating for Damon, who had prior experience in such an environment from shooting both 2010’s True Grit and 2000’s All the Pretty Horses in New Mexico. “It’s beautiful yet desolate. It’s where Georgia O’Keeffe went to paint, basically, so it has very much that feeling,” he says. “It’s got that expansive desert beauty. It’s a remarkable place.”

Oppenheimer, also starring Emily Blunt, Robert Downey Jr., Florence Pugh, and Rami Malek, is opening in theaters on July 21—the same day as Greta Gerwig’s highly anticipated Barbie movie. Fans are divided on which to see first, and a debate—fittingly referred to as the bomb vs. bombshell—has been raging online ever since the movies were announced to have the same release date. Not that Damon was aware: “This is the first I’m hearing about it, actually. I haven’t paid any attention to that,” he says. 

Even so, he offers a solution. “People are allowed to go see two movies in a weekend. Oppenheimer is one of them!” he says with a laugh. As a parent of four daughters, though, one may assume his family will choose Barbie. How does that make him feel? “I’ll have to ask them that. If that’s the case, they’ll see two movies that weekend!”

Before he takes off on his Oppenheimer press tour, Damon is focusing on his advocacy work. For over a decade, the actor-writer-producer has been dedicated to ending the global water crisis through Water.org, an NGO he founded with engineer Gary White. The organization’s efforts have made extraordinary strides, reaching more than 40 million people around the world, but there is still a lot of work to be done.

“It’s a problem we solved for ourselves in the West a hundred years ago, so it is frustrating,” Damon says. “What if we cured cancer, and in a hundred years people were still dying from cancer—it would really be unconscionable. So that’s part of what drives the work that we do. The issue is totally solvable, and solvable in our lifetime. It’s really a matter of educating people about what’s going on and trying to enlist their energy behind the cause.”

To raise funds for Water.org and attract awareness for his ongoing humanitarian efforts, Damon is partnering with Stella Artois—their collaboration began in 2015 and has provided access to safe water for more than 4.5 million people—for their latest “Let’s Do Dinner” campaign, which inspires people to connect over a meal. Damon, Zoe Saldaña, Jeremy Allen White, and Ludacris are inviting fans to join them in New York this September for a feast, promoted as the “World’s Most Fascinating Dinner.”

If he could invite anyone to dinner, who would he choose? Naturally, Damon goes with his longtime friend Ben Affleck. “Good conversation is what you’re looking for, and Ben, he’s a conversational prizefighter,” Damon says. “He’s got a very, very, very fast brain. He knows a lot, and he’s very funny. He and I go back so far that we have a common frame of reference that usually we’re in peels of laughter quickly, and that’s how normally the evening goes.”

Damon says dinner table conversations with Affleck—preferably over pasta or paella, his favorite—focus on running their independent film production company, Artists Equity. Plus, Damon adds, “we have these very unique lives, and we had unique lives together as children. We did theater together in the ’80s in high school, and traveled to New York together, and auditioned for things. We were on buses and trains and drove across the country maybe 10 times together, and all the way up to becoming famous together. So there’s never a shortage of things to talk about.”

Beyond their strong kinship, Damon also values Affleck’s creativity and feedback. “He’s always been a really valuable sounding board because our lives are similar in many weird ways,” he says. “So, he’s been a huge help to me.”