The two big movies hitting theaters this weekend couldn't be more different.

There's Oppenheimer, Christopher Nolan's sprawling biographical thriller about the man known as the father of the atomic bomb, which the director has said will leave viewers "absolutely devastated." And there's Greta Gerwig's Barbie, a fantasy comedy with original songs and enough pink paint to prompt a real-life shortage.

Together, they form Barbenheimer. Or is it Oppenbarbie? Boppenheimer?

Whatever you call it, it's blown up into a cultural juggernaut.

Warner Bros. and Mattel unleashed a powerful Barbie marketing blitz, with over 100 official brand collaborations. Retailers and restaurants have followed suit, offering their own twist on "Barbiecore."

And while Oppenheimer has taken a more subdued approach, all the hype appears to have given both movies a boost.

For weeks people have been making memes and merchandise celebrating the mashup, effectively transforming a box-office battle into an unlikely double feature.

And it seems many people are actually committing to the bit: The National Association of Theatre Owners projects that more than 200,000 moviegoers will attend same-day viewings of both movies across North America this weekend.

"This weekend has captured the cultural imagination in an unprecedented way," association President and CEO Michael O'Leary, told NPR in a statement. "People ... are flocking to the theatres in groups, with family, friends, neighbors, to celebrate two different, but amazing motion pictures."

Sixteen percent of the Alamo Drafthouse Cinema chain's guests have bought tickets to both films, a spokesperson for the chain, which has 39 locations, told NPR in an email Friday. Roughly two-thirds of those seeing both are starting with Oppenheimer, the spokesperson said.

NPR spoke to more than a half-dozen people at a Washington, D.C., movie theater who were there to see one or both movies Friday night. Several of them doing the double feature — either on the same day or back-to-back nights — said they were in it largely for the experience.

Mishaela Robison, who saw Barbie on Thursday, was back at the theater with two friends the next night to watch Oppenheimer and then Barbie again. They said they had decided earlier in the day to double on Barbie because they had loved it so much, and because they'd bought a movie subscription pass months ago to lower the cost.

They agreed they probably wouldn't be seeing the former — at least on opening weekend — if not for the latter.

"I wouldn't see Oppenheimer, but I would see Barbenheimer," Robison said.

What's the deal with these movies?

Both movies come from directors with devoted fanbases, feature ensemble casts and grapple with existential dread — to varying degrees.

Oppenheimer tells the story of American physicist J. Robert Oppenheimer (played by Peaky Blinders' Cillian Murphy), who directed the Los Alamos Laboratory during World War II and helped develop the country's first nuclear weapons. Nolan has described him as "the most important person who ever lived."

Upon seeing the first successful bomb test in the New Mexico desert in 1945, Oppenheimer reportedly quoted a Hindu scripture: "Now I am become Death, the destroyer of worlds" — now available on a T-shirt in pink curlicue script, as it happens.

The three-hour epic is based on the Pulitzer-Prize winning book American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer by Martin Sherwin and Kai Bird. It's the 12th film by Nolan, whose previous blockbusters include "The Dark Knight" trilogy, Inception and Dunkirk.

Barbie, on the other hand, follows the Mattel icon (played by Margot Robbie) as she experiences an existential crisis: "Do you guys ever think about dying?" she asks on the dance floor at one point in the trailer.

She and Ken (a very committed Ryan Gosling) leave idyllic-looking Barbieland behind to explore the real world and discover "the truth about the universe."

Indie director Gerwig wrote the screenplay with her partner Noah Baumbach. This is her third film as solo director, after Lady Bird and Little Women.

The movie, which clocks in at just under two hours, amounts to both corporate propaganda and Malibu metacommentary, NPR's Aisha Harris writes.

Why did they come out on the same day?

It's increasingly rare for two such high-profile movies to hit theaters on the same day.

Some think it might have to do with Nolan leaving Warner Bros. (after its controversial decision to release its 2021 movies in theaters and on its streaming service simultaneously) and make Oppenheimer with Universal instead.

Their theory is that Warner Bros. chose to release Barbie the same day out of spite. When asked about this by Insider at a recent press event, Nolan chuckled and refused to answer.

Opposite blockbusters have been pitted against each other in the past, like 10 Things I Hate About You opening against The Matrix in 1999. And, in a much-discussed parallel, Nolan's The Dark Knight premiered on the same day as Mamma Mia in the summer of 2008.

Experts say releasing two different genres of movies on the same day can actually be good for business, especially if they appeal to distinct demographics.

And it certainly appears to be fueling ticket sales for both Barbie and Oppenheimer, whose target audiences may not be as segmented as some originally thought.

One Twitter user went viral back in April for suggesting that there would be little overlap. He was immediately inundated with tweets — many from women in STEM — proving otherwise.

The Barbenheimer frenzy has reached a fever pitch in the weeks since.

Viral social media memes have poked fun at everything from the movies' opposing aesthetics to viewers' requisite costume changes to the sheer volume of the hype itself.

People have started making Barbie/Oppenheimer posters featuring a massive pink mushroom cloud. And sites like Etsy and Redbubble are selling all kinds of crossover T-shirts, mixing and matching the movies' slogans and visuals.

"It's Mattel versus the Manhattan Project and BarbenHeimer," Paul Dergarabedian, a senior media analyst for Comscore, told NPR's Mandalit del Barco. "That just means that this is going viral, and that's good news for both Barbie and Oppenheimer."

What does an internet phenomenon look like in real life?

The crowd at the Regal Gallery Place in downtown D.C. was awash in hues of bright pink and glittering rhinestones on Friday night, as groups gathered in the lobby for evening showings of Barbie and, in some cases, Oppenheimer too.

Jeffrey Williams, rocking a replica of Robbie's Western-inspired outfit from the movie, was celebrating not only opening night but his 26th birthday. He had called ahead back in May to reserve a theater to screen Barbie with more than 50 friends.

"I'm just an extra human being ... if the outfit doesn't sell that enough, and so I thought it would be a fun way to celebrate," said Williams, who plans to see Oppenheimer next weekend. "I think it's probably the biggest movie cultural day in a while, so can't pass that up."

Even movie regulars said they were surprised by the size of the crowds.

Deneen Nabinett and her daughters say they come to the theater every Friday, but had to split their double feature into two nights in order to get their preferred seats. They saw Oppenheimer first on Thursday, and Nabinett said — on her way out of Barbie — that the order didn't really matter.

"Either way we wanted to see both of them, so I'm just glad it worked out," she said.

Not everyone NPR spoke with was in the midst of a double feature.

Brandon Thomas said he's a fan of Nolan and has been waiting to see Oppenheimer for months — and says while he doesn't care much about Barbie, he'll probably see it eventually.

"I'm just glad people are in the theaters," he added.

And the costumes weren't only for Barbie. Robison dressed up for Oppenheimer, wearing a vintage, long-sleeved turquoise dress that she said her grandmother used to wear to work when she was around her age.

"It really reminds me of Barbie, even if it's not a Barbie fit, because it's about the ties of femininity and there's a really good line in [the movie] about mothers and daughters and the work mothers do so their daughters can see how far they've come," she explained. "And I have composed a very nice text to send her about all of this."

Robison, 24 and her friend Margaret Murphy, 23, compared Barbenheimer to another ongoing cultural phenomenon — Taylor Swift's Eras Tour, for which people have been dressing up in aesthetically similar outfits and shelling out money for Swift-themed merchandise and experiences, too.

"I feel a little bit of fomo with the Eras Tour," Murphy said. "And so getting to have my own little Eras Tour, where I got a dress for Barbie last night, and I felt like a little princess going to see Barbie, and it being so influential for my life, it felt like such a good, well-rounded moment."

The two even took a page out of the Eras Tour playbook by making friendship bracelets, which Swifties have been exchanging in the crowds at concerts. But instead of referencing Swift lyrics or album titles, their beaded creations said things like "Kenergy" and "Barbenheimer."

Robison said she had been inspired by that embrace of femininity and expression of solidarity and figured they would transfer well to Barbie too — she'd been giving out bracelets at the theater.

"And hopefully it'll be a cultural moment people remember," she added. "So maybe it'll go in a museum in a hundred years."

What's the ideal viewing order?

There's been so much chatter about seeing both movies that it's even spurred a spirited online debate: Which one should you watch first?

Spending five-plus hours in a movie theater is no small commitment, and there's been a lot of discussion on how best to go about it. Do you start with Oppenheimer and some strong coffee, and finish with Barbie and a dance party? Or do you ease in with a Barbie brunch so you can drag your depleted self straight to bed when it's all over?

While public opinion seems to favor ending on a lighter note, there are compelling arguments to be made for each side, as Slate reports.

Some experts have weighed in, too.

Robbie, Barbie herself, called it a "perfect double bill" at her movie's premiere last week.

"I think actually start your day with 'Barbie,' then go straight into 'Oppenheimer' and then a 'Barbie' chaser," she said.

Tom Cruise, whose latest "Mission: Impossible" movie opened in theaters last week, said at his premiere that he plans to see both, likely starting with Oppenheimer. Others have endorsed his approach.

"If you see Oppenheimer last then you might be a bit of a psychopath," Barbie actor Issa Rae said.

Gerwig told The Hollywood Reporter that she also recommends treating Barbie as a palate cleanser.

"I want to have mimosas and drinks and cocktails after Barbie, I don't want to, like, sulk," she said. "That's just my plan, as long as you're seeing Barbie I don't care."

What's Hollywood saying?

Those who worked on the movies appear to be enjoying the rivalry-turned-alliance.

A picture of Gerwig and Robbie posing with their Oppenheimer theater tickets last month, for example, sent the internet into another minor frenzy.

"I love that there's solidarity though, where people tried to pit us against one another but now it's turned into like a double-feature situation," Gerwig told THR.

She also told USA Today that she feels "very shiny" to be associated with Oppenheimer, adding that "a rising tide lifts all boats."

Nolan told Insider that many in the industry have been longing for "a crowded marketplace with a lot of different movies."

"That's what theaters have now, and those of us who care about movies are thrilled about that," he said.

Oppenheimer actor Emily Blunt, who wore "Barbie" pink heels to her movie's premiere, similarly told USA TODAY that the other film's cast has been "so supportive" toward hers.

"It doesn't have to be competitive!" she said. "It's really cool and that's what we want: that full spectrum of what you can see in movie theaters. We love it."

An important note: Now that SAG-AFTRA is on strike, the actors are officially prohibited from promoting their movies. That's why the Oppenheimer stars walked out of the London premiere last week, and why Robbie's glamorous parade of Barbie-inspired red carpet outfits was cut short.

And don't worry, you can watch the movies without crossing the proverbial picket line.

SAG-AFTRA is not calling for a consumer boycott of movie theaters or streaming services at this time, National Executive Director and Chief Negotiator Duncan Crabtree-Ireland told NPR in an email.

"There may well come a time when we ask fans to send their message of support through direct economic action, but for now, we hope that they will inform themselves about our cause and share that information with their network of family, friends, and colleagues," he said.