Impossible is often just a starting point on a Christopher Nolan film and “Oppenheimer,”about the father of the atomic bomb, was no exception. In fact, it's often where inspiration was born.

During one especially stressful stretch, filmmakers lost their White House set five days before they had one day to shoot with Gary Oldman, who was flying in to play President Harry S. Truman. The wild scramble to find and construct a new Oval Office is detailed in a making-of documentary included in the newly available home entertainment release.

Looking back on that moment now, producer Emma Thomas can’t help feeling bad about the timing. But she marveled at what the crew accomplished. She told them at the time that if there were ever a zombie apocalypse, they were the people she’d want to be with.

“There’s nothing film crews can’t do. They will move mountains if they have to,” Thomas told The Associated Press. “Every day there’s something that happens and you have to figure out a way out of it. But that’s where the magic happens.”

For some, like production designer Ruth De Jong, that would involve building Los Alamos and finding Washington D.C. in New Mexico. For others, like cinematographer Hoyte van Hoytema and editor Jennifer Lame, it was making an “opera of faces and emotions” compelling for three hours.

Key craft department heads spoke to the AP about the challenges and triumphs of making this film, which has earned more than $950 million at the box office.

“Because Chris holds himself to the same standards, everyone’s willing to go there with him,” Thomas said.

YOU CAN’T HIDE IN IMAX

Aging 18 principal actors across multiple decades is hard enough, but as makeup lead Luisa Abel and head of hair design Jaime Leigh McIntosh quickly learned, there is no hiding in IMAX. There would be no help from CGI, either.

“We were in the elements a lot and a lot of the actors have prosthetic pieces on. Even younger actors have pieces on before they were meant to be older because I think everybody looks a lot younger now than people did in that era,” Abel said.

They mapped out detailed aging diagrams for each character, which helped enormously in a non-chronological shoot. And Nolan was involved in it all — down to Cillian Murphy’s haircuts.

“He really pays attention to every detail for every department,” McIntosh said. “As an artist it’s incredibly helpful to have a director who is communicative and can give you feedback.”

A LAST MINUTE REQUEST

For as precisely planned as “Oppenheimer” was there were still some last-minute fits of inspiration. A day before they shot Oppenheimer’s post-Trinity test speech in the auditorium, Nolan asked costume designer Ellen Mirojnick to put the audience in bright colors.

Luckily, she was able to get a costumer friend in Los Angeles to pull a big batch of 1940s clothes, in reds, yellows, greens and blues, and ship them to New Mexico within 20 hours. It wasn’t part of the plan but, Mirojnick said, it was the right note for this disorienting scene where Oppenheimer starts having horrific visions about his creation.

“I can’t imagine what it would be if it wasn’t that, because it feels like this kind of crazy dream ... and an insight into his state of mind,” Thomas said. “Who would have thought that the color of the costumes could do that? But they do.”

LEANING INTO THE CLAUSTROPHOBIA OF ROOM 2022

There was old tape on one of the walls of the narrow, dingy room De Jong found in a shaving company’s old headquarters in Southern California used for Oppenheimer’s security clearance hearing. It was the perfect claustrophobic, unglamourous and period-specific setting for a humiliating ordeal designed to make Oppenheimer feel small.

“Don’t clean this up,” Nolan said. They didn’t.

It was tight, and hot, and the only people who could fit in the room were the actors (usually at least 6 at any given time), Nolan and van Hoytema.

“We like shooting in small spaces with these cameras,” van Hoytema said, recalling the small boat hulls in “Dunkirk.” “All clumped up together is our favorite modus operandi.”

And those scenes ended up being some of Lame’s favorite to edit.

“There’s nothing more interesting than to watch amazing actors sitting in a room. I find it challenging but also immensely satisfying,” Lame said. “It’s amazing what Hoyte and Chris did with room 2022. Every time you went in there, it felt like a totally different kind of scene: It had a different feeling to it, or it had slightly different lighting or the shots were more menacing on certain characters.”

Someone told her that they could have watched Kitty’s testimony, a big moment for actor Emily Blunt near the end of the film, for “20 minutes.” That moment also provided an opportunity for musical innovation with Ludwig Göransson’s score, blending blends Kitty’s theme — a piano and cello — with Oppenheimer’s – a violin.

“It’s a waltz,” he said. “It’s like they’re dancing together.”

WHEN PERFECT ISN’T RIGHT

For Göransson, “Oppenheimer” was a personal journey that’s allowed him to work alongside his wife, violinist Serena McKinney, and also one that challenged him in unexpected ways.

On the first recording of “Can You Hear the Music,” which has 21 big tempo changes, they did it eight bars at a time. When he glued it all together, it sounded perfect — but perfect felt wrong.

“What I wanted to capture was the energy that I’d seen in the visuals, when I sat there with Andrew Jackson and Chris Nolan in the IMAX theater and they showed me the first visual experiments — like the molecules going around and the energy of being on the brink of discovery,” he said.

They went back and recorded the piece in one take.

“It was like night and day,” he said. “There’s a there’s an energy and a flow that comes in that room of four to six string players playing together and changing tempo together.”

That song alone has been streamed almost 60 million times and viewed 1.5 billion times on TikTok.

BIG EXPLOSIONS AND TINY ELECTRONS

Nolan knew that the Trinity test, the first detonation of a nuclear weapon, would have to be the showstopper for the film both visually and sonically. He even built in about 30 seconds of near-silence before the sound of the explosion hits the spectators, at three different distances.

It was a high-pressure moment for sound designer Richard King, who knows that explosions are uniquely hard to record.

“You can rarely get them to sound as impressive as you want them to sound,” he said. “I knew it should have a unique quality to it, something you’ve never heard before. It needed to be like a wall hitting you, like a cosmic door slamming.”

Knowing Nolan’s preference for practical visuals and sounds recorded during production, King challenged himself to use only those derived from the real world. Visual effects lead Andrew Jackson was similarly strict with himself to stay rooted in reality even when creating the most otherworldly effects.

And the mushroom cloud isn’t even his proudest achievement.

“The huge explosions are very effective, but for me it’s the smaller things,” Jackson said. “I loved the spinning electrons. They’re simple but effective and I think they’re really beautiful.”

The electrons show a glimpse into Oppenheimer’s mind — visions which would also provide thematic bookends in his journey. Göransson said it was only on a recent watch that he noticed how the chilling end moments of the film parallel the “Can You Hear the Music” montage from earlier with Lame’s quick cuts. But instead of “innocent dreams about adventure and science,” it’s now the end of the world. And that’s reflected in the music too.

“With a slight change in tone, you can have music that’s so uplifting and inspiring” he said. “At the end, it’s full of dread.”