For more than 40 years, Steven Spielberg has been asking audiences the same question: What if we're not alone?

From the friendly alien at the heart of E.T. to the mysterious visitors in Close Encounters of the Third Kind, some of his most celebrated films have explored humanity's fascination with life beyond Earth.

Now, the Oscar-winning director is returning to that theme once again with Disclosure Day, a sci-fi thriller starring Emily Blunt, Josh O'Connor, Colman Domingo, Colin Firth and Eve Hewson.

The film imagines a world on the brink of a revelation: proof that non-human intelligence exists and has been hidden in plain sight.

At the centre of the story are Blunt's character, meteorologist Margaret Fairchild, and O'Connor's Daniel Kellner, a cybersecurity expert who uncovers evidence of a long-running cover-up and finds himself pursued as governments and powerful corporations race to contain the truth.

Speaking at the UK premiere in Leicester Square, Spielberg told the BBC he remains captivated by the question that has inspired some of his most iconic work, and his view on the possibility of extraterrestrial life has evolved over the decades.

"My view has become more realistic," he said. "There's a lot of mystery and things that are undisclosed but I've become more optimistic that people are going to be able to discover things that we have not been allowed to discover."

The film arrives at a time when discussions about unidentified aerial phenomena, government transparency and artificial intelligence have moved from the fringes of popular culture into mainstream debate.

While Disclosure Day centres on the possibility of extraterrestrial life, many of its themes focus on trust, secrecy and how societies respond when long-held assumptions are challenged.

Most importantly, according to the 79-year-old filmmaker, it centres ultimately on humanity.

"It's about empathy and bringing people together" and an event like discovering the existence of aliens "would bring people together", he said.

That hopeful message was echoed by the cast, many of whom said the film feels particularly relevant at a time of growing political and social division.

'Something is out there'

Josh O'Connor, who plays cybersecurity expert Daniel Kellner, said the script immediately resonated with him.

"When the script came through, I read it in one go in a rush, and it was thrilling, it felt so needed as it's a film about hope and humanity and understanding."

He suggested that discovering intelligent life beyond Earth could force people to look beyond their differences.

"When there's a lack of understanding of each other, maybe something from outside might unite us.

"I wonder whether the idea of hate is a human invention because none of the documented close encounters are nasty or violent."

The 36-year-old actor also admitted he believes there is likely something beyond Earth, although he is in no hurry for humanity to solve the mystery.

"I definitely think there's something out there, but I don't know if we'll discover it in our lifetimes, and I don't mind if we don't," he said. "The sense of mystery used to be so strong and we've lost that now."

Emily Blunt, who stars as weather presenter Margaret Fairchild, told me she hoped any confirmation of extraterrestrial life would inspire wonder rather than fear.

"If we found out there were aliens, I'd hope people were astonished, humbled and awestruck by it," she told the BBC.

The Devil Wears Prada actor added that it's "mathematically insane to imagine we are the only civilisation" and one of the film's key messages "is not to be afraid of what we don't know."

The film's release also comes as Hollywood continues to debate the growing role of artificial intelligence in filmmaking. Earlier this week Martin Scorsese received backlash after endorsing an AI tool and calling it "creatively freeing".

Blunt recently revealed that some of the unusual vocalisations required for her character were created by her rather than generated using AI, as it was "up to me to make the most fully rounded performance."

Spielberg agreed, and both said they can see how advancements in AI can benefit us and be useful as a production tool, but should not replace creative talent.

"It depends on what the AI is," Spielberg explained. "To find locations or organise schedules is great, but not to replace the writer, actor or director, I don't believe in that."

Meanwhile, Colman Domingo said one reason he was excited to join the project was the chance to help bring Spielberg's vision to life.

Like several of his co-stars, the Euphoria actor said he believes there may be life beyond Earth.

"We all go out and see stars, and I can imagine that there's someone out there looking at me," he said.

While acknowledging that proof of alien life could dramatically alter society, he argued the impact could ultimately be positive.

"It would be incredible if we all knew and understood it as a truth. That might upend some things in society, but that's not that bad given how polarised the world is right now."

Colin Firth described the film as a "rollercoaster" that explores empathy, fear and humanity's response to the unknown and said viewers "will be left with a lot of conversation points".

As for Spielberg, he remains optimistic that answers may come sooner rather than later.

Asked whether in our lifetime we will discover that there is life beyond earth, the director replied: "Yes."

"And I'll accept whatever they are."