Cillian Murphy discusses the 'naivety' of Robert Oppenheimer

Cillian Murphy believes that Robert J. Oppenheimer was ultimately "naive" for believing that the invention of the atomic bomb would lead to the end of warfare.

Christopher Nolan's movie tells the story of the birth of the atomic bomb via The Manhattan Project. It is based on the book 'American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer' which was co-written by Kai Bird and Martin J. Sherman.

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So far it is a box office hit and has received almost universal acclaim from critics, with particular praise reserved for Murphy's performance.

Within the movie, Oppenheimer struggles with the morality of creating a bomb that would go on to kill hundreds of thousands of people in Nagasaki and Hiroshima at the end of World War Two.

READ MORE: Cillian Murphy is glad he wasn't cast as Bruce Wayne for Batman Begins

In his own mind, he believes it is a means to an end of forcing every country in the world to agree that such bombs should not be used in fear of their power.

“I do think that he believed it would be the weapon to end all wars," Murphy told NME.

“He thought that (having the bomb) would motivate countries to form a sort of nuclear world governance.

“He was naïve. Chris (Nolan) used this amazing phrase. We were talking about Oppenheimer’s arc and he said, ‘You know, he’s dancing between the raindrops morally.’ That unlocked something in my mind when I was preparing.”

After the bombings in Japan, Oppenheimer would campaign against the use of the bombs and especially the creation of a new hydrogen bomb. He was subsequently ostracised by the government and some sections of the scientific community.

Robert Downey Jr. full of praise for Murphy

Oppenheimer features an all-star cast including Murphy Emily Blunt, Matt Damon, Robert Downey Jr., Florence Pugh, Rami Malek, Benny Safdie, Josh Hartnett, Kenneth Branagh, Jack Quaid, Gary Oldman and more.

Murphy has long been a collaborator with Nolan, working with the director on projects like Batman Begins and Inception. This time is different, however, in that he is the leading man, and Murphy's co-star Downey Jr. was full of praise for the Irishman's performance in the new movie.

"He is so beyond exceptional … been on some tough projects ... I have never seen anyone have a bigger lift in the history of my career than Cillian Murphy playing Oppenheimer," he said on the Armchair Expert podcast.

"He is perfectly disposed to have the relationship with Chris Nolan, to have this opportunity come up, and to have the wherewithal, the gift and the intestinal fortitude to survive making it."