Every decade or so, a film passes from box-office hit to cultural phenomenon. That’s what is happening with The Dark Knight, the latest instalment in the Batman franchise. Even in Hollywood, nobody can quite believe how big a hit the $180m film, the second Batman movie to be directed by Christopher Nolan and to star Christian Bale as the superhero, has become. “It’s a film that is rewriting the record books every day, redefining our notions of what a blockbuster can be,” says Paul Dergarabedian, president of the box-office tracker Media by Numbers.

This weekend, The Dark Knight will overtake the $461m the original Star Wars made in North America to become the second-highest-grossing movie there of all time. Its distributor, Warner Bros, is tamping down the possibility that it might pass the $600m made by Titanic. The studio has been keen to highlight the part played by its secret six-month, multimillion-dollar anti-piracy campaign to ensure digital copies of the film didn’t leak out before it opened. Warners counts it a triumph that the first pirated copy didn’t appear on the internet until 38 hours after the film was released. “The first weekend, there was this huge, pent-up demand and eagerness by audiences to see this movie,” Dergarabedian says.

Its box-office numbers have certainly been boosted by the usual adolescent fan boys returning to see it three, four, five times. Fan girls going repeatedly to worship at the celluloid shrine of Heath Ledger can’t be discounted, either: the movie is being seen by almost as many women as men, and by as many people over 25 as under.

Why has The Dark Knight, exceedingly bleak and violent, touched such a cultural nerve? Some believe it was the intense and to some extent morbid interest generated by Ledger’s untimely death. Warner Bros capitalised on this by featuring his leering, paint-smeared face on almost all the movie’s advertising. And his mesmerising performance as the Joker justifies the marketing hype.

That doesn’t, however, fully explain why the film has become such an extraordinary cultural phenomenon. Some commentators in America believe the film has become a touchstone, beguiling audiences with what appears to be popular, comic-book entertainment, but explores some of the most critical social and ethical issues we face today — in particular, the issues being wrestled with by countries, notably America, fighting the “war on terror”. As those who have seen it will know, The Dark Knight explicitly examines how far it is permissible for individuals and society to go in the fight against “evil”.

“Nolan turns the Manichean morality of comic books — pure good vs pure evil — into a bleak post-9/11 allegory about how terror (and, make no mistake, Ledger’s Joker is a terrorist) breaks down those reassuring moral categories,” writes Dana Stevens in the online magazine Slate. If the references weren’t obvious enough, the Time magazine critic Richard Corliss calls the Joker “the Bin Laden of movie villains”.

Both conservatives and liberals have been rushing to claim that The Dark Knight has become such a phenomenon because it validates their beliefs about the ethical issues at the heart of the war on terror. “There seems to me no question that The Dark Knight is at some level a paean of praise to the fortitude and moral courage that has been shown by George W Bush in this time of terror and war,” the conservative novelist Andrew Klavan writes in The Wall Street Journal. “Like W, Batman is vilified and despised for confronting terrorists in the only terms they understand. Like W, Batman sometimes has to push the boundaries of civil rights to deal with an emergency, certain that he will re-establish those boundaries when the emergency is past.”

Kyle Smith, film critic for the New York Post, takes this allegory an amusing — and perhaps disturbing — step further. “Batman is not charming,” he writes. “He isn’t popular, partly because he’s a zealot and partly because he doesn’t bother to explain himself to the press. He is independently wealthy, having spent years as the head of an industrial company. His methods are disturbing, his operations bathed in darkness. He is misunderstood, mistrusted, endlessly pursued by the attack dogs of the night. . . And he lives in an undisclosed location. Isn’t it obvious? Batman is Dick Cheney with hair.”

Commentators on the left appear to have seen a completely different film. The Dark Knight “takes the viewer on a sometimes traumatic but ultimately redemptive and humanistic journey towards a post-9/11 ethic”, writes Michael Dudley, of the Institute of Urban Studies, on the left-wing website AlterNet. Dudley believes that when Batman does use extra-legal methods — “the dark side”, as Cheney once put it — it backfires on him and the city he is trying to protect. Batman beats up the Joker in jail, a scene reminiscent of the “enhanced interrogation techniques” used by the CIA on terrorist suspects, and uses a computerised tracking system to plug into every mobile phone in the fictional city of Gotham, much like the “Total Information Awareness” wiretapping programme espoused by the Bush administration.

The Dark Knight, Dudley concludes, “warns against abandoning our principles out of fear, grief and hatred, as well as abdicating our moral agency to external authorities — both of which comprised the hallmark moral syndrome of the years following 9/11”. Nolan has not hidden his desire to explore these key ethical issues. “What Batman is doing is heroic, but it can be seen as vigilantism, as a dark force outside the law,” he says. “That’s a very, very dangerous road to go down. He’s always riding a knife edge in moral terms.”

While commentators on the right and left slug it out, in the Joker Nolan has, I suspect, touched a rawer nerve in all of us by confronting his own deepest psychological fears. In a number of interviews, the British director has said that what really frightens him is not so much terrorism on behalf of a different world view, but a force for evil much less explicable: “Anarchy and chaos — even the threat of anarchy and chaos — are the most frightening things society faces, especially in this day and age,” In the film, the Joker explicitly defines himself: “I’m an agent of chaos.”

It is initially hard to see where Nolan’s deep-seated fear of social “chaos” comes from. He lives a quiet family life in West Hollywood, which is almost crime-free. He’s very rich. He works in a controlled, close-knit environment, with his brother Jonathan as scriptwriter and his wife, Emma Thomas, as producer. People who meet Nolan, who had a public-school education at Haileybury, are struck by his meticulous, deliberately old-fashioned, almost Edwardian demeanour. He invariably dresses in either a dark suit or a blazer, and often wears a waistcoat, with a crisply ironed white shirt and cuff links — clothes that seem to externalise his psychological need for order and control. In an interview not long ago, he admitted: “It’s definitely something I have a fear of — not being in control of your own life.” A reporter for Newsweek was astonished to discover that, at all times, in case of some kind of unspecified existential calamity, Nolan keeps on him two passports, his British one and his American one.

Beneath this outward desire for order, it’s possible that, with the Joker, Nolan is exploring his own most radical fear (and, it seems from the film’s success, ours, too): the fear of psychological chaos, of madness, the unravelling of firm mental grounding, the complete loss of psychological control. Read in this way, the Joker represents nothing as banal as Bin Laden, but the id, “the dark, inaccessible part of our personality”, as Freud put it, the base human instincts, unconscious, amoral and utterly selfish. “We call it a chaos, a cauldron full of seething excitations,” Freud wrote. Nolan calls it the Joker. And the director has, apparently, found a multimillion-dollar way to tap our darkest anxieties and have the last laugh.

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