I recently found myself on Radio 5 Live's Simon Mayo show with film-maker Spike Lee. Discussing his forthcoming hurricane Katrina documentary, When the Levees Broke, Lee revealed that it will include testimony from people who don't believe that what happened was entirely accidental. 'Speaking to the black citizens of New Orleans,' he said, 'many of them told me that they will swear on a stack of bibles that they heard explosions and they think that the levees were blown up.'
Although he stopped short of endorsing the suggestion that the poverty-stricken Ninth Ward was deliberately flooded to spare the French Quarter, Lee insisted: 'As a documentary film-maker, I think it is my duty to let these people voice their opinions. All these things are in the air and people do not put it past the government to do some crazy stuff.'
Coincidentally, around the same time, I received an anonymously mailed package containing a DVD which purported to tell 'what really happened on 11 September 2001'. The DVD, entitled Loose Change: 2nd Edition, began with a warning that I could be arrested 'under section 802 of the US Patriot Act' for 'possession of this information' and a plea that I 'distribute this to friends, family and complete strangers before it is too late to do so'.
The film argued that the World Trade Centre was blown up from inside, that the Pentagon was struck by a cruise missile and that United Airlines Flight 93, in which terrorists were officially reported to have been overpowered by passengers, did not crash in Shanksville, Pennsylvania, but landed safely in Ohio.
This all sounded like baloney to me. But just to be sure, I contacted respected British film-maker Paul Greengrass, who's putting the finishing touches on his thoroughly researched, fact-based docudrama, United 93. Greengrass's film made headlines last week when trailers were reportedly pulled from New York cinemas. But controversy surrounding the movie was first sparked by conspiracy theorists who insist that flight 93 was actually shot down by the US air force and who dismiss the 'official version' of events as a lie. '9/11 has replaced the Kennedy assassination as the epicentre of this great upsurge of conspiracy theories,' concedes Greengrass, 'and flight 93 is right at the heart of it. Do I believe those conspiracies? No. The stuff about the plane being shot down is simply not true. But you have to ask why a document as exhaustive and accountable as the 9/11 Commission report has failed to dispel these myths.'
Indeed, the body of people who deny the official version of what happened on 11 September, the so-called '9/11 Truth Movement', is growing by the day. Several celebrities have thrown their conspiratorial hats into the ring, with Charlie Sheen telling America's GCN radio network last month: 'Nineteen amateurs with box cutters taking over four commercial airliners and hitting 75 per cent of their targets, that feels like a conspiracy theory.' He added that the plane that hit the South Tower 'didn't look like any commercial jetliner I've flown on any time in my life' and that it appeared to him that 'those buildings came down in a controlled demolition'. Strong stuff.
Yet a worrying number of people still believe that the Apollo missions were faked, a claim which finally earned diehard conspiracy theorist Bart Sibrel a punch on the nose from astronaut Buzz Aldrin, who did not take kindly to being called 'a coward and a liar'. The claims of the Apollo conspiracy theorists clearly owe less to reality than they do to the plot of the Seventies cult movie Capricorn One in which an American mission to Mars is faked here on Earth by Nasa stooges.
Conspiracy theories do provide great plots for movies - and vice versa. John Frankenheimer's 1962 film The Manchurian Candidate may have been based on a potboiler by Richard Condon, but among conspiracy theorists, its central brainwashing premise is taken as barely disguised fact.
Similarly, most of what the public knows about the Kennedy assassination is based on a string of excitably dramatic movies, from David Miller's Executive Action (1973) to Oliver Stone's JFK (1991), which viewers have mistaken for verifiable truth. The real reason people believe in such wild conspiracies is simple - it's more reassuring. In the case of 9/11, there is something perversely comforting about the idea that, behind all the chaos, the American government was always in control, carefully orchestrating the events of that terrible day. A similar desire to impose order on chaos may underlie those hurricane Katrina theories. If the levees were deliberately detonated, then at least the government did something, even if that something was malicious. How much worse to accept that the citizens of New Orleans were simply abandoned by the authorities and left to fend for themselves.
'Conspiracy theorists are not to be sneered at,' says Paul Greengrass. 'They're interesting, thoroughly engaged and they're responding to a profound unease. But they do tend to simplify very complex situations.'
I used to take solace in Gail Brewer-Giorgio's bonkers books Is Elvis Alive? and The Elvis Files, which argued that a fit and healthy Presley had carefully planned and faked his death in 1977, fled Graceland in a helicopter and restarted his life in privacy and seclusion. I embraced this story simply because it was less depressing than accepting that my hero had got too fat, sloppy and drug-addled to live.
In the end, the facts won out and I had to abandon my adolescent fantasies. Others should do the same. It is chaos, rather than conspiracy, which really rules the world.