I've been encountering a lot of famous fictional people recently. Or fictional famous people – it being a little tricky to come up with a precise description of what I have in mind. What I mean are real people reimagined – as the actress Greta Garbo is in Frank McGuinness's play Greta Garbo Came to Donegal. Or as Charlie Chaplin is in Glen David Gold's novel Sunnyside. Or Marilyn Monroe and Frank Sinatra cropping up in Andrew O' Hagan's forthcoming novel The Life and Opinions of Maf the Dog and of his friend Marilyn Monroe. These people aren't invented, obviously, since so much of how they behave and – in some cases – what they actually do is based on the historical record. And yet they're clearly not real either, since they're phantasms of celebrity.

They do an odd thing to the works they inhabit – though it's a thing that's closely related to the way in which celebrity can bend real life out of shape as well. The first of these might be described as False Recognition, the synaptic trick which means that people who are well known live in a far more communicative world than the rest of us. Walking down the street you spot a familiar face and think "I've seen that person before somewhere – I'd better adopt default friendliness". Quite often the specific identification ("I saw it on screen last Thursday evening, in that slightly duff thriller") arrives after the encounter itself. You smile and nod in a way that says "Hi, how are you! Long time no see". And it's only 20 seconds later that you realise it's not a "long time" but "never".

Onstage or in a book something similar takes place – the writer isn't working from scratch but building on a whole set of assumptions about this character. They're working with someone you know, after all – and can choose to amplify that familiarity, going with the grain of received opinion, or to contradict it. But either way you're inclined – quite factitiously – to greet the character as an old friend. Everyone else in the room might be a stranger, but you at least have something in common with this person. And here, at least, there's no prospect of embarrassment in your meeting.

But stars – as Einstein successfully predicted – also bend light around them. They affect the gravitational field that so that every event takes on a slightly different colouration and aspect. That's true in real life (the day on which you buy the newspaper standing next to Greta Garbo is never going to be confused for any of the thousands of days on which you do exactly the same thing not standing next to her), but also on stage and in the pages of a book. And it's in the nature of celebrity that it oddly blurs the distinction between fictional fame and the real thing. The real Greta would have brought an air of unreality to ordinary life, tugging you towards the fictional realm in which she's usually most present to you. The fictional Greta, on the other hand, pitching up in an entirely imagined world, paradoxically pulls it closer to reality, a little scrap of documented truth stitched into the fabric of the thing. And perhaps what this confirms is another truth – that celebrities (as opposed to the humans that find themselves celebrated) are neither quite real nor quite fictional, but a strange hybrid of the two, a collaborative artwork created by millions.

Sometimes it works

Curiously, there's an echo (or premonition) of Avatar Syndrome in the novel The Museum of Innocence, by Orhan Pamuk (pictured), an exhaustive inventory of the emotions and incidents in an ill-fated Istanbul romance. "Sometimes", the narrator Kemal recalls at one point, "Füsun would become so engrossed in the film on television that I'd long to be that film's hero". This occurs in a chapter that is six and half pages long and consists exclusively of sentences beginning "Sometimes". The resulting list compresses countless nights of unconsummated love into a portrait of the contingencies and banalities of life. As it happened it was also the chapter where my rising impatience with the microscopic detail of Pamuk's novel broke out into audible protest – though I recovered sufficiently to recognise that trying the patience of the reader may well have been one of the effects he was after.

It made me wonder, though, about similar novelistic gestures, in which a writer deliberately cramps his or her own style. George Perec's achievement in writing an entire novel – La Disparition – without the letter "e" doesn't quite count I think, since it doesn't involve a sudden interruption of an otherwise relatively conventional novel. Joyce's Ulysses might similarly be ruled out, since so many of its chapters impose a self-inflected restraint – though knowingly constructing a chapter containing only one full stop surely qualifies. I'd be interested to know of other examples if anyone can think of them.

* "Get a life!", that time-honoured taunt at nerds who have allowed their enthusiasms to get out of hand takes on a certain urgency in the light of reports that fans of Avatar – James Cameron's 3D space epic – have been reporting feelings of suicidal depression after watching the film. This is hardly the first time that a work of art has been linked to terminal gloom. Goethe's novel The Sorrows of Young Werther is supposed to have sparked a wave of youthful suicides after its publication in 1774 and the Thirties song "Gloomy Sunday" was also charged – without a great deal of evidence – with inducing an epidemic of self-murder among those who heard it.

In both those cases, though, the art work itself implicitly made a case for ending it all. Avatar Syndrome, by contrast, appears to brought on by the viewer's realisation that they're going to have to live in this world, as boring old humans, rather than as Na'vis in the rainforest idyll depicted on screen. They're blue, in other words, because they can't be blue, with a tail and a cat-like nose. Sneer at them to get a life and they would reply that they've already got one – it just doesn't seem up to much anymore. B-movie schlock horror often used to market itself with the warning that the weak of heart might expire during the screening and leave on a stretcher with a sheet over their face. Avatar could presumably now make history by warning sensitive viewers about fatal side-affects that can occur after the final credits. Or, possibly, by becoming the first film that can claim to be an active force in Darwinian selection.