From the first sentence, the first word, the first nervily in-drawn breath, this compulsively watchable picture announces itself as the unmistakable work of Aaron Sorkin. His whip-smart, mile-a-minute dialogue made The West Wing deeply addictive on TV, and after uncertain works such as Charlie Wilson’s War and the strange, small-screen drama Studio 60 on the Sunset Strip – in which Sorkin’s distinctive, faintly martyred seriousness was bafflingly applied to the backstage shenanigans of a fictional television comedy – this writer is triumphantly back on form. He’s found an almost perfect subject: the creation of the networking website Facebook, and the backstabbing legal row among the various nerds, geeks, brainiacs and maniacs about who gets the credit and the cash.

Part boardroom drama, part conspiracy thriller, the story is adapted from Ben Mezrich’s non-fiction The Accidental Billionaires. There appears, however, to be nothing accidental about it. The film version perfectly displays Sorkin’s gift for creating instantly believable sympathetic-yet-irritating characters, and the chief of these is Facebook’s driving force, Mark Zuckerberg, played with exemplary intuition by Jesse Eisenberg. He is a borderline sociopath, never smiling, never raising his voice, never conceding an argument, driven to create his masterpiece through the unforgettable pain of being dumped in the movie’s opening scene. What perfect casting Eisenberg is. (I couldn’t help remembering, incidentally, his character’s disparagement of Facebook in the movie Zombieland: jeering at idiots with status updates like: “Limbering up for the weekend.”) Sorkin gives everyone great lines. It’s pretty much a non-stop fusillade of put-downs, insights and zingers. I wonder if the real-life Zuckerberg has ever physically said as many words as this in his entire life.

David Fincher’s direction creates just the right intensity and claustrophobia for a story that takes place largely in a stupefyingly male environment at Harvard University in 2003, shown in flashback from various acrimonious legal proceedings. Here, computer-science student Zuckerberg has the same sense of entitlement and self-congratulation as everyone else, but combined with social resentment about being barred from snobby fraternities and clubs. When his girlfriend Erica (Rooney Mara) breaks up with him, the director shows how the emotionally wounded Zuckerberg embarks on a retaliatory campaign not far from the sinister world of Fincher’s serial-killer films Se7en and Zodiac. He blogs vengefully about Erica and, in an evil-genius frenzy, creates Facemash, a spiteful and misogynistic site that invites the guys to rate campus girls against each other. (Slightly leniently, the movie explains it away a little by emphasising that Zuckerberg has had a couple of beers.) It is from this beginning that the smilier, friendlier Facebook emerges. But we have been cleverly shown the site’s nastier, more paranoid origins: a clue to its unspoken world of friend-number envy, cyber-stalking and anxiety about having no friends at all.

Zuckerberg gets investment from fellow geek Eduardo Saverin, played by Andrew Garfield, of whose marginally superior social success he is jealous and whom he later betrays by cutting him out of the action in favour of web entrepreneur Sean Parker, smoothly played by Justin Timberlake. Wealthy alpha-male twin brothers Cameron and Tyler Winklevoss (both played by Armie Hammer) plan to launch their own site, called The Harvard Connection, and try to recruit Mark as their tame techie-nerd; initially dazzled by their cachet, Zuckerberg plays them along, fatally delaying their launch while secretly getting his own up and running. Shrewdly, Sorkin and Fincher show how the Winklevosses are afraid to sue, because that’s not the action of an effortlessly superior Harvard man.

Probably conceived when Facebook was at the top of the heap, the movie now arrives in cinemas at a time when Twitter has overtaken it in zeitgeisty importance: a lesson in how fast-moving internet trends can be. It would be great to see a movie about an ageing Australian-American media mogul trying to stay with-it and hip by tragically investing in MySpace – what tremendous scenes of rage-filled incomprehension there could be as the great man rants in front of downward-trending graphs. Or perhaps a Made in Dagenham-type British comedy about that once whiter-than-white-hot phenomenon Friends Reunited, run by a blameless couple in a spare room of their Barnet home: a dark destroyer of marriages, a reopener of school-day wounds, far more toxic than Facebook could ever be.

The success of The Social Network lies in capturing the fever of Facebook’s startup, while subversively implying that it created money and ephemeral buzz, but not a whole lot else; there is very little about the interconnectivity and creativity that its evangelisers often claim. With its fanatical rivalry, envy and preeningly clever half-wits butting heads, the film reminded me a little of the BBC’s excellent TV play Life Story from 1987, the story of Francis Crick and James Watson and their ill-tempered race to discover the structure of DNA before anyone else. (Sam Mendes and Pippa Harris are reportedly developing a remake.) Yet that was a story with something substantial at its close. This has … well, what? At the end, all is loneliness. This is an exhilaratingly hyperactive, hyperventilating portrait of an age when Web 2.0 became sexier and more important than politics, art, books – everything. Sorkin and Fincher combine the excitement with a dark, insistent kind of pessimism. Smart work.