It is 1965, and at a cinema near you, The Sound Of Music is showing for the first time. And there's another new film with some catchy tunes - Doctor something... ah, yes, Zhivago.

But never mind historical fiction.

In the real world - the high-rise, hi-fidelity present - the future beckons. The Americans have just mastered the art of 'docking' two spacecraft, and even as we hum Lara's Theme, Early Bird, a satellite that will revolutionise telecommunications is being slung into orbit. By the end of the decade, they say, we'll have a man on the moon. There will be no holding us. Who knows what humankind will be doing by the end of the century? Who knows what our world will be like 12 months into the next millennium?

In a Hertfordshire film studio, two men are doing their best to predict the answers to these very questions. The American director Stanley Kubrick and the English science-fiction writer Arthur C Clarke are shooting a film called 2001: A Space Odyssey, and are determined that their fantasy will be entirely plausible. 'I never considered 2001 as a strict prediction,' Clarke will say in retrospect, 'but as more of a vision, a way things could work.'

Yet their attention to detail verges on the obsessive. Will the first men on the moon see more stars than we can through our atmosphere? After much debate, they decide that they will. It is, as the Surveyor lunar probe will soon show, the right decision. They spare no effort in getting such minutiae right, consulting experts on everything from spacewalks to exploding bolts.

But what of the broader vision? How clearly do they see what, for us, is now the present? At about the time he was debating stellar visibility, Clarke did make one prediction: by 2001, a colony 1,000-strong would be established on the moon. But even as he spoke, the US was sending its first combat troops into Vietnam. Years later, Clarke said that the sheer expense of Vietnam pushed serious space travel on to the slow-burner in the last decades of the 20th century.

It goes without saying, then, that, in terms of its plot line, Space Odyssey is light years off beam. Patently, there is no colony on the moon. And although there has been an upturn in planetary exploration recently, the mapping and prospecting of the solar system is conducted exclusively by remote-controlled machines. Humans remain earthbound, or venture into orbit in small groups; the nearest we have come to the vast artificial moon that wheels silently through the early part of the film is the relatively unimpressive assemblage of labs and locker rooms of the International Space Station currently under construction.

To say that the only lasting benefit from the space programme of the 60s is the non-stick frying pan is, of course, an exaggeration. But only a slight one. Sure, we've grown some enormous crystals, and our flying telescopes tell us awesome things about the universe. But it's hardly the bright future that flashed on to our screens in 1968. When the film was released, MGM issued journalists with a booklet setting it in context. Space travel, naturally, would be far advanced. The wheeling space station is served by a fleet of plush PanAm shuttles, and provides a springboard into deeper space while offering luxury hotel facilities for visiting VIPs. In the real world, MGM believed that commercial spacecraft would be making scheduled trips to the moon by 2001.

Meanwhile, life on earth would have moved on apace. Terrestrial transportation would frequently include travel by ballistic rocket, reducing the maximum journey time anywhere on the planet to less than an hour. A dozen nuclear power stations would supply the US with all its electricity, and 'cancer, senility, mentally retarded children will no longer exist'.

In his quest for veracity, Kubrick asked several firms to supply him with designs for possible future products, some of which appeared in the film or its publicity material. The result was that Space Odyssey always looked cool, whereas The Man From Uncle looked downright naff. One company, Hamilton, came up with a gadgetal wristwatch that would not look out of place in a modern high-street jeweller's. Parker produced an 'atomic pen' that would be perfectly convincing if only the word 'atomic' were replaced with 'turbo'.

The 'smart ring' that American Express said would identify account holders is not a million miles away from today's smart card; the Whirlpool food dispensing galley would be at home in any burger bar; and as for the Bell Telephone videophone used by one character, well videophones are now a fact of life.

Maybe Kubrick didn't predict that BBC reporters would no longer speak in BBC English, but from the Velcro footwear worn by the weightless flight attendants to the computer displays with their astounding graphics and modern typefaces, the film looked - and still looks - totally convincing.

And the leading character? According to the MGM booklet, 'ultra-intelligent computers will be constructed within about the next 30 years', and these will be 'capable of performing every intellectual activity'. MGM was talking, of course, about HAL, the Discovery's all-singing, all-talking onboard super-computer that steals the show. But while artificial intelligence of the order displayed by HAL seemed an achievable goal to scientists in the mid-60s, the reality has fallen short of expectations. In terms of hardware, of course, all those knobs and flashing lights are already a thing of the past. Honeywell, Burroughs and IBM supplied Kubrick with projections for computer design in 2001, yet none foresaw the miniaturisation of computers or the invention of the Macintosh interface that would make it possible to take command of the Discovery using a mouse and a screen.

But as for what HAL could do - as for what HAL was, even who HAL was - with the exception of his chess-playing skills, today's computers don't come close. Sure, they can speak, but they haven't a clue what they're on about. And while some can just about recognise human speech, their grasp of meaning is only about canine in terms of ability. They might peer through digital cameras instead of the whirring shutter that we hear on the Discovery at one point (oops!), but when it comes to scene analysis they still can't see for looking.

The fact is that, in the 35 years since HAL was conceived, scientists have come to see just how distant is this goal called artificial intelligence. We might have cracked the hardware problems, but the software is another matter. As one researcher put it, even if we could build a machine of sufficient complexity, we couldn't begin to program the thing.

Ask them to perform specific tasks, of course, and our finest, tiniest processors cut quite a dash. In a way, that's where Kubrick and Clarke got it really wrong. For in the real 2001, computers are tiny specialists embedded in our car dashboards or sitting in our hands. Do Dave or Frank carry a PalmPilot in the film, or is that a clipboard we see before us?

As Clarke says, Space Odyssey was never intended as a set of predictions - just as a plausible vision of a possible future reality. It was entirely plausible in 1968 that, by the end of the century, we'd be sending astronauts to the outer reaches of the solar system in spaceships run by devious, lip-reading super-computers. But then, it was also plausible that PanAm would still be in business.