Is there anyone out there?

(Aboard the giant space station) "..

(Aboard the giant space station) ". . . There was now a barber's shop, drug store, movie theatre and a souvenir shop" (2001: A Space Odyssey)

When Commander Bill Shepherd finally drifts into his bunk aboard the International Space Station tomorrow night, he will have passed into the New Year 16 times, because his speeding spaceship crosses the international dateline every 90 minutes. But even circling the Earth at the speed of a rifle bullet, he has no hope of catching up with the 2001 that Arthur C. Clarke and Stanley Kubrick imagined in 1968. Space Station One (in the film) is now Space Station Alpha (an unofficial title for an unfinished station). Bill Shepard and Russian crewmate Sergei Krikalev have bunks, but flight engineer Yuri Gidzenko sleeps on the floor of the cramped cabin. There is a smell, and the air-conditioning makes a terrible racket. Until this month's delivery of solar power units, there wasn't even enough electricity to heat the whole station. Needless to say, there are currently no plans for a cinema.

It would be easy to say that the future has arrived, and that it hasn't lived up to expectations. But in reality, Kubrick's breathtaking science-fiction epic will forever be more about the past and the future than it is about today. It is a time machine that transports us back to the 1960s, and a mind machine that challenges us to look forward, farther than most of us dare. If the past is a different country, 1968 now seems like a different planet. The obscene war in Vietnam, the assassinations of Martin Luther King and Robert F. Kennedy, ugly repression and riots in Northern Ireland, the Russian invasion of zechoslovakia, the ever-present threat of nuclear annihilation - and then 2001. At a cinema near you, in the cold, bitter winter of 1968, a film that said we would not only survive the annus horribilis, but in 30 years, we would be reaching for the stars. 2001: A Space Odyssey was not just a science-fiction film, it was a comfort blanket for a frightened and disillusioned generation.

The film star Rock Hudson stormed out of the Hollywood premiere demanding: "Would somebody please tell me what the hell that was all about?" For several weeks, the $10 million epic (almost universally panned by the critics for "having no plot") teetered on the brink of commercial failure. Then slowly, imperceptibly at first, the theatres started filling - with young people drawn to the film by wordof-mouth. The psychedelic special effects of the "star gate" sequence became part of the lexicon of the 1960s drug culture and the film would later be marketed with blatant ambiguity as "The Ultimate Trip". But 2001 was much, much more than a drug movie. It was Kubrick's version of Homer's Odyssey and cinema's answer to James Joyce's Ulysses.

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Rock Hudson's bewilderment nicely echoed the perplexity of an earlier generation that was faced with Joyce's play on complex Homeric themes. Leopold Bloom's odyssey through Dublin in 1904 is repeated on a cosmic scale a century later in Kubrick's film by star traveller David Bowman. Drawn to Jupiter by the Siren song of the aliens' monolith, he must confront the Cyclops - a one-eyed computer called HAL - before he can journey through the star gate (Odysseus's Charybdis?) to confront his own human imperfections and become reborn as a star child. This does not happen by way of the Ormonde Hotel, Barney Kiernan's pub and Holles Street Hospital, but the Joycean themes abound as Bowman progresses, like Bloom, "in a mood of drugged surrender to the impression of the moment".

But, unlike Joyce, Kubrick and Clarke have chosen to describe a world in which women are relegated to subservient roles - a myth-breaking flaw in their omniscience, since they were already writing at a time when "the times, they are a changing". Other "errors" are not so egregious, some even offering unexpected insights into the swift pace of human exploration and the awesome potential for unexpected discoveries. Writing in the 1960s, the great visionary Clarke imagined that humanity's first close-up view of the moons of Jupiter would come as Bowman's huge spaceship entered the Jovian system in 2001. In fact, this awe-inspiring vista first unfolded before a global television audience in 1979 - less than 10 years after the film premiered. Clarke could never have imagined that television viewers on Earth would be looking on as the Voyager's robotic probes swooped in over enormous volcanoes spewing molten sulphur across the tormented surface of a moon called Io. Nor could he possibly have predicted that the year 2001 would open in a flurry of new signals from Jupiter, as attention focuses on a Jovian moon which may harbour life.

In 2001, Clarke imagined - with eerie prescience - that Europa would be a moon "covered with glittering hunks that looked like stranded icebergs". When the Galileo spacecraft zoomed in for a closer look in 1996, scientists were astounded to see giant icebergs frozen in a marble-coloured landscape that team leader Randy Tufts decided to name after another place of breathtaking beauty: Connemara. But it is what has been discovered beneath the icebergs of Europa that has turned modern planetary science into a true space odyssey.

At three-and-a-half minutes past 10 (Irish time) this morning, the Cassini spacecraft, en route to Saturn with a European capsule on board, will sweep above the cloud-tops of Jupiter and aim its instruments at the icebound moon, Europa. The Jupiter Millennium Flyby (www.jpl.nasa.gov/jupiterflyby/) is part of an urgent new survey of a world the size of a small planet that appears to harbour beneath its icy surface a vast salt-water ocean. Europa - a sideshow in 2001 - has taken centre stage (along with Mars and Saturn's moon called Titan) in a 21stcentury search for life beyond Earth.

When Arthur C. Clarke began writing in the 1940s, there was thought to be a real possibility - bordering on an expectation - that life would be found on Mars or Venus and that intelligent life might betray its existence at any moment; by the time 2001 was first screened in 1968, hopes of finding life elsewhere in our Solar System had been dashed by early spacecraft reconnaissance of our planetary neighbours; now, on the eve of 2001, the pendulum is swinging back towards something bordering expectation that primitive life forms may be detected at Mars or Europa. But the central theme of 2001 remains at the heart of one the greatest questions that continues to haunt our species. Is there anybody out there?

Arthur C. Clarke and Stanley Kubrick were convinced that contact was inevitable and even perhaps imminent, so much so that Kubrick tried to get insurance against the possibility of such extraterrestrial contact destroying the premise of his film. In more recent years, advances in astronomy and biology have generally helped to strengthen the conviction of many scientists that life of some sort is widespread in the universe. Which leads to another fundamental question: Where are they?

Astronomer Paul Horowitz of Harvard University has calculated that there could be as many as a thousand technologically advanced civilisations in our own Milky Way Galaxy alone. This is a breathtaking proposition, since it follows that if that many were extant today, then a truly huge number must have existed over the lifetime of the galaxy - perhaps as many as 12 billion. Yet not one of these civilisations has left a recognisable trace? This is a very big problem.

Arthur C. Clarke and Stanley Kubrick span three million years in 2001, bringing humanity from the dawn of consciousness to its first encounter with superior intelligence in 2001. As the 21st-century dawns, a number of scientific teams have begun to look beyond 2001 to the next three million years, in research that raises profound philosophical questions for our species and appears to place new limits on the possibility of advanced extraterrestrial civilisations.

Stanley Kubrick's legendary cinematic device at the beginning of 2001 effortlessly compressed three million years into an instant when an ape hurled a bone which morphed into a spaceship. In cosmic timescales this was not artistic licence, it was scientific truth: even by the standards of our 4.5 billion-year-old Earth, the human species has evolved to its present stage virtually instantaneously.

So what of "3,000,001: A Space Odyssey"? With technologies that Kubrick and Clarke were able to foresee three dozen years ago, humans could begin the process of colonising our galaxy within a very few centuries, establishing bases at several nearby star systems. In time, those colonists would despatch their own expeditions, and within 10,000 years our descendants could have inhabited every hospitable stellar system within 200 lightyears. At that rate, most of the galaxy would have been settled within three million years, in an expansion that would appear to a cosmic observer to have happened in about the same time it took Kubrick's ape to throw a bone into space.

Stanley Kubrick (who also made Dr Strangelove; or How I Learned to Stop Worrying and Love the Bomb) would have laughed hollowly at the notion that humanity could survive its own destructive impulses for so long, but the calculations of today's futurists cast a long and thought-provoking shadow over deliberations about the future of our species. If it takes just three million years for a technological civilisation to colonise the galaxy, then the skies should already be teeming with star ships, unless: 1) The Milky Way's "biological clock" was reset by some galactic cataclysm (recent research has focused on gargantuan explosions of gamma radiation and on collisions with clouds of anti-matter), so that advanced life forms have only been evolving for a few billion years.

2) Technological civilisations - all of them - destroy themselves sooner or later.

Or:

3) We are truly alone.

Leo Enright is a documentary filmmaker and broadcaster.

2001: Filming the Future by Piers Bizony (Aurum Press, £14.99 in UK). 2001 A Space Odyssey (special edition) by Arthur C. Clarke, with a new introduction by science fiction writer Stephen Baxter (Orbit Books, £12.99 in UK).