'Matrix' sequel pushes back film boundaries with 'greatest special effect' seen

Hollywood is billing it as the greatest special effect of all time. In the film The Matrix, the characters had to wrestle with the question of whether everything they saw was real or computer-generated. Now in its sequel, Matrix Reloaded, viewers will get the same experience – and they won't be able to tell either.

In a central scene in the new film, to be released on 15 May, Neo, the hero character played by Keanu Reeves, fights his nemesis, a black-suited "agent" called Smith, played by the actor Hugo Weaving. But not one Smith: the fight scene contains hundreds of them, all indistinguishable, all apparently the real people, as close inspection even of the film-quality trailer, available on the internet, suggests.

Except that they are not. At the beginning of the scene, the real Reeves and Weaving walk into the scene, which takes place in a city-block landscape. But once the action starts, there is an indistinguishable transition – and while reality clearly stopped some time earlier because there are hundreds of Agent Smiths on the screen, there's no way to tell just when.

Generating all those virtual characters and choreographing a fight in which the camera swoops and whirls and where occasionally time stops took vast resources of computing power – probably more than has even been used on a single film – spread over years.

"The point is to be able to construct events that are so complex, in terms of what human bodies need to do, that the total effect is impossible choreography," said John Gaeta, the special effects supervisor in this and the first Matrix film – as well as the third, which will follow in November. The two new films were shot simultaneously in Australia over a 270-day stretch from 2001 to 2002, at a total cost of more than $300m (£200m). Then the post-production to create what appears on the screen began. Mr Gaeta was the inventor of "bullet time", where time seems to stop during a moving scene while the camera pans. But that technique, which requires dozens of cameras and rigorous computer post-production to wipe away the cameras, has now become commonplace.

For the next film, he went further – capturing the tiniest details of the actors' faces, to be able to generate them in a computer and produce entirely lifelike movements from them. It required the efforts of 270 technicians capturing data from five cameras filming the real scene where a team of kung-fu extras practised the form of the fight that would become Neo and Smith.