(Photograph) - When Eric Haseltine, chief scientist for Disney's Imagineering, says some of the actors in the film Titanic are not real, he is not casting a slur on Leonardo di Caprio's acting skills. He simply means that many of the film's extras were completely computer-generated. These "cyberactors" are currently only convincing from a distance, but in time we will see computer-generated actors up close - and then we will not be able to tell who is real. "Twenty years from now Steven Spielberg could do a whole movie from a PC,"predicts Haseltine. But there is "science behind the magic. You have to make it look real and make the physics convincing." For a scene in the film A Bug's Life (above) in which two bugs get stuck inside a water droplet, "it took sophistication to get the optical and mechanical distortions right." Haseltine uses millions of tiny mirrors each controlled by computer.