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The absolutely neat thing about the dinosaurs in the movie Jurassic Park is that they possess enough artificial life so that they can be reused as cartoon dinos in a Flintstones movie.

They won't be completely the same of course. They'll be tamer, longer, rounder, and more obedient. But inside Dino will beat the digital heart of T. Rex and Velociraptor -- different bodies but the same dinosaurness. Mark Dippe, the wizard at Industrial Light and Magic who invented the virtual dinosaurs, has merely to alter the settings in the creatures' digital genes to transform their shape into lovable pets, while maintaining their convincing screen presence.

Yet the Jurassic Park dinosaurs are zombies. They have magnificent simulated bodies, but they lack their own behavior, their own will, their own drive for survival. They are ghostly muppets guided by computer animators. Someday, though, the dinosaurs may become Pinocchios -- puppets given their own life.

Before the Jurassic dinosaurs were imported into the photo-realistic world of a movie, they dwelt in a empty world consisting solely of three dimensions. In this dreamland -- let's think of it as that place where all the flying logos for TV stations live -- there is volume, light, and space, but not much else. Wind, gravity, inertia, friction, stiffness, and all the subtle aspects of a material world are absent and have to be faked by imaginative animators.

"In traditional animation all knowledge of physics has to come from the animator's head, " says Michael Kass, a computer graphics engineer at Apple Computer. For instance, when Walt Disney drew Mickey Mouse bouncing downstairs on his rear end, Disney played out on drawing paper his perception of how the law of gravity works. Mickey obeyed Disney's ideas of physics, whether they were realistic or not. They usually weren't, which has always been their charm. Many animators exaggerated, altered, or ignored the physical laws of the real world for a laugh. But in the current cinematic style, the goal is strict realism. Modern audiences want E.T.'s flying bicycle to behave like a "real" flying bicycle, not like a cartoon version.

Kass is trying to imbue physics into simulated worlds. "We thought about the tradition of having the physics in the animator's head and decided that instead, the computer should have some knowledge of physics."

Say we start with flying logo dreamland. One of the problems with this simple world, Kass says, is that "things look like they don't weigh anything." To increase the realism of the world we could add mass and weight to objects and a gravity law to the environment, so that if a flying logo drops to the floor it falls at the same acceleration as would a solid logo falling to Earth. The equation for gravity is very simple, and implanting it in a small world is not difficult. We could add a bounce formula to the animated logo so that it rebounds from the floor "of its own accord" in a very regular manner. It obeys the rule of gravity and the rules of kinetic energy and friction which slow it down. And it can be given stiffness -- say of plastic or metal -- so that it reacts to an impact realistically. The final result has the feel of reality, as a chrome logo falls to the floor and bounces in diminishing hops until it clatters to a rest.

We might continue to apply additional formulas of physical rules, such as elasticity, surface tension, and spin effects, and code them into the environment. As we increase the complexity of these artificial environments, they become fertile ground for synthetic life.

This is why the Jurassic dinosaurs were so lifelike. When they lifted their legs, they encountered the virtual weight of meat. Their muscles flexed and sagged. When the foot came down, gravity pulled it, and the impact of landing reverberated back up the leg.

The talking cat in Disney's summer of '93 movie Hocus Pocus was a virtual character similar to the dinosaurs, but in close-up. The animators built a digital cat form and then "texture-mapped" its fur from a photographed cat, which it perfectly resembled except for its remarkable talking. Its mouth behavior was mapped from a human. The thing was a virtual cat-human hybrid.

A movie audience watches autumn leaves blowing down the street. The audience does not realize the scene is computer-generated animation. The event looks real because the video is of something real: individual virtual leaves being blown by a virtual wind down a virtual street. As in Reynolds's flocks of virtual bats, there is a real shower of things really being pushed by a force in a place with physical laws. The virtual leaves have attributes such as weight and shape and surface area. When they are released into a virtual wind they obey a set of laws parallel to the real ones that real leaves obey. The relationship between all the parts is as real as a New England day, although the lack of details in the leaves wouldn't work in close-up. The blowing leaves are not so much drawn as let loose.

Letting animations follow their own physics is the new recipe for realism. When Terminator 2 wells up from a molten pool of chrome, the effect is astoundingly convincing because the chrome is obeying physical constraints of liquids (such as surface tension) in a parallel universe. It is a liquid in simulation.

Kass and Apple colleague Gavin Miller came up with computer programs to render the subtle ways in which water trickles down a shallow stream, or falls as rain on a puddle. They transferred the laws of hydrology into a simulated universe by hooking up the formulas to an animating engine. Their video clips show a shallow wave sweeping over a dry sandy shore under a soft light, breaking in the irregular manner of real waves, then receding, leaving wet sand behind. In reality it's all just equations.

To make these digital worlds really work in the future, everything in creation will have to be reduced to equations. Not just the dinosaurs and water, but eventually the trees the dinos munched on, the jeeps (which were digital in some scenes of Jurassic Park), buildings, clothes, breakfast tables, and the weather. If this all had to happen just for the movies, it wouldn't. But every manufactured item in the near future will be designed and produced using CAD (computer-assisted design) programs. Already today, automobile parts are simulated on computer screens first, and their equations later transmitted directly to the factory lathes and welders to give the numbers actual form. A new industry called automatic fabrication takes the data from a CAD and instantly generates a 3-D prototype from powered metal or liquid plastic. First an object is just lines on a screen; then it's a solid thing you can hold in your hand or walk around. Instead of printing a picture of a gear, automatic fabrication technology "prints" the actual gear itself. Emergency spare parts for factory machines are now printed out in hi-impact plastic on the factory floor; they'll hold out until the authentic spare part arrives. Someday soon, the printed object will be the authentic part. John Walker, founder of the world's premier CAD program, AutoCAD, told a reporter, "CAD is about building models of real-world objects inside the computer. I believe in the fullness of time, every object in the world, manufactured or not, will be modeled inside a computer. This is a very, very big market. This is everything."

Biology included. Flowers can already be modeled in computers. Przemyslaw Prusinkiewicz, a computer scientist at the University of Calgary, Canada, uses a mathematical model of botanical growth to create 3-D virtual flowers. A few simple laws apparently govern most plant growth. Flowering signals can get complicated. The blossom sequence on a stalk may be determined by several interacting messages. But these interacting signals can be coded into a program quite simply.

The mathematics of growing plants was worked out in 1968 by the theoretical biologist Aristid Lindenmeyer. His equations articulated the distinction between a carnation and a rose; the difference can be reduced to a set of variables in a numerical seed. An entire plant may only take a few kilobytes on a hard disk -- a seed. When the seed is decompressed by the computer program, a graphical flower grows on the screen. First a green sprout shoots up, leaves unfurl, a bud takes shape, and then, at the right moment, a flower blossoms. Prusinkiewicz and his students have scoured the botanical literature to discover how multiple heads of flowers bloom, or how a daisy forms, and how an elm or oak fork their distinctive branches. They have also compiled algorithmic laws of growth for hundreds of seashells and butterflies. The graphical results are entirely convincing. A still frame of one of Prusinkiewicz's computer-grown lilac sprays with its myriad florets could pass for a photograph in a seed catalog.

At first this was a fun academic exercise, but Prusinkiewicz is now besieged with calls from horticulturists wanting his software. They'll pay a lot of money if they can get a program that will show their clients what their landscape designs will look like in ten years or even next spring.

The best way to fake a living creature, Prusinkiewicz found, is to grow it. The laws of growth he has extracted from biology and then put into a virtual world are used to grow cinematic trees and flowers. They make a wonderfully apt environment for dinosaurs or other digital characters.

Brøderbund software, a venerable publisher of educational software for personal computers, sells a program that models physical forces as a way of teaching physics. When you boot-up the Physics program on your Macintosh you launch a toy planet that orbits the sun on the computer screen. The virtual planet obeys the forces of gravity, motion, and friction written into the toy universe. By fiddling with the forces of momentum and gravity, a student can get a feel for how the physics of the solar system works.

How far can we press this? If we kept adding other forces that the toy planet had to obey, such as electrostatic attraction, magnetism, friction, thermodynamics, volume, if we kept adding every feature we saw in the real world to this program, what kind of solar system would we eventually have in the computer? If a computer is used to model a bridge -- all its forces of steel, wind, and gravity -- could we ever get to the point that we could say we have a bridge inside the computer? And can we do this with life?

As fast as physics is encroaching into digital worlds, life is invading faster. To see how far distributed life has infiltrated computational cinema, and to what consequences, I took a tour of the state-of-the-art animation labs.