The Science of Avatar

by Stephen Baxter

  And recall that all the aircraft we see onscreen, save for their more complex components like missile tracking and guidance electronics, have had to be manufactured in the stereolithography plants on Pandora. It has been necessary to choose designs, however elderly, that did not need the most modern exotic materials technology, such as (in 2154) exotic ceramics and nanomaterials, beyond the reach of the matter printers. Again, the Samson is one such veteran design. A lack of ground support on Pandora for more advanced systems is another factor.

  But this is an instance where we also have to allow for some creative licence. Avatar is about a clash of cultures, the heavy-handed technological human civilisation versus the graceful Na’vi, living lightly in their world. The heavier the human tech, and the grungier it looks, the more striking that contrast is going to be, in every shot when we see the two sides in opposition. And the echoes of Vietnam are deliberate, including references to Apocalypse Now (1979), with its famous scenes of helicopter gunships flapping over the jungle.

  The depiction of much of the military hardware in the movie, and the way it is used, is thus thoroughly realistic, at least in terms of today’s technology. One item you won’t see walking around modern battlefields, however, is an AMP suit.

  Standing four metres tall on two legs and with its two grasping hands, the Mk-6 Amplified Mobility Platform has a sealed cabin within which its operator (wearer?) rides. The suit’s motions are slaved to the operator’s through servo armatures moved by the operator’s arms, as we see when Quaritch “boxes” inside a suit, with the machine’s huge arms aping the colonel’s jabs. Foot-pedals actuate the legs. The suits come heavily armoured, with weapons ranging from automatic cannon to an ugly-looking slasher knife. The suits have a good deal of built-in smartness, such as an autonomous ability to keep their balance, and even a “walk-back” facility if the operator is disabled. But the amplification of strength and range of motion between the operator’s movements and the suit’s response takes a lot of training to master.

  The AMP suit is an outcome of modern-day experiments in developing powered “exoskeletons” for military purposes. An exoskeleton would be like a wearable robot, a mobile machine like a suit of armour with limb movement at least partially supported by the power supply. The aims would be to provide greater strength and speed, as well as armour protection and sensory enhancements, with none of the loss of the fine control the wearer would have over her own body movements. Other applications, perhaps of partial exoskeletons rather than complete ones, might include prosthetics and medical care—an aid to nurses in lifting heavy patients delicately, for example.

  The first experimental exoskeleton was co-developed by General Electric and the U.S. military in the 1960s. This programme was said to have been inspired by the powered armour featured in the 1959 Robert Heinlein science-fiction novel Starship Troopers, a classic case of the interaction of science fiction and science. Later fictional examples include Marvel’s Iron Man, and of course the “power loader” machines of James Cameron’s own Aliens (1986).

  That first GE suit was too heavy, its motions too violent and uncontrolled. A light and capacious power unit has always been a nagging design issue. But developments continue on various fronts. Lockheed Martin’s appropriately named HULC (Human Universal Load Carrier) is a pair of battery-powered hydraulic legs that reinforce a soldier’s limbs, and give her the ability to carry heavy weights at around fifteen kilometres per hour. Exoskeletons are also being studied as part of the U.S. military’s “Future Force Warrior” advanced technology demonstration project—a lightweight, wearable infantry combat system designed to address the needs of the “Army After Next” in the future. There’s even a civilian-grade exoskeleton, the HAL-5 (Hybrid Assisted Limb), a full-body machine made by the company Cyberdyne; this is already on sale in Japan, and is in use as a support by elderly and infirm people.

  You might alternatively regard the AMP suit not as an exoskeleton but rather as an example of a “mecha,” a name given to ambulatory manned fighting robots in some genre fiction. The distinction between mecha and exoskeletons is vague, but roughly speaking a mecha is piloted, while an exoskeleton is worn. The tripodal fighting machines of H. G. Wells’ War of the Worlds are early examples of mecha, as are the “Walkers” of the Star Wars films. Unlike exoskeletons, little military investment seems to have been made in mecha—but a subsidiary of John Deere did produce an experimental six-legged walking harvester! I’ve yet to spot any of those in my local forests.

  In the Avatar timeline AMP suits were derived from earlier exoskeleton designs deployed in various war theatres on Earth, and developed for off-world use on the moon and Mars. The suits are formidable weapons in the right circumstances, as we see in the movie during the climactic fight at the remote link shack, when Quaritch in his suit is able to defeat a thanator—and then is able to use his suit’s precision of movement to reach inside the shack to interfere with the equipment there. The suit’s bipedal locomotion could be useful in situations such as Pandora’s dense forests, where the mobility of wheeled vehicles would be impaired. But an AMP suit would always be vulnerable to simple trip-wires, and bolas: thrown weighted ropes, like the one the Na’vi warriors use to bring down Jake. The mighty Star Wars Walkers were similarly vulnerable to bolas.

  The ability to wage war on the planet of another star is a quite remarkable accomplishment by those interstellar master traders RDA. But ultimately it is not just the Na’vi RDA finds itself fighting, but Pandora itself: a living world.

  PART SIX

  LIVING WORLD

  “Our great mother Eywa does not take sides, Jake; only protects the balance of life.”

  —Neytiri

  21

  A CLIMAX ECOSYSTEM

  Among Avatar’s most wondrous sequences are those showing Jake Sully’s first encounter, in his avatar body, with the rich environment of the Pandoran forest. OK, it ended up with a lot of running away from a thanator. But who could forget Jake’s discovery of those big spiral trumpet-like plants (the helioradians) that, at a touch, shrank down into the ground?

  How did Avatar’s designers dream up such a marvellous and convincing world?

  First impressions: the ecosphere we see on Pandora is evidently a kind of rain forest, dominated by the tremendous trees that are so important to the Na’vi. Various other flora include what look like Earth’s ferns, palms, bamboos and grasses. Pandora is evidently an environment as rich in resources and energy flows as tropical Earth, and natural selection has produced an ecology as diverse and complex as anything on Earth.

  However Pandora’s conditions differ from Earth. The lower gravity, thicker air, strong magnetic fields and different day–night cycles have all shaped the evolution of life, as we will see. One obvious example is gigantism; thanks to the lower gravity, many of the plants we see are like terrestrial forms grown huge. As for magnetism, the anemonid is a carnivorous plant that absorbs metals from the soil, giving it the ability to use Pandora’s magnetic field for movement, a feature RDA’s biologists refer to as “magnetonasty.” And a plant called sol’s delight, or Calamariphyllum elegans—“elegant squid-like plant”—is “magnetotropic,” that grows in the direction of magnetic fields. The “delight” name comes from the fact that the plant helps RDA’s miners detect unobtanium deposits by conveniently straining towards them.

  But in devising this ecology, as with other aspects of the movie, the designers have always kept in mind the audience’s needs. They have given us a world that is strange, but with elements of the familiar from Earth, twisted and distorted to give an impression of the alien. That’s why Pandora is green! Plants on Earth are green because of the chlorophyll in their cells, the chemical compound that supports photosynthesis, processing the energy of sunlight for growth. Maybe, as sunlight is such an easily accessible energy source, on worlds with transparent atmospheres like Pandora and Earth some kind of photosynthesis is always likely to evolve. But there are different chemical ways to ac
hieve photosynthesis; leaves don’t have to be green. The greenness of Pandora is a design choice.

  The trees are the single most important element of the Pandoran forest, as in all forests on Earth. The main canopy tree is called the beanstalk palm, growing as much as a hundred and fifty metres tall. To the Na’vi it is tautral, the “sky tree.”

  Earth’s greatest trees, the sequoias, don’t grow as high as this, but they are remarkable organisms in themselves. Today, sequoias are confined to a strip of the Pacific coast of North America. They flourish in the mountains, which trap moisture coming off the ocean; the tallest specimens grow in valleys and gullies where streams flow year-round and there is regular fog drip, which helps keep the trees’ upper leaves supplied with moisture. The sequoias are part of a habitat which supports many species of plants and animals. In the 1990s, tree-climbing biologists discovered a treetop ecology based on soil that had formed high above the ground from leaf mulch and other decayed vegetable matter.

  Sequoias can be as tall as a Saturn V rocket, and older than Christianity. They are remarkable inhabitants of planet Earth.

  Meanwhile in the undergrowth, deep, rich, dense and luminous, visually the Pandoran forest has something of the feel of the underwater world—you might be reminded of a coral reef, perhaps. In fact on some coral reefs there is a shrinking-trumpet plant like the helicoradians Jake encountered, the “Christmas tree worm,” Spirobranchus giganteus, that does indeed withdraw into a tube when disturbed. The woodsprites, “seeds of the sacred tree,” look a lot like jellyfish. Much larger jellyfish-like beasts float by like natural airships. The Mother Tree in the Tree of Souls has tendrils that resemble the tentacles of sea creatures. This oceanic influence is no surprise. After James Cameron completed the very aquatic movies The Abyss and Titanic, he made six deep ocean expeditions, filming in 3D. At the time of writing he is planning an expedition to the Pacific’s Mariana trench, the deepest point on Earth, a point nobody has visited since 1960.

  And Cameron did base his vision of the forests of Pandora (partly) on the coral reefs he encountered in the ocean’s depths. This is appropriate because a coral reef, like a rain forest, is an example of a “climax ecosystem,” a complex and rich environment in which large numbers of animals and plants have coevolved.

  It was Charles Darwin himself who first figured out how coral reefs work. Corals themselves are tiny anemone-like organisms that leave behind tough little skeletons. (In the past, reefs have also been built by other organisms such as algae, sponges, molluscs and tube worms.) With time these skeletons can heap up into huge reefs; Australia’s Great Barrier Reef stretches for two thousand kilometres around the north-east coast of Australia.

  The secret of a reef as a habitat for life is that it “fills in” what would otherwise be an empty column of water above a flat ocean floor. A reef is a highly complicated three-dimensional structure, full of crevices and folds and cracks, ripe for colonisation by other life forms. On land, forests do the same thing, the tall trees rising up from the ground to vastly increase the effective surface area available for life. And so coral reefs are thick with fish, molluscs, sponges, echinoderms (starfish and sea urchins) and other forms of life, all shaped by evolution into complex chains of symbiosis, competition and cooperation—just as we glimpse in the Pandora forests. (Ironically, on Earth the coral reefs that are such an inspiration for Avatar are dying back. This is an ecological disaster but also a human one, as there will be economic losses for fisheries and tourist resorts, and coastlines will be left less protected from the ocean.)

  But on Pandora, within that intricately interconnected biosphere, there are a rather large number of living things that bite.

  The first truly spectacular animal that avatar-Jake confronts is a hammerhead titanothere. This is a massive six-legged quasi-rhino, heavily armoured, with a “hammerhead” muzzle reminiscent of another aquatic creature, a hammerhead shark. And the beast has a spectacular threat display, designed to scare off any ambitious predators, and indeed would-be rivals from within the titanothere’s own species; these are very territorial animals.

  But the hammerhead, a herbivore, is somewhere near the bottom of Pandora’s land-based food chain. The hammerhead eats the Pandoran equivalent of grass, shrubs, leaves, and in turn is eaten by predators like the viperwolves. These scary beasts are six-legged pack hunters that run like dogs, but are also nifty climbers thanks to their ape-like paw-hands. And they are highly intelligent, as you can tell from onscreen evidence of communication as they hunt Jake. There are evidently creatures that prey on the viperwolves in turn, such as the thanator, a beast like a lion or a panther, a relative of the viperwolf.

  Similarly there is a food chain of the air. The mountain banshees, graceful pterosaur-like flyers, are also pack hunters, aerial equivalents of the viperwolves—and again an even scarier hunter preys on them, the mighty leonopteryx.

  We always see the thanator alone, like the leonopteryx, and this makes sense from what we know of food chains on Earth. On our planet each step of consumption up the chain is only about ten per cent efficient, in terms of nutrient value. A thousand tonnes of grass can support a hundred tonnes of hammerhead meat, which can only support ten tonnes of viperwolf meat, which can only support one tonne of thanator meat… So if you are an “apex predator,” as a thanator or a leonopteryx is believed to be on Pandora—or a lion, or a tyrannosaurus rex on Earth—the land can only support a small number of your kind. It’s thought that the range of a single tyrannosaur might have been hundreds of kilometres; a thanator’s range is three hundred square kilometres. On Pandora or Earth, for six limbs or four, the rules of the natural economy are set in stone.

  This dog-eat-dog (or viperwolf-eat-viperwolf) aspect of life on Pandora is reflected in something else we see onscreen: arms races between predator and prey.

  To escape a big fast scary predator, you either evolve to run fast, like the slender deer-like hexapedes, or you evolve heavy armour, like the hammerheads—or you do both, like the direhorses. Another possibility is to use threat displays like the hammerheads, effectively startling away the hunter, if you’re lucky. Meanwhile your hunter in response is evolving to run ever faster, brandishing ever sharper teeth… The end result of an evolutionary arms race is a killing monster like a thanator or a tyrannosaur hunting down a tank-like prey animal like a hammerhead or a styracosaurus—which was a rhino-like dinosaur with a horn on its nose, bony bosses over its eyes and cheeks, and a bony frill over its neck with even more long and pointy horns.

  Although Pandora is presented to us as a world of natural harmony, nature is evidently red in tooth and claw here: a world so tough that even apex predators like the thanators need to be armoured. And while the forest has a dreamy oceanic visual feel, the ferocious predators and their heavily armoured prey drew inspiration from the mighty creatures of Earth’s dinosaur age.

  But there are gentler elements too. Many of the animals are social, the direhorses, the buffalo-like sturmbeests in their herds, the banshees in their flocks. And we glimpse family groups, the sturmbeest on the move protecting their calves, the direwolf cubs playing.

  You’ve no doubt observed that many of Pandora’s animals share common features: six legs, two neural whips (called “queues” in the Na’vi, as they are wrapped in braids of hair), supplementary breathing holes, and four eyes. This applies to flying creatures like the banshee and leonopteryx, as well as to the ground animals from the hammerheads to the thanators. (The exceptions to the general plan are the Na’vi and their apparent relatives the prolemuris, as we’ll see in the next section.) This convincing consistency is a testament to the disciplined imagination of the movie’s designers, and to their inventiveness, such as in the plausible-looking gait of the many six-limbed animals, and the sensible-looking flapping of four wings.

  The antenna-like neural whips are used to link the nervous systems of animals, and to link Na’vi to animals, and indeed to link Na’vi to Na’vi. While a Na’vi has just on
e queue, many animals have two whips. The equine direhorses connect with each other through their whips, bonding emotionally but also passing on information about food sources and threats. We’ll look more closely at neural queues when we come to consider the Na’vi themselves, as well as the Eywa neural network.

  What of the multiple breathing holes shown on many of the animals? On Earth some insects have “spiracles,” additional body vents to take in air. On Pandora the vents are for supercharging—taking in more oxygen quickly, a feature that is particularly useful for flying creatures, and we do see prominent vents on the banshees, which, like birds, burn up a lot of energy and need efficient heat-loss systems. But the vents are also a relic of an early stage of the movie’s design process; Cameron wanted some of the animals he envisaged to have the feel of automobiles, and the air vents are a trace of that source of inspiration!

  Those multiple eyes are another striking feature. Why would you need two sets of eyes? On Earth, though insects may have many sets of eyes, one pair seems standard issue across the animal kingdom—though a bivalve mollusc known as the “thorny oyster” (Spondylus) has multiple eyes scattered around the edge of its shell. There is a South American fish called the anableps that rises to the water’s surface to seek prey in the air, but while it hunts it is in constant danger of threats from below. So each of its eyes works as two separate optical systems, an upper one for aerial vision and a lower one for aquatic vision; the creature can watch for danger from below while it stares up into the air for its food. These systems have separate retinas, but there is only one optic nerve per eye—two eyes acting as four.