I get it: Ender's Game is not a science movie, or even a hard sci-fi movie. In many ways it's barely sci-fi at all, falling closer to the coming-of-age hero fantasy narratives of Percy Jackson or (ducking) The Phantom Menace. But it certainly contains plenty of science fiction tropes and settings, many of which dovetail with themes from other recent science fiction films. As I watched it, I was intrigued by these recurring elements, and by the ways they riff on--or contradict--recent scientific discoveries.
Ender Wiggin directs an epic space battle. Surely there's a better way. (Credit: Summit Entertainment) Note that I'm referring only to the film, not the book. I'm not out to ruin anyone's fun, so I'm avoiding spoilers as far as possible. I'm not here to write a critical review of Ender's Game (it is entertaining for the younger audience, and let's leave it at that). And my point is not to fact-check the movie, but to place it in the context of the things we actually know about biology, evolution, and the physics of other worlds. Science goggles engaged. Why are aliens so thirsty? Aliens in the movies are always coming to Earth because they covet our water; they do it again in Ender's Game. This theme dates back at least to the late 19th-century quasi-scientific studies of Percival Lowell, whose 1895 book Mars depicted the planet as a dry, dying world populated by aliens who had constructed enormous canals in an attempt to save their civilization. Science goggles: Lowell turned out to be wrong about Mars in just about every way. The canals that he perceived were an optical illusion or a psychological delusion; Mars harbors no complex life forms, and its surface air pressure is so low that liquid water would instantly boil away. Nevertheless, his ideas inspired War of the Worlds, A Princess of Mars, the Martian Chronicles, and many sci-fi stories. Interestingly, one of the big lessons of recent astronomical research is that water is really not rare at all. Many planets, satellites, and asteroids are full of water. The moon has water, and even Mercury seems to have water ice at its poles. Mars has enough moisture in its soil that you could potentially extract two pints of drinking water from each cubic foot of Mars dust. If you are a thirsty alien, there are much easier ways to get a drink than conquering Earth. Jupiter's moon Europa is covered with a layer of water and ice roughly 100 miles thick, a total volume considerably more than Earth's oceans. What's so great about Earth? Let's assume Ender's Game got it wrong and aliens are not coming for our water. Earth is still an unusual planet. What might aliens be interested in here? Would they come to eat us, a la the Twilight Zone or the movie Signs? Science goggles. Humans-as-food also seems highly unlikely. If aliens have the resources to travel between the stars and get to Earth, they surely have the resources to make food locally or raise a whole bunch of space cows It also seems quite likely that Earth life would be poisonous or indigestible to alien biology. What about other kinds of other basic resources? Again, probably not. Interstellar travel takes so much energy to travel that coming to Earth for basic resources would be like building a billion-dollar rocket to get you to Wal-Mart so you could steal some T-shirts. The latest studies of planetary systems around other stars seem to hint that planets like ours--liquid water, oxygen atmosphere--may be rare, although the data we have so far are extremely sketchy. But if Earthlike worlds are rare, coming here to colonize the planet seems at least conceptually justifiable. Another possibility is tourism (including hunting tourism, as in the Predator movies), or scientific study (in which careless visitors might not even realize they are trampling on us). Humans do these things. Aliens might too. What would aliens really look like? [mild spoiler here] In Ender's Game, as in many other recent sci-fi movies (such as Starship Troopers and Men in Black, even District 9) the aliens have insect-like physiology. Science goggles. Insectoid aliens are an interesting possibility, one that shows some creative thinking: There is no reason that aliens would have to be mammals like us. Creatures that colonize and move from location to location would be natural space travelers. And although aliens need not have any kind of humanoid form, it is likely they would have heads, legs, eyes, and other familiar sensory structures, because such things have evolved repeatedly and independently on Earth. The bad science in these insectoid aliens: A lot of them are basically giant bugs that look like scaled-up ants or grasshoppers. Such creatures would collapse under their own weight, because real structures don't scale like that. Mass increases with the cube of volume, which is why elephants need thick legs whereas ants can make do with spindly limbs. And while we might recognize the aliens' overall body plans, you can bet that any real creatures from another would look unlike anything on Earth. Blame movies like Them! for brainwashing both movie-makers and movie viewers into thinking giant ants actually make biomechanical sense.
One step takes Ender from 1-g to zero-g aboard a space station. Er...not quite. (Credit: Summit Entertainment) Why is it so hard to get gravity right? Ender's Game does make some good-faith effort to show how artificial gravity is created on a spinning ship. The move also correctly depicts how, in a non-spinning part of a space station, people experience weightlessness. This is a common science-fiction problem: It is difficult to create the special effect of weightlessness through large sections of a movie, and audiences find it distracting to see their characters floating around in weird and unfamiliar ways. Props to the movie Gravity for embracing this. Science goggles. NASA experimented with (very slight) artificial gravity way back in 1966 on the Gemini 11 mission. But the basic dynamics of what it's like to feel fake gravity and weightlessness in space, which 2001: A Space Odyssey nailed perfectly 45 years ago, get very muddled in Ender's Game. Nobody wants a lecture about centrifugal acceleration and rotating reference frames in a popcorn movie, but it sure would have been cool to see the elaborate acrobatics needed to shift from the high-gravity to low-gravity to zero-g sections of the space station. In a movie that is all about training and skill, that could have even become a dramatic plot element. Then again, even Gravity flubbed some key aspects of, er, gravity. If space tourism really takes off in the next couple years, more and more people will know firsthand how gravity really works in free-fall. Even a near-space ride on a helium balloon could give tourists a taste of weightlessness. Or you can watch a live video feed from the International Space Station. Where are the robots? This is something that puzzles me in many science fiction movies (and TV shows as well). Future civilizations that have the ability to build giant space stations and warp drives capable of interstellar travel still seem to do almost everything by hand. Even combat missions seem to depend primarily on human pilots--the whole Star Wars universe operates this way. [very mild spoiler] Most of the combat in Ender's Game seems to involve pilots as well, even if they are mostly unseen. Science goggles. The United States military already relies heavily on unmanned drones, and the idea of sending autonomous robots into combat is so real that the United Nations is currently debating measures to control it and the U.S. is working on the relevant technology. Putting people in the spaceships makes for better drama, of course, and sometimes is crucial to the plot (as in Battlestar Galactica). As a vision of future technology, though, piloted spaceships are a lot like the old 1960s sci-fi shows (Star Trek, notably) that didn't consider things like mobile computing and the Internet. One notable technology lesson from the past half century is that advances in computing happen much more quickly than advances in propulsion. There really has been only one notable advance in rocketry since the days of Apollo: solar-electric ion propulsion, currently used to send the Dawn spacecraft to Ceres
and OSIRIS-REx to the near-Earth asteroid Bennu
(and the upcoming BepiColumbo mission to Mercury). By the time we are able to travel to other stars--assuming that is even possible on a human timescale--we'll probably have ships with artificial intelligence that makes it unnecessary to send people unless we want to. In fact, robots might become our real explorers while we watch the footage down here on Earth, or maybe human minds will be uploaded as software. The secret Achilles heel of interstellar sci-fi stories: energy. Almost all the fun things that people do in science fiction take a lot of energy. Iron Man's flying suit is an energy hog, which is the #1 reason why nobody could build such a suit in real life. The kind of interstellar travel shown in Ender's Game (and many, many other sci-fi worlds), which allows near-instantaneous travel across light years of space, depends on discoveries that go beyond the known laws of physics. But it is clear that no matter how they work, they would require a fantastic amount of energy.
Voyager 1 is the only true interstellar spacecraft humans have created. (Credit: NASA) Science goggles. How much energy? Propulsion guru Marc Mills estimates that sending an unmanned, slower-than-light probe to the nearest star would take on the order of a million times as much energy as the entire planet generates today. Even the less ambitious parts of the sci-fi landscape are challenging. It is easy to imagine how to build giant space stations or robot soldiers; surprisingly, it is much harder to imagine how we would power these things. The flip side is that any civilization that did figure out how to tap into an essentially limitless supply of power could satisfy almost any need without raiding other worlds. That gets back to my first two points, about water and other resources. With enough power to reach the stars, you could probably convert Mars into a habitable planet, or build giant space colonies, or fabricate just about any conceivable thing you could want out of moon dust or stray asteroids. Sorry, Ender. Star Trek gets this one right: If you have access to the kind of energy needed to travel from star to star, you will be exploring (aka, seeking out "new life and new civilizations") or defending your territory, not scrounging around for basic resources. Follow me on Twitter: @coreyspowell