Kiang and her colleagues also considered plant life on planets circling F- and K-class stars. For the F-class stars, their conclusions were that plants might have a predominantly bluish coloration. This would be another spectral signature of life, producing an “edge” in the spectral area where photosynthesis reflected light away. Their conclusion was that it is plausible but not proven that the spectral signature of plant life could be detected over interstellar distances. At the very least, her articles give science fiction writers something new to chew over [139].
The reason why the search for life in the universe nowadays centers on the search for vegetation is very simple: we can find it without it having to signal us. Waiting for the aliens to call was always dicey and hinged on a lot of arguments that a lot of people considered unscientific. However, the possibility of vegetation on other worlds relies on well-understood scientific principles. For this reason the search for alien life is much better funded today than it was forty years ago: it has a much better chance of success. However, finding alien vegetation or bacteria is not nearly as exciting as finding other intelligences—someone to talk to. I take this up in the next chapter.
NOTES
1. One subtlety, however, is that relatively speaking its effective luminosity in the infrared compared to the Sun’s luminosity in the infrared will be higher than the number quoted because the Sun emits most of its light in the visible region of the spectrum. The Sun is a weak emitter at wavelengths near 10 µm, which is where the Earth emits most of its light.
CHAPTER SIXTEEN
THE MATHEMATICS OF TALKING WITH ALIENS
16.1 THREE VIEWS OF ALIEN INTELLIGENCES
Apart from space travel, contact with alien races and civilizations is the theme of science fiction. In this chapter we will examine the issue of communication with alien races. There are, of course, many hurdles to overcome in any communication with intelligent aliens. The first is whether any exist at all. Science fiction writers tend to adopt one of three views:
1. Alien life is common across the galaxy.
2. Alien life is rare, but intelligent aliens exist.
3. Alien life is nonexistent.
Let’s discuss each of these views in turn.
16.1.1 Alien Life Is Common across the Galaxy
The view that alien life is common across the galaxy is perhaps the most typical view in science fiction stories written from the early 1900s to the 1980s. In popular culture, the TV show Star Trek in the 1960s exemplified this view. The show featured a new alien culture and civilization almost every week, with recurring examples of the Vulcans, Klingons, and Romulans. Each of the new series in the franchise introduced new intelligent alien species until there are probably now several hundred in the Star Trek canon. To some extent this is because many of the writers for the original series were also well-known science fiction novelists, including Norman Spinrad, Theodore Sturgeon, and David Gerrold, who got his start writing for the show. Larry Niven wrote an episode for the short-lived animated series in which he injected the Kzinti, an alien race from his Known Space stories.
TV science fiction has tended to follow the leader in this regard: the show Babylon 5, while different in tone and mood from Star Trek, was set on a space station crowded with representatives of dozens of other spacefaring races. This is also typical of science fiction movies as well, the premier example being the Star Wars saga. It is also true of the recent Avatar, at least implicitly, as humanity finds an example of an intelligent alien race living on an inhabitable moon of a gas giant planet in the nearest star system to our own.
From what I can tell, ideas in the movies and on TV tend to be about 20 years behind science fiction novels and stories. The idea of the inhabited universe seemed to peak in the early 1980s. Again, alien contact is a pervasive theme in science fiction. William Gibson’s novel Mona Lisa Overdrive marginally involves contact with aliens from Alpha Centauri, although it is completely unimportant to the plot; the novel could have been easily rewritten without it [96].1 There are many stories in which the existence of alien races is present in the background, so to speak, but is unimportant to the plot: many of Asimov’s works fall into this category. The usage seems often to be more a way of signaling the work as science fiction rather than contributing anything of substance to it. However, this is verging on literary criticism, which I promised I wouldn’t do.
Among written works, Niven’s Known Space stories are among the best examples of this idea. Niven has invented many different and fascinating alien races, from the humanoid (the Kzinti and Pak) to the vaguely mammalian (Pierson’s Puppeteers) to the nonhumanoid (the sessile but telepathic Grogs and the very alien Outsiders). Again, the idea is quite common: Robert Heinlein’s juvenile novel Have Space Suit—Will Travel features two alien races at the beginning of the novel (the mother-thing’s race and the race of the aliens trying to invade Earth) but leads to the human race being put on trial before an assembly of literally thousands of other intelligent alien races by the end of the novel [114]. I cannot end this discussion without also mentioning Olaf Stapledon’s amazing Star Maker, a broad “history” of the universe and the quest of its many races to understand its maker [225]. The novel is a classic of science fiction by its best English-language author: descriptions of the alien races are many and varied, including crustacean-like creatures, creatures in the form of intelligent boats, intelligent vegetation, and so on. The science is outdated, but it is still one of the best science fiction works ever written.
The notion of a “crowded universe” stems from the principle of mediocrity, otherwise called the Copernican principle: the idea that our planet is a typical planet circling a typical star in a typical galaxy (in perhaps a typical universe. …) From everything we know about astronomy, physics and chemistry, this is true, especially now that we know of more than 700 planets circling other stars. However, the “Great Silence” has called this idea into question over the last 20 years or so. Enrico Fermi was perhaps the first person to express the problem: if many races have evolved in our galaxy, then they probably evolved over the course of billions of years. However, given a species capable of traveling among the stars, even at speeds of only a fraction of the speed of light, it would take only millions of years to explore the galaxy. So why aren’t they here yet? Or if star travel is impossible, if there are many races out there who want to talk to us via radio communications, why haven’t they contacted us yet [132]? SETI has been around in one form or another for fifty years, but the silence has been unbroken.
16.1.2 Alien Life Is Rare but “Out There” for Us to Find
Perhaps there aren’t thousands or millions of other races in the galaxy; perhaps there are only one or two other races. The best exemplar of this idea is the novel The Mote in God’s Eye, by Larry Niven and Jerry Pournelle, which involves the first contact between humans and “moties,” humanoid aliens whose runaway population problems cause them to exist in a state of almost perpetual warfare. The reason it takes humanity over a thousand years as a spacefaring civilization to discover the moties has to do with the features of the “hyperspace” drive (invented by Dan Alderson of Caltech to the authors’ specifications) [186].
There aren’t a lot of novels involving only one alien race out there simply because if you postulate one, you might as well postulate as many as you want.
16.1.3 We Are Alone
One of the earliest major works of science fiction from which aliens were noticeably absent was Asimov’s famous Foundation trilogy, centering on the decline and fall, then subsequent rebirth, of the “galactic empire.” Asimov felt that the absence of aliens was odd enough that in later books in which he combined his robot stories with the Foundation, he went through a lengthy explanation of why the galaxy was devoid of intelligent life apart from humanity.
However, the idea that humanity is the only intelligent race in the galaxy has become, if not the majority position, at least a position among a significant minority, perhaps even a plur
ality, of science fiction writers since the 1980s. Again, popular culture tends to reflect this. Until the final episode, the reimagined Battlestar Galactica featured a universe devoid of alien life. The show focused more on the interaction of the human race with the Cylons, who could be termed an alien species that humanity itself created.
The reason for this gradual change lies in a paradox. Even as scientists have accepted the Copernican principle and have learned that planets, the potential sites of life in the universe, are common, they have also learned that the planets themselves vary enormously from one another, and that the conditions leading to life on a planet are probably very restrictive. Beyond this is the question of the evolution of life on a planet into an intelligent, tool-making civilization capable of space travel, or at least of radio contact with similar civilizations. Most physicists and astronomers tend to feel that once life begins on a planet, the evolution of some species capable of interstellar communication is almost inevitable [239]. The idea is that because evolution proceeds by random changes favoring survival characteristics, and (from the human experience) intelligence and tool using are very much aids to survival, then the evolution of an intelligent species is almost inevitable, given time and the random selection of the fittest.
Evolutionary biologists feel differently. They point out that the evolution of the human race required the convergence of a number of unlikely events. For example, if the dinosaur-killing comet hadn’t smashed into the Yucután Peninsula 65 million years ago, mammals might not have become the dominant biological order on the planet.
16.2 MOTIVATION FOR ALIEN CONTACT
If the aliens exist, the second hurdle to overcome is devising a plausible reason for them to contact us. There are good reasons for noncontact: Star Trek’s Prime Directive is a good example from science fiction. Historical meetings between technologically advanced civilizations and less advanced ones in Earth’s own history underscore the dangers of such contacts. Perhaps the aliens are avoiding contact because they don’t want to harm us. Stanislaw Lem illustrated the dangers of such issues [149]. Cosmic timescales being what they are, an advanced civilization may be millions or billions of years older than our own. Any revelations they may choose to send us might be meaningless (like discussing quantum physics with the ancient Phoenicians) or, if practical, extraordinarily harmful (like sending plans for a nuclear bomb to 1939 Europe). However, if the aliens do choose to visit us or talk to us, why might they do so? Some reasons follow.
16.2.1 War with Us
The astronomers tacitly assume that we and the little green monsters would welcome each other and settle down to fascinating conversations. Here again, our own experience on Earth offers useful guidance. We’ve already discovered two species that are very intelligent but technically less advanced than we: the common chimpanzee and pygmy chimpanzee. Has our response been to communicate with them? Of course not. Instead, we shoot them, dissect them, cut off their hands for trophies, put them on display in cages, inject them with AIDS virus as a medical experiment and destroy or take over their habitats.… If there really are any radio civilizations within listening distance of us, then for heaven’s sake let’s turn off our own transmitters and try to escape detection, or we’re doomed.
—JARED DIAMOND, THE THIRD CHIMPANZEE [61, PP. 214–215]
The idea of war with alien races dates back to H. G. Wells’s War of the Worlds, published in 1898 [248]. The excerpt from Jared Diamond tells you pretty much all you need to know about the conception of the aliens: they are space vampires who survive by exsanguinating human blood and injecting it directly into their veins. They are bent on conquering Earth because Mars, in the novel an older world than Earth, is gradually becoming unfit for life (à la Percival Lowell’s ideas). Wells, a passionate socialist, extrapolated the motives and actions of European colonialists in the Americas and Africa for his Martians. The book spawned imitators, especially in movies and TV, where several film adaptations of the novel were made, plus Orson Welles’s famous 1938 radio broadcast and movies ranging from Plan 9 from Outer Space to Independence Day. It’s not as popular a theme in science fiction literature as in the movies because of the fundamental difficulties of space travel and the perhaps mistaken idea that advanced civilizations would have moved beyond the need for warfare.
The complementary idea of humans as interplanetary or interstellar aggressors is less common; the recent movie Avatar is almost a lone example among science fiction movies. Olaf Stapledon explored this idea in some of his novels published in the 1930s. In particular, Last and First Men involves the human race exterminating a race of sentient underwater creatures on Venus. This was because the decay of the Moon’s orbit and its ultimate impact on Earth were making Earth unlivable [225]. Despite the scientific inaccuracies, the story provides an interesting psychological study of the Fifth Men, the branch of the human race responsible for the genocide. Stapledon discusses the psychological swings between elation and despair this race faced as it debated the morality of destroying another sentient race to ensure its own survival. His consideration of these moral issues makes Stapledon all but unique among science fiction writers past or present, and his novels are worth reading today. The same idea in a different guise crops up in his novel Odd John, about a race of supermen living among ordinary humans. There the debate is over the morality of exterminating the normal human race to ensure the survival of the more evolved species.
This begs the question of whether interstellar warfare is possible. Here the answer is easy: if interstellar travel is possible, then interstellar warfare is possible. The issue has to do with energetics. Let’s say that an alien civilization has the capability of creating a starship capable of traveling at 86% the speed of light. The reason for this particular velocity is that the relativistic gamma factor at this speed is 2, meaning that the kinetic energy at this speed is equal to the rest mass energy, Mc2. Our canonical 10,000 kg starship has a kinetic energy of 9×1020 J, the equivalent enegy of 200,000 H-bombs. A few other ways of visualizing this are:
1. The United States uses about 9×1019 J of energy in a year, so this is about the total energy use of the United States over a 10-year period.
2. Most asteroids impact the Earth at speeds of about 30 km/s, so if the spaceship impacted Earth, it would have the same effect as an asteroid of mass 200,000,000 kg hitting Earth. This isn’t quite in the dinosaur-killer league but it is substantially larger than the comet that impacted Tunguska, Siberia, in 1908.
3. In a prior chapter we saw that turning on the engines for a spaceship of such size would irradiate the Earth with gamma rays equivalent in power to the total energy the Earth receives from the Sun, potentially sterilizing the planet.
The last item is interesting, in that the drive for an interstellar spaceship makes a good weapon all by itself. The first time I encountered this idea was in the story “The Warriors” in Larry Niven’s collection Tales of Known Space, in which a human spacecraft destroys a Kzinti using its engine, which uses a laser for propulsive power (this is essentially the idea of the photon rocket of chapter 9) [181]. You don’t need the drive to be a laser; the propulsion system for any macroscopic spacecraft capable of star travel must be capable of inflicting a lot of damage on a planetary civilization simply by the laws of physics. This make one part of the movie Avatar ridiculous. At the end of the movie, the triumphant Na’avi send the humans back to Earth on the spacecraft they arrived in. However, there is no way in which they could have “deweaponized” the starship, which was capable of traveling at two-thirds light speed and was considerably larger than 10,000 kg. The humans could render Pandora uninhabitable simply by turning on its engines. Better for the Na’avi just to kill them all. Jake Sully, of all people, should have spotted this flaw in the plan.
Any star drive is a weapon capable of inflicting horrific, potentially world-sterilizing damage. Any civilization capable of star travel is capable of interstellar warfare. Greg Bear explored this potential in his novels The
Forge of God and Anvil of Stars; in the first, Earth is destroyed by an alien race, and the children of the survivors set out to destroy the aliens responsible in the second [32][34]. The reason the aliens have for destroying the world is a little puzzling; it seems essentially to be a preemptive strike on their part, a pervasive racial paranoia that if they don’t destroy us, we will eventually come out and destroy them. I guess this is a possible motivation, the flip side of the worry shown in Diamond’s quotation at the opening of this chapter, but it seems over the top. In Niven and Pournelle’s Footfall, the motivation is that the invading aliens represent a faction that lost a war on their home planet and need Earth as a new home. We see Niven’s use of problem limitation here, as any race of beings capable of traveling across the cosmos should be able to pummel twentieth-century Earthlings into submission in a matter of seconds, but the aliens portrayed are not very bright beings created as servants of a highly advanced alien race that killed itself off long before the story begins. The elephant-like aliens are using borrowed technology and have a psychology appropriate to herd animals, allowing humans to dominate them (after a hard fight) despite their initially dropping an asteroid on Earth [187].
Alien invasion doesn’t need to be particularly energy expensive; various writers have posited invasion by alien microbes carried across interstellar distances by stellar winds or virtual invasions when alien broadcasts effectively invade our computer systems or give us bad information, as in the movie Species. The motive for these attacks is a little hard to judge except for the general rule, “all inhuman aliens are bastards,” which seems to be the base assumption of most TV or movies. Humans, of course, broadcast computer viruses essentially for the fun of it, so assuming that alien races would be too evolved to broadcast the interstellar equivalent of ILOVEYOU is probably unwise.
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