In science fiction universes such as Star Wars, the existence of zillions of species of aliens is taken for granted. But when a society who has zero knowledge of alien species actually meets one for the very first time, well, that's a catastrophic event. Dare I say a Paradigm shift or Epistemological rupture?

And that occurs with the mere knowledge that aliens exist.

Seconds later things become real tense. While the possibilities of wonderful advances in science and inter-species trade are astronomical, sadly the same can be said for the chances of the extinction of the human race. When the existence of your species is on the line, you'd better step real cautiously and take as few risks as possible.

Subsequent first contacts with other alien species are likely not to be quite as wrenching on human society, but the danger of human extinction is always going to be at full strength no matter how routine first contact situations becomes. You never know if the next new alien species is the one that is a xenophobic axe murderer, itching to eradicate the human race with a relativistic bombardment or something.

Naturally The Encyclopedia of Science Fiction has an extensive article on the topic, including lots of examples.

"'When did life start on your world? —And let me say, that's a nice hat.' And then he or she would say, 'It's my helmet, it's my space helmet, because your atmosphere is just—it's no good for me,' and so on. I'd want to know where they came from. I'd want to know why they wanted; what were they doing asking me what I was doing? It would be great to know, though, we're not alone. That would be a heck of a thing. It would change the world."
Bill Nye the Science Guy, "How to Talk to an Alien"

Since man has known what sort of sphere we live on, we have looked at the stars and wondered: are we alone? In this vast, empty Universe, are there any other intelligences gazing up at our star from under an alien moon?

A common theme in Speculative Fiction, science fiction writers have loved to speculate for decades what that pivotal moment will be like: the day we first make contact with an extra-terrestrial intelligence. Writers have invented everything from truly Starfish Aliens to Rubber-Forehead Aliens and every scenario from aggressive aliens or humans to peaceful coexistence, and everything in-between.

The name for the trope and the term itself comes from the 1945 Murray Leinster novelette First Contact. This is not the same as first contact, lowercase, which describes any first contact between two cultures.

Expect someone to make a statement or speech about what a pivotal moment this is for the human race. You may find religious fanatics who claim the aliens are devils, angels, or even gods. Unless the aliens are Sufficiently Advanced or it is Handwaved, there may be communication difficulties and misunderstandings, sometimes leading to outright warnote . Scientists will want to study the aliens, ofttimes without the aliens' consent. The aliens will usually be more technologically advanced, although not always more sociologically advanced. A specific group of specialists may be formed to create a First Contact Team in order to plan for every contingency.

If taking place in America, it may turn out that First Contact actually happened decades ago in Roswell, New Mexico, and that the government has been keeping it under wraps ever since.

Speculation about First Contact scenarios has led many scientists and philosophers to consider that the human race may not be ready for such contact — they often argue that the multitude of armed conflicts and the pollution of our own world as reasons that an extra-terrestrial lifeform may pass Earth by, which Hollywood will pick up on when they feel their movie needs a message.

Compare Alien Among Us. Contrast with Absent Aliens. See also First Contact Math, Boldly Coming (a.k.a. Thirty-Fourth Contact), Faeries Don't Believe in Humans, Either.

For the novelette, see "First Contact". For the film, see Star Trek: First Contact. For the webcomic, see First Contact.

Naturally, this is the step between The Masquerade and The Unmasqued World.

(ed note: see TV Trope page for list of examples)

Contact Motivation

An alien civilization of similar technological advancement to Terra could contact us Earth-folk first. In pulp SF this was traditionally by an alien flying saucer landing on the US White House lawn. The standard motives from 1950's SF novels are, according to Solomon Golumb:

  • Help!
  • Buy!
  • Convert!
  • Vacate!
  • Negotiate!
  • Work!
  • Discuss!

Sir Arthur C. Clarke notes that the nasty little short story by Damon Knight adds an eighth motive: Serve!

Any or all of these motivations could apply to explorers from Terra, deciding to openly contact some alien civilization they become aware of.

But don't forget the ever popular Interstellar Trading.


(ed note: A decade before the events in the novel, the alien Maseni land on Terra and become our best friends. Sadly, a large percentage of the human population has an acute attack of Future Shock. Neophobes, the entire lot of them.)

     “You have this compulsion to talk with zanies,” Brutus said. “We never encounter a batch of Pure Earthers that you pass by; you’ve always got to stop and have a few words with them.”
     “They fascinate me,” Jessie said.
     “Sometimes, I think you could be one of them, with a little nudge,” the hell hound said, contemptuously.
     Jessie ignored the hound’s sneering remark. He said, “The Pure Earthers are borderline Shockies; if they’d been just a hair more upset by the Maseni landing and all that’s come since, they’d be in one of the homes. I’ll never have the chance to see any real Shockies, but I can get an idea what they must be like from studying the Pure Earthers.”
     “Why this interest in Shockies?” Brutus asked.
     “You know why. My parents are Shockies.”
     “Oh, yeah,” Brutus said. “I forgot.” But he hadn’t forgotten at all. He was just looking for something more to sneer about. “They went starkers when the Maseni touched down, a couple of wide-eyed blubbers.”
     Jessie watched the approaching Pure Earthers. “That’s right.”

     The first Maseni interstellar ships had landed a decade ago, in the second week of October, 1990. Within a year, the population of Earth—regardless of nationality, race, ethnic group, or education—had been roughly divided into three types of reactions.

     First, there were those who were profoundly shocked by these developments, but who were able to cope and reorder the nature of their lives and the limits of their perceptions of the universe. These were about forty-five percent of the population.

     Another forty-five percent were simply unable to adjust. These were the Shockies. They were jolted by the realization that mankind was not the most intelligent species in existence, a fact scientists had predicted for years but which the Shocldes had always rejected as “holcum” or “bunkum” or “crap,” or “heresy” or “craziness”. They were further jolted to discover— thanks to the Maseni—that the supernatural world actually existed, that the denizens of nightmare were real (vampires, werewolves, etc.). And they were crushed to discover that (insert deity of choice) was not quite the being they had always thought. Not only were their patriotic and racial convictions smashed, but so was their spiritual belief…

     Shockies behaved in one of three ways:
  1. Uncontrolled rage that led to murder, bombing, rape and rampages of undirected violence.
  2. As they had always acted before, refusing to acknowledge that the Maseni existed or that their world had changed at all, no matter how much that changed world impinged on their fantasy.
  3. Or they simply became catatonic, staring off into another world, unable to speak, unable to feed themselves or control their own bodily functions.
     Cultural shock, severe, horrible.

     Space-program scientists had long theorized the extent of such a sickness an alien race should ever be found, but none of them had realized how far-reaching the illness would be.

     “Are you going to bleed for them forever?” Brutus asked. “Haven't you ever heard of ‘survival of the fittest’? Did the Cro-Magnon man weep for the Neanderthal?”
     “These were my parents,” Blake said. “My mother and father. If they could have just accepted change, a little bit—”
     “Then they’d have been Pure Earthers,” Brutus said. “Would you have been any happier with that?”
     “I guess not.”

     The Pure Earthers, at first, had no name and operated under no central organization; that development had required five years in the making. But they were all alike, and they could function coherently as a group; the Pure Earth League was an inevitable product of the Maseni landing. Those citizens who had not gone starkers but who were also unable to cope, about ten percent of the world population, agitated for an end of Human-Maseni relations and a return to the simpler life. They were, of course, doomed to extinction. Their own children, more accustomed to seeing Maseni and supernaturals in the streets, were falling away from the older folks; succeeding generations would give fewer and fewer bodies to the Cause.

     Millennium City was a 200-store shopping mall, most of it under a single roof, with indoor pedwalks, indoor and outdoor parks, fountains, convention facilities, hotels, more fountains, amusement centers, free theaters and museums, robot guides to help you find your way, a three hundred million credit wonder that had been completed only a year before. It was staffed exclusively by robots and was efficiently run, enormously profitable.

     Only ten years earlier, it could never have been built —and not only because Maseni technology was required to construct it. Ten years ago, the city of Los Angeles simply would not have had the room, in the heart of its west side, to contain such a lavish, three-hundred-acre structure. Then, there had been too many people, too much crowding.

     Now, a decade after the Maseni landing on Earth, the city was only half as populated as it had been. Forty-five percent of the city’s people had gone starkers and ended up in homes for Shockies. Many of these, in the following ten years, either took their own lives or died from too long in a catatonic trance. For the most part, the Shockies were those who were already hopelessly at odds with their times; they were, in many cases, those who ignored the warnings of ecologists and continued to have large families, polluting the Earth with excess flesh. Removed from the mating cycle, they no longer contributed to the population boom.

     Those who adapted to the Maseni and the other changes, tended to have no families, or small ones. As the Shockies died, the population dropped, and land became available. With the welfare rolls almost wiped out, and with vital services crying for good workers, everyone again had a job and everyone was more affluent than any time in the nation’s history. There was not only room to build Millennium City, but also credits to spend there.

     Old office buildings were torn down, as were rows and rows of shabby houses where no one lived any more. They razed factories that had once produced useless gadgets and flashy gewgaws, for none of these things were now in demand; society had suddenly become aware of its own power and of the true value of possessions. Millennium City not only provided services and products, but a place to feel at ease, a center for commerce which was, at the same time, a business establishment and a community meeting place.

From THE HAUNTED EARTH by Dean Koontz (1973)

Contact Anti-motivation

There are also anti-motivations. Even if the human race does not want to go all genocidal on a newly discovered alien civilization's posterior, neither do you want to make it easy for them to kill you. As far back as Murray Leinster's classic "First Contact" (1945) the warning is when one of your starships unexpectedly encounters an alien starship, neither can let the other discover the location of their home planet. At least without finding their location as well. If the Terran starship stupidly lets the Blortch starship find the location of Terra, well Terra is at the Blortch's mercy. The Blortch can send their entire star fleet to blow Terra to Em-Cee-Squared, secure in the knowledge that the Terran star fleet has no idea where in the universe to dispatch a retaliation task force.

This only happens when mutually alien ships stumble over each other in deep space. Naturally if the Terran exploration ship encounters the Blortch ship while both are orbiting the Blortch homeworld, well the cat is already out of the bag. Then the problem is how does the Terran ship get the vital information back to Terra without leading the Blortch back to your home.

Things can get quite ugly. In Michael McCollum's Antares Passage (1998) all ships have explosive charges on their navigation computers and the astrogators have been brainwashed to commit suicide if they are in danger of being captured by the enemy. In the beforementioned "First Contact", the human and alien ship try to destroy each other in battle, knowing that neither one dare run for home.

If you are really desperate, you will have to trigger the ship's self-destruct mechanism.

“Blasters, sir? What for?”

The skipper grimaced at the empty visiplate.

“Because we don’t know what they’re like and can’t take a chance! I know!” he added bitterly. “We’re going to make contacts and try to find out all we can about them—especially where they come from. I suppose we’ll try to make friends—but we haven’t much chance. We can’t trust them a fraction of an inch. We’ daren’t! They’ve locators. Maybe they’ve tracers better than any we have. Maybe they could trace us all the way home without our knowing it! We can’t risk a nonhuman race knowing where Earth is unless we’re sure of them! And how can we be sure? They could come to trade, of course—or they could swoop down on overdrive with a battle fleet,that could wipe us out before we knew what happened. We wouldn’t know which to expect, or when!”

Tommy’s face was startled.

“It’s all been thrashed out over and over, in theory,” said the skipper. “Nobody’s ever been able to find a sound answer, even on paper. But you know, in all their theorizing, no one considered the crazy, rank impossibility of a deep-space contact, with neither side knowing the other’s home world! But we’ve got to find an answer in fact! What are we going to do about them? Maybe these creatures will be aesthetic marvels, nice and friendly and polite—and, underneath, with the sneaking brutal ferocity of a mugger. Or maybe they’ll be crude and gruff as a farmer—and just as decent underneath. Maybe they’re something in between. But am I going to risk the possible future of the human race on a guess that it’s safe to trust them? God knows it would be worthwhile to make friends with a new civilization! It would be bound to stimulate our own, and maybe we’d gain enormously. But I can’t take chances. The one thing I won’t risk is having them know how to find Earth! Either I know they can’t follow me, or I don’t go home! And they’ll probably feel the same way!

He pressed the sleeve-communicator button again.

“Navigation officers, attention! Every star map on this ship is to be prepared for instant destruction. This includes photographs and diagrams from which our course or starting point could be deduced. I want all astronomical data gathered and arranged to be destroyed in a split second, on order. Make it fast and report when ready!”

He released the button. He looked suddenly old. The first contact of humanity with an alien race was a situation which had been foreseen in many fashions, but never one quite so hopeless of solution as this. A solitary Earth-ship and a solitary alien, meeting in a nebula which must be remote from the home planet of each. They might wish peace, but the line of conduct which best prepared a treacherous attack was just the seeming of friendliness. Failure to be suspicious might doom the human race—and a peaceful exchange of the fruits of civilization would be the greatest benefit imaginable. Any mistake would be irreparable, but a failure to be on guard would be fatal.

From FIRST CONTACT by Murray Leinster (1945)

(ed note: The tiny group of human interstellar colonies contact an alien race called the Qax. Shortly afterward the Qax conquered humanity and implemented the Qax Occupation)

      Like everybody else Parz had never actually seen a Qax. He suspected that they were physically extensive—otherwise, why use Spline freighters to travel?—but, in any event, it was not their physical form but their minds, their motivation, that was so fascinating. He'd become convinced that it was only by knowing the enemy—by seeing the universe through the consciousness of the Qax—that men could hope to throw off their heavy yoke of Occupation.
     He had come to suspect, for instance, that comparatively few individuals comprised the Qax race—perhaps no more than thousands. Certainly nothing like the billions that had once totaled humanity, in the years before the development of AS technology. And he was sure that there were only three or four Qax individuals assigned to the supervision of Earth, orbiting in the warm bellies of their Spline freighters.

     This hypothesis had many corollaries, of course.
     The Qax were immortal, probably—certainly there was evidence that the same Governor had ruled Earth from the beginning of the Occupation. And with such a small and static population, and with all the time in the world, each Qax would surely come to know the rest of its species intimately.
     Perhaps too well.
     Parz imagined rivalries building over centuries. There would be scheming, maneuvering, endless politicking... and trading. With such a small and intimate population surely no form of formal policing could operate. How to build consensus behind any laws? How to construct laws that would not be seen to discriminate against individuals?

     ...But there were natural laws that governed any society. Parz, drifting into a contemplative doze, nodded to himself. It was logical. The Qax must work like so many independent corporations, in pure competition; they would swim in a sea of perfect information about each other's activities and intentions, kept in some semblance of order only by the operation of the laws of economics. Yes, the theory felt right to Parz. The Qax were natural traders. They had to be. And trading relationships would be their natural mode of approaching other species, once they started spreading beyond their own planet.
     Unless, as in the case of humanity, other opportunities, too soft and welcoming, beckoned...

     Parz didn't believe—as many commentators maintained—that the Qax were an innately militaristic species. With such a small number of individuals they could never have evolved a philosophy of warfare; never could they have viewed soldiers (of their own race) as expendable cannon fodder, as a renewable resource to be husbanded or expended to suit the needs of a conflict. The murder of a Qax must be a crime of unimaginable horror.
     No, the Qax weren't warlike. They had defeated humanity and occupied the Earth merely because it had been so easy.

From TIMELIKE INFINITY by Stephen Baxter (1992)

     “Yes. The region of the galaxy from which you have come is that which we call the desert. It is an area almost entirely devoid of planets. Would you mind telling me which star is your home?”
     Cohn stiffened.
     “I’m afraid our government would not permit us to disclose any information concerning our race.”
     “As you wish. I am sorry you are disturbed. I was curious to know — ” He waved a negligent hand to show that the information was unimportant. We will get it later, he thought, when we decipher their charts.

     “There are no charts,” he grumbled, “no maps at all. We will not be able to trace them to their home star.”

     The reports were on his desk and he regarded them with a wry smile. There was indeed no way to trace them back. They had no charts, only a regular series of course-check coordinates which were preset on their home planet and which were not decipherable. Even at this stage of their civilization they had already anticipated the consequences of having their ship fall into alien hands.

From ALL THE WAY BACK by Michael Shaara (1952)

(ed note: human ("monster") ship has surprised the alien Ryall planet and Ryall ship the Space Swimmer)

     “I have a message for you from Ossfil of Space Swimmer.”
     “Proceed with the message.”
     “‘The monsters have me surrounded and I am unable to reach the gateway. I am taking evasive action, but will not be able to escape. Request instructions. Ossfil, commanding Space Swimmer.’“
     Varlan muttered a few deep imprecations to the evil star before replying. “Transmit the following: ‘From Varlan of the Scented Waters to Ossfil of Space Swimmer. As a minimum, you will destroy your astrogation computer and trigger the amnesia of your astrogator. After that is done, you may act on your own initiative.’“

     “What of the astronomical data in his computer?”
     “I have given the order that he destroy his computer and trigger his astrogator’s amnesia. Failing that, of course, he will destroy his ship.”

     “It is regrettable, Varlan of the Scented Waters, but I still have considerable astronomical data in my brain, including knowledge of the positions of many of the gateways throughout the hegemony.”
     Varlan “blinked” in horror at Salfador’s revelation.

     “You must have been fitted with an amnesia spell. Give me your trigger code and I will excise the knowledge from your brain,” she said.
     The miserable look on Salfador’s features was all the answer she needed. Even so, he said, “I’m afraid that I was never fitted with such. I had not intended to be an astrogator on a starship, and therefore, had no need.”

     To ask a philosopher to camp in the woods like a barbarian was unthinkable. Even more unthinkable, however, was allowing Salfador to fall into the grasp of the monsters. Finally, she said: “You know what you must do, of course.”
     Salfador signaled his agreement. “I have already done so. There are many poisons in the medical kits. I injected myself with one before coming here. Do not fear. My death will be quite painless.”

(ed note: the humans have captured the alien ship Space Swimmer, and are puzzling over the alien's strange behavior)

     “Naw. Shot him with a dart. He’ll be all right, ‘cept that he’s crazy as a high plateau jumper.”
     “How so?”
     “I found him amidships in one of the equipment rooms. He had this big bar he’d ripped out of some machinery and was using it to beat holy hell out of some access panel. Looked to me like he wanted to get through it and into the machinery beyond.

     “What did you say just now, Corporal?” he asked.
     “I said this damned crazy centaur attacked me, sir...”
     “No, about his trying to smash a machine. What machine?”
     “‘Fraid I don’t recognize this alien machinery too good, sir.”
     “Take me to it.”
     Sayers led the way, followed by Philip Walkirk and Sergeant Barthol. They moved through gloomy corridors until they reached a small compartment almost at the very center of the spherical ship.
     “Yonder machine over there, sir!” Sayer said, playing the beam from his hand lamp over a dented access panel.
     Philip gazed at the panel, blinked, and then emitted a low whistle.
     “This thing important, sir?” Barthol asked.
     “You might say that,” Philip replied. “What Corporal Sayers refers to as ‘yonder machine’ is their astrogation computer. The fact that he was trying to beat it to death may mean that their normal destruct mechanism failed to operate properly.”
     “That good, sir?”
     Philip Walkirk’s sudden laughter startled the two noncoms. “That box, Sergeant, may well contain information vital to the conduct of the war.”
     “What information, sir?”
     “If we’ve been very, very lucky, we may just dredge up a foldspace topology chart for the whole damned Ryall hegemony!”

(ed note: an alien Species called the Makers needs a faster-than-light starship drive. Over a period of several thousand years they send out STL robot space probes with artificial intelligence to seek out other species, and ask them about FTL.

Probe 53935 was passing by the solar system in 2065 CE when it spotted the signature of an FTL starship around Procyon. It didn't have enough reaction mass to head to Procyon, so it decided to visit Terra and bargain for some remass. Ordinarily it would have ignored Terra because they were too technologically primitive to be worthwhile.

Due to some unfortunate squabbles between have and have-not nations, the probe was destroyed by the Pan-African alliance. A part of the probes AI survived. It decided to commit suicide and told the Terran forces to back out of the blast radius.

The United Nations convinced the AI to make a bargain. The UN would mount a STL expedition to Procyon and transport the AI there. It would then help the AI fulfil its prime directive and carry the secret of FTL back to the Maker civilization. In exchange the AI would give the UN some of the Maker's technology.

About 300 years later the colonist at Procyon called "Alphans" find the secret of FTL, and head back to Terra in their first starship. They bring along the AI. They treat the original bargain made with the AI to be a sacred trust, and are committed to bringing the secret of AI back to the Makers.

Unfortunately the government of Terra is apprehensive, and feel zero obligation to honor the bargain.)

      “Williams is concerned that there are a great many species in this galaxy who would regard a starship full of humans the way we would look upon an ownerless cow with a bag of gold strapped to its neck. He fears an attack on Earth should the Alphans lose the secret of the FTL drive to aliens.”
     “Why attack us?”
     “We are potential competitors.”
     “Surely there are security measures we could take to hide the location of our home system, Sergei. Hypnosis, drugs, orders for astrogators to suicide on capture, that sort of thing.”
     Vischenko shook his head. “It might not be that simple, Executive. An FTL starship leaves a radiation wake wherever it goes. Using the proper instruments, this trail can be detected decades later. That was how the probe knew that Procyon was the site of an FTL base. It is also the reason we were so quick to detect the Alphans’ arrival. By the way, we are still tracking their wake. Scientists tell me we’ll be able to watch it all the way back to Procyon, some twelve light-years distant.”
     Duval considered Vischenko’s words for long seconds, and then nodded slowly. “I’m beginning to see your point. We’ll proceed with caution, at least until we know what we’re up against.”

     “Well,” (Henri) Duval (the equivalent of a World President) asked, turning to his one-time mentor, “what do you think?
     Josip Betrain was an old man, even by contemporary standards. He was also a sick man. He suffered from a degenerative nerve disorder that caused his body to twitch continuously. After fifteen decades of life, Betrain had not long to live. That fact gave him an unusually clear view of things, and made him a particularly valued advisor to the Chief Executive.
     “You are trying to decide whether we should participate in this adventure of theirs to search out the probe’s creators?”
     “And you want my advice?”
     “I presume that was a rhetorical question since you know damned well that I do.”
     “My advice to you, Executive, is simple. You are going to end up going out to the stars whether you like it or not. You had best like it.”
     Duval sighed “You know, Josip, I sometimes think you overplay your role as my Oracle of Delphi. Would you care to explain your last remark?”
     “Nothing mysterious about it. If you decide to allow the expedition, you will have to build a fleet of ships of your own to accompany them. It is patently obvious that they will never find the Maker world on their own. The logistics are far too great for their society to handle. And, Henri, if you decide that fulfilling this ‘Promise’ of theirs endangers the Earth, then you will need that star fleet even more.
     “I don’t follow you.”
     “Sure you do. However, when the facts are unpleasant, even a Chief Executive tends to avert his eyes. Therefore, let history record that it was from my lips that the fateful words first fell.” Betrain drew himself up and seemed to gather strength from somewhere within. When he spoke, the usual hoarse whisper was replaced by a reedy monotone.
     “If Professor Williams’ scenario is correct, Executive, it is your solemn duty to prevent the Alphans from giving the FTL secret to any alien species whatsoever! That includes the beings that built the probe. Once the secret is out, it is out!  Obviously, the only way to stop the spread of a dangerous technology is at the source. To do that, you will have to take control of Procyon VII itself. You may well be forced into becoming that which you have long despised — an imperialist aggressor who launches an unprovoked attack against people who have done nothing to deserve it.”
     “I take it then, Josip, that you agree with Professor Williams’ assessment of the danger?”
     “I do not!” the old man growled. There was a deep rattle in his chest and he was overcome with a wracking cough. After the spasm passed, he lifted himself upright, stared at Duval with rheumy eyes, and continued. “Study your history, man! Every forward step the race has ever taken was opposed by someone afraid of what we would find. So far, the ‘naysayers’ have been 100% wrong. As a result, history does not speak kindly of leaders who lose their nerve at critical moments.
     “But my opinion doesn’t count. Neither does yours. We cannot lose sight of the possibility that the Colin Williams’s of this world might be right this time. Maybe the galaxy is full of alien monsters just waiting for a shipload of hayseed humans to blunder into their clutches.”

From PROCYON'S PROMISE by Michael McCollum (1985)

Mind Enslaving Aliens


Mid-last-century a popular theme was your best friend who lives next door suddenly having their entire personality utterly transformed by Invaders From Outer Space. Most analysis is of the opinion that this is a thinly disguised allegory for the second red scare in the US.

The original Invasion of the Body Snatchers had the hapless humans killed and replaced with perfect duplicates. In this section we are concerned with the creepy sub-trope of the victims not being killed, but merely mentally enslaved and controlled like meat puppets. Bonus horror points for the controlling aliens actually burrowing into the victims body in order to take control of the brain.

Examples include the neural parasite from ST:TNG Conspiracy, the flying parasites in ST:TOS Operation: Annihilate!, Redjac in ST:TOS "Wolf in the Fold", The Invisibles from The Outer Limits, The Vang series by Christopher Rowley, the slug from The Hidden, Hivers in A Hat Full of Sky, the Goa'uld in Stargate SG-1, the The Drakh Keepers from Babylon 5, the Vaylen in the Iron Empires graphic novels, the energy being from Kronos, and Robert Heinlein's The Puppet Masters. Arguable examples include the Ceti eel from Star Trek: The Wrath of Khan and the Centaurian slug from Star Trek: The Future Begins

(Zuul is defeated by God Mars)
Emperor Zuul: Mars! I can't die! I won't!
Emperor Zuul: My cells are all over the universe! Somewhere out there, I will be reborn!
Takeru: What?
Emperor Zuul: Bwahahahaha! Emperor Zuul of Gishin is only a shell occupied by one of my cells!
Super Robot Wars Z2: Hakai-Hen

A form of Body Horror common in alien invasion plots. Aliens, rather than invading in their own form, insert themselves into (usually unwilling or unaware) humans, whereupon they completely take over the host's body, suppress their will, and generally make them not themselves. They generally do this because their natural form is some kind of grub or other not-very-formidable state.

They may have limited or total access to the host's memory, but can generally fool casual observers. A possessed host typically gains increased strength, and sometimes additional wacky powers. They may also be able to affect a Voice of Evil or glowing eyes, to let the audience know what's up.

This will fool everyone until the critical moment, even though a possessed host usually starts exhibiting really strange symptoms such as a lack of emotion, a surplus of emotion, violent rampages, festering sores, a flue gill, or a penchant for ketchup.

Sometimes, the possession process actually kills the host, turning them into a Parasite Zombie with Marionette Motion. If the host is left alive then they may or may not remain aware while possessed. No matter what the case is, it generally takes a Deus ex Machina to remove the parasite without killing the host.

The method by which the parasite enters the host body varies; it might be injected, it may latch on to the host's skull or spine, or it may enter as some kind of Energy Being. Crawling in through the mouth or ears is also very popular. Often a Festering Fungus. This trope may also be used as a metaphor for venereal disease. A controlling alien that doesn't invade the body is The Hypnotoad.

Also, for some reason, possessed bodies often melt when killed.

Very popular in films during the Cold War era, as it made such a handy parallel for communism. One of the most self-aware film examples is The Faculty.

Sub-Trope of Body Snatcher. Can overlap with And I Must Scream.

Compare with Living Doll Collector. Contrast They Look Like Us Now, where the Masquerade is limited to posing as human without being able to replace/control specific individuals. Compare & constrast Marionette Master, someone who uses actual puppets.

(ed note: see TV Trope page for list of examples)


The benign version is when the burrowing alien is not a parasite but actually a symbiont. One that helps the human: repairing bodily damage, curing disease, and granting superhuman powers (often psionic). And no enslaving at all, the alien is a partner. Technically the correct term is "symbiont" even though science fiction authors mistakenly use the term "symbiote".

Examples of symbioses include Needle, Through the Eye of a Needle, and Insidekick. The alien symbiont in Needle helped the protagonist survive being stabbed through the heart. The symbiont in Insidekick gave the protagonist incidental powers like a prolonged life span and teleportation.

"Of all the parasites I've had over the years, these worms are among the — hell, they are the best!"
Fry, Futurama

In biology, a symbiote (or symbiont) is a living organism that lives in symbiosis with another organism. Symbiosis literally means "living together," and it comes in three variations:

  • Mutualism - both organisms benefit from each other's presence.
  • Commensalism - one organism flourishes, the other isn't affected.
  • Parasitism - one organism is harmed, the other flourishes.

In fiction, all types are very frequent guests in Science Fiction and Fantasy. The Heroic Host specifically gets their powers from such an arrangement, though the specifics vary.

Compare Puppeteer Parasite (parasites that control other organism's brains) and Face Full of Alien Wing-Wong (parasites who use our bodies for reproduction), which could be subtropes of this. Also compare Chest Burster. See also Heart Drive for a similar phenomenon involving biological Soul Jars.

For details on hosts for symbiotes, see Body and Host.

Symbiotic Possession and Translator Microbes are versions of Mutualism that are particularly common in Speculative Fiction.

When The Symbiote covers the host's body as some sort of costume, whether for good or bad, it's almost invariably a Clingy Costume.

(ed note: see TV Trope page for list of examples)


(ed note: Albert is a somewhat overweight undercover tax investigator, looking into corporate malfeasance on the plante Antar. The corporation discovers this, and hires some local alien Mafia thugs to kill Albert. At the edge of the jungle all of them are surprised by a native animal Earthmen call a Bandersnatch. It is an insane combination of talons, teeth and snakelike neck mounted on a crocodilian body. The Mafia torpedoes run away, Albert faints.

As it turns out, the Bandersnatch is hosting a symbiont called a Zark. It is concerned with how Albert passed out cold, and decides to take up residence inside Albert's body.)

      Curiously, the Zark sent out a pseudopod of its substance through the open mouth of its disguise. The faintly glittering thread oozed downward and struck Albert's head beside his right eye. Without pausing, the thread sank through skin and connective tissue, circled the eyeball and located the optic nerve. It raced inward along the nerve trunk, split at the optic chiasma, and entered the corpora quadrigemina where it branched into innumerable microscopic filaments that followed the main neural paths of the man's brain, probing the major areas of thought and reflex.
     The Zark quivered with pleasure. The creature was beautifully complex, and, more important, untenanted. He would make an interesting host.
     The Zark didn't hesitate. It needed a host; giving its present mass of organic matter pseudo-life took too much energy. The Bandersnatch collapsed with a faint slurping sound. A blob of iridescent jelly flowed from the mouth and spread itself evenly over Albert's body in a thin layer. The jelly shimmered, glowed, disappeared inward through Albert's clothing and skin, diffusing through the subcutaneous tissues, sending hair-like threads along nerve trunks and blood vessels until the threads met other threads and joined, and the Zark became a network of protoplasmic tendrils that ramified through Albert's body.
     Immediately the Zark turned its attention to the task of adapting itself to its new host. Long ago it had learned that this had to be done quickly or the host did not survive. And since the tissues of this new host were considerably different from those of the Bandersnatch, a great number of structural and chemical changes had to be made quickly. With some dismay, the Zark realized that its own stores of energy would be insufficient for the task. It would have to borrow energy from the host—which was a poor way to start a symbiotic relationship. Ordinarily, one gave before taking.
     Fortunately, Albert possessed considerable excess fat, an excellent source of energy whose removal would do no harm. There was plenty here for both Albert and itself. The man's body twitched and jerked as the Zark's protean cells passed through the adaptive process, and as the last leukocyte recoiled from tissue that had suddenly become normal, his consciousness returned. Less than ten minutes had passed, but they were enough. The Zark was safely in harmony with its new host.
     Albert opened his eyes and looked wildly around. The landscape was empty of animate life except for the odorous carcass of the Bandersnatch lying beside him. Albert shivered, rose unsteadily to his feet and began walking toward Vaornia. That he didn't run was only because he couldn't.

     Inside the city walls, Vaornia struck a three-pronged blow at Albert's senses. Sight, hearing and smell were assaulted simultaneously. Natives slithered past, garbed in long robes of garish color. Sibilant voices cut through the evening air like thin-edged knives clashing against the grating screech of the ungreased wooden wheels of dak carts. Odors of smoke, cooking, spices, perfume and corruption mingled with the all-pervasive musky stench of unwashed Vaornese bodies.
     It was old to Albert, but new and exciting to the Zark. Its taps on Albert's sense organs brought a flood of new sensation the Zark had never experienced. It marveled at the crowded buildings studded with jutting balconies and ornamental carvings. It stared at the dak caravans maneuvering with ponderous delicacy through the swarming crowds. It reveled in the colorful banners and awnings of the tiny shops lining the streets, and the fluttering robes of the natives. Color was something new to the Zark. Its previous hosts had been color blind, and the symbiont wallowed in an orgy of bright sensation.
     The Zark, meanwhile, was not idle despite the outside interests. The majority of its structure was busily engaged in checking and cataloguing the body of its host, an automatic process that didn't interfere with the purely intellectual one of enjoying the new sensations. Albert's body wasn't in too bad shape. A certain amount of repair work would have to be done, but despite the heavy padding of fat, the organs were in good working condition.
     The Zark ruminated briefly over what actions it should take as it dissolved a milligram of cholesterol out of Albert's aorta and strengthened the weak spot in the blood vessel with a few cells of its own substance until Albert's tissues could fill the gap. Its knowledge of human physiology was incomplete, but it instinctively recognized abnormality. As a result, it could help the host's physical condition, which was a distinct satisfaction, for a Zark must be helpful.

(ed note: In the city Albert beats up the alien who ratted him out to the corporation. Albert is arrested and put in a jail cell. The corporation bribes an alien cop to put deadly poison in Albert's food.)

     Since it takes a little time for substances to diffuse across the intestinal epithelium and enter the circulation, the Zark had some warning of what was about to happen from the behavior of the epithelial cells lining Albert's gut. As a result, a considerable amount of the alkaloid was stopped before it entered Albert's body—but some did pass through, for the Zark was not omnipotent.
     For nearly five minutes after finishing the meal, Albert felt normally full and comfortable. Then hell broke loose. Most of the food came back with explosive violence and cramps bent him double. The Zark turned to the neutralization and elimination of the poison. Absorptive surfaces were sealed off, body fluids poured into the intestinal tract, and anti-substances formed out of Albert's energy reserve to neutralize whatever alkaloid remained.
     None of the Zark's protective measures were normal to Albert's body, and with the abrupt depletion of blood glucose to supply the energy the Zark required, Albert passed into hypoglycemic shock. The Zark regretted that, but it had no time to utilize his other less readily available energy sources. In fact, there was no time for anything except the most elemental protective measures. Consequently the convulsions, tachycardia, and coma had to be ignored.
     Albert's spasms were mercifully short, but when the Zark was finished, he lay unconscious on the floor, his body twitching with incoordinate spasms, while a frightened guard called in an alarm to the medics.
     The Zark quivered with its own particular brand of nausea. It had not been hurt by the alkaloid, but the pain of its host left it sick with self-loathing. That it had established itself in a life-form that casually ingested deadly poisons was no excuse. It should have been more alert, more sensitive to the host's deficiencies. It had saved his life, which was some compensation, and there was much that could be done in the way of restorative and corrective measures that would prevent such a thing from occurring again—but the Zark was unhappy as it set about helping Albert's liver metabolize fat to glucose and restore blood sugar levels.

     The Zark observed his actions curiously. Now why was its host twisting that rod of metal out of the woodwork? (Albert is trying to escape from the jail cell) It didn't know, and it was consumed with curiosity. It had found no way to communicate with its host so that some of the man's queer actions could be understood; in the portions of the brain it had explored, there were no portals of communication. However, there still was a large dormant portion, and perhaps here lay the thing it sought. The Zark inserted a number of tendrils into the blank areas, probing, connecting synapses, opening unused pathways, looking for what it hoped existed.
     The results of this action were completely unforeseen by the Zark, for it was essentially just a subordinate ego with all the lacks which that implied—and it had never before inhabited a body that possessed a potentially first-class brain. With no prior experience to draw upon, the Zark couldn't possibly guess that its actions would result in a peculiar relationship between the man and the world around him. And if the Zark had known, it probably wouldn't have cared.

(ed note: Fred Kemmer, evil CEO of the corporation is waiting on the rooftop of an adjacent building with a long barreled sniper blaster rifle. He sees Albert crawl out the window about a hundred feet above the ground. As Albert crawls down the building, the evil CEO uses the rifle to blast away the brick Albert is standing on. Albert falls to his doom.)

     As the pavement rushed at him, he had time for a brief, fervent wish that he were someplace else. Then the thought was swallowed in an icy blackness.
     Fred Kemmer lowered the blaster with a grin of satisfaction. He had figured his man correctly, and now the spy would be nothing to worry about. He watched the plummeting body—and gasped with consternation, for less than ten feet above the pavement, Albert abruptly vanished!

(ed note: The Zark has activated many dormant parts of Albert's brain, including the part that allows humans to mentally teleport themselves. Albert materializes blocks away in a safe part of the city, instead of becoming a red splat on the pavement.

Albert again finds the alien who ratted him out, and starts questioning the alien about the illegal tobacco project the evil corporation is running on the planet. The alien gives Albert nothing but lies, but as it turns out the Zark has also activated the dormant part of Albert's brain that gives him the ability to telepathically read the alien's mind. Without the alien realizing it, Albert picks the alien memory clean of all the important details of the corporation's evil plot.)

     His mind turned to his room in the hostel with its well-fitted wardrobe and its first-aid kit—and again came that instant of utter darkness—and then he was standing in the middle of his room facing the wardrobe that held his clothing.
     He felt no surprise this time. He knew what had happened. Something within his body was acting like a tiny Distorter, transporting him through hyperspace in the same manner that a starship's engine room warped it through the folds of the normal space-time continuum. There was nothing really strange about it. It was a power which he should have—which any normal man should have. The fact that he didn't have it before was of no consequence, and the fact that other men didn't have it now merely made them abnormal.
     He smiled as he considered the possibilities which these new powers gave him. They were enormous. At the very least, they tripled his value as an agent. Nothing was safe from his investigation. The most secret hiding places were open to his probings. Nothing could stop him, for command of hyperspace made a mockery of material barriers.
     He chuckled happily as he removed his pajama jacket and reached for the first-aid kit. From the gash in his sleeve, there should be a nasty cut underneath, and it startled him a little that there was no greater amount of hemorrhage. He cleaned off the dried blood—and found nothing underneath except a thin red bloodless line that ran halfway around his arm. It wasn't even a scratch.
     Yet he had felt Shifaz' blade slice into his flesh. He knew there was more damage than this. The blood and the slashed sleeve could tell him that, even if he didn't have the messages of his nerves. Yet now there was no pain, and the closed scratch certainly wasn't the major wound he had expected. And this was queer, a fact for which he had no explanation. Albert frowned. Maybe this was another facet of the psi factors that had suddenly become his.
     He went at a steady pace, occasionally turning his glance to the road, impressing sections of it upon his memory so that he could return to them via teleport if necessary. He found that he could memorize with perfect ease. Even the positions of clumps of grass and twigs were remembered with perfect clarity and in minute detail. The perfection of his memory astonished and delighted him.
     The Zark felt pleased with itself. Although it had never dreamed of the potential contained in the host's mind, it realized that it was responsible for the release of these weird powers, and it enjoyed the new sensations and was eager for more. If partial probing could achieve so much, what was the ultimate power of this remarkable mind? The Zark didn't know, but, like a true experimenter, it was determined to find out—so it probed deeper, opening still more pathways and connecting more synapses with the conscious brain.
     When hiding from the second airboat, he disturbed a kelit in the thick brush growing beside the road. The little insect-eater chittered in alarm and dashed off to safety across the highway. And Albert, looking at it, was conscious not only of the external shape but the internal as well!
     He could see its little heart pounding in its chest, and the pumping bellows of the pink lungs that surrounded it. He was aware of the muscles pulling and relaxing as the kelit ran, and the long bones sliding in their lubricated joints. He saw the tenseness of the abdominal organs, felt the blind fear in the creature's mind. The totality of his impressions washed through him with a clear wave of icy shock.
     Grimly, he shrugged it off. He had ESP. He ought to have expected it—it was the next logical step.

(ed note: Albert is captured by the evil corporation again, since they figured out he is using hyperspace jumps to teleport so can be stopped with a hyperspace damper. Evil CEO Kemmer tortures Albert to find out Albert's contacts.)

     Albert felt helpless. He couldn't run and he couldn't fight. But he wasn't ready to give up. His perception passed over and through Kemmer with microscopic care, looking for some weakness, something that could be exploited to advantage. Kemmer had to have a vulnerable point.
     He did.
     There was a spot on the inner lining of the radial vein in Kemmer's left arm. He had recently received an inoculation, one of the constant immunizing injections that were necessary on Antar, for there was a small thrombus clinging to the needle puncture on the inner wall of the vessel. Normally it was unimportant and would pass away in time and be absorbed, but there were considerable possibilities for trouble in that little blob of red cells and fibrin if they could be loosened from their attachment to the wall.
     Hopefully, Albert reached out. If he couldn't move himself, perhaps he could move the clot.
     The thrombus stirred and came free, rushing toward Kemmer's heart. Albert followed it, watching as it passed into the pulmonary artery, tracing it out through the smaller vessels until it stopped squarely across a junction of two arterioles.
     Kemmer coughed, his face whitening with pain as he clutched at his chest. The pain was a mild repayment for his recent agony, Albert thought grimly. A pulmonary embolism shouldn't kill him, but the effects were disproportionate to the cause and would last a while. He grinned mercilessly as Kemmer collapsed.

(ed note: Albert escapes and contacts his boss. The corporation is caught red-handed by the information Albert has gathered and is brought to justice. Albert's boss has a new assignment for him, a tough cased suited for an agent with psi powers.)

     Inside Albert, the Zark alerted. A new assignment! That meant another world and new sensations. Truly, this host was magnificent! It had been a lucky day when he had fallen in running from the Bandersnatch. The Zark quivered with delight—
     And Albert felt it.
     Turning his perception inward to see what might be wrong, he saw the Zark for the first time.
     For a second, a wave of repulsion swept through his body, but as he comprehended the extent of that protoplasmic mass so inextricably intertwined with his own, he realized that this thing within him was the reason for his new powers. There could be no other explanation.
     And as he searched farther, he marveled. The Zark was unspecialized in a way he had never imagined—an amorphous aggregation of highly evolved cells that could imitate normal tissues in a manner that would defy ordinary detection. It was something at once higher yet lower than his own flesh, something more primitive yet infinitely more evolved.
     The Zark had succeeded at last. It had established communication with its host.
     "I was always afraid that you might suspect before I could tell you," the Zark replied. "It was an obvious line of reasoning, and you are an intelligent entity—the most intelligent I have ever inhabited. It is too bad that I shall have to leave. I have enjoyed being with you."
     "Who said anything about leaving?" Albert asked.
     "You did. I could feel your revulsion when you became aware of me. It wasn't nice, but I suppose you can't help it. Yours is an independent race, one that doesn't willingly support—" the voice hesitated as though searching for the proper word—"fellow travelers," it finished.
     Albert grinned. "There are historical precedents for that statement, but your interpretation isn't quite right. I was surprised. You startled me."
     He fell silent, and the Zark, respecting the activity of his mind, forbore to interrupt.
     Albert was doing some heavy thinking about the Zark. Certainly it had protected him on Antar, and with equal certainty it must have been responsible for the psi powers he possessed. He owed it a lot, for without its help he wouldn't have survived.
     There was only one thing wrong.
     Sexless though it was, the Zark must possess the characteristics of life, since it was obviously alive. And those characteristics were unchanging throughout the known universe. The four vital criteria defined centuries ago were still as good today as they were then—growth, metabolism, irritability—and reproduction. Despite its lack of sex, the Zark must be capable of producing others of its kind, and while he didn't mind supporting one fellow traveler, he was damned if he'd support a whole family of them.
     "That need never bother you," the Zark interrupted. "As an individual, I am very long-lived and seldom reproduce. I can, of course, but the process is quite involved—actually it involves making a twin out of myself—and it is not necessary. Besides, there cannot be two Zarks in one host. My offspring would have to seek another."
     "And do they have your powers?"
     "Of course. They would know all I know, for a Zark's memory is not concentrated in specialized tissue like your brain."
     A light began to dawn in Albert's mind. Maybe this was the answer to the corporate conscience he had been wishing for so wistfully on Antar (police agents with the ability to bring corporations to justice for their crimes). "Does it bother you to reproduce?" he asked.
     "It is annoying, but not painful—nor would it be too difficult after a pattern was set in my cells. But why do you ask this?"
     "The thought just occurred to me that there are quite a few people who could use a Zark. A few of the more honest folks would improve this Confederation's moral tone if they had the power—and certainly psi powers in law enforcement would be unbeatable."
     "Then you would want me to reproduce?"
     "It might be a good idea if we can find men who are worthy of Zarks. I could check them with my telepathy and perhaps we might—"

From INSIDEKICK by J. F. Bone (1959)

(ed note: At the galactic multi-species Sector Twelve General hospital, the galactic Monitor Corps brings in a spacecraft containing a previously unknown alien species with a physiological classification of EPLH. The alien is unconsious, and suffering from a skin disease. The Monitor Corps is uneasy, since the alien ship's log speaks about two passengers but only one is currently present. The Monitor Corps thinks the alien is guilty of eating the other passenger (the ship's doctor). The doctors of the hospital don't care, they have a duty to cure the patient.

But the unconscious patient's body appears to fight any attempt to cure it. The doctors inject a drug to cure the skin disease. The patient's body neutralizes it. They try to surgically remove the diseased skin tissue. The tissue grows roots into the patient's body which grow deeper as they watch.

And Dr. Prilicla the telepath insists that the patient is conscious, even though it is obviously unconsious.

Dr. Conway reads the ship's logs, and finds that the patient's species is obsessed with longevity. Longevity treatments are known to give the possessor an increased fear of dying. Such species would be constantly trying to get a better, more efficient doctor for itself. Then suddenly Dr. Conway realizes what is going on...)

      Feeling happy and excited and at the same time very much unsure of himself, Conway stumbled across to the intercom and ordered some very unusual equipment, checked again that the patient was so thoroughly strapped down that it would be unable to move a muscle, then he said, "My guess is that the patient is perfectly sane and we've been blinding ourselves with psychological red herrings. Basically, the trouble is something it ate."
     "I had a bet with myself you would say that sometime during this case," said O'Mara (Dr. Conway's boss). He looked sick.
     The equipment arrived—a slender, pointed wooden stake and a mechanism which would drive it downward at any required angle and controlled speeds. With the Tralthan's help Conway set it up and moved it into position. He chose a part of the patient's body which contained several vital organs which were, however, protected by nearly six inches of musculature and adipose, then he set the stake in motion. It was just touching the skin and descending at the rate of approximately two inches per hour.
     "What the blazes is going on?" stormed O'Mara. "Do you think the patient is a vampire or something!"
     "Of course not," Conway replied. "I'm using a wooden stake to give the patient a better chance of defending itself. You wouldn't expect it to stop a steel one, would you." He motioned the Tralthan forward and together they watched the area where the stake was entering the EPLH's body. Every few minutes Prilicla reported on the emotional radiation. O'Mara paced up and down, occasionally muttering to himself.

     The point had penetrated almost a quarter of an inch when Conway noticed the first coarsening and thickening of the skin. It was taking place in a roughly circular area, about four inches in diameter, whose center was the wound created by the stake. Conway's scanner showed a spongy, fibrous growth forming under the skin to a depth of half an inch. Visibly the growth thickened and grew opaque to his scanner's current setting, and within ten minutes it had become a hard, bony plate. The stake had begun to bend alarmingly and was on the point of snapping.
     "I'd say the defenses are now concentrated at this one point," Conway said, trying to keep his voice steady, "so we'd better have it out."
     Conway and the Tralthan rapidly incised around and undercut the newly-formed bony plate, which was immediately transferred into a sterile, covered receptacle. Quickly preparing a shot—a not quite maximum dose of the specific he had tried the previous day—Conway injected, then went back to helping the Tralthan with the repair work on the wound. This was routine work and took about fifteen minutes, and when it was finished there could be no doubt at all that the patient was responding favorably to treatment.

     Over the congratulations of the Tralthan and the horrible threats of O'Mara—the Chief Psychologist wanted some questions answered, fast. Prilicla said, "You have effected a cure, Doctor, but the patient's anxiety level has markedly increased. It is almost frantic."
     Conway shook his head, grinning. "The patient is heavily anestheticized and cannot feel anything. However, I agree that at this present moment…" he nodded toward the sterile container "…its personal physician must be feeling pretty bad."
     In the container the excised bone had begun to soften and leak a faintly purplish liquid. The liquid was rippling and sloshing gently about at the bottom of the container as if it had a mind of its own. Which was, in fact, the case.

     Conway was in O'Mara's office winding up his report on the EPLH and the Major was being highly complimentary in a language which at times made the compliments indistinguishable from insults. But this was O'Mara's way, Conway was beginning to realize, and the Chief Psychologist was polite and sympathetic only when he was professionally concerned about a person.
     He was still asking questions.
     "An intelligent, amoebic life-form, a organized collection of submicroscopic, virus-type cells, would make the most efficient doctor obtainable," said Conway in reply to one of them. "It would reside within its patient and, given the necessary data, control any disease or organic malfunction from the inside. To a being who is pathologically afraid of dying it must have seemed perfect. And it was, too, because the trouble which developed was not really the doctor's fault. It came about through the patient's ignorance of its own physiological background.
     "The way I see it," Conway went on, "the patient had been taking its rejuvenation treatments at an early stage of its biological lifetime. I mean that it did not wait until middle or old age before regenerating itself. But on this occasion, either because it forgot or was careless or had been working on a problem which took longer than usual, it aged more than it had previously and acquired this skin condition. Pathology says that this was probably a common complaint with this race, and the normal course would be for the EPLH to slough off the affected skin and carry on as usual. But our patient, because the type of its rejuvenation treatment caused memory damage, did not know this, so its personal physician did not know it either."
     Conway continued, "This, er, resident physician knew very little about the medical background of its patient-host's body, but its motto must have been to maintain the status quo at all costs. When pieces of its patient's body threatened to break away it held onto them, not realizing that this could have been a normal occurrence like losing hair or a reptile periodically shedding its skin, especially as its master would have insisted that the occurrence was not natural. A pretty fierce struggle must have developed between the patient's body processes and its doctor, with the patient's mind also ranged against its doctor. Because of this the doctor had to render the patient unconscious the better to do what it considered to be the right thing.
     "When we gave it the test shots the doctor neutralized them. They were a foreign substance being introduced into its patient's body, you see. And you know what happened when we tried surgical removal. It was only when we threatened underlying vital organs with that stake, forcing the doctor to defend its patient at that one point.
     "When you began asking for wooden stakes," said O'Mara dryly, "I thought of putting you in a tight harness."
     Conway grinned. He said, "I'm recommending that the EPLH takes his doctor back. Now that Pathology has given it a fuller understanding of its employer's medical and physiological history it should be the ultimate in personal physicians, and the EPLH is smart enough to see that."

From RESIDENT PHYSICIAN by James White (1961)

Lack of Aliens To Contact

Drake Equation

Back in 1961, there was a scientific conference held in the Green Bank facility about the search for extraterrestrial intelligence. In it, the host Dr. Frank Drake presented his now-famous "Drake Equation". The equation calculates N, which is the number of civilizations in our galaxy that it would be possible to communicate with by radio. After all, this equation was invented for a conference about communicating with aliens by radio.

It is a pity that we have not got a clue about the values of the last four parameters.

This means that the equation is pretty worthless for calculating the actual number of radio-using aliens out there. But it can be useful to study how proposed values for the parameters will affect N.

Note that N is the number of radio-using alien civilizations. Science fiction authors have been using the Drake Equation to calculate the number of alien civilizations, which is not quite the same thing. But close.

Authors can start off with a desired value for N, and work backwards to find values for the other parameters that will give the desired result. Or use their personal best guess for the parameters and see what value of N pops out.

The Drake Equation is:

N = R* × ƒp × ne × ƒl × ƒi × ƒc × L


  • N = the number of civilizations in our galaxy with which radio-communication might be possible
  • R* = the average rate of star formation in our galaxy
  • ƒp = the fraction of those stars that have planets
  • ne = the average number of planets/moons that can potentially support life per star that has planets
  • ƒl = the fraction of planets that could support life that actually develop life at some point
  • ƒi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
  • ƒc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
  • L = the length of time for which such civilizations release detectable signals into space

Current Estimates

R* the average rate of star formation in our galaxy
NASA and ESA data suggest current rate of star formation is about 7 per year.
ƒp the fraction of those stars that have planets
Microlensing surveys suggest this is pretty close to 1.
ne the average number of planets/moons that can potentially support life per star that has planets
0.4 if you are optimist, 0.1 if you are a pessimist.
0.4 is based the probability a planet is in the star's habitable zone, determined by solar heating. 0.1 is based on the galactic habitable zone, determined by regions of the galaxy with enough heavy elements and lack of near-by deadly supernovae.
Things get more uncertain when you consider that many moons (such as Europa or Titan) might support life. This drastically increases the number of habitable sites in a given solar system.
And proponents of the Rare Earth hypothesis say in order for their hypothesis to be true, it must be so closed to zero that Terra is the only one. Which violates the mediocrity principle and the Copernican principle, as well as being no fun at all for science fiction authors.
ƒl the fraction of planets that could support life that actually develop life at some point
The first SWAG parameter.
1.0 if you are an optimist, 0.13 if you are a pessimist.
1.0 is baased on the fact that life arose on Terra almost immediately after favorable conditions arose. 0.13 is based on an estimate by Charles H. Lineweaver and Tamara M. Davis based on a statistical argument derived from the length of time life took to evolve on Terra.
ƒi the fraction of planets with life that actually go on to develop intelligent life (civilizations)
The second SWAG parameter.
The value of this parameter is controversial, which is a code word for "who the heck knows?" Pretty much every value between 0.0 and 1.0 has been proposed, depending upon the proposer's particular axe to grind.
ƒc the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
The third SWAG parameter.
Also controversial. Some civilizations who have the technology to communicate might be paranoid enough that they keep silent. Yet other civilizations might not have the technology to communicate, but do have technology sufficiently noisy that it can be detected. Again: "who the heck knows?"
L the length of time for which such civilizations release detectable signals into space
The fourth SWAG parameter.
Most controversial of all. At its most innocuous, this could measure how long it takes for a civilization to become paranoid about giving away their position. At its most controversial, this could measure the average lifetime of a technological civilization, which is where the debate turns ugly. Over population, global warming, global thermonuclear war, and other terms for the Four Horsemen of the Apocalypse start being thrown around, and the discussion rapidly goes downhill from there.
More science-fictionally L could measure how long it takes a civilization to be cut short in an unexpected apotheosis by a Vingian Singularity

There have been several suggested modifications to the Drake Equation.

Alien civilizations might colonize other worlds. In a paper called The Great Silence — The Controversy Concerning Extraterrestrial Intelligent Life they derive three equations to calculate the effects of this on N. These equations require calculus so I'm not going to bother writing about them. You can find them in the report.

A given planet might give rise to several alien civilizations. An additional parameter is added for the Reappearance Factor, the average number of times a planet engenders alien civilizations. Like the other parameters this is very hard to estimate. A lot depends upon what kills off a given civilization, specifically how much it spoils the planet for making a new civilization. A little thing like global thermonuclear war and nuclear winter would eradicate a civilization but the planet would totally recover in a few million years. But if the primary star grew so swollen that it vaporized the planet, that would be the end. Another factor is that the first civilization to arise on a planet might use up all the fossil fuels and easily reached ores. The subsequent civilizations are at a disadvantage. They have to jump directly to off-shore oil drilling instead of just shooting a bullet in the ground like Jed Clampett.

An alien civilization, perfectly capable of sending radio messages, just might be paranoid enough that they keep silent. There might be civilization-killers lurking about, no sense attracting their attention. This is called the METI factor, for Messaging to ExtraTerrestrial Intelligence.

The July 2013 issue of Popular Science in an article about the TV show Doctor Who adds the parameter ƒd, which is the fraction of civilizations that can survived an alien attack from space. The "d" is for "Dalek".

The Fermi Paradox

Sooner or later one has to confront the Fermi Paradox. A good overview of the problem is David Brin's Xenology: The Science of Asking Who's Out There and The 'Great Silence': the Controversy Concerning Extraterrestrial Intelligent Life. For more detail, try Where Is Everybody?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life by Stephen Webb.

The Great Filter

The Fermi Paradox points out that:

  • There is a high probability of large numbers of alien civilizations
  • But we don't see any

So by the observational evidence, there are no alien civilizations. The trouble is that means our civilization shouldn't be here either, yet we are.

The nasty conclusion is that our civilization is here, so far. But our civilization is fated for death, and the probability is death sooner rather than later. This is called The Great Filter, and it is a rather disturbing thought.

And the problem is not just that we see no alien civilizations. It is the fact that humans exist at all. Terra should by rights be an alien colony, with the aliens using dinosaurs as beasts of burden and all pre-humans exterminated eons ago as pests.

Using slower-than-light starships it would be possible to colonize the entire galaxy in 5 million to 50 million years. By one alien civilization. Naturally the time goes down the higher the number of civilizations are colonizing.

So during the current life-span of our galaxy, it would have been possible for it to be totally colonized 250 to 2500 times. At a minimum.

The Fermi Paradox asks why isn't Terra an alien colony right now?

Granted an alien civilization might not be interested in colonization. There might be thousands of civilizations all content on their home planets, with nary a thought of colonization at all. But remember it only takes one. For anti-colonization bias to be a solution to the Fermi paradox, every single freaking civilization would have to share it with no exceptions at all. If there is even one then the galaxy is colonized in the blink of a galactic eye.

Again, the problem with no alien civilizations existing is that it implies our civilization should not exist either. A galaxy with 400 billion stars and 13.8 billion years of time to play with, it should have produced either millions of civilizations or zero civilizations. But not just one civilization. Violates the mediocrity principle and the Copernican principle, that does. Every single time people have theorized that Terra has a central specially favoried position in the universe, it has turned out to be ludicrously wrong.

Which means our civilization exists so far, but it is due to become extinct quite soon.

This means it is going to be real bad news if we discover any alien life forms at all in our solar system, even bacteria. It will imply that life is common in the universe, life on Terra is not special, The Great Filter must have wiped out all the other civilizations, and we are next.

The Great Filter does not necessarily mean 100% of all species become extinct around our level of development. A more merciful solution would be some filter that makes 100% of all species at our level of development stop trying to communicate with other species, and never ever attempt interstellar colonization. A candidate filter is The Singularity if you can make post-singuarlity species 100% non-communicating and non-colonizing (i.e., Fermi Invisible). Therein lies the rub. Since a singularity is literally where future prediction is impossible, making all singularities for all species 100% anything is probably impossible.

Other Fermi Paradox Solutions

Naturally there are quite a few solutions proposed. Stephen Webb's book has fifty of them. Some examine the Drake Equation's parameters with an eye towards finding unexpected constraints on the values.

The Wikipedia article has a broad outline of various classifications the solutions fall into. Refer to that article for details.

  • Few, if any, other civilizations currently exist
    • No other civilizations have arisen (see also Rare Earth Hypothesis)
    • It is the nature of intelligent life to destroy itself
    • It is the nature of intelligent life to destroy others (Berserker Hypothesis)
    • Life is periodically destroyed by naturally occurring events
    • Human beings were created alone
    • Inflation hypothesis and the youngness argument (multiple universes with synchronous gauge probability distribution)
  • They do exist, but we see no evidence
    • Communication is improbable due to problems of scale
    • Intelligent civilizations are too far apart in space or time
    • It is too expensive to spread physically throughout the galaxy
    • Human beings have not been searching long enough
    • Communication is improbable for technical reasons
    • Humans are not listening properly
    • Aliens aren't monitoring Earth because Earth is not superhabitable
    • Civilizations broadcast detectable radio signals only for a brief period of time
    • They tend to experience a technological singularity
    • They are too busy online
    • They are too alien
    • They are non-technological
    • The evidence is being suppressed (the Conspiracy Theory)
    • They choose not to interact with us
    • They don't agree among themselves (no talking with Terrans until Galactic UN is in agreement)
    • Earth is deliberately not contacted (Zoo Hypothesis)
    • Earth is purposely isolated (Planetarium Hypothesis)
    • It is dangerous to communicate
    • The Fermi paradox itself is what prevents communication (implies that communcation is lethal)
    • They are here unobserved

Several of the "Few if any civilization currently exist" entires are possible candidates for The Great Filter. If you can figure out how to make them 100% lethal.

Dr. Geoffrey A. Landis has a possible non-Great Filter solution based on Percolation Theory. In A Fire Upon The Deep, Vernor Vinge postulates a solution based upon Terra being located in the less desirable geographic region of the galaxy, which is a location based solution as is the Percolation solution.

A Great Filter solution is in Toolmaker Koan by John McLoughlin. It argues that any intelligent species that invents tools starts a process of accelerated progress that inevitably leads to extinction by warfare over dwindling resources.

A more nasty Great Filter solution is in the classic The Killing Star by Charles Pelligrino and George Zebrowski, Run To The Stars by Michael Rohan, and Antares Dawn by Michael McCollum (see below). It boils down to a variant on the Berserker Hypothesis.

Fermi's Nightmare

When we’re considering what kind of tropes to use in a science-fictional setting, we need to be aware of an observation most commonly called the Fermi Paradox. It goes something like this:

  • The galaxy is very large (at least a hundred billion stars) and very old (billions of years).
  • Stars with planets appear to be very common, and it seems reasonable to assume that many of those planets provide conditions suitable for life.
  • Given enough time, there seems to be a significant probability that any planet supporting life will eventually give rise to an intelligent species capable of tool use and a high-technology civilization.
  • If a high-technology civilization becomes capable of interstellar travel, even using very slow methods, it should be able to colonize the entire galaxy within a few million years. If easier or faster interstellar travel turns out to be possible, that process could take considerably less time.
  • Therefore, we should see evidence of previous visits to and colonization of our own solar system. Possibly a lot of such evidence.
  • We don’t. Where is everybody?

An astute reader will notice that there’s all manner of hand-waving in that argument. When Enrico Fermi walked through it back in 1950, we didn’t know very much about the galaxy around us. Most of the probabilities and quantities implicit in the argument were unclear. Today we have more evidence for a few items – we know that most stars probably have planets, for example, because we’ve detected thousands of them in recent years. Still, at a lot of points we’re arguing from a sample size of one – our own situation – and that’s always dangerous.

It’s entirely possible that Fermi’s observation isn’t a paradox at all. Perhaps life is much rarer than we assume. Or perhaps complex life is vanishingly rare – the universe may be crammed full of bacteria, with the appearance of big tool-using animals like us as an aberration. Or perhaps high-technology civilizations almost never figure out the trick of interstellar travel, either because they don’t survive long enough, or because interstellar travel is even harder than we think. We need more data.

On the other hand, when we want to design a space-operatic setting, we have to implicitly assign values to several of those quantities. So it behooves us to assign values that make sense together, and don’t run us straight into Fermi’s Paradox at warp speed.

I’d like to suggest the following general rule:

If a given science-fiction setting has multiple interstellar civilizations, and the typical civilization undergoes territorial expansion at a rate of 1% per year, then no civilization should be expected to survive longer than 1,000 years. For every factor of ten by which the growth rate is reduced, the allowable lifespan for interstellar civilizations will increase by a factor of ten.

The reasoning here is fairly straightforward.

Starting with a single fully occupied star system, a civilization which grows at 1% per year doubles its territory in not quite 70 years. Now it fully occupies two star systems (or, more likely, it has that one home system and small colonies in several other star systems). In another 70 years, it fully occupies four systems. In another 70 years, it fully occupies eight. The power of compound-interest expansion: in about 2,500 years that civilization has fully occupied one hundred billion star systems, and at that point the Milky Way is full to bursting.

If there are multiple interstellar cultures around, and that kind of growth is typical for them, then we have a problem. In the past billion years, Earth should have been overrun many times over. The Fermi Paradox is in full force, unless something comes along to eat civilizations for dinner long before they reach that point. That could be a recurring natural disaster, or an intelligent super-cultural force that cuts young civilizations short. Or maybe civilizations tend to stop their territorial expansion, turn to other concerns, and then die out. It’s your setting, your choice.

For the purpose of this general rule, I stipulate that the lifespan limit is only 1,000 years. This is a nice round number, and it permits us to assume the presence of many interstellar civilizations at any given time, all of them following the same dynamics of growth and decay.

If we want star-faring cultures to live longer, then we have to adjust the other parameter in the model, their typical rate of growth. Given how the math works, if we divide the growth rate by ten, the allowable lifespan in turn grows almost exactly by a factor of ten. So if we want our interstellar civilizations to last on the order of ten thousand years, we need to assume a growth rate of 0.1% per year. A hundred thousand years, 0.01% per year.

Notice what this says about interstellar cultures, assuming that we aren’t living in a “Rare Earth” universe in which there just aren’t any intelligent beings other than ourselves. The Fermi Paradox seems to suggest that longevity requires very slow growth. The growth rates required to permit the existence of million-year-old civilizations are so low that they’re just about indistinguishable from a steady state.

Perhaps this shouldn’t surprise us. After all, on our little planet and for most of human history, our own population growth rates were very low. Only the Industrial Revolution, and subsequent improvements in agricultural technology, sanitation, and medicine, permitted us to undergo a period of rapid expansion. Human population growth peaked at a little over 2% in the early 1960s, is currently back down to a little over 1%, and may not be sustainable at even that pace for very long. The galaxy as a whole is a much bigger field of endeavor . . . but given even a little time, compound interest has a way of overwhelming such differences in scale.

Now, notice one other implication: none of this should be a surprise to any culture that manages to figure out the trick of interstellar travel. By the time such a culture has been out among the stars for a while, it should have a good estimate for every parameter in the relevant mathematics. Which means that if our characters live in a fast-growing interstellar civilization, or they know of other such cultures, they should be very worried.

Why? Well, let’s look at a specific science-fictional universe that I’ve been playing with for some time: the one in the popular Mass Effect series of video games.

In Mass Effect, humanity emerges out into the galaxy in the mid-22nd century, to find a number of other interstellar civilizations already well-established. The oldest of these civilizations date back to about three thousand years ago. We learn of dozens or even hundreds of colony worlds settled in that time, some of them with populations in the billions, which would suggest a typical territorial growth rate that’s modest but still significant – say, about 0.2% or so per year. We also learn that there have been plenty of former interstellar cultures, all of them now extinct.

In the course of the first Mass Effect game, the protagonist discovers the existence of the Reapers, a force of godlike sentient machines that periodically sweep the Milky Way and exterminate all advanced civilizations. The story details the effort to delay the return of the Reapers, and then to defeat them and win the survival of galactic civilization once they do return.

It’s all very well-done space opera, with plenty of attention given to a plausible setting and plot. But there’s one detail that should set off alarms for us: the protagonist has a great deal of difficulty persuading anyone in authority that the Reapers even exist, until it’s far too late.

From one perspective, of course, this is fine. The hero forced to act on her own, because those in authority don’t take a threat seriously, is a perfectly useful trope to apply. Yet after we’ve given the Fermi Paradox some thought, we have to ask how the rulers of any galactic civilization could remain fully ignorant of the implications.

Notice what our general rule suggests for this universe. Interstellar cultures growing at about 0.2% per year tell us that the maximum lifespan for any civilization is somewhere around five thousand years. Most of that time has already passed. Just about everyone who’s paying attention should probably be looking around with a great deal of apprehension right now.

We know that interstellar travel is easy, and that civilizations can grow with significant speed. We know that there have been other interstellar cultures before our own. Why wasn’t the galaxy already full when we arrived? Why are all those other cultures extinct?

What made them extinct? What might be waiting to make us extinct before we manage to fill up the galaxy with our own colonies? Shouldn’t we be trying to find out?

If you’re a potential author, maybe your fictional galaxy won’t have anything in it like the Reapers. But there has to be something to keep the galaxy from becoming over-crowded, many times over during its long history. You need to take a moment and consider what that might be.

From FERMI'S NIGHTMARE by Sharrukin (2015)

Upper Limits

This is from a paper called Upper limits on the probability of an interstellar civilization arising in the local Solar neighborhood by Daniel Cartin.

The researcher was examining that part of the Fermi Paradox which was asking why the solar system was not colonized by aliens billions of years ago. Heck, after a couple of decades of examination by NASA et al we have not even found the battered remains of an alien space probe. Or any other signs of an extraterrestrial visit.

Dr. Geoffrey A. Landis proposed a possible solution based on Percolation Theory. But this analysis assumed that stars were arranged on simplistic cubic lattice, which seemed to Cartin to be a spherical cow. In an earlier paper, Cartin decided to use an actual dataset of the real positions of all known star systems within 40 parsecs (130 light-years).

In the earlier paper Cartin also turned the the analysis on its head. He made the question: supposing each star system is the point of origin for a space-faring civilization with a given sociological drive and technological prowess, how many could reach the Solar System with their colonization process?

Cartin made p the probability that an alien civilization arising on a given star will colonize a particular "neighbor" star system. Dmax is the maximum travel distance of the civilization's spacecraft (in parsecs), this determines which star systems are "adjacent." A Monte Carlo simulation was used to calculate the number of alien origin systems that could reach the Solar System (as a function of φ(p, Dmax).

However, for this paper, Cartin asked a different question: for this calculated function φ(p, Dmax) and the evident lack of visitors to the Solar System, what are the upper limits on the likelihood of spacefaring life originating on a given habitable planet, as a function of p and Dmax? In other words, since Terra don't got no alien tourists in all of history, can we figure the odds of starship riding aliens?

Cartin figures that obviously the number of alien civilizations reaching the solar system must be equal to the number of alien origin stars that could possibly reach us, multiplied by the probability of an alien star-faring civilization arising at each star system. Since there ain't no evidence that any aliens actually reached us, the probability of an alien species willing and able to execute a colonization program must be simply the inverse of the probability of such civilizations evolving in a given star system. Cartin uses a break-down of relevant factors in much the same format as the Drake equation in order to solve for the probability. And he also used the real star database of known stars within 40 parsecs.

The results are in the graph above.

Remember p the probability that an alien civilization arising on a given star will colonize a particular "neighbor" star system. Dmax is the maximum travel distance of the civilization's spacecraft (in parsecs).

The contour lines are the probability of ƒ times ƒS, where:

  • ƒ the fraction of planets in the habitable zone of the spectral class of the star in question that develop life
  • ƒS the fraction of life-bearing planets that go on to develop a star-faring civilization

(the two probabilities are multiplied because that's how you calculate the probability of both of them happening)

So the graph displays the contour lines of the maximum values of ƒ × ƒS of a star-faring alien civilization which actually reached our Solar System. For given values of p and Dmax. The lines are maximum values given the fact that apparently no alien civilizations actually reached the solar system.

In other words, you pick your best guess at alien-interstellar-empire-lust p, and starship-range Dmax, and the graph will tell you the maximum possible odds for the birth of an alien civilization that could have reached us.

Avatar's Dark Forest

Article names are a play on The Dark Forest Rule.


Diamond-hard science-fiction

When evoking the 2009 film Avatar, people may remember beautiful visuals, heavy-handed exposition, then-bleeding edge special effects, a hippie message with the subtlety of a terminal-velocity anvil, nice-looking combat scenes featuring the worst cavalry tactics since Agincourt (from Poland the Na'Vi are not), Pocahontas IN SPAAACE, one memorable dedicated villain, and yet another bland hero to out-native the natives and lead them against Big Evil Corp. All this is hiding a subtler, bleaker and more interesting narrative, in one of the hardest-SF stories ever featuring aliens.

Hard SF? Really?

A bold claim for a film with Space Blue Elf First Nations, but special care has in fact been given to keep everything as realistic as possible. For exemple, let's look at one of the very first shots of the film:

This may be the most realistic spacecraft from the entire history of film-making. In fact, it has a feature almost any type of spacecraft needs but that I have never seen elsewhere in any film or show ever: radiators. Specifically, badass giant red-glowing radiators to evacuate the massive waste heat produced by the kind of reactors a starship needs (and give both cool visuals and, in other works, potential plot points). While looking strange and completely unlike common SF starships, it feels believable and actually made for deep space — and that's because it is. It has been designed by actual astronautic engineers as a workable antimatter interstellar slower-than-light transport starship based on known science and what engineering could be developed once enough time and resources are sunk into it. This very design may well be built someday for interstellar missions. In fact, we could start working on it right now if we had enough industrial capacity in space (or enough rockets to launch said industrial capacity in orbit) and a more efficient way to produce and store antimatter. Two things that we know we could solve if enough time and money was dedicated to it. And if we learned about the impossibly vast amounts of money to be made by mining Pandora (more on that in the next part), the investment would probably be made - Avatar is the rare bird where even economics make sense.

One may wonder who in their right mind would give such a ridiculous name to such a technological marvel of space engineering, but there is precedent: VentureStar was the name of a promising Space Shuttle replacement program in the 1990, killed by politics after billions were invested. Had it been completed, it would have in fact borne an outward resemblance to the Valkyrie shuttles used for orbit-to-surface movement (we can see one near a docking port of the starship). After all, there are few known possible shapes for Single-Stage-to-Orbit shuttle crafts. This name is one of those cases where reality doesn't have to make sense the way fiction does.

Similarly, in lieu of the more outlandish designs that are common in soft-SF, human vehicles and weapons are grounded in reality. Weapons are variants of today's firearms and rockets. Flying vehicles are using existing technology, if more refined engineering. For example, ducted fans have advantages but are difficult to make at those dimensions and power levels. With lower gravity and higher atmospheric density in addition to advanced manufacturing techniques, they become a justifiable choice.

Mech suits are often glaringly unrealistic, but in this particular case, they make sense.

The main problem with bipedal vehicles is the unbearable pressure at the leg joints: as a biped is made taller, the weight supported by the joint, depending on volume, grows faster than the surface of said joints supporting it. This is why, on Earth, sea creatures can be much larger than land animals that have to use legs. Here, this problem is avoided in two ways: the AMP suits are reasonably small, and gravity is lower.

As to why use legs in the first place, legs are much more useful than wheels and threads in the uneven terrain of a jungle, and they can move faster and take less room than a multi-legged spider tank, while flying is energy-consuming and cause a nasty, noisy downwash.

Those suits are in fact used not unlike what is anticipated for exoskeletons today: for transporting heavier weapons, and for moving heavy charges around - a deceptively important job for any army. They are also useful for their enclosed cockpit and life support, allowing for greater autonomy and better environmental tolerances than portable gas mask and bottles. Air conditioning seems particularly useful in such a place.

Let's pay attention for a moment to the gas giant Polyphemus hanging behind the world Pandora in that shot of the starship. You will note that, in all shots for a given location, it is always in the exact same position in the sky. This is because Pandora is not a planet but a moon orbiting said gas giant, and as astronomers will tell you, such moon will always en up tidally locked, like the Moon is around Earth: the same side is always facing the orbited body. As such, the same way the Earth is always at the same position for a Moon-dwelling astronaut, Polyphemus lay immobile in the sky of Pandora.

This is especially visible when seeing distant lands, where the gas giant appears at a very different angle in the sky. Even without knowing the details of orbital mechanics, this change reinforces the impression of great distance already given by the very different biomes replacing the jungle. This is an interesting example of an obscure (to the audience) point of realism being used for great visual narrative effect.

Similarly, the environment appears believable because for the needs of the film, actual biologists came up with its elements and did their best to create as realistic a forest ecosystem as they could — but more on that below.

The always interesting Sci-Fi Interfaces (one of the inspirations for this blog) has yet to publish articles on the user interfaces of Avatar, but at a glance, they seem to be equally believable.

(For the sake of this analysis, the tomfoolery of quantum entanglement superluminal communication will be ignored. At most, we could suppose that the popular but utterly wrong explanation of how the system works has been propagated by shoddy, sensationalist journalism instead of, say, wormholes, and leave it at that. It is still diamond-hard SF, even if there is a chip in said diamond.)

Why is that important?

This is capital to determine the narrative contract between the author and the audience.

Now, the narrative contract is a rather grandiose-sounding for how the audience is determining what kind of story the work is about and building expectations based on it. For example, if you are reading gritty detective fiction set in the 1930, the narrative contract states that the story is set in a realistic historical environment. So the protagonist should not pull a smartphone and check on Wikipedia when needing to check a fact - unless this is a deliberate detail added to hint at a major reveal (like time travel or that it is all reenactment). On the other hand, if the big reveal is that someone was a Nazi spy, this would fit right in.

Similarly, whether a story is more unconstrained soft-SF or more realistic hard-SF sets different expectations, and tells us different things about what it is about.

Soft-SF can get away with unrealistic technology and different scientific principles, for example space fighters battling as if they were WWII naval planes, but it cannot rely on too advanced real science without first explicitly establishing it first. For example, Star Wars cannot suddenly start to include relativistic time effects after those has never been shown to exist, and would need to do some serious exposition first if the story needed those.

On the other hand, the base assumption of hard-SF is that everything works as we know it, even obscure science and advanced engineering, unless explicitly shown otherwise, and its world works exactly like the one we are living in.

Now that we established that Avatar is very carefully constructed hard-SF, having even called professional scientists and engineers of varied fields in order to be the most realistic, we cannot handwave seemingly unrealistic elements as "It's just [soft-]SF". We have to try and explain it, and accept the consequences on the story.

And there are very strange elements there indeed.

Pandora and Fermi

Pandora, the world where the action takes place, is very close to the Solar System. Travel from Earth to Pandora took less than 7 years with a not-so-far-future realistic slower-than-light starship. In fact, there are at the very most a few star systems that are close enough — indeed, supplemental material tells us that it is actually the Alpha Centauri system*, literally the closest one to ours.

* The star system is Alpha Centaury, and the planetary system (the planets orbiting one star) is Alpha Centaury C. Technically the Solar System is a planetary system, but I also include such independent planetary systems into the star system definition and this article is already way too long to play with nomenclature.

For reference, our galaxy contains literally hundreds of billions of star systems — there are about fifty star systems in or galaxy alone for each living human today. And there are at least as many galaxies in the Universe, and probably much, much more.

So it seems that among this literally unimaginable amount of star systems, literally our closest neighbour also contains a planet where complex life appeared. And this life, by the miracle of convergent evolution, looks pretty much exactly like our own: green trees, flowers, dandelion seeds, canine predators…

The whole ecosystem can feel unnatural, artificial, but this may be an artefact of its uncanny chance resemblance with our own.

Barring an astronomical coincidence, this tells us that life as we know it is common, and that it converges to Earth-like forms even in relatively different atmosphere and gravity. So among those countless stars of our galaxy, we can expect at least billions of them to have an Earth-like ecosystem with reasonable certainty.

Even if a rare local event had made possible the appearance of complex life a few hundred million years ago, it would still have had to affect a large portion of the galaxy, as Alpha Centauri C was nowhere near us at that time.

There is also the question of timing: life as we know it on Earth isn't that old, compared to the age of the Universe. Our galaxy is twelve billions years, and modern-looking life is a few hundred of billions old. For about 99% of its age, Earth looked less like what we know than Pandora does. And for twice as long, there wasn't even an Earth yet in the galaxy.

There is a hypothesis that gamma rays burst were more common in the past, and that until about a few billion years ago, direct hits would have regularly destroyed complex life before it had a chance to develop. Similarly, most galaxies today may still be uninhabitable.

So right as earth is born, the galaxy becomes inhabitable and life can develop, maybe the same is true for Pandora. Both develop at a similar pace, and somehow stumble into life as we know it at about the same time.

This is stretching probabilities and hypothesis a bit, but it is plausible. Had Pandora been devoid of intelligent life, if we discovered it today, it would restrict quite a few models but not fundamentally overturn them. We would have deduced that intelligent* life is vanishingly rare, with a probably of emerging and surviving to humanity's spacefaring levels of less than one in a billion from an Earth-like ecosystem.

After all, a technological civilization like ours is very visible: radio, antimatter-powered starships, stellar engineering, Dyson spheres everywhere, galactic energy networks… Those may look out of reach today, but their science is known, and they are "merely" engineering and industrial challenges. We can expect to take a dig at those in a few hundred thousand years, an instant for cosmic time. If elder civilisations, even by a measly few million years, had emerged before us, they could have already started engineering around the entire galaxy if not beyond, including in our own Solar system. We looked for signs of those. Hard. The sky is empty.

* "intelligent" being used here as an admittedly crude shorthand for "capable of making advanced tools and developing technology"

This is how we already know today that highly visible, Human-style technological civilisation is astronomically rare at best. And this is the basis of the Fermi paradox: with such a vast and ancient Universe, why are we seemingly the only ones around?

The obvious explanation is that the probability of emergence and survival to spacefaring stages is so low that, even if in absolute numbers there may be many others in the unfathomable vastness of the Universe, the closest ones are simply in galaxies too far away for us to detect them. After all, according to what we know, even the billions of light-years of the observable Universe are at best a tiny fraction of its total size.

This implies that something, generally called a Great Filter, is severely lowering the chances of spacefarers. Some have already been ruled out: we now know that planets are common, so it cannot simply be that most star systems are empty. Pandora would rule out rareness of life at all, procaryotes, multi-cell organisms and of complex life as we know it.

And our own history rules out that civilisations simply extinguish themselves: sure, we have had setbacks and way too many close calls, but our chances to survive those and future ones, even if in the low percents, is not nearly enough to balance the astronomical odds necessary for a Great Filter — think of it that way: even if one out of a thousand makes it to the stellar engineering phase, a million civilisations should still be running around if even one star system out of a hundred let a civilisation emerge.

Unfortunately for all parties involved, as we will see in Part II, Pandora was not devoid of intelligent life, which will bring us to evoke other solutions to the Fermi Paradox...

From AVATAR'S DARK FOREST - PART 1 by Eth (2018)

The Na'Vi anomaly

In the first part, we determined that perhaps surprisingly, Avatar is one of the most realistic hard-SF films ever produced. As such, seemingly unrealistic elements, that could simply be accepted in other settings, are jarring here and demand an explanation - namely our Space Blue Elves friends the Na'Vi.

The easy answer would be to declare it incoherent, that the author wanted Pocahontas with aliens and threw money at it to paint superficial realism. However, the easy answer is not always the most interesting - and, after all, "the author didn't care" is not what we are interested in here. Instead, let's see what conclusions we can draw from the seemingly impossible Na'Vi presence in a realistic setting.

Facing the Great Filter

In the previous article, we discussed the Fermi paradox and how the presence of an Earth-like ecosystem is restricting the possible solutions. However, Pandora also has a native technological society, and this may be the worst possible news humankind could ever get.

All the previous solutions discussed were based on an assumption: that the Great Filters that made technological life so vanishingly rare (one known space-faring civilisation in the local billion-light-years cube) are behind us, and we are the lucky ones that actually evolved to technological use. However, this implies that there has been, at most, very few technological species in the quintillion stars around us. Our own example show that, in cosmic time, a civilisation goes near-instantly from cutting stone to starships to, presumably, Dyson spheres everywhere. Our own example also tells us that the survival rate of such a species between those stades is at worst one in a few thousands, something we can round at 100% given the odds otherwise used working with Great Filters.

Given that assumption, what are the chances that one randomly chosen star system, say the one that happens to be the closest when we start throwing starships around, has a native technological civilisation? Around one in a quintillion, give or (mostly) take a few zeroes. Even if it was a trillion times more probable, scientists would still round it to zero without an afterthought.

Do the Na'Vi really count as a technological species? Of course: they have the same technological level than humankind a mere cosmic instant of ten thousand years ago — in fact, parts of humankind are still using those technologies right now. Blink and they may as well be making starships on their own. The important is not whether they cut stone or plutonium but whether they have the capabilities to build technological tools — and they indeed have the same as us: interpreted language, concepts, good hands and the understanding of making tools to make better tools. From there, Dyson spheres are only a matter of time and avoiding the occasional extinction event.

So the assumption that technological species are rare is ruled out. Those have to be so common, millions must be born in the galaxy right now. Which means that an unknown mechanism is systematically preventing technological civilisations from rising to visible galactic engineering levels. The Great Filter is still before us. Even worse: if we can understand that it is before us, then at least some others can as well. And if none have escaped it, it means that such knowledge won't help us either. The presence of a nascent technological species right next to us means, literally, that we are doomed to extinction.

Or does it?

Apes and Angels

As we have seen, technological species like ours are, at least at the pre-space level, extremely short-lived. And yet, right at the very moment we emerge, so do the Na'Vi. Even stranger, the Na'Vi are physically closer to humans than any other species to ever evolve on Earth. They are even closer to modern humans than most extinct human species, from whose we still bear DNA.

Which is especially weird when comparing other Pandoran animals with terrestrial ones: beyond superficial resemblance that could be attributed to convergent evolution, there are differences that are absent from the Na'Vi: armor plates on large animals, secondary breathing holes on the chest, multiple pairs of eyes, absence of hair...

And this is no mere outward resemblance: for it to be possible to mix their DNA with human DNA and create the Avatars in the first place, both would have to work on the same principle and be closer than with almost any species from Earth. This proves that convergent evolution is not the explanation here.

Finally, you would expect alien society and language, had they one in the first place, to be radically different from ours. And yet, a Na'Vi tribe could be dropped on some corner of the Earth after a few cosmetic changes and anthropologists wouldn't even notice the difference.

As such, coincidence alone cannot explain the existence of the Na'Vi. They necessarily have a link with humankind, which can be explained by the other particularity of Pandora

The alien behind the alien

The human expedition missed a capital point: the Na'Vi are not the only intelligence to dwell on Pandora. The biggest piece of evidence was also the easiest to overlook: an animist Na'Vi religion worshipping Eywa, a Mother Nature-like divinity linked to all living things. Earth has those, after all, and yet an alien overmind has yet to be discovered here.

However, the evidence missing on Earth is present on Pandora, to be discovered by a former soldier lacking the mental tools or training to realize what he found, or by scientists that fail to communicate their findings (scientist and science communicator are very different jobs) or, for that matter, realize that there is was much bigger picture to look at.

Those are obvious in retrospect. The Na'Vi neural queue, an organ that allows them to connect to many high-level life-forms all around the food chain and seemingly inexplicable by natural evolution. he Trees of Voice that are both part of an immense brain-like network of vast complexity - and the Na'Vi can use their neural queue to connect to it and hear their dead ancestors, whose mind is apparently preserved by said network. The Tree of Souls, described as a vital organ of Eywa and that can even create neural connections to humans directly, who testify directly talking to the overmind.

And, of course, commandeering varied animals in great numbers and in formation to destroy a human formation threatening said vital organ. Note that the human formation is attacked before the actual bombing starts, and less threatening vehicles were previously ignored, showing understanding of both human intent and abilities.

Eywa also repeatedly communicate with the Na'Vi by directing floating motiles, the woodsprites. It is shown to take interest in a specific human Avatar and direct the actions of a Na'Vi individual.

The obvious conclusion is that the Na'Vi were created by Eywa based on a detailed human template, showing both immense biotechnological prowess and advanced interstellar capabilities. The question is, why?

Now, it is always hazardous to divine intent from actions when lacking so much context, especially when applied to an unknown alien mind. However, we can make informed deductions from basic, universal logic.

First, we can expect Eywa to follow the same drives as any living organisms, or at least any that can survive long enough to evolve to such a degree: survival instinct and at least some drive to expansion and/or reproduction to compensate major accidents that may cause the death of the organism on an individual world. It has also demonstrated knowledge of humans and understanding of their behaviour, showing clear intend to learn about them.

As such, the most probable reason for the Na'Vi existence is to assist Eywa in studying humans.

Initially, they may or may not have been created for studying a human-like population in a controlled environment, the way we study rat behaviour by putting them in boxes in a laboratory. However, at the time of the depicted events, they are clearly there to directly interact with humans. We can see it when Eywa deliberately instruct a Na'Vi to interact with an Avatar with divergent behaviour. But the biggest clue is unobtanium.

Too good to be true

Unobtainium (with a 'i') is originally an engineering joke: a material that has all the proprieties needed, but either doesn't exist, is inaccessible or is too expensive. It has since then been adopted by science-fiction fans and critics to describe a material with fantastic properties that, while not forbidden by known science, does not seem to exist so far. This is a good way to take some liberties with known science and engineering while keeping the setting realistic, or at least believable.

Unobtanium (without the 'i'), to be found in vast quantities on Pandora and the reason the massive expenses of interstellar travel can see a return of investment, certainly qualify: a room-temperature superconductor with presumably massive power density, the figure of tens of millions of $ per kg (though inflation may give or take a few zeroes) is believable for present or near-future technology. Supplemental material hints as a grave energy crisis on Earth and unobtanium being used to build fusion reactors, which is indeed one of the obvious applications.

Now, some may say that it is a very stupid name to give to any actual material. Imagine if in Lord of the Rings, the One Ring was called the MacGuffin and Frodo's mithril shirt was the Plot Armor. However, remember in the first part: actual people called a high-technology space vehicle the VentureStar. And apparently, their heirs somehow thought it a good idea to use the same name for an interstellar vehicle. Those people have a history of giving very stupid names to incredible things.

Nevertheless, for it to be called that, and to be of such value, it is obviously incredibly, absurdly rare and impossible or near-impossible to manufacture in the Solar System. And yet, massive quantities of surprisingly pure Unobtanium mineral are to be found on a planet in the nearest star system, that also happens to host an alien overmind awaiting human interaction. Presumably no other nearby star system has such a mineral orgy, otherwise corporate interests would have avoided the headache of natives and go for the biggest profit.

The one thing that can drive humankind to stretch its nascent interstellar capabilities to their limit, but that is only worth so much due to the present conjoncture — specific technologies and industry and a major energy crisis that could have been avoided with better planning — and be presumably useless an instant before (steam machine don't use superconductors) and after (alternatives would be found). Again, this shows precise, up-to-date knowledge of humankind, impressive resources and a willingness to use them for this project.

This is the equivalent of some ancient Mediterranean merchants that would leave baubles on an unknown shore and go back on their boats to observe the natives. Were the natives interested in trade, they would take the baubles and replace them with local goods. The Na'Vi themselves may be the equivalent of repeating the words of the natives, while observing their reactions, in order to start deciphering their language — if it was human-shaped drones with speech generators that were sent instead of the actual merchants.

Unfortunately, humans took the baubles, replaced them with beach pebbles lying around, attempted to beat the drones and steal their things, and then got angry and started to throwing rocks around. All the while never realizing that those bizarre metal islands off shore that were't there yesterday had more firepower than a volcano chain.

Killing Star

It is, in fact, even worse: as humankind reach interstellar capabilities, and with explosive technological and industrial progress, it becomes by nature a menace to any neighbour. Take the VentureStar, for example. The only difference between a transport starship and an interstellar relativistic missile (ISRM) is that a transport ship carries giant engines to brake when reaching destination. And an ISRM has enough kinetic energy from its velocity alone to devastate an entire planet. This only gets worse once you start making Dyson spheres, those can be used for example to emit Nicoll-Dyson lasers.

If a nascent spacefaring civilisation shows risks of using such means for violence, the obvious move to protect one's own survival is to destroy them before they can do serious damage. This is the Killing Star scenario.

And humankind has just showed itself to be violent, unreliable, often irrational, aggressive, divided, untrustworthy, cunning, expansionist and with fast-expanding capabilities. Which is, in fact, the worst, most dangerous combination possible.

Even if Eywa had reasons to avoid a first strike, it now has to extinguish the human menace for its own survival.

Note that a human first strike against Eywa, following the same Killing Star reasoning, would be futile. Not only can we expect it to be but one of many worlds hosting such planetary mind, it also has superior interstellar capabilities than humans, and ones that are so far undetectable to human sensors - despite the vast energies required for interstellar, well, anything. So even assuming that Eywa can be destroyed by a surprise human attack before launching its own second strike (and assuming Pandora contains the whole individual), and this is a big if already, there are unknown but presumably vast numbers of other worlds ready to second strike anyway.

A merciless ecological indictment

This, beyond the trompe l’œil Hollywood story, is the actual message of the film. Whether the author intended it so is unknown* but irrelevant: hidden depth, accidental or otherwise, is still depth.

* I would bet against it, but don't mind old cynical me and give him the benefit of the doubt

You can be certain that even without knowing about the presence of an actual alien, many scientists recognized what was going on the first time science probes or teams were sent on Pandora. Native near-human life and unobtainum were obvious enough clues. However, powerful corporate interests and, presumably, corrupt demagogic governments afraid of the energy crisis, controlled by people both incapable of understanding the science or caring about long-term consequences, overruled them.

Those consequences are (literally) calling the wrath of (a) Mother Nature (alien star god) upon humankind, in ways that are difficult to grasp in their details but obvious in the absolute, inevitable catastrophe they will bring. One could even imagine self-deluding populists claiming that whatever bad happens, we will be able to fix it with some techno-industrial solution. Or that if some alien wants war, we'll simply beat them.

Sounds familiar?

So it seems that ultimately, yes, humankind is now doomed to extinction — not by a Great Filter, this time, but its own tragically avoidable folly. Or is it? As we will see next, even star gods are afraid of the dark…

From AVATAR'S DARK FOREST - PART 2 by Eth (2018)

Exterminomachy and Consequences

RocketCat sez

This is really nasty, but far too plausible. There are too many human beings who would find the paranoid logic to be perfectly reasonable.

It's sort of like a self-fulfilling Berserker Hypothesis.


Little is known of the culture, former civilization, and even biology of the skrandar species. Extreme xenophobes, they had little interaction with the species of the Worlds even post-contact. The destruction of their homeworld along with the rest of Skranpen (Charred Waste)’s1 inner system in the self-induced nova of their sun (on detecting the relativistic approach of the Serene Fleet) has left little archaeological evidence available for study. Even the name of the Skranpen system, like that of the species, is phonemically generated and institute-assigned. What little is known of the skrandar is based on abstractions from damaged and disabled examples of the skrandar berserker probes and the two identified replication sites captured in the Exterminomachy.

What has been extracted from these sources (see declassified reports tagged PYRETIC PHAGE) suggests that the skrandar were in the grip of a peculiar type of madness at the end. It is believed among crypto-archaeologists that the skrandar had a preexisting cultural obsession with the Precursor Paradox: namely, why, when we see evidence of elder races and Precursor civilizations aplenty, and both life and intelligence appear to be relatively common within the Starfall Arc, has the galaxy not been colonized and/or hegemonized long since by ancient civilizations?

(Indeed, given the relative isolation of the Skranpen system, this paradox must have weighed even more heavily on the minds of the skrandar than on those species which originated in more populous galactic neighborhoods.)

The leading hypothesis, therefore, is that xenognosis came as a severe trauma to the skrandar; upon seeing the impossible, in the light of a presumed filter preventing starfaring civilizations from existing, they collectively went mad. If, they reasoned, there was – must be – some reason for the destruction of starfaring civilizations, then they themselves could only escape that fate by becoming that reason. And so they turned as a species to the manufacture of berserker probes designed to cull all other sapient, starfaring life.

It is easy for us today, looking back on the Exterminomachy, to attribute the tragedy of the skrandar solely to some inherent flaw in the species. But consider this: the skrandar were isolated, by their own choice. They had the opportunity, therefore, to go mad quietly, unknown to the rest of the civilized galaxy, hearing no voices but their own unreason.

For this reason, among others, the Exploratory Service at this time maintains its pro-contact, pro-intervention, pro-socialization policy towards emerging species. Whatever the short-term cultural impact of xenognosis might be, in the longer term, they very much endorse the view that an ounce of prevention today is better than a gigaton of cure tomorrow.

1. While identified here as a system of the Charred Waste constellation, the Skranpen system is not connected to the stargate plexus; it is, however, located centrally in the constellation in real space.







(ed note: OMRD stands for "Office of Military Research and Development")

From CONSEQUENCES by Alistair Young (2015)

Radio Silence


That is the expected number of intelligent civilizations in our galaxy, according to Drake’s famous equation. For the last 78 years, we had been broadcasting everything about us – our radio, our television, our history, our greatest discoveries – to the rest of the galaxy. We had been shouting our existence at the top of our lungs to the rest of the universe, wondering if we were alone. Thirty-six million civilizations, yet in almost a century of listening, we hadn’t heard a thing. We were alone.

That was, until about five minutes ago.

The transmission came on every transcendental multiple of hydrogen’s frequency that we were listening to. Transcendental harmonics – things like hydrogen’s frequency times pi – don’t appear in nature, so I knew it had to be artificial. The signal pulsed on and off very quickly with incredibly uniform amplitudes; my initial reaction was that this was some sort of binary transmission. I measured 1679 pulses in the one minute that the transmission was active. After that, the silence resumed.

The numbers didn’t make any sense at first. They just seemed to be a random jumble of noise. But the pulses were so perfectly uniform, and on a frequency that was always so silent; they had to come from an artificial source. I looked over the transmission again, and my heart skipped a beat. 1679 – that was the exact length of the Arecibo message sent out 40 years ago. I excitedly started arranging the bits in the original 73 x 23 rectangle. I didn’t get more than halfway through before my hopes were confirmed. This was the exact same message. The numbers in binary, from 1 to 10. The atomic numbers of the elements that make up life. The formulas for our DNA nucleotides. Someone had been listening to us, and wanted us to know they were there.

Then it came to me – this original message was transmitted only 40 years ago. This means that life must be at most 20 lightyears away. A civilization within talking distance? This would revolutionize every field I have ever worked in – astrophysics, astrobiology, astro-

The signal is beeping again.

This time, it is slow. Deliberate, even. It lasts just under five minutes, with a new bit coming in once per second. Though the computers are of course recording it, I start writing them down. 0. 1. 0. 1. 0. 1. 0. 0... I knew immediately this wasn’t the same message as before. My mind races through the possibilities of what this could be. The transmission ends, having transmitted 248 bits. Surely this is too small for a meaningful message. What great message to another civilization can you possibly send with only 248 bits of information? On a computer, the only files that small would be limited to…


Was it possible? Were they really sending a message to us in our own language? Come to think of it, it’s not that out of the question – we had been transmitting pretty much every language on earth for the last 70 years… I begin to decipher with the first encoding scheme I could think of – ASCII. 0. 1. 0. 1. 0. 1. 0. 0. That’s B... 0. 1. 1 0. 0. 1. 0. 1. E…

As I finish piecing together the message, my stomach sinks like an anchor. The words before me answer everything.


From RADIO SILENCE credited to bencbartlett ()

The Dark Forest Rule

In 2006 author Liu Cixin wrote a novel named 三体 (The Three-Body Problem) which won the Chinese Science Fiction Galaxy Award in 2006 and the 2015 Hugo Award for Best Novel. It proposed a solution to the Fermi Paradox which was plausible enough to get analyzed in a paper published in the Journal of the British Interplanetary Society (The Dark Forest Rule: One Solution to the Fermi Paradox).

It is very similar to the scenario set out in Pelligrio & Zebrowski's The Killing Star.

The Dark Forest Rule has two basic hypotheses:

  1. Survival is the primary requirement of civilization
    (civilizations that don't care if they live or die won't last long)

  2. Civilization grows and expands continuously, whereas the total cosmic materials remain constant
    (all warfare boils down to two monkeys and one banana)

and two basic concepts:

  1. Suspicion Chain: poor communication between different civilizations in the universe results in civilizations distrusting each other
    (you can't trust that mysterious tribe who lives over the hills, I'll bet you they have horns growing out of their heads and eat human flesh)

  2. Technology Explosion: technologies in civilizations may achieve explosive breakthroughs and development at any time, which are beyond the accurate estimation of any distant civilization with its own technological level
    (you never know when some other nation will unexpectedly invent the Ultimate Weapon while your back is turned)

The result of combining these hypotheses and concepts:

  1. Civilizations in the universe are competing for resources
    (there ain't enough to share)

  2. Civilization cannot trust other civilizations
    (because they have horns growing out of their heads and eat human flesh)

  3. Civilizations cannot be confident about the advancement of their technology
    (at any moment those horned flesh eaters who want our galactic resources might invent a Nicoll-Dyson Beam and kill us all)

In other words It's The Law Of The Jungle. "Every man for himself," "anything goes," "need of the sole outweights the need of the many," "survival of the strongest," "survival of the fittest," "kill or be killed," "dog eat dog" and "eat or be eaten." Basically the "state of nature" as proposed by Thomas Hobbes.


“Universe is a dark forest. Every civilization is a hunter with gun in hand and he sneaks in the forest. He must be careful enough as there are other hunters in the forest. If he discovered other lives, he can only do one thing: shoot it. In this forest, other lives are hell and constant threats. Any life that will expose his existence will be killed soon. This is the picture of universe civilizations”

From THE THREE-BODY PROBLEM by Liu Cixin (2006)

The hypothesis "survival is the primary requirement of civilization" is not saying that there are no alien civilzations that are moral-advocating or selfless. The hypothesis is saying that such civilizations will be slaughtered by survivalist civilizations. Much like how the Roman civilization was defeated by the Goths and the Song Dynasty was defeated by Mongolian cavalry. In other words "nice guys finish last."

The hypothesis "civilization grows and expands continuously, whereas the total cosmic materials remain constant" does not mean that civilizations will fight because they are greedy for all the resources. It means civilization will fight because they do not know how many resources will ensure survival, the only safe assumption is "all of them." In a broader sense all activities of all living civilizations increase entropy (by the second law of thermodynamics). Therefore other civilizations must be killed to slow down the heat death of the universe, thus prolonging the time for this civilization to live.

The limit of the speed of light means that two-way communication between civilizations can take years to centuries. This helps create the suspicion chain. But even with rapid communication you will instantly find yourself in the middle of The Prisoner's Dilemma which is the suspicion chain raised to the second power.

In addition, even limited communication with another civilization might inadvertently trigger in them a technological explosion, and suddenly you will find that you've brought a knife to a gun fight.

Given all that, the only safe strategy is to instantly try and kill any alien civilizations you come across. Especially since chances are they will have followed the same train of logic, and will instantly try to kill you once they discover you exist.

If you kill them, the worst thing that might happen is you'll discover they were a non-expanding moral-advocation race. Which is a shame, but even so they were creating entropy.

If you leave them alone, you are rolling the dice and risking the extinction of your entire species.

Of course when you try to kill them, you'll have to be covert about it. Just in case they turn out to be more powerful than you are. You'll have to try to avoid letting them discover that your species even exists in the first place. Keeping in mind that if they are incredibly more advanced than you are, they will have found you first and you are doomed. But there isn't much you can do about that. Given the "Apes or Angels" scenario, chances are there will be a huge technological inequality between the two civilizations. Meeting between civilizations of the same tech level will be rare.

The big draw-back to instantly killing a newly discovered alien civilization is that another ultra-highly advanced alien civilization will notice your attack (that is, a civilization vastly more advanced than you are). Then they will probably obliterate you. If you are worried about that, the best strategy is to try and hide your entire civilization, and avoid contact with anyone.

Unless the ultra-highly advanced alien civilization does not obliterate you, for fear that a third ultra-ultra-ultra-highly advanced alien civilization will notice the attack and obliterate them.

So, the answer to the Fermi Paradox is either:

  1. All the other civilizations have been killed except for a couple of bloodthirsty ones

  2. All the other civilizations are doing their best to hide, either to avoid attracting the attention a killer civilization or because they are a killer civilzation which thinks that killing is too much of a risk

The Killing Star

From The Killing Star by Charles Pellegrino and George Zebrowski (you really should read this book):

The great silence (i.e. absence of SETI signals from alien civilizations) is perhaps the strongest indicator of all that high relativistic velocities are attainable and that everybody out there knows it.

The sobering truth is that relativistic civilizations are a potential nightmare to anyone living within range of them. The problem is that objects traveling at an appreciable fraction of light speed are never where you see them when you see them (i.e., light-speed lag). Relativistic rockets, if their owners turn out to be less than benevolent, are both totally unstoppable and totally destructive. A starship weighing in at 1,500 tons (approximately the weight of a fully fueled space shuttle sitting on the launchpad) impacting an earthlike planet at "only" 30 percent of lightspeed will release 1.5 million megatons of energy -- an explosive force equivalent to 150 times today's global nuclear arsenal... (ed note: this means the freaking thing has about nine hundred mega-Ricks of damage!)

I'm not going to talk about ideas. I'm going to talk about reality. It will probably not be good for us ever to build and fire up an antimatter engine. According to Powell, given the proper detecting devices, a Valkyrie engine burn could be seen out to a radius of several light-years and may draw us into a game we'd rather not play, a game in which, if we appear to be even the vaguest threat to another civilization and if the resources are available to eliminate us, then it is logical to do so.

The game plan is, in its simplest terms, the relativistic inverse to the golden rule: "Do unto the other fellow as he would do unto you and do it first."...

When we put our heads together and tried to list everything we could say with certainty about other civilizations, without having actually met them, all that we knew boiled down to three simple laws of alien behavior:


    If an alien species has to choose between them and us, they won't choose us. It is difficult to imagine a contrary case; species don't survive by being self-sacrificing.


    No species makes it to the top by being passive. The species in charge of any given planet will be highly intelligent, alert, aggressive, and ruthless when necessary.



Your thinking still seems a bit narrow. Consider several broadening ideas:

  1. Sure, relativistic bombs are powerful because the antagonist has already invested huge energies in them that can be released quickly, and they're hard to hit. But they are costly investments and necessarily reduce other activities the species could explore. For example:
  2. Dispersal of the species into many small, hard-to-see targets, such as asteroids, buried civilizations, cometary nuclei, various space habitats. These are hard to wipe out.
  3. But wait -- while relativistic bombs are readily visible to us in foresight, they hardly represent the end point in foreseeable technology. What will humans of, say, two centuries hence think of as the "obvious" lethal effect? Five centuries? A hundred? Personally I'd pick some rampaging self-reproducing thingy (mechanical or organic), then sneak it into all the biospheres I wanted to destroy. My point here is that no particular physical effect -- with its pluses, minuses, and trade-offs -- is likely to dominate the thinking of the galaxy.
  4. So what might really aged civilizations do? Disperse, of course, and also not attack new arrivals in the galaxy, for fear that they might not get them all. Why? Because revenge is probably selected for in surviving species, and anybody truly looking out for long-term interests will not want to leave a youthful species with a grudge, sneaking around behind its back...

I agree with most parts of points 2, 3, and 4. As for point 1, it is cheaper than you think. You mention self-replicating machines in point 3, and while it is true that relativistic rockets require planetary power supplies, it is also true that we can power the whole Earth with a field of solar cells adding up to barely more than 200-by-200 kilometers, drawn out into a narrow band around the Moon's equator. Self-replicating robots could accomplish this task with only the cost of developing the first twenty or thirty machines. And once we're powering the Earth practically free of charge, why not let the robots keep building panels on the Lunar far side? Add a few self-replicating linear accelerator-building factories, and plug the accelerators into the panels, and you could produce enough anti-hydrogen to launch a starship every year. But why stop at the Moon? Have you looked at Mercury lately? ...

Dr. Wells has obviously bought into the view of a friendly galaxy. This view is based upon the argument that unless we humans conquer our self-destructive warlike tendencies, we will wipe out our species and no longer be a threat to extrasolar civilizations. All well and good up to this point.

But then these optimists make the jump: If we are wise enough to survive and not wipe ourselves out, we will be peaceful -- so peaceful that we will not wipe anybody else out, and as we are below on Earth, so other people will be above.

This is a non sequitur, because there is no guarantee that one follows the other, and for a very important reason: "They" are not part of our species.

Before we proceed any further, try the following thought experiment: watch the films Platoon and Aliens together and ask yourself if the plot lines don't quickly blur and become indistinguishable. You'll recall that in Vietnam, American troops were taught to regard the enemy as "Charlie" or "Gook," dehumanizing words that made "them" easier to kill. In like manner, the British, Spanish, and French conquests of the discovery period were made easier by declaring dark- or red- or yellow-skinned people as something less than human, as a godless, faceless "them," as literally another species.

Presumably there is some sort of inhibition against killing another member of our own species, because we have to work to overcome it...

But the rules do not apply to other species. Both humans and wolves lack inhibitions against killing chickens.

Humans kill other species all the time, even those with which we share the common bond of high intelligence. As you read this, hundreds of dolphins are being killed by tuna fishermen and drift netters. The killing goes on and on, and dolphins are not even a threat to us.

As near as we can tell, there is no inhibition against killing another species simply because it displays a high intelligence. So, as much as we love him, Carl Sagan's theory that if a species makes it to the top and does not blow itself apart, then it will be nice to other intelligent species is probably wrong. Once you admit interstellar species will not necessarily be nice to one another simply by virtue of having survived, then you open up this whole nightmare of relativistic civilizations exterminating one another.

It's an entirely new situation, emerging from the physical possibilities that will face any species that can overcome the natural interstellar quarantine of its solar system. The choices seem unforgiving, and the mind struggles to imagine circumstances under which an interstellar species might make contact without triggering the realization that it can't afford to be proven wrong in its fears.

Got that? We can't afford to wait to be proven wrong.

They won't come to get our resources or our knowledge or our women or even because they're just mean and want power over us. They'll come to destroy us to insure their survival, even if we're no apparent threat, because species death is just too much to risk, however remote the risk...

The most humbling feature of the relativistic bomb is that even if you happen to see it coming, its exact motion and position can never be determined; and given a technology even a hundred orders of magnitude above our own, you cannot hope to intercept one of these weapons. It often happens, in these discussions, that an expression from the old west arises: "God made some men bigger and stronger than others, but Mr. Colt made all men equal." Variations on Mr. Colt's weapon are still popular today, even in a society that possesses hydrogen bombs. Similarly, no matter how advanced civilizations grow, the relativistic bomb is not likely to go away...

We ask that you try just one more thought experiment. Imagine yourself taking a stroll through Manhattan, somewhere north of 68th street, deep inside Central Park, late at night. It would be nice to meet someone friendly, but you know that the park is dangerous at night. That's when the monsters come out. There's always a strong undercurrent of drug dealings, muggings, and occasional homicides.

It is not easy to distinguish the good guys from the bad guys. They dress alike, and the weapons are concealed. The only difference is intent, and you can't read minds.

Stay in the dark long enough and you may hear an occasional distance shriek or blunder across a body.

How do you survive the night? The last thing you want to do is shout, "I'm here!" The next to last thing you want to do is reply to someone who shouts, "I'm a friend!"

What you would like to do is find a policeman, or get out of the park. But you don't want to make noise or move towards a light where you might be spotted, and it is difficult to find either a policeman or your way out without making yourself known. Your safest option is to hunker down and wait for daylight, then safely walk out.

There are, of course, a few obvious differences between Central Park and the universe.

There is no policeman.

There is no way out.

And the night never ends.

From THE KILLING STAR by Charles Pellegrino and George Zebrowski

Regarding your discussion of the "Killing Star" hypothesis, I have an interesting analysis I haven't seen elsewhere. It relies on the fact that technology is not static, and the likelihood that it's a lot easier to build a relativistic interceptor operating over planetary distances than it is to build a relativistic missile operating over interstellar ones.

If two interstellar civilizations A and B discover one another (and we assume no faster-than-light travel), there are three possible relative technology levels: A is more advanced, B is more advanced, or A and B are at an exactly equivalent level.

If A is more advanced, they have nothing to fear from B. (Consider the immense difference in capabilities between an F-15 and an F-22, despite the fact that the F-22 is only a couple of decades more advanced.) A's defenses can probably stop any attack by B and their retaliation for any attack would likely wipe B out. So A has no reason to launch a pre-emptive strike against B, because it's more cost-effective to just build interceptors (which can also be used against any hypothetical C, D, etc.). And as with nuclear war, the interceptors don't have to be 100% effective — just effective enough to make B uncertain that his attack will leave A unable to retaliate. By the same token it would be suicide for B to try an attack against a more advanced A.

If B is more advanced, the same reasoning applies in reverse.

If A and B are (miraculously) at exactly the same level of technology, then A might decide it's necessary to launch a pre-emptive attack against B. But here's the kicker: if A launches a fleet of relativistic kill vehicles, they are obsolete when they arrive at B by the distance in light-years between A and B. A's attack is likely to fail. B's retaliation will, too. Consequently they have no reason to attempt strikes against each other.

While this doesn't necessarily refute the Zebrowski "kill them on detection" hypothesis, it does introduce enough uncertainty that rational alien civilizations might decide it's less risky to try peaceful coexistence first.

From James Cambias (2006)

Attacking with relativistic rockets may be a good idea if there are only two technological species, but if there are two then it seems to me that it is likely there will be more. Using a relativistic rocket to destroy a planet will reveal your position AND indicate that you are hostile to any possible third race that is out there.

To extend the Central Park analogy, the muzzle flash when you fire off your gun reveals your position and identifies that you are hostile to anyone else out there.

Bill Seney

After The Killing Star I found a flaw in Pellegrino's logic, called him, explained it to him, and he conceded the point.

Here it is: OK, you've detected radio signals from X light years away and, following the logic, prepare to send a planet-killer at the source. Only ... will the civilization still be killable by a single fractional-C strike when you get there? If it isn't, you now have definitely pissed-off neighbors that want you dead. And civilizations advance.

By the time you've registered the signal and can send a planet-killer back, optimistic assumptions about the speed of your NAFAL (not as fast as light) drives (say, 0.2c) suggest it's been a minimum of 6 * X years since the target civilization's radio output became detectable (which will be some time after the discovery of radio).

Everything hinges on your estimate of the interval between commencement of large-scale radio emissions and self-sufficient offworld colonies; call that N. The radius in lightyears beyond which you don't dare try for the kill is N / 6 . For a reasonable conservative assumption about N — say, 300 years, that comes to 50 lightyears. Not a large distance.

Go ahead and play with the assumptions — speed of NAFAL drives, the radio-to-colonies interval. It's pretty hard to come up with a plausible scenario in which launching the civ-killer looks like a good idea.

Eric Raymond (2015)

Run To The Stars

From Run To The Stars by Michael Scott Rohan (1982). The heroes have discovered the Dreadful Secret that the BC world government is hiding: explorers have discovered the first known alien species, and BC is sending a huge missile to kill all the aliens.

"Alien," muttered Ryly, and coughed rackingly, unpleasant in the confined space. "The Colony - people, that was different, but - Bellamy, hey, hold on. Think a minute. So what you say's true - couldn't the BC still be right? I mean, these're aliens, man! Better we'd never contacted them, but now they've found us - hell, we can't trust them! We can't be sure! It's the human race at stake."

"Ye're sayin' that genocide - worse than that, even - that ye like the idea?" demanded Kirsty.

"Hell, no, think I'm Stalin or somethin'? Like I said - better we'd laid low, shut up, kept to ourselves, safe, Earth and the Colony both. But these things, we can't afford to take a risk with them! Better the missile cleans the mistake off the slate, things quiet down an' we're safe again. I don't like it, I hate it - but then I'm not so wild about some of the things you feel you were justified in doin' either..."

..."Ryly, you're no fool, but you're bloody well talking like one. That missile can be tracked, man! With the mass it'll have by the time it connects it'll leave a wake of gravitational disturbance - on interstellar radiation, for a start - pointing right back this way. That's why it's a one-shot weapon - no second chances! Safe? What's safe? As if we could somehow hide away from the rest of the universe. Not as long as we use any kind of broadcast communication, we can't Think of it! Just round here, in our own little neighborhood, three planets inhabited, two with intelligent life, two with roughly the same kind of life! There must be millions of inhabited worlds out there, whatever the experts spout. Some like us, some not. Sooner or later one of them's bound to track back our communications overspill and find us. What then? Under the bed?"

"If that missile hits the target," said Kristy venomously, "we'll have tae hide. Shrink back into our own wee system, never make a noise, never stir outside it. What if any other race ever found out what we'd done? Then we'd never be safe. They'd never trust us. Not for an instant. There's bound to be some of them who think like you, Ryly. We'd be giving them grand evidence, wouldn't we? They'd wipe us out like plague germs and feel good about it!"

My own imagination was striking sparks off Kirsty's and kindling an evil flame. "Unless..." I began, and actually had trouble shaping the thought. "Unless we got them first. At once, on first contact. A pre-emptive strike, before they could possibly have a chance to find out about us. Hellfire, isn't that a glorious future history for us! A race of paranoid killers, skulking in our own backwater system when we might have had the stars! Clamping down on exploration, communications, anything that might lead someone else to us and make us stain our hands again with the same old crime... Carrying that weight down the generations. What would that make of us?"

"Predators," breathed Kirsty, "Carrion-eaters - no, worse, ghouls, vampires, killing just tae carry on our own worthless shadow-lives."

From RUN TO THE STARS by Michael Scott Rohan (1982)


Daniel Krouse brought to my attention some important new ideas on this matter:

Peter Watts wrote a book, "Blindsight" that covers a first contact scenario from a new and interesting angle ... I wanted to share with you an excerpt that I feel would serve as a good example on your Aliens page. It has a lot in it actually, as the whole of it tackles first contact from an evolutionary and game theory POV and raises some good points (such as the possibility that even our TV signals could be considered a hostile action). But my favorite bit and the part I include here is where he expands on Powell and Pellegrino's 3 assumptions with a 4th one: Technology implies belligerence.

Daniel Krouse

Once there were three tribes. The Optimists, whose patron saints were Drake and Sagan, believed in a universe crawling with gentle intelligence — spiritual brethren vaster and more enlightened than we, a great galactic siblinghood into whose ranks we would someday ascend. Surely, said the Optimists, space travel implies enlightenment, for it requires the control of great destructive energies. Any race which can't rise above its own brutal instincts will wipe itself out long before it learns to bridge the interstellar gulf.

Across from the Optimists sat the Pessimists, who genuflected before graven images of Saint Fermi and a host of lesser lightweights. The Pessimists envisioned a lonely universe full of dead rocks and prokaryotic slime. The odds are just too low, they insisted. Too many rogues, too much radiation, too much eccentricity in too many orbits. It is a surpassing miracle that even one Earth exists; to hope for many is to abandon reason and embrace religious mania. After all, the universe is fourteen billion years old: if the galaxy were alive with intelligence, wouldn't it be here by now?

Equidistant to the other two tribes sat the Historians. They didn't have too many thoughts on the probable prevalence of intelligent, spacefaring extraterrestrials — but if there are any, they said, they're not just going to be smart. They're going to be mean.

It might seem almost too obvious a conclusion. What is Human history, if not an on going succession of greater technologies grinding lesser ones beneath their boots? But the subject wasn't merely Human history, or the unfair advantage that tools gave to any given side; the oppressed snatch up advanced weaponry as readily as the oppressor, given half a chance. No, the real issue was how those tools got there in the first place. The real issue was what tools are for.

To the Historians, tools existed for only one reason: to force the universe into unnatural shapes. They treated nature as an enemy, they were by definition a rebellion against the way things were. Technology is a stunted thing in benign environments, it never thrived in any culture gripped by belief in natural harmony. Why invent fusion reactors if your climate is comfortable, if your food is abundant? Why build fortresses if you have no enemies? Why force change upon a world which poses no threat?

Human civilization had a lot of branches, not so long ago. Even into the twenty-first century, a few isolated tribes had barely developed stone tools. Some settled down with agriculture. Others weren't content until they had ended nature itself, still others until they'd built cities in space. We all rested eventually, though. Each new technology trampled lesser ones, climbed to some complacent asymptote, and stopped — until my own mother packed herself away like a larva in honeycomb, softened by machinery, robbed of incentive by her own contentment. (ed note: Read the book for that bit to make sense)

But history never said that everyone had to stop where we did. It only suggested that those who had stopped no longer struggled for existence. There could be other, more hellish worlds where the best Human technology would crumble, where the environment was still the enemy, where the only survivors were those who fought back with sharper tools and stronger empires. The threats contained in those environments would not be simple ones. Harsh weather and natural disasters either kill you or they don't, and once conquered — or adapted to — they lose their relevance. No, the only environmental factors that continued to matter were those that fought back, that countered new strategies with newer ones, that forced their enemies to scale ever-greater heights just to stay alive.

Ultimately, the only enemy that mattered was an intelligent one.

And if the best toys do end up in the hands of those who've never forgotten that life itself is an act of war against intelligent opponents, what does that say about a race whose machines travel between the stars? The argument was straightforward enough. It might even have been enough to carry the Historians to victory — if such debates were ever settled on the basic of logic, and if a bored population hadn't already awarded the game to Fermi on points. But the Historian paradigm was just too ugly, too Darwinian, for most people, and besides, no one really cared any more. Not even the Cassidy Survey's late-breaking discoveries changed much. So what if some dirtball at Ursae Majoris Eridani had an oxygen atmosphere? It was forty-three light years away, and it wasn't talking; and if you wanted flying chandeliers and alien messiahs, you could build them to order in Heaven. (ed note: Again, read the book to understand Heaven) If you wanted testosterone and target practice you could choose an afterlife chock-full of nasty alien monsters with really bad aim. If the mere thought of an alien intelligence threatened your worldview, you could explore a virtual galaxy of empty real estate, ripe and waiting for any God-fearing earthly pilgrims who chanced by. It was all there, just the other side of a fifteen-minute splice job and a cervical socket. Why endure the cramped and smelly confines of real-life space travel to go visit pond scum on Europa?

And so, inevitably, a fourth Tribe arose, a Heavenly host that triumphed over all: the Tribe that Just Didn't Give A Sh*t. They didn't know what to do when the Fireflies showed up. So they sent us, and — in belated honor of the Historian mantra — they sent along a warrior, just in case. It was doubtful in the extreme that any child of Earth would be a match for a race with interstellar technology, should they prove unfriendly. Still, I could tell that Bates' presence was a comfort, to the Human members of the crew at least. If you have to go up unarmed against an angry T-rex with a four-digit IQ, it can't hurt to have a trained combat specialist at your side.

At the very least, she might be able to fashion a pointy stick from the branch of some convenient tree.

From BLINDSIGHT by Peter Watts (2006)

We Know You Are Out There


We made a mistake. That is the simple, undeniable truth of the matter, however painful it might be. The flaw was not in our Observatories, for those machines were as perfect as we could make, and they showed us only the unfiltered light of truth, The flaw was not in the Predictor, for it is a device of pure, infalliable logic, turning raw data into meaningful information without the taint of emotion or bias. No, the flaw was within us, the Orchestrators of this disaster, the sentients who thought themselves beyond such failings. We are responsible.

It began a short while ago, as these things are measured, less than 66 Deeli ago, though I suspect our systems of measure will mean very little by the time anyone receives this transmission. We detected faint radio signals from a blossoming intelligence 214 Deelis outward from the Galactic Core, as photons travel. At first, crude and unstructured, these leaking broadcasts quickly grew in complexity and strength, as did the messages they carried. Through our Observatories we watched a race of strife and violence, populated by a barbaric race of short-lived, fast-breeding vermin. They were brutal and uncultured things which stabbed and shot and burned each other with no regard for life or purpose. Even their concepts of Art spoke of conflict and pain. They divided themselves according to some bizarre cultural patterns and set their every industry to cause of death.

They terrified us, but we were older and wiser and so very far away, so we did no fret. Then we watched them split the atom and breech the heavens within the breadth of one of their single, short generations, and we began to worry. When they began actively transmitting messages and greetings into space, we felt fear and horror. Their transmissions promised peace and camaraderie to any who were listening, but we had watched them for too long to buy into such transparent deceptions. They knew we were out here, and they were coming for us.

The Orchestrators consulted the Predictor, and the output was dire. They would multiply and grow and flood out of their home system like some uncountable tide of Devourer worms, consuming all that lay in their path. It might that 68 Deelis, but they would destroy us if left unchecked. With aching carapaces, we decided to act, and sealed our fate.

The Gift of Mercy was 84 strides long with a mouth 2/4 that in diameter, filled with many 44 weights of machinery, fuel, and ballast. It would push itself up to 2/8th of light speed with its onboard fuel, and then begin to consume interstellar Primary Element 2/2 to feed its unlimited acceleration. It would be traveling at nearly light speed when it hit. They would never see it coming. Its launch was a day of mourning, celebration, and reflection. The horror of the act we had committed weighed heavily upon us all; the necessity of our crime did little to comfort us.

The Gift had barely cleared the outer cometary halo when the mistake was realized, but it was too late. The Gift could not be caught, could not be recalled or diverted from its path. The architects and work crews, horrified at the awful power of the thing upon which they labored, had quietly self-terminated in droves, walking unshielded into radiation zones, neglecting proper null pressure, safety or simply ceasing their nutrient consumption until their metabolic functions stopped. The appalling cost in lives had forced the Orchestrators to streamline the Gift's design and construction. There had been no time for the design or implementation of anything beyond the simple, massive engines and the stablizing systems. We could only watch in shame and horror as the light of genocide faded in infrared against the distant void.

They grew, and they changed, in a handful of lifetimes. They abolished war, abandoned their violent tendencies and turned themselves to the grand purpose of life and Art. We watched them remake first themselves, and then their world. Their frail, soft bodies gave way to gleaming metals and plastics, they unified their people through an omnipotent communications grid and produced Art of such power and emotion, the likes of which the Galaxy has never seen before. Or again, because of us.

They converted their home world into a paradise (by their standards) and many 106s of them poured out into the surrounding system with a rapidity and vigor that we could only envy. With bodies built to survive every environment from the day-lit surface of their innermost world, to the atmosphere of their largest gas giant and the cold void in between, they set out to sculpt their system into something beautiful. At first we thought them to be simple miners, stripping the rocky planets and moons for vital resources, but then we began to see the purpose to their construction, the artworks carved into every surface, and traced across the system in glittering lights and dancing fusion trails. And still, our terrible Gift approached.

They had less than 22 Deeli to see it, following so closely on the tail if its own light. In that time, oh so brief even by their fleeting lives, more than 1010 sentients prepared for death. Lovers exchanged last words, separated by worlds and the tyranny of light speed. Their planet-side engineers worked frantically to build sufficient transmission to upload countless masses with the necessary neural modification, while those above dumped lifetimes of music and literature from their databanks to make room for passengers, Those lacking the required hardware of the time to acquire it consigned themselves to death, lashed out in fear and pain, or simply went about their lives as best they could under the circumstances.

The Gift arrived suddenly, the light of its impact visible in our skies, shining bright and cruel even to the unaugmented ocular receptor. We watched and we wept for our victims, dead so many Deelis before the light of their doom had even reached us. Many 64s of those who had been directly or even tangentially involved in the creation of the Gift sealed their spiracles was past as a final penance for the small roles they had played in this atrocity. The light dimmed, the dust cleared, and our Observatories refocused upon the place where their shining blue world had once hung in the void, and found only dust and the pale gleam of an orphaned moon, wrapped in a thin, burning wisp of atmosphere that had once belonged to its parent.

Radiation and relativistic shrapnel had wiped out much of the inner system, and continent-sized chunks of molten rock carried screaming ghosts outward at interstellar escape velocities, damned to wander the great void for an eternity. The damage was apocalyptic, but not complete. From the shadows of the outer worlds, tiny points of light emerged, thousands of fusion trails of single ships and world ships and everything in between, many 106s of survivors in flesh and steel and memory banks, ready to rebuild. For a few moments we felt relief, even joy, and we were filled with the hope that their culture and Art would survive the terrible blow we had dealt them. Then came the message, tightly focused at our star, transmitted simultaneously by hundreds of their ships.

"We know you are out there, and we are coming for you."


From WE KNOW YOU ARE OUT THERE by Panini's Cupcake (2008)

Why I Don't Worry


Last time I explained why I don't lie awake nights worrying that contact with extraterrestrial civilizations will lead to humanity getting conquered by invading alien armies. It's just too hard to be worth the effort.

But what if the aliens don't want to conquer the Earth? What if they just want to wipe us out?

It's actually easier to destroy rival civilizations across interstellar distances than it is to conquer them. Conquest, after all, involves fairly large armies, supplies — and above all, deceleration when the starships reach the target system. Relativisitic warheads don't need any reaction mass or energy to slow down (though they might need a motor for terminal guidance). A few bricks hitting the Earth at 99.9 percent of lightspeed would do as much damage as the asteroid which killed the dinosaurs. (And those bricks could be intelligently targeted to maximize the harm they do.)

At least one conference, featuring the likes of Isaac Asimov and Jill Tarter (I can't find a link to reference it), proposed that launching a salvo of relativistic projectiles would be the optimum strategy for any species which so much as detects another advanced civilization nearby. Get them before they get us!

As with interstellar conquest, I don't buy it. There are sound logical reasons why first strikes across interstellar distances are very bad ideas.

Hi There! Launching an interstellar death-barrage is not something you can hide. The energy output of a relativistic rocket is very bright. Any civilization with immense space-based telescopes (like the kind we're planning to use for detecting extrasolar planets) can spot them at arbitrarily large distances. If the projectiles are launched using some kind of ground-based laser or maser system, the launching beam is like a beacon shining in the direction of the target.

This is important for two reasons.

First, the target world gets some warning that the strike is on its way. That means they can they could launch a counter-strike during the flight time of the projectiles.

(How do they know it's a salvo of projectiles rather than a fleet of friendly starships? The color and brightness of the exhaust reveals the energy output involved; the Doppler shift reveals the acceleration profile and thus the mass of the payload. If someone's launching small objects at very high velocities, it's not a friendly gesture. About the only way to fool the target is to go all-in and launch a very big projectile, at a velocity which might match the mission profile for a starship. But when the "starship" fails to start decelerating, the target system still gets a clue something is amiss, and a slower vehicle could be intercepted.)

Second, other civilizations can also see this happening — civilizations the would-be genocidal lunatics don't know about. And even if you're kind of on the fence about the wisdom of firing off pre-emptive genocidal relativistic kill-vehicle attacks on other civilizations, watching someone else do it would overcome a lot of objections, and move the demonstrated genocidal lunatics to the top of everyone else's hit list. So … don't do it.

Time Lag, Again. I think we all agree that attacking a superior civilization is a bad idea, right? Some piddly Kardashev Class I outfit decides to take pot-shots at a big-time Kardashev II crew, they're gonna get messed up but good. Stands to reason.

This means, of course, that if you are a big-time Kardashev II civilization, you really don't have to worry much about the Kardashev I peons bothering you. They may be primitive, but they're not stupid. They know you can mess them up if they start something.

So nobody's going to be shooting at superior civilizations, and nobody's going to be shooting at inferior civilizations, either. What does that leave? Well, you can target civilizations at about your level of technology, just in case they have similar ideas about you.

See the problem yet? Time lag! Suppose you launch your attack at a peer civilization 50 light-years away. Even if the missiles are going nearly the speed of light, they're still going to spend half a century getting there. During which time the target civilization has half a century of technological progress. So if your aggressors are Stalin's Russia, launching the missiles in 1950, the weapons arrive in Clinton's America in 2000, equipped with interceptors which can easily handle them.

This is especially important because of course you can't know just how much progress a distant civilization will make during the transit time. Maybe you're advanced enough to catch them off-guard and wipe them out … but maybe you aren't, and now you've got an implacable enemy.

Of course, the odds of even detecting a peer or near-peer civilization are remote. Given the immense age of the universe and the long time-scale of life on Earth, it's highly improbable that any aliens we detect would be close to us in technology. It's far more likely that we'll pick up indications of Godlike Kardashev II civilizations, or send out probes which observe species just figuring out how to make tools, than beings with similar capabilities to our own.

The gods are safe from us, and we're safe from the primitives. So nobody has to get pre-emptively violent.

Deterrence. Once you're capable of building weapons which can strike across interstellar distances, you're also capable of hiding weapons across interstellar distances — tucking away a little counter-strike force in nearby star systems, or deep in the Kuiper Belt. There's no way for an attacker to know in advance if you've got some entertaining surprises in store — and the consequences for that attacker are likely to be dire if you do.

This means that the rational assumption, for anyone interested in keeping their species and civilization intact, is to assume all possible adversaries have just such a counterforce in being. So don't attack them.

If I can think of these things, so can alien strategic planners. And really, it's difficult to imagine any being with the ability to construct interstellar vehicles thinking it's a good idea to launch unprovoked attacks on newly-discovered civilizations. There are simply too many unknowns.

So that's why I don't worry about E.T. trying to wipe us out. Back to whatever you were doing.


For stories about primitive and super-advanced extraterrestrials, buy my ebook Outlaws and Aliens!

The Prisoner's Dilemma

The problem of whether to commit genocide upon an alien race or not is vaguely related to the famous "prisoner's dilemma".

The problem is that the Prisoner's Dilemma makes it all too likely that Paranoia beats reason. For those unfamiliar with it... here's the Space version.

Race A and B both have roughly comparable technology, but don't understand each other. Each race has 2 options: Launch missiles or Ignore each other.

If Both races open fire, both races are devastated but not destroyed.

If one race opens fire and the other ignores it, they're utterly exterminated.

If both races ignore each other, they live in peace and are fine.

The problem is, neither can really communicate with each other. And although the cooperative choice of ignoring each other is best, the risks of them firing first while you ignore them are too great. Thus, this scenario via game theory, will always result in missiles being exchanged.

Laura 'Nephtys' Reynolds
Race B IgnoresRace B Attacks
Race A IgnoresBoth live constant fearRace A exterminated
Race B lives free of fear
Race A AttacksRace A lives free of fear
Race B exterminated
Both are devastated but not destroyed

As the Wikipedia article shows, the dilemma comes when you assume that each race is trying to maximize it's survival.

Say you are Race A. If Race B ignores you, your best outcome is to attack. Then you do not have to live in fear, spend resources on building defenses, and so on. If race B attacks, your best outcome is still to attack, since the alternative is extermination.

And since Race B will make the same determination, both races will attack and be devastated but not destroyed.

An outside observer will note that if the two races are taken as a group, the best outcome of the group is for both races to cooperate. If either attacks, the outcome for the group will be worse. And if both attack, both races receive a worse outcome than if they had both ignored each other.

So if both races selfishly look out for themselves, both will attack and the result is devastation. If both races altruistically think about the group, both will ignore and both will live. And if one race is selfish while the other is altruistic, yet again it will be proven that nice guys finish last.

And it actually doesn't matter if they can communicate with each other or not, a given race cannot be sure if the other is being truthful. If the two races can communicate, they run into the "cooperation paradox". Each race must convince the other that they will take the altruistic option despite the fact that the race could do better for themselves by taking the selfish option.

Cooperatewin some-win somelose all-win all
Defectwin all-lose alllose some-lose some
CooperateD, DC, B
DefectB, CA, A

Of course the prisoner's dilemma is a very artificial set-up, in real life the results would not be quite so clean-cut. To the right are two formulations of the prisoner's dilemma matrix.

In the Detailed matrix, A, B, C, and D are various outcomes, and the relative value of the outcomes are B > D > A > C. If those relative values are true, the prisoner's dilemma is present. In the first example, B = alive and free from fear, D = alive but in constant fear, A = alive but devastated and C = exterminated.

The prisoner's dilemma does have some vague similarities to the old cold war doctrine of Mutual Assured Destruction, though they are actually not very closely related. The prisoner's dilemma also does not work in those cases where what is bad for one player is equally bad for the other. An example is the game of "chicken" as seen in the 1955 film Rebel Without A Cause, where the drivers of both cars race to a deadly cliff and the first one to "chicken out" loses. But game theorists are working on a new approach called "Drama Theory" (warning: commercial website. No endorsement implied.)

"Gently, Sandy," First Lieutenant Cargill interjected. "Dr. Horvath, I take it you've never been involved in military intelligence? No, of course not. But you see, in intelligence work we have to go by capabilities, not by intentions. If a potential enemy can do something to you, you have to prepare for it, without regard to what you think he wants to do."

From THE MOTE IN GOD'S EYE by Larry Niven and Jerry Pournelle (1975)

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