Now we are really sailing off into terra incognito. "Here be dragons" and all that. But if you have starships, you almost have to have aliens (Isaac Asimov's Foundation trilogy being the most notable exception). The "science" is called Astrobiology, the famous "science in search of a subject". Unfortunately it only offers vague generalities. You can keep up on the latest news, but for now if you want aliens, you are going to have to create them yourself.

Suggested reading includes The Encyclopedia of Science Fiction's entry on "Aliens", Steve Colgan's Worlds of Possibility blog, Life Everywhere by David Darling, The Science of Aliens by Clifford Pickover and Aliens and Alien Societies by Stanley Schmidt.


[first use unknown]

Sometimes contrasted with `sentient' because even low animals can feel. `sapient' is usually an adjective, `sophont' usually a noun.


[first use unknown, but goes back at least to 1940s]

General SF term for an extraterrestrial or alien possessing human-level intelligence (see sophont).

Etymologically, and in mainstream English the word means "feeling" but is rare and now archaic.


[From Poul Anderson's `Polesotechnic League' stories, going back at least to 1963]

An evolved biological intelligence. Implies human-level cognitive and linguistic ability but not necessarily tool use. More specific and etymologically correct than sentient. Still less common than that term, but has been used by multiple writers.

From An SF Glossary by Eric S. Raymond (2006)

sapient, adjective \ˈsā-pē-ənt, ˈsa-\

Possessing or expressing great sagacity

sentient, adjective \ˈsen(t)-sh(ē-)ənt, ˈsen-tē-ənt\

Able to feel, see, hear, smell, or taste. Responsive to or conscious of sense impressions. Aware

ALIENS. Intelligent races who are not EARTH HUMANS. The term as such is never used for non-intelligent species, however unearthly, though in TECHJARGON these may be called Alien Life Forms. Nor is it used for Earth Humans who must register with the immigration service. In general, Aliens fall into two distinct groups, REALLY ALIENS and ALIENS WITH FOREHEAD RIDGES.

1) Really Aliens are truly unearthly. Frequently reported species include Energy Beings, HIVE ENTITIES, Giant Insectoids (who may also be Hive Entities), and Blobs of Protoplasm. The occasional intelligent bear or radish may also appear, or practically anything else. Except for the Energy Beings, most seem to be hydrocarbon life forms, but methane breathers who thrive at -200 C will sometimes turn up.

What they all have in common is that they are Really Alien. Exosemanticists have their work cut out understanding them, and exopsychologists in figuring out what they're all about. Relations between humans and Really Aliens are necessarily limited, since we have so little in common with them. Only rarely will anybody get to know one on a personal level. TRADE with them is sporadic, and even WARFARE seems less frequent than it used to be in the GOLDEN AGE. This is partly because it is not clear what we would fight them over, and partly because they may have an alarmingly high TECHLEVEL, making war with them a dangerously one-sided proposition. Dangerous at least for us. See COSMIC BACKGROUND HISTORY.

2) Aliens with Forehead Ridges. Much more common - especially in HOLLYWOOD SCIFI - than Really Aliens, these are species that look almost exactly like Earth Humans, except for some distinguishing visible feature such as, well, forehead ridges, or odd-shaped ears, or whatever. Sometimes they look rather less like humans, in which case (if friendly) they often resemble large teddy bears.

Not only do Aliens with Forehead Ridges mostly look like Earth Humans, they tend to act like Earth Humans as well, or at least one particular (real or speculative) Earth Human culture. A particular race of Aliens with Forehead Ridges may all have a culture like that of medieval Japan, or one based entirely on music, but you will very rarely find more than one culture per species. (The Vulcans and Romulans of Trek fame are a rare exception.)

Because of the similarity (or at least comprehensibility) of cultures, Earth Humans can have far more complex and intimate relations with Aliens with Forehead Ridges than with Really Aliens. We can not only communicate, Trade, and fight, but form joint business ventures, cheat each other at cards, and even fall in love.

Indeed, Aliens with Forehead Ridges raise a profound question in evolutionary biology. Convergent evolution might well produce a generally humanoid body plan, just as sharks and dolphins have a similar overall configuration. But Aliens with Forehead Ridges have much more than a general similarity to Earth Humans. They have the same secondary sex traits - as species-specific as you can get. Only their males have much facial hair, and their females often have bodacious figures. Often, indeed, they are INTERBREEDABLE species. This leads to some speculation that they may be of Earth Human descent. (Or else Earth Humans are descended from them, though this raises troublesome questions about chimpanzees.)

Perhaps because of these awkward issues, Aliens with Forehead Ridges have become much less common in written SF (save for media tie-ins) than they were some decades ago. In written SF, the KNOWN GALAXY seems increasingly to be inhabited only by Earth Humans. However, Aliens with Forehead Ridges continue to thrive in Hollywood Scifi. This is for an obvious reason: the audience wants aliens of some sort, and Aliens with Forehead Ridges are the only kind that can be played by members of the Screen Actors' Guild.

Alien Biology

Building Blocks

In a science essay "Not As We Know It" (VIEW FROM A HEIGHT, 1963), Isaac Asimov notes that life on Terra is based on proteins dissolved in water solvent. He points out some other possibilities. Note that the "temperature" column has the information needed to set the borders of a solar system's circumstellar habitable zone for that particular biochemistry. Temperatures assume the planet has about 1 atmosphere worth of pressure.

Macromolecule in
at 1 Atm
Fluorosilicones in Fluorosilicones 400°? to
500°? C
Silanes (chains of silicon atoms) are too unstable. Silicones (chains alternating silicon and oxygen atoms) are more suitable for making "silicon life" protein analogues.

James Cambias notes that such life will consume carbon dioxide (and other carbon compounds) out of the air, combining it with silicon to create complex silicone compounds. Oxygen will be released but that will immediately combine with silicon to make silicon dioxide sand. The atmosphere will become depeleted in carbon dioxide. This might cool the planet off enough that fluorocarbon-sulfur life will take over the planet.
Fluorocarbons in Molten Sulfur113° to
445° C
Earth proteins are too unstable at liquid sulfur temperatures. They can be stabilized by substituting fluorine atoms for hydrogen atoms, resulting in complex fluorocarbons.

James Cambias notes that such life forms will probably evolve in an atmosphere poor in oxygen but rich in fluorine. However, such life will create atmospheres with oxygen as they release oxygen from carbon dioxide+sulfur dioxide as their metabolism creates complex fluorocarbon molecules. There actually might be enough oxygen in the atmosphere for humans to breath (but the temperature would kill them).
Proteins in Water0° to
100° C
Because water is hydrogenated oxygen, the proteins will have to have more oxygen than nitrogen in their make up. This is "life as we know it." Pretty much all life on Terra falls under this catagory.

James Cambias notes that such life will consume carbon dioxide out of the atmosphere and release oxygen, thus converting the planet's primordial atmosphere into a biologic oxygen containing atmosphere.
Proteins in Liquid Ammonia-77.7° C to
-33.4° C
Because ammonia is hydrogenated nitrogen, the proteins will have more nitrogen than oxygen in their make up. Earth proteins are too stable at liquid ammonia temperatures, ammonia life proteins will have to be more unstable than their Earth analogues.

James Cambias notes that such life forms will probably require a planet with a methane-ammonia atmosphere. As with protein-water life, it will consume carbon dioxide and produce oxygen. However, the oxygen will react with methane to produce carbon dioxide and water. The water will immediately freeze out of the atmosphere, the carbon dioxide will be consumed. Thus the atmosphere will gradually lose all its methane and become much lower in pressure.
Lipids in Liquid Methane-183.6° C to
-161.6° C
Polar liquids will not dissolve non-polar substances and vice versa (oil and water don't mix). Proteins are polar, so they won't dissolve in liquid methane. Complex protein-like polylipids will have to be used instead.

James Cambias notes that such life forms will probably require a planet with a methane-hydrogen atmosphere. As with protein-water life, it will consume carbon dioxide and produce oxygen. However, the oxygen will react with methane to produce carbon dioxide and water while the oxygen will react with hydrogen to produce more water. The water will immediately freeze out of the atmosphere, the carbon dioxide will be consumed. Thus the atmosphere will gradually lose all its methane and hydrogen thus becoming much lower in pressure.
Lipids in Liquid Hydrogen-253° C to
-240° C
Liquid hydrogen is also non-polar, so polylipids will be needed.

James Cambias notes that the temperature will be much higher in the immense pressures of a gas giant world.

In classic science fiction, the buzz-word was "Silicon-based Life". Life on Terra is based on Carbon, since carbon can join with not one, not two, not even three, but a whopping four other atoms. This allows the construction of complex molecules like proteins and DNA, a requirement for living creatures. The only other element that can do this is Silicon, so the SF writers seized it. They are also fond of harping on the fact that while most carbon-based animals on Terra exhale gaseous carbon dioxide, a poor silicon-based critter would breath out silicon dioxide, i.e.,sand. In "A Martian Odyssey" by Stanley Weinbaum is a silicon life creature that "exhales" bricks of silicon dioxide, which it uses to build a pyramid around itself.

Other chemical elements that are not impossible as the basis for alien life forms include ammonia, boron, nitrogen, and phosphorus. There are even more extreme possibilities.

There are several possibilities for the composition of alien blood. But when it comes to telepathy, you are on your own (perhaps you could use the Laws of Magic).

In James Blish's The Star Dwellers, the "angels" are a species of energy creature that inhabit nebulae, and love to curl up in the cozy warmth of a starship's Nernst-effect fusion reactor. They are long-lived, the eldest were born shortly after the birth of the universe about 13 billion years ago. The Starfish from Glen Cook's Starfishers are vast creatures composed of fusion fires and magnetic fields. The human Starfishers protect the Starfish from the "sharks", and in exchange the Starfish give "ambergris nodes" which are the sine qua non of tachyon communication equipment. Magnetic nebula life appears in William Tedford's Nemydia Deep and "magnetovores" (i.e., organisms that consume magnetism) living in the solar corona are in David Brin's Sundiver. There are photovores around the galactic core in Gregory Benford's Sailing Bright Eternity (also described in Benford's article in the August 1995 issue of Fantasy & Science Fiction magazine, A Scientist's Notebook: Life at Galactic Center).

An example of electronic life is the superconducting mentality in Sir Arthur C. Clarke's "Crusade".

One of the odder aliens is the Qax from Stephen Baxter's Timelike Infinity. Their "bodies" are organized clusters of millions of tiny whirlpools in still ponds. Another odd one was the Monolith Monsters. They were not invading aliens so much as an extraterrestrial chemical reaction. Instant monster: just add water.

Ain't Gonna Look Like Mr. Spock

But even if you handwave that away and declare that there are lots of different species of aliens, there is plenty of room for imagination. Especially in the alien's anatomy. Just here on Terra, we can find jellyfish, tarantulas, viruses, and giraffes. Face it, if these fellow Earth-creatures don't resemble us, a totally alien race from another planet ain't gonna look like Mr. Spock. Personally if I open an SF novel only to discover yet another cat-like alien I may need a nausea bag.

There is a good list of aliens with truly alien body types in TV Tropes.

There might be creeping jellies, giant crystals, intelligent plants, mobile fungoids, energy creatures, fusion plasma beings dancing in solar coronas, liquid or gaseous life, swarming hive intelligences, superintelligent shades of the colour blue, and natural "electronic" life forms in pools of liquid helium. They might not be made of meat. They might not even be composed of matter as we know it, like the Cheela from Dr. Robert Forward's Dragon's Egg who are made of neutronium and white dwarf star matter.

Some extraterrestrial creatures inhabit the depths of space itself. In Sir Arthur C. Clarke's Childhood's End was a creature that lived in deep space among asteroid belts. It resembled a huge eye, about twenty feet in diameter. Its survival depended upon the range and resolving power of its eye. Large creatures include the living O'Neil colonies in John Varley's Gaean trilogy and the living planet from Stanislaw Lem's Solaris. Biggest of all is the intelligent nebula from Fred Hoyle's The Black Cloud. Well, actually Olaf Stapedon's intelligent galaxies in Star Maker are bigger, but let's not get carried away.

A "hive" intelligence would resemble an intelligent ant-hill, where each ant would be but a cell in the hill's "body". Individual ants may die, but the hill goes on. Examples include the "Boaty Bits" from FARTHEST STAR by Jack Williamson and Frederik Pohl, the "Godtalkers" from THE DRAGON NEVER SLEEPS by Glen Cook, the "Tinker Composite" from THE MIND POOL by Charles Sheffield, the "Mantis" from GREAT SKY RIVER by Gregory Benford, and the Martians from LAST AND FIRST MEN by Olaf Stapedon. If the alien is composed of a hive of several species, it is some times called an "anthology intelligence." Go to The Tough Guide to the Known Galaxy and read the entry "HIVE ENTITY".

A good example of a hive intelligence was in Olaf Stapedon's classic Star Maker. The "cells" composing an individual were free-flying birds linked telepathically. Birds might be born or die, but the flock-individual lived on. A more modest version were the "Tines" in Vernor Vinge's A Fire Upon The Deep. One might even consider an anthill to be a hive organism, an individual who's cells are ants.

And don't forget the inflatable aliens from John Brunner's The Crucible of Time. Or the bizarre one from Damon Knight's Stranger Station.

HIVE ENTITY. A type of REALLY ALIEN intelligent species - one of the most Really Alien of all - organized along lines rather like the social insects. In a Hive Entity, individuals members of the community count for nothing, and indeed most of them have no individual intelligence to speak of. They are specialized for various functions (particularly warriors), and exist entirely to serve the Hive Entity as a whole.

A Hive Entity's intelligence may reside in specialized "brain" individuals, which have only vestigial legs and even digestive systems, and are themselves entirely dependent on various kinds of "slave" individuals. Or the intelligence may somehow be spread out collectively though the whole Hive Entity, each individually-mindless inhabitant in effect contributing a few neurons to the whole. (Or some combination of these.) Some Hive Entities may not really be intelligent at all, but have evolved the ability to blow up other people's spacecraft the same way that some ants have evolved the ability to keep aphids as cattle.

When encountered in the KNOWN GALAXY, Hive Entities are almost invariably hostile. They apparently have nothing to offer in trade, much less arts or ideas, and you can't even negotiate a peace treaty with them, because there isn't really anyone to negotiate with. In WARFARE they are at once mindlessly ruthless - attacking in endless waves like giant army ants, which they also tend to look like - and malevolently intelligent. Putting no value on their own automaton lives, they obviously have no concept of valuing anyone else's.

In fact, Hive Entities are basically the ultimate totalitarians. It is no surprise that they appeared in written SF, so far as I know, around the mid 20th century CE, the same time that giant ants showed up in HOLLYWOOD SCIFI. Hive Entities were, and are, Nazis, Stalinists, and ChiComs, magnified to the Nth degree and let loose to give better races a harsh lesson in the precious value of individualism.

Which is really too bad. Taken in themselves, Hive Entities are a fascinating concept, precisely because they really are Really Alien. Yet if in fact they are intelligent, they must have ideas of some sort, however hard for them to express in a way we can understand. If the intelligence is spread through the hive community, the time scale of its thinking might be drastically slower than our own, maybe taking weeks to form the equivalent of a sentence. This indeed could make them tricky to deal with at first, since on our time scale they would necessarily act on reflex.

But if we EARTH HUMANS, and similar species, really want to demonstrate individual intelligence, we might actually try figuring the Hive Entities out, and see if we and they might have something to contribute to each other, instead of fighting pretty mindless wars with them. Don't hold your breath, though. It hasn't happened in fifty years, so far as I know.

But maybe the Hive Entities' mental time scale is longer than that.

From The Tough Guide to the Known Galaxy by Rick Robinson

Nowhere in space will we rest our eyes upon the familiar shapes of trees and plants, or any of the animals that share our world. Whatsoever life we meet will be as strange and alien as the nightmare creatures of the ocean abyss, or of the insect empire whose horrors are normally hidden from us by their microscopic scale.

Sir Arthur C. Clarke, 1962

"As I remember," he said, collecting his thoughts rapidly, "the biologists asked themselves the question, 'If we had no preconceived ideas, and were starting with a blank sheet of paper-how would we design an intelligent organism?"'

"I'm not much of an artist," Floyd apologized, after he had managed to borrow paper and pencil, "but the general conclusion was something like this."

He sketched quickly, and when he had finished Mr. Kelly said, "Ugh!"

"Well," chuckled Floyd, "beauty lies in the eye of the beholder. And talking of eyes, there would be four of them, to provide all-round vision. They have to be at the highest part of the body, for good visibility-so."

He had drawn an egg-shaped torso surmounted by a small, conical head that was fused into it with no trace of a neck. Roughly sketched arms and legs were affixed at the usual places.

"Getting rid of the neck removes a fundamental weakness, we only need it because our eyes have a limited field of view, and we have to turn our heads to compensate."

"Why not a fifth eye on top, for upward vision?" asked Kaminski, in a tone of voice which showed what he, thought of the whole concept.

"Too vulnerable to falling objects. As it is, the four eyes would be recessed, and the head would probably be covered with a hard protective layer. For the brain would be somewhere in this general region-you want the shortest possible nerve connections to the eyes, because they are the most important sense organs."

"Can you be sure of that?"

"No-but it seems probable. Light is the fastest, longest-ranging carrier of information. Any sentient creature would surely take advantage of it. On our planet, eyes have evolved quite independently, over and over again, in completely separate species, and the end results have been almost identical."

"I agree," said Whitehead. "Look at the eye of an octopus-it's uncannily human. Yet we aren't even remote cousins."

"But where's the thing's nose and mouth?" asked Mrs. Kelly.

"Ah," said Floyd mischievously, "that was one of the most interesting conclusions of the study. It pointed out the utter absurdity of our present arrangements. Fancy combining gullet and windpipe in one tube and then running that through the narrow flexible column of the neck! It's a marvel we don't all choke to death every time we eat or drink, since food and air go down the same way."

Mrs. Kelly, who had been sipping at a highball, rather hastily put it down on the buffet table behind her.

"The oxygen and food intakes should be quite independent, and in the logical places. Here."

Floyd sketched in what appeared to be, from their position, two oversized nipples.

"The nostrils," he explained. "Where you want them- beside the lungs. There would be at least two, well apart for safety."

"And the mouth?"

"Obviously-at the front door of the stomach. Here."

The ellipse that Floyd sketched was too big to be a navel, though it was in the right place, and he quickly destroyed any lingering resemblance by insetting it with teeth.

"As a matter of fact," he added, "I doubt if a really advanced creature would have teeth. We're rapidly losing ours, and it's much too primitive to waste energy grinding and tearing tissues when we have machines that will do the job more efficiently."

At this point, the Vice-President unobtrusively abandoned the canape he had been nibbling with relish.

"No," continued Floyd remorselessly. "Their food intake would probably be entirely liquid, and their whole digestive apparatus far more efficient and compact than our primitive plumbing."

"I'm much too terrified to ask," said Vice-President Kelly, "how they would reproduce. But I'm relieved to see that you've given them two arms and legs, just like us."

"Well, from an engineering viewpoint it is quite hard to make a major improvement here. Too many limbs get in each other's way; tentacles aren't much good for precision work, though they might be a useful extra. Even five fingers seems about the optimum number; I suspect that hands will look very much the same throughout the universe even if nothing else does."

"And I suspect," said Kaminski, "that the people who designed our friend here failed to think far enough ahead. What's the purpose of food and oxygen? Why, merely combustion, to produce energy-at a miserable few percent efficiency. This is what our really advanced extraterrestrial will look like. May I?"

He took the pen and pad from Floyd, and rapidly shaded the egg-shaped body until the air and food intakes were no longer visible. Then, at waist level, he sketched in an electric power point-and ran a long cable to a socket a few feet away.

There was general laughter, in which Kaminski did not join, though his eyes twinkled.

"The cyborg-the electromechanical organism. And even he-it is only a stepping stone to the next stage-the purely electronic intelligence, with no flesh and-blood body at all. The robot, if you like-though I prefer to call it the autonomous computer."

From The Lost Worlds of 2001 by Sir Arthur C. Clarke (1972) know how there are creatures that dwell in the most inaccessible, inhospitable places above, on and under the Earth and in her oceans? I am talking about life-forms you can find in any handbook of zoology, as opposed to those fearsome beings of the Cthulhu Cycle which which we are now so familiar. Well, there are also creatures which exist in the most obscure and random corridors and corners of time, in lost and unthinkable abysses of space, and in certain other twilight places which are most easily explained by referring to them as junctions of forces neither temporal nor spacial, places which by all rights should only exist in the wildest imaginings of theoreticians and mathematicians...

...Suffice to say, then that there are extreme forms of life within and without this universe of ours. And I know it to be so for I have seen or learned of many such forms.

for instance:

...intelligent energies in the heart of a giant alien sun who measure time in ratios of nuclear fission and space in unimaginable degrees of pressure! There are wraithlike biological gasses which issue at the dark of their moon from the fissures of a fungoid world in Hydra, to dance away their brief lives until, exhausted, they die at dawn, scattering the sentient seeds of mushroom minds which will sprout and take root, and whose crevice-deep roots will in turn emit at the dark of the moon euphoric, spore-bearing mists of genesis.

There is a dying purple sun on Andromeda's rim whose rays support life on all seven of its planets. On the fourth planet there are exactly seventeen forms of life, or so it would appear. On closer inspection, however, a zoologist could tell you that these forms are all different phases of only one life-form! Consider the batrachian and lepidopterous cycles of Earth life and this might not seem too astonishing, until I tell you that of these seventeen phases two are as apparently inanimate mineral deposits, six are aquatic, two others amphibious, three land-dwelling cannibals, three more are aerial and the last is to all intents and purposes a plant while all of its preliminary stages (excluding the mineral phases) were animal...

Brian Lumley, The Transition of Titus Crow (1975)

The starcraft gathered the fabric of time and space. Chayn passed stars and groupings of stars, dense clusters of young stars and swirling clouds of dust and gas giving birth to new light in their depths. Black holes tunneled through the space-time structure into elsewhere, glowing ominously as matter spiraled down to annihilation. Chayn could perceive it all, but he focused his attention on the mind fields.

Uncountable multitudes of worlds circles perhaps a third of the stars in his view. Most were lifeless, barren worlds of rock and snow, but even the tiny fraction that had given birth to life emanated a broad mind field that he could sense everywhere. There were worlds of microscopic life and paradises of forests and jungles teaming with dramas of life and death. There were worlds ancient and wise in the ways of evolution, but what Chayn watched for were the sparks of intense awareness, life on levels near his own. Intelligence too far in advance of him were incomprehensible, aware of his passage, but apathetic. Most life forms on his own level were alien, different in inexplicable ways. He felt he could adapt to some of those strange and beautiful worlds if necessary, but he staved his hunger and waited for the worlds of man.

The Watcher told him that man had lived for eons, evolving to the greatness of the stargods, but that man in this galaxy had recently arrived in fleets of starships after sleeps of many millennia. The worlds of man were new here while Earth recycled its continents and evolved new species of life...

...Danger lay immediately ahead, a gulf of darkness between two arms of the galaxy. Chayn approached the starless void with caution. In that incredible abyss four hundred light years across, he could sense another kind of life -- the star travelers. He could sense such small concentrations of explorers only where they stood out like specks of brightness, even the blank minds of those who slept in the frozen oblivion of suspended animation...

One of the star travelers in view piloted a starcraft similar to his own. Two others were primitive vehicles of metal driven by fusion or antimatter-propulsion units to velocities below that of the speed of light ... At first Chayn thought the pilot of the starcraft like his own would seek communication with him, but the entity was highly evolved and looked upon him as a curiosity. Chayn knew himself to be a primitive, more typical of the life forms frozen in their crude ships of metal...

...Chayn's fear intensified as he neared the abyss. Mindspiders lurked in the darkness, many species of them littering the void with invisible webs. Some dangled thin and scraggly. Others spread magnificently, a light year in diameter. Even in that moment, he felt the shock, the utterly brilliant flare of terror of alien minds encountering the web in the far distance. Particles rose to lethal intensities of radiation. Bodies died and the ship heated to incandescence. The mindspiders fed upon disembodied consciousness. Few of the primitives could perceive such danger lurking in the abyss...

...Ahead, he sensed an old, torn web. Even the mindspiders had their predators in their own realm. This one was gone, the web deteriorating.

William Tedford, Timequest Trilogy Book 1: Rashanyn Dark (1981)

Hammond's head spun with their tales of spaceman's life, tales of the vast glooms of cosmic clouds that ships rarely dared enter, of wrecks and castaways in the unexplored fringes of the galaxy, of strange races like the thinking rocks of Rigel and the fish-cities of Arcturus' watery worlds and the unearthly tree-wizards of dark Algol.

Edmond Hamilton, The Star of Life (1947)

Aliens will not resemble anything we've seen. Considering that octopi, sea cucumbers, and oak trees are all very closely related to us, an alien visitor would look less like us than does a squid. Some fossils in the ancient Burgess shale are so alien that we can't determine which end of the creature is up, and yet these monsters evolved right here on Earth from the same origins as we did.

Johan Forsberg

Ecosystem Classification

In the Traveller role playing game, it broke down animal types into four broad classes: Herbivore, Omnivore, Carnivore, and Scavenger. They were further broken down into sub-types:

  • Herbivore: Animals that eat unresisting food. Plant-eaters, but also whales eating krill and anteaters eating ants.
    • Grazers: Herbivores that devote most of their time to eating. They may be solitary or grouped in herds. Their primary defense is running away very fast. Examples: antelope, moose, whale.
    • Intermittents: Herbivores that do not devote most of their time to eating. They tend to be solitary. They tend to freeze when encountering another animal but will flee if attacked by something larger. Examples: chipmunk and elephant.
    • Filters: Herbivores that pass the environment through their bodies. Grazers move towards food, filters move a flow of water or air through their body in order to gain food. They generally suck, trip, push or pull anything at close range into their digestive sack. They are solitary and tend to be slow-moving. Examples: barnacle.
  • Omnivore: Animals that eat food regardless of its resistance. For instance: bears eat berries as well as small animals.
    • Gatherers: Omnivore that display a greater tendency to herbivorous behavior. They are similar to Intermittents. Examples: raccoon and chimpanzee.
    • Hunters: Omnivore that display a greater tendency to carnivorous behavior. Similar to small or inefficient chasers. Examples: bears and humans.
    • Eaters: Omnivore that does not distinguish its food, it consumes all that it confronts. Examples: a swarm of army ants.
  • Carnivore: Animals that eat violently resisting food by attacking and killing said food.
    • Pouncers: Carnivore that kill their prey by attacking from hiding, or by stalking and springing. Generally solitary since it is hard to coordinate such attacks. If they surprise their prey they will attack, but will sometimes attack even when surprise is lost. If they themselves are surprised they will flee. Examples: cats.
    • Chasers: Carnivore that kill their prey by attacking after a chase. They tend to be pack animals. Examples: wolves.
    • Trappers: Carnivore that passively allow their prey to enter a created trap, whereupon the prey is killed and eaten. They tend to be solitary and slow, but will attack literally anything that enters the trap. Examples: spider and ant lion.
    • Sirens: Similar to Trappers, except it creates some kind of lure to draw prey into the trap. Sometimes the lure is specific to some prey animal, sometimes the lure is universal. Examples: angler fish, Venus fly trap.
    • Killers: Carnivore that devote much attention to killing, a blood lust. They have a raw killing instinct. Attacks are fierce and violent. They do not care how large their opponent is. Examples: shark.
  • Scavenger: Animals that share or steal the prey of others, or that takes the nasty unconsumed left over bits.
    • Intimidators: Scavenger that steal food from other animals by frightening or threatening. They approach another animal's kill and force it away by appearing to be a threat. Examples: coyote.
    • Hijackers: Scavenger that boldly steal food from another animal. Hijackers are stronger or larger than the victim animal, so that it cannot effectively object. Examples: lion, tyrannosaurus rex.
    • Carrion-Eaters: Scavengers that take dead meat when it becomes available, often waiting patiently for all other threats to disperse first. Examples: buzzard.
    • Reducers: Scavengers that act constantly on all available food. They eat the remains of food after all other scavengers are finished with it. They are generally microscopic. Examples: bacteria.

Note that the animal type which an intelligent alien evolved from will give clues as to that alien's psychology.

Here on Terra, Carnivores and Omnivores tend to have their eyes aimed forwards working together, so as to allow binocular vision to gauge the distance to their prey. In self-defense, Herbivores (i.e., the prey) tend to have monocular vision, eyes on the side of their face aimed left and right working separately. This allows them to approximate 360° vision thus reducing the blind spot a carnivores can use for ambush purposes.

Body Type Classification

In his Lensman series, E.E. "Doc" Smith invents an alien body type classification system, though he gives precious few details. In the system, human beings are classified as AAAAAAAAAAAA to twelve places, and aliens have other letter codes depending upon how they vary from humans. The fifth place is for number and type of arms, the sixth is for number and type of legs, and seventh place is skin.

...The thing's bodily structure was RTSL, to four places. No gross digestive tract - atmosphere-nourished or an energy-converter, perhaps. Beyond four places was pretty dim, but Q P arms and legs - Dhilian, eh? - would fit, and so would an R-type hide.

...As she was wafted gently across the intervening space upon a pencil of force, Kathryn took her first good look at the precisionist himself-or herself. She - it - looked something like a Dhilian, she thought at first. There was a squat, powerful, elephantine body with its four stocky legs; the tremendous double shoulders and enormous arms; the domed, almost immobile head. But there the resemblance ended. There was only one head-the thinking head, and that one had no eyes and was not covered with bone. There was no feeding head-the thing could neither eat nor breathe. There was no trunk. And what a skin!

It was worse than a hide, really-worse even than a Martian's. The girl had never seen anything like it. It was incredibly thick, dry, pliable; filled minutely with cells of a liquid-gaseous something which she knew to be a more perfect insulator even than the fibres of the tegument itself.

"R-T-S-L-Q-P." She classified the creature readily enough to six places, then stopped and wrinkled her forehead. "Seventh place-that incredible skin-what? S? R? T? It would have to be R . . .

..."VWZY, to four places." Con concentrated. "Multi-legged. Not exactly carapaceous, but pretty nearly. Spiny, too, I believe. The world was cold, dismal, barren; but not frigid, but he-it-didn't seem exactly like an oxygen-breather - more like what a warm-blooded Palainian would perhaps look like, if you can imagine such a thing. VWZYTXSYZY to ten places.

...Classification, straight Z's to ten or twelve places, she - or it - seemed to be trying to specify. A frigid race of extreme type, adapted to an environment having a temperature of approximately one degree absolute.

...physically, his classification to four places is TUUV; quite a bit like the Nevians, you notice.To ten places it was TUUVWYXXWT.

From Children of the Lens by E.E. "Doc" Smith (1947)

James White adapted the system to his Sector General novels, with the the more reasonable specification that human beings were not the measure of all things, i.e., in the Sector General system humans are classified as DBDG, not AAAAAAAAAAAA.

Conway muted the speaker which carried the conversation between ship and receptionist into the gallery and said, "This is as good a time as any to explain our physiological classification system to you. Briefly, that is, because later there will be special lectures on this subject."

Clearing his throat, he began, "In the four-letter classification system the first letter indicates the level of physical evolution, the second denotes the type and distribution of limbs and sense organs and the other two the combination metabolism and pressure and gravity requirements, which in turn give an indication of the physical mass and form of protective tegument possessed by the being. I must mention here, in case any of you might feel inferior regarding your classification, that the level of physical evolution has no relation to the level of intelligence...

Species with the prefix A, B and C, he went onto explain, were water breathers. On most worlds life had originated in the sea and these beings had developed high intelligence without having to leave it. D through F were warm-blooded oxygen-breathers, into which group fell most of the intelligence races in the galaxy, and the G and K types were also oxygen breathing but insectile. The Ls and Ms were light-gravity, winged beings.

Chlorine-breathing life-forms were contained in the 0 and P groups, and after that came the more exotic, the more highly-evolved physically and the downright weird types. Radiation-eaters, frigid-blooded or crystalline beings, and entities capable of modifying their physical structure at will. Those possessing extra-sensory powers sufficiently well-developed to make walking or manipulatory appendages unnecessary were given the prefix V, regardless of size or shape.

Conway admitted to anomalies in the system, but these could be blamed on the lack of imagination by its originators. One of the species present in the observation gallery was a case in point - the AACP type with its vegetable metabolism. Normally the A prefix denoted a water breather, there being nothing lower in the system than the piscatorial life forms. But the AACPs were vegetables and plants had come before fish.

From Star Surgeon by James White (1963)

Alien Communication

There are some notes on talking to aliens here.

In the real world, communication with hypothetical extraterrestrials is such a huge problem that it may never be properly solved. Researchers are having enough problems trying to talk to porpoises, and they are from our own planet. Alien thought processes might be forever inscrutable. There is a good list of examples of inscrutable alien languages on TV Tropes.

In C. J. Cherryh's Chanur novels, the methane-breathing Tc'a species are almost impossible to be communicated with, since their brains are multi-part and their speech decodes as complex matrices of intertwined meanings. In Piers Anthony's KIRLIAN QUEST, the Slash use modulated laser beams. As did the deep space beings in Jack Williamson's TRAPPED IN SPACE. In Charles Sheffield's PROTEUS novels, the Logeinan life form uses an area of skin that has changing color dots. As does the intelligent squid in Arthur C. Clarke's The Shining Ones.

And just imagine the headaches of trying to communicate with a species that uses various scents and smells instead of sound. Or radio waves. Or modulated laser beams. Or rapid changes in skin color. Or all four combined.

...the vast majority of sentients (alien races) cannot directly communicate with each other.

Some species operate on different time lines, or are out of phase with the four dimensions we can perceive, are too small or too large, or perhaps, if they had to acknowledge us, they would have to kill us.

So even when an atomic matrix life form that feeds off the microwave hum left over from the Big Bang and excretes time lives in the same solar system with your typical silicon-based life form that eats rocks and excretes hydrogen, communication between them may be close to impossible.

Luckily it's not really a big deal, because they usually don't have anything to talk about. Or so it appears, right up until said atomic matrix life form begins a simple operation to make the local sun go nova in order to harvest neutrinos, and to their surprise, are vigorously opposed by those gritty little creatures clinging to their large orbiting rocks, who have had to start throwing anti-matter around to get their attention, and things usually deteriorate from there.

From Buck Godot: The Gallimaufry by Phil Foglio

"This man Boyce," said Karellen. "Tell me all about him." The Supervisor did not use those actual words, of course, and the thoughts he really expressed were far more subtle. A human listener would have heard a short burst of rapidly modulated sound, not unlike a high-speed Morse sender in action. Though many samples of Overlord language had been recorded, they all defied analysis because of their extreme complexity. The speed of transmission made it certain that no Interpreter, even if he had mastered the elements of the language, could ever keep up with the Overlords in their normal conversation.

From Childhood's End by Arthur C. Clarke (1954)

Alien Psychology

The psychology of an alien species is any body's guess. It could be so alien as to be forever beyond our understanding. It could be quite human. Or somewhere in-between.

There is a sophisticated alien psychology generation system in the role-playing game GURPS: Uplift, and a good tutorial on TV Tropes.

Some clues to an alien species psychology might be found in their ecosystem classification. For instance, herbivores might be skittish, only comfortable in groups, and tend to flee if they feel threatened.

In James P. Hogan's The Gentle Giants of Ganymede, on the giant's planet the herbivores evolved a third circulatory system full of toxins which made their flesh poisonous to carnivores. It was so effective that carnivores became extinct. The herbivores evolved to look like animal illustrations from a nursery or kindergarten story book, all cute, plump and cuddly. The result was that the giant psychology has no confrontation, pride, or sense of danger.

Larry Niven's Puppeteers evolved from herbivores. They are the cowards of the universe, their leader is called "The Hindmost" because it is the furthest from any danger. In Puppeteer society, courage is seen as a mental illness. Puppeteers are pragmatic to a fault. Human traits such as wishful thinking and superstition are nonexistent. This means there is no level of danger that they'd consider to be an acceptable risk, the only acceptable level is 0%. They are willing to go to any lengths to protect themselves from perceived danger and provide a safer environment for themselves.

In Niven and Pournelle's classic novel Footfall, the alien Fithp are herd creatures. They do not understand how or why you would possibly initiate diplomacy before first fighting to see which party was dominant. When a Fithp is defeated, it surrenders, and thereafter becomes totally devoted and subservient to its conqueror.

Fithp are horrified when they defeat humans in battle, the humans surrender, then the humans suddenly break their surrender and counter-attack. To the Fithp, this is mad-dog behavior, and the humans are treated as such.

However aliens can have such a bizarre psychology as to be forever beyond comprehension, as in Terry Carr's "The Dance of Changer and the Three"

The Dance of the Changer and Three

(ed note: on the mineral-rich planet, the miners make contact with the alien energy-creatures native to the place (the Loarra). They receive permission to mine. After mining for four years, the Loarra show up and kill everybody outside of the mountain and destroy all the mining equipment)

After a while I sent out a fourth “eye.” One of the Loarra came over, flitted around it like a firefly, blinked through the spectrum, and settled down to hover in front for talking. It was Pura Pur who was a thousand million billion life cycles removed from the Pur we know and love, of course, but nonetheless still pretty much Pur.

I sent out a sequence of lights and movements that translated, roughly, as, “What the hell did you do that for?”

And Pur glowed pale yellow for several seconds, then gave me an answer that doesn’t translate. Or, if it does, the translation is just “Because.”

Then I asked the question again, in different terms, and she gave me the same answer in different terms. I asked a third time, and a fourth, and she came back with the same thing. She seemed to be enjoying the variations on the Dance; maybe she thought we were playing.

Well … We’d already sent out our distress call by then, so all we could do was wait for a relief ship and hope they wouldn’t attack again before the ship came, because we didn’t have a chance of fighting them, we were miners, not a military expedition. God knows what any military expedition could have done against energy things, anyway. While we were waiting, I kept sending out the “eyes,” and I kept talking to one Loarra after another. It took three weeks for the ship to get there, and I must have talked to over a hundred of them in that time, and the sum total of what I was told was this:

Their reason for wiping out the mining operation was untranslatable. No, they weren’t mad. No, they didn’t want us to go away. Yes, we were welcome to the stuff we were taking out of the depths of the Loarran ocean.

And, most importantly: No, they couldn’t tell me whether or not they were likely ever to repeat their attack.

Satan's World

(ed note: Chee Lan is a Cynthian, an alien resembling an angora cat. Adzel is a Wodenite, resembling a cross between centaur and a dragon. The team is trying to figure out the psychology of the Shenna of Dathyna.)

He drained his beer. Soothed thereby, he lit his pipe, settled back, and rumbled, "We got our experience and information. Also we got analogues for help. I don't think any sophonts could be total unique, in this big a universe. So we can draw on our understanding about other races.

"Like you, Chee Lan, for instance: we know you is a carnivore—but a small one—and this means you got instincts for being tough and aggressive within reason. You, Adzel, is a big omnivore, so big your ancestors didn't never need to carry chips on their shoulders, nor fish either; your breed tends more to be peaceful, but hellish independent too, in a quiet way; somebody tries for dictating your life, you don't kill him like Chee would, no, you plain don't listen at him. And we humans, we is omnivores too, but our primate ancestors went hunting in packs, and they got built in a year-around sex drive; from these two roots springs everything what makes a man a human being. Hokay? I admit this is too generalistic, but still, if we could fit what we know about the Shenna in one broad pattern—"

On Dathyna, the predicament was worse. The solar bombardment was always greater than Earth receives. At the irregular peaks of activity, it was very much greater. Magnetic field and atmosphere could not ward off everything. Belike, mutations which occurred during an earlier maximum led to the improbable result of talking, dreaming, tool-making herbivores. If so, a cruel natural selection was likewise involved: for the history of such a planet must needs be one of ecological catastrophes.

The next radiation blizzard held off long enough for the race to attain full intelligence; to develop its technology; to discover the scientific method; to create a worldwide society which was about to embark for the stars, had perhaps already done it a time or two. Then the sun burned high again.

Snows melted, oceans rose, coasts and low valleys were inundated. The tropics were scorched to savanna or desert. All that could be survived. Indeed, quite probably its harsh stimulus was what produced the last technological creativity, the planetary union, the reaching into space.

But again the assault intensified. This second phase was less an increase of electromagnetic energy, heat and light, than it was a whole new set of processes, triggered when a certain threshold was passed within the waxing star. Protons were hurled forth; electrons; mesons; X-ray quanta. The magnetosphere glowed with synchrotron radiation, the upper atmosphere with secondaries. Many life forms must have died within a year or two. Others, interdependent, followed them. The ecological pyramid crumbled. Mutation went over the world like a scythe, and everything collapsed.

No matter how far it had progressed, civilization was not autonomous. It could not synthesize all its necessities. Croplands became dustbowls, orchards stood leafless, sea plants decayed into scum, forests parched and burned, new diseases arose. Step by step, population shrank, enterprises were abandoned for lack of personnel and resources, knowledge was forgotten, the area of the possible shrank. A species more fierce by nature might have made a stronger effort to surmount its troubles—or might not—but in any event, the Dathynans were not equal to the task. More and more of those who remained sank gradually into barbarism.

And then, among the barbarians, appeared a new mutation.

A favorable mutation.

Herbivores cannot soon become carnivores, not even when they can process meat to make it edible. But they can shed the instincts which make them herd together in groups too large for a devastated country to support. They can acquire an instinct to hunt the animals that supplement their diet—to defend, with absolute fanaticism, a territory that will keep them and theirs alive—to move if that region is no longer habitable, and seize the next piece of land—to perfect the weapons, organization, institutions, myths, religions, and symbols necessary—

—to become killer herbivores.

And they will go farther along that line than the carnivora, whose fang-and-claw ancestors evolved limits on aggressiveness lest the species dangerously deplete itself. They might even go farther than the omnivora, who, while not so formidable in body and hence with less original reason to restrain their pugnacity, have borne arms of some kind since the first proto-intelligence developed in them, and may thus have weeded the worst berserker tendencies out of their own stock.

Granted, this is a very rough rule-of-thumb statement with many an exception. But the idea will perhaps be clarified if we compare the peaceful lion with the wild boar who may or may not go looking for a battle and him in turn with the rhinoceros or Cape buffalo.

The parent stock on Dathyna had no chance. It could fight bravely, but not collectively to much effect. If victorious in a given clash, it rarely thought about pursuing; if defeated, it scattered. Its civilization was tottering already, its people demoralized, its politico-economic structure reduced to a kind of feudalism. If any groups escaped to space, they never came back looking for revenge.

A gang of Shenna would invade an area, seize the buildings, kill and eat those Old Dathynans whom they did not castrate and enslave. No doubt the conquerors afterward made treaties with surrounding domains, who were pathetically eager to believe the aliens were now satisfied. Not many years passed, however, before a new land-hungry generation of Shenna quarreled with their fathers and left to seek their fortunes.

The conquest was no result of an overall plan. Rather, the Shenna took Dathyna in the course of several centuries because they were better fitted. In an economy of scarcity, where an individual needed hectares to support himself, aggressiveness paid off; it was how you acquired those hectares in the first place and retained them later. No doubt the sexual difference, unusual among sophonts, was another mutation which, being useful too, became linked. Given a high casualty rate among the Shenn males, the warriors, reproduction was maximized by providing each with several females. Hunting and fighting were the principal jobs; females, who must conserve the young, could not take part in this; accordingly, they lost a certain amount of intelligence and initiative. (Remember that the original Shenn population was very small, and did not increase fast for quite a while. Thus genetic drift operated powerfully. Some fairly irrelevant characteristics like the male mane became established in that way—plus some other traits that might actually be disadvantageous, though not crippling.)

At length the parricidal race had overrun the planet. Conditions began to improve as radiation slacked off, new life forms developed, old ones returned from enclaves of survival. It would be long before Dathyna had her original fertility back. But she could again bear a machine culture. From relics, from books, from traditions, conceivably from a few last slaves of the first species, the Shenna began rebuilding what they had helped destroy.

But here the peculiar set of drives which had served them well during the evil millennia played them false. How shall there be community, as is required for a high technology, if each male is to live alone with his harem, challenging any other who dares enter his realm?

The answer is that the facts were never that simple. There was as much variation from Shenn to Shenn as there is from man to man. The less successful had always tended to attach themselves to the great, rather than go into exile. From this developed the extended household—a number of polygynous families in strict hierarchy under a patriarch with absolute authority—that was the "fundamental" unit of Shenn society, as the tribe is of human, the matrilineal clan of Cynthian, or the migratory band of Wodenite society.

The creation of larger groups out of the basic one is difficult on any planet. The results are all too likely to be pathological organizations, preserved more and more as time goes on by nothing except naked force, until finally they disintegrate. Consider, for example, nations, empires, and world associations on Earth. But it need not always be thus.

The Shenna were reasoning creatures. They could grasp the necessity for cooperation intellectually, as most species can. If they were not emotionally capable of a planet-wide government, they were of an interbaronial confederacy.

Especially when they saw their way clear to an attack—the Minotaur's charge—upon the stars!

From Satan's World by Poul Anderson (1968). Collected in David Falkyn: Star Trader

Alien Lebensraum

Desirable Real Estate

As a rule, species that inhabit terrestrial planets (such as our species) do not have much interaction with aliens who live on gas giants. In the general this is because we and they have little or no common frames of reference which makes communication difficult. In the specific it is because we and they do not covet each other's real estate so there is no reason to go to war. In Poul Anderson's galactic novels, the human galactic empire and several gasworlder empires interpenetrated each other and ignored each other.

There are exceptions, such as Kevin J. Anderson's Saga of Seven Suns series. In the first novel, the human empires are unaware of the existence of the Gasworlders ("Hydrogues"). This proves to be unfortunate, when the humans test a device which converts gas giants into blazing suns, this makes the Hydrogues very angry. Hilarity ensues.

Many point to the ecosystems at the Galapagos black smokers as proof that life is possible in underground oceans on, say, Europa. However, if this is true, the implication is that such life will be far more common than terrestrial life. After all, there are several such moons in our solar system, and only one Terra (Europa, Enceladus, Ganymede and Titan). If there are four such moons, then throughout the universe iceball life will outnumber liquid water life four to one, on average. Such life turns up in The Killing Star by Charles Pelligrino and George Zebrowski.

The late Carl Sagan popularized the notion that floating organisms could exist in the temperate regions of Jupiter's atmosphere. He postulated an entire ecosystem, with aerial plankton grazed on by sky whales, who were preyed on in turn by flying sharks. Sir Arthur C. Clarke expanded upon this theme in "A Meeting With Medusa" and in 2010. These stories featured creatures that were sort of a cross between a titanic jellyfish and a zeppelin. The medusae were herbivores, but armed against the marauding sharks. They had high-voltage lighting projectors and serrated arms like kilometer long chainsaws. There are also sky whales in Dr. Robert Forward's Saturn Rukh.

However, if the aliens like to live on the same kinds of planets that Terrans do, the way to bet is that eventually there will be war. The only wild card is if one or both species like living in mobile asteroid habitats (Macrolife). Or if a species is a primitive civilization with the misfortune to live in an Elder God Galaxy, and has to keep a real low profile in order to survive.

As a side note, one can use the time between apes and angels for the "average lifespan of a technological civilization". Insert this into the Drake equation along with a few other guesses and you can calculate the average distance between alien civilization homeworlds. (and of course the distance between Terra and the closest aliens).

I say "homeworlds" because they might have colonized nearby stars to form an empire. In this case the homeworld will probably be in the center of the empire's sphere of influence. Therefore the closest aliens will be the average distance between minus the radius of their empire. Go to The Tough Guide to the Known Galaxy and read the entry "HOMEWORLD".

If you already have an idea of how close you want civilizations to be spaced, you work the Drake equation backwards. Keep altering the values until you get the spacing you want. But now you have to live with the consequences of those various values, and their implications.

It will be even worse if the average lifespan of a technological civilization is shorter than expected, due to premature death by nuclear holocaust or unexpected apotheosis by a Vingian Singularity.

HOMEWORLD. This may have any of three related but distinct meanings.

1) Someone's native PLANET; where they were born, or at least their permanent residence address.

2) The capital Planet of an EMPIRE, especially if the Empire builders started out there.

3) The Planet where an intelligent race originated. In this sense, the Homeworld of all EARTH HUMANS is of course Earth, even if they have lived for generations on a COLONY.

Alien 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".

Contact Motivation

An alien civilization of similar technological advancement to Terra could contact them first. 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!

Trade is always a good motive. In H. B. Fyfe's little classic "In Value Deceived", a alien exploration starship is searching for a way to alleviate the famine on their homeworld. They make first contact with a human starship on some barren little world. On a tour of the human's ship, they are thunderstruck when they see the hydroponic installations. It's the key to salvation for their people!

But of course they feign disinterest. They ask for one as a souvenir. They don't notice the similar disinterest with which the humans ask for an alien heating unit. The one that produces all that pesky ash. Stuff like uranium and gold nuggets.

Both aliens and humans are surprised when both parties make quick good-byes after the trade and take off before the trade is regretted. They both think "gee, the other guys act like they cheated us."

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 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 encounter 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.

“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)

“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!”

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 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.

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.

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

Dr. Geoffrey A. Landis has a possible solution based on Percolation Theory. A more depressing 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 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.

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.

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 rule of thumb:

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 rule of thumb, 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 rule of thumb 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)

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")

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
A Minor Flaw

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
Another Minor Flaw

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)

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)

Alien Tech Level

Apes or Angels

Sir Arthur C. Clarke made a famous observation about space explorers discovering aliens. If one considers the millions of years of pre-history, and the rapid technological advancement occurring now, if you apply that to a hypothetical alien race, one can figure the probabilities of how advanced the explorers will find them. The conclusion is "we will find apes or angels, but not men."

Why? Consider the history of Planet Earth. Let the height of the Empire State building represent the 5 billion year life of Terra. The height of a one-foot ruler perched on top would represent the million years of Man's existence. The thickness of a dime will represent the ten thousand years of Man's civilization. And the thickness of a postage stamp will represent the 300 years of Man's technological civilization. An unknown portion above represents "pre-Singularity Man", the period up to the point where mankind hits the Singularity/evolves into a higher form/turns into angels. Say another dime. Above that would be another Empire State building, representing the latter 5 billion years of Terra's lifespan.

If you picked a millimeter of this tower at random, what would you most likely hit? One of the Empire State buildings, of course. So, assuming only one civilization develops on a planet, chances are the first-in-scout starship Daniel Boone will discover mostly planets that are currently empty of alien civilizations (but they might have an almost 50% chance to discover valuable Forerunner artifacts or other paleotechnology).

As a matter of terminology, a long-extinct star faring alien civilization are commonly called "Forerunners", "Precursors", "Ancients", "Elder race", "Progenitors", or "Predecessors". Their thousand year old ruins are sobering, but their high-tech artifacts are generally far in advance of current tech levels and are of course both incredibly valuable yet incredibly dangerous. Archaeologists who stumble over such remains have a tendency to be killed by pirates, and their artifacts stolen.

If you only use the section with an alien civilization, you have a ruler and two dimes worth of apes and angels, and a postage stamp worth of near Human civilization. Ergo: apes or angels, but not men.

Mark Alan Barner of Anaheim explains it this way:

Apes or Angels

Consider the high improbability that any two Earth-like planets will form and evolve to the exact and ideal conditions that develop and support carbon-based life.

Consider also the number of mass extinctions that have occurred in Earth's past. It is unlikely that the same number of these would occur on another Earth- like world at exactly the same time and with the exact same frequency.

Finally, consider the cultural developments in Earth's history, and apply a few "What Ifs." What if Democracy had never developed beyond the conceptual stage? What if Rome had never fallen? What if Columbus had never received any financial backing from the Spaniards? What if the Nazis had developed the atomic bomb first?


Would any of one of these events have delayed or advanced human development by as much as 0.001%? One value given for the age of the Earth is 4.567 billion years. A +/- 0.001% change would set human evolution back by 4.567 million years (Apes), or advance it by 4.567 million years (Angels).

Thus, by "Apes & Angels" one could say that any two worlds that formed at exactly the same time, and that have had billions of years to go from dust to sentient life, could differ by as much as 9.134 million years in evolution!

A divergence of only 0.000001% would still separate the two extremes by 9.134 thousand years. With this value, one alien world could have a bronze-age culture (year = 2560 BCE), while another could be far ahead of our own, both culturally and technologically (year = 6574 CE). Maybe not "Apes & Angels" but perhaps "Spearchuckers & Supermen"?


Mark Alan Barner
My Example

The planet Earth will have a life-span of roughly ten billion years. Mankind (Homo sapiens) appeared on Earth approximately 100,000 years ago. The bronze age began about 5300 years ago. The Industrial Revolution began about 250 years ago.

When will we humans evolve into angels? Vernor Vinge thinks the Singularity will happen no later than the year 2030. But I'll be generous and use 500 years from now, using John Barnes' rule of thumb. How long will the angels last? No idea. For lack of anything else, let's say 100,000 years from now, placing us current humans midway between apes and angels.

Now, assuming that the Daniel Boone only visits planets that be hosts to alien species, and assuming that each planet will only produce one alien species (which is a very questionable assumption), this means that the chance of discovering a living alien species is about 200,000/10,000,000,000 = 0.00002 = one chance in 50,000.

The poor Daniel Boone will on average have to visit fifty thousand planets in order to find one alien species. (Of course the Daniel Boone will probably be targeting planets about the same age as Earth and using other strategies to drastically reduce the number it will have to visit.)

Now, say that somehow the Daniel Boone manages to visit enough planets to discover 267 alien species. What level with they be at? Doing the math, 133 in 267 will be angels, 126 in 267 will be cave men, 7 in 267 will be on par with ancient Egypt, and only one in 267 will be a technological species. Keeping in mind that in this case, "technological" means it has technology ranging from steam power to something out of Star Wars (the 1760's to the 2500's).

The Daniel Boone will encounter 126 planets full of cave-man level aliens that they can play "Chariots of the Gods" with, and will have to avoid 133 planets with god-like species eager to put our intrepid explorers into giant petri dishes for their experiments with primitive life forms.

If these figures do not suit you, this is your opportunity to play with the various values until more reasonable numbers appear. But you will be forced to live with the implications of any values you change.

In those science fiction novels that care about technical details, there are some solutions mentioned. They all rely upon some method to start all the alien species in a stellar region simultaneously. This means that they will all develop at roughly the same rate, and encounter each other at roughly the same technological level. Solutions include postulating some alien race at the dawn of galactic history seeding planets, or disasters like gamma-ray bursters destroying all life in a galactic zone, forcing the planets to start re-evolving life starting at the same point in time.

Outside Context Problem

An Outside Context Problem was the sort of thing most civilisations encountered just once, and which they tended to encounter rather in the same way a sentence encountered a full stop. The usual example given to illustrate an Outside Context Problem was imagining you were a tribe on a largish, fertile island; you’d tamed the land, invented the wheel or writing or whatever, the neighbours were cooperative or enslaved but at any rate peaceful and you were busy raising temples to yourself with all the excess productive capacity you had, you were in a position of near-absolute power and control which your hallowed ancestors could hardly have dreamed of and the whole situation was just running along nicely like a canoe on wet grass… when suddenly this bristling lump of iron appears sailless and trailing steam in the bay and these guys carrying long funny-looking sticks come ashore and announce you’ve just been discovered, you’re all subjects of the Emperor now, he’s keen on presents called tax and these bright-eyed holy men would like a word with your priests.

That was an Outside Context Problem; so was the suitably up-teched version that happened to whole planetary civilisations when somebody like the Affront chanced upon them first rather than, say, the Culture.

The Culture had had lots of minor OCPs, problems that could have proved to be terminal if they’d been handled badly, but so far it had survived them all. The Culture’s ultimate OCP was popularly supposed to be likely to take the shape of a galaxy-consuming Hegemonising Swarm, an angered Elder civilisation or a sudden, indeed instant visit by neighbours from Andromeda once the expedition finally got there.

In a sense, the Culture lived with genuine OCPs all around it all the time, in the shape of those Sublimed Elder civilisations, but so far it didn’t appear to have been significantly checked or controlled by any of them. However, waiting for the first real OCP was the intellectual depressant of choice for those people and Minds in the Culture determined to find the threat of catastrophe even in Utopia.

From Excession by Iain M. Banks (1996)

Technology Level

As far as technological advancement goes, there is a crude measure in the Kardashev scale.

Kardashev Scale
TypeDescriptionPower (W)
IA civilization that is able to harness all of the power available on a single planet.~1016
IIA civilization that is able to harness all of the power available from a single star.~1026
IIIA civilization that is able to harness all of the power available from a single galaxy.~1036

Carl Sagan estimated that humanity is currently around Type 0.7. A Type II would probably have some kind of Dyson sphere to harvest all the star's energy. Type III would probably be as far advanced from us as we are from one-celled amoebae. Terran space explorers would be wise to avoid areas where Type III civilizations are operating. Otherwise they might suffer a similar fate to that of an ant trying to cross an interstate highway. And for similar reasons: not because the Type III hates lower races, but because the lower races are so far beneath their notice that Type IIIs cannot be bothered to keep track of them. Do you ever think about the ants you run over in your automobile? Even with a Type II the situation might be analogous to a puppy-dog chasing a monorail.

Things might get worse if a human explorer succeeded in attracting the attention of a Type III. They might react as you would, reaching for a cosmic spray-can of insecticide. Or use the explorer with the same lack of concern shown by cancer researchers to their laboratory rats. Maybe more like the lack of concern they show to the cells in their tissue cultures.

In the Babylon 5 episode, "Mind War", surveyor Catherine Sakai's encounters a ship from a Type III civilization near the rim system Sigma 957. In a titanic display of cosmic force, the alien ship almost destroys hers like an automobile running over a beetle. She is rescued by Ambassador G'Kar. Later, she asks for answers.

Catherine: Ambassador! [He stops.] While I was out there, I saw something. What was it?

G'Kar [pointing at something on a flower]: What is this?

Catherine [examining the flower, as we see it in closeup]: An ant.

G'Kar [learning a new word]: Ant!

Catherine: So much gets shipped up from Earth on commercial transports, it's hard to keep them out.

G'Kar [suiting words to actions]: I have just picked it up on the tip of my glove. If I put it down again, and it asks another ant, "What was that?" how would it explain? There are things in the universe billions of years older than either of our races. They are vast, timeless. And if they are aware of us at all, it is as little more than ants, and we have as much chance of communicating with them as an ant has with us! We know, we've tried! And we've learned we can either stay out from under foot, or be stepped on.

Catherine: That's it? That's all you know?

G'Kar: Yes. They are a mystery. And I am both terrified and reassured to know that there are still wonders in the universe --- that we have not yet explained everything. Whatever they are, Ms. Sakai, they walk near Sigma 957. They must walk there alone!

G'Kar walks away. Catherine studies the ant for a moment and then turns away, shivering. The ant goes on about its own business.

From "Mind War", Babylon 5

Dr. Robert A. Freitas Jr. points out that it isn't just Type III civilizations that are dangerous, it is also Type III individuals. As civilizations technologically advance, members of that civilization have access to increasing amounts of energy. For example, your average medieval peasant could never hope to own something as destructive as an AK-47 automatic rifle or a few drums of fuel oil mixed with ammonium nitrate.

Imagine a family picnic. Some ants show up. Little Billy gets annoyed, tracks the ants back to their nest, dumps a cup of kerosene onto it and lights a match. The ant nest is annihilated. Billy gets called back to the picnic for ice cream.

Imagine a gathering of Type III entities. Some human starships show up. Little Beta-Lambda gets annoyed, tracks the starships back to Earth, and seeds it with five gigatons of neutronium antimatter. Earth is annihilated. Beta-Lambda gets called back to the gathering for euphoronic frequencies.

David Given opines:

I can picture the ships entering a system, making contact with a highly advanced civilization, some skirmishing, diplomacy, etc. leading to a treaty and peaceful relations --- and then the invading civilization discovers that it's actually been dealing with the god's non-sentient (on the god's scale) immune system.

David Given

In more detail: The Terran Empire might encounter an advance alien civilization, and engage in trade or battle with them. Only later they may discover that the "alien civilization" is the cosmic equivalent of a hyper-advanced entity's immune system. The entity would probably never become aware of the Terran Empire, much as you are never aware of the many tiny infections that are quietly taken care of by your immune system. The members of the "alien civilization" might be intelligent, but they are as unintelligent compared to the hyper-entity as your white corpuscles are compared to you.

The reassuring point is the fact that even though human being have a reasonably technologically advanced civilizations, amoebae still exist. It is possible that a hyper-advanced civilization could reach a state where we could not detect their existence, much as amoebae could not detect us. Paul Hughes proposes a corollary to Clarke's Third Law: Any sufficiently advanced intelligence is indistinguishable from nature. There are such civilizations in Sir Arthur C. Clarke's 2001 A Space Odyssey and Paul J. McAuley's Eternal Light. David Zindell's War in Heaven contains quite a few god-like entities who still occasionally notice humanity, however they are mostly concerned with efforts to circumvent the restrictions place upon them by the other god-like entities.

Exotic Civilizations: Beyond Kardaschev

When it comes to speculating about the nature of advanced extraterrestrial civilizations and possible answers to Fermi's Paradox, almost everyone assumes the basic structure and intent of such a civilization should exists somewhere on the Kardaschev Level, as I discussed in Part 1. I think the lack of any evidence to their existence using this model, could be the result of human scientific chauvinism. For example, as I and John Smart has argued there is a distinct possibility that advanced civilization's could decide that moving out into space in the traditional expansive convert-the-universe-into-computronium agenda is not be the best way to go. Instead they may convert their local resources into ultra-miniaturized "femto-tech", where all of further advancement occurs at an increasingly miniaturized "internality" and/or they actually reach a plateau of complexity/novelty. In this scenario, such singularity intelligence never leaves their home planet. Instead 99.999% of their existence, exploration and creation happens in inner space, not outer space. In such a scenario it's possible that such a civilization would remain undetectable in their own solar system, not to mention hundreds or thousands of light years away.

Then there is something altogether more exotic to consider, which also has significant historical precedent - evolutionary ontological transcendence. What do I mean by this? Amoebae are our distant biological ancestors. They are still around this planet in absolute abundance. They are in your house, plants, trees, even in your car, yet they have no awareness of any of it. Their entire reality is composed of basic chemical functions and nutrient intake. Even something as simple as an insect like an ant is beyond their comprehension. Ants are much further along the evolutionary chain, with a great deal more complexity than an amoeba. For one thing, ants have a nervous system and brain that gives them some rudimentary sensory experience and cognitive abilities. An ant's tiny brain and its chemical sensing and processing are radically advanced emergent phenomena completely outside of the very limited ontological space of an amoeba. If nothing else, an ant’s brain is programmed to serve the hive mind, which it is a part. In any case, the amoeba doesn’t have a clue.

Ants in turn are not aware of human civilization. They have no concept of humanity, language, buildings, cars, airplanes, the ocean, the moon, earth, stars, mathematics, space travel. Almost everything we take for granted is completely outside of the limited ontological space that composes an ant's existence.

Now we come to us, to humanity with all of our culture and technological achievements, at the dawn of the cybernetic and space age. We are in the midst of the greatest acceleration of change in all of earth’s history. At some point soon, we will be crossing a critical threshold when all change up to this point will be nothing compared to what’s coming next. We are at the dawn of ushering in greater-than-human intelligence. Whether this exponentiating intelligence is achieved exclusively through artificial intelligence or as I believe a symbiosis between the biological and technological worlds, doesn’t matter. What matters is that greater-than-human intelligence is coming in our lifetimes. And since it was our limited intelligence that created this greater intelligence, then it only makes sense that this greater intelligence will be even more effective in creating even greater intelligence still. There is no reason to believe that this intelligence will not bootstrap itself beyond our current comprehension very, very fast. This is what is called a Singularity, an event horizon, beyond which we can’t understand.

So ask yourself this, why can't this ontological transcendence apply the other way around... to us? If you look at our limited understanding of computational physics, this bootstrapped intelligence will likely exceed human intelligence way more than human intelligence exceeds ants or amoebae. We are not talking about a similar jump up in ontological space, but something much, much greater.

So if other alien civilizations have passed through their own technological singularity, then why or how would we even be able to recognize them at all? Looking at from this historical evolutionary perspective it just doesn't make sense at all. We don't recognize this advance civilization because they are as much beyond as we are above the amoebae. As the character Spock once said in an old Star Trek episode, "the Organians are as advanced above humanity, as humanity is advanced above the amoeba".

Of course, most "level headed" scientists will say such comparisons are incorrect, since we have "science" now, but this could simply be an advanced form of chauvinism. But consider this, everything we call science today was and is the product of very small 3-lb pieces of gray matter of domesticated primates on a small rock around an ordinary star. We assume that our science, our understanding of things like Kardaschev energy signatures, Berkenstien bounds, and other physical limits will apply to this greater intelligence. It might, but my hunch is that all of our understanding of science is mostly chauvinism. An elaborate set of self-consistent rules defined by ontological limits programmed into us by our genes, much like an ant is programmed to not think outside of the hive mind. From this perspective then, advanced extraterrestrial intelligence is invisible to us, indistinguishable from nature as we are capable of understanding or experiencing it, possibly because our entire ontological domain was created by them in the first place!

So like Robert Anton Wilson before me, and Arthur C. Clarke before him, I present my own,

Hughes' Corollary to Clarke's Law:

Any sufficiently advanced intelligence is indistinguishable from nature.

I think this is as good an answer as any to Fermi's Paradox, and one that has plenty of historical ontological precedent.

Of course we could use every scientific concept we have today to speculate on the nature of these ET's, and where they might be. Perhaps they have engineered their own basement universes, or trancended to higher dimensions. Cosmological and Grand Unified theories seem to be constantly under revision these days. We may never know until we ourselves evolve to that level.

From Exotic Civilizations: Beyond Kardaschev by Paul Hughes (2004)


Now if a highly advanced alien civilization is extinct, the gold rush will be on as everybody realizes that incredibly valuable alien technology is literally just lying around for the taking. Xenoarcheologists will be busy excavating paleotechnology, then rushing to the patent office. Blue Tyson thinks the proper term is actually "xenopaleotechnology" and admittedly he does have a point.

Drawbacks will include quite a few unfortunate realities:

  • The fact that everybody else has the same idea and they probably have guns.
  • The fact that "everybody else" includes other alien civilizations (some of which you have not encountered before) who probably also have guns.
  • The tendency for the astromilitary to seize and classify as top-secret any such paleotechnology in the name of national security, leaving you with nothing.
  • The hazard that the Forerunner race you are looting may not be extinct but just mostly extinct.
  • The risk that abandoned alien installations could be guarded by still working deadly automatic defenses.
  • The fact that monkeying around with such technology is insanely dangerous.

Jouni Pohjola notes that pretty much all of the above points are the reason for combat archeology (think Indiana Jones), as sceen in Ken MacLeod's Newton's Wake. According to TV Tropes, combat archeology is mostly involved with jumping through wormholes and gunning down post-singularity alien robots.

In some of Andre Norton's space science fiction (noteably The X Factor) archeologists investigate wilderness planets looking for Forerunner artifacts. Often when they discover some, they will abruptly be raided by "Jacks" (presumably short for "skyjacker") who will kill all the archeologists then plunder the site for anything valuable. Working Forerunner technology is valuable but rare, Jacks mostly rely upon the large number of mega-wealthy entitled individuals who will pay top dollar for unique Forerunner works of art and jewelry.

Ben McGee notes that xenoarcheology will probably be much like H. P. Lovecraft's story "At the Mountains of Madness". Tekeli-li! Tekeli-li!

In the TV show Babylon 5, there was a corporation called Interplanetary Expeditions or "IPX". It was dedicated to researching the ruins of advanced civilizations that are now extinct, in the quest to find new technologies that they can patent and profit from. In other words: paleotechnology is their entire business model and revenue stream.


There were several star faring civilizations that preceded us into the galaxy and their artifacts are a tantalizing source of discovery and frustration. Sometimes, these forerunner artifacts can trigger a scientific breakthrough.

rulebook to Stellar Crusade (1988)

Star Gods

Call it the Star Gate.

For three million years, it had circled Saturn, waiting for a moment of destiny that might never come. In its making, a moon had been shattered, and the debris of its creation orbited still.

Now the long wait was ending. On yet another world, intelligence had been born and was escaping from its planetary cradle. An ancient experiment was about to reach its climax.

Those who had begun that experiment, so long ago, had not been men - or even remotely human. But they were flesh and blood, and when they looked out across the deeps of space, they bad felt awe, and wonder, and loneliness. As soon as they possessed the power, they set forth for the stars.

In their explorations, they encountered life in many forms, and watched the workings of evolution on a thousand worlds. They saw how often the first faint sparks of intelligence flickered and died in the cosmic night.

And because, in all the galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped.

And sometimes, dispassionately, they had to weed.

The great dinosaurs had long since perished when the survey ship entered the Solar System after a voyage that had already lasted a thousand years. It swept past the frozen outer planets, paused briefly above the deserts of dying Mars, and presently looked down on Earth.

Spread out beneath them, the explorers saw a world swarming with life. For years they studied, collected, catalogued. When they had learned all that they could, they began to modify. They tinkered with the destiny of many species, on land and in the ocean. But which of their experiments would succeed they could not know for at least a million years.

They were patient, but they were not yet immortal. There was so much to do in this universe of a hundred billion suns, and other worlds were calling. So they set out once more into the abyss, knowing that they would never come this way again.

Nor was there any need. The servants they had left behind would do the rest.

On Earth, the glaciers came and went, while above them the changeless Moon still carried its secret. With a yet slower rhythm than the polar ice, the tides of civilization ebbed and flowed across the galaxy. Strange and beautiful and terrible empires rose and fell, and passed on their knowledge to their successors. Earth was not forgotten, but another visit would serve little purpose. It was one of a million silent worlds, few of which would ever speak.

And now, out among the stars, evolution was driving toward new goals. The first explorers of Earth had long since come to the limits of flesh and blood; as soon as their machines were better than their bodies, it was time to move. First their brains, and then their thoughts alone, they transferred into shining new homes of metal and of plastic.

In these, they roamed among the stars. They no longer built spaceships. They were spaceships.

But the age of the Machine-entities swiftly passed. In their ceaseless experimenting, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light. They could become creatures of radiation, free at last from the tyranny of matter.

Into pure energy, therefore, they presently transformed themselves; and on a thousand worlds, the empty shells they had discarded twitched for a while in a mindless dance of death, then crumbled into rust.

Now they were lords of the galaxy, and beyond the reach of time. They could rove at will among the stars, and sink like a subtle mist through the very interstices of space. But despite their godlike powers, they had not wholly forgotten their origin, in the warm slime of a vanished sea.

And they still watched over the experiments their ancestors had started, so long ago.

From 2001 A Space Odyssey by Sir Arthur C. Clarke

...a Starprobe had been destroyed after it had entered a solar system. Perhaps it had made contact with the mysterious Hunters of the Dawn, who had left their marks upon so many worlds, so close to the Beginning itself.

From The Fountains of Paradise by Sir Arthur C. Clarke

I been readin' 'bout how maybe they is planets peopled by folks with Ad-vanced brains On the other hand, maybe we got the most brains ... maybe our intellects is the universe's most Ad-vanced.

Either way, it's a mighty soberin' thought.

From Pogo the Possum by Walt Kelly

As if beckoned by those who had gone before, I half-floated between the titanic snowdrifts, quivering and afraid, into the sightless vortex of the unimaginable.

Screamingly sentient, dumbly delirious, only the gods that were can tell. A sickened, sensitive shadow writhing in hands that are not hands, and whirled blindly past ghastly midnights of rotting creation, corpses of dead worlds with sores that were cities, charnel winds that brush the pallid stars and make them flicker low. Beyond the worlds vague ghosts of monstrous things; half-seen columns of unsanctifled temples that rest on nameless rocks beneath space and reach up to dizzy vacua above the spheres of light and darkness. And through this revolting graveyard of the universe the muffled, maddening beating of drums, and thin, monotonous whine of blasphemous flutes from inconceivable, unlighted chambers beyond Time; the detestable pounding and piping whereunto dance slowly, awkwardly, and absurdly the gigantic, tenebrous ultimate gods the blind, voiceless, mindless gargoyles whose soul is Nyarlathotep.

From Nyarlathotep by H. P. Lovecraft (1920 )

They too might look across the 50,000 light-years to the core of the Galaxy, glimpse the titanic forces flickering there among the most ancient of the stars - and marvel at the mentalities that must control them.

From The Lost Worlds of 2001 by Sir Arthur C. Clarke

Our Galaxy is now in the brief springtime of its life - a springtime made glorious by such brilliant blue-white stars as Vega and Sirius, and, on a more humble scale, our own Sun. Not until all these have flamed through their incandescent youth, in a few fleeting billions of years, will the real history of the universe begin.

It will be a history illuminated only by the reds and infareds of dully glowing stars that would be almost invisible to our eyes; yet the somber hues of that all- but-eternal universe may be full of color and beauty to whatever strange beings have adapted to it. They will know that before them lie, not the milions of years in which we measure the eras of geology, nor the billions of years which span the past lives of the stars, but years to be counted literally in trillions.

They will have time enough, in those endless aeons, to attempt all things, and to gather all knowledge. They will not be like gods, because no gods imagined by our minds have ever possessed the powers they will command. But for all that, they may envy us, basking in the bright afterglow of Creation; for we knew the universe when it was young.

From PROFILES OF THE FUTURE by Sir Arthur C. Clarke

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