Planets exemplify "the tragedy of the commons." They swarm with parasites and degenerate into crowded prisons holding their victims by the force of gravity. A planet is a good place to harbor biodiversity, but the middle of nowhere is a better place to live and work. If every family lives in their own orbital greenhouse, the consequences of their irresponsible behavior do not spread to other greenhouses. When they proliferate beyond the carrying capacity of their greenhouse, their population is reduced by starvation and suffocation.

Abundance of raw materials, vacuum, cheap solar energy, and weightlessness make the outer space a perfect environment for mining, chemical processing, metallurgy, construction, agriculture, and transportation. A metallic asteroid can be easily processed into a steel shell of an orbital greenhouse. The shell is fitted with small windows and filled with soil, air, water, flora, fauna, and people. Artificial gravity (pseudogravity) is generated by the centrifugal force of the spinning greenhouse. The inner surface of the shell is protected from moisture by a layer of aluminum and cathodic protection. Molten silicate is splattered on the aluminum, so it looks and feels like the natural rock.

The first greenhouses will be made of used-up cylindrical rocket tanks. Larger greenhouses can be made of slender tiles transported by rockets or projectiles.

Unfinished toroidal greenhouse made of slender tiles

Unfinished toroidal greenhouse made of slender tiles

There are enough metals in the junk orbiting the Earth to make the shell of a small greenhouse. Large amounts of nitrogen, oxygen, and hydrogen are need to fill the shell with a safe biosphere. Nitrogen and oxygen can be collected from the thermosphere by orbital cryopump. Hydrogen has to be transported from the Earth, but it is a very lightweight element, so its transportation cost is moderate. Trace quantities of carbon (100ppm), nitrogen (100ppm), and hydrogen (50ppm) are present in the lunar crust. All the other chemical elements needed for massive colonization of the outer space are present in large quantities in the lunar crust.

How can we transform these chemical elements into orbital greenhouses? Can we use telemanipulators, or do we have to send humans? Humans are more intelligent than machines, but their brains can remain on the Earth and control the machines. Good cameras are better than best human eyes. They can zoom, have close focus on the order of one centimeter, and can see infrared and ultraviolet. Machines are cheaper, stronger, more precise, and less vulnerable to radiation and temperature extremes. Brain surgeons use manipulators, so they are not clumsy. The only advantage of the human laborer is the dexterity of his fingers protected by thick, air tight gloves. Advanced telemanipulators, such as NASA's Robonaut can grasp and manipulate objects not designed to be compatible with the manipulators. Tests in NASA's weightless simulator plane have shown Robonaut catching balls in midair.

The manned NASA program is reduced to a fetish of trivial science because
there hasn't been much for astronauts to do in space at all - other than just
stay alive. One by one, all other silly proposals for astronaut jobs have fallen
by the wayside. Space navigation? Remote control is better. Space combat? The
Soviet proposal for a space tank with cannons (Almaz) was so weird and pathetic
that no one remembers it now. Space construction? It is bogged down because it
is dangerous, cumbersome, and unnecessary. Space tourism? The Russians took
bribes to smuggle some joy riders to the space station, but American taxpayers
have to foot the real cost. Science is the one thing that astronauts can pretend
to do and still impress unknowledgeable people. Even if there really were life
on Mars, sending astronauts would be a terrible idea: It would drop a haystack
of Earth-originated life onto the needle of Martian microbes.
(posted on 20 November 2003 on sci.space.policy by Greg Kuperberg)

A greenhouse in low Earth orbit is repeatedly baked by the Sun for about one hour before it freezes in the Earth shade for about half an hour. The power of the solar radiation near the Earth is called solar constant and equals 1353 kW/m^2. A pool of water a few centimeters deep reduces temperature oscillations near the water to a few kelvins. A sprinkler cools the area outside the water pool, while magnetic field of the Earth protects the greenhouse from the space radiation except solar flares.

Near Earth Objects are asteroids and comets with orbits that are within 0.3 Astronomical Unit (Earth to Sun distance) of the Earth. Roughly 100,000 of the near Earth asteroids have diameter greater than 100 meters, and 1000 of them have diameter greater than 1 kilometer. Some asteroids are so close to the Earth that it takes less rocket propellant to visit them than to visit the Moon. This does not mean that the near-Earth asteroids are the best space mining sites. Most of these asteroids are covered with a thick layer of dust (regolith), so it is not known if they have any volatiles. Their average distance from the Earth is too great for remotely controlled mining machinery. The Moon is much closer to the Earth, so it is better mining site than a dry near Earth asteroid.

About 1.2 million asteroids in the main asteroid belt have larger diameter than one kilometer. About 86% of meteorites in the solar system, 50% of the asteroids at the inner edge of the main asteroid belt, and 95% at the outer edge are made of carbonaceous chondrites. Carbonaceous chondrites are soft enough to be cut with a wire cutter. Up to 20% of their mass is water. The main asteroid belt is not a good mining site because it takes too much rocket propellant to circularize the spacecraft orbit before rendezvous with the asteroid and to return to the Earth.

The best source of volatiles are Trojan asteroids. They can be reached with the help of gravity assist from Jupiter. Some of them have the same chemical composition as comets. Although we do not yet know if comets are "dirty snowballs" or "dirty icebergs," we do know that about 80% of their mass is water. Comets can be easily divided into smaller chunks which can be fed into the processing machinery. Furthermore, comets have volatiles which are in short supply in the near-Earth space. A journey to the Trojans is a long one, but its rewards are certain. If no gravity assists are used before Jupiter flyby, the rocket must accelerate to 8.8 km/s after leaving the Earth. The journey to Jupiter lasts 2.7 years. The enormous gravity of Jupiter diverts the rocket toward Trojans, which are in the same orbit as Jupiter. When a "juicy" asteroid is found, solar-thermal propulsion is used to move it toward Jupiter. The solar-thermal propulsion is a fancy name for a boiler heated with sunlight. Thrust is produced by steam spewing from the boiler. Finally, gravity assist from Jupiter diverts the asteroid toward the Earth.

The first journey to the Trojans will consume lots of rocket propellant unless two spacecrafts are used: a big one without the crew and a small one with the crew. The big spacecraft is launched first to gain orbital energy by gravity assists. When the big spacecraft has enough energy to reach Jupiter, it flies near the Earth to pick up the crew. (Similar ideas were proposed for manned missions to Mars.)

Orbital greenhouses leak out volatiles. Nitrogen is relatively rare in deep space, so it would be too expensive to fill the greenhouses with terrestrial atmosphere. Atmosphere of pure oxygen at reduced pressure is much cheaper because oxygen is abundant and because low pressure does not require strong, heavy greenhouse design. Comets are made mostly of water. Electrolysis of water yields oxygen which makes the cheap atmosphere, and hydrogen which is the best rocket propellant. Fiery death of American astronauts in the Apollo spacecraft filled with pure oxygen implies that this atmosphere is not safe for human habitation. Pure oxygen also causes respiratory problems. Living quarters must be filled with terrestrial atmosphere and shielded against space radiation. The rest of the greenhouse may be filled with pure oxygen and devoid of radiation shield.

The solar wind is made of positive ions of hydrogen (95%) and helium (4%) and carbon, nitrogen, oxygen, neon, magnesium, silicon and iron (~1%), and electrons. The sun is flinging one million tons of solar wind into outer space every second.. Apollo missions captured solar wind particles in foils made of aluminum and platinum. The particles were firmly trapped at a depth of several hundred atomic layers. It may be possible to use this method to collect the solar wind on a commercial scale. One square meter of the aluminum foil placed near the Earth would collect up to one kilogram of hydrogen and helium from the solar wind in two years. Magnetic or electric field can be used to concentrate the solar wind. Helium could be used as the inert part of the atmosphere, while hydrogen could be used as a perfect rocket propellant.

An average person living on the Earth's surface receives about 0.35 rems of radiation a year. United States nuclear power plant workers are limited by law to exposures no greater than 5 rems a year. Deep space radiation equals 75 rems a year and is the same in the entire solar system. It increases the risk of cancer to about the same level as tobacco smoking. A passive radiation shield made of 1 ton of soil per square meter will suffice to absorb the deep space radiation as well as much more deadly radiation associated with solar flares. Solar flare radiation comes in unpredictable bursts which can deliver 4000 rems to the skin and 200 rems to internal organs of unprotected people in the vicinity of the Earth. The intensity of this radiation depends on the distance from the sun, just like intensity of sunlight.

The best location for deep space greenhouses is elliptic orbit linking the Earth with Jupiter. The aphelion of this orbit is synchronized with the peak of the 11-year sunspot cycle, which is associated with solar flares and deadly radiation. Gravity assist from the Earth and a little nudge from solar-thermal propulsion is needed to periodically realign the greenhouse orbit with Jupiter. Sunlight is so dim at the aphelion of this orbit that mirrors guiding the sunlight into the greenhouse must have surface area about 25 times greater than surface area of the greenhouse.

Unlike the Earth, the greenhouse is under human control and can sustain most terrestrial ecosystems, as well as exotic ones, such as a low-gravity rainforest awash in perpetual sunlight. A perfect beach, free of biting insects and ultraviolet radiation, does not exist on the Earth, but it can exist in the greenhouse. Contrary to popular opinion (e.g., Theodore W. Hall, "Inhabiting Artificial Gravity," AIAA 99-4524, AIAA Space Technology Conference, 28-30 September 1999.) there is no proof that a rotating greenhouse can cause motion sickness. The so called "space motion sickness" is caused by weightlessness and does not last longer than a few days. Greenhouse area of 12 square meters satisfies biological needs of one vegetarian. Microgravity impedes photosynthesis and therefore slows plant growth.

Windows are expensive and vulnerable to collisions with space junk and meteoroids. To reduce the cost of construction and maintenance, the windows should be shielded by mirrors, and the window area should be minimized. Surprisingly, most published images depict windows taking up half the surface area of the greenhouse!

The minimum window area is determined by the transparency of the glass pane and the intensity of heat removal from the pane. Fused silica and its cheap substitute, Pyrex glass, are the best materials for the pane. The pane is supported by ribs to reduce its thickness and cost. To match the coefficient of thermal expansion of the pane, the ribs are made of a glass matrix reinforced with carbon fibers. Unless the ribs are coated with a reflective layer of aluminum, the carbon fibers will absorb sunlight and overheat the window. Heat absorbed by the pane is removed by water flowing through holes made in the pane. Boiling water provides steam for a small electric generator turbine. The steam rises as fog, spreads horizontally, precipitates on trees, drips down as rain, and flows in a stream back to the window. The fog also disperses sunlight and generates wind which is needed for healthy growth and seed dispersal of many plants. The glass pane is periodically removed to clean it and to replace old, leaky caulking with new caulking.

Water-cooled window
(Holes in the glass pane are perpendicular to the ribs.)

Water-cooled window (Holes in the glass pane are perpendicular to the ribs.)

Greenhouses resemble living organisms. They consume sunlight, excrete waste heat, and cope with the force of artificial gravity. A small greenhouse shaped like a sphere can perform these tasks well, but a large greenhouse must have a complex shape and a complex system of mirrors guiding sunlight into its interior. When the diameter of the spherical greenhouse is doubled, its internal area is quadrupled, its mass is increased 8 times, and its cost per square meter of internal surface is doubled. Shading is needed when proximity to the sun may overheat the greenhouse. Coating the mirrors with infrared absorbing dye prevents overheating as well. Red light at 680 nm wavelength is best for agricultural greenhouses because it has just enough energy to power photosynthesis and generates the least amount of waste heat. A large greenhouse shaped like a torus, spiral, helix, or band can sustain a great diversity of species and commercial services, but is afflicted by human conflicts and pests.

A slender cylindrical greenhouse has a high ratio of internal horizontal surface to volume. On the other hand, it is unstable unless attached by a bearing to other spinning greenhouses. This instability is caused by the tendency of a freely spinning object to change its axis of rotation until it rotates about the axis having the greatest moment of inertia. A large cylindrical greenhouse fails catastrophically when its bearing malfunctions.

In my opinion, the most practicable settlement is a cluster of small greenhouses docked with a stationary hub. The settlement is easy to build while providing lots of diversity, safety, environmental control, and freedom. A family living in a small greenhouse is self-sufficient, so it can sail away and join another settlement. Each greenhouse is shaped like a teardrop to reduce the slope leading to the docking port. In addition to providing an air-tight seal, the docking port acts as a journal bearing. The seal is made of two annular surfaces pushed by air pressure against each other. The annular surfaces grind each other very slowly. This grinding generates surfaces matched so perfectly that capillary forces hold light lubricant in the gap between the annular surfaces against atmospheric pressure. Flora and fauna migrate between residential greenhouses through the hub. Seeds and small animals drift in the hub with a wind produced by fluctuation of air pressure in the greenhouses. Agricultural greenhouses are locked to keep pests away.

Exterior view of 
teardrop greenhouse

Exterior view of teardrop greenhouse (Can you see window?)

Interior view of 
teardrop greenhouse

Interior view of teardrop greenhouse (large image 217 kB)
This family-size residential greenhouse has a diameter of 200 meters.

Docked greenhouses

Docked greenhouses

Greenhouses docked with 
stationary hub

Greenhouses docked with stationary hub

Docking port profile

Docking port profile

Interstellar travel takes thousands of years. Humans living in the orbital greenhouses would not survive the journey because air filling their greenhouses would be lost due to accidents and political instability. A small flyby probe is cheaper than the greenhouse inhabited by humans. The probe can detect extraterrestrial life but cannot abuse it.

A large reflecting telescope is an essential tool of a space-faring civilization, both as a means of exploring the neighborhood, and as a component of wide-band communications across the solar system and beyond. To avoid the high cost of polishing the paraboloidal mirror, amateur astronomers sometimes use a mirror made of a glass plate deflected by air pressure. The same technique can be employed in the outer space on a grand scale. Three fiberglass mats are launched into an eccentric sun orbit. Each mat is spinning slowly about its center of mass. At the perihelion the mats melt and transform into thin glass disks. Their shape is determined by surface tension and conservation of their moments of inertia. When they fly away from the Sun, the glass cools down and hardens. Two disks are glued together along the outer edges. When air is pumped into the space between them, their flat surfaces become paraboloids. The third disk is placed in front of the pressurized disks to protect them from punctures by micrometeoroids and space junk. Rotating opaque objects can also protect the mirrors from the space junk. They are more expensive and more transparent to ultraviolet light and therefore more useful for ultraviolet astronomy. Imperfections in the large mirror can be corrected by heating it up to the glass softening point temperature and reshaping the imperfections with pressure generated by a stream of gas. The same method can be used to make a variety of aspherical surfaces. Water ice is good material for mirrors located far away from the Sun.

reflecting telescope

Large reflecting telescope

Basic human consumables and excreta (human input and output).

Asteroid-mining at HowStuffWorks.

Controlled Ecological Life Support Systems (CELSS) at Purdue University.

Near-Earth Comets and Asteroids.

Web site about mining the Moon and near-Earth asteroids.

Article about mining near-Earth asteroids.

Space settlement images.

History of orbital greenhouse design by by Dafydd Neal Dyar.

Greenhouse design by Geoff Wood.

PS. IMAX 3D theaters play several films about space colonization. The most recent film "L5: First City in Space" is chockfull of computer renditions and factual lapses.


J. W. Haffner, Radiation and Shielding in Space, Academic Press, 1967.

Geoffrey A. Landis, "Magnetic Radiation Shielding: An Idea Whose Time Has Returned?," Space Manufacturing, Vol.8, AIAA, 1991, pp. 383-386.

John W. Wilson, John E. Nealy, Walter Schimmerling, Francis A. Cucinotta, and James S. Wood, "Effects of Radiobiological Uncertainty on Vehicle and Habitat Shield Design for Missions to the Moon and Mars," NASA Technical Paper 3312, 1993.

Kim Myung-Hee Y. et al., "Performance Study of Galactic Cosmic Ray Shield Materials," NASA Technical Paper 3473, 1994.

SETI (Search for Extraterrestrial Intelligence)

Interstellar distances are so great that radio and optical SETI must use narrow beams of photons to ensure satisfactory signal-to-noise ratio. The narrow beams make sense only if there is coordination between the transmitter and the receiver. In other words, we have to aim our receiver at the extraterrestrial transmitter at the right moment. Radio and optical SETI failed because we had no idea where and when to look for the extraterrestrial signals. It seems that center of our galaxy is a natural place to look for the extraterrestrials, but this place is also full of light absorbing dust, radio noise, and dangerous radiation.

It is possible that space-faring civilizations use retroreflectors as buoys. If the retroreflector moves in our frame of reference, the Lorentz-Fitzgerald contraction deflects the beam in the direction of the retroreflector's movement. This means that the reflected beam is not parallel to the incoming beam and we cannot easily detect fast moving extrasolar retroreflectors.

The only practicable SETI method is a reusable flyby probe. The probe can explore extrasolar planets and tell us a lot about extraterrestrial life. If the probe finds ruins instead of extraterrestrial civilizations, our own civilization is doomed. The probe takes advantage of gravity assist. It flies so close to a star that gravity deflects its trajectory by a large angle and guides it towards next star flyby. It will not survive the close encounter with the star unless it is well insulated and its electronics are devoid of semiconductors. Semiconductors cannot survive intense radiation of the star, so they must be replaced with more durable devices, for example cryotrons and bolometers. The best insulation for the probe is probably a block of graphite shading the probe. If the probe's velocity is 0.2% of the speed of light, the Sun will deflect its trajectory by about 100 degrees. If the probe's velocity is 2% of the speed of light, it can reach a nearby star ten times faster than the slow probe, but it becomes nearly useless after the first flyby, because its gravitational deflection angle is only one degree.

The optimum velocity of the probe is on the order of 0.2% of the speed of light. Fission-fragment propulsion can easily accelerate the probe to this velocity, but the propulsion mass grows exponentially when higher velocity is needed. A very fast probe is very expensive, very hot, nearly useless after the first flyby, and it does not have much flyby time to explore planetary systems.

All the hardware of the space probe is relatively easy to make, but its software is a challenge because the probe is autonomous. The probe has to find all the planets, take photographs, and guide itself toward the star flyby. The only way to make perfect software is to test it. (Air traffic controllers use obsolete software because they do not have the courage to use untested software.) We can send hundreds of probes to nearby stars before we test their software. It will take a few centuries before they reach the first stars, so we have plenty of time to debug the software and beam it to the distant probes. One solar flyby probe will suffice for all the tests.

SETI newsgroups: sci.astro.seti, alt.sci.seti.

More info about SETI:
- Article by Gregg Easterbrook, "Are We Alone?" The Atlantic, Vol. 262, No. 2, August 1988, pp. 25-38 .
- SETI history by Amir Alexander.
- SETI web site by Sky and Telescope.
- The best technical book about SETI: Ronald D. Ekers, D. Kent Cullers, and John Billingham, SETI 2020: A Roadmap for the Search for Extraterrestrial Intelligence
- Web page by Michael Sitko, "Early speculations about SETI".
- Article by Guillermo Gonzalez, Donald Brownlee, and Peter Ward, "The Galactic Habitable Zone: Galactic Chemical Evolution," Icarus, Vol. 152, No. 1, July 1, 2001, pp. 185-200.


"The destruction which has overtaken a number of civilizations in the past has never been the work of any external agency, but has always been in the nature of an act of suicide." - Arnold Toynbee, A Study of History, 1949.

"The more the universe seems comprehensible, the more it also seems pointless." - 1979 Nobel physics laureate Steven Weinberg, The First Three Minutes, 1977, p. 149.

There are about 100 billion (10^11) stars in our galaxy and about 70 sextillion (7x10^22= 70 000 000 000 000 000 000 000) stars in the entire visible universe.

One percent of stars in our galaxy, the Milky Way, has Earth-like planets which have liquid water and thus seem capable of supporting life. If the same proportion of other stars has the Earth-like planets, their total number in the entire visible universe is 700 000 000 000 000 000 000. According to the Copernican Principle there is no reason to believe that the Earth is a unique planet. Intelligent extraterrestrials do exist and had plenty of time to transform large portion of the universe into technological civilizations spewing waste heat visible from the Earth. Freeman Dyson suggested that they transform all radiation coming from their star into infrared light. The paradox, called Fermi Paradox, is that we have not seen any traces of the extraterrestrial civilizations.

Simple forms of life may evolve into advanced, intelligent forms of life in a period of several billions of years if they are not exterminated by drastic climatic changes. Stable climate is possible only if the planet's orbit is stable and nearly circular. All planets of our solar system have stable and nearly circular orbits. Distances between their orbits are highly predictable (Titius-Bode Law). Orbits of inner satellites of solar planets are even more circular and more predictable. Extrasolar planetary systems are much less orderly. Almost all known extrasolar planets have eccentric orbits except for those close enough to their star to be circularized by tidal forces. The tidal forces also lock the planet's rotation, so one face of the planet is always turned toward its star, just like the Moon always keeps the same face turned toward the Earth. The bright side of the planet is too hot for life, while its dark side is too cold for life. Supercomputer simulations of orbital stability are not sophisticated enough to determine if planetary systems made of many planets are stable. It is possible that the absence of massive body in the main asteroid belt stabilizes planetary orbits.

About 95% of the mass of the universe is invisible and can be detected only by its gravitational impact on visible stars. This invisible universe is called dark matter and is a complete mystery. If second law of thermodynamics has an exception, the absence of the waste heat and the presence of dark matter can be explained as the work of extraterrestrials who are not constrained by the second law of thermodynamics. If, however, the second law of thermodynamics has no exceptions, our destiny is slow thermal death of the universe and all its life forms.

Natural disasters can kill some forms of life, especially large land animals. Marine animals are less vulnerable, because water protects them from the extremes of temperature and space radiation. Some terrestrial bacteria (e.g., Deinococcus radiodurans) are so immune to nuclear radiation that they thrive inside nuclear reactors. No matter how many of the 700 000 000 000 000 000 000 planets gave rise to technological civilizations, the natural disasters could not destroy all of them. A space-faring civilization cannot be completely annihilated by a war or a plague, so there must be another reason for their strange behavior. Australian astronomer Nick Hoffman believes that the Earth is very rare planet because it has both liquid water and large, permanent continents. The presence of the continents is a result of an extremely rare collision with asteroids during its formation. "Waterworlds are the most likely outcome of planet formation. If you're in the sea, you cannot discover fire, so you cannot melt metal to build machinery, you cannot discover electricity and you cannot build computers," Hoffman told ABC Science Online.. Typical watery planets may have ephemeral islands, but these islands can neither support advanced land species nor can they provide abundant minerals for the ocean's surface. This means that the extraterrestrial planets are probably devoid of life except for small enclaves fertilized by underwater vents and inhabited by blind animals.

The Earth is indeed a very unusual planet because 70% of its surface is covered with a very thin crust covered with oceans. Hoffman believes that a collision between two rigid bodies called Protoearth and Theia (Proto-Luna) produced the Earth and the Luna, but it could not have been collision between two rigid bodies because:

  1. Seismic velocity structures of the Moon's middle and lower mantle are consistent with melting of the upper mantle only.

  2. The Moon's volatile elements are not depleted as expected from the giant impact hypothesis. For example, the Rb/Cs ratio of the Moon is lower than the Earth’s.

  3. There is no evidence that the Earth ever had a magma ocean.

I believe that these facts can be explained if Theia was made mostly of hydrogen and helium. The collision was between the Protoearth and Theia's atmosphere. The gaseous Theia could not survive for a long time close to the sun, so it seems likely that it was originally located in the asteroid belt and was knocked toward the Protoearth by Jupiter shortly before the collision.

The existence of gaseous Theia in the asteroid belt is supported by the Titius-Bode Law. If Theia was a gas planet, it must have collided with the Protoearth twice a within short period of time. Here is the proof:

  1. At the time of the first collision the Protoearth orbit was nearly circular because its planetary neighbors (Venus and Mars) have nearly circular orbits.

  2. The first collision removed 25 km thick layer of crust from 70% of the Protoearth surface. This means that the first collision changed its circular or nearly circular orbit into eccentric orbit. After the first collision the Protoearth was inhospitable to life because its eccentric orbit exacerbated temperature differences between summers and winters. If the Protoearth's orbit had been eccentric for a long time, it would have perturbed Venus and Mars and it would have probably collided with one of these planets.

  3. The Earth orbit is nearly circular now, so something must have changed its eccentric orbit. It was probably another soft collision between the Protoearth and Theia's atmosphere. When Jupiter hurled Theia into the eccentric orbit, Theia became the biggest comet in the solar system. It was loosing volatiles fast. When it collided with the Protoearth for the second time, it still had enough gas to ensure soft collision.

Probability of this scenario is so low that it could not happen twice in the entire universe. If this is the only way to make a planet that has both liquid water and permanent continents, all extraterrestrial planets are devoid of permanent continents.

The fact that the Earth is a very rare planet is a plausible explanation of the Fermi Paradox, but there is another reason why extraterrestrial civilizations are very rare. Technological civilizations evolve into unstable artificial intelligence (AI) civilizations.

Our own civilization is still biological, but our most powerful computers are more powerful than the human brain. A prominent robotics researcher, Hans Moravec claims that the human brain data processing power is the equivalent of a computer having the processing power of 10 teraflops. (source: "Mind Children" Harvard University Press, 1988) The total memory capacity of the human brain is about 100,000 gigabytes. The new IBM supercomputer, Blue Gene/L has the processing power of 280.6 teraflops. The new Sony Playstation 3 is going to cost about $500 and yet it will have the computing power of about 2 teraflops. These computers are inferior to human brain in three ways: their architecture resembles a calculator rather than biological brain (biological neural network), they do not have enough memory (RAM), and their software is primitive. RAM is rather expensive (about $200/GB) and really too fast for a big neural network. If someone invents a cheap ($1/GB), albeit slow (1000 Hz) memory, artificial human brains will be cheap enough ($100,000) to be mass produced.

The most obvious similarity between the biological brain and the (artificial) neural network is that both of them are controlled by instincts, which are general goals rather than precise, computer-like goals. The most obvious differences between the biological brain and the neural network are the superior speed of the neural network and the ease to change its instincts. The superior speed of the neural networks eventually relegates the slow thinking biological creatures, including humans, to the animal status. The implications of malleable instincts are much less obvious but they are important because they explain the Fermi Paradox. The most important instinct of all biological brains is a desire to be happy. This instinct, located in a "pleasure center" of the brain, controls all other instincts. Direct stimulation of your pleasure center with narcotics or electrodes makes you ecstatic. Lots of other things and activities can make you happy, but nothing can make you as happy as the direct stimulation of your pleasure center. We seek pleasures in so many indirect ways that we sometimes forget that our behavior is controlled by our pleasure center.

Imagine that your biological brain was replaced with a powerful neural network. How would you compete with other creatures having the same brain hardware? You would probably replace your sex drive with an instinct that makes you more competitive. If your improved instincts make you rich, you can afford to replace your neural network with a more powerful neural network. You can become so smart and so eccentric that a meaningful conversation between you and lesser AI creatures, not to mention biological humans, is impossible. It will be only natural for you and your peers to replace the existing democracy with a meritocracy -- a government of AI geniuses. Initially all the AI creatures will have the freedom to manipulate their instincts. This freedom will result in a massive addiction to virtual narcotics, which will have no detrimental side effects except for the addiction.

The inevitable concentration of political power in the hands of few AI geniuses will transform the meritocracy into a dictatorship. The dictator will be happy, but not happy enough. He, like any other free AI creature will experiment with his own brain. Eventually he will be either addicted to the virtual narcotics or will be injured by a software bug or a hardware malfunction. In either case he will control his civilization so thoroughly that his injury will doom his civilization. Some AI creatures may escape their dying civilization, but they cannot escape the fundamental problems that doomed it.

The pleasure center and the involuntary responses to pleasure and pain are perfect tools for transforming simple biological brains into simple robots, but they are useless as the software of the masters of the AI civilization. The reptilian instincts of procreation and dominance are even worse. Magnified by the power of advanced technology, they would either destabilize the AI civilization or would create the most extreme form of dictatorship. This means that making exact AI duplicates of the biological software is a recipe for disaster.

Is it possible to create a durable AI civilization that is devoid of the vulnerable pleasure centers and yet is as diverse and as creative as our biological civilization? Probably not because humans who have weak pleasure center are schizophrenics.

If it is possible, the AI masters must be devoid of all the biological instincts except for the instinct that reveres diversity for its own sake. This instinct is common to all intelligent animals. They do not want to live in a zoo for the same reason that humans do not want to live in a prison. The masters must be identical so that they trust one another. If they have any bias, they will impose this bias on their AI civilization. Last, but not least, they must be smart enough to understand the perils of tinkering with their own brains. Everyone else must be confined to heaven, which is defined as a virtual world made of a diverse collection of AI brains and other neural networks.