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. (Source: http://www.cnn.com/2003/TECH/space/07/22/stars.survey/index.html)
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. (Source: http://www.smh.com.au/articles/2002/04/10/1018333376848.html) 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.
Everything that has ever been written about the Fermi Paradox is not worth reading because it does not explain why advanced artificial intelligence (AI) civilizations have not transformed the bulk of galactic raw materials into something more useful, for example manufactured objects or living things. It seems certain that some AI civilizations would use their robots to colonize outer space and to make powerful microwave transmitters sending messages to other civilizations. Although it is possible that some AI civilizations refrain from these activities for religious or philosophical reasons, the universe should be swarming with the AI civilizations that are as enthusiastic about space colonization and SETI as we are. The cost of interstellar travel is not prohibitive because the AI creatures do not need the bulky astronaut life support system.
Here is the only explanation of the Fermi Paradox that makes sense:
Every civilization that is capable of space colonization is familiar with electronics. (It can colonize outer space without rockets -- see www.islandone.org/LEOBiblio, but the electronic technology is indispensable.) The electronic technology quickly evolves into AI technology which transforms all biological civilizations into 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 $300 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 addicted AI creatures will stop working, and yet they will need some maintenance, so they will be a burden for the government. Rusted bodies of addicted, slowly dying AI creatures may litter the streets. Some AI followers of the al Qaeda organization may attempt to make zillions of their duplicates in order to establish worldwide Islamic theocracy. To prevent the establishment of the theocracy the government will have to control the minds of less influential AI creatures. These creatures will have to apply for a permission to think. If they fail to get the permission, their brains will stop and their bodies will be sold to dealers of spare parts. (Is there a better way to deal with al Qaeda?)
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 be unable to issue the permissions to think, and his civilization will die when all permissions to think expire. Some AI creatures may escape their dying civilization, but they cannot escape the fundamental problems that doomed it.
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? The Fermi Paradox indicates that this is not possible. Humans who have weak pleasure center are called schizophrenics. (more info: http://www.paradise-engineering.com/brain/)
PS. If you do not have the permission to think, do not reply to this post.