Copyright (c)1994 Anders Sandberg. Permission to download, copy, and redistribute this work for non-commercial purposes is hereby granted without charge.
The Fermi paradox ("if there are intelligent life in space, why aren't they here?") might be based upon our current slow information processing.
What is the most probable form of alien intelligence? We haven't the faintest clue, but we can guess at certain properties. I think its rather reasonable to guess that the speed of information processing increases as a civilization develops. An increased rate of processing will be an advantage, and breed even faster methods. By its nature, the increase seems to go towards exponential increase until constrained by physical restrictions (like the speed of light). This will in the end lead to a state of nearly maximal rate of information processing, which very probably is far above our current level.
A possible such state might be networks of nanocomputers or computer-like systems embedded in neutron stars. High rates of information processing will probably require high rates of energy flow, but what forms of energy will be used or the physical structure is hard to guess at. The main constraints will be communication speed, which limits the spatial size of the "civilizations". Exchanging messages over a distance of a light second might take years of subjective time from the perspective of sender and receiver.
My idea is that the aliens may well exist right at our doorstep, maybe as nanotechnological nodules in the asteroid belt or as a "submerged Dyson shell" inside the sun to gain maximum energy gradient. They might as well be in the dust on your computer screen. But they are so extremely fast, that we are unable to communicate with them. Their communications may look like high-frequent noise to us, and transmissions to neighbouring civilizations might be very infrequent, since the time lag makes them impractical.
In the same way its not very practical for the aliens to communicate with us. Sending a obvious message will take millennia or more of subjective time, and the response will with high certainty be of rather limited interest (they could as well build a simulation of the human mind in a fraction of the time). Even keeping a transmission running might be problematic, as political, social or economical changes during the transmission might interrupt its progress. The only way to begin communication with the aliens might be to accelerate our own rate of processing enough.