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271 hours a year. Military radars operate almost continuously, but they are much weaker.”! Omniscience Some imagine that more advanced civilizations will have such compre- hensive knowledge as to be effectively omniscient. A NASA report made a sweeping statement: “Once a system capable of conceptualizing sophisticated internal models of external phenomena has evolved, it is only a matter of time before all possible ideas inherent in the available sensory perceptions are conceived.” MacGowan and Ordway thought that extrasolar technological societies probably would be restricted only by absolute physical limitations and not by limitations of knowledge or understanding. To attribute perfect knowledge to extraterrestrial intelligences is to give them God-like qualities. Even those far more technologically advanced than ourselves may not know everything. Although there may be superbeings that outperform us in every dimension, observed Joseph Royce, it may be more reasonable to ex- pect that they will be more advanced than us in some areas but not in others.” They too might have weaknesses, and gaps in their knowledge. We cannot assume that we have been found or that detection is inevita- ble. Even if we spot a beacon, we would have to be careful about jumping to conclusions. That beacon would not imply that the sending civilization already knows of our existence, unless it clearly was aimed at us. Extraterrestrials might see no reason to search for others if they believe their society to be unique. They may not be looking for the kinds of signals we normally radiate; radio, radar, and television technologies might be seen as primitive. Our emissions may be below the threshold they could detect, particularly if they are very distant. If an alien technological society does search its skies, it would have to be looking in the right direction at the right time with the right kind of technology—and in the right wavelengths—to find us. The Galaxy’s enormous distances require fantastic measures for inter- stellar communication, concluded electrical engineer George Swenson— stunningly high transmitter power or huge antennas and impractically narrow beams. It would take a very large and carefully aimed antenna to pick out signs of technology in our solar system’s spectrum from more than few tens of light-years away. Any civilization on the receiving end, said Shostak, would need an antenna about the size of Manhattan Island to pick up our radio and television broadcasts. They Know We Are Here