There are currently eleven active SETI (search for extraterrestrial intelligence) programs on telescopes around the world. They operate at microwave and optical frequencies, as either sky surveys or targeted searches in the direction of (primarily) solar-type stars. Each is attempting to detect an electromagnetic biosignature of a technological civilization. Although detectable technologies will be far older than our own, these searches are constrained by our current understanding of physics and the terrestrial technologies available in the 21st century. Moore's Law suggests that most of these detection technologies will improve their capacity exponentially. Thus if any of the current strategies is valid, a thorough exploration of the Milky Way Galaxy should be possible within decades (not centuries), and success, or a significant null-result is predictable. Giving up, incorporating new search strategies based on emergent technologies, or adding beacon transmission to the listening strategies are all future possibilities.
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