How to Search for Dead Cosmic Civilizations

Abraham Loeb: The rate of growth of new technologies is often proportional to past knowledge, leading to an exponential advance over time. This explosive process implies that very quickly after a civilization reaches technological maturity, it will develop the means for its own destruction through climate change, for example, or nuclear, biological, or chemical weapons. Developments of this type, over mere hundreds of years, would appear abrupt in the cosmic perspective of billions of years. If such self-destruction is common, this could explain Fermi’s paradox, which asks “where is everybody?” — and could imply that relics of dead civilizations should be abundant in space. When exploring habitable worlds around other stars, we might therefore find planets with burnt-up surfaces, abandoned mega-structures, or planetary atmospheres rich with poisonous gases and no sign of life. Even more intriguing is the possibility that we will find technological relics flying through our solar system with no detectable functionality, such as pieces of equipment that lost power over the millions of years of their travel and have turned into space junk.

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