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Despite the naive storylines about interstellar travel in science fiction, biological creatures were not selected by Darwinian evolution to survive travel between stars. Such a trip would necessarily span many generations, since even at the speed of light, it would take tens of thousands of years to travel between stars in our galaxy’s disk and 10 times longer across its halo. If we ever encounter traces of aliens, therefore, it will likely be in the form of technology, not biology. Technological debris could have accumulated in interstellar space over the past billions of years, just as plastic bottles have accumulated … Read more