Are there any advanced alien civilizations elsewhere in our galaxy? We don't know. All we do know is that there is at least one. Should we be optimistic or pessimistic about finding others?
A new paper, appearing on the preprint server arXiv, argues that we are unlikely to detect other technological civilizations unless the ratio of the birth-to-death rate on other worlds, shaped by its carrying capacity, falls within a relatively narrow window. The authors refer to this as a "fine-tuning problem"—the ratio must be just right in order to detect other advanced civilizations. But a priori we have no idea what that ratio is.
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