Why have humans never found aliens?
Dr Tarter reckoned that decades of searching had amounted to the equivalent of dipping a drinking glass into Earth’s oceans at random to see if it contained a fish. Dr Wright and his colleagues built on Dr Tarter’s work to come up with a model that tries to estimate the amount of searching that alien-hunters have managed so far. They considered nine variables, including how distant any putative aliens are likely to be, the sensitivity of telescopes, how big a portion of the electromagnetic spectrum they are able to scan and the time spent doing so. Once the numbers had been crunched, the researchers reckoned humanity has done slightly better than Dr Tarter suggested. Rather than dipping a drinking glass into the ocean, they say, astronomers have dunked a bathtub.