Just call, will you

摘要

Our galaxy may be teeming with intelligent civilisations, but none of them wants to talk to us. That's the only obvious way to understand years of radio silence, say ET researchers. Today's searches for extraterrestrials are based on the idea that advanced civilisa-tions will communicate with a radio beacon somewhere close to the frequency naturally emitted by hydrogen atoms. Although we aren't yet trying to attract the attention of alien intelligences in this way, the rationale is that this would be the best way for an advanced civilisation to get noticed because observers are more likely to be looking there than at some randomly chosen frequency. From 1988 until 1993, the Megachannel ET Assay (META) based at Harvard University scanned the sky and investigated more than 10 trillion signals of this type.