Why sending messages to extraterrestrials is controversial

FOR 75 years, astronomers have been searching for extraterrestrial intelligence. SETI involves listening for radio or optical signals sent by intelligent civilisations. No artificial signals have yet been detected. The failure of SETI is called “The Great Silence”, but despite this, many scientists are confident that intelligent aliens exist. There are thought to be at least 10 billion habitable worlds in our galaxy, and billions of years have passed in which any life on them could have developed intelligence and technology.

METI, or messaging extraterrestrial intelligence, has been less common. It involves talking rather than listening. To some,…