THE cosmos is quiet. Eerily quiet. After decades of straining our radio ears for a whisper of civilisations beyond Earth, we have heard nothing. No reassuring message of universal peace. No helpful recipe for building faster-than-light spacecraft or for averting global catastrophes. Not even a stray interstellar advertisement.

Perhaps there's nobody out there after all. Or perhaps it's just early days in the search for extraterrestrial intelligence (SETI), and we're listening to the wrong star systems or at the wrong wavelengths.

There is another possibility, says Douglas Vakoch, head of the Interstellar Message Composition programme at the SETI Institute in Mountain View, California, which ponders the question of how we should communicate with aliens. "Maybe everyone's listening but no one is transmitting. Maybe it takes an audacious young civilisation like ours to do that."

So should we start sending messages into the void? And if so, how can we make ourselves understood to beings we know nothing about?

One astronomer has already stepped up to the challenge. Alexander Zaitsev at the Russian Academy of Science's Institute of Radio Engineering and Electronics in Moscow has sent four interstellar messages since 1999, each beamed to no more than a handful of nearby sun-like stars. Zaitsev's efforts are pretty small scale, however, and so far his group is more or less alone except for some low-power operations offering to send your message to the stars for a fee.

Read more: Earth calling: A short history of radio messages to ET

That could be about to change. Perhaps bored with spending so long hearing nothing, the wider SETI community is starting to consider a more active approach. They will get together to discuss whether to go for it at a meeting in April in League City, Texas. Vakoch, who will chair these sessions, is all in favour. "I have long held the position that after broad-based international consultation, we should be doing active SETI," he says.

It's an approach that worries ex-astronomer and science fiction author David Brin, who was a member of the International Academy of Astronautics SETI panel until 2006. He resigned when the committee backtracked on the wording of a protocol that called for discussion before deliberately broadcasting into space. "I dislike seeing my children's destiny being gambled with by a couple of dozen arrogant people who cling to one image of the alien," says Brin. Since then three other members have quit for similar reasons. Vakoch has some sympathy with Brin's point of view. "These issues are much too important and too complex to be resolved after only a few days of discussion."

If the enthusiasts for active SETI get their way and there is a real effort to send a message, the n

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