I shot an arrow into the air

The controversial practice of "active SETI" was news to Lex Alexander, as it was to me before I read the Seed article about Alexander Zaitsev. Lex writes:

We've been sending radio signals into space for more than a century now. God alone knows what any intelligent life that receives them might make of them.

Also, I thought SETI was primarily about LISTENING for radio signals. I didn't know we were broadcasting intentionally. What would we send? "24" reruns? Pi?

An "Interstellar Rosetta Stone," for one; here's an annotated excerpt.

Diffuse transmissions and targeted ones are two different things, as the excellent article in Seed points out:

Even if something menacing and terrible lurks out there among the stars, Zaitsev and others argue that regulating our transmissions could be pointless because, technically, we've already blown our cover. A sphere of omnidirectional broadband signals has been spreading out from Earth at the speed of light since the advent of radio over a century ago. So isn't it too late? That depends on the sensitivity of alien radio detectors, if they exist at all. Our television signals are diffuse and not targeted at any star system. It would take a truly huge antenna—larger than anything we've built or plan to build--to notice them.

Alien telescopes could perhaps detect Earth's strange oxygen atmosphere, created by life, and a rising CO2 level, suggesting a young industrial civilization. But what would draw their attention to our solar system among the multitudes? Deliberate blasts of narrow-band radiation aimed at nearby stars would -- for a certain kind of watcher -- cause our planet to suddenly light up, creating an obvious beacon announcing for better or worse, "Here we are!"

Lex also asks whether I've seen the Jodie Foster movie Contact. I sure have, and loved it. I also enjoyed the Carl Sagan novel that inspired it, but nothing in the novel thrilled me like the sequence in the movie in which the lonely techs first receive the alien transmission.

My former student Sarah Ong writes, meanwhile:

Ah yes...diplomacy...from a government that doesn't officially believe in aliens :)

Since there's little, if any, evidence for them -- beyond the theoretical -- disbelief seems a reasonable response to me. But active SETI is controversial in part because it's beyond any government's ability to stop. For now, scientific and other non-governmental organizations conceivably could stop or discourage such efforts -- but one day, Seed speculates, this sort of targeted transmission will be possible from any backyard, and there'll be no stopping it then.