Oberhaus, in his otherwise dense and wide-ranging book, says little about interstellar transmissions after the second Cosmic Call, though there have been some. As recently as 10 October 2016, ‘a simple response to an elemental message’ (Asrem) – a 27,653,733 byte message containing responses to climate change by artists from around the world – was broadcast in the direction of Polaris from the European Space Agency’s Cebreros Station in Spain. But Asrem was never supposed to be a serious attempt to talk to an alien species. It’s difficult to persuade people to pay for those. All federal funding for Seti in the US was cut in 1993; since then, work towards making contact with extraterrestrials, with the exception of China’s recently completed 500-metre Aperture Spherical Telescope, has all been privately funded – and by far the greater portion of that funding has gone on Seti rather than Meti. Transmitting is not only much more expensive than receiving – or attempting to receive – it’s also perceived as highly risky. After Drake’s broadcast in 1974, the astronomer Martin Ryle asked the International Astronomical Union to ban interstellar messaging, explaining in a letter to Drake that it was ‘very hazardous to reveal our existence and location to the Galaxy; for all we know, any creatures out there might be malevolent – or hungry.’
Extraterrestrial Languages is not light; published by the MIT Press, it reads like an academic work. I was surprised, after finishing it, to discover that Oberhaus was a science writer and not an academic himself. But it is worth the effort, not least because it shows how many areas of thought the seemingly simple question ‘how do we communicate with aliens?’ touches on: Chomskyan linguistics, physics (microwaves would be the best medium, because they get through the atmosphere, and the galaxy’s background noise is quietest in those wavelengths), and existential risk (Martin Ryle, the former Astronomer Royal, warned that broadcasting our position to the universe might be the equivalent of shouting in a jungle), to name three.