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Earth Calling the Cosmos

Earth Calling the Cosmos


By Seth Shostak, Senior Astronomer

For more than six decades, a small group of scientists has been trying to pick up radio transmissions from other planetary systems, motivated by the fact that doing so would demonstrate that someone intelligent is out there. This effort, known as SETI (the Search for ExtraTerrestrial Intelligence), is straightforward and technically fairly straightforward, as it doesn’t require interstellar travel for either the aliens or the Earthlings. It’s a strictly passive endeavor – using big antennas feeding highly sensitive receivers that can sniff out signals over a broad range of the radio dial.

But some researchers believe we should be taking a more active role in probing nearby space. They argue we should prod the aliens with signals of our own, inviting them to respond; an exercise known as “active SETI.” Rather than hope that the extraterrestrials have launched signals our way, we could knock on their door and get their attention.

In practice this amounts to sequentially aiming a powerful radio transmitter at one star system after another while transmitting a friendly message that, one hopes, will trigger a similarly friendly response.

This sounds straightforward, but there are some decisions to be made. To begin with, how do we encode the message in a way that space aliens, whose English abilities are surely sub-par, will understand. In addition, what information should we transmit? Shakespeare’s collected works? The Harvard five-foot shelf?

Recently, a new addition to the art of cosmic composition has appeared. It’s the work of a global team of researchers led by Jonathan Jiang of the Jet Propulsion Laboratory in Pasadena, California. Like many of its predecessors, the new communication scheme makes a call back to the short pictogram transmitted from the Arecibo, Puerto Rico radio telescope in 1974. Mathematics, physics, astronomy, and biology are the touchstones for these pictograms – all subjects that are presumed to be required coursework for extraterrestrials. We won’t share a common language with the aliens, but we can certainly presume a shared familiarity with science and math.

However, the idea of trying to initiate contact is not looked upon kindly by some people in the research community, who see the possibility of a calamitous outcome to betraying our existence to unknown beings. It’s been likened to shouting in a dark forest.  The potential consequences could be dire, so we mustn’t take chances. We should keep our heads down.

That’s a popular point of view, one that was even endorsed by Stephen Hawking. But I don’t agree.  Laying low might seem like cheap insurance against catastrophe, but that’s not the way I see it.

I believe that the costs of laying low would be substantial. After all, Homo sapiens might be around for a long time, and insisting that we never, ever point a powerful radio transmitter skyward could prove to be a weighty albatross burdening our descendants.

But remember that we can only be threatened by species that have the means to either come here or send their weaponry our way. Either option demands a degree of technical sophistication that’s far beyond our own. But if they’re that advanced, then they can be presumed to have large antennas and sensitive radio receiving equipment, and to have had such technologies for a while. That means that irrespective of their personal natures, they can detect the transmissions we’ve already sent into space: The television, radio, and radar signals we’ve been lofting skyward since World War II.

In other words, it’s entirely too late to worry about giving away our position. That’s been done. Additionally, if we were to accede to the alarmist position that strong transmissions to the sky should somehow be forbidden, what happens when we establish colonies or waystations elsewhere in our solar system? Do we set limits on any transmissions to these outposts because of the inevitable “spill” radiation that would continue into deep space? And what about the use of radar for establishing the orbits of long-period comets as a matter of defense against the type of deadly impact that doomed the dinosaurs? Do we give that up too?

The paper from Jiang et al. suggests yet another scheme for sending an informative postcard to other Milky Way inhabitants. The public reaction to this work has been modest, even if some of the graphics – which portrayed nude humans – were not. Some people seem to think that the real issue with active SETI is the impropriety of sending images of unclothed human bodies into space. These guardians of terrestrial decorum seem less concerned with whether doing so might be a suicidal move for life on Earth than with keeping aliens from seeing what we look like underneath our clothes. From my point of view, both worries are wacky.

Originally appeared at

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