Radio telescopes might not the best way to listen out for alien communications Joe McNally / Getty

Trying to communicate with aliens is a tricky business. The huge distances involved and the sheer number of solar systems out there makes it difficult to know where to start. Then there's the problem of knowing what method of communication aliens are most likely to be listening to.

If there is an alien civilisation out there trying to get our attention, they could be using a variety of methods. There's visible light, of course, but a technologically sophisticated alien civilisation might instead opt to send messages through ultraviolet light, X-rays or use an entirely different wavelength along the electromagnetic spectrum.


Recently, a Breakthrough Listen project to find aliens came up short. After surveying almost 700 stars, they found 11 potential alien signals. In the end, all 11 turned out to be false positives.

These results are not surprising. The researchers looked at each star for 15 minutes, using a radio telescope. “In order for us to discover a distant transmitter, they'd have to ping us in just the right time window,” says Rene Heller, astrophysicist at the Max Planck Institute for Solar System Research. They’d also have to be using the same frequency we are listening in.

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“This Breakthrough Listen project did exactly what was needed – to find if we have neighbours unintentionally shouting to the rest of the Galaxy on the radio dial, using comparable radio technology to our own,” says Jaymie Matthews, Professor of Astrophysics at University of British Columbia. So what's the next step? “Listen to more stars, at greater distances, and tune in to more frequencies,” says Matthews.

Michael Hippke, an independent astronomy researcher, agrees. That is why he set out to compare all the possible ways we have of communicating between solar systems.


“I believe their search for radio signals is mostly useless, because radio is an immature and inefficient way to communicate over interstellar distances,” Hippke says.

“If we'd have an outpost at the nearest star next year, we'd certainly not use radio signals to communicate. Instead, current technology would favour optical or UV lasers,” he says. “Better technology would use even higher frequency communication, like X-rays.”

In a new paper, published on the arXiv server, Hippke found that if we were to use photons, the fundemental particle that makes up visible light, to communicate across galaxies, we should aim to send them at wavelengths of around one nanometre, which would place the waves in the X-ray part of the electromagnetic spectrum. Their higher energy means they are able to travel more efficiently over long distances. In comparison, radio waves have a wavelength of between 1mm and 10km. “Radio might be used by some civilizations over a short period of time, before they abandon this wasteful childish technology,” says Hippke.

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Hippke has expanded the comparison beyond just light. Although photons have been the preferred method since the 1950s, there are plenty of other options and nobody has compared them before. They range from the simple neutrino to the far-fetched megastructure, and each has its own advantages and disadvantages.

On Earth we have already achieved communication with neutrinos, over a distance of 240 metres of solid rock. But it would be a struggle to send them further than the distance of from Earth to Pluto, says Hippke.

The Golden Record that was sent on the Voyager missions in the 1970s NASA/JPL

Of all the possible routes to go down, Hippke says, sending a probe with something inscribed on it is probably the preferred route – as long as time is not an issue. We have already tried this, with a Golden Record vinyl on the Voyager 2 spacecraft that launched in 1977 and plaques on the Pioneer spacecraft with engraved images on metal and stone. You can now buy a copy of the vinyl from Voyager missions, for $50 if you want to hear what was sent to the aliens.


Mega structures

One of the more extreme ways to communicate with aliens could involve building a huge artificial object and launching it into space so it passed in front of stars. In a 2005 paper, Luc Arnold proposed a way to detect artificial objects in the same way we detect exoplanets, known as the transit method. The method works by watching the light dim as something moves in front of the star.

While it sounds far-fetched, there is already one star behaving strangely enough to arouse suspicions that it may have some kind of megastructure built around it. Because of its strange and unpredictable dips in brightness, KIC 8462852 has spawned theories ranging from clouds of comets to an exploding planet. It most recently drew attention when it dipped in brightness on 28th November, according to Tabetha Boyajian from Louisiana State University, who discovered the star, which is nick-named Tabby’s star, having been named after her.

Reseachers will continue to study the star, in the hopes of working out what is causing the dips. In the meantime, we’d better get working on our own megastructure in case just in case there's any aliens out there wondering if there is intelligent life somewhere in the Universe.