The hero of The Man in the Moone, a novel written in the late 1620s by the Anglican bishop Francis Godwin, is carried to the moon in a sky chariot pulled by a flock of wild swans. He spends the next few months among the peaceful ‘Lunars’ and gains a measure of fluency in their language, which ‘consisteth not so much of words and letters’ as of melodies ‘that no letters can expresse’. Godwin’s cosmonaut, Gonsales, in many ways had an easy time of it. He could point at a swan or a star and the Lunars would whistle one tune or another. Tune by tune Gonsales pieced together his Lunar vocabulary. But almost the only thing we know for certain about aliens is that they don’t live close enough to see us pointing. We know of a handful of possibly habitable planets, but none is less than four light years away – or 24 trillion miles. And the Lunars aren’t that unlike humans: they’re tall but anthropomorphoid, and even claim to be Christian. More recent sci-fi – such as Ted Chiang’s ‘Story of Your Life’, the inspiration for the film Arrival, in which humans try to communicate with heptapods who perceive all time simultaneously – features aliens that are much more alien. The more we learn about ourselves and the universe, the more we appreciate that aliens probably won’t just be humans with longer limbs and waving antennae. How do you communicate with a planet-sized slime with ESP that eats electricity?
The 19th-century approach to breaking the cosmic ice was to attract attention with a huge (preferably exploding) drawing. The German mathematician Carl Friedrich Gauss wanted to plant a visual proof of Pythagoras’ theorem, comprising a right-angled triangle bordered on each side by squares, in the Siberian tundra. The borders of the shapes were to be marked out by trees and their interiors filled with wheat: this would demonstrate to anyone able to view the diagram from space that humans had mastered both mathematics and agriculture. In Austria, Joseph von Littrow proposed digging trenches in the Sahara, filling them with kerosene and setting them ablaze. Charles Cros, a poet and inventor, petitioned the French government to fund the construction of a huge mirror capable of burning messages onto the Martian and Venusian deserts, while the will of Anne Goguet, a French socialite, left 100,000 francs to the Académie des sciences to be awarded to the first person to communicate successfully with aliens, with the proviso that they couldn’t be Martians, whose existence was already ‘sufficiently well known’. Tristan Bernard satirised the alien-seekers in a story in which humanity, on receiving an unintelligible message from Mars, writes huge messages across the Sahara: ‘I beg your pardon?’ ‘Nothing.’ ‘What are you making signs for then?’ ‘We’re not talking to you, we’re talking to the Saturnians.’
In 1896, the Victorian polymath Francis Galton published a short story in which he describes a message received from Mars – conveyed in a Morse code-like sequence of long and short pulses of light – that begins by illustrating basic mathematical principles, using them as the foundation for progressively more complicated ideas. This encapsulated the scientific community’s best idea of what a message from or to space should look like. Mathematics is the same throughout the universe (they assumed), so using mathematics as the foundation for the message, rather than flaming trenches, seemed a good way of making it universally intelligible. When Guglielmo Marconi started experimenting with radio in the 1890s, transmitting messages like Galton’s to outer space began to look like a realistic possibility. ‘That it is possible to transmit signals to Mars,’ Marconi said, ‘I know as surely as if I had a gun big enough or powder strong enough to shoot there,’ and he endorsed the mathematical style of message outlined in Galton’s story: ‘By sticking to mathematics over a number of years one might come to speech.’ The challenge of communicating with aliens by radio was taken up enthusiastically by Nikola Tesla, who claimed to have intercepted a signal from ‘another world, unknown and remote’. It began with counting: ‘One … two … three …’
The search for extra-terrestrial intelligence – Seti, as it became known – was renewed in 1960 with a programme of long-distance observation conducted by the astronomer Frank Drake. He called it Project Ozma, after the rightful ruler of Oz in the Frank L. Baum stories, and pointed a National Radio Astronomy Observatory telescope at the stars Epsilon Eridani and Tau Ceti, which are similar enough to our sun to sustain life in their planetary systems. The telescope – really a large, high-powered radio – was tuned to 1420 MHz, which as the radiation frequency of neutral hydrogen, the most abundant element in the universe, was considered to be the most likely frequency for alien communication.It searched for messages like the one from Galton’s story, containing basic mathematical concepts – counting, prime numbers, or a regular on-off. But there was only silence.
After the disappointment of Ozma, the National Academy of Science requested a meeting to decide Seti’s future. Invitees included Carl Sagan and the neuroscientist John Lilly, who believed that dolphins had a level of intelligence comparable to that of humans and had been trying to prove it using experiments that involved feeding the dolphins LSD. The group was so impressed with Lilly’s presentation, which promised a more proactive approach to the problem than scanning space for signals, that they called themselves the ‘Order of the Dolphin’ (perhaps Lilly had brought his stash with him). Dolphins are more intelligent than the majority of Earth’s species: they are skilful mimics and problem-solvers, and they communicate with one another using an extensive vocabulary of clicks and whistles. Sagan hoped that attempting to converse with dolphins would generate insights into how to go about conversing with other intelligent but physiologically different species, and took a trip to Lilly’s lab. But although the dolphins had learned to understand simple instructions from humans, Sagan found that no human had managed a word of ‘dolphinese’. Further research with dolphins, notably Denise Herzing’s work in the Bahamas using an underwater musical keyboard, has shown that they can be taught symbols for objects – Herzing was able to teach them a new whistle for sargassum – but how do you explain sargassum to a sentient vapour on an oceanless planet a hundred thousand light years away?
A joint American-Soviet conference on ‘communicating with extraterrestrial intelligence’ (Ceti) was held in 1971 at Byurakan Astrophysical Observatory, on the slopes of Mount Aragats in Armenia. Sagan, who presided, told the attendees that ‘the word “Ceti”’ was ‘appropriate in three different respects’: first, the acronym fitted,
second, it is the Latin genitive for whale, which is of some interest to this discussion; the cetaceans are undoubtedly another intelligent species inhabiting our planet, and it has been argued that if we cannot communicate with them we should not be able to communicate with extraterrestrial civilisations. And finally, one of the two stars which was first examined by Frank Drake in Project Ozma, the first experimental undertaking along these lines, was Tau Ceti.
But the momentous occasion produced little in terms of practicable strategies. James Elliot, who discovered the rings around Uranus, suggested detonating all of Earth’s nukes simultaneously on the far side of the moon. X-rays from the explosion would be detectable 190 light years from Earth, Elliot calculated, though if the aliens didn’t happen to be watching Earth at the time they’d miss the show. Marvin Minsky, a pioneer of artificial intelligence, more usefully suggested sending a cat into space: Felix wouldn’t make it far alive, but if discovered by aliens his corpse might provide them with a wealth of information about the chemical conditions on Earth and the kinds of pattern into which matter here is organised.
On 2 March 1972, the Pioneer 10 probe became the first craft to be sent into space with enough velocity to leave the solar system. Appended to its fuselage was a plaque designed by Sagan and his wife, Linda, depicting male and female humans alongside a diagram of the solar system, a drawing of the probe itself and a representation of the ‘spin-flip transition’ of a hydrogen atom. The spin-flip transition, which occurs when the spin of the atom’s electron reverses direction, is what causes it to emanate electromagnetic waves at the 1420 MHz frequency that Drake thought best suited to alien communications: showing the spin-flip on the Pioneer plaque was a way of indicating that although we might not have picked up the phone we at least knew how to operate the switchboard. The probe is currently heading out of the solar system at a speed of 25,000 miles an hour: Sagan and Drake estimated that it will take longer than the age of the Milky Way, more than 13 billion years, for it to come within thirty Astronomical Units of another star. Aliens with technology much more advanced than ours may be able to detect the probe before then, otherwise it’ll be a while before we get a reply.
The Voyager probes, launched in 1977, carried much more information, in the form of a copper phonograph record in a gold-plated cover etched with the diagrams from the Pioneer probes and containing field recordings from around the world, music including Beethoven and West African folk, an hour’s worth of the sound of brainwaves, a clip of Sagan laughing and greetings in 55 different languages. Instructions for how to play the record are inscribed on the record in binary, but even if an alien did manage to put the record on the turntable – kicking back, perhaps, in its alien armchair with a glass of alien wine in one tentacle – it probably wouldn’t know what to make of the sounds, which are unlabelled.
In Extraterrestial Languages, his history of speaking to aliens, Daniel Oberhaus sharply distinguishes simple attempts to communicate with extraterrestrials (Ceti, or ‘active Seti’) from attempts to compose messages that an alien might understand. The records and plaques on the probes are Ceti, like the plans to nuke the moon and set the Sahara on fire, since their content is unlikely to be intelligible, even if the aliens recognise it as the handiwork of a not unintelligent species. ‘Messaging extra-terrestrial intelligences’ (Meti), on the other hand, requires the development of a self-interpreting language, as Galton, Marconi and Tesla realised. The second half of the 20th century saw several serious attempts at this undertaking. The zoologist Lancelot Hogben outlined his ‘Astraglossa’ at a meeting of the British Interplanetary Society in 1952: ‘Numbers will initially be our common idiom of reciprocal recognition,’ he announced, ‘and astronomy will be the topic of our first factual conversations.’ The Astraglossa used long and short radio pulses to communicate the foundations of mathematics, combining them in increasingly complex formulations, just like the message in Galton’s story, until it was capable of describing celestial events.
In 1960, the Dutch mathematician Hans Freudenthal published a more highly developed system for interstellar communication: Lincos (from lingua cosmica), ‘a language that can be understood by a person not acquainted with any of our natural languages or even their syntactic structures’. Like Hogben’s, Freudenthal’s system began by defining simple mathematical concepts, but he avoided formal definitions, preferring to use examples instead. Numbers could be directly understood from pulsing radio waves – one pulse meant one, two pulses two – and once numbers had been defined, so the relative terms ‘greater than’, ‘less than’ and ‘equal to’ could be: ‘1 blippity 2’, ‘3 blippity 5’, ‘5 blipbloop 3’, ‘3 blipbloop 2’, ‘2 bloopbloop 2’ and so on.
The first Meti broadcast was made in 1974 by Drake and Sagan from the Arecibo radio telescope in Puerto Rico to a star cluster 22,000 light years away. The message they sent used a system of Drake’s devising that relied on bitmaps: binary digits arrayed to form images, with each digit representing a pixel in an on or off state. Here’s a pictorial bitmap of a cross, for example:
Drake and Sagan’s message consisted of 1679 bits. The choice of 1679, a semiprime (the product of two primes, in this case 73 x 23), was supposed to indicate the message’s layout: 73 rows and 23 columns. The message included binary representations of ‘the first ten numbers, the atomic numbers of the five elements in DNA, the formulas for the bases of DNA’s nucleotides, the total number of nucleotides, according to knowledge at the time, a graphic of DNA’s helical structure, a graphic of a human, a graphic of the solar system, and a graphic of the Arecibo telescope’ – a huge amount of information for such a short message. But although it may have had more chance of being intercepted by an alien than the graphic messages aboard the probes, Drake and Sagan’s messages similarly relied, as Drake acknowledged, on the aliens possessing ‘brains and logic very similar to ours’. To decode the messages the aliens would have to have vision and a system of graphic representation – a tall order for a species we know nothing about.
The second Meti broadcast, undertaken 25 years later, in 1999, was more ambitious. Facilitated by the Russian astronomer Alexander Zaitsev, who coined the term Meti, Cosmic Call 1 was intended to ‘overcome the Great Silence in the universe, bringing to our extraterrestrial neighbours the long-expected annunciation “you are not alone”’. Zaitsev and his colleagues broadcast his message from the Yevpatoria telescope in Ukraine, at the time the second most powerful radar on Earth, using a bitmap-based messaging system inspired by Freudenthal’s Lincos. Here’s how they defined the number 4:
The four tiles arranged in a square represent a count of four, like the four blobs on a dice; the key-like symbol means ‘equals’; the cross-x-cross-cross pattern represents 4 in binary (0100); then there’s another ‘equals’; then 4 represented in the message’s own numerical notation system. So 4 = 4 = 4. Over the course of 23 ‘pages’ of bitmaps the Yevpatoria message progressed from basic mathematics to physics to astronomy to human biology, culminating in a list of questions for the recipient. It was transmitted in binary to a star in the Cygnus constellation at a rate of 100 bits per second. It won’t arrive until 2051, and we can’t expect a reply this century.
Developments in computer science have suggested new avenues for Meti, including the tantalising possibility of being able to interact with an alien – learn from them, adjust the presentation of the data accordingly – instead of simply confronting them with a load of information that they may not be able to understand. Software in its compiled form consists of binary data, which means it can be broadcast by radio in the same way as Cosmic Call 1. The alien on the receiving end just needs to be able to recognise the signal as executable binary code and have a machine on which to run it, and if they meet the first requirement it’s highly likely they’ll meet the second. The first computer scientist to apply software engineering to Meti was Paul Fitzpatrick from MIT, who in 2003 created Cosmic OS, a text-based role-playing game that teaches the user about humanity. Fitzpatrick’s game wasn’t beamed into space, but on 6 July 2003 a second Cosmic Call message was broadcast from Yevpatoria and included the executable binary code for Ella, a chatbot developed by a natural language processing specialist called Kevin Copple. Ella’s ‘personality’ is derived from a huge cache of linguistic data enriched by wisecracks and trivia: according to Oberhaus she ‘enjoys playing Atlantic City blackjack, telling jokes, predicting fortunes and reciting poems’. Aliens who don’t share our sense of humour may find interactions with Ella baffling, but the store of linguistic information packaged with Ella’s code may reveal something about humanity, provided the aliens can recognise it as linguistic information.
Though we’ve made headway with the message, there’s been little progress on the medium since Marconi. We’re still using radio – though laser may in future provide a less messy alternative – and picking a frequency on which to receive or broadcast involves some major assumptions. Drake’s magic frequency, 1420 MHz, falls inside the 1-3 GHz range of microwave frequencies that are particularly susceptible to warping by clouds of free electrons, which expands the bandwidth: the bandwidth of the Ozma telescope may have been too narrow to pick anything up. In space, ‘the most detectable signal that uses the least amount of power’ is at 70 GHz – but messages at these frequencies would be impeded by the Earth’s atmospheric gases, making it impossible for us to receive them. Our planet may be constantly being pelted by alien messages that never make it through the wall of gas.
Meti messages have been transmitted on frequencies between 1 GHz and 10 GHz, the window of the electromagnetic spectrum that is unimpeded by Earth’s atmosphere and relatively quiet in interstellar space (frequencies below 1 GHz are muddy with emanations from quasars, pulsars and nebulae). Radio communication works by modulating either the amplitude (AM) or the frequency (FM) of the wave. The Cosmic Call messages have relied on frequency shift keying, which represents binary data by modulating between two frequencies (representing 0 and 1) at a given bitrate – for example, between 1420 and 1450 MHz at a rate of one bit per second. Cosmic Call was broadcast on the 5.01 GHz band: 0 was represented by 5,010,000 kHz, 1 by 5,010,024 kHz. But for messages transmitted this way to make any sense, the person at the other end needs to know the bitrate of the transmission. The message 00110101 begins with a burst at one frequency, then a burst of the same duration at another, but without knowing the bitrate the alien can’t tell whether this represents 01, or 0011, or 000000111111 (in decimal, that would be 1, 3 or 63). For this reason, the Yevpatoria messages were designed to include a ‘clock’: a transmission oscillating between 0 and 1 at the bitrate of the data.
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.’
Drake’s message probably wasn’t especially hazardous, but as our technology and messaging systems have improved, concern over Meti’s risks has grown. Oberhaus mentions the San Marino Index, a safety measure proposed by the Hungarian astronomer Iván Almár in 2005, which gauges the risk of a Meti transmission by considering the intensity of the transmission and the message’s informational content, or how much we’re giving away about ourselves. Unfortunately, the things that make a Meti message risky are the same things that make it more likely to elicit a response. Like AI research, Meti has the potential to expose us to a vastly superior intelligence that could either solve all our problems or obliterate us entirely. Historically, encounters between technologically better and worse-off societies haven’t worked out well for the worse-off. In the middle of a crisis calling for help is seductive, but there’s no guarantee that the aliens that get the message will be anything like the friendly Lunars.