A still from 'Independence Day: Resurgence'

ET phones it in: Searching for signs of alien life

Little green men from outer space are science fiction, aren’t they? As the new ‘Independence Day’ sequel hurls yet another swarm of aliens at us, take a look at the real science behind the search for the extraterrestrial.

After two decades of peace, alien hordes are invading again in the summer sci-fi blockbuster ‘Independence Day: Resurgence’. Hollywood loves this story, essentially inspired by ‘The War of the Worlds’, H G Wells’ influential 1897 novel of marauding Martians. It’s all nonsense, of course, but our desire to find signs of alien intelligence among the stars is very real.

A serious search began in 1961 when Frank Drake at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, decided to listen for alien signals. This was the start of what is known as the Search for Extraterrestrial Intelligence, or SETI. In a bid to persuade colleagues that this was valid science, Drake conceived the Green Bank Equation. It took into account the rate of planetary formation and the likelihood of planets orbiting their parent stars in temperate regions suitable for life. Drake made guesses about some of these factors. Subsequent discoveries proved him right. Today we know there are billions of planets in habitable zones. Whether any are inhabited is another matter.

Drake was influenced by a September 1959 Nature magazine article, ‘Searching for Interstellar Communications’ by Giuseppe Cocconi, a senior figure in Europe’s nuclear research community, and Cornell University physicist Philip Morrison. “Interstellar communication across the galaxy is practical, so far as we know, only with electromagnetic waves,” they wrote, before suggesting we look for signals around the 1,420MHz, 21cm wavelength range, because this is “a unique, objective standard of frequency that must be known to every observer in the universe”.

Vast clouds of hydrogen, the basic building material of the cosmos, drift like tenuous ghosts through the interstellar void. The restless atoms generate a characteristic radio trace, known as the Hydrogen Line. All radio astronomers are familiar with it, so smart aliens must be, too. According to Cocconi and Morrison, any unusually strong signal on that frequency will stand out like a beacon against the background hiss. “The probability of success is difficult to estimate,” they conclude. “But if we never search, the chance of success is zero.”

Just such a signal was found on 15 August 1977, coming from an apparently empty region of space. Jerry Ehman at Ohio State University’s Big Ear radio observatory circled the pulse on his printout and wrote ‘Wow!’ in the margin. Ever since, it’s been called the ‘Wow!’ signal. Unfortunately, it never repeated. In July 2007, Ehman marked the 30th anniversary of the detection with a painstaking forensic re-evaluation. “All of the possibilities of a terrestrial origin have been either ruled out or seem improbable,” he concluded. Noise pollution wasn’t responsible because the Hydrogen Line is a carefully protected frequency.

Antonio Paris, a professor of astronomy at St Petersburg College in Florida, suggests that one of two small, recently discovered comets might have traversed that region of the sky in 1977 without being spotted. Faintly glowing hydrogen in the tail, energised by the Sun, could have triggered the fuss. Paris has crowdfunded $20,000 to conduct a radio search in January 2017, when the prime cometary candidate traverses the area again, and once more in 2018, for the second candidate. If the results prove negative, the ‘Wow!’ signal will retain its mystery.


Drake and other SETI pioneers started with a few hours’ observation time borrowed from radio dishes engaged mainly on other work. Today, the Allen Telescope Array (ATA) at the Hat Creek Observatory in California has widened the search parameters. More than 40 small antennas combine to act as one large telescope. Distributed computing enables millions of frequencies to be scanned and analysed, expanding the range far beyond the Hydrogen Line, even while the ATA conducts conventional astronomical work on other frequencies. A project called SETI@home enables hundreds of thousands of domestic computers on ‘down time’ to sift through parcels of data, looking for unusual patterns.

Funding for SETI is brittle. The ATA depends largely on Microsoft co-founder Paul Allen. A new initiative, known as Breakthrough Listen, might help. Russian entrepreneur Yuri Milner, Google co-founder Sergey Brin and Facebook co-founder Mark Zuckerberg have sourced $100m to secure thousands of hours of observation time across the coming decade, using some of the world’s largest radio dishes and crunching the data with help from SETI@home.

Is radio the way forward? Some SETI researchers think aliens would use optical light for its directional efficiency and high data rate. Nasa uses laser communications in space. Although alien beams probably would not be directed at us, if we happened to intercept even a short pulse it would be easy to spot as its spectrum would be unusually precise. Breakthrough Listen resources will be dedicated to an optical search, too.

What if we do find them?

Despite the beliefs of conspiracy fans, the United Nations (UN) has no policy about alien contact. Yet it does have guidelines and a scoring system, called the Rio Scale, to rank the likely impact of such an event. The scale was created by Iván Almár from the Konkoly Observatory, Budapest, and renowned SETI astronomer Jill Tarter in October 2000, during the 51st International Astronautical Congress in Rio de Janeiro.

The balance of impact versus likelihood is something that governments juggle when planning for potential catastrophes. Epidemics and terrorism are considered high consequence, high probability risks. Substantial resources go into trying to prevent them. The probability of an asteroid impact is deemed very low and not much effort goes into planning for one. Despite this, some governments fund modest research because the consequences of an asteroid strike would be very high. While no one suggests that discovering an alien signal would be dangerous, Tarter and Almár urged governments to think about the social disruption that might result. The Rio Scale claims to be ‘our best chance of avoiding misinterpretation and sensationalism’.

An omnidirectional beacon or stray signal from thousands of light years away would rank as a wonderful scientific discovery with a low score on the Rio Scale. A signal aimed directly at us scores more highly. A signal from just tens of light years away, aimed at us and containing information, tops the score as a societal disruptor and would cause all governments serious concern.

Is it realistic to expect aliens to signal us, while we are not making similar efforts in return? For the time being at least, we have no sensible choice on this matter, according to Britain’s Astronomer Royal, Lord Martin Rees, an enthusiastic SETI theorist. “Even if the emergence of life on other planets tracked what’s happened on Earth, there would be a lack of synchronisation because of the different age of planets and the different pace of evolution,” he explains.

“The only relevant civilisations are those that are ahead of ours, perhaps by millions of years. Given that we are likely to be retarded by comparison, it makes sense for us to do the easy thing and listen rather than transmit.”

Physicist Paul Davies, a professor at Arizona State University with an interest in SETI, thinks that radio and laser searches are perfectly worthwhile, although he cautions that “laser came a hundred years after radio. What difference is a hundred years going to make to a civilisation a million years more advanced than ours? If aliens are using neutrino beams to send messages, we have our work cut out to find them”.

Even if aliens are considerate enough to send us a primitive radio signal, should we risk replying to anyone so near to us, in terms of interstellar distances, that we could converse back and forth within one or two human generations? On the other hand, if we failed to reply, would we be missing out on humanity’s greatest opportunity for scientific, philosophical and even spiritual progress? Lord Rees says: “I can’t take seriously those who think we should hide our existence. ‘They’ would probably know about us already.”

Much depends on whether or not we think that aliens would be friendly. This debate has exercised us for decades and the only way we can explore it is by staring into the mirror and contemplating our own reflections.

To tell or not to tell?

The International Academy of Astronautics (IAA) supports the SETI Post-Detection Task Group, an occasional gathering of two dozen researchers, chaired by Paul Davies, that includes Iván Almár, Jill Tarter, and SETI colleagues Seth Shostak and Martin Rees. In 1996, the group published an advisory Post-Detection SETI Protocol, which is taken seriously by international astronomers and within the UN.

The group as a whole takes an optimistic stance about publicising a SETI discovery, but Davies personally harbours reservations. “A signal from something or someone clearly intelligent could be disruptive, and I think a public announcement might be rash unless we knew more about what it meant.”

However, many scientists would be outraged by any attempt to withhold the news, and Davies concedes that such a momentous discovery could end up on a SETI@home volunteer’s Twitter account “before anyone could stop it”.

When the first ‘Independence Day’ movie was released in 1996, noted futurist Arthur C Clarke (the inventor of communications satellites) didn’t much like it, and he told me that the invasion premise was unrealistic. “If they’ve solved the economic and social problems of building giant starships and roaming across the universe, there can’t be anything they’d need to steal from us.” The problem is that you never know what strangers might want from you. The Aztec communities of 16th century Mexico prized beautiful bird feathers far above gold and were amazed, then appalled, by the Spanish Conquistadors’ deadly obsession with the uninteresting yellow metal.

In April 2010, Professor Stephen Hawking warned viewers of the Discovery TV channel: “We only have to look at ourselves to see how intelligent life might develop into something we wouldn’t want to meet.” He drew a bleak portrait of our first contact with advanced aliens, saying: ‘I think the outcome would be much as when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans.”

Independence Day: Resurgence will be released in UK theatres on 22 June 2016.

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