My mother rarely calls to talk about my research. In April, however, she rang to ask: ‘Do you agree with Stephen Hawking?’ That’s usually an easy question to field. On topics ranging from the behaviour of black holes to the structure of the early universe, a safe answer is yes. But that wasn’t what my mother wanted to know. She wanted to know whether I agreed with the recently retired Lucasian Professor of Mathematics that trying to contact aliens was a bad idea. Any extraterrestrial civilisation that could receive our communiqués and act on them, Hawking warned, might show up on our doorstep, and wouldn’t necessarily be friendly. ‘Such advanced aliens,’ Hawking said, might be ‘looking to conquer and colonise whatever planets they can reach.’ In no time at all, the word spread from Hawking’s voice synthesiser to the world’s blogosphere. Soon even my mother was calling.

And so it was that the word ‘aliens’ seemed to be on everyone’s lips (and screens) in time to mark the 50th anniversary of SETI, the Search for Extraterrestrial Intelligence. Though astronomers have long dreamed about alien intelligences, just like everyone else, the modern history of SETI began with a brief article in Nature in 1959, when two astrophysicists at Cornell, Giuseppe Cocconi and Philip Morrison, postulated that there existed a uniquely well-suited frequency, nestled in the microwave portion of the electromagnetic spectrum, at which intelligent civilisations might seek to communicate with us. Frank Drake, an astronomer at a newly established radio astronomy observatory in West Virginia, reasoned along similar lines. In 1960 he conducted his own search of the skies, hoping to catch some telltale sign of intelligence chiming in at the special frequency. He heard mostly white noise; one heart-thumping squawk, he later realised, came not from the sky but from a top-secret military installation nearby. Not easily discouraged, he attracted colleagues to the topic, and SETI was underway.

Cocconi and Morrison’s Nature article makes for interesting reading today. It appeared less than two years after Sputnik I had been launched, and combined hard-headed calculation with an almost giddy optimism, the ‘can-do’ and ‘gee-whiz’ spirit that marked the early years of the space age. Why look for signals from aliens? Because there are so many stars out there, Cocconi and Morrison explained. Many are similar to our sun, which means that Earth-like conditions, in which our own species evolved, might be fairly common throughout the galaxy. Cocconi and Morrison were further convinced that countless civilisations were likely to have developed ‘scientific interests’ and ‘technical possibilities much greater than those now available to us’. Where there are Earth-like conditions, there could be life. Where there was life, there would be science.

In their brief paper, Cocconi and Morrison performed a strange rhetorical loop-the-loop. Given the latest advances in science and technology, how should we anticipate that advanced aliens would try to contact us? Humans had recently learned about a process in hydrogen atoms that emitted microwaves at a frequency called the ‘21-centimetre line’, first measured in a Harvard laboratory in 1951. Since hydrogen was the simplest and most abundant element in existence, surely it provided a ‘unique, objective standard of frequency, which must be known to every observer in the universe’; after all, even we already knew about it. According to Cocconi and Morrison’s calculation, the frequency of the 21-centimetre line lay in a sweet spot of the electromagnetic spectrum, away from naturally occurring sources of background noise. Given this universal property, aliens might reasonably expect any civilisation to design sensitive receivers tuned to the frequency early in their development of radio astronomy, as indeed we had done. Therefore the only ‘rational’ choice the aliens could make would be to assume that some day we would follow the same scientific-technological developmental pathway that they did – or that we imagined they did. Reasoning about others was inevitably a projection of ourselves.

One needn’t be a psychoanalyst or hold a PhD in cultural studies to discern a certain amount of wishful thinking in Cocconi and Morrison’s article. Not only were advanced extraterrestrial civilisations likely to exist but the aliens were probably gentle, benign elders, monitoring our stellar neighbourhood because they were ‘expecting the development of science near the Sun’, and ‘patiently’ beaming out signals to us, ever hopeful that our return beacon might announce that ‘a new society has entered the community of intelligence.’ Before Morrison began his work on SETI, he had served on the Manhattan Project. He inspected both Hiroshima and Nagasaki just weeks after the bombings in 1945 as part of the first scientific survey team. Shaken by the experience, he turned his energies to the arms-control movement. In the early 1950s he was hounded by red-baiting critics for what they considered radical ideas about ‘world government’. No wonder he turned to the skies in search of more rational, welcoming civilisations.

Drake picked up where Cocconi and Morrison left off. Helping to organise discussions for a workshop on SETI in 1961, he jotted down an equation, now known as the ‘Drake equation’, in order to have some means of estimating how likely it was that advanced alien civilisations were out there. Variables included the average rate at which new stars form; the fraction of those stars that form planets; the fraction of those planets that develop conditions suitable for life and so on. The final term in his equation, L, denoted the average lifetime of advanced alien civilisations. Where Cocconi and Morrison’s paper reflected the hopeful buoyancy of the early space age, Drake’s equation bore the marks of its Cold War origin. For Drake, as for most of his colleagues, L was a stand-in for all-out nuclear war. Cocconi and Morrison assumed that life led inexorably to science. Drake took the next step: science led inexorably to nukes.

The assumptions governing the thinking of the SETI pioneers are clearly explained by Paul Davies in his new book, The Eerie Silence: Are We Alone in the Universe? Davies works in cosmology and astrobiology and heads a unit at Arizona State University called the Beyond Center for Fundamental Concepts in Science. (Some of his seminal early work refined physicists’ notion of the vacuum: he literally knows everything about nothing.) His main concern on the question of extraterrestrial life is to disentangle necessary and sufficient conditions. The presence of water or amino acids seems necessary for life (at least for life as we know it) on some distant planet; but their mere presence is far from sufficient for life to emerge. The same goes for the existence of Earth-like planets orbiting Sun-like stars. When Cocconi, Morrison and Drake were formulating their search strategies, astronomers had no direct evidence of planets outside our solar system. The first one was discovered in 1992 and since then hundreds of ‘exoplanets’ have been identified, with improvements in observing techniques promising to reveal many more. But, as Davies rightly points out, even if exoplanets turn out to be exponentially plentiful in our galaxy, life may prove to be an even more exponentially improbable occurrence. The easy leap made in the early days of SETI – from stars to planets to life to intelligent life – was never more than a conjecture. So the ‘eerie silence’ – no confirmed SETI contacts despite 50 years of concerted listening – might simply mean that life as we know it is rare, not that civilisations inevitably self-destruct in nuclear holocaust.

Where Cocconi and Morrison assumed that intelligent civilisations would inevitably pursue scientific investigations, Davies counters that science is not universal, even here on earth. Moreover, the idea, common in the 1950s and 1960s, that better science leads inevitably to improved technology, seems difficult to square with the historical record. Ancient Chinese civilisations developed astounding technologies but little of what looks like Western-style science. If science and technology could follow such contingent paths among members of our own species over a relatively short time period (cosmologically speaking), why should we assume that extraterrestrial civilisations would march, lock-step, from intelligence to science to technology?

But a larger question concerns our scientific knowledge: is our representation of the natural world universal? Throughout the half-century of SETI, Cocconi, Morrison, Drake and their followers have argued over which regions of the electromagnetic spectrum it would be most ‘rational’ to target for a search. They have based their arguments on naturally occurring processes like the 21-centimetre hydrogen line or similar emissions from other constituents of water molecules. But who is to say that other advanced civilisations – even if they pursue something like scientific investigation – would carve up the confusion of nature in the same way as we do? We now think in terms of atoms, electrons, quantum transitions and electromagnetic waves, but are those the only ways of making sense of physical phenomena? Can the intellectual history of Western science really be a universal phenomenon, with the current state of our science being a fixed point in the evolution of intelligence everywhere in the cosmos?

Davies currently chairs the SETI Post-Detection Taskgroup of the International Academy of Astronautics, a committee charged with developing a protocol to be followed in the event that signals of possible extraterrestrial origin are detected. Few topics elicit as much blog-addled conspiracy talk as purported government cover-ups of UFOs and alien contacts. Davies’s group aims to steer a middle path between military-style secrecy and indiscriminate public airing of every false alarm. The current protocol calls for credible evidence to be shared first with other astronomers by means of a body called the Central Bureau for Astronomical Telegrams of the International Astronomical Union. (One can’t help but smile at the name of the committee: telegrams to announce the findings, no less.) The international community of professionals would then vet the evidence and try to rule out possible alternative explanations, such as terrestrial signals like the ones which fooled Frank Drake back in 1960. Next, the discoverer of the putative signal should alert the International Telecommunication Union, the International Council of Scientific Unions and finally the secretary general of the United Nations. Only then should the discoverer announce the finding to the public.

Conspicuous in their absence from the long list of ‘telegram’ recipients are any national governments. In large part, that is because SETI activities no longer receive government funding. Nasa’s first grant for SETI research was given to Philip Morrison in 1975, and soon money was flowing to research groups across the country. With much fanfare, Nasa inaugurated its own observational programme on Columbus Day 1992, 500 years after the explorer reached the New World. All told, Nasa spent nearly $57 million on SETI between 1975 and 1993 and had pledged an additional $100 million – modest sums compared to most ‘big science’ appropriations, but real money nonetheless. A year after the Columbus Day festivities, Congress killed all federal funding for SETI.

The 1993 debates in Congress over the funding of SETI proved to be a dress rehearsal for bigger targets. Soon afterwards, legislators killed funding for the Superconducting Supercollider, a mammoth particle accelerator that would have dwarfed CERN’s Large Hadron Collider. The supercollider would have cost a thousand times more than Nasa’s annual expenditure on SETI, but although SETI operations were small and efficient, well-managed and on budget, it had few contractors to rally to its defence and little political ‘pork’ to distribute across congressional districts. It also fell through the cracks between disciplines. It used tools from physics and astronomy without being central to either field, even as it trod on the toes of biologists who knew about life, evolution and intelligence.

Beyond the budget cuts and the usual political horse-trading, SETI also suffered from an image problem. Advocates acknowledged the ‘giggle factor’. Grandstanding politicians wondered why the government should spend millions of dollars to search for extraterrestrial intelligence, when one could just plunk down ‘75 cents to buy a tabloid at the local supermarket’, as one Congress member complained in 1990. On introducing the final amendment to kill funding in 1993, Senator Richard Bryan announced: ‘This hopefully will be the end of the Martian-hunting season at the taxpayer’s expense.’ Since then, a few Silicon Valley entrepreneurs have put money into SETI and scaled-back efforts continue.

With all its talk about aliens, SETI is often lumped together with occult topics or pseudosciences. Searching for references to Cocconi and Morrison’s article on the internet, one finds links to the paper alongside books by the New Age shamanism expert Carlos Castaneda and mystico-environmentalist tracts on the Gaia hypothesis. In the absence of confirmed contacts, critics argue, the search has been sustained by faith, hope and speculation; its supporters respond by saying that SETI received high marks from three decadal reviews by the US National Academy of Sciences. The drive to improve detection capabilities led to major advances in microwave electronics and signal extraction. Drake’s original search relied on a single-channel receiver; by the mid-1990s, SETI devices could simultaneously scan 250 million channels. The US Federal Aviation Administration and the National Security Agency both expressed interest in SETI spin-offs and other SETI techniques were quietly incorporated into methods to simulate the inner workings of thermonuclear weapons. SETI still can’t shake off the nuclear spectre.

And SETI might indeed make its greatest contribution in the nuclear arena. Some of the most hazardous by-products of the nuclear age, including isotopes of plutonium, have half-lives of hundreds of thousands of years. One challenge is to find places on Earth that are likely to remain geologically stable over such a time-scale, where such waste can be buried. A second challenge is to design symbols to warn our descendants, 300,000 years from now, not to go digging in these areas. As the historian Peter Galison has been documenting, the US nuclear agencies have sought the wisdom of diverse experts – linguists, anthropologists, sculptors – to imagine how we might plausibly communicate with terrestrial beings in the impossibly distant future. After all, the Latin alphabet dates back a mere 2600 years; only hubris could lead us to imagine that familiar modes of communication will be recognisable in the year 300,000 AD.

Alongside linguists and artists, nuclear bureaucrats have also enlisted experts in SETI. Struggling to communicate with our future selves calls for the same kind of radical imagination that SETI requires. Both efforts criss-cross the boundaries between disciplines; both require experts to project from what we know about our own civilisation to facilitate communication with some distant other. They are mirror images, twin children of the nuclear age.