Human Universe (10 page)

Today SETI is a global scientific effort, analysing data from telescopes used primarily for radio astronomy. The organisation also has a dedicated collection of telescopes designed specifically to detect signals from extraterrestrial civilisations at the Hat Creek Radio Observatory near San Francisco. The Allen Array, named after Microsoft founder Paul Allen who donated over $30 million to fund the construction of the project, consists of 42 radio antennae able to scan large areas of the sky at multiple radio frequencies, including the 21cm hydrogen line. If there are any civilisations making a serious attempt to contact us with technology at least as advanced as our own within a thousand light years, the Allen Array will hear them.

In the early 1960s, the scientific community was sceptical about such endeavours and Frank Drake was perceived as a maverick. It’s important to be sceptical in science, but as Fermi understood, a back-of-the-envelope calculation with some plausible assumptions suggests that the search for ET may not be futile. Indeed, the alternative view that our civilisation is unique or extremely rare in a galaxy of a hundred billion suns appears outrageously solipsistic, and the sceptical finger might as easily be pointed at the cynics. There was, however, a handful of scientists who understood the importance of asking big questions, and together with Peter Pearman, a senior scientist at America’s prestigious National Academy of Sciences, Drake organised the first SETI conference in November 1961. The Green Bank meeting was small, but the list of attendees, who named themselves The Order of the Dolphin, was impressive.

Philip Morrison was there, as was his co-author of the seminal 1959
Nature
paper, Giuseppe Cocconi. I have a professional connection with Cocconi, who was a noted particle physicist and director of the Proton Synchrotron accelerator at CERN in Geneva. Cocconi was instrumental in discovering early experimental evidence for the pomeron, an object in particle physics known as a Regge trajectory that I have spent most of my career studying. The eminent, highly respected astronomer Otto Struve also attended. Struve publicly stated his belief in the existence of intelligent extraterrestrial life, perhaps because he had recently suggested a method for detecting alien planets outside our solar system (see
here
). Nobel Laureate Melvin Calvin, most famous for his work on photosynthesis, was present, along with future Hewlett Packard vice president for R&D Barney Oliver, astronomer Su-Shu Huang, communications specialist Dana Atchley and the colourful neuroscientist and dolphin researcher John Lilly. The most junior attendee was a 27-year-old postdoc. called Carl Sagan. I would love to have been there, although I’d have spent the whole time chatting with Cocconi about pomerons.

In preparation for the meeting, Drake drew up an agenda designed to stimulate a structured conversation amongst the group. If the search for intelligent extraterrestrial life was to be taken seriously, it was clear in Drake’s mind that the discussion should be rigorous and provide a framework for future research. The way to do that is to address the problem quantitatively rather than qualitatively; to break it down into a series of probabilities that can be estimated, at least in principle, using observational data.

Drake focused on a well-defined question – the one we discussed above: how many intelligent civilisations exist in the Milky Way galaxy that we could in principle communicate with? Drake’s brilliant insight was to express this in terms of a simple equation containing a series of probabilities. What is the fraction of stars in the galaxy that have planets? What is the average number of planets around a star that could support life? What is the fraction of those planets on which life begins? What is the probability that, given the emergence of simple life, intelligent life evolves? Given intelligence, how likely is it that the intelligent beings build radio telescopes and are therefore capable of communicating with us? Multiply all these probabilities together, and multiply by the number of stars in the Milky Way, and you get a number – the number of intelligent civilisations that have ever existed in the Milky Way.

This isn’t all Drake did, however, because he was interested in the number of civilisations that we might be able to speak to now, and that requires the addition of a rather thought-provoking term – the average lifetime of civilisations from the moment they develop the technology to communicate. If a civilisation arose a billion years ago and vanished shortly afterwards, then we would never be able to talk to them. The question of the lifetime of a civilisation may have been more vivid in the early 1960s than it is today. The Manhattan Project had been the training ground for many of the great physicists, and the Cuban missile crisis was less than a year away, propelling the world, in Soviet Premier Khrushchev’s words to President Kennedy, towards ‘… the abyss of a world nuclear-missile war’. To me, and to the participants at the Green Bank conference, the idea that a civilisation might destroy itself is both ludicrous and likely. We are pathetically inadequate at long-term planning, idiotically primitive in our destructive urges and pathologically incapable of simply getting along. More of this later! Putting the lifetime term into the equation was therefore scientifically valid and a political masterstroke; merely confronting the question should give us pause for thought at the very least.

To complete the equation with the lifetime term included – recall that it should give the number of currently contactable civilisations in the Milky Way – a little thought will convince you that the whole lot must be multiplied by the current rate of star formation in the galaxy. That might not be immediately obvious, but I have confidence you can demonstrate to yourself that it’s the correct thing to do. Homework is good.

The completed equation, which is known as The Drake Equation, is shown here.

When Drake wrote down his equation, only R was known with precision. Star formation had been closely studied in parts of our galaxy and the data suggested a value of around one new star per year. The rest of the terms were unknown in the 1960s, and we will spend the majority of this chapter exploring them, given over 50 years of astronomical and biological research. Despite the lack of experimental data, however, the Green Bank participants spent the meeting debating each one of the terms in the Drake Equation. This is the power of Drake’s formulation. It’s not yet possible to make a measurement of the fraction of planets on which life emerges with any sort of precision, but it is possible to look at the experience we have on Earth, and increasingly in the wider solar system, and make an informed guess. The probability of the emergence of intelligence given simple life is also a difficult question, but we do know that it took over 3 billion years on Earth, and that may give us a clue. Drake’s equation is valuable therefore because it provides a framework for discussion and debate, focuses the mind and suggests a direction for future research, just as Drake intended.

The Green Bank meeting did produce a consensus number, based on the not inconsiderable expertise of the participants: there are of the order of 10,000 civilisations present now in the Milky Way with whom we could communicate if we had enough radio telescopes and the will to conduct a systematic search. Interestingly, Philip Morrison, veteran of the Manhattan Project, felt that the lifetime of technological civilisations may be so short that this number could well be zero, although he observed that ‘… if we never search, the chance of success is zero’.

I had the privilege of meeting Frank Drake during the filming of
Human Universe
. In my view he is one of the greatest living astronomers. Frank collects and cultivates orchids, and by complete coincidence I arrived at his house when his
Stanhopea
orchid was flowering. These delicate and complex flowers bloom for only two days every year, and the chance of seeing one on a random visit is therefore small. Frank turned to me and said ‘well, so it is with SETI – we’ve learned that we must search over and over and over through the years, until we are in the right place at the right time to make the discovery’. There is ‘hope’ in its name, and there is nothing wrong at all with admitting a dash of hope.

Throughout the 1960s and 1970s, SETI projects both big and small continued to develop across the planet. Soviet scientists joined their American contemporaries in pointing radio receivers to the sky in the hope of detecting a signal in the noise. NASA considered funding Project Cyclops, a $10 billion super-array of 1500 dishes that could listen for signals originating up to 1000 light years from Earth. It never progressed beyond the planning stage, but the scale of the project demonstrates that SETI was considered to be a serious scientific endeavour. By the mid-1970s, various projects had come and gone but none had detected the faintest hint of a significant signal. This failure, combined with a lack of progress in pinning down any of the terms in the Drake Equation – it was not even certain that planets existed in large numbers beyond our solar system – made the search look increasingly futile. Not only was there a deafening silence, no one had much idea where to look or how hard to listen. NASA didn’t lose faith, however, and in 1973 Ohio University’s ten-year-old Big Ear telescope was optimised for a SETI survey and began taking data.

Four years later, on 18 August 1977, Jerry R. Ehman, then a volunteer at the Big Ear, received a knock on the door of his house. It was a Thursday morning and, as usual, standing at the door was a technician carrying reams of paper printouts. This was an age when a state-of-the-art hard disk could hold only a couple of megabytes, and every few days someone had to visit the telescope, print out the data and wipe the disks clean. Ehman put the three days’ worth of printed data onto his kitchen table and began searching. He was confronted with dozens of pages covered in hundreds of letters and numbers.

The list of numbers and letters depicts the strength of the signal hitting the telescope at different times. A space denotes low intensity, and higher intensities are registered as numbers from 0 to 9. For stronger signals still, letters between A and Z are used. Most of the data the ‘Big Ear’ recorded contained no letters; a stream of 1s and 2s signified sweeps across the general radio hiss of the sky. That morning, however, Ehman stumbled across something different. At approximately 10.16pm Eastern Standard Time on 15 August, a radio pulse of extreme intensity entered the antennae, recorded with the alphanumeric code 6EQUJ5. The signal lasted for 72 seconds, precisely the length of time a transmission of distant origin would register as the rotation of the Earth swept the telescope past the source. This is extremely important. If the signal had been caused by some kind of Earth-based interference, it would be highly unlikely to rise and fall in this manner, precisely and coincidently simulating the rotation of the Earth and the telescope’s field of view on the sky. The peak was marked by the letter U, the strongest signal ever recorded by the Big Ear, denoting an intensity over 30 times that of the background emission of the galaxy. Equally strangely, the signal had a wavelength of 21cm – the hydrogen line favoured by Morrison and Cocconi in their 1959
Nature
paper. A smoking gun for extraterrestrial communication?