Human Universe (11 page)

With a now-famous flourish, Ehman circled the six characters and scribbled ‘Wow!’ on the printout. He then continued as a research scientist should, and looked to see if it happened again. He flicked through page after page, but the event of 10.16pm on 15 August was a solitary blip in the background noise. This presented a problem, because it should have happened again. The Big Ear telescope scans each part of the sky twice, separated by 3 minutes, so there should have been a similar Wow! signal in the data 3 minutes afterwards. None was present. This doesn’t rule out an intelligent extraterrestrial origin; perhaps ET just turned the transmitter off a minute or so after it was first detected. Who knows?

The origin of the Wow! signal was narrowed down to a point in the sky in the direction of the constellation Sagittarius. Tau Sagittarii, a stable orange star twice the mass of our Sun and around 122 light years away, is the closest bright star to the source. Since August 1977 multiple attempts have been made to recover the signal using the world’s most sensitive radio telescopes. Many hours have been spent listening, but nothing unusual has ever been detected again. Today, over 35 years later, there is no satisfactory explanation, but no serious scientist, no matter how embedded in SETI, would claim it as definitive evidence of intelligent extraterrestrial communication. Scientific results have to be repeatable, and the observation has never been repeated. For the moment, the Wow! signal remains an interesting anomaly in an otherwise silent sky. It is the stuff of dreams; the faintest of whispers in a great silence.

Two days after Jerry Ehman spotted the Wow! signal, the human race responded with a long-planned contribution to the interstellar conversation. In an explosive, serendipitous moment, the Voyager 2 spacecraft blasted into the sky above Space Launch Complex 41 at Kennedy Space Centre, followed two weeks later by its twin Voyager 1.

The Voyager missions were designed to take advantage of a rare planetary alignment to study the outer solar system gas giants Jupiter, Saturn, Uranus and Neptune. I remember the launch – I had collected a series of PG Tips tea cards called ‘The Race Into Space’, in which the Grand Tour mission was described as ‘the most ambitious unmanned space project known’. Using the newly proposed gravity assist, a spacecraft could accelerate around Jupiter, Saturn and Uranus to encounter Neptune only a decade from launch. The Voyagers delivered, I suspect, way beyond their designers’ wildest dreams, returning the first detailed pictures of the esoteric moons of Jupiter and Saturn, and in the case of Voyager 2, sweeping onwards to become the only spacecraft to date to visit Uranus and Neptune, where it photographed the distant ice moon Triton in the summer of 1989.

At the time of writing, on 8 July 2014, Voyager 1 is the most distant man-made object at over 127 astronomical units from Earth, so distant that radio waves take over 17 ½ hours to reach it. This puts Voyager 1 at the very edge of the solar system, on its way into interstellar space. The bus-sized spacecraft has enough electrical power to continue to communicate with its home world until around 2020, at which point it will fall silent. In 40,000 years it will drift within 1.6 light years of the red dwarf star Gliese 445 in the constellation of Camelopardalis. Voyager 2 will reach Sirius, the brightest star in the night sky, in 296,000 years.

The Voyagers are accompanied on their lonely flights out of our solar system by a dream – an unusually sentimental and hopeful afterthought to a scientific mission bolted to their sides almost 40 years ago.

The Voyager Golden Record is our message in a bottle. An old-fashioned phonograph record constructed of gold-plated copper floating through the universe, it contains what some would term a surreal mixture of sound recordings, images and information. It was designed to provide an alien civilisation with information about who we are, what we know and what our planet is like. There are 116 images on the disc; the first 30 or so are scientific, illustrating our solar system, our home world, the structure of DNA, the anatomy of our bodies, our reproduction and our birth. Anatomy takes up more room than any other subject, perhaps reflecting our own fascination with what aliens might look like. In the most magnificently colloquial and futile gesture towards the aliens’ moral sensibilities, no nudity was allowed! I find it hard enough to imagine the inner workings of alien brains, but I cannot begin to fathom what it must be like inside the mind of a person who raised such an objection to the depiction of the human body. ‘How do these beings reproduce? Perhaps they use those ten dangly things on the ends of their arms? Disgusting!’

The illustrations go on to detail our planet’s landscapes and the variety of life on Earth, before dedicating 50 images to our lives and the civilisation we’ve constructed – from the Great Wall of China to a supermarket. Finally, there are images of the scientific instruments we have used to explore the universe from microscopes to telescopes, including the Titan rocket that launched the Voyagers into space. Chosen by a committee chaired by Carl Sagan, the disc also contains music and sounds, including human greetings in 55 languages, recordings reflecting ‘the sounds of the Earth’, and the ultimate 1977 mix tape featuring 90 minutes of music from Beethoven to Chuck Berry. Sagan wanted the Beatles’ ‘Here comes the Sun’ on the disc, but EMI refused copyright permission for the universe. I like to imagine that Carl Sagan put the song on the record anyway in a great cosmic two-fingered salute to corporate Earth. That would have been pure Sagan – ‘You’re most welcome to go fetch it’.

The outside cover of the golden disc is more functional. As well as instructions on how to play back the images and sounds at precisely
revolutions per minute for the audio, and how to build a record player, it also contains a map so that any extraterrestrial civilisation will be able to trace the record back to our planet. The map uses the position of 14 pulsars whose precise locations are marked relative to the Sun. The pulsars are identified by their fingerprints – each has a unique and unvarying rate of rotation. The most important piece of content on the cover is the key to unlock the information – a diagram illustrating the spin configurations of a hydrogen atom. The 21cm hydrogen emission line is a fundamental and universal property of nature, a Rosetta Stone that will allow an alien scientist to unlock the secrets of Earth. The disc also contains one last invisible source of information: electroplated onto the surface of the cover is an ultra-pure sample of uranium 238, an isotope with a half-life of 4.468 billion years. This is Voyager’s clock, a way for any civilisation to determine the age of the record, assuming that they aren’t creationists who disagree with radiometric dating. Perhaps these are the sorts of aliens that would also be offended by nudity.

For all the thought and care that went into these discs, neither Voyager spacecraft is heading towards any particular star; these tiny craft constructed by human hands will almost certainly never be found. The vastness of space swallows travellers, and of course Voyager’s scientists and engineers knew this. That, however, is not the point; the act of launching these gilded emissaries into space expresses something important. It’s my childhood science fiction dream of living in a Star Wars galaxy filled with life and possibilities. It is a desire to reach out to others, to attempt contact even when the chances are vanishingly small; a wish not to be alone. The golden discs are futile and yet filled with hope; the hope that we may one day know the boundaries of our loneliness and lay to rest the unsettling internal noise that accompanies the enduring silence.

Friends of space, how are you all? Have you eaten yet?

Come visit us if you have time.

Margaret Sook Ching, Voyager Golden Record

Let us now return to Frank Drake’s equation and use it as intended, as a framework to address in a systematic manner the question of our solitude. Recall that the equation consists of a series of terms which, when multiplied together, give an estimate of the number of currently contactable civilisations in the Milky Way galaxy. At the 1961 Green Bank meeting only the first term – the rate of star formation in the Milky Way – was known with any precision. Over half a century later, we can do much better. The next term in the equation is the fraction of stars in the Milky Way that have planets orbiting around them – most definitely a prerequisite for an intelligent civilisation to emerge. It’s true that the civilisation may not have remained confined to its home world, and we will discuss this possibility later on. But it must be true that for life to emerge and evolve to the point where it can build spacecraft, a planet of some sort is required.