The turning point in our understanding of the universe may be conveniently dated at 1600, just before Galileo pointed his first telescope towards the stars. Shakespeare belongs to the century before the great intellectual revolution.
Doubt that the stars are fire,
Doubt that the sun doth move …
he wrote, circa 1600. He was wrong on both counts.
Of course, we know that the sun does move – but not in the way that Shakespeare imagined. He thought it moved around the earth, as common sense seems to indicate, and had no idea how distant – and how big – it really is. And the stars aren’t fire – although for reasons that were not understood until well into this century. They are much too hot! Fire is a low-temperature phenomenon in the thermal range of the universe – much of which is simmering briskly at several million degrees, where no chemical compounds can possibly exist.
During the seventeenth century the telescope revealed for anyone who had eyes to see that the moon provided at least one other example of a world with mountains and plains – though not rivers and oceans. The moving points of light that were the planets now turned out to have appreciable discs – and one of them, Jupiter, had its own retinue of moons. Clearly, the earth was not unique; nor, perhaps, was the human race.
This was a shocking – even heretical – thought, at least to those brought up in the Aristotelean school. Anyone who preached it too loudly, especially near Rome, was likely to get into serious trouble with the Inquisition. The classic example is, of course, Giordano Bruno (1548-1600), who was one of the first European advocates of the doctrine of an infinite universe and the ‘plurality of worlds’. Refusing to recant, he was burned at the stake in 1600. I wonder how many modern scientists would be prepared to emulate him in defence of their theories.
A couple of years ago, to my great surprise, I was asked to present a paper to the Pontifical Academy of Science, and could not resist having a little dig at the Vatican Astronomer.
‘When I was invited to speak here,’ I told Dr George Coyne mischievously, ‘my first choice of subject was: “After Giordano Bruno – Who?”‘
George didn’t hesitate for a moment. ‘If you had used that title, Arthur,’ he said deadpan, ‘the answer would have been – “You.”‘
And while we’re on the subject of Jesuit astronomers, I’d like to remind you of one of the greatest ironies in the history of science. In 1582 that remarkable man, Father Matteo Ricci, arrived in China with all the latest wisdom of the West. The Chinese regarded Occidentals as barbarians (and probably still do, though they’re too polite to say so), but by tact, intelligence and sheer goodness Father Ricci persuaded them that their superstitious concept of an enormous universe enduring for vast aeons was all nonsense: God put the earth in the centre of everything, and Adam and Eve in the garden, only a few thousand years ago.
As he proudly wrote: ‘The Fathers gave such clear and lucid explanation on all these matters which were so new to the Chinese, that many were unable to deny the truth of all that they said; and, for this reason, the information on this matter quickly spread among all the scholars of China.’ Well! Poor Father Ricci! While he was persuading the Chinese to take a Great Leap Backward to Ptolemaic astronomy, Copernicus was destroying its very foundations in Europe. A few decades later Galileo (with an anxious glance over his shoulder at Bruno) would finish the job of demolition.
For the last 300 years – not very long in human history -all educated persons have known that our planet is not the only world in the universe, and that its sun is one of billions. The great voyages of the seventeenth and eighteenth centuries, during which European explorers ‘found’ whole cultures that didn’t even know they’d been lost, also prompted speculation about life on other planets. It seemed only reasonable that our enormous cosmos must be populated with other creatures, some of them perhaps far more advanced than we are. The alternative – that we are utterly alone in the universe – seemed both depressing and wildly megalomaniac.
But how to prove it, one way or the other? We children of the Space Age can no longer remember how enormous even the solar system seemed, only a lifetime ago. Now the Voyager spaceprobe is heading for its appointment with Neptune – which, as recently as 1930, marked the frontier of the Empire of the Sun. That is an impressive achievement; even so, it will be tens of thousands of years before Voyager can cross the gulf to the nearest star.
Fortunately, we do not have to rely on physical contact to discover if there is intelligent life elsewhere in the universe. We now assume that any contact is likely to be by radio. Yet this in itself would have seemed incredible until well into this century. We take radio so much for granted that we forget how miraculous it is. Even the most far-sighted prophet could not have predicted it – which is yet another example of what I call Comte’s Fallacy.
Around 1840 the French philosopher, Auguste Comte (1798-1857), was rash enough to make the following pronouncement about the limits of our knowledge concerning the heavenly bodies: ‘We see how we may determine their forms, their distances, their bulk, their motions, but we can never know anything of their chemical or mineralogical structure; and much less, that of organized beings living on their surface.’ Comte’s monumental gaffe was in the same class as Father Ricci’s. Within a few decades, the invention of the spectroscope had utterly refuted his assertion that it was impossible to discover the chemical nature of heavenly bodies. By the end of the century, precisely that was the main occupation of most professional astronomers. Only the amateurs were still concerned with what Comte believed must always be the entire body of their science.
So it is very dangerous to set limits to knowledge or to engineering achievements. No one could have anticipated the spectroscope; and no one could have imagined radio. They both exemplify Clarke’s well-known Third Law: ‘Any sufficiently advanced technology is indistinguishable from magic.’
There may be ‘magical’ inventions or discoveries in the future which will settle the question of intelligent life in the universe, but I do not think we really need them. Today’s electronics can probably do the job – given a few more decades of determined application. The giant radio telescopes which have been built for purely scientific purposes are quite capable – and this is a splendid example of ‘serendipity’ – of detecting the sort of radio signals one would expect from an advanced civilization in our immediate galactic neighbourhood. As is well known, a number of such searches have been made – and are being made right now – though so far with negative results. It would be ridiculously optimistic to expect success, since we have had the capacity for making such a search for less than half a human lifetime.
Yet already this ‘failure’ has produced a kind of backlash, and has prompted some scientists to argue, ‘Perhaps we are alone in the universe.’ Dr Frank Tipler, the best-known exponent of this view, has given one of his papers the provocative title, ‘There Are No Intelligent Extra-Terrestrials’. Dr Carl Sagan and his school argue (and I agree with them) that it is much too early to jump to such far-reaching conclusions.
Meanwhile the controversy rages; as has been well said, either answer will be awe-inspiring. The question can only be settled by evidence, not by any amount of logic, however plausible. I would like to see the whole debate given a rest while the radio-astronomers, like goldminers panning for gold dust, quietly sieve through the torrents of noise pouring down from the sky.
There is another – and much more speculative – line of approach to this problem. Let me give an analogy to explain what I mean. If a visiting traveller had surveyed our planet from space 10,000 years ago, he would have seen many signs of life – forests, grasslands, great herds of animals – but no trace of intelligence. Today, even a casual glance would reveal cities, roads, airfields, irrigation systems – and, at night, vast constellations of artificial light. (Incidentally, you’ll never guess where the most conspicuous of those displays are to be found.
The people who operate the military reconnaissance satellites were amazed to find that enormous areas of the Pacific Ocean are brighter than London or New York. You can blame the Japanese fishing fleets: they’re pouring megawatts of light into the sea to attract squids – and doing heaven knows what to the local ecology in the process.)
These ‘advertisements’ of terrestrial civilization would have been beyond the imagination of our Stone Age ancestors. Can one set any limits to what might be achieved by a really advanced, long-lived society, with thousands of centuries of spacefaring behind it? In particular, might it not have – literally – set its sign among the stars, as we have done upon the earth? As long ago as 1929 the physicist, J.D. Bernal, in one of the most daring works of scientific imagination ever penned, wrote: