The Cosmos from Neolithic to now

Tom Wilkie traces the history of astronomy from Ancient Egypt to Einstein

Six thousand years ago, the priests of ancient Egypt fixed 365 days as the length of the year by watching the constellations from the roofs of their temples. Sirius the Dog Star played a vital role: the flooding of the Nile coincided with the day when the star was just visible at its rising, immediately before sunrise. To measure the length of the year, the priests simply counted off the days between two successive such risings.

Egypt's sophisticated civilisation was built on generations of knowledge about the positions of the stars and the sun. And Neolithic burial mounds, oriented east-west without the aid of a compass, shows that even Stone Age people knew the dates of vernal and autumnal equinoxes - the only two days in the year when the sun rises exactly in the east and sets exactly in the west.

As the late Lancelot Hogben noted, in his classic Mathematics for the Million, "Primitive man saw death and generation, sleep and waking, the basic rhythms of fertility and decay, mirrored in the changing heavens. The rising of new constellations, the lengthening and shortening of the sun's shadow announced the time of lambing, seed sowing, and the drying cornstalk. The recurring phases of the moon coincided with the rhythm of woman's fertile life."

Around 2800bc, the Great Pyramid of Cheops was constructed, using centuries of astronomical observation. The sides are oriented exactly north-south and east-west. The south face of the pyramid was so placed that the rays of Sirius at its highest altitude struck it at right angles. A ventilation shaft leading to the royal chamber was so accurately placed that the dead Pharaoh was illuminated by the Dog Star when it crossed the meridian.

The geometers of Alexandria

Classical astronomy comes not from Greece, but from the Egyptian city of Alexandria. There the curators of the city's fabulous library used geometry to measure the size of the Earth and its distance from the sun and moon.

The Greek Anaxagoras had shocked the court of Pericles by declaring that the sun was as big as the mainland of Greece. But Eratosthenes of Alexandria (275-194bc) shrank Greece itself into insignificance beside the Earth, whose circumference he measured. (We now know that he was only about 50 miles out.)

Hipparchus, another Alexandrian, determined the distance to the moon to be about a quarter of a million miles - not much more than 5 per cent out. The culmination of the Alexandrian system was the publication by Ptolemy, in around ad150, of his Almagest, which was mainly a compilation of earlier work. It ruled supreme for more than a thousand years. As late as the 15th century, when Europeans began to explore the world, navigators learned the arts of map making and seamanship from the pages of the Almagest.

But it was the religious significance of the Ptolemaic scheme that ensured its persistence in Christendom. The enormous scale of the universe, as revealed by Alexandrian measurements, dethroned the local gods of the ancients, while preparing the psychological ground for a universal God, creator of all, above and beyond the stars. Alexandria was fertile ground for such ideas; it had the largest Jewish community outside Palestine, and they had brought with them the concept of monotheism.

In Ptolemy's universe the Earth was at the centre. The sun, moon, stars, and planets were its acolytes, moving round the earth in perfect circles. Since simple circles did not account for the apparent changes in the size of the moon, or the motion of the planets, Ptolemy devised a complex scheme: each heavenly body moved along a small circle, centred on a larger circle in the main orbit.

This scheme appealed to the Church. At the centre of things physically was the home of humanity, who was at the centre of things religiously, having been created in God's image.

The scheme also appealed to the scholastics, with its emphasis on the "perfect" geometrical form of the circle. This in turn was a mystical representation of the perfection of God. Over 1,300 years, what had started out as an empirical system founded upon observation hardened into a doctrinal article of faith.

Astronomy and trade

In ad1420, Henry the Navigator, crown prince of Portugal, set up an observatory near Cape St Vincent. There he started a school of seamanship.

If trading ships laden with spices and other valuable cargoes were to return to port safely, the crew had to be able to fix their position by measuring both latitude and longitude. Latitude is easy to calculate by the position of the Pole Star, but longitude requires a way of measuring time. Before the invention of spring-driven clocks which could keep time on board ship, the starry sky, with the moon or a planet as hour hand, was the only clock available. So in the period of the Great Navigations, nearly 1,300 years after the publication of Ptolemy's Almagest, astronomy had once more become a part of the practical life of humanity. It was no longer merely a matter of theology; it was vital to commerce.

More than a century after the foundation of the Portuguese observatory, the Polish Catholic priest Nicholas Copernicus and the German Lutheran mathematician Johannes Kepler improved on Ptolemy's method. In his book De Revolutionibus, published in 1543, Copernicus defended the doctrine of Aristarchus, that the Earth and planets travelled around the sun. So far as the sun and the fixed stars were concerned, the Ptolemaic view, that sun and planets travelled around the earth, was almost as plausible. Difficulty only arose in accounting for the positions of the planets, once used to determine longitude.

Copernicus made virtually no observations, and his system, because it insisted on circular orbits, was little more accurate than Ptolemy's. The real birth of modern cosmology is due to Tycho Brahe, a Rabelaisian Danish nobleman with a silver nose (he lost the one he was born with in a duel). In the half century which followed the death of Copernicus, and before the invention of the telescope, Tycho Brahe compiled the most accurate astronomical data in history. But he was unable to make sense of it. For the last year of his life, he bickered with the man who could, Johannes Kepler. Only when Brahe died in 1601, of overindulgence, did Kepler inherit his job and his data.

It took Kepler eight years of studying the data on the planet Mars to make a fundamental conceptual break with the old systems: the only way to make sense of the observations was to assume not only that Mars orbited the sun, but that its paths was an ellipse not a circle. And the old idea that the planets moved at the same speed all the time also went on to the scrapheap.

From Galileo to Newton

Within half a century, Isaac Newton was able to deduce Kepler's results from his universal theory of gravity. However, the scene had been set for him not just by Kepler's long, laborious and detailed calculations, but by the Carl Sagan of the Renaissance world: the flamboyant Italian astronomer Galileo Galilei. His books were the Tomorrow's World of his times - written in a racy, accessible style dripping with invective against opponents of his ideas.

The man was an entrepreneur of science. In 1609 he built one of the first telescopes and discovered four moons of Jupiter, which he called the Medicean stars to flatter the Grand Duke of Tuscany, Cosimo de' Medici, from whom he hoped to get a job - telling him that there were no further stars to discover, to be named after anyone else. (He then wrote to the King of France to say that any new stars would be named after him.)

Eventually, he came into conflict with the Church. In 1632, the Pope and the Inquisition reacted angrily to the publication of his famous Dialogue Concerning the Two Chief Systems of the World, a work which categorised adherents to the old system (the Pope, of course, was one of them) as "mental pygmies". Galileo was forced to recant and kept under house arrest for the rest of his life.

In 1642, the year Galileo died, Isaac Newton was born at Woolsthorpe, near Grantham, Lincolnshire. Whereas Galileo appears to have been an attractive extrovert, Newton was a rather bitter, quarrelsome man. He did, however, produce in 1687 one of the most important scientific works ever written: Philosophiae Naturalis Principia Mathematica. This tour de force not only covered the motion of material bodies, but also expounded a universal theory of gravitation that made sense of all astronomical observations. The moon and planets moved in a clockwork universe guided by the force of gravity, and their position at any time could be calculated from first principles.

Curiously, Newton himself was not convinced that his solar system would be stable for all time (he conceived a role for God's angels, nudging the planets back into line from time to time). Producing the Principia seems to have precipitated a nervous breakdown, though he later recovered.

Newton's work remained unassailed for more than two centuries, until Einstein revolutionised modern physics with the theory of relativity at the beginning of this century. This marked the start of the 20th century's understanding of the cosmos

What has God got to do with it?

The discovery of billions upon billions of galaxies need not bother theologians, but the discovery of even one little green man would have immense theological implications. The conflicts between astronomy and religion ended a long time ago. Modern cosmology is one of the sciences most enthusiastically embraced by Christians. The Big Bang, which implies that the universe had a moment of creation, is more compatible with the idea of a Creator than a steady state universe. The titanic size of the universe merely makes the God who can create such a thing more wonderful.

This attitude is frequently misunderstood by scientists, who tend to sprinkle God over their theories as a sort of invigorating spice for a dish whose substance comes from elsewhere. The most famous example is Stephen Hawking's claim that if we could penetrate the equations at the heart of the Big Bang, then "we would know the mind of God". Another example is Paul Davies, the British-born physicist who last year won the $1m Templeton prize for progress in religion.

Most of this amounts to no more than the 18th-century belief known as deism, itself a reaction to the discovery by Newton and Kepler of general laws governing the movement of everything in the universe. The universe had come to seem a gigantic piece of clockwork, which God needed only to wind up before setting it on its course. The trouble was, this was not a very interesting or important role for Him, and soon it was rationalised away altogether. The great French mathematician Pierre Laplace, when asked by Napoleon where God came into his system, replied: "I have no need of that hypothesis."

His conclusion that if we knew the exact position and momentum of every particle in the universe at any one moment, we could infallibly predict the past and future of the universe, marks the furthest point the forces of mechanistic science reached in their attempts to squeeze divine action out of the picture. It has been upset in this century by chaos theory, which shows that complex systems are necessarily unpredictable. The larger the universe, the less chance of it being a simple clockwork excluding divine action. Thus the discoveries of modern astronomy have helped religious belief.

Christian orthodoxy has long since come to terms with the historical and scientific untruth of Genesis: with the immense age of the Earth, and even, to some extent, with Darwinism. However, there are two specific difficulties which a very large universe raises for orthodox Christianity, and both are concerned with the role of man.

One is that it seems a very large stage on which to mount such a small show. The universe was around for perhaps ten billion years before the Earth formed, and will be around for as long again. Modern theologians tend to repudiate the view that Homo sapiens is the only species God cares about on Earth. It is a natural extension to wonder whether our solar system contains the only life He thinks of, too. Some scientists, and theologians, believe it does. Fr Christopher Moss, a Jesuit astronomer at Cambridge, suggests that, "the possibility of life emerging spontaneously... in the visible universe is virtually nil."

Such arguments can seem necessary from a theological perspective because the Incarnation is in orthodox Christianity the central event of the history of the universe. This idea would lose much of its force if the universe were full of intelligent, ensouled life, all of which would presumably need redemption. It might even be worse if some of these races turned out not to need redemption.

Abundant life in the universe would raise other difficulties. Explanations for our specialness might not be needed. God may be driven from biology, as Laplace drove Him from physics. The only safe prediction is that, somehow, the religious imagination will survive this and other disappointments. Andrew Brown