Although he was surely as complex a character as any other haunting the corridors of power and influence in seventeenth-century Italy, Galileo has become one of the more sympathetic characters in scientific history, an honest man cruelly oppressed by the enforcers of religious and intellectual orthodoxy.20 Isaac Newton, on the other hand, presents much more of an enigma; a brilliant scientist whom we very much want to admire, but also a dark, brooding man, his personality seemingly pinched and bare. It is odd that such a profound intellect should have been so insecure about money and position, so temperamental and suspicious. While his ideas on motion have endured, his works on alchemy and vitalism have not. And he managed to gather about himself a host of eager rivals and competitors and suffered cruelly from the common problem that major discoveries seem to come in bursts, often being developed quite independently by more than one person at the same time. Many a schoolchild has damned Newton for inventing the accursed calculus (which he called ‘fluxions’) that he and Leibnitz invented independently. Newton was not helped by his great brooding sulks; he would start work on a subject, become dissatisfied because the answer didn’t satisfy his own high standards, and then put it aside for a few years. Meanwhile others would be closing in on a solution.
England’s greatest scientist, Newton was born in 1642, the year that Galileo died. He took over the science of Galileo’s time and created a new intellectual sphere, a new world of mechanical laws with which we are still far more comfortable than we are with the modern world of quantum physics, where Einstein’s relativity and Heisenberg’s uncertainty reign. The ancients, particularly Aristotle, had thought that all matter was naturally at rest unless acted on by another force. This is again a weighty piece of common sense: when we see a stone on the ground, it does not move until we kick it. The question is, why does it then slow down and stop? Newton rewrote the science of motion and mechanics in a masterpiece of uncommon sense and mathematical precision.21 He showed that all matter is in uniform motion (constant velocity, including a velocity of zero) unless acted on by an external force. Exactly opposite to Aristotle’s view of motion, Newton showed that an object will remain still or continue to move at a constant speed in the same direction unless some external force changes things. A moving stone slows down because a force of friction has slowed it, not because it somehow wants naturally to come to rest. A thrown stone describes a parabola through the air, not because it naturally tends to progress in a perfect theoretical circle, but because a force – gravity – has diverted it from the direction in which we threw it. Single forces always act in straight lines, not circles. Any trajectory other than a straight line must be the result of multiple forces acting together.
One of Newton’s most brilliant insights (with the assistance of Robert Hooke) was that the mechanism that keeps the planets in their elliptical orbits around the sun according to the rigid rules discovered by Kepler is the same as that which controls the fall of an apple from a tree, or shapes the trajectory of an arrow shot from a bow. From this he could predict that a projectile fired into the sky at a high enough velocity would continue indefinitely straight out into space. But one fired at some lower velocity would be attracted back to the earth by the opposing force of the earth’s gravity, and if the two sets of forces balanced, then the projectile would settle into orbit around the earth – just as the earth and the other planets orbit the sun, and just as the moon and communication satellites orbit the earth.
Nothing would be the same after Newton’s strict mathematics. Not even the simplest aspect of daily life on earth could be considered immune from the laws of science and the probing of scientists. Kepler’s laws of planetary motion might be glossed over as remote and literally other-worldly but Newton’s laws of motion touched every intimate detail of existence and were correspondingly subversive. Newton accelerated one of the great movements in science – which is to take the mystery out of everything. He also helped to explain some of the contemporary puzzles in the heliocentric model of the universe. If the earth is hurtling through space at many thousands of miles per second, why are we not all blasted off by the wind? If the earth revolves, and those in the northern hemisphere are standing up, why don’t the upside-down Australians fall off? The answer is that gravity holds our atmosphere in place, so there is no cosmic gale, and it holds the Antipodeans in place too. For everyone, ‘down’ is towards the centre of the earth. Science had given nature a new uncommon sense. And, in addition to the technical importance of Newton’s mathematics, the concept of a ‘balance of forces’ keeping the moon circling the earth and the earth in orbit around the sun, very quickly became a valuable metaphor for the description and explanation of a wide range of secular phenomena, including Malthus’s ideas about population growth being held in check by negative factors and Darwin’s ideas on evolution.
Newton’s emphasis on matter and motion related centrally to the Epicurean school and their theories of the nature of matter itself. These ideas had been revised and extended in more modern times by the great French philosopher Descartes (René des Cartes, 1596–1650) whose physical theories Newton in turn largely supplanted. Beyond Galileo’s collision with the Inquisition, if any one man could be said to have started the fields of science and religion on their course of conflict (or perhaps simply of divergence), it is Descartes. By sheer force of intellect and powerful original thought, he created a whole new approach to philosophy, brilliantly turning upside down the old, classical authorities to which the Church turned for support during the Middle Ages. Born in France and educated at the Jesuit college at La Fleche in Anjou, Descartes was Galileo’s younger contemporary and a philosopher who wrote about everything from pure mathematics to human physiology, from the origins of the solar system to the fundamentals of human understanding. All his philosophy started with rejection of previous authority, none of which could be as reliable as one’s own senses and intuition. Every schoolchild knows (or should know) his dictum: ‘Cogito, ergo sum.’ These three words, translated as ‘I think, therefore I am,’ represent his last resort after having rejected everything else in an attempt to find an incontrovertible reality – a truth – upon which to base a philosophical system.
The rigour of his methods was grounded first in mathematics: ‘Those who are seeing the strict way of truth should not trouble themselves about any object concerning which they cannot have a certainty equal to arithmetical or geometrical demonstration.’ Galileo, in one of his most famous passages, had put things even more eloquently: ‘Philosophy is written in that great book which ever lies before our gaze – I mean the universe – but we cannot understand if we do not first learn the language and grasp the symbols in which it is written. The book is written in the mathematical language … without the help of which it is impossible to conceive a single word of it, and without which one wanders in vain through a dark labyrinth.’22
As a young man Descartes wandered the capitals of Europe before settling in Holland in 1628. From the beginning he thought intensely about epistemology: the question of how we know, and especially how we can find ultimate, objective ways of knowing what is right and true. Again this turns on his basic premise, ‘Cogito, ergo sum.’