Lost Pioneers of Science

Medieval scholars were the first to make the connection between maths and science and anticipated the discovery of inertia long before Newton. So why have their discoveries been forgotten, asks James Hannam.

Historians have never quite shaken off the idea that the medieval era was one of stagnation. As for my own subject of medieval science, it almost sounds like an oxymoron. How could any rational knowledge exist among all that superstition? As Charles Singer wrote of science in the Middle Ages: ‘There is no reason to reverse the decision that in this domain, the period is one of intellectual degradation.’

The story we all learnt at school is that science was invented by the ancient Greeks but then languished until the Renaissance. Medieval people supposedly all thought that the Earth was flat while the Church allegedly banned human dissection and burnt scientists at the stake.

In fact, the myth that Christianity held back science was invented during the 19th century and, despite concerted attempts by today’s scholars to kill it off, it simply refuses to die. In reality, the medieval Church demanded that every student should study maths and science in the new universities. More people were exposed to these subjects than at any time in the past. And, because the universities were selfgoverning bodies answerable directly to the pope, students and masters enjoyed an unprecedented level of academic freedom. Of course this was circumscribed by the demands of the faith, but that did not stop a few individuals, largely forgotten today, from making significant advances in science.

Thomas Bradwardine is a good example. While he was a master at Merton College, Oxford during the early 14th century he made a breakthrough which challenged the ancient Greek conception of how science should operate. Using the latest mathematical techniques, he developed a formula that provided a universal description of motion.

Aristotle had declared that since mathematics and physics were different subjects, you could not use one of them to prove something in the other. Bradwardine realised that this was a mistake. Mathematics is essential in all branches of science because nature obeys mathematical laws. This is one of the most fundamental tenets of modern science, restated by Galileo Galilei when he declared: ‘Science is written in this grand book … it is written in the language of mathematics.’

Bradwardine himself left Oxford to pursue a successful career in the Church, which culminated with his appointment as Archbishop of Canterbury. Unfortunately, he had barely been enthroned when he died of the Black Death in 1349.

The equation of motion generated by Bradwardine was based on Aristotle’s physics and was consequently inaccurate. However, a member of the next generation at Merton, William Heytesbury, derived a correct formula. He showed that, when an object accelerates at a uniform rate, the distance it moves is equal to how far it would have moved if it had travelled at its average speed. This is known as the mean speed theorem and it describes the velocity of an object falling under gravity. Although Heytesbury did not know the theorem’s application to gravity, it was later used by Galileo in his own analysis of freefall.

Meanwhile, in Paris, the rector of the university, John Buridan, struck several blows against the ancient Greek science that he had inherited. Aristotle had said that no object can move unless there is something else moving it. When you stop pushing something, he declared, it should stop. Buridan could see this was wrong. When he threw a stone, it kept moving after it had left his hand even though nothing was in contact with it. So he postulated a quality called ‘impetus’. This was a force impressed onto the stone by the thrower and proportional to its weight and speed. As the stone travels, said Buridan, its impetus is drained by air resistance. When it reaches zero, the stone stops.

Impetus is an important step towards the modern concept of momentum. This is also a quality of moving objects related to their velocity and mass. More generally, Buridan could see that, in the absence of friction, there would be nothing to expend impetus and so an object should keep moving forever. He couldn’t see any such cases on Earth, but he observed how regularly the planets travelled across the sky. Perhaps, he suggested, God had set them moving at the Creation and, because there was no resistance in the heavens, they would keep going until Doomsday. Here, Buridan begins to explore the idea of inertia, also known as Newton’s First Law.

Still looking at the planets, Buridan had another inspired idea. He realised that just because they appeared to be moving across the sky each night, he could not immediately tell whether it was the Earth or the sky which was rotating. The Greeks had been almost unanimous that the Earth is stationary. But Buridan said that if the Earth was rotating, there was no reason that we should be able to feel it. He considered the case of a man who is standing on the deck of a moving ship looking at a stationary one. On a calm sea the man would be unable to tell whether it is his boat moving or the other one. This introduced the concept of relative motion. Copernicus used precisely the same argument in his book The Revolutions of the Heavenly Spheres 200 years later.

Buridan’s most brilliant pupil was Nicole Oresme. As well as being a gifted mathematician, Oresme also wrote a diatribe against astrology and eventually rose to the rank of Bishop of Lisieux. His greatest scientific achievement was to prove the mean speed theorem geometrically. He also showed that when you plot a graph of an object’s speed against time, the area under the graph correlates to the distance travelled. Thus Oresme started to use graphs to model moving objects 300 years before René Descartes is supposed to have come up with the idea.

How did all the achievements of medieval science come to be forgotten? In short, they were incorporated into the celebrated work of Copernicus and Galileo, neither of whom saw any reason to give notice of their predecessors. Coupled with the general hostility towards medieval philosophy during the Renaissance, this served to obscure completely the achievements of Buridan, Bradwardine and their contemporaries. But we should now give them the credit that is their due and acknowledge that modern science began in the Middle Ages.

James Hannam’s God’s Philosophers: How the Middle Ages Laid the Foundations of Modern Science is published by Icon Books.