First of all, a very merry Christmas to you or, if Christmas is not your thing, I hope your day is going as well as can be expected. Today is the birthday of Isaac Newton. Well, it sort of is. It depends how you look at it. Newton was born on December 25th 1642. But in 1752, when Britain adopted the Gregorian Calendar, his birthday became January 4th 1753. But, as he died in 1726, that didn’t trouble him, so it needn’t trouble us either.
Newton had a difficult start in life. Firstly, his father died three months before he was born and secondly, he was born extremely prematurely. Newton was so small that his mother said he would have fitted into a quart pot, that’s two pints. Then, when he was three, his mother remarried and left him behind with his grandmother when she went to live with her new husband. Newton clearly did not enjoy this arrangement. When he was nineteen, he wrote a list of what he considered to be his sins. Among them was “Threatning my father and mother Smith to burne them and the house over them”. There are others that betray his quick temper: “Punching my sister” and “Wishing death and hoping it to some”. But most are more innocent. Eating an apple in church and baking pies on a Sunday.
Newton was a natural philosopher, which is what we would now call a scientist. He was born in the same year that Galileo died and, at that time, everyone was still pretty shocked by Galileo’s suggestion that the earth was not at the centre of the universe. He grew up in difficult times, the Civil War, the beheading of Charles I, Oliver Cromwell’s Commonwealth and the restoration of Charles II all happened before he was twenty.
He studied at Trinity College, Cambridge where he worked hard and read all the latest scientific ideas. By this time everyone was pretty happy to accept the earth and other planets went round the sun, but the question was how. Descartes thought that all things in the universe were part of a machine, like a clock. Newton wasn’t so sure. He thought it all seemed a bit vague and the only statements that you could really say were true were ones you could prove by experiments or calculations.
In 1665 the whole university had to close because of an outbreak of bubonic plague. Newton went home, but continued to work there. It was from this time that his famous falling apple story originates. According to Newton, it was an apple falling in his garden that made him think that the force that pulled the apple towards the ground was the same force that kept the moon in orbit. He spent a long time trying to work out what the strength of that force must be, but he couldn’t quite make his calculations work and he put them aside. But he did manage to figure out a way of calculating the speed of the falling apple at any point between the tree and the ground. He had invented a terrifically complicated branch of mathematics called calculus. With calculus it is possible to work out how all sorts of things change, not just velocity. It is used to predict the movements of the stock market and to see what the effects of climate change might be.
It was also at this time that he made his discovery that white light was made up from all the colours of the rainbow combined. You probably know he did this using a prism. But before this, he did another experiment on himself. He took a large needle, stuck it between his eyeball and his skull and wiggled it around a bit to see how it affected his vision. He saw white, dark and coloured circles. Don’t try this at home. He also noticed that the curved edges of the lens in a telescope tended to work in the same way as a prism and create coloured flares around the object being observed. Telescopes were, in those days, many feet long and quite cumbersome. Newton built himself a much shorter telescope, which used mirrors instead of a lens, that was free from the colour distortion. He had invented the reflecting telescope. It was only six inches long but could magnify forty times, much better than a telescope ten times as long. The huge telescopes we use today, even the ones we launch into space, are based on Newton’s model. He thought of it as just a toy, but one of his friends took it to show Charles II and, as a result, he was made a member of the Royal Society and became pretty famous.
But Isaac Newton was working on other things as well, that he didn’t tell anyone about. Isaac Newton was an alchemist. Alchemists were an odd lot by today’s standards. They used a series of complex experiments to try to produce a substance called ‘The Philosopher’s Stone’. With it, they believed they could cure all illnesses, make themselves immortal and make lead into gold. There were lots of alchemists in sixteenth and seventeenth century Europe who were employed by royalty and noblemen to make gold for them. The penalty for failure was high. They would be hanged from a gilded scaffold, perhaps wearing a suit of tinsel, just to draw extra attention to their hubris. Alchemy was actually forbidden in Britain because the government was worried that they would use their fake gold to debase the currency. No one really knows why Newton took up alchemy, or what he was trying to do. We do know that he thought there was some lost knowledge about the world that was to be found in the form of coded alchemical recipes hidden in Greek myths. His notes on these experiments are oddly worded, which is not unusual for alchemists. He refers to ‘the green lion’ and ‘the minstrel blood of the sordid whore’. It’s all very esoteric and not at all what you would expect from a person we think of as such an important figure in the Age of Reason.
It wasn’t just his Alchemy that Newton kept a secret. He also had some pretty dangerous religious views that he kept to himself. He didn’t believe in the Holy Trinity. He did believe in an all powerful God, but the more he read, the less he believed that Jesus was divine. If anyone had found out, he would certainly have lost his job and his credibility and probably would have been imprisoned. He owned more than thirty bibles and studied them intensely. He used them, combined with astronomical information to date the beginning of civilization to around 980 BC. He also looked to the future and calculated that the apocalypse would happen no sooner than the year 2060, which is looking a bit closer to us than it did to him. He applied the same level of attention to this as he did to his scientific work and spent about thirty years on it. Newton actually wrote more about alchemy and theology that he did about maths and science, though these writings were not discovered until fairly recently. For him religion and science were equally important in his quest to understand the universe.
By the time he was in his early forties though, he went back to physics. Edmund Halley asked him a question about the shape of orbit described by a planet. Newton had worked it out ages ago and it was an ellipse. Astronomers thought that the planets were held in orbit around the sun by some force, but they didn’t know what it was. Newton used his calculus to prove that it was gravity that made the planets move the way they did. But he wanted to know why they remained in motion. He worked tirelessly over the next eighteen months to figure it out. The result was his most famous work ‘Principia Mathematica’. It was hugely important and explained how the whole universe might work and how everything in it obeyed the same laws of gravity. If you throw a ball it travels in an arc because it is must eventually fall back to earth. But planets also travel in an arc for basically the same reason. His Principia is where he came up with his three laws of motion. That an object will tend to remain travelling in a straight line, that its speed depends on the force that started it moving and that for every action, there is an equal and opposite reaction. The moon remains in orbit around the earth because the speed that it is moving is balanced by the pull of the Earth’s gravity. The proportions are just right to stop it either drifting away from us or falling down to earth. If this was true for the earth and the moon, it could be true for the whole of the solar system, the whole of the universe. He called it his ‘Universal Law of Gravitation’.
In case you’re feeling intimidated by his towering intellect, here’s one more story about Newton. He is credited with having invented the cat flap. As any cat owners will know, you waste a lot of time opening and closing doors for them when they want to go in and out. To get round this problem, he cut a hole in the door of his workroom. But then his cat had kittens. So he cut a smaller hole next to it for the kittens to go through. It didn’t occur to him that the kittens would just follow their mother through the big one.