What Goes Up . . . Newton

A Little History Of Science: What Goes Up . . . Newton

I doubt if you have ever met anyone as smart as Isaac Newton – I haven’t. You might have met people as unpleasant as he was. He disliked most people, had temper tantrums, and thought that almost everybody was out to get him. He was secretive, vain and would forget to eat his meals. He had lots of other disagreeable characteristics, but he was clever, and it’s the cleverness that we remember today, even if it’s quite hard to understand what he thought and wrote.

Isaac Newton (1642–1727) might have been disagreeable no matter what had happened to him, but his childhood was pretty awful. His father died before he was born, and his mother, who didn’t expect him to live, left him with her parents after she remarried and had another family. He hated his stepfather, disliked his grandfather and wasn’t very fond of either his mother or his grandmother. In fact, from an early age, he started not liking people. He preferred to be alone, as a child and as a very old man.

It was obvious, however, that he was very smart, and he was sent to the grammar school in Grantham, near where he lived, in Lincolnshire. He learned good Latin (he could write in English and Latin with equal ease), but spent most of his time at school making models of clocks and other mechanical gadgets and constructing sundials.

He also did his own thing when he went up to Trinity College, Cambridge, in 1661. He was supposed to read the ancient masters such as Aristotle and Plato. He did read them a little (he was a meticulous note-taker, so we know what he read), but his favourites were the moderns: Descartes, Boyle and other exponents of the new science. Reading was all right, but he wanted to figure things out for himself. To do this he devised many new experiments, but his greatest genius was in mathematics and how it could be used to understand more about the universe.

Newton worked out many of his ideas in an incredibly productive couple of years. No scientist except Einstein has ever done so much in so short a space of time. Newton’s most amazing years were 1665 and 1666. Some of this time he spent at his mother’s home in Woolsthorpe, Lincolnshire, because the plague epidemic that was then sweeping England had led the University of Cambridge to close its doors and send the students home. It was during this time that Newton saw ripe apples falling off trees in his mother’s garden. It probably wasn’t as dramatic as stories have it, but it did remind him of a problem that still needed explaining: why things fall down to earth.
He was busy with lots of scientific matters during this period.

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Take mathematics, for instance. Galileo, Descartes and many other natural philosophers (that is, scientists) had made great strides in developing mathematics as a subject and, even more importantly, in using it to understand the results of their observations and experiments. Newton was an even better mathematician, and he was brilliant in using it in his science. To describe things like movement and gravity mathematically, algebra and geometry are not enough. You must be able to consider very small units of time and movement: an infinitesimal amount, in fact. When examining a bullet fired from a gun, or an apple falling from a tree, or a planet going around the sun, you must focus on the distance it goes in the smallest conceivable moment of time. Many natural philosophers before Newton had seen the problem and thought up various solutions. But Newton, still in his twenties, developed his own mathematical tools to do the job. He called it his method of ‘fluxions’, from the word ‘flux’ which means something changing. Newton’s fluxions did the kind of computations that we still do in the branch of mathematics now called calculus. By October 1666, when he had finished a paper written just for his own satisfaction, he was the foremost mathematician in Europe, but nobody but Newton knew it. He didn’t publish his mathematical discoveries straightaway; instead, he used them, and only eventually shared his methods and results with his acquaintances.

Besides mathematics, Newton began to investigate light. Since ancient times, it had been assumed that sunlight is white, pure and homogeneous (meaning composed of all the same thing). Colours were thought to be caused by modifications of this essentially pure ray. Newton studied Descartes’ work on light and repeated some of his experiments. He used lenses and then a glass object, called a prism, which could break up light. He famously allowed a tiny beam of light into his darkened room, through a prism and then on to the wall twenty-two feet (nearly seven metres) away. If light was homogenous, as Descartes and many others had thought, the projection on the wall ought to be a white circle, the same shape as the hole through which it had passed. Instead, the light appeared as a wide multicoloured band. Newton hadn’t exactly made a rainbow, but he was on the way to explaining how they are formed.

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During these plague years, Newton also pushed forward with his work on mechanics: the laws governing bodies in motion. We have seen how Galileo, Kepler, Descartes and others had developed ideas to explain (and write out mathematically) what happens when a cannon-ball is fired, or the earth moves around the sun.

Robert Hooke, too, had been interested in this. Newton read the writings of these men, but he also went further. He once wrote to Hooke, ‘If I have seen further it is by standing on the shoulders of giants.’ Do you remember riding on your parent’s shoulders?

Suddenly being twice or three times as tall reveals all sorts of things you couldn’t see by yourself. And that is what Newton was getting at. His wonderful image describes how each scientist, and each generation of scientists, can benefit from the insights of those who came before. This is the essence of science. But Newton was also himself a giant, and he knew it. The problems arose when Newton didn’t feel that others recognised this.

Newton’s troubles with Robert Hooke began when Newton offered his very first paper to the Royal Society. The Society did what good scientific journals still do today: they sent it to another expert to comment on. We call this ‘peer review’, and the process is part of the openness that scientists pride themselves on. The Royal Society chose Hooke to read the paper since he, too, had investigated light.

Newton did not like Hooke’s comments at all, and even wanted to resign as a Fellow of the Royal Society. The Society quietly ignored his letter of resignation.

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Following his amazing burst of creative energy in the 1660s, Newton turned his attention to other matters, including alchemy and theology. As always, he kept careful notes on his reading and experiments, which are still being read by people who want to understand this side of Newton’s thinking. At the time, he kept these thoughts and investigations fairly quiet, especially his religious views, which differed from the doctrines of the Church of England. Cambridge University required its students to agree to the Church’s beliefs.

Fortunately for Newton and for science, he had powerful supporters at the university, so he was able to become a Fellow of Trinity College, and later was even elected Lucasian Professor of Mathematics, without ever having to swear that he believed in all the Church’s doctrines. He held this professorship for more than twenty years. Unfortunately, he was a terrible teacher, and his students couldn’t understand what he was talking about. Sometimes, when he arrived, there was nobody to lecture to.

He always talked about respectable subjects like light and motion, not the alchemy and theology that he was secretly pursuing – perhaps those would have been more exciting for his students!

By the mid-1680s, Newton’s research into mathematics, physics and astronomy was becoming known. He had written many papers and published a few, but he often remarked that his scientific work was just for himself alone, or for those who came along after his death. In 1684, the astronomer Edmund Halley visited Newton in Cambridge. (Look out for Halley’s Comet, named after Edmund Halley, in 2061 when it is next due to be visible from earth.) Halley and Hooke had been discussing the shape of the path taken by one object orbiting around another (such as the earth around the sun, or the moon around the earth). They wondered if gravity would affect the object’s path, acting by what we now call the ‘inverse square law’.

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Gravity is only one of several examples of this law. It means that the force of gravity decreases by the square of the distance between the two objects, and of course, increases in the same ratio as they get closer together. The attraction will be mutual, but the mass of the two objects is also important. If one object – say, the earth – is very large, and the other – say, an apple – is very small, the earth will do almost all the attracting. Chapter 12 explained how Galileo used a ‘square’ function in his work on falling bodies. We will also see it in later chapters, for Nature does seem to like things to happen as a function of something squared, whether it be time, acceleration or attraction. When you’re working with squares (3 × 3 = 9, or 32, for example), remember that Nature might be smiling. Halley’s visit made Newton put aside his theology and alchemy.

He set to work and produced his greatest book, one of the most important in the history of science, even if it is not an easy read. Today it is known as the Principia but its full Latin title (Newton wrote it in Latin) is Philosophiae naturalis principia mathematica (‘Mathematical principles of natural philosophy’: remember ‘natural philosophy’ was the old name for science).

Newton’s book gave the full details of how his new mathematics could be applied, and explained many aspects of physical nature in numbers rather than wordy descriptions. Only a few people could understand it easily in Newton’s lifetime, but its message was appreciated much more widely. It was a new way to see and describe the universe.

Many aspects of Newton’s view of the world and the heavens were contained in his three famous laws of motion, which he wrote in the Principia. His first law stated that every body either stays at rest or moves in a straight line unless something else – some force – acts upon it. A rock on a mountainside will stay there forever unless something – wind, rain, a human being – causes it to move; and, without any disturbance (‘friction’), it would move in a straight line forever.

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His second law stated that if something is already moving, a force can change its direction. How great the change depends on the strength of the force, and the change of direction occurs along a straight line, in the direction of the new force. So, if you swat a falling balloon from the side, it will move sideways; if you swat it from above, it will go down more quickly.

His third law of motion concluded that for any action, there is always an equal and opposite reaction. This means that two bodies always act upon each other equally but in opposite directions. You can swat a balloon, and it will move away from your hand, but it will also deliver an action on your hand (you will feel it). If you swat a large boulder, the boulder won’t move, but your hand may bounce back, and it will be sore. This is because it is harder for lightweight objects to influence heavy ones than vice versa. (We saw that it was the same with gravity.) These three laws brought together the puzzles of earlier natural philosophers. In Newton’s hands, they explained many observations, from the movements of the planets to the trajectory of an arrow shot from a bow. The laws of motion made it possible to view the whole universe as a giant, regular machine, like a watch that keeps time because of its springs, levers and movements. Newton’s Principia was recognised as a work of great power and genius. It turned this reclusive, troubled man into something of a celebrity.

His reward was a well-paid post as the Warden of the Mint, the place where the government made its coins and regulated the country’s supply of money. Newton threw himself into this new job with great gusto, tracking down counterfeiters and overseeing the nation’s money supply. He had to move to London, so he resigned all his Cambridge connections and spent the last thirty years of his life in the capital, becoming President of the Royal Society.

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During his London years, Newton significantly revised the Principia, including some of his further work, as well as answering various criticisms that people had raised since its publication.

Scientists often do this. Not long after Robert Hooke died, Newton published his second major scientific work, Opticks (1704), about light. Newton and Hooke had quarrelled a lot over which of them had done what first and how to understand the results of their experiments into what light was and how it behaved. Newton had done much of the work for this book nearly forty years earlier, but he had been reluctant to publish it while Hooke was alive. Like Principia, Opticks was very important. We’ll encounter some of its conclusions in later chapters, when other scientists were standing on Newton’s shoulders.

Newton was the first scientist to be knighted, becoming Sir Isaac. He enjoyed power but not much happiness. He was not what one would call a nice man, but he was a great one, one of the most truly creative scientists who has ever lived, celebrated for the amazing contributions he made to our understanding of the universe. Newton’s Principia was the highpoint of the astronomy and physics that had been so actively pursued by Kepler, Galileo, Descartes and many others. In his book, Newton brought the heavens and earth together in one system, for his laws applied throughout the universe. He offered mathematical and physical explanations of the way the planets move and the way bodies fall towards the earth. He provided the foundations of physics that scientists used until the twentieth century, when Einstein and others showed that there was more to the universe than even Sir Isaac had imagined.