Portrait of Isaac Newton

Robyn Williams:  Hello again, Robyn Williams. In a couple of weeks in The Science Show, I shall invite you to consider the top 100 Australian scientists and ask why you should bother to know who they are, or were. But today, one of those I and others would image to be one of the tops internationally of all time, along with Pasteur, Currie, Galileo and Einstein. I’m talking about Isaac Newton. Who? Said a bunch of possible backers of a Newton movie. Well, is 2024 a post-Newton era? Although he certainly changed the course of history.  This is Sharon Carleton’s engrossing portrait.

Sharon Carleton: After I'd finished reading, watching, and listening to everything I could find about Isaac Newton, the first thing Dean Rickles, Professor of History and Philosophy of Science at Sydney University, said to me was, 'Don't believe a word of it.'

Dean Rickles: Isaac Newton is basically presented these days as the paragon of rationality. And he's sort of the spokesperson for the Enlightenment period, so that sort of requires quite a lot of creative bookkeeping to keep him in good order. So a lot of the stories that you will read and hear about in podcasts and so on are completely false, or at least they only have a grain of truth.

The most famous Newton story is obviously the apple, the idea that he saw an apple falling from the tree and reasoned that, well, that is pretty much the same as the Moon falling in an orbit towards the Earth. And anything that falls is falling as a result of this universal principle of gravity. That doesn't seem to be true, and it seems to have come from a biography of Newton, written with Newton's help, by his friend, William Stukeley. This was inserted to give a little bit more flesh to the story because he would have been working on this near the apple tree, possibly even sitting under the apple tree while he was thinking about these things, but it seems there was no eureka moment that led to this. He'd been mulling over these things for a long, long time.

Sharon Carleton: Let me, if I may, put some more so-called facts about Newton to you. Just tell me, are they true or false. He was an alchemist.

Dean Rickles: It's true that he was an alchemist, but not in the sense that we think of alchemists today, namely of sort of pseudo-scientific kinds of chemists doing primitive work in chemistry. So alchemy means something very, very different and it has to do with…it's almost like a kind of magic and they believe that they're transmuting, not metals into gold and other substances, but by doing that, they're transmuting themselves basically and their souls in a certain way. So there's a sort of magical principle involved.

Sharon Carleton: Newton believed that life on Earth was sustained by dust from the tails of comets.

Dean Rickles: Again, strange but true. He has this theory that maybe life on Earth is fed by the vapours that are coming from these comet tails and sort of put there by the Sun's heat.

Sharon Carleton: Newton believed he'd only recovered the knowledge of the ancients. They already knew it before and he was just recovering their knowledge.

Dean Rickles: This is true as well. I mean, because he believed in all of these biblical ideas, he believed in also the deluge and the catastrophes, so he thought that a lot of ancient knowledge had been destroyed in that but had been preserved in certain clues.

Sharon Carleton: When you say the deluge, he thought we lost all that knowledge in the flood, Noah's Ark type thing?

Dean Rickles: Basically he believed fully in that idea, the cataclysmic cycles idea, and he thought the same way about lots of ancient knowledge, it was hidden from the profane or from the swine, you know, 'Don't cast your pearls before swine,' and you had to seek it. So he viewed himself as a seeker.

Sharon Carleton: He was a heretic, true or false?

Dean Rickles: True.

Sharon Carleton: He never laughed.

Dean Rickles: It seems to be true. There are two famous stories about the two times he laughed. The first story concerned something about Euclidean geometry, and somebody…he'd lent a book, Euclid's Elements, to a friend, and the friend said, 'What's the point of Euclid's geometry?' And Newton said, 'If you don't understand that, you really don't get the point of Euclid's elements,' and apparently laughed at that. You have to know geometry to understand that. Euclid's geometry is all about points, so it's the worst kind of pun you've ever heard. But apparently, that was his kind of thing.

The other time he left was somebody mentioned the idea that comets spiral into suns towards the end of their lives. And then Newton said, 'Well, that's not really what you need to be worrying about. You need to be worrying about the fact that comets can go into our sun,' and then had a good giggle about that, because who doesn't like to have a giggle about existential calamities? That was apparently the two times he laughed.

Sharon Carleton: Isaac Newton was an unequalled genius and neurotic, a perfect subject for the millions of words written about him, all conjured from a heady mix of knowns and unknowns. Monash University's first mechanical engineering graduate, and later lecturer in aerodynamics, also happens to be one of Australia's foremost playwrights, David Williamson. His play Nearer the Gods is a dark comedy about how Newton's laws of motion almost didn't make it.

David Williamson: Well, the fact that I had a science background made me fully acquainted with the importance and the stunning change that Newton's thoughts made to our understanding of the universe. So I was always in awe of the man. But when I started to research him in depth, I realised what a highly complex and interesting character he was. Newton was very neurotic, possibly Asperger's in a very interesting way, and with a mathematical mind the likes of which we've probably never seen before or since.

Sharon Carleton: And on a personal level, he was very difficult.

David Williamson: Oh, he was a difficult and cranky man, there's no doubt about it, but a very dramatic man because of that, and that's what attracted me to telling the story.

Sharon Carleton: How are you going about getting this made into a film?

David Williamson: Director Bruce Beresford was very taken with the script and the story, and he's in the process of getting a film up, which would be very exciting. There was just this prejudice in our society that stories like Romeo and Juliet about passionate love or dire drama or melodrama are the only ones that are interesting. But in fact, the world of science is full of all of those things, and Newton was no exception.

Sharon Carleton: So what is Isaac Newton's legitimate scientific legacy? Has his natural philosophy of 300 years ago stood the test of Einstein, shall we say? Physics professor Tony Williams, from Adelaide University.

Tony Williams: Newton's key contributions, apart from the contributions he made in optics, are classical mechanics, through his Newton's laws, the law of universal gravitation, and calculus itself, which is a modern mathematical tool. And while in 1905 Einstein proposed the laws of special relativity, Newton's laws still remain true when all speeds are small compared to the speed of light. And the speed of light, of course, is 30,000 [sic 300,000] kilometres per second, or 3x10⁸ metres per second, which is extraordinarily fast. So all of our everyday experience is for velocities much less than the speed of light, and so Newton's laws apply in our everyday lives.

And then, of course, in around early 1900s, shortly thereafter, Einstein had an explanation of the photoelectric effect where photons knocked electrons out of metals, for which he got the Nobel Prize. And then Bohr had a model of the atom. And those two things, combined with other things that were happening at the time, really led to quantum mechanics. And of course, quantum mechanics is also totally different to Newton's classical physics, laws of classical mechanics, as we call it, but again, if you look at systems that are large, that is systems which are made up of many, many billions and trillions of atoms, then the laws of quantum mechanics reduce back to Newton's laws again.

Later, in around 1913, Einstein came up with his general theory of relativity, which basically is a generalisation of his universal law of gravitation or the inverse square law, and general relativity superseded Newton's theory of gravity. But again, in the limit where the gravitational fields are sufficiently weak and where the gravitational fields are sufficiently slowly varying, Newton's laws again apply. So it's not correct to say that Newton's laws are wrong in any sense, it's just that they apply in the sphere in which he applied them. And when we go to the extremely strong force limit, or to the extremely tiny limit of atoms and below, or when we go to the extreme fast limit where velocities approach the speed of light, then of course Newton's laws break down.

Sharon Carleton: Tom Levenson is an author and Professor of Science Writing at the Massachusetts Institute of Technology.

Tom Levenson: Isaac Newton's legacy is thriving. We live in a world of forces and momentum and inertia. We live in a world where we use Newton's principles to understand the flight of a cricket ball or the flight of a rocket to the Moon. Newton was the person who set in motion the habits of thought, the ways of constructing an argument, the ways of building a model of physical reality that we now call modern physics and modern science. He was the person who turned motion into number, matter into number. That's a pretty good legacy.

Sharon Carleton: An intriguing side of Isaac Newton the scientist is that he had an inherent dislike of sharing, even publishing his findings. This led to some ugly priority disputes, as they're called; who got there first. It took the extraordinary belief of astronomer Edmund Halley (yes, of comet fame) to cajole him into publishing his greatest work. As Halley says of his hero, 'Nearer the gods no mortal may approach.' And in 1687, Newton sent out into the world his revolutionary Principia Mathematica.

And just a quick note for our Latin lovers, the name of Newton's book in cassical Latin is pronounced prin-kipia. In church Latin it's prin-chipia, and in English Latin, which Newton would likely have spoken, it's prin-sipia, so they're all correct.

However you choose to pronounce it, this book profoundly changed our understanding of matter and motion, on Earth and in space. Newton set out to explain all physical phenomena with a few generalised laws. It's one of the highest achievements in the history of knowledge. The first print run ran to 200 or 300 copies, and only four have annotations written by Newton himself. Cambridge University has three and the other is right here in Australia, at the University of Sydney. Manager of rare books Julie Sommerfeldt is the privileged custodian.

Julie Sommerfeldt: If you're looking at the book closed, it's very unassuming. It's a plain brown leather binding, very, very ordinary looking. This copy went missing for over 140 years. Eventually it was found to have been locked in an old clocktower in Kent, a castle in Kent, owned by the James family. A group of books made their way to Australia. They had been inherited by a Sydneysider who didn't want them and he asked for advice with the intent of selling them, and the honourable Bruce Smith, he was an attorney at law, a barrister, he was specifically asked to look at this group of books and advise on them. He ended up purchasing this copy of Principia. Once he realised what he had on his hands, he obviously discovered the annotations throughout and recognised that some of them were in Newton's own hand, he published several letters to the publication Nature back in 1908:

Reading: Sir, among a number of books which I bought was a copy of Newton's Principia. I found that it contained nearly five pages of manuscript additions and corrections for a second edition, written in Latin. The notes are punctiliously detailed, and the alterations in the body of the text are made with almost microscopic care.

Julie Sommerfeldt: We received the book in 1961 when heirs of Bruce Smith donated it to the library. It's like a window through time to explore how his amazing mind works. Sometimes students come and they request it and look at it in the reading room, and they're just sort of hunched over it in awe, turning the pages, their faces are just lit up. They can't believe they're sitting in front of something with Isaac Newton's own handwriting from all those centuries ago. It's quite extraordinary.

Tony Williams: Yes, well, of course, it's not just the annotation that's extraordinary, the Principia itself was an extraordinary piece of work. It laid out Newton's three laws which describe and lead to all the classical physics, it described the universal law of gravitation, which is the force of attraction between two massive bodies, and he used that law to explain planetary motion, he explained the tides, he explained the bulging of the Earth at the equator, and he explained the motion of comets and many other things with that law in the Principia. He also established the geometrical form of calculus, so he, along with Gottfried Leibniz, is considered the founder of modern calculus.

Sharon Carleton: But was calculus included in the Principia?

Tony Williams: Yes, he did it in a form of geometry, he used geometry to generate his understanding of the consequences of this inverse square law. He may not have done it in a way we necessarily recognise today, but he used the principle infinitesimal geometric shifts to basically derive modern calculus.

Tom Levenson: And that was, in some sense, the first truly scientific cosmological account of reality. Before that you had religious descriptions of how the world works and how the world fits into the universe, but this was the time you put it in a single place, with a single argument, developed from beginning to end from the first principles of the handful of axioms he started with, all the way out to why the tide laps at London Bridge.

Sharon Carleton: There are few enough people today who would have read the Principia cover to cover, let alone totally understood it, and even fewer when it was written. Many fellow natural philosophers found Newton's laws of gravity obscure because they couldn't be explained by mechanical means. Plus, you had to understand astronomy, Latin and mathematics. One among a select few not only understood but translated, criticised, expanded, and interpreted the work. But this scientist had one debilitating flaw: she was a woman, and mistress of the Enlightenment philosopher Voltaire.

Katherine Brading: I wish that she wasn't primarily remembered for being Voltaire's mistress because far more importantly, as far as I'm concerned, she was a wonderful philosopher, and she translated Newton's Principia into French, and her translation is still the translation that's used in France today. It was used as a resource by the people who most recently translated the Principia into English in its most recent version.

Sharon Carleton: Katherine Brading is a science history philosopher at Duke University in North Carolina. And the woman in question is Émilie du Châtelet, a French aristocratic in the first half of the 18th century. Unusually for the day, her father apparently encouraged her precocious quest for knowledge, inviting leading astronomers to talk to his 10-year-old daughter, and by the time she was 12, she could speak four languages.

Katherine Brading: At the age of 18, she married into an old and noble family, her husband was older than she was, but this made her very well placed within society, gave her all sorts of responsibilities at court and for running her husband's estate. But as a young woman, she sort of came to this realisation that there was more to her mind and to her brain that she was making use of, and she became very interested in mathematics and philosophy and physics. This is around the time when she met Voltaire again, their friendship really began again when she was about 28 in 1733. Before long, they were working together on philosophy and various other things.

Sharon Carleton: I've read that she actually had to dress as a man to get into the mathematical discussions in the cafes of Paris, she had to actually fight for her education.

Katherine Brading: It would certainly be in keeping with her character that she would have done whatever she needed to do to be in the places that she wanted to be.

Sharon Carleton: Voltaire was a political firebrand, always in trouble. He was either criticising Christianity, slavery, censorship, or any of his pet causes. And soon enough, the police were after him and he had to get out of Paris quickly.

Katherine Brading: She offered him a safe place to stay at the Du Châtelet estate, and then the following year decided to leave Paris and join Voltaire there. And that at the time would have been very problematic, except that it was accepted by her husband. And here they did all sorts of experiments and writing.

Sharon Carleton: What was Émilie working on there?

Katherine Brading: So we know that she worked with Voltaire on his Elements of Newton's Philosophy, and this is something that is credited with bringing Newton and spreading Newton's views quite widely. They did some experiments on the nature of heat and things together. And then unbeknownst to Voltaire, she wrote her own essay on the nature and propagation of heat and fire and submitted that to a competition. And at the end of that, she began working on her first big published work, which is Foundations of Physics.

Sharon Carleton: Unusually for the time, Voltaire did credit Émilie for the work she did with him saying, 'She dictated and I wrote.'

Katherine Brading: He certainly consulted her on the details of the physics and increasingly of the metaphysics and the philosophy that surrounded the physics. His intention in writing this was really to promote Newton's views in France, whereas Du Châtelet's interest was in philosophy itself and in the physics itself, so she had this very different view that when we're working on these kinds of issues, we shouldn't be partisan by nations. She says that the search for truth is the only thing in which the love of your country must not prevail. About a book of physics, one must ask if it is good, not if the author is English, German or French.

Sharon Carleton: Du Châtelet's most ambitious project was translating Newton's Principia into French, working from the original Latin. She didn't trust the English version. She didn't just convert words, she created her own version of the text. That is, according to another Du Châtelet connoisseur Patricia Fara, an historian of science at Cambridge.

Patricia Fara: Émilie du Châtelet decided to undertake not only the literal translation of the text itself, but also three types of interpretation. For newcomers, she converted the complex mathematics into elegant prose, supplemented by her own examples. Next, she turned to calculus, translating Newton's geometry into the new continental algebra. Finally, she summarised recent mathematical research and experimental vindication of Newton's theories. Good translations are vital for spreading new ideas, and modern international science would not have developed without them.

Sharon Carleton: Émilie du Châtelet was recognised in her own time, but then largely forgotten. The German philosopher Immanuel Kant, who actually admired her intellect still mocked her, saying that 'because she could hold learned discussions on mechanics, she might as well have a beard'. Perhaps she would have been better remembered if she did have a beard.

Isaac Newton was troubled, extremely introverted, aggressive, vindictive, and insecure to the point of being unhinged at times. His early life was not happy. He was born prematurely in rural Lincolnshire on Christmas Day, 1642. His father had died three months earlier. He was an unhealthy baby, not expected to thrive. And before he was three, his mother had married the Reverend Barnabas Smith, who was keen on having his own children, but not on caring for poor, puny Isaac, who was left with his grandparents, no father, and now no mother. By all accounts, he had a loveless lonely childhood. It left the young lad with definite feelings of animosity towards both his stepfather and his mother. When he was older, he made a 'list of sins' he thought he had committed:

Reading: Threatening my father and mother Smith to burn them and the house over them.

Sharon Carleton: Science historian Dean Rickles:

Dean Rickles: After his stepfather died, his mother wanted Newton to stay at home, to leave school and basically tend the farm. Fortunately, Newton had enough people who knew about his gifts to persuade his mother otherwise. He did go back to school, and then made it into Cambridge shortly after where he entered as a sizar, which is not a particularly nice position, it's what poor people used to go to Cambridge as, where they got all of the full tuition, they got their meals and rooms and all of these kinds of things, but they had to do duties, which was usually looking after richer students. What's interesting about that is that they could have afforded it, they were actually quite wealthy by that time, the Newtons, but they decided to send him in as a sizar, in this slightly humiliating position. I would imagine he had a bit of resentment, given how gifted he was and the fact that he was doing menial work for less gifted people. But really, I think his gifts emerged so rapidly, he sort of elevated himself above that position pretty quickly.

Sharon Carleton: Then came the bubonic plague years of 1665 and '66 when Newton returned home to work on his theories of optics, calculus and gravity. He also had a strong view on how the disease was cured:

Reading: Combining powdered toad with the excretions and serum, made into lozenges, and worn about the affected area, drives away the contagion and draws out the poison.

Sharon Carleton: Much, much later in life, he told his collaborative biographer that actually most of his ground-breaking achievements came about in that one heady period of the plague, away from Cambridge, when he was in his mid 20s. But is that another Newton fallacy?

Dean Rickles: It's probably a myth, or maybe not a myth but it could be a coincidence that this happened when he was at the height of his powers. These years are known as his miraculous years, 1666 is the annus mirabilis, where he invented integral calculus. He did these experiments on optics, he discovered this universal law of gravitation. He was working towards all of this anyway in Cambridge, and it's actually difficult to say whether he wouldn't have done even more had he have been allowed to remain in Cambridge where his duties were completely minimal. He had absolute isolation to do that, who's to say whether in going back for these two years during the plague years he wasn't slowed down by the menial tasks that he would have inevitably had to do on the farm, he was back on his parents' farm.

Sharon Carleton: It's very hard for science historians to try and make sense of Newton's disturbed character, his mental health and his scientific method, given his taciturn secretiveness, and the lack of diaries and personal correspondence he left behind. This is from Tom Levenson's book on Newton:

Tom Levenson: [reading] A wealth of myth has sprung up around Newton's emotional life, and the possible existence of a sexual one. He was an irascible man, a great hater. Without doubt, he was a prude. Hence the legend of the bloodless semidivine hero of the mind. But for all such adulation then and since, the real Newton was a human being, capable of great feeling—affection as well as enmity, loyalty as well as implacable disdain.

Sharon Carleton: Voltaire, Émilie du Châtelet's lover, who apparently heard it from Newton's doctor, believed Newton was a virgin to the end. Some post Freudian biographers concluded he was a repressed homosexual, who would have suffered enormously given his puritanical upbringing and his strict literal reading of biblical constraints.

Dean Rickles: There's obviously plenty of psychological material in his childhood. Recent work suggests that he probably wasn't a repressed homosexual. He had lots of male friends, but remember, Cambridge at this time was all male, his friends are going to be male friends. Every now and again he would have a slight infatuation with one of his friends. I think the point of Newton was that it was entirely and by design supposed to be a life of the mind. So he's trying to be something like one of the older-style philosophers in this Platonic tradition that you're supposed to almost cut yourself off from the material world.

Sharon Carleton: In David Williamson's play Nearer the Gods (and, hopefully, in a film to come) there is an inferred sex scene.

David Williamson: There is no direct evidence that Newton was gay, but the indirect evidence is fairly overwhelming. Whether it was ever consummated or not, I don't know. But later in life, later than when my play is set, he had a passionate longing for a young male, just a crush, who knows, but throughout Newton's life there are strong suggestions that even if it was only a tendency, it was certainly there. So I did write a scene.

He had someone who shared his lodgings at Cambridge for 20 years called John Wickins. For that 20 years he was virtually Newton's servant, Newton made him his servant. He did all the legwork for Newton's brilliant scientific work. He was an extraordinary character and a very likeable character. And I thought over those 20 years it's highly likely there was something quite close between those two. So being a dramatist, I made it happen.

Sharon Carleton: But was it just the drama, or do you think that actually does go some way, as you inferred in that scene, to explaining Newton?

David Williamson: In Newton's time, to be an atheist was a crime punishable by prison sentences, stocks. To be in any way deviant from the norm was hugely dangerous, and to be homosexual was especially dangerous. Newton strongly believed in God, he didn't believe in the Church of England, the Holy Trinity, he thought all the churches on Earth were vile and corrupted. And he spent the last part of his life working out when God was coming to Earth again to cleanse the world.

Dean Rickles: Without a doubt, he was a heretic. He believed in what's called antitrinitarianism. So he despised this idea that Jesus and God had the same kind of level of power, and he thought that there was only one true God. It wasn't that he didn't believe in Jesus, he thought he was a messenger, just like many other messengers. He was definitely a heretic.

Sharon Carleton: Isaac Newton spent more time studying and analysing the Bible than on what we'd call scientific matters. He wrote literally millions of words about his scriptural studies. But it would be a couple of centuries before these unorthodox views became widely known. The papers of the philosopher John Locke are held at Oxford University. There's a single sheet with Locke's note of 1691 written on the back, but the writing on the paper itself is in Isaac Newton's hand. It's a chart, a timeline of revelations and prophecies in the Bible, which he had decoded. He thought he'd found secret numerological codes and prophecies hidden in those scriptures.

Dean Rickles: I think he viewed the work he was doing in the natural sciences, in natural philosophy as it was called, as pretty much on a par with what he was doing with his biblical investigations. But it was a basically a quest for fundamental ultimate truths, which he thought lie in the fact that the universe was a creation of a divine creator, so that when he was doing his physics, when he was thinking about things moving around in space time, they're moving around in God's temple. And he even talks about the arena for where things are happening (space and time) as the sensorium of God. This is sort of a very deeply biblical physics, which usually gets ignored of course, it's usually presented as this perfectly mathematical precise system.

What you've got to remember as well is that he was writing his work on these biblical themes when he was at the height of his powers. So we imagined that he was only working on his calculus and the science of mechanics, but this was just a part of what he was working on at that time, and he was probably spending more time, even then at the height of his powers, on these biblical concerns.

Sharon Carleton: Prophecies and physics worked together for Newton. At that time, natural philosophy and pseudoscience, magic and chemistry were intermingled. And then comes alchemy. Roughly a million of the 10 million words of private writing that Newton left behind are alchemical manuscripts. Was he looking for a universal elixir of life? A single unifying theory perhaps? One of Newton's biographers in the 1800s lamented that he'd actually gone to the trouble of transcribing the work of a notable alchemist.

Reading: We cannot understand how a mind of such power, so nobly occupied with the abstractions of geometry and of the material world, could stoop to be even the copyist of the most contemptible alchemical work.

Sharon Carleton: The economist and Newton authority John Maynard Keynes was the first person to see some of Newton's theology and alchemy manuscripts, which had been kept hidden for a couple of centuries. The papers were sold in 1936 by an English earl. A Cambridge University committee had decided that the historical and theological papers cannot be considered of any great value and didn't even attend the sales. Keynes, a collector of rare books, did go. And the Newton revealed in the manuscripts he bought was a shocking surprise and far from the cold, hard realist Newton had been painted. After having poured over the contents, Keynes wrote:

Reading: Newton was not the first of the age of reason, he was the last of the magicians, the last of the Babylonians and Sumerians, the last great mind which looked out on the visible and intellectual world with the same eyes as those who began to build our intellectual inheritance rather less than 10,000 years ago. In vulgar modern terms, Newton was profoundly neurotic. All his unpublished works on esoteric and theological matters are marked by careful learning, accurate method, and extreme sobriety of statement. They are just as sane as the Principia if their whole matter and purpose were not magical.

Sharon Carleton: Dean Rickles:

Dean Rickles: The Philosopher's Stone is this idea that you can transmute base metals into gold, and it's supposed to be connected with immortality. In keeping with this idea of ancient knowledge being buried through symbols and clues and all of these kinds of things, whenever you're thinking about alchemy in these times, you have to treat all of the substances as symbolic representations of something else, usually something spiritual. In this case, the base metal, usually lead, is supposed to refer to our material substance, the body, matter. The idea of transmuting lead into gold is to elevate your material condition into something gold, i.e. spiritual. So it's basically elevating your material existence into something more soul-like, finding your soul.

Sharon Carleton: So what experiments did Newton do to try and do that himself?

Dean Rickles: They would have been doing actual chemical experiments using real materials like antimony and cinnabar and all of these kinds of substances, which all had, again, some specific meaning in alchemy that, again, is supposed to refer to these hidden truths, these mysteries. So each time they're doing these processes, it's symbolic for some other process, some sort of hidden process.

Sharon Carleton: Around his 50th birthday in 1692, Newton had a complete mental or emotional breakdown. Some believed it occurred after traumatic love affair. Others think that his alchemical experiments, which included tasting metals such as mercury, arsenic, gold and lead, contributed to it. He became paranoid, depressed, irrational. It's said he didn't even recognise his masterpiece, the Principia. He never again concentrated in the same way, nor did any fresh scientific work. It probably lasted for a couple of years. But he emerged, as he said:

Reading: …without the former consistency of mind.

Sharon Carleton: And then something strange happened; after three and a half decades, he left his academic isolated life in Cambridge behind. As John Maynard Keynes wrote:

Reading: There's a complete change in his way of life. He possessed in exceptional degree almost every kind of intellectual aptitude; lawyer, historian, theologian, no less than mathematician, physicist, astronomer, and when the turn of his life came to put his books of magic back into the box, it was easy for him to drop the 17th century behind him and to evolve into the 18th century figure which is the traditional Newton.

Sharon Carleton: Isaac Newton accepted a job in the city and took up residence in the Tower of London as warden of the Royal Mint in 1696. This would be another 30-year stint. Dr Patricia Fara is an historian of science at Cambridge University. She is reading from her book on Newton called Life After Gravity:

Patricia Fara: [reading] He ran the Royal Mint, revamped the British economy, and moved in fashionable aristocratic circles. In the spring of 1695, while Newton was still in Cambridge but looking for an escape, the national debt had reached crisis level. As the value of golden guineas soared, silver plummeted, making it even more difficult to pay the wages of soldiers fighting overseas. The government decided to consult some of the country's leading financiers and scholars, including John Locke, Christopher Wren, and Isaac Newton. That autumn, Newton submitted his carefully thought-out advice, but after many discussions and half-hearted measures, the government decided that all the silver coins in the country should be recalled, melted down, and then reissued. Although Newton had opposed that scheme, within a few months he was responsible for carrying it out. The wardenship was not the most senior position in the Mint, but it came with a fat salary and light responsibilities.

Biographers often glide over those London years as if they were an embarrassment, an unfitting epilogue for the career of an intellectual giant. Even though Newton took his responsibilities at the Mint very seriously, his admirers are determined to maintain his status as a scientific icon. According to standard accounts, Newton sublimated his own intellectual desires for the sake of his country by abandoning the intellectual life he adored and reluctantly devoting his great mind to rescuing the nation's plummeting currency. However unconvincing that argument might sound, it is widely accepted, especially by scientists whose own identity and job satisfaction are tangled up with an unrealistic image of a venerated genius.

Economists see matters differently. More interested in falling stock markets than in falling apples, they are untrammelled by assumptions that the life scientific is the only one worth living. According to them, once Newton had tasted fame and the possibilities of wealth, he wanted more of both. Despite being educated as a physicist, I side with the economists and their more realistic, if jaundiced, perceptions of human nature.

He shared the ambitions of his wealthy friends to make London the world's largest and richest city, the centre of a thriving international economy. Like many of his contemporaries, he invested his own money in merchant shipping companies, hoping to augment his savings by sharing in the profits.

An uncomfortable truth is often glossed over: until 1772, it was legal to buy, own, and sell human beings in Britain. Newton knew that the country's prosperity depended on the triangular trade in enslaved people—and when he was meticulously weighing gold at the Mint, he must have been aware that it had been dug up by Africans whose friends and relatives were being shipped across the Atlantic to cultivate sugar plantations, labour down silver mines, and look after affluent Europeans. This was a collective national culpability, and there is no point in replacing the familiar 'Newton the Superhuman Genius' by the equally unrealistic 'Newton the Incarnation of Evil'.

By exploring activities and attitudes that are now deplored, I aim not to condemn Newton, but to provide a more realistic image of this man who was simultaneously unique and a product of his times.

Sharon Carleton: So Newton bought shares in unsavoury enterprises. But what is perhaps even more surprising is that as warden of the Mint, Isaac Newton became a first class, often ruthless detective. As Patricia Fara said, the Royal Mint then was on the verge of collapse. It was decrepit, corrupt, and inefficient. While at the same time, England depended on it for her daily life at home and her soldiers abroad. Science writer, Tom Levenson:

Tom Levenson: It was chaos when Newton first arrived at the Mint, and the reason it was chaos is because the Mint was trying to do something that had never been done before in English finance, they were trying to take in all the physical silver money that was circulating throughout the entire kingdom, bring it into the Mint, melt it back down and re-coin it, make new coins that would be sound and reliable and hard to counterfeit and all those good things that you want money to be.

As of the 1690s, England's money was basically awful, much of it was clipped, that is to say criminals had snipped off little bits of silver, put the coin back out there, kept the silver and just made their little, you know, 2%, 3%, 5% off every coin to the point that England's currency contained much, much less silver than it was supposed to. And this was actually having an enormous effect on both everyday life and on sort of national and international statecraft. Hard currency, the specie of a country was how you paid for things like armies in the field. And England in the 1690s was years into what became the Nine Years' War with France. It was a great power rivalry, actually the first war in more than 100 years of a long war. By 1695 when Newton came to the Mint, England was literally running out of money with which to pay the troops and buy them gunpowder and uniforms and so forth. And there was a real risk that England would lose that war, not because of a defeat on the battlefield, but by financial collapse. It was a total mess.

Sharon Carleton: How did Newton start then with the production, the re-coining? What did he do?

Tom Levenson: When Newton arrived at the Mint, I think no one had any expectations for him. Why would you expect this sort of thin, theoretical-minded guy who'd spent his entire life in the university and so forth, how could he run one of the largest metalworking shops in England? Well, it turned out that Newton was great at it. He was in some ways the first time and motion analyst, you know, manufacturing consultant.

He went down into the men's workshops, where there was a whole series of machines, hundreds of horses that were turning big rolling mills and this kind of thing, and looked at what each stage of the process was, from the rolling mills to the final coin stamping machines. He worked out exactly how to make sure that the silver was of the right purity, not too pure because then you'd be spending the king silver on coins that were too valuable, but not debased using less silver than you should. More than anything else, he had a rigorous quantitative mind, he did the experiments to find out the things he needed on some of the machines, including, most importantly, that silver content, and then he just turned out to be a good, tough manager.

Sharon Carleton: Coining, or making counterfeit coins with the monarch's head embossed on one side, was considered treason, punishable by death. And Isaac Newton had no qualms about going after these forgers. But first it meant Newton had to familiarise himself with the messy, human, conflicting evidence of a courtroom. As Tom Levenson says in his book, Newton and the Counterfeiter:

Tom Levenson: [reading] The behaviour of bodies in motion could be observed and mapped against mathematical predictions. No one knew better than Newton how to shape a chain of cause and effect until only one possible conclusion remained.

Sharon Carleton: Juries, of course, didn't always see it his way.

Tom Levenson: He fairly rapidly realised that every coiner and every counterfeiter has one big problem. It's fine to make a fake coin in some attic in a bad part of town, you have to get out into the world, and that's the point of vulnerability. That's where there's a person with their hands on a fake coin, that if you can get your hands on them, you have a way into the entire system.

The first thing he did is he developed to a system of agents, people who, unlike him, could plausibly go into the parts of town and the kinds of transactions, the kinds of places where you will be buying stuff with counterfeit shillings or whatever you may have.

Sharon Carleton: This is the underworld, in other words.

Tom Levenson: This is the underworld, yeah, this is quite risky. And one of the great things is Newton kept absolutely meticulous accounts down to the farthing. There are records of buying a suit of clothes for one of his agents that would be suitable for hanging out in low company and these kinds of things. And he himself would actually sometimes go to certain places, not necessarily the most dangerous in town, but places where he could meet or encounter or discuss things with some of his 'no better than they needed to be' assistants, spies, runners. Ultimately he got a pretty good picture of what was going on and he arrested a number of not terribly large-scale or successful counterfeiters, and would take them to court and present the evidence to the judges. These people would often end up very badly indeed, they'd get hanged. There were some very large operators who were acting in London. That's where his real duty and also his greatest difficulty came about.

Sharon Carleton: Do we know how many people he was responsible for sending to the gallows?

Tom Levenson: I certainly am not sure what the total number would be. There are records of Newton's interrogations, we have some idea of how many people he himself talked to, that were caught up in his nets. We also know that he was really skilful, I mean, to the point of being…well, not diabolical, but certainly not somebody you want against you, in doing things like turning people; he'd capture somebody, he'd get them to the point where they knew they were going to face the gallows if they didn't cooperate, and they'd run back out into the world and snare more people. He was very good at the traditional, still used police tactic of capturing small fish and letting them loose again to lead them to the bigger fish and so on up the chain.

Sharon Carleton: Like so much about Newton, there are conflicting views about his time at the Mint. One particular Cambridge historian condemned Newton for the bloody ruthlessness of his pursuit of counterfeiters and clippers. Frank Manual thought the blood of these villains (rather like a vampire) nourished Newton's damaged mind.

Tom Levenson: In Manual's day I think it really was a case that Freudian interpretations were a relatively new tool, it was very exciting, and it was a way to sort of impose a present-day logic on the past, on 300 years before.

Sharon Carleton: That doesn't mean to say it didn't happen though, because even in your book you do mention one of the few pieces of evidence that's there, that perhaps some of the methods of getting the information out of people wasn't very pleasant.

Tom Levenson: Yes, being caught by a policeman and thrown into a really nasty jail and held there, perhaps starving if you didn't have enough money to bribe your jailers, all that kind of stuff is really, really unpleasant. But that was true for everyone who was caught up in England's penal system at that time. Newton wasn't special in sending people to Newgate. That's where they went. He wasn't special in the use of, well, maybe tightening the leg iron a little bit tighter than you might like to remind people they were at risk of harm. Yes, bad things happen when you get caught up in people who have ultimately absolute power over you.

But there's no evidence at all that Newton was this uniquely damaged individual, riven by rage and a psychotic desire to make up for whatever horrible things had been done to him as a kid. That's what I object to in Manual's account of all this, is he assumes that somehow these bad things that happened to prisoners under constraint in the English jails, that was somehow a unique diagnostic for Newton's personal pathology. That's an imagined account of Newton's character and a projection of our horrors at the seeming injustices that were done in the name of justice at that time.

Sharon Carleton: The most famous of Newton's underworld adversaries, a man named William Chaloner, was to successfully pit his wits for years against the biggest brain in Europe. He was a petty criminal who used to sell sex toys, write pamphlets warning (ironically) about corruption at the Mint, and was a nasty informer on his own underworld colleagues.

Tom Levenson: Newton caught William Chaloner by doing good old-fashioned police work. That's the beauty of it. And here he caught several people who were involved in Chaloner's operations. He knew Chaloner was the target because Chaloner had actually publicly challenged Newton in his management of the Mint, so Newton was very much aware of Chaloner as somebody trying to gain access to ways to subvert Mint operations. I think it was the classic thing; he found people who were involved with Chaloner, he put them at great risk of life and limb, sent them back out in the world to engage with Chaloner again, and finally, Chaloner was surrounded by more of Newton's agents than his own men and was caught.

And then just to put the final nail in literally what would be Chaloner's coffin, all the time that Chaloner was held in Newgate before he was tried for his crimes, Newton had one or often more of his own agents in the cells with him, prisoners he'd got on other matters, that he was trading reprieves and in some cases releases for information about the prisoner he really wanted to make sure it did, in fact, go to the gallows. There was no brilliant stroke of insight or some great scientific or mathematical deduction, it was simple good police work.

Sharon Carleton: Tom, how do we sum up Newton's time the Mint?

Tom Levenson: He saved the re-coinage and saved the functioning of England's everyday economy and to some extent saved England's national credit with overseas bankers and moneymen essential to the prosecution of the wars that it was almost continuously fighting. England wouldn't have collapsed but England might have had to withdraw from a war on the continent.

Sharon Carleton: Isaac Newton remained at the Mint until his death in 1727. He was there nearly as long as he was at Cambridge. He'd also become president of the Royal Society, despite his purported disdain for the organisation, after the death of his old scientific adversary, Robert Hooke. Sir Isaac, as he'd become, said:

Reading: If I have seen further, it is by standing on the shoulders of giants.

Sharon Carleton: But again, with Newton, was this quite as it seemed? Was he being humble, or waspish? Science historian Dean Rickles:

Dean Rickles: So the usual interpretation of this remark is that it was a backhanded reference to Robert Hooke, who famously had a hunchback. I think we can be a little bit more charitable with Newton here. If you remember the many millions of words that he wrote on ancient philosophers' works, and the fact that he spent a lot of time writing out by hand lots of works of alchemy and so on by other figures, you can see that he had extreme admiration for lots of people, people like Pythagoras and so on. So he might have been making a completely earnest remark about his appreciation for those figures, but not necessarily his contemporaries, who, as that remark also makes clear, he believed he did see further than.

Sharon Carleton: A complicated man indeed. Newton believed the end of the world was prophesised in the Bible, which was:

Reading: A history of the future.

Sharon Carleton: The saintly will be saved, and the rest of us would perish. He thought a comet, much like the one of 1680, might fall into the Sun, increasing its heat, so as to burn up all life on Earth. His calculations led him to believe it would happen in the 21st century. So, should we be afraid?

Dean Rickles: Given Newton's view of what the Apocalypse was, namely a revelation of truths, then you should be afraid only if you're afraid of the truth.

Robyn Williams: Afraid of the truth? Well sometimes. It’s often terrifying these days. But what about the film of Isaac Newton? What happened next? Well producer Bruce Beresford told me recently that he’d seen many of the fellows with money, who might back such a venture, and said Bruce, they’d never heard of Mr Newton. Oh well, we live in hope. That special Science Show was written and presented by Sharon Carleton. The Science Show is produced by David Fisher and next week, Sharon returns with a man who certainly knew why we should know personally, many of the scientists and what they did, H.G. Wells the lowly born but massively brilliant man, who invented a kind of Wikipedia, and who launched modern science fiction, who predicted and named the atom bomb, and much else. A very naughty man too! The Science Show next time. I’m Robyn Williams.