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Audio Interviews

Prof. Rob Iliffe, on Isaac Newton (Part 1)

Professor Rob Iliffe, Oxford University.

(Interview from September 2022, Oxford)

Newton, Part 1Rob Iliffe & Alyssa Goodman
00:00 / 22:29

00;00;10;24 - 00;00;34;07 Rob Iliffe I’m Rob Iliffe, professor of history of science at Oxford University. I've worked on Newton for a long time, probably 40 years. I did a Ph.D. at Cambridge on Newton's Science and Religion, and then have done work in various fields. Always going back to Newton. It's hard to get away from him. He always drags me back ... just when I think I've got away from him. 00;00;34;23 - 00;00;59;20 Rob Iliffe I started with other people. I started a project 20 odd years ago, almost 25 years ago, called the Newton Project. We're aiming to put everything Newton ever wrote online, and we've already put almost all of his theology, most of his personal papers and most of his mathematics and physics is already available online for free as part of the Newton project. 00;00;59;29 - 00;01;13;01 Rob Iliffe Also his the papers he did at the Royal Mint when he was warden and then master of the Mint for three decades. But I work in other things as well, particularly on the scientific imagination. 00;01;13;06 - 00;01;37;23 Alyssa Goodman That's great. And that's actually a perfect segue to ask just a few questions of you. They may take a little while to answer, but there are only a few questions. And so the first one. ...So you said that in the Newton Project, which is wonderful., thank you very much, there's millions and millions of words. And and if I remember what you've said in the past, it's like half of them are almost more than half of them are about theology, not about physics or science in any way. 00;01;37;23 - 00;01;39;01 Alyssa Goodman Is that the right ratio? 00;01;39;12 - 00;01;53;08 Rob Iliffe Yeah, I think probably 60% of the materials are on theology, and theology is divided up into different parts, but it's clearly an abiding interest or obsession for him throughout his whole life. 00;01;53;09 - 00;02;14;08 Alyssa Goodman And so, yes, as we've discussed, the whole Prediction Project is about how people think about the future. And the one diagram I forgot to show you is where the difference between modern science and so-called ancient science, what we would be called science, is that when they would make a prediction, they would just STOP there. So they'll have some system to make a prediction. 00;02;14;08 - 00;02;33;00 Alyssa Goodman And now I've made the prediction and now I will just move on with my life. Whereas in modern science, as you know, people make a prediction, they check how well it came out and then they kind of go around and around this system. What we're trying to do in the whole project is explain to people that today's predictive systems like, say, weather prediction, can be checked. 00;02;33;04 - 00;02;58;29 Alyssa Goodman You know, if you say it's going to be 30 degrees one day and it's 34 degrees, there was something wrong with your model. Go back, try to fix the model. So Newton, was or wasn't actually even ever thinking about predicting the future? So the real question is when Newton was doing his work, at some level, what I've read is that he was trying to understand, you know, what is God's plan for the universe, what's going on? 00;02;58;29 - 00;03;15;04 Alyssa Goodman And is physics the way to understand that? Was he also ever thinking about predicting the future , per se, and if he was, was it more of a physics-based approach or more, for lack of a better word, religious reasons? 00;03;16;10 - 00;03;48;00 Rob Iliffe Well, I think Newton, from a very, very early age, he was born in 1642 (if you were in England, elsewhere, he was born in early 1643). That's because there's a different dating system. But when he was about 30 years old, we know he became very interested in trying to understand the Bible. So the Hebrew Bible in the New Testament and trying to... he's only doing what most other scholars are doing, but he wants to make a coherent theory of everything. 00;03;48;00 - 00;04;22;25 Rob Iliffe So that it all sticks together in a consistent form. So that part that involved dating things. There was a general view, uh, that the world was created in about 4000 B.C. So before Christ. Newton doesn't deviate from that. And the there's a general view also that the world will exist for about 6000 years in total. And if you look at where Newton lived at the time he lived, it means that he and most people thought there's about 200 years to go, 300 years to go before the end of the world. 00;04;23;23 - 00;04;50;16 Rob Iliffe And and that view of an imminent apocalypse is very prevalent amongst the kind of people, the kind of Protestants among whom Newton grew up. And essentially Newton becomes an expert on it in the past, not just the past thousand years or the past 200 years, but also going back to the beginnings of recorded history. 00;04;51;20 - 00;04;56;25 Rob Iliffe And he's very wary about talking about the future. I mean, you see that throughout everything he does. He's very cautious. 00;04;56;26 - 00;04;59;14 Alyssa Goodman Because he really believes the future is only going to last 200 years. 00;04;59;14 - 00;05;23;27 Rob Iliffe Well, no, it's not that. I think he thinks [interruption] I think he thinks it's hubris to try and work out exactly when the world is going to end. And he has a more general view, that one, you know, as an empiricist, as someone who believes that we should gather large amounts of data first before we make a conclusion, he's very wary about saying things that are going to happen in the future. 00;05;23;27 - 00;05;57;02 Rob Iliffe That is to say, assigning dates to the future. And he because he thinks also and this is embedded in in both the Hebrew Bible and the New Testament, that those people who pretend they're prophets and make predictions that turn out to be false bring religion into disrepute. So for all these reasons, he's not prepared to make these predictions about specific dates, but he knows in general, because he believes in revelation, he believes in that last book of the New Testament and its relationship to Isaiah and Ezekiel. 00;05;57;10 - 00;06;04;01 Rob Iliffe He has a view in general about what the structure of the future is going to be like, but he's not going to assign dates to it. 00;06;04;07 - 00;06;25;05 Alyssa Goodman Would he have there’s the future of humanity and then is literally the future of the universe, right? So in other words, here he is looking at astronomical data forever., and so what would he have thought if the world, would really, if his world, was going to end in 200 years? Did he think the solar system would keep going after 200 years or the whole universe ends? 00;06;25;10 - 00;07;06;27 Rob Iliffe Well, I think that's a very interesting question because I think there really is a divide at one level between his religious views about the future and the kind of apocalyptic physical views about the future that he develops after the Principia Mathematica is published in 1687. And we know that in some private interviews, he suggested that the Great Comet of 1680 would be would be a mechanism of God to destroy this solar system and thereby thereby pave the way for creating a new one, you know, sort of after five or six revolutions, I think he's got a periodicity of about 560 years. 00;07;07;29 - 00;07;22;23 Rob Iliffe In one of these periods, the comet would crash into the sun and there would be a supernova and then there would be a new... I think God would take some of the planets from Jupiter, some of the satellites of Jupiter, and put them in the places where... 00;07;23;01 - 00;07;24;03 Alyssa Goodman ...the planets were before... 00;07;24;03 - 00;07;29;26 Rob Iliffe ...where Venus, Earth and Mars were before. And then new life would be created. I mean, that's his point. 00;07;29;26 - 00;07;30;19 Alyssa Goodman He wrote about that. 00;07;30;22 - 00;07;36;09 Rob Iliffe He did what? He spoke about it. He didn't He left hints and clues about it. 00;07;36;09 - 00;08;01;26 Alyssa Goodman So we know that he and Halley were very close and that Halley famously predicted what is now called Halley's Comet and its return after even Halley was dead, so was Newton around when Halley made that prediction, and what would he have thought of that? Because that was I mean, it was less than 200 years in the future. But here he was predicting an exact date for something, and, was that, would that have been considered hubris? 00;08;02;03 - 00;08;45;09 Rob Iliffe Yeah. I mean, I think that there are two things about comets. I mean, one of them is that people before Halley had thought the comets might return, so they thought about periodicity, particularly after Kepler, obviously because of Kepler’s work on elliptical orbits. And so if you believe in periodicity, you you go back through history and you try and see whether there were, you know, periods, roughly equivalent periods, and how he did that, he was not the only person to do that, but he he took the comet of 1682 and saw that one had appeared roughly 76 years earlier and then went back 75, 76 years before that and so on and so forth. 00;08;45;22 - 00;09;09;29 Rob Iliffe So that historical work is a precursor towards making of it's an obvious precursor, a necessary precursor for saying that he's going to return in future. The other thing that's important about comets and which is a key issue for Newton in writing the Principia is when astronomers saw pairs of comets. So you see a comet traveling towards the Sun, and then you see another comet... 00;09;11;02 - 00;09;11;15 Alyssa Goodman Not always the same comet? 00;09;12;06 - 00;09;36;11 Rob Iliffe Two months later, which is going in, not the opposite direction necessarily, but in a very, very different direction. And the key question, which of course is very, very much related to the issue of periodicity, is whether those two things are the same comet or whether they're not. But if they are the same comet, what's the mechanism by which they approach the sun and then travel in front of the sun or travel around the sun? 00;09;36;11 - 00;09;59;21 Rob Iliffe Is it magnetic or is it not magnetic? And that kind of thinking that Newton exhibits and that kind of idea that Newton discusses with other people after the Great Comet of 1680 is absolutely necessary in order for him to write, or to think about, orbital dynamics in the Principia Mathematica. 00;10;01;02 - 00;10;15;14 Alyssa Goodman So if I remember right, he had worked out a lot of the math that was in the Principia way before it was published. And so [yes] this comet would have come along when how much of the book was already written? 00;10;16;04 - 00;10;40;12 Rob Iliffe Well, I think that the book itself started really with a very small sort of essay at the end of 1684, and it gradually expands over the next two years to become this this great work, which is composed of three books. But many of the problems, the techniques had been developed in the 1670s. And so they were well known to Newton. 00;10;40;21 - 00;11;18;27 Rob Iliffe But the issue for Newton that, you know, the great triumphs of the Principia, are the shape of the earth, the theory of coments, and tidal motion. So all of those Newton makes, you know, he does things that I think are unimaginable to people before to to his contemporaries before he does them, and the techniques he develops that this, you know, the extraordinary philosophy that underpins the Principia then becomes a basis for other people following him to make relatively accurate predictions, as we see in the 1870s. 00;11;18;27 - 00;11;25;18 Alyssa Goodman And would he have been okay with those in terms of whether or not that's hubris to do that? 00;11;25;18 - 00;11;45;14 Rob Iliffe No, I think he's he he's very much okay with that, with that kind of thing. I mean, he alternatively very, very proud and arrogant about his own achievements and also very humble. And I think that's the case with many people. You can be both those things at the same time. But he he he's very proud and he only lived until 1727. 00;11;45;14 - 00;12;09;14 Rob Iliffe So he did see significant advances in orbital dynamics in the ability to deal with, you know, problems, anomalies in the in the physics of the solar system that were gradually removed right up to Laplace and you know and and they're based on Newtonian dynamics. 00;12;09;29 - 00;12;34;15 Alyssa Goodman I was talking yesterday with some of the Mesopotamian experts here and about how much the Mesopotamian civilizations cared about comets and comet returns. And and the story was that they were very interested in things like, you know, the phases of Venus in the phases of the moon. And it's not really clear what the ...I mean, the comets are recorded... but what they were doing with it doesn't seem completely clear. 00;12;34;15 - 00;12;53;05 Alyssa Goodman And and it's interesting because they were apparently trying to figure out if things weren't as they thought they were going to be or the gods trying to tell them something? And so there's a superstition about, you know, comets and astronomical things that seems to go back to the beginning of human history, so we could broaden the comet story to all of that. 00;12;53;05 - 00;13;08;08 Alyssa Goodman The next question is, if Newton were to look at this infamous Path to Newton, and, you know, there's this comment which is attributed to him, but as far as I understand, he didn't say, about, or he said it sarcastically about standing on “the shoulders of giants.” 00;13;08;08 - 00;13;11;23 Alyssa Goodman Is it that he said it sarcastically or he didn't say it at all? Will you tell me? 00;13;11;23 - 00;13;17;04 Rob Iliffe He wrote that he wrote it in a letter to Robert Hooke in February 1676. 00;13;17;05 - 00;13;17;15 Alyssa Goodman Right. 00;13;18;06 - 00;13;43;23 Rob Iliffe And I think, you know, you can read it two ways. One is to say one is the humble way and say to say, look, there's all these people who've come before me, including you, Hooke..... implying that, you know, he's in the past, and so on and so forth, which is relatively humble. But I think he does see himself as somebody who has seen further you know, “if I have seen further, it is because I'm standing on the shoulders of giants.” 00;13;44;02 - 00;13;45;18 Rob Iliffe But he does think he's seen further. 00;13;45;26 - 00;14;03;05 Alyssa Goodman Right. Yes, I'm sorry, I forgot the quote. I knew that it was the connection to Hooke, and I knew that various people or I know that various people have accused him of essentially taunting Hooke or or teasing, to say giants, but but that he's.... “Yes, I've stood on his shoulders. But I'm so great.” 00;14;03;11 - 00;14;19;05 Rob Iliffe You know, he does because the quote from, you know, one of the original forms of the quote is to say that, you know, Christians are like dwarves sitting on the shoulders of giants who'd come before them. But Newton is not going to compare himself to a dwarf. That's the point. 00;14;19;06 - 00;14;39;02 Alyssa Goodman Right? Right. That's great. That's a funny then if you were actually looking at this and he was you know, if we look carefully, right, we have all these people in different civilizations who are contributing, you know, at first data and then explanations. And if you remember the stuff that's gold, you’re not colorblind, right? Okay. The stuff is gold is is turns out to be wrong. 00;14;39;03 - 00;15;13;01 Alyssa Goodman According to modern physics and stuff, that's green is basically right. And then here at the top, we have the instruments that were needed in order to make the kind of observations or calculations that this mathematics here, which is what gets added over time, also required. And of course we attribute calculus to Newton, which is debatable. We should probably talk about that too, about whether, you know, Leibniz needs more credit or whether some ancient civilizations had the hints of calculus that we didn't quite record and keep. 00;15;13;22 - 00;15;39;05 Alyssa Goodman That's a separate keep that as a side question. But in terms of Newton, as the person in the world who knows the most about Newton, if Newton we're looking at this, what would he say? Would Newton say, oh, yes, you know, Descartes was particularly important or I really wish Aristotle hadn't said those things about the universe being completely spherical, or were there characters along here who were particular heroes or villains or interesting to him? 00;15;39;21 - 00;15;55;26 Rob Iliffe I think Newton sees the history of the world in terms of the sacred history, and he incorporates the history of natural philosophy, as he would say it into that, into that giant hopper of a of a structure. 00;15;55;28 - 00;15;56;07 Alyssa Goodman Okay. 00;15;56;10 - 00;16;21;21 Rob Iliffe And if you're looking at the the way he sees it like other people is is is the inverse of what we think today. So Newton thinks of progress as going back in time. That is to say, as you go forward in time and you discover more and more things, you are getting back to what people right at the start of the time knew, right at the start of human history. 00;16;21;21 - 00;16;22;20 Alyssa Goodman Really? 00;16;22;20 - 00;16;31;00 Rob Iliffe Yeah. Because at the beginning of time people like Adam and Noah and their followers, they, they knew they were Newtonians. 00;16;31;04 - 00;16;31;20 Alyssa Goodman Okay. 00;16;31;21 - 00;16;52;02 Rob Iliffe Right? And then gradually idolatry came in, stuff became misunderstood. Bits and pieces of history are bits and pieces of philosophies that people like Plato and Aristotle are good. But essentially these people perverted and polluted the pristine truths that had once been. 00;16;52;11 - 00;17;08;10 Alyssa Goodman Now, when you say they are Newtonians... would he be saying that the very first humans were Newtonians in that they understood how the world works and how it connected to God, or that they also understood the math associated? 00;17;08;10 - 00;17;15;04 Rob Iliffe No, I, just well, no, he doesn't go into detail, he’s clear that there's no evidence for that whatsoever. 00;17;15;04 - 00;17;15;18 Alyssa Goodman Right. 00;17;16;11 - 00;17;21;19 Rob Iliffe But, they’re Newtonians is in the sense that they believe in something like universal gravitation. 00;17;21;19 - 00;17;22;06 Alyssa Goodman Okay. 00;17;22;06 - 00;17;27;23 Rob Iliffe They know the inverse square law. They know all this kind of thing. And they veil it in mysteries. 00;17;28;29 - 00;17;32;16 Alyssa Goodman So they know an inverse square law, but they wouldn't call it an “inverse square law”? 00;17;33;09 - 00;17;41;10 Rob Iliffe Well, he did. He doesn't go into detail and he talks about the pre Aristotelians, but particularly Pythagoras and so on and so forth. 00;17;41;11 - 00;17;41;21 Alyssa Goodman Right. 00;17;42;05 - 00;18;09;12 Rob Iliffe And you know, maybe from a philosophical point of view, people like Aristarchus and Hipparchus. And people who are heliocentrists. Those people still have the remnants, although they are in control of the remnants of the true philosophy that have become forgotten over time. And that's what Newton believed. And strangely enough, that is what he believed. 00;18;09;12 - 00;18;33;23 Alyssa Goodman That is very strange. And so did he care--in other words, when I learned calculus--the way I understood calculus best was by thinking often of geometric analogs. And so you mentioned Pythagoras , and ... did he care about sort of mathematical connections back to Euclid and Pythagoras and all of that? And did that have anything to do with this? 00;18;33;23 - 00;18;48;16 Rob Iliffe He does. I mean, he's a big fan of Apollonius. He's a big fan of Euclid, obviously. And I think that the Principia is structured in a deliberate way to to look like it's a geometrical treatise. 00;18;48;16 - 00;18;49;09 Alyssa Goodman Right. 00;18;49;09 - 00;19;00;16 Rob Iliffe But it but it does have it does have forms of mathematics that break the bounds of ... so he deals with, you know, very, very small things. 00;19;00;16 - 00;19;03;25 Rob Iliffe It deals with limits and so on and so forth. 00;19;04;22 - 00;19;10;11 Alyssa Goodman And you mentioned treatise... I mean, written almost as, as a long series of proofs? 00;19;10;11 - 00;19;14;00 Rob Iliffe Yeah, yeah, yes. With our we with as little algebra as possible. 00;19;14;04 - 00;19;19;01 Alyssa Goodman Right. Yeah. I did find that amazing ...having looked through it, It does not look like a math book. 00;19;19;01 - 00;19;43;02 Rob Iliffe And there's hardly any calculus. Right. And you know, in the Enlightenment, people argued. So in the late 18th, 19th century, people argued that he understood, if you like, like Leibnizian, Lagrangian, analytic mechanics, but chose not to express his work in that way because he thought that the geometrical representation was superior. 00;19;43;02 - 00;19;43;09 Alyssa Goodman Yeah. 00;19;43;16 - 00;20;01;29 Rob Iliffe But ,and there were lots of people who said he actually wrote a book in this other form, but then decided to transform it into a more geometrical style. But there's no evidence of that at all-- it's absurd. That he the way he conceived the Principia is the way that it appeared. 00;20;03;02 - 00;20;12;06 Alyssa Goodman And what about this whole controversy about whether there were other forms of calculus, you know, a thousand years before or 50 years before or...? 00;20;13;14 - 00;20;59;10 Rob Iliffe I don't... there are there are elements that you find in people who work on on on very, very small, infinitesimals. So that there's stuff that you find in the the English mathematician John Wallace. There's the stuff in Descartes that is very important, very useful in terms of techniques. There are various other bits and pieces that are tools, you know, there are various tools that needed to be brought together in order to create the the sort of beautiful inverse relation between differential and integral calculus, what Newton called “tangents” and “qudratures.” 00;21;00;18 - 00;21;28;15 Rob Iliffe And, you know, the fact that Leibniz discovered something or algorithms, theorems, that are virtually identical at the same time is because, you know, there were a lot of people who were working on things like infinite series, series expansions, and so on and so forth, and all these things are a family of problems that Newton and Leibniz together sort of found general solutions to. 00;21;28;16 - 00;21;29;29 Alyssa Goodman Right, they kind of unified... 00;21;29;29 - 00;21;43;25 Rob Iliffe Yeah, and it's not ... there's an interesting question I was talking to somebody yesterday about this actually ... but the question for historians is whether what Leibniz and Newton did is the same thing. So historians would say that they're very different things. 00;21;43;27 - 00;21;44;07 Alyssa Goodman Okay. 00;21;44;13 - 00;21;46;19 Rob Iliffe But the mathematicians would say that. 00;21;46;19 - 00;21;51;25 Alyssa Goodman they’re very similar. I mean, you go from an infiinte series to a continuous function, it's like, okay... 00;21;52;09 - 00;21;55;26 Rob Iliffe Exactly. So you take you pick depends on which discipline. 00;21;55;26 - 00;22;28;10 Alyssa Goodman You come from.

Prof. Rob Iliffe, on Isaac Newton (Part 2)

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