When Galileo wrote the opening pages of the Dialogue, he said twice that Italian science and trade was now in danger of being overtaken by northern rivals. How true a prophecy that was. The man that he had most in mind was the astronomer Johannes Kepler, who came here to Prague in the year 1600 at the age of 28, and spent his most productive years here. Here he devised the three laws that turned the system of Copernicus from a general description of the Sun and the planets into a precise mathematical formula. That was the state of affairs when Newton was born in 1642 that Christmas day. Kepler, of course, was dead. Galileo had died in that year. And not only astronomy, but science stood at a watershed: the coming of a new mind that saw the crucial step from the descriptions of the past to the explanations of the future.
New ideas and new principles now moved forward in the protestant seafaring nations of the north: England and the Netherlands. England was becoming republican and puritan. Dutchmen came over the North Sea to drain the English Fens. The marshes became solid land. A spirit of independence grew in the flat vistas and the mists of Lincolnshire. When Newton was born at his mother’s house in Woolsthorpe in 1642, his father had died some months earlier. In a little while his mother married again, and Newton was left in the care of a grandmother. He was not exactly a homeless boy, and yet from that time he shows none of the intimacy that parents give. All his life he makes the impression of an unloved man. He never married. He never seems to be able to flow out in that warmth which makes achievement a natural outcome of thoughts honed in the company of other people. On the contrary. His achievements were solitary, and he always feared that others would steal them from him.
The two years after Newton graduated at Cambridge (1665 and 1666) were years of plague, and he spent the time when the university was closed at home. Here he struck his vein of gold: mathematics. He invented what we now call the calculus, which Newton called fluxions. Newton kept fluxions as his secret tool. He discovered his results with it, but he wrote them out in conventional mathematics. Here Newton also conceived the idea of universal gravitation, and at once tested it by calculating the motion of the moon around the Earth. The moon was a powerful symbol for him.
I deduced that the forces which keep the planets in their orbs must be reciprocally as the squares of their distances from the centers about which they revolve. And thereby compared the force requisite to keep the moon in her orb with a force of gravity at the surface of the Earth, and found them answer pretty nearly.
The understatement is characteristic. His first rough calculation had in fact given the period of the moon close to its true value—about 27 and a quarter days.
When the figures come out right like that, you know that the secret of nature is open in the palm of your hand. It’s a key that you’ve put into the lock and turned it, and nature has yielded in numbers the conformation of her structure. But if you’re Newton, you don’t publish it. When he went back to Cambridge in 1667, Newton was made a fellow of his college, Trinity. Two years later, his professor resigned the chair in favor of Newton. He was then 26.
Newton published his first work in optics. It was conceived, like all his great thoughts, in the plague year 1666. But not at home. Newton had come back here to Trinity College Cambridge for a short interval within the plague. It’s odd to think that a man whom we think of as the master of explanation of the material universe should have begun by thinking about light. There are two reasons for that. First of all, this was a mariner’s world. All the problems arose from seafaring. The telescope was a salient problem of the time. And indeed, Newton was first aware of the problem of color in white light when he was grinding lenses for his own telescope.
But of course there is, beneath this, a more fundamental reason. Physical phenomena consist always of the interaction of energy with matter. We see matter by light. We are aware of the presence of light by the interruption by matter. And that thought makes up the world of every great physicist. In 1666 Newton here began to think about what caused the fringes at the edge of a lens, and looked at it by a prism. Every lens at its edge is a little prism. Now, of course, the fact that the prism gives you colored light is at least as old as Aristotle. But alas, there weren’t any explanations at the time, because they had this extraordinary quality. They simply said the white light comes through the glass, and it’s darkened a little as the thin end, so it only becomes red. It’s darkened a little more where the glass is thicker, so it becomes green. It’s darkened a little more where the glass is thickest, so it becomes blue. Marvelous. Explains absolutely nothing, sounds very plausible.
The only thing that he doesn’t explain, as Newton pointed out the moment he let the sunlight in through a chink through his prism, was this: the sun comes in at this end as a circular disk, but it comes out at this end as an elongated shape. Everybody knew the spectrum was elongated. That also had been known for 2,000 years. But it takes a powerful mind like Newton to break his head on explaining the obvious. And Newton said that the obvious is that the light is not modified, the light is physically separated. That’s a fundamentally new idea on scientific explanation. Quite inaccessible is contemporaries. Robert Hooke argued with him. Every kind of physicist argued with him, until Newton got so bored with all the arguments that from that time on he really refused to have anything to do with debate at all, and certainly with the debaters like Hooke. But let us begin at the beginning.
In Newton’s own words, in the year 1666:
I procured me a glass prism to try therewith the celebrated phenomena of colors. And in order thereto, having darkened my chamber and made a small hole in my window shuts to let in a convenient quantity of the sun’s light, I placed my prism at his entrance that it might thereby be refracted to the opposite wall. It was at first a very pleasing divertissement to view the vivid and intense colors produced thereby. But after a while, applying myself to consider the more circumspectly, I saw that the light tending to one end of the image did suffer a refraction considerably greater than the light tending to the other end. The true cause was detected to be no other than that light consists of a heterogeneous mixture of differently refragible rays.
The elongation of the spectrum was now explained by the fanning out of the colors. Blue is bent or refracted more than red.
Then I placed another prism so that the light might pass through that also, and again be refracted before it arrived at the wall. This done, I took the first prism in my hand and turned it to and fro slowly about its axis to make the several parts of the image successively pass through the hole, that I might observe to what places on the wall the second prism would refract them. When any one sort of rays have been well-parted from those of other kinds, it hath afterwards obstinately retained its color, not withstanding my utmost endeavors to change it. I have refracted it with prisms and reflected it with bodies which in daylight were of other colors. I have intercepted it with a colored film of air interceding compressed plates of glass, transmitted it through colored mediums and through mediums irradiated with other sorts of rays and diversely terminated it, and yet could never produce any new color out of it.
If light were modified by glass, the second prism should produce new colors. Newton called this the critical experiment. It proved that once the colors are separated by refraction they cannot be changed any further.
But the most surprising and wonderful composition was that of whiteness. I have often with admiration beheld that all the colors of the prism being made to converge, and thereby to be again mixed, reproduced light entirely and perfectly white. Hence therefore it comes to pass that whiteness is the usual color of light, for it is a confused aggregate of rays imbued with all sorts of colors as they are promiscuously darted from the various parts of luminous bodies.
That letter was written to the Royal Society shortly after Newton was elected a fellow in 1672. He was rather proud of his achievement.
A naturalist would scarce expect to see ye science of those colors become mathematical, and yet I dare affirm that there is as much certainty in it as in any other part of optics.
Newton had begun to have a reputation in London, as well as in the university, and a sense of color seems to spread into that metropolitan world as if the spectrum scattered its light across the silks and spices the merchants brought to the capital. A metropolitan reputation meant inevitably new controversies. Results that Newton outlined in letters to London scientists were bandied about. That was how there began after 1676 a long and bitter dispute with Gottfried Wilhelm Leibniz about the mathematical invention that Leibniz called the calculus and Newton called fluxions. Newton would never believe that Leibniz—a powerful mathematician himself—had conceived it independently.
Newton thought of retiring altogether from science into his cloister of Trinity. The great court was a spacious setting for a scholar in comfortable circumstances. He had his own small laboratory and his own garden. In Neville’s court, Wren’s great library was being built. Newton subscribed 40 pounds to the fund. It seemed that he might look forward to a donnish life devoted to private study. But in the end, if he refused to bustle among the scientists in London, they would come to Cambridge to put their arguments to him.
Newton had conceived the idea of a universal gravitation in the plague year of 1666, and had used it very successfully to describe the motion of the moon around the Earth. It seems extraordinary that in the twenty years that followed he should have made almost no attempt to publish anything about the bigger problem of the motion of the Earth around the sun. But the facts are plain. Only in 1684 did there arise in London an argument between Sir Christopher Wren, Robert Hook, and Edmund Halley, as a result of which Halley came to Cambridge and said to Newton: “What would be the path of a body that moves around the sun under a force which falls off as the square of the distance?” “Why, of course,” said Newton, “an ellipse.” “My God,” said Halley, “we’ve all been trying to prove that. Show me.” And Newton said, “Well, I don’t exactly have the proof. I’ll send it to you.”
It took three years, from 1684 to 1687, before Newton wrote out the proof, and it came out as long as that. And, as a system of the world. Of course it was sensational from the moment it was published. It is a marvelous description of the world subsumed under a single set of laws, but much more. It is also a landmark in scientific method. We think of the presentation of science as a series of propositions, one after another, as deriving from the mathematics of Euclid. And so it does. But it’s not until Newton turned this into a physical system that modern scientific method really begins. And we can see in this book actually where the stumbling blocks were. For instance, I’m convinced that it’s because at section 12 on: “how does a sphere attract a particle?” that we see the immense mathematical difficulties that he had to overcome before he could publish.
When Newton was challenged on such questions as, “you haven’t explained why gravity acts,” “you haven’t explained how action at a distance could take place,” or indeed, “you haven’t explained why rays of light behave the way they do,” he always answered in the same terms: “I do not make hypotheses”—by which he meant: I do not deal in metaphysical speculations, I lay down a law and derive the phenomena from it. Exactly what he had said in his work on optics, and exactly what had not been understood by his contemporaries in optics.
Now, if Newton had been a very plain, very dull, very matter-of-fact man, all that would be easily explicable. But, you see, he was not. He was really a most extraordinary wild character. He practiced alchemy. In secret he wrote immense tomes about the Book of Revelation. He was convinced that the law of inverse squares was really already to be found in Pythagoras. And for such a man—who in private was full of these wild metaphysical and mystical speculations—to hold this public face and say, “I make no hypotheses,” that is an extraordinary expression of that secret character.
Well, the public face was very successful. Of course, he couldn’t get promotion in the university because he was a Unitarian, therefore he couldn’t become a parson, therefore he could not possibly become the master of a college. So in 1696 he went to London to the Mint, in time he became master of the Mint, became a knight, after Hooke’s death accepted the presidency of the Royal Society in 1703, and to his death in 1727 dominated the intellectual landscape of London. The village boy had made good. The sad thing is that I think he’d made good not by his own standards, but only by the standards of the eighteenth century. The sad thing is that it was that society whose criterion he accepted when he was willing to be a dictator in the councils of the establishment and count that success.
An intellectual dictator is not a sympathetic figure, even when he’s risen from humble beginnings. Yet, in his private writings, Newton was not so arrogant as he seems in his public face so often and so variously represented.
To explain all nature is too difficult a task for any one man, or even for any one age. It is much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things by conjecture without making sure of anything.
By the time Newton was in his seventies, little real scientific work was done in the Royal Society. England under the Georges was preoccupied with money. These are the years of the South Sea bubble, with politics, and with scandal in the coffee houses. Nimble businessmen floated companies to exploit fictitious inventions. Writers poked fun at scientists, in part from spite, and in part for political motives, because Newton was a bigwig in the government establishment. The group of Tories who later helped John Gaye to satirize the government in the Beggars’ Opera also helped him in 1717 to write a play, Three Hours After Marriage. There the butt of the satire is a pompous aging scientist under the name of Dr. Foster.
[Theater performance]
The first topic of fun naturally is alchemy. The technical jargon is quite correct.
[Theater performance]
The scientific references come thick and fast now to the troublesome problem of finding the longitude at sea, to the invention of the differential calculus that Newton called fluxions, and of course to astronomy.
[Theater performance]
It seems irreverent to us that Newton should have been subject to satire in his lifetime, and subject to serious criticism too. But the fact is that every theory, however majestic, has hidden assumptions which in time will make it necessary to replace it. And Newton’s theory, beautiful as an approximation to nature, was bound to have the same. Newton confessed. The prime one is this, that he said at the outset: “I take space to be absolute.” By that he meant that space is everywhere flat and infinite, as it is in our own neighborhood. And Leibniz criticized that from the outset—and rightly. After all, it’s not even probable in our own experience. We are used to living locally in a flat space, but as soon as we look in the large at the Earth, we know it not to be so.
The Earth is spherical, so that the point at the north pole can be seen by two observers on the equator, each of whom says, “I’m looking due north”—which is inconceivable in the flat Earth. Newton was really behaving like a flat Earth on a cosmic scale, sailing out into space with his footrule in one hand and his pocket watch in the other, mapping spaces if it were everywhere as it is here. And that’s not necessarily so. It isn’t even as if space has to be spherical everywhere—that is, have a positive curvature. It might well be that space is local, lumpy, but it has saddle points like this. At that time they were all speculations. But Leibniz had said the prophetic words: “I hold space to be something purely relative, as time is.”
Time is the other absolute in Newton’s system. Time is crucial to mapping the heavens. We don’t know in the first place how far away the stars are, only at what moment they pass across our line of sight. So the mariner’s world called for the perfection of two sets of instruments: telescopes and clocks. First, then, improvements in the telescope. They were now centered in the new Royal Observatory at Greenwich. The ubiquitous Robert Hook had planned that when he was rebuilding London with Sir Christopher Wren after the Great Fire. The sailor trying to fix his position, longitude and latitude, off a remote shore, from now on would compare his reading of the stars with those at Greenwich. The Meridian of Greenwich became the fixed mark in every sailor’s storm-tossed world, the Meridian and Greenwich Mean Time.
Second, as an essential aid to that, the improvement of a clock. The clock becomes the symbol and the central problem of the age, because Newton’s theories could only be put to practical use at sea if a clock could be made to keep time on a ship. The government offered a prize of 20,000 pounds for that, and the London clockmakers (John Harrison, for instance) built one ingenious clock after another, designed so that their several pendulums should, between them, correct for the lurch of the ship.
A ship indeed is a kind of model of a star. How does a star ride through space, and how do we know what time it keeps? The ship is a starting point for thinking about relative time. These technical problems set off a burst of invention, and established the preoccupation with time that’s dominated science and our daily lives ever since.
It’s a nice reflection that the clock as we know it—the pocket dictator of modern life—had since the Middle Ages fired the skill of craftsmen who wanted not to know the time of day, but to reproduce the motions of the starry heavens.
The universe of Newton ticked on without hitch for about 200 years. If his ghosts had come to Switzerland any time before 1900, all the clocks would have chimed hallelujah in unison. And yet, just after 1900, here in Bern, not 200 yards from the clock tower, a young man came to live, Albert Einstein, who was going to set them all by the ears.
Time and light first began to go awry just about this time. It was in 1881 that Michelson carried out an experiment, which he later repeated with Morley in six years, in which she fired light in different directions and was taken aback to find that, however the apparatus moved, always he came back with the same speed of light. That was quite out of keeping with Newton’s laws. And it was that small murmur at the heart of physics which first set scientists agog and questioning about 1900. It’s not certain that the young Einstein was quite up to date about this. He had not been a very attentive university student. But it is said that, by the time he came here to Bern, he had already asked himself, oh, quite ten years early, as a boy in his teens, what our experience would look like seen from the point of view of light. Einstein was always full of beautiful, simple illustrations of such principles, and I shall take a read out of his book.
Go to the bottom of this clock tower and get into the tram he used to take every day on his way to work as a clerk in the Swiss patent office. The thought that Einstein had had in his teens was this: what would the world look like if I rode on a beam of light? Suppose this tram were moving away from that clock on the very beam with which we see what the clock says. Then, of course, the clock would be frozen. I, the tram, this box riding on the beam of light, would be fixed in time. Time would have a stop. That’s an extraordinary paradox.
I won’t go into its implications or others that Einstein was concerned with. I will just concentrate on this point: that if I rode on a beam of light, time would suddenly come to an end for me. And that must mean that, as I approach the speed of light—which is what I’m going to simulate in this tram—I am alone in a box of time and space which is more and more slowly departing from the norms around me. Such paradoxes make two things clear. An obvious one: there is no universal time. But a more subtle one: that experience runs very differently for the traveler and the stay at home, and for each of us on his own path. My experiences within the tram are consistent. I discover the same laws, the same relations between time, distance, speed, mass, force that every other observer discovers. But the actual values that I get for time, distance, and so on are not the same that the man on the pavement gets.
That’s the core of the principle of relativity. But the obvious question is: well, what holds his box and mine together? The passage of light. Light is the carrier of information that binds us. And that’s why the crucial experimental fact is the one that puzzled people since 1881: that when we exchange signals, then we discover that information passes between us always at the same pace. We always get the same value for the speed of light. And then, of course, naturally, time, space, mass, must be different for each of us. Because they have to give the same laws for me in here, for the man outside, consistently, and the same value for the speed of light.
Is that real? Yes, we know enough now about cosmic and atomic processes to see that, at high speeds, that is true. If I were really traveling at half the speed of light, say, then what I have been making three minutes and a little would be half a minute longer for the man on the pavement. We’ll take this tram up towards the speed of light and see what the appearances look like.
The relativity effect is that things change shape. The tops of the buildings seem to bend inward and forward towards me. The buildings also seem crowded together. I’m traveling horizontally, so horizontal distances seem shorter, but the heights remain the same. Cars and people are distorted in the same way: thin and tall. And what is true for me looking out is true for the man outside looking in. The Alice in Wonderland world of relativity is symmetrical. He sees the tram crushed together: thin and tall.
The tram did not reach the speed of light. It stopped very decently near the patent office. Einstein got off, did a day’s work, and often of an evening stopped here at the Cafe Bollwerk. The work at the patent office was not very taxing. To tell the truth, most of the applications now look pretty idiotic. An application for an improved form of pop gun. An application for the control of alternating current, of which Einstein wrote succinctly: it is incorrect, inaccurate, and unclear.
In the evenings at the Cafe Bollwerk, he would talk a little physics with his colleagues. He would smoke cigars and drink coffee. But he was a man who thought for himself. He went to the heart of the question, which is: how in fact do, not physicists, but human beings communicate with one another? What signals do we send from one another? How do we reach knowledge? And that is the crux of all his papers: this unfolding of the heart of knowledge, almost petal by petal, so that the great paper of 1905 is not just about light or, as its title says, the electrodynamics of moving bodies. It goes on in the same year to a postscript, saying energy and mass are equivalent. E = mc2.
That comes from a profound insight into the processes of nature herself, but particularly into the relations between men, knowledge, nature. Physics is not events, but observations. Relativity is the understanding of the world not as events, but as relations. Einstein looked back to these years with pleasure. He said to my friend Leo Zillard many years after, “They were the happiest years of my life. Nobody expected me to lay golden eggs.”
Of course, he did go on laying golden eggs: quantum effects, general relativity, field theory, and the confirmation of his early work. E = mc2 was confirmed in time, of course. Even the point about clocks running slow. Einstein died fifty years after the great 1905 paper, in 1955, but by then one could measure time to a thousand millionth of a second. And therefore it was possible to look at that odd prediction, also in the 1905 paper, in which he says: think of two men on the Earth, one at the North Pole, one at the equator. The one at the equator is going round faster than the one at the North Pole. Therefore, his watch will lose.
And that’s just how it turned out. This is how the experiment was done by a young man called Hay at Harwell. He imagined the Earth squashed flat into a plate, so that the North Pole is at the center and the equator runs around the rim. Put a radioactive clock at the center, put another radioactive clock on the rim, and let it turn. And sure enough, the clock at the rim keeps time more slowly than the clock at the center. At this moment, in this disk, the center is aging faster than the rim with every turn.
It’s almost impertinent to talk of the ascent of man in the presence of two men, Newton and Einstein, who stride like gods. Of the two, Newton is the Old Testament God. It’s Einstein who was the New Testament figure. He was full of humanity, pity, a sense of enormous sympathy. His vision of nature itself was that of a human being in the presence of something God-like, and that’s what he always said about nature. He was fond of talking about God. “God doesn’t play at dice.” “God is not malicious.” Finally, Niels Bohr one day said to him, “Stop telling God what to do!” But that’s not quite fair. Einstein was a man who could ask immensely simple questions. And what his life showed, and his work, is that when the answers are simple, too, then you hear God thinking.