Third Thoughts: The Universe We Still Don’t Know

By Steven Weinberg

“The phrase ‘public intellectual’ is much bandied about. Just a few real heavyweights in the world merit the title, and Steven Weinberg is preeminent among them.”
—Richard Dawkins

“Weinberg has a knack for capturing a complex concept in a succinct, unforgettable image… One of the smartest and most diligent scientists around.”
—Nature

In this wise and wide-ranging meditation, one of the most captivating science communicators of our time challenges us to reconsider the entanglement of science and society. From the cosmological to the personal, from astronomy and quantum physics to the folly of manned spaceflight and the rewards of getting things wrong, Steven Weinberg shares his views on the workings of the universe and our aspirations and limitations. Third Thoughts aims to provoke and inform and never loses sight of the human dimension of scientific discovery.

“One of the 20th century’s greatest physicists…shares his strongly-held opinions on everything from the Higgs boson to the state of theoretical physics and the problems of science and society.”
—Forbes

“This book should be read not only for its insightful and illuminating explanations of a wide range of physical phenomena but also for the opportunity it affords to follow the wanderings of a brilliant mind through topics ranging from high-energy physics and the makeup of the cosmos to poetry, and from the history and philosophy of science to the dangers of economic inequality… [A] captivating book.”
—Mario Livio, Science

• Language: English
• Publisher: Harvard University Press
• Release date: Aug 6, 2018
• ISBN: 9780674989726

Steven Weinberg

Steven Weinberg writes and illustrates kids' books about dinosaurs, roller coasters, beards, and chainsaws. He lives in the Catskills in New York.

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Index

Preface

This is the third collection of my essays for general readers published by Harvard University Press. Some of these essays are polemics on subjects such the harm done by inequality, the folly of programs of manned space flight, the wrongheadedness of some fashions in writing history, the danger of global warming, and the importance of support for public goods, including basic science. As before, they present a point of view that is rationalist, realist, reductionist, and devoutly secular.

Other essays aim at explaining aspects of modern physics and cosmology and their past in nontechnical terms. In some cases footnotes have been added to clarify things that may have been obscure in the essays as originally published. I fear that the reader will find some scientific topics repeated from one essay to another, including broken symmetry, weak and strong nuclear forces, the early universe, and the multiverse. It can’t be helped—these days, these topics are much on the minds of many physicists.

As in the earlier collections, Facing Up and Lake Views, most of these essays were published in the New York Review of Books, in newspapers, and in other periodicals. Essays 20, 23, and 25 are brief talks given at university graduations, and have not been previously published. Essay 24 has not been published until now because everyone who read it disagreed with it, but I am fond of it and so bring it out here.

In this volume I have departed from my practice in earlier essay collections, in which I arranged all essays together in chronological order. I have here instead sorted the essays out into four broad categories, and arranged them in chronological order only within each category. But these categories should not be taken too seriously. In discussing historical matters in Part I, I have had to explain aspects of physics and astronomy, and I have not been able to discuss physics and astronomy in Part II without giving some account of their history. Both science and its history also intrude here and there in Parts III and IV, on public and personal matters.

I owe a great debt to editors who have helped to bring these essays to the reading public. In particular, thanks are due to Michael Fisher, who first suggested that Harvard University Press bring out a collection of my essays, to Jeff Dean, for good advice and for seeing the current collection through to publication, and to the late Robert Silvers, who worked with unending skill and patience to improve my articles in the New York Review of Books. I take this opportunity to give special thanks to Louise Weinberg. Taking time from her own writings on law, she read the early drafts of many of these articles, provided the titles for many of them and for Facing Up and To Explain the World, suggested the Grimshaw painting for the jacket of this volume, and gave valuable advice about rearranging material. Many obscurities and puerilities were avoided through her help.

From past experience, it seems that at my rate of writing it takes about a decade to produce enough new essays for assembly in a collection. I hope nevertheless that this will not be my last collection. But given actuarial realities, perhaps this would be a good time for me to add a word of thanks to readers who over many years have put up with my polemics and explanations, and have thereby given me a precious contact with the world beyond physics.

I

Science History

1

The Uses of Astronomy

This essay had its start in a lecture I gave on the deck of the bark Sea Cloud while cruising the Aegean Sea. The passengers were mostly friends from Austin, visiting sites of the ancient world. In the spirit of the voyage I volunteered to give an evening talk on a subject that had lately fascinated me, Greek astronomy.

A few years later I recycled this lecture in a talk at the Harry Ransom Center in Austin. The HRC has a superb collection of materials related to literature and other arts, but it has not concentrated much on science. Nevertheless, in September 2009 it was able to put on a grand show, Other Worlds: Rare Astronomical Works, including early editions of Copernicus and Galileo. As an enthusiastic amateur in the history of science I was glad to be asked to give an evening talk to help celebrate this exhibition. I was also glad to have this chance to take a swipe at a bête noire, NASA’s wasteful program of manned space flight.

I then sent a written version of my HRC talk to Robert Silvers at the New York Review of Books. It was published the following month, on October 22, 2009, illustrated with a copy of one of the HRC exhibits, the frontispiece of Galileo’s Dialogue Concerning the Two Chief Systems of the World, showing figures representing Aristotle, Ptolemy, and Copernicus. This is pretty much the essay that appears below, with only a few corrections. Later it also served as the basis of chapter 6 of my book To Explain the World.

A few years ago, I decided that I needed to know more about the history of science, so naturally I volunteered to teach the subject. In working up my lectures, I was struck with the fact that in the ancient world, astronomy reached what from a modern perspective was a much higher level of accuracy and sophistication than any other natural science. One obvious reason for this is that visible astronomical phenomena are much simpler and easier to study than the things we can observe on the Earth’s surface. The ancients did not know it, but the Earth and Moon and planets all spin at nearly constant rates, and they travel in their orbits under the influence of a single dominant force, that of gravitation. In consequence the changes in what is seen in the sky are simple and periodic: the Moon regularly waxes and wanes, the Sun and Moon and stars seem to revolve once a day around the celestial pole, and the Sun traces a path through the same constellations of stars every year, those of the zodiac.¹ Even with crude instruments these periodic changes could be and were studied with a fair degree of mathematical precision, much greater than was possible for things on Earth like the flight of a bird or the flow of water in a river.

But there was another reason why astronomy was so prominent in ancient and medieval science. It was useful, in a way that the physics and biology of the time were not. Even before history began, people must have used the apparent motion of the Sun as at least a crude clock, calendar, and compass. These functions became much more precise with the introduction of what may have been the first scientific instrument, the gnomon, attributed by the Greeks variously to Anaximander or to the Babylonians.

The gnomon is simply a straight pole, set vertically in a flat, horizontal patch of ground open to the Sun’s rays. When during each day the gnomon’s shadow is shortest, that is noon. At noon, the gnomon’s shadow anywhere in the latitude of Greece or Mesopotamia points due north, so all the points of the compass can be permanently and accurately marked out on the ground around the gnomon. Watching the shadow at noon from day to day, one can note the days when the noon shadow is shortest or longest. That is the summer or the winter solstice. From the length of the noon shadow at the summer solstice one can calculate the latitude. The shadow at sunset points somewhat south of east in the spring and summer, and somewhat north of east in the fall and winter; when the shadow at sunset points due east, that is the spring or fall equinox.²

Using the gnomon as a calendar, the Athenian astronomer Euctemon made a discovery around 430 BC that was to trouble astronomers for two thousand years: the four seasons, whose beginnings and endings are precisely marked by the solstices and equinoxes, have slightly different lengths. This ruled out the possibility that the Sun travels around the Earth (or the Earth around the Sun) with constant velocity in a circle with Earth at the center, for in that case the equinoxes and solstices would be evenly spaced throughout the year. This was one of the reasons that Hipparchus of Nicea, the greatest observational astronomer of the ancient world, found it necessary around 150 BC to introduce the idea of epicycles, the idea that the Sun (and planets) move on circles whose centers themselves move on circles around the Earth, an idea that was picked up and elaborated three centuries later by Claudius Ptolemy.

Even Copernicus, because he was committed to orbits composed of circles, retained the idea of epicycles. It was not until the early years of the seventeenth century that Johannes Kepler finally explained what Hipparchus and Ptolemy had attributed to epicycles. The Earth’s orbit around the Sun is not a circle but an ellipse; the Sun is not at the center of the ellipse but at a point called the focus, off to one side; and the speed of the Earth is not constant, but faster when it is near the Sun and slower when farther away.

For the uses I have been discussing, the Sun has its limitations. The Sun can of course be used to tell time and directions only during the day, and before the introduction of the gnomon its annual motions gave only a crude idea of the time of year. From earliest recorded times, the stars were put to use to fill these gaps. Homer knew of the stars’ use at night as a compass. In the Odyssey, Calypso gives Odysseus instructions how to go from her island eastward toward Ithaca: he is told to keep the Bear on his left. The Bear, of course, is Ursa Major, a.k.a. the Big Dipper, a constellation near the North Pole of the sky that in the latitude of the Mediterranean never sets beneath the horizon (or, as Homer says, never bathes in the ocean). With north on his left, Odysseus would be sailing east, toward home.³

The stars were also put to use as a calendar. The Egyptians very early appear to have anticipated the flooding of the Nile by observing the rising of the star Sirius. Around 700 BC the poet Hesiod in Works and Days advised farmers to plow at the cosmical setting of the Pleiades constellation—that is, on the day in the year at which the Pleiades star cluster is first seen to set before the Sun comes up.

Observing the stars for these reasons, it was noticed in many early civilizations that there are five stars, called planets by the Greeks, that in the course of a year move against the background of all the other stars, staying pretty much on the same path along the zodiac as the Sun, but sometimes seeming to reverse their course. The problem of understanding these motions perplexed astronomers for millennia, and finally led to the birth of modern physics with the work of Isaac Newton.

The usefulness of astronomy was important not only because it focused attention on the Sun and stars and planets and thereby led to scientific discoveries. Utility was also important in the development of science because when one is actually using a scientific theory rather than just speculating about it, there is a large premium on getting things right. If Calypso had told Odysseus to keep the Moon on his left, he would have gone around in circles and never reached home. In contrast, Aristotle’s theory of motion could survive through the Middle Ages because it was never put to practical use in a way that could reveal how wrong it was. Astronomers did try to use Aristotle’s theory of the planetary system (due originally to Plato’s pupil Eudoxus and his pupil Callippus), in which the Sun and Moon and planets ride on coupled transparent spheres centered on the Earth, a theory that (unlike the epicycle theory) was consistent with Aristotle’s physics.

They found that it did not work—for instance, Aristotle’s theory could not account for the changes in the brightness of the planets over time, changes in brightness that Ptolemy correctly understood to be due to the fact that each planet is not always at the same distance from the Earth. Because of the prestige of Aristotle’s philosophy some philosophers and physicians (but few working astronomers) continued through the ancient world and the Middle Ages to adhere to his theory of the solar system, but by the time of Galileo it was no longer taken seriously. When Galileo wrote his Dialogue Concerning the Two Chief Systems of the World, the two systems that Galileo considered were those of Ptolemy and Copernicus, not Aristotle.

There was one more reason that the usefulness of astronomy was important to the advance of science: It promoted government support of scientific research. The first great example was the Museum of Alexandria, established by the Greek kings of Egypt early in the Hellenistic era, around 300 BC. This was not a museum in the modern sense, a place where visitors can come to look at fossils and pictures, but a research institution, devoted to the Muses, including Urania, the muse of astronomy. The kings of Egypt supported studies in Alexandria of the construction of catapults and other artillery and of the flights of projectiles, probably at the Museum, but the Museum also provided salary support to Aristarchus, who measured the distances and sizes of the Sun and Moon, and to Eratosthenes, who measured the circumference of the Earth. The Museum was the first of a succession of government-supported centers of research, including the House of Wisdom, established around 830 AD by the caliph al-Mamun in Baghdad, and Tycho Brahe’s observatory Uraniborg, given to Brahe by the Danish king Frederick II in 1576. The tradition of government-supported research continues in our day, at particle physics laboratories like CERN and Fermilab, and on unmanned observatories like Hubble and WMAP and Planck, put into space by NASA and the European Space Agency.

In fact, in the past astronomy benefited from an overestimate of its usefulness. The legacies of the Babylonians to the Hellenistic world included not only a large body of accurate astronomical observations (and perhaps the gnomon), but also the pseudoscience of astrology. Ptolemy was the author not only of a great astronomical treatise, the Almagest, but also of a book on astrology, the Tetrabiblos. Much of royal support for compiling tables of astronomical data in the medieval and early modern periods was motivated by the use of these tables by astrologers. This appears to contradict what I said about the importance in applications of getting the science right, but the astrologers did generally get the astronomy right, at least as to the apparent motions of the planets and stars, and they could hide their failure to account for human affairs in the obscurity of their predictions.

Not everyone has been enthusiastic about the utilitarian side of astronomy. In Plato’s Republic there is a discussion of the education to be provided for future philosopher kings. Socrates suggests that astronomy ought to be included, and his stooge Glaucon hastily agrees, because it’s not only farmers and others who need to be sensitive to the seasons, months, and phases of the year; it’s just as important for military commanders as well. Poor Glaucon—Socrates calls him naïve, and explains that the real reason to study astronomy is that it forces the mind to look upward and think of things that are nobler than our everyday world.

Although surprises are always possible, my own main research area, elementary particle physics, has no direct applications that anyone can foresee,⁴ so it gives me little joy to note the importance of utility to the historical development of science. By now pure sciences like particle physics have developed standards of verification that make applications unnecessary in keeping us honest (or so we like to think), and their intellectual excitement incites the efforts of scientists without any thought of practical use. But research in pure science still has to compete for government support with more immediately useful sciences, like chemistry and biology.

Unfortunately for the ability of astronomy to compete for support, the uses of astronomy that I have discussed so far have largely become obsolete. We now use atomic clocks to tell time, so accurately that we can measure tiny changes in the length of the day and year. We can look up today’s date on our watches or computer screens. And recently the stars have even lost their importance for navigation.

In 2005 I was on the bark Sea Cloud, cruising the Aegean Sea. One evening I fell into a discussion about navigation with the ship’s captain. He showed me how to use a sextant and chronometer to find positions at sea. Measuring the angle between the horizon and the position of a given star with the sextant at a known chronometer time tells you that your ship must lie somewhere on a particular curve on the map of the Earth. Doing the same with another star gives another curve, and where they intersect, there is your position. Doing the same with a third star and finding that the third curve intersects the first two at the same point tells you that you have not made a mistake. After demonstrating all this, my friend the captain of the Sea Cloud complained that the young officers coming into the merchant marine could no longer find their position with chronometer and sextant. The advent of global positioning satellites had made celestial navigation

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