PGS Books: How Old Is the Universe? by David Weintraub

Astronomers have made the very public claim that they know the age of the universe pretty accurately: 13.7 billion years old. But how exactly do they know how old the universe is? David Weintraub answers this question in his accessible and detailed book How Old Is the Universe?

Astronomers, he explains, did not simply decide one day that 13.7 billion years sounded reasonable; they do not simply believe that the universe came to exist at one special moment 13.7 billion years ago. Rather, they have come to recognize and agree that this is the answer, because many independent lines of inquiry and evidence all yielded this same answer. What is this evidence? This one compelling, fundamental, and deceptively simple question deserves a thorough answer—an answer that requires knowledge of a great swathe of modern astronomy.

In answering the central question of his book, Weintraub discusses the many phenomena, concepts, and principles at the heart of modern astronomy and cosmology, including black holes, dark matter and dark energy, and the accelerating universe. By challenging readers not to simply accept astronomers’ answer to this fundamental question, but rather to understand the answer, he reveals how various areas of astrophysical research fit together and support each other, how evidence drawn from all of these areas of research allows the astronomical community to answer deep questions about the physical nature of our universe, how science and scientists work, and how—when astronomers say that the age of the universe is 13.7 billion years—the answer rests on solid foundations, built one stone at a time from painstakingly gathered evidence.

Owen Gingerich calls How Old Is the Universe? “a splendid merger of science history and cutting-edge astronomy.” It’s this blend of history and up-to-the-minute science, along with Weintraub’s insights into the nuts and bolts of scientific discovery, that makes the book so unique and fascinating, a true delight by an expert researcher and distinguished teacher of astronomy.

Weintraub is also the author of another Princeton University Press book: Is Pluto a Planet?: A Historical Journey through the Solar System

You can watch a video of Weintraub lecturing on how astronomers have discovered the age of the universe here.

PGS Series: Princeton Primers in Climate

We hear a lot of noise and confusion on the subject of climate. As the subject has become politicized, the climate system has become a subject of high interest outside of the climate and Earth science community, and even outside of the scientific community altogether. Here at Princeton University Press, we felt that it was high time to launch a new series of books that gives scientifically minded readers the facts on how climate works.


Princeton Primers in Climate takes the complex climate system, and breaks it up into all its component parts, to explain how each part works and contributes to the working of the whole. Each book in the series is short, affordable, conversational and accessible in tone, and also quantitative. The books do include a handful of key equations (not beyond first-year, college level calculus). This is because these books are about the facts – the physics – of how climate works, so a few equations are needed to make the science absolutely clear. They are meant to reach a wide, interdisciplinary audience of readers who have no specialized background in this field, but who can handle a little bit of physics and math. For anyone looking for succinct and readable books on this frequently misunderstood subject, written by leading researchers in the field of climate science, these primers reveal the physical workings of the global climate system with unmatched accessibility and detail.

Published in November, the first title in the series is The Global Carbon Cycle. Written by David Archer, notable climate scientist and frequent contributor to, the book looks at the carbon cycle – an essential driver of the climate system – and its impact on climate across different geological timescales, from the deep past up to the present day. The carbon cycle is something of a thermostat for Earth’s climate, given the direct cause and effect relationship between the amount of CO2 in the atmosphere and global temperature. Interestingly, however, it can stabilize the Earth’s climate or amplify natural or man-made variations in climate, depending on the timescale you’re looking at. In this sense, it was a co-conspirator both in past ice ages and in times when the Earth went through warm periods and had no ice at all.

To discover how exactly carbon influences the climate system over the short and the long term, this is the book to read. Firmly grounded in advanced climate science research but written in an accessible style, The Global Carbon Cycle makes an essential contribution to current debates surrounding climate change – by clarifying exactly what we know and don’t know about this fundamental part of the climate system.

Stay tuned for forthcoming books in this exciting new series, including The Oceans and Climate by Geoffrey K. Vallis, Natural Climate Change by Mark Cane, Atmospheric Processes by David Randall, Climate Sensitivity by Jeffrey Kiehl, Planetary Climates by Andrew Ingersoll, The Cryosphere by Shawn J. Marshall, Paleoclimate by Michael L. Bender, and Terrestrial Hydrology and the Climate System by Eric F. Wood.

PGS Series: In a Nutshell

The In a Nutshell series may sound like a cute branding idea, but as Ingrid Gnerlich, Senior Editor in Physical Sciences explains below, the books selected for this series are intended to be definitive textbooks for courses in physical science. That said, they are also terrific points of departure for anyone interested in these areas of study.

In a Nutshell is a new series of modern, concise, and well-priced textbooks on core subjects in the physical sciences. Meant for advanced undergraduates and graduate students, this high-profile series includes A. Zee’s Quantum Field Theory in a Nutshell, 2nd edition, Gerald Mahan’s Quantum Mechanics in a Nutshell, Elias Kiritsis’ String Theory in a Nutshell, Carlos A. Bertulani’s Nuclear Physics in a Nutshell, and Dan Maoz’s Astrophysics in a Nutshell.

Released this month, our newest title in the series is Gerald Mahan’s Condensed Matter in a Nutshell. This excellent book focuses on an exciting, fast-moving area of physics that, over the past couple decades, has seen many new experimental advances, one of which was the focus of this year’s Nobel Prize in Physics (the discovery of the remarkable two-dimensional material, graphene). Groundbreaking research in this field – from studies of the origin of high-temperature superconductivity to the properties and applications of graphene – has challenged accepted beliefs and raised deep questions about the emergent behavior of condensed matter systems.

Mahan’s premier textbook covers all the foundational topics of the field, as well the latest experimental advances, such as high-temperature superconductivity, the quantum Hall effect, graphene, nanotubes, localization, Hubbard models, density functional theory, phonon focusing, and Kapitza resistance. Full of illuminating examples and problems, this is an excellent introduction to this hot area of physics and a great resource for a two-semester graduate course in condensed matter and material physics.

As Sidney Nagel put it, “This book is a great place to start learning about the vast array of phenomena that nature is able to produce around us in the form of materials. It hardly fits in a nutshell – it covers a great many topics, both traditional and current, in condensed matter physics. It is more akin to Hamlet’s assertion that he could be bounded in a nutshell, and count himself a king of infinite space. The prodigious knowledge of the author shines through in the choice of topics.”

Upcoming books in this exceptional textbook series include Christopher Tully’s Elementary Particle Physics in a Nutshell, Anupam Garg’s Electromagnetism in a Nutshell, and A. Zee’s Gravity in a Nutshell. Stay tuned for future In a Nutshell titles!

Like Princeton Global Science? Subscribe to our RSS Feed here:

PGS Series: Princeton Frontiers in Physics Series

Princeton University Press publishes an amazing number and variety of book series. Here, Ingrid Gnerlich, Senior Editor in Physical Sciences describes the rationale behind the series Princeton Frontiers in Physics and the types of books it will encompass.


The power to question is the basis of all human progress.

– Indira Ghandi

The margins of exploration and discovery – the edges of the unknown – have always been a source of fascination to humankind. The mythical apple of knowledge has persistently tantalized, and nowhere is this truer than within the physical sciences, where curiosity is embraced as the beating heart of the field. The borderlands between curiosity and knowledge – between the question and the answer – are among the most thrilling realms of human experience, a testing ground for human intelligence, creativity, and self-awareness. The first and essential step towards discovery, however, is the formulation of a smart question – a question that illuminates even in the asking.

Every generation of scientists must learn, as early as possible, the skill of asking smart questions. The questions a scientist (or student of science) asks will define his or her career – and may even have the more sweeping effect of redefining the boundaries of modern knowledge and changing the course of human history. When one asks a question – say, “Why does the apple fall from the tree?” – with the intention of answering it scientifically, one must formulate a reasonable explanation for why the fruit behaves as it does. This hypothesis serves as something of a “temporary” answer, and one can have as many hypotheses as one likes. However, this first crack at an answer, as sensible as it may seem, must then withstand a barrage of testing and comparison against observations of the real world. If the real world matches the hypothesis, like two puzzle pieces that fit together, the hypothesis may be elevated in status to be called a theory, which is in turn further probed and tested until it becomes generally accepted (or not) by the scientific community. This point of general acceptance is as close as one can come to reaching truth in the sciences. However, it is perhaps better described not as truth, but rather as a point of enlightenment – a step along a journey of discovery. No scientific theory, even one that is generally accepted, is ever immune to being further refined, corrected, or even proved wrong. This said, a theory can only be sculpted, weakened, or overturned if one has the ammunition of reproducible evidence, acquired through observation and experimentation.

Some observations and experiments can be done using the naked eye. But, some cannot. Enter new technologies, the tools humans use to make the necessary observations to provide evidence in support of hypotheses and theories. One could not observe the distant universe without telescopes, reveal the evolving cosmos in different wavelengths of light without special detectors, expose the workings of the microbial world without microscopes, probe the oceanic depths without submarines, or explore Mars without robotics. Theory, observation, and instrumentation are the three essential tools scientists use to answer the questions they pose. Take one tool away, and the course towards scientific discovery is obstructed.

What are the key questions that are moving the frontiers of the physical sciences forward, and where are we in our search for the answers? Enter the Princeton Frontiers in Physics series – the home for short, sophisticated introductions to the evolving frontiers of the physical sciences. This new series focuses on rapidly developing, sexy areas of research that are of intense, wide interest. Each book will examine a particular, provocative question, which drives research in a hot area of ongoing scientific inquiry in the physical sciences. To some questions, partial answers are known; to others, even more challenging questions are revealed in the process of answering. But in all cases, the questions are the right ones, in that they are moving the boundaries of knowledge forward and revealing truth as part of the process of inquiry. Each carefully chosen author is a luminary and active researcher in the field in question; some are theorists, while some are observers, experimentalists, or instrument-builders. Topics range widely – from the question of how the first stars and galaxies formed, to the nature of dark matter, to the future of quantum information science – but all are housed under the grand umbrella of physics research.

The first title in our new series, How Did the First Stars and Galaxies Form?, focuses on how and when “first light” – the very first stars and galaxies – evolved from out of minute fluctuations in the dark, nearly uniform soup of matter and energy that was the early universe. The author, Abraham Loeb, is professor of astronomy and director of the Institute for Theory and Computation (ITC) at Harvard University. He has worked on a broad range of research areas in astrophysics and cosmology – including the first stars, the epoch of reionization, the formation and evolution of massive black holes, gravitational lensing, and gamma-ray bursts – and he was among the first theorists to trigger current research on the first stars and quasars.

A theoretical simulation of the merger of two galaxies–Andromeda and the Milky Way–to form Milkomeda. The images show Andromeda approaching the Milky Way. The left hand side of each screen shows the gas that surrounds the galaxies, while the right hand side of each screen shows the distribution of stars. Following this merger, the night sky will change dramatically. We will no longer see a line of stars forming the Milky Way, instead we will see stars distributed all over the sky. Even the Sun will be pushed out by this merger. And in the very distant future, Milkomeda will be the only galaxy visible to us as all other galaxies are pulled away from us and eventually exit our horizon. Taken from Abraham Loeb’s video here.

The question of how stars and galaxies first formed is fundamentally important in the fields of cosmology and astrophysics. It is thought that, at the end of the so-called cosmic “dark ages,” the universe was transformed from a smooth, simple state into a clumpy, complex, hierarchical one. Structures in the form of the first stars coalesced around dense “clumps” or “mini-haloes” of dark matter a couple hundred million years after the Big Bang, and they completely changed the early universe by seeding it with light and the first heavy elements. [Image 1] Without these stars, and subsequent galaxies, our solar system (and we) would never have evolved. Though astrophysicists have formulated a quite mature and well-accepted theory for how and when the first stars and galaxies formed, and are using efficient, new computational tools to investigate this theoretical framework, we are only beginning to be able to test our theoretical understanding with actual observations of the very distant, early universe. The field is entering a new and exciting period of discovery, in which new observational probes are becoming available, and researchers are pushing at the frontiers of knowledge, uncovering new areas of debate, controversy, research, and discovery as they advance the boundaries of their field – and continue to try to definitively answer the title question of this book.

This title is just the first of many that are forthcoming in this exciting new series. Stay tuned for more intriguing, yet refreshingly pithy books that seek to define the state-of-the-art of modern knowledge – by posing provocative, seemingly simple questions that inspire and guide the frontiers of inquiry.

Some forthcoming titles in Princeton Frontiers in Physics:

  • Joshua Bloom (Berkeley), What Are Gamma-Ray Bursts?
  • Paul Steinhardt (Princeton), How Did the Universe Begin?
  • Peter Fisher (MIT), What Is Dark Matter?
  • Charles Bailyn (Yale), What Does a Black Hole Look Like?
  • Tony Zee (UCSB), Can the Laws of Physics Be Unified?

PGS Editors: Professor’s soul-searching reinvention of “Physics for Poets” captures the hearts and minds of students

Berkeley physics professor, Richard Muller, speaks out about the need to revolutionize the way physics is taught to non-science students – by respecting students’ intelligence and passion to learn and by being unafraid to crash through the mathematics glass ceiling to “get to the interesting stuff right away.”

Richard Muller’s course at Berkeley is a phenomenon…  “Physics for Future Presidents,” a course on essential topics in physics for students from any disciplinary background, attracts over 1000 students per year at Berkeley alone and has been voted Best Class of Berkeley by its students. You might well wonder: what is the secret to this course’s extraordinary success?  Many schools have introductory-level courses that have been dubbed “physics for poets,” “rocks for jocks,” and other such less-than-inspiring names.

Is “physics for future presidents” some kind of joke, a cheap twist on the same old-same old?  Or, considering the radical leap in enrollment that Berkeley has witnessed since Muller took over this course, is there something revolutionary about Muller’s approach?  What could have won over all of those “poets” and “jocks,” those humanists, those athletes, business, pre-law, political science, and pre-med majors, those non-science majors who normally stay safely insulated from a subject that supposedly doesn’t come naturally to them?

The answer is simple: respect.   As the author writes, “Is science too hard for world leaders to learn?  No, it is just badly taught.”  The onus (indeed, the blame, as some instructors would have it) is not on the student – the “poet” or “jock,” who is supposedly unable to understand physics; the weight of responsibility is on the teacher: right where it should be.  Muller staunchly believes that if he cannot make a fascinating subject interesting, it’s his fault, not his students’.  This insight led him to revolutionize the way he taught physics at Berkeley, and the results are impressive:  “Students recognize the value of what they are learning” he says, “and are naturally motivated to do well.  In every chapter they find material they want to share with their friends, roommates, and parents.”  And share they did.  Word about Muller’s fascinating class spread, and course enrollment quickly rose from 34 students per semester to over 500 students per semester at a university in which physics is not a required course.  To professors teaching conceptual physics at other universities across the country to the more typical class sizes of 30-odd students:  the gauntlet has been thrown.

From Muller’s perspective, a student majoring in a non-science discipline is part of the next generation of our world’s citizens and leaders.  In this science- and technology-driven age, our citizens and leaders need to make smart decisions on a daily basis about energy, climate change, terrorism and counter-terrorism, health, the internet, satellites, remote sensing, ICBMs and ABMs, DVDs and HDTVs, etc.  In other words, economic and political issues increasingly have a strong high tech component.  As Muller cautions the future leaders in his class, “Misjudge the science and make a wrong decision.”  Yet, incredibly, we live in a world in which many of our citizens and leaders have never studied physics and do not understand basic concepts of science and technology.  Muller aims to change that.

He has just published a textbook, entitled Physics and Technology for Future Presidents, to help other professors and teachers adopt his new approach at their own schools and to work as a driving force in reinventing the way physics is taught.  The book handily covers the most interesting and most important topics in contemporary physics and is imbued with the same clarity and verve that characterizes Muller’s lectures.  It is specially designed to attract new students, and to teach them the physics they need to know to be effective world leaders and informed citizens.  Already, his approach is catching on, and new “Physics and Technology for Future Presidents” courses are popping up all over the place – at institutions like Boston College, the University of Chicago, the University of Colorado, and the University of North Carolina, just to name a few, and even in high schools around the country.Everywhere, Muller’s call to revolutionize physics education is inspiring teachers to give themselves a good dose of self-criticism, to thoughtfully evaluate the way in which they teach the next generation – and to embrace the responsibility of change.  Non-science students don’t want to be treated like children and merely entertained.  They don’t want to be sculpted into miniature scientists, nor should they.  “They want a good course, well-taught, that fills them with important information and the ability to use it well,” Muller has observed.  Easier said than done, but given the obvious importance of the task at hand, certainly worth the soul-searching and effort Muller has invested.  And, the rewards have been sweet.

Physics is about how the world works – quite a fundamentally important topic, few would argue – and is naturally inspiring.  Starting from there, what then is the key to unlocking the joy of discovery in your students?  Respect.  Immerse your students in the subject and everything that it is – from the amount of energy produced by a solar cell to quantum teleportation.  Motivation follows.  Then teach.   Teach as if you’re teaching your next president…

Because you never really know, do you?

Learn more about Richard Muller’s new textbook Physics and Technology for Future Presidents.

Watch Muller’s lectures online here:|2009-D-69330&semesterid=2009-D

Read the book’s preface here:

An instructor’s manual is available. See this site for more details:

Video is provided courtesy of UCBerkeleyNewsCenter

PGS Dialogue: Steven Gubser, author of The Little Book of String Theory

Cosmic branes, microscopic black holes, wiggling strings –
These are a few of his favorite things…

Professor Steven Gubser is a string theorist at Princeton University, and the author of the most up-to-the-minute, pocket-sized guide to all that’s stringy in the universe. One might wonder how he managed to tuck such a large topic into such a tiny book without using a few of string theory’s hidden extra dimensions! Here, he answers a few questions about his quest for a “theory of everything,” which successfully unites general relativity (the theory of gravity) with quantum mechanics (the physics of the very small).

When did you first realize that you wanted to be a scientist – and a physicist – as your profession in life?

It was a gradual thing. I liked math a lot when I was a child. I did really well in an international physics competition when I was 17, and as a result I thought maybe physics was the subject where I had the best chance of professional success.

How did you first encounter string theory?

I figured at first I wanted to work on Einstein’s theory of General Relativity, so I took a course on that topic at Princeton. It was taught by Igor Klebanov, a string theorist who eventually became my PhD advisor.

What is string theory, anyway? Why is it important?

String theory is based on the idea that the fundamental constituents of matter need not be particles, but instead could be strings, meaning tiny moving objects with one dimension of spatial extent. It is important because, on one hand, it is the likeliest candidate for a theory that will describe all the forces of Nature in a single mathematical framework; and on the other, because it incorporates many of the central ideas of other branches of theoretical physics and is sometimes able to feed new ideas and calculations back into these other fields. A good example of the feedback is the recent activity relating string theory to nuclear collisions, which is the topic of Chapter 8 of my book.

You have 3 very young daughters… How do you describe to them what their father does when he goes to work in the morning?

My seven-year-old knows the words “string theory” and remembers me writing the book and drawing rough drafts of the illustrations. She loves to draw, and she titles some of her pictures string theory. They usually have a lot of strings in them, and often some dots or blobs that could be D-branes. So I’d say she’s doing pretty well on artistic depictions of the subject.

Your book is filled with surprising and vivid metaphors that help the reader to understand the concepts of string theory. Just by way of example, what sorts of metaphors would you use to explain a couple of the more challenging ideas in your book – string dualities and supersymmetry?

To explain the concept of duality in string theory, I would compare it to allegory. Sometimes allegory is used to broaden one’s view of real events by relating them to something fictional. For example, in the movie, Pan’s Labyrinth, there was a fantasy world which had an allegorical relation to the Spanish Civil War. String dualities similarly relate one theory to another, but in a much closer way than allegory in film or literature. Still, there’s a gain in understanding when you see the same physics cast in apparently different language. Some string dualities are even the basis of the most successful recent calculations relating string theory to experiment.

Regarding supersymmetry, the metaphor that comes to mind is… wallpaper. The idea of supersymmetry, as I explain in chapter 7 of my book, is that there are extra dimensions of space and time, but not like the usual ones (time, length, and so on), and not even like the little curled-up ones that are widely discussed. The extra dimensions of supersymmetry aren’t even described by numbers in the usual sense. They’re described by a different sort of number which enters into the quantum mechanical formulation of fermions. That’s a lot to get your head around, which is why I bring up wallpaper. All wallpapers are two-dimensional: height and width. But they’re distinctive in the way they have different patterns, or sometimes even textures. Supersymmetry extends spacetime in a way that’s not too different: in supersymmetry, there’s an extra property throughout space and time which is as distinctive as a pattern of wallpaper.

In your book, you explain that string theory reveals that there may be many more dimensions than just the 3 dimensions (plus perhaps 1 more for time) that we normally see around us. Some readers might confess that they have some difficulty visualizing the extra dimensions you describe in your book… Can you visualize more than 3 dimensions? Has string theory changed the way you view the world around you?

String dualities became a big deal just when I was starting to work on string theory. What impressed me about them the most was that the dimension of spacetime could change as you pass through a duality. That suggested to me that dimensions aren’t as fixed a notion as I had previously thought.

In answer to your first question, it’s easy enough to visualize extra dimensions. Keeping the usual ones in mind at the same time is what’s hard!

The Large Hadron Collider (LHC) in Switzerland, the highest-energy particle collider in the world, is attempting to answer some important questions in physics… Is it attempting to provide evidence in support of some of the ideas of string theory?

I’m sure LHC experimentalists would prefer to remain neutral on the question of what theories their data will support. But definitely, the LHC is well-positioned to test the existence of supersymmetry at the electroweak scale, and that’s one of the fondest hopes of string theorists.

Some critics of the field of string theory maintain that it does not have a viable future, because it is not experimentally verifiable. You made a decision not to deal explicitly with the recent “String Wars” in your book – even going so far as to include no names in the book (beyond the venerable Einstein). What was the reason for your decision?

I decided not to include names in the book (actually, not even Einstein’s beyond the introduction!) because I considered it a distraction from the main material, which is the physics of string theory. Although the colorful personalities of string theorists could perhaps have provided some entertaining reading, I think that analogies, like supersymmetry’s relation to wallpaper, illustrate more about the actual ideas than do the quirks of the practitioners.

In the absence of an observation that supports one or another aspect of string theory, how will the research community decide on where the field will go next? What will be the future of string theory?

People vote with their feet. If, for example, the LHC produces some amazing new discovery that suggests a new avenue of theoretical research, probably a lot of people will totally drop string theory and pursue it. But good ideas have a way of coming up again and again, and there are enough good ideas in string theory now that I am quite confident that it will have a lot to tell us both in the near future and in the distant future. One of my colleagues, Paul Townsend, put across this point with a succinct aphorism: One day, we will discover the ultimate theory of the universe. And we will call it string theory.

  • The book is also part of Science Essentials, a new series that brings cutting-edge science to general readers.

The Physicist behind PUP’s bestselling book QUANTUM FIELD THEORY IN A NUTSHELL, an interview with A. Zee

bookjacketATTENTION physics students, instructors, and other scientifically minded readers!  During your next visit to, take a spare minute to look up the textbook, QUANTUM FIELD THEORY IN A NUTSHELL, by A. Zee.  You can expect to be bowled over by over 50 five-star reader reviews, ranging in tone from positively giddy to intensely grateful.  Some readers take this book to bed with them.  Some compare the book to the Feynman lectures.  To others it is “a breeze of fresh air,” a “real literary gem,” “enchanting,” a “classic” to read and reread, both for its physics and its witty humor. Clearly, the book, which recently was updated and expanded for a 2nd edition, is a phenomenon.  How did this happen, and who is the man behind it?  To provide answers to these questions and others, please find here is a rare interview with the author, professor of theoretical physics at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara.

An interview with A. Zee:

1. You were born in China, educated in Brazil, pursued your undergraduate degree at Princeton, and then your Ph.D. at Harvard… When did you first realize that you wanted to be a scientist — and, a physicist, in particular — as your profession in life?

When my family emigrated from Hong Kong to Brazil, we went by boat around the tip of Africa. The journey lasted for some 50 days, with stops at various ports along the way. What an eye-opening and formative experience for me! I recommend it to any kid. Back in those days we had the opposite of the information overflow we have today, and my mother was not sure when and if my schooling would resume, so she bought a pile of junior high or high school level textbooks for me to read in Brazil. I had lots of fun on the ship with my brothers and sister and newfound friends, but the moment I opened the physics book I was hooked. In hindsight, the book was terrible by modern pedagogical standards. The great physicist Murray Gell-Mann recalled how he hated physics as it was taught to him: all about memorizing “the 7 kinds of simple machines” and stuff like that. The book I devoured on the boat belonged to that category: I remember reading about the lever and the pulley. But in fact I was amazed that they worked because of a fundamental principle, that of energy conservation. I learned that, even behind everyday phenomena, there is something profound.

I have benefitted from good fortune all my life. One piece of good fortune is that the apartment my father had rented in the humongous city of Sao Paulo was by pure coincidence within walking distance of the American consulate. I soon discovered that the US Information Service maintained a library there. I still remember reading a book about how to manage a forest commercially, the different kinds of trees, when to cut them down, that sort of thing. It was wonderful that I was not confined in some school and tied to some specific curriculum and that I could read whatever interested me. Decades later, after I wrote “Fearful Symmetry”, somebody from the State Department asked me to represent the US at a symmetry festival at the Center for the Performing Arts in Mumbai. I was more than happy to do so, paying back in some small way. The USIS shipped a pile of my book to India, and I joked that I finally learned how American foreign aid worked.

Later, after my father got his business in order, I went to an American school, and some of the teaching nuns had the good sense of excusing me from sitting in class for certain subjects. I was sent to the library.  It was not much more than a large room with a small collection of books, but sitting there alone, surrounded by all that knowledge, was wonderful. I have a vivid image of coming across a book on linear algebra and reading about matrices.

2. Who were your intellectual and personal heroes as you were growing in your studies and profession?  Who inspired and mentored you?  Who was your best teacher?

A friend of mine somehow had a Russian book about puzzles in physics and math, which fascinated me to no end. (I still admire how the Russians train their physicists.) My memory is hazy, but somewhere, somehow, I also came across a popular book by George Gamow (to whom I paid homage when I wrote “An Old Man’s Toy/Einstein’s Universe”.) He said that according to a certain professor John Wheeler at Princeton University, the atomic nucleus could take on different shapes, including that of a doughnut. That really motivated me to go to Princeton and find out from this Wheeler about this doughnut nucleus.

Among my many pieces of good fortune is that Princeton gave me a full scholarship. Perhaps I said on my application that I wanted to find out about the doughnut nucleus, but more likely the American nuns wrote strong letters about me. In response to a recent article in Physics Today about Wheeler’s influence on various physicists, I wrote how Wheeler always made students feel important. In my sophomore year, he suggested that I calculate the emission of gravitational wave from a rotating neutron star. Even at that age I realized that I was merely plugging in numbers into the appropriate formulas in Landau and Lifschitz, but, whenever I showed Wheeler my calculation, he would be literally wild with excitement, heaping on praise and encouragement. Before I knew it, there appeared a manuscript by Zee and Wheeler. What would have been my first physics paper was, however, never published (but referred to as “to be published” in a long review article Wheeler later wrote), perhaps partly because Murph Goldberger and Sam Treiman (who would both mentor and influence me many years later, each in his characteristic way) decided to “rescue me from relativity” and point me towards particle theory. I immediately lost interest in gravitational waves and wanted to know about quantum field theory instead. By the way, Wheeler was quite gracious about my “escape from relativity” and even arranged for me to go to Harvard to work with Steve Weinberg, about whom he raved to me. As it happened, I did not end up working for Steve, but, many years later, when I visited Texas, he got me into writing popular-level books.

3. When did you first encounter quantum field theory?  What is your own story of how you first came to understand quantum field theory?  From whom/what book did you learn the subject?  What was your first reaction to the subject?

For reasons that now escape me, I went from John Wheeler to Arthur Wightman who told me about exactly solvable field theory in 2-dimensional spacetime. (For reasons I did not appreciate at the time, the move did not please Goldberger.) At his suggestion, I spent a hot humid summer in Princeton reading the massive and not entirely coherent book by Schweber on quantum field theory. In the fall, I went to Wightman and asked him what book I should read next, he answered, “Read Schweber again.” Wightman is a very kind and patient man (I remember standing there wondering why he was willing to spend so much time on me as he carefully explained some elementary point about quantum field theory on the blackboard), given to cryptic pronouncements. He once said to me something like “Football is algebraic, while basketball is geometric.” I have been thinking about this ever since.

4. What is quantum field theory, anyway?  How would you describe it to the person sitting next to you on an airplane?

Funny you should ask. Recently I flew back from Indiana University, where I gave a colloquium about quantum field theory, and I was thinking about this upcoming interview. During the entire flight the man sitting next to me was watching some violent war movie on his laptop. I didn’t think he would be thrilled if I described to him what was on the first page of my book.

5. When did you first switch roles, from student to teacher?  What subject did you teach?

As a matter of fact, the first course I ever taught as a beginning assistant professor at Princeton was quantum field theory.

6. When did you first teach QFT to students?  What was your experience?

The most striking experience I now associate with the first time I taught quantum field theory? As I described on page xvii in the preface to the first edition of my book, I was amazed by the extraordinary quality of the solutions to the homework problems written up by my teaching assistant. His name?  Ed Witten.

7. Do you notice that students ask the same kinds of questions you did, or do students ever surprise or challenge you with the questions they ask?

On page 454 I told the story that, when I took Schwinger’s field theory course (which the better students at Harvard sat in on, year after year), the students understood that they were not allowed to ask questions. More seriously, I think that, to teach well and to write a good textbook, one has to be able to anticipate the questions to some extent. It is a form of empathy, the ability to put oneself in the mental framework of a typical student or reader. Many theoretical physicists fall into the trap of assuming that the typical student is like a typical denizen of their world.

8. How has your method of teaching this subject changed over the years?  How do you clarify some of the most difficult concepts to students?

Most people, even physicists, do not realize that the last few decades have been a golden age of quantum field theory. The subject made enormous progress, with one triumph after another leading to “a victory parade that made the spectator gasp with awe and laugh with joy,” to quote my thesis advisor Sidney Coleman (see page 473). Thus, my book is definitely not based on my lecture notes for the course on quantum field theory I alluded to above, from when I first taught the subject. Indeed, people should be warned that portions of various classic field theory texts have long gone out of date or are downright misleading.

9. What inspired you to write books?  When did you decide to write a book?  When did you decide that you wanted to attempt to explain the subject of QFT “in a nutshell”?

During that visit to Texas, I mentioned to Weinberg that for some years I had been urged to write up the notes of the class I gave when I first taught. He suggested writing a popular-level book instead, and that was the origin of “Fearful Symmetry” which I first published some 25 years ago and which Princeton now publishes. I knew that I still wanted to write a textbook eventually. The discussion started when the late Sam Treiman (also mentioned above) was on your board. As is clear to my readers, and as I explained in the two prefaces, I wanted to emphasize the profound concepts of quantum field theory more, and the formalism and computational techniques less. The latter are important, of course, but there are, alas, too many theoretical physicists walking around who can calculate without grasping the concepts. Unfortunately, our educational system fosters computational prowess since that is mostly what homework problems are about. One could hardly test for original thinking on a final exam. That’s why some of the exercises in my book are open-ended, which, of course, throws the students in my course for a loop. They do not know to cope with an exercise asking for something other than plugging in the appropriate formula.

10. What was most challenging about writing this particular book?  What was most satisfying in the end?

Writing a text in quantum field theory poses many challenges, of course. One of them is simply knowing when to stop. The subject is simply too rich, so there is bound to be complaints that I left out this or that topic (amidst complaints also that the book is too thick.) The satisfaction and challenges in writing a textbook and a popular-level book are completely different. In my popular-level books, such as “Fearful Symmetry”, I tried to convey to the reader, through vivid analogies and imageries, a flavor of what drives fundamental physics. In writing a textbook, I feel that, at the risk of sounding corny, I am passing on something to the next generation. I am expressing my gratitude to those who invented quantum field theory and to those who taught me quantum field theory, as I explained in more detail in the two prefaces. My hope is, of course, that — if I’m lucky — some readers of my book will be among those who will push quantum field theory forward. As I mentioned in the second edition, this has already happened since the first edition came out: I have already met some dashing young physicists who told me that they studied the subject from my book. The positive response of readers and of the physics community at large has been gratifying and makes the drudgery of actually writing the book worthwhile.

11. How do you feel your book explains this subject better or differently than other books?

I already touched upon this in (9). Every textbook writer has, or at least should have, a personality. I admire Weinberg profusely (and almost became his student, as I said), but his books are not what I could, or would want to, write. I prefer a lighter touch, with anecdotes and fictitious characters. My favorite is Confusio. Isn’t he yours too?

12. What other books are you working on?

After the gratifying success of my quantum field theory book, I decided to work on another textbook, titled “Einstein Gravity in a Nutshell”. In some sense, I am now writing about the second most beautiful subject in theoretical physics after quantum field theory. The book is written in the same style as my quantum field theory book, with the same light touch. Even Confusio is making a return appearance. In comparison to 10 years ago, I find myself more willing to fill in the gaps. As I write, I also keep shifting the book towards the more introductory end, so that I now start with a review of Newtonian mechanics and the action principle. I feel that it is important for students to get the foundation right rather than to master every technical detail. But I also consciously try not to “dumb down” the book (even though that’s surely the best way to increase sales.) Accessible and elementary are two different things. Einstein gravity, like quantum field theory, is a rich subject, and one difficulty for me is to know when to stop.

13. Do you feel that book writing helps you to look at subjects afresh or differently?   Do you seek to inspire others with your books?  What did you learn by writing this book?

The answers to the first two questions are absolutely and absolutely. In answering the third question I am afraid that I might get into my pet peeve: namely, that you can’t please everyone, as I quoted Ricky Nelson in the preface of the book as saying. For example, in looking over my teaching evaluations, I read one student’s complaint that I don’t do enough calculations in the course. But, my decades of teaching experience as my guide, this very same student, or others of his type, would surely complain that he is not getting enough concepts if the professor were to cover the board with long calculations. Sometimes I don’t understand the weaker students in my course. By the time you get so far as to take quantum field theory, you should be all fired up about the beauty of theoretical physics; it should be a passion, a way of life. If you don’t care about the subtlety and beauty of the concepts, but want to shut yourself in a cell calculating for the rest of your life, then you might have chosen the wrong profession to go into. You should be gasping with awe and laughing with joy. If not, do something else.

14. What do you think is the most important lesson for physics students to learn, if they want to become successful, professional physicists?  What do you wish you would have learned earlier on in your studies?

I often asked my class, “What are you waiting for?” Are you waiting for a piece of paper before you start solving some of the great mysteries of theoretical physics at the most fundamental level? The leading physics journals actually do not ask to see a photostat of your diploma before they accept your paper. Did Newton wait? Did Schwinger wait? Did Dirac wait? The sad truth is that, if you spend your time worrying about getting through the homework and about acing the final exam, you probably won’t make it to the top level anyway. So, think more, and let your youthful creativity flow. You don’t have to become an expert first. Indeed, by the time some people become experts, they are dead, or living but calcified.

In fact, I am rather reluctant to give advice to young theorists unless I know that person well. With so many different personality types, advice that would work for one kind of person would surely not be beneficial to another. Perhaps I could say this. If you are all fired-up about theoretical physics, make two lists. On the first list are problems that, if you solve one of them, could land you a job at a respectable university.  On the second list are problems that, if you solve one of them, would have people dancing in the street. A former postdoc still sends me a email every time he publishes a paper, to ask me if people are dancing in Santa Barbara. The sad reality is that young people need to spend most of their time on the first list to get ahead and survive.


15. What in particular inspires you about quantum field theory?  One published review of your book commented, “The purpose of Zee’s book is not to turn students into experts — it is to make them fall in love with the subject. And Zee succeeds brilliantly.”  What is so beautiful about the subject that people seem to fall in love with it upon reading your book – as attested to by the glowing comments on

In my book, “Fearful Symmetry,” I tried very hard to convey the notion of beauty in physics. This is hard, because even I would find it unconvincing to state that elementary physics, particularly the way it is taught, is beautiful. To fundamental physicists, beauty is associated with elegance and simplicity, and simplicity means symmetry. Simple, however, does not mean simple-minded. To us fundamental physicists, simple and profound are closely linked. I would go so far as to say that the truly profound statements I know in fundamental physics are almost laughably simple, once you grasp them. But, of course, you can’t grasp them unless you know the language. A rough analogy is perhaps a great poem that makes you see things in a simple way, but in order to see, you would have to experience life first. Another analogy is that, to read the poem, you have to know the language the poem is written in; and so, a physics textbook at the level of quantum field theory, which focuses on technical details, is like a book on poetry that spends hundred of pages explaining how the letters of the alphabet came about or how to write in different scripts. The most profound truths in physics are the most obvious, but of course they are only obvious in hindsight.