Read an Excerpt
Chapter 1
Surveying the Universe
It seems to be an extraordinary moment. On the one hand, we face daunting challenges: climate change, global pandemics, the threat of nuclear war. On the other hand, as a species, we have knowledge of the world-and the universe-around us beyond anything humans might have imagined even a century ago. No matter what happens, we have an unprecedented understanding of the natural world of which our daily experiences sample only a tiny corner. Our lives play out on scales of centimeters, meters, kilometers, perhaps thousands of kilometers. But we know about nature on smaller scales-far, far smaller than the size of an atomic nucleus. We also know about the universe out to unimaginably large distances. Even more amazing is what we know-really know-about events billions of years ago, and we can make statements with near certainty about what will happen to the universe for the next few tens of billions of years. An extraordinary moment indeed.
Most of us have heard about faraway stars and galaxies, have some inkling that the universe emerged from a big bang billions of years ago. But precisely how large and how old is the universe? Where did it come from? What is its ultimate fate? How do we find answers to these questions?
We are aware of atoms and maybe somewhat aware of things smaller than atoms. How can we possibly know about atomic nuclei that are far too small to see with the most powerful microscopes? How do these tiny things control the operation of the universe at large, as well as events like making a sandwich, using a credit card, or driving to work? From the largest scales to the smallest scales, our universe can seem impossibly mysterious. Can we do more than speculate about the architecture of the cosmos and its building materials? Can we construct experiments that will answer our questions about reality at such fantastic scales?
As I write this, we are still confronting the Covid-19 pandemic. From this ordeal, we're all now familiar with the significance of powers of 10. In the early stages of the outbreak, the number of cases was growing by nearly a factor of 10 every week. Here is what that meant for projections about cases in the United States.
March 2, 2020 100
March 10, 2020 1,000
March 18, 2020 10,000
March 25, 2020 100,000
April 3, 2020 1,000,000
April 7, 2020 10,000,000
From 100 people to 10 million people sick in a matter of five weeks. After that, in this case, the growth would have slowed, only because it would have been harder for the virus to encounter people who had not already been infected. Fortunately, states and local communities, to a large extent, adopted shelter-in-place restrictions within a few days of March 11, 2020, a little less than two weeks after the exponential growth began. Two weeks later, about the time from exposure to the virus to visible symptoms, the effects of the partial lockdown started to be felt. So on March 10, there were 994 cases, just under our thousand expected, 9,307 on March 18, somewhat further below our 10,000 expected. But by March 25, the effects of social distancing became visible, with 68,905 cases. On April 3, 250,000 cases, and on April 11, 509,000-a factor of 200 less than our worst-case scenario. The drastic measures we took as a society saved millions of lives. Had we acted earlier, even more would have been saved; had we waited longer, an even greater catastrophe would have unfolded. Indeed, states and localities that acted earlier generally did better. Around the world, similar stories played out. Subsequent months saw waxing and waning of the virus, tied to behaviors, improved treatment strategies, and the eventual rollout of vaccines.
But powers of 10 need not always tell such a grim story. They are a valuable tool for thinking about nature. We humans occupy a tiny planet in a vast universe. At the same time, there is a world of far tinier things-molecules, atoms, protons, neutrons, and electrons. Powers of 10 are also a useful concept in these happier pursuits. In 1977, while a graduate student visiting the Smithsonian Institution with my brother, I watched the video Powers of Ten, by Charles and Ray Eames (a couple best known for their work in industrial design). This beautiful film summarized our understanding of nature at that time, on the largest and smallest scales. Starting with a couple enjoying a beautiful spring day, occupying a space maybe two meters across in each direction, it explored scales progressively larger by factors of 10-parks, cities, states, nations, the planet, the solar system, galaxies, and clusters of galaxies. It then proceeded in the other direction, describing smaller scales-parts of the human anatomy, then cells, atoms, and the nuclei of atoms. It summarized for me pretty well what I was learning in my studies. To be honest, there was a good deal I didn't yet know in that film.
A lot has happened in the subsequent decades. We understand nature at scales several powers of 10 larger and several powers of 10 smaller, and we have clues to many more powers of 10 in each direction. I have been a witness to, and in some cases a participant in, many of these developments. Telling the story of nature on this vast range of scales is the subject of this book. The story follows this progress in physics, astrophysics, and cosmology. I will only occasionally mention the spectacular discoveries of the past century in biology, medicine, computer and cognitive science, and other fields.
These advances have been the product of dedicated work of experimenters and theorists. The dichotomy between the two can be a confusing one, but one which will, I hope, become clear in these pages. While I seriously considered a career in experimental physics, as a student I fell in love with theoretical physics. This was, professionally, a risky choice, and some of my mentors discouraged me, telling me that the competition was just too stiff. While I believed them, and was by no means convinced I had the stuff for theory, I was in love with the subject. My graduate student days were spent studying phenomena at the smallest scales then accessible, about one-third the size of an atomic nucleus, or 10 centimeters (a hundredth of a trillionth of a centimeter). I have to confess that I was hardly a brilliant student, but my teachers had faith in me, and I went on to do a postdoctoral fellowship at the Stanford Linear Accelerator Center in Menlo Park, California. Here, I was involved in interpreting experiments on still smaller length scales. Among my mentors were Sidney Drell, a leading voice for nuclear arms control, and Leonard Susskind, then a brash young theorist, who had recently come to Stanford. Still, though, I had a hard time finding my way in that period. The problems I worked on didn't really move me.
After two years at Stanford, I moved to a similar position at the Institute for Advanced Study in Princeton. The Institute is an institution exclusively devoted to theory, and it is famed, in part, because of the faculty of its early days. This includes, most notably, Albert Einstein, but also figures like J. Robert Oppenheimer (who headed the atomic bomb effort at Los Alamos during the Second World War), John von Neumann (an early computer pioneer), and George Kennan (the diplomat who shaped much of US policy relative to the Soviet Union in the early days of the Cold War). Its current faculty-including Edward Witten, Nathan Seiberg, Juan Maldacena, and Nima Arkani-Hamed-are among the premier living theoretical physicists in the world. In this environment, I found my scientific bearings and started to probe questions beyond the level of our then current understanding. From there, I went on to five productive years on the faculty of the City College of New York, before moving, for family reasons, back to the West Coast, joining the faculty at the University of California at Santa Cruz. I have spent the subsequent three decades there.
UC Santa Cruz sits amidst towering redwoods, overlooking Monterey Bay. When first established in 1965, it was committed to a radical, 1960s vision of education and engagement. Its unofficial motto was "We are not Berkeley," meaning that its faculty and administration were committed to their students, not just to research. That vision survives, but for serendipitous reasons, UCSC also became a research powerhouse. The astronomy enterprise of the UC system, the Lick Observatory, moved its headquarters to the Santa Cruz campus from Mount Hamilton. Earth scientists were attracted to the campus by its proximity to major fault systems, marine biologists by the rich ecology of the nearby bay; biologists, chemists, and mathematicians were excited by the opportunity to work in the natural beauty of this landscape. UCSC also became a center for particle physics, because of the commissioning of a revolutionary new instrument for particle physics nearby at the Stanford Linear Accelerator Center.
I arrived much later, in 1990, imagining a hippy-dippy institution in the woods. And so it was, but I discovered at the same time a rich intellectual and scientific environment. For the same personal reasons that brought me to Santa Cruz, I actually lived "over the hill" on the other side of the Santa Cruz Mountains, in San Jose, part of the Silicon Valley. Fortunately, from the very start, I had a car pool with a group of colleagues. At the time, this group included four high-energy physicists, working on experiments at the Stanford Linear Accelerator Center, the Fermi National Accelerator Laboratory (Fermilab located near Chicago), and CERN, the big European laboratory in Geneva. There were also two astronomers. Two of the experimenters were playing leading roles in the Superconducting Super Collider (SSC), planned as the world's largest particle accelerator, then in the initial stages of construction near Dallas, Texas. It was designed to accelerate two beams of protons to enormous energies, and then to smash them together, examining the products of the collisions. In a multibillion-dollar project involving thousands of PhD scientists, my car pool partners had the principal responsibility for tracking particles just as they emerged from the collision. One of the astronomers was working on understanding planets. At that time, the existence of planets beyond our solar system was a matter of speculation. All that changed starting in 1995 with the first discovery of an extrasolar planet. Astronomers at Santa Cruz made crucial contributions to the breakthrough technology and to the underlying planetary theory. The other astronomer was a cosmologist, one of the originators of the theory of how dark matter led to the formation of the stars and galaxies.
In 1993, President Bill Clinton recognized that as the costs of the SSC rose, it became more and more vulnerable to the surging politics of government spending. Congress finally killed the project one day in the fall. I expected my colleagues to spend a few days mourning, but by the next morning, they were in the car discussing a call they had received from the big laboratory in Geneva, Switzerland, inviting them to join a project there, known as the Large Hadron Collider (LHC), still in early stages of development. They agreed, and immediately launched into work on the development of a large detector for elementary particles, known as ATLAS. It would be fifteen years before this machine was ready to operate. There were many successes and setbacks on the way, involving science, technology, and funding. The most devastating was a magnet failure, in 2008, which greatly damaged the machine. The recovery took two years, but by 2010, the accelerator was up and working well. In 2012, two experimental teams at the LHC discovered the Higgs particle.
As a theorist, my work involves, among other things, trying to understand the results of experiments and to anticipate possibilities for future experiments. My close connections with experimental colleagues have helped keep me honest, focused on questions we can really hope to answer in experimentally verifiable ways-or at least to distinguish those we can and those we can't. Much of my research effort is devoted to sorting out precisely these issues. What might account for the mass of the Higgs boson? What might the dark matter consist of and under what circumstances might we hope to find it? Is string theory subject to experimental test? Our conversations in the car were often about our children, restaurants, sports, and politics (real and academic), but they were mostly about science. Just as my car pool partners have tried to teach me about the challenges of building electronics that can withstand intense bursts of radiation, they have suffered through my explanations of the latest theoretical ideas and their promise and limitations.
My students at UCSC have also kept me focused on what's exciting in science. I frequently teach a course with the title "Modern Physics." It starts with Einstein and relativity, moves to the development of quantum mechanics, and then proceeds through the spectacular developments of the twentieth and early twenty-first centuries. This book will cover an even broader sweep of ideas, and my hope is to convey excitement about what we understand, and appreciation of the mysteries we currently confront.
The discovery of the Higgs particle, of dark matter and dark energy, along with precision studies of the big bang, illustrate an understanding of our place in the universe beyond anything that humanity has ever known. At the same time, we have burning questions. For some of these, we have a clear path to answers, for others less so. I firmly believe that this science is not so far removed from the ordinary events of our lives that we can't all share in both the understanding and the most pressing questions. I intend to illuminate what questions are likely to be resolved, say, over the next decade, by experiments or new theories, and which ones may not be accessible.
This book will explore many orders of magnitude beyond those which the creators of the Powers of Ten video could contemplate. We will journey across scales both voluminous and microminiature, but we'll also travel the scales of time. Our clock will start, t=0, at the big bang. On this clock, our present instant is about 13 billion years later, or 13 x 10 years. From our present moment, we'll look back to times when stars and galaxies began to form-1 billion years after the big bang, and further to the earliest times we completely understand-three minutes after the big bang, when hydrogen and helium were produced in a hot, cosmic soup. But we'll look back much earlier-to times for which we have only scattered bits of evidence, when the universe was perhaps a billionth of a second old, when matter itself may have been created. Ultimately, we'll peek behind the curtain of the big bang, asking what may have come before, and encounter controversial ideas like the multiverse. This idea provides a compelling explanation of one-and maybe more than one-of nature's greatest mysteries. It is even conceivable that we could find observational evidence for this bizarre possibility.
