by David Kaiser
Figure 18.1. Beginning in the late 1960s, physicist Joseph Weber claimed to have detected gravitational waves using his large bar detector at the University of Maryland, though he failed to convince fellow experts. (Source: Special Collections, University of Maryland Libraries. © 1969 by the University of Maryland.)
Around that time, Rainer Weiss taught an undergraduate course at the Massachusetts Institute of Technology. He assigned as a homework problem the task of investigating a new approach for detecting the waves, different from the one Weber had used. (Students, take note: sometimes homework problems herald Nobel Prize–worthy advances.) What if physicists tried to detect gravitational waves by scrutinizing tiny shifts in the interference patterns of laser beams that had traveled separate paths before recombining at a detector? Gravitational waves should stretch and squeeze a region of space in a particular pattern as they travel through it. Such a disturbance would alter the lengths along which the laser beams traveled, putting the two laser beams out of phase with each other by the time they both reached the detector—a difference that could give rise to a measurable interference pattern. (Two physicists in Moscow, Michaeil Gerstenstein and V. I. Pustovoit, had proposed a similar idea in 1962, though their work was little known in the West at the time.)4
The idea was audacious, to say the least. To detect gravitational waves of the expected amplitude using the interference method, physicists would need to be able to distinguish distance shifts of about one part in a thousand-billion-billion. That’s like measuring the distance between the Earth and the Sun to within the size of a single atom, while controlling all other sources of vibration and error that could swamp such a minuscule signal. Little wonder that Kip Thorne, another LIGO laureate, assigned a homework problem of his own in his massive 1973 textbook, Gravitation—the book he wrote with Charles Misner and John Wheeler—guiding students to the conclusion that interferometry was hopeless as a method for detecting gravitational waves. (Okay, students: maybe some homework problems can be skipped.) After investigating the idea further, however, Thorne became one of the most tenacious advocates for the interferometric approach.5
Convincing Thorne was the easy part; attracting funding and students proved much more difficult. Weiss’s first proposal to the National Science Foundation, in 1972, was rejected; a follow-up proposal in 1974 received modest funds for a limited feasibility study. He faced considerable difficulty attracting students and convincing his colleagues that the project was worthwhile. As he reported to a program officer at the National Science Foundation in 1976, “Gravitation research, although viewed as fascinating, is considered too hard and unfortunately profitless not only by the average student but also by much of the physics faculty. In short, the atmosphere if not outright hostile to such research is certainly skeptical.” Two years later, Weiss observed in another funding proposal that he had “slowly come to the realization that this type of research is best done by secure (possibly foolish) faculty and young post-doctorates of a gambling bent.”6
As the size of the anticipated project grew—interferometer arms that would stretch kilometers, not meters, decked out with state-of-the-art optics and electronics—so, too, did the projected budget and organization. Sociologist Harry Collins chronicles the next steps in his engrossing study Gravity’s Shadow: The Search for Gravitational Waves (2004). The project’s expanding size and complexity required political mastery as much as physics know-how. Concerns quickly emerged within the scientific community that LIGO would absorb too many resources from other projects, and thus, the proposed laser observatory pitted some astronomers against physicists in quite bitter, public disputes. Meanwhile, the project’s leaders learned about interference from more than just laser beams: at one point, efforts to establish one of the two large detectors in Maine foundered on political rivalries and backroom deals among congressional staffers.7
Remarkably, the National Science Foundation approved funding for LIGO in 1992; it was (and remains) the largest scientific project ever funded by the foundation. The timing was propitious: the following year, Congress eliminated funding for enormous scientific projects like the Superconducting Supercollider, whose projected price tag was about forty times larger than LIGO’s. After the dissolution of the Soviet Union, physicists learned with whiplash speed that Cold War–era justifications for investing in scientific research no longer held predictable sway in Congress. Beginning in the mid-1990s, meanwhile, budgetary brinksmanship entered a whole new era. For more than two decades, planning for long-term projects has had to contend with frequent threats (occasionally realized) of government shutdowns, compounding a budgetary climate focused on short-term projects that can promise quick results. It is difficult to imagine a project like LIGO getting a green light if proposed today.
Yet LIGO demonstrates some benefits of taking a longer view. The project has exemplified a close coupling between research and teaching, well beyond the suggestive homework problems from the early days. Several undergraduates and scores of graduate students were coauthors on the LIGO team’s historic article detailing the first direct detection of gravitational waves, published in February 2016. Since 1992, the project has spawned nearly six hundred PhD dissertations in the United States alone, from one hundred universities across thirty-seven states. The studies have ranged well beyond physics, including pathbreaking studies in engineering and software design.8
Figure 18.2. Rai Weiss (center) congratulated by members of the MIT portion of the LIGO collaboration upon the announcement that Weiss had shared the 2017 Nobel Prize in Physics. Also shown (from left to right) are Slawomir Grass, Michael Zucker, Lisa Barsotti, Matthew Evans, David Shoemaker, and Salvatore Vitale. (Source: Photograph by Jonathan Wiggs, Boston Globe, courtesy of Getty Images.)
LIGO shows what we can accomplish when we fix our eyes on a horizon well beyond a given budget cycle or annual report. By building machines of exquisite sensitivity and training cadres of smart, dedicated young scientists and engineers, we can test our fundamental understanding of nature to unprecedented accuracy. The quest sometimes yields improvements for technologies of everyday life—the GPS navigation system benefited from efforts to test Einstein’s general relativity—even though such spin-offs are difficult to forecast.9 But with patience, tenacity, and luck, we can sometimes catch a glimpse of nature at its most profound.
19
A Farewell to Stephen Hawking
Stephen Hawking delighted in reminding audiences that he was born three hundred years to the day after the death of Galileo, on 8 January 1942. Imagine how Hawking would have reacted could he have known that he would die on 14 March 2018—the hundred and thirty-ninth anniversary of Albert Einstein’s birth.
I never got to know Professor Hawking, and yet I found myself mourning his passing as if I had lost a close colleague. Like so many people of my generation, I grew up in a world in which Hawking’s name was nearly as familiar as Einstein’s. In one way or another I’ve been grappling with his ideas for my entire career.
Hawking’s breakaway best seller, A Brief History of Time, appeared in 1988, while I was in high school. By that time I was already immersed in popular books about the wonders of modern physics; the 1980s saw a boom in high-quality, inexpensive paperbacks inviting readers to sample some of the choicest mysteries of quantum theory or admire the austere grandeur of Einstein’s general theory of relativity. Yet Hawking’s book felt different. It became a sensation, sought by people who had never noticed the raft of earlier books. Hawking’s was a book to own and, for some, to read.1
A Brief History of Time offered a tour of Hawking’s most significant contributions to the field. His earliest work centered on Einstein’s general relativity, the work that had thrust Einstein himself into the spotlight decades earlier. According to the theory, space and time are as wobbly as a trampoline. They can bend or distend in the presence of matter and energy. Their curvature, in turn, gives rise to all the phenomena we associate with gravity. Gravitation, according to
this line of thinking, is not a force—the outcome of one object tugging on another, as described by Isaac Newton’s equations—but a mere consequence of geometry.
Hawking’s first major contribution, which he began to develop in his PhD dissertation at the University of Cambridge, was essentially to push Einstein’s idea until it broke. What if matter were to become packed so densely within a region of space that spacetime itself ruptured? Hawking, along with his colleague Roger Penrose, clarified the conditions under which solutions to Einstein’s equations must devolve into a “singularity,” quite literally a point of no return. The Penrose-Hawking singularity theorems (as they came to be known) indicate that under extreme conditions—the centers of black holes, perhaps even the start of our universe itself—spacetime can simply end, a cosmic variant of Shel Silverstein’s famous sidewalk.
The singularity theorems apply to “classical” spacetimes—that is, to descriptions of space and time that ignore quantum theory, that other great pillar of modern physics. Soon after Hawking completed his PhD in 1966, he began to attack questions at the troublesome boundary between relativity, which describes the largest objects in the cosmos, and quantum theory, which governs matter at the atomic scale. He stumbled upon his most famous finding in the mid-1970s while puzzling through scenarios in which pairs of quantum particles might find themselves near a black hole. If one were to fall in while the other escaped, Hawking suggested, the black hole would appear, to a distant observer, as if it had emitted radiation—precisely what black holes were not supposed to allow. In other words, “black holes ain’t so black,” as he put it in A Brief History: they glow. What’s more, this radiation could shape a black hole’s fate. Over astronomical timescales, the black hole could evaporate, its once-enormous mass seeping out as cosmic static.
These puzzling ideas—equal parts bizarre and exciting—spawned many others, some of which continue to challenge the physics community to this day. Theoretical physicists still grapple with whether information tossed into a black hole could really disappear forever. Must it be scrambled beyond any possible reconstruction, with only a meaningless bath of radiation remaining? Any such process would violate quantum theory, for which a sacrosanct rule is that information can be neither created nor destroyed. Scores of theorists have turned Hawking’s arguments around and poked them from every angle, trying to find where the weak joint might lie in the uneasy combination of quantum theory and relativity. Meanwhile, closer to my own research, Hawking’s ideas about the big bang and whether our universe could have emerged from an initial singularity continue to animate studies in cosmology.
Famously, Hawking’s descriptions of black holes and the big bang came interlaced throughout A Brief History of Time with stories of his personal life. He was diagnosed with the degenerative disease amyotrophic lateral sclerosis (ALS) in 1963, at age twenty-one—just as he was beginning his doctoral studies—and was expected to live only a few more years. In his book, Hawking wrote of his determination to carry on, bolstered by meeting Jane Wilde (whom he married in 1965) and soon by the arrival of their three children. Surely these triumphs—the sheer, stubborn fact that Hawking continued to live—drove the fascination with his book just as much as his clever descriptions of warping spacetime did.
Figure 19.1. Stephen Hawking, shown here in October 1979, produced a string of major insights into the fundamental nature of space, time, and matter while struggling with the degenerative disease ALS. (Source: Photograph by Santi Visalli, courtesy of Getty Images.)
Propelled by the book’s popular success, Hawking rapidly became a full-blown celebrity. He kept up a remarkable travel schedule even as the effects of his ALS became more severe. In October 1999, he visited Harvard for three weeks, just as I was finishing my PhD there. Lines snaked around city blocks once tickets became available for his lectures. (Until then, the only time I had seen lines that long in Cambridge was when Star Wars: The Phantom Menace came out, the previous spring.) Between lectures, Hawking and his sizable entourage of nurses and assistants regrouped in the physics building, near my own tiny office. I never dared approach the famous professor myself, but I remember sitting with some of his assistants late into the night, lost amid the buzz and hum. To be in the vicinity of Hawking was to be immersed in an extended web of activity, of people and machines clicking together, a phenomenon documented in the anthropologist Hélène Mialet’s fascinating study Hawking Incorporated (2012).2
Almost two decades later, I had a different sort of encounter with Hawking. During the spring of 2017, several colleagues and I invited him to join a brief essay we were writing, trying to articulate for a broad audience some of the most significant insights that cosmologists had developed and tested about the earliest moments in cosmic history. At first, Hawking objected to the wording of a particular paragraph. My colleagues, who had known him for decades, assumed that he would never change his mind; he could be famously stubborn. Being innocent of that experience, I suggested a modest edit to address his concern. I will never forget the euphoria, the next day, when I received the email from his assistant saying that Hawking liked the edit and would sign on as a coauthor of the essay. Hawking might have generated enduring truths about the cosmos, but at least I could tame a wayward dependent clause or two.3
I imagine that Hawking’s well-known stubbornness helped keep him alive. He refused to succumb to his disease, outliving his original prognosis by half a century. But the side of him I think of most is his sense of humor, even showmanship. How fitting, I have often thought, that as he lost control over most of the muscles in his face, his expression settled into an impish grin. He seemed media-savvy in a way that Einstein, too, grew to be. As recently as January 2016, for example, Hawking held his own—comedically, if not strategically—with comic actor Paul Rudd in a short film about quantum chess.4
I never met Stephen Hawking, but the idea of him—and several of his own ideas—have been with me for much of my life. May his example continue to inspire young people to beat the odds and to ask big, ungainly questions about the universe.
ACKNOWLEDGMENTS
Most of the chapters in this book first appeared as essays, and those earlier versions benefited enormously from talented and patient editors. I am grateful to Sara Abdulla (Nature, chapter 5); Thomas Jones (London Review of Books, chapter 12); Angela von der Lippe (W. W. Norton, chapter 9); Anthony Lydgate (New Yorker, chapters 4 and 19); Paul Myerscough (London Review of Books, chapters 1, 6, 10–12, 14, 17); George Musser (Scientific American, chapter 13); Corey Powell (Aeon, chapter 3); Jamie Ryerson (New York Times, chapter 18); Dave Schneider (American Scientist, chapter 16); and Michael Segal (Nautilus, chapter 2). From this remarkable set I want to single out Paul Myerscough at the London Review of Books for special thanks. More than a third of the contents of this book originally appeared as short pieces in the LRB. I still remember how nervous I felt, sending in my first piece to Paul a decade ago. (That first essay happens to be the chapter that opens this collection, on Dirac.) Surely a pro like Paul would see through my pretense. On the contrary, he read the piece with care, helped tighten up a few saggy spots—and then kept asking for more. Over the years I have written more than a dozen pieces for the LRB, working with Paul on most of them. I learned how to be a physicist and historian in graduate school. To the extent that I have developed any confidence (let alone skill) as a writer, I credit Paul for his quietly persistent coaxing and coaching.
I have enjoyed the great privilege of discussing several of the topics described in these chapters with remarkable colleagues, including Carl Brans, Angela Creager, Joe Formaggio, Peter Galison, Michael Gordin, Alan Guth, Stefan Helmreich, John Krige, Patrick McCray, Erika Milam, Heather Paxson, Lee Smolin, Matt Stanley, Alma Steingart, Kip Thorne, Rai Weiss, Alex Wellerstein, Benjamin Wilson, Anthony Zee, and Anton Zeilinger. Several friends, colleagues, and students shared comments on individual chapters, and it is a pleasure to thank Marc Aidinoff, Marie Burks, Michael Gordin, Yoshiyuki Kikuchi, Robe
rt Kohler, Roberto Lalli, Bernard Lightman, Kathryn Olesko, Alma Steingart, Bruno Strasser, Marga Vicedo, Benjamin Wilson, and Aaron Wright for their helpful feedback.
K. C. Cole, Nell Freudenberger, Alan Lightman, Julia Menzel, and David Singerman read and commented on the full manuscript. The book benefited in countless ways from each of their thoughtful suggestions. I am especially indebted to Alan Lightman for sharing insights with me about his own writing process, including his thoughts on what makes a collection of essays more than the sum of its parts. I have enjoyed Alan’s writing for many years—his nonfiction essays and his novels alike—and so I was deeply honored when he kindly agreed to contribute a foreword for this volume. Nell Freudenberger’s detailed comments on an early draft of the manuscript really gave the project life and helped to convince me that the collection just might work as a book. Her talents as a novelist are inspiring, and her feedback on my draft felt like a master class in the craft of storytelling. David Singerman’s meticulous comments on the penultimate draft were a perfect bookend to Nell’s early feedback. He marked up nearly every page. On large matters and small, he helped me keep the most important points in focus.
I am also grateful to Karen Merikangas Darling at the University of Chicago Press for her enthusiasm about the project from the start and for her constructive feedback on the evolving manuscript; and to my literary agent, Max Brockman, for his unstinting encouragement and sound advice.
Lastly I thank my beloved wife, Tracy Gleason, and our children, Ellery and Toby. They have served as sounding boards and helpful critics, never shying away from telling me that a metaphor had gone astray or an analogy for this or that physics concept just wouldn’t cut it. A few years ago, when I was away from home at a conference, my phone buzzed. Tracy had texted to ask me what Hawking radiation was; Toby had just asked her about it over dinner. (Typical text message in our family.) I chuckled to myself, wondering how best to get the gist across in some reply texts, surreptitiously tapped out while seated at my conference dinner. Before I began, though, Tracy texted again. “Never mind,” she wrote. “Toby just explained it to me.” He was ten years old at the time. I don’t know what his explanation sounded like; both had forgotten the details by the time I got home from my trip. What mattered was that Toby had been curious, eager to learn more, and not afraid to try to puzzle through a few steps on his own. Ellery has made clear her own preferences for dinnertime discussion topics. Back when she was eight, her birthday present to me was a T-shirt featuring a large picture of her face contorted in her most dramatic, pleading expression, with the caption “Not the Higgs boson again!” But I know she protests too much; she was the one who talked through my then-inchoate analogy about quantum entanglement tests and twins ordering desserts. Hopefully Ellery and Toby will have more questions after reading this book. It is dedicated to them, with all my love.