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  In Memory of

  Bruce Koci and Per Olof Hulth

  I readily believe that there are more invisible than visible things in the universe. But who shall describe for us their families, their ranks, relationships, distinguishing features and functions? What do they do? Where do they live? The human mind has always circled about knowledge of these things, but never attained it.

  —THOMAS BURNET (1692) (From the Latin motto to Coleridge’s “The Rime of the Ancient Mariner”)

  Introduction: Making Mistakes

  The universe can’t exist the way it is without the neutrinos, but they seem to be in their own separate universe, and we’re trying to actually make contact with that otherworldly universe of neutrinos. And as a physicist, even though I understand it mathematically and I understand it intellectually, it still hits me in the gut that there is something here around surrounding me, almost like some kind of spirit or god that I can’t touch, but I can measure it. I can make a measurement. It’s like measuring the spirit world or something like that.

  —PETER GORHAM

  In November 2013, the international collaboration that operates the IceCube Neutrino Observatory announced that they had detected high-energy neutrinos coming from outer space. This heralded the birth of a new form of astronomy, based not on the usual cosmic messenger, light, but on perhaps the strangest of the known elementary particles, the neutrino. It was also the culmination of a quest that had first fired the imagination of a small group of visionaries more than fifty years earlier and seen many heroic attempts and failures along the way.

  Part of the reason this journey has taken so long is that it takes an unusual telescope to see an unusual particle. IceCube is unlike any other telescope you’ve ever seen or heard of, and in fact no one ever will see it, because it’s buried more than a mile deep in the ice at the geographic South Pole. The collaborators couldn’t even see it while they were building it. Francis Halzen, the Belgian theorist at the University of Wisconsin who dreamed up the idea, says it was like building a telescope in a darkroom.

  This instrument doesn’t employ lenses and mirrors in the fashion of the usual telescope. Presently, and it may grow, it consists of eighty-six kilometer-long “strings” of unadorned light detectors, housed in spherical glass pressure vessels about the size of basketballs. These “strings of pearls” have been lowered into eighty-six two-and-a-half-kilometer-deep holes that were drilled in the ice by a gargantuan hot water drill and allowed to freeze in place. Thus, the topmost pearls are one and a half kilometers—or about a mile—down. The holes have been drilled in a hexagonal grid pattern that covers a square kilometer on the surface of the ice. Hence, the more than five thousand detectors in this unique device monitor about one cubic kilometer, or a billion tons, of what the scientists were thrilled to discover to be very clear, deep Antarctic ice. It is the clearest natural substance known, clearer even than diamond.

  Scientific American once called this telescope the “weirdest” of the seven wonders of modern astronomy. And perhaps the weirdest thing about it is that it doesn’t look up at the southern sky from its location on the bottom of the world; it looks down into the ice. IceCube is designed to look through the planet at the northern sky. Since the neutrino is the only known particle that can pass all the way through a planet without being absorbed or deflected off course, any particle that reaches this particular cube of ice from the northern direction must be a neutrino. The instrument uses the Earth as a shield to block other types of particle, which might create a false signal.

  The reason the neutrino can pass so easily through a planet is that it doesn’t like to show its face. It is sometimes known as the ghost particle. It may be the most plentiful particle in the universe—several hundred billion will pass through your eyeballs by the time you finish reading this sentence—but it is rarely seen, and it won’t hurt your eyes, because it barely interacts with any kind of matter. This makes it very hard to detect. As Nobel laureate and amateur stand-up comedian Leon Lederman once said, “A particle that reacted with nothing whatever could never be detected. It would be a fiction. The neutrino is barely a fact.” Your average neutrino will pass unscathed—and therefore undetected—through a slab of lead one light year, or six trillion miles, thick. Thus it has no problem passing through the Earth, which is considerably less dense than lead and less than paper-thin in comparison to a light year, and most will pass right on through IceCube as well. Every once in a while, however, one will react with the ice in or around the detector or the bedrock below it and produce a charged particle, which will speed along in the same direction as its parent neutrino, dragging a cone of pale blue light along with it. IceCube’s light sensors pick up this light, and by watching the way it passes through the three-dimensional grid of detectors, the scientists can determine the direction of the charged particle and the direction of its parent neutrino, in turn. This makes IceCube a telescope.

  * * *

  As it happens, the reticence that makes the little particle so hard to detect has the beneficial side effect of making it a wonderful complement to light when it comes to astronomy. Since the neutrino can pass through extremely dense media that are opaque to all wavelengths of light, it can carry information from regions of space that are inaccessible to the usual telescope, such as the interiors of stars—including the exploding ones known as supernovae—or regions of our galaxy that are obscured by interstellar dust—the black hole at our galaxy’s core, for example.

  One motivation for inventing this new astronomy is to see into the inner workings of the most violent events in the universe: supernovae, active galactic nuclei, supernova remnants, gamma ray bursters, colliding galaxies, and other strange beasts, some not yet imagined. The scientific possibilities also extend to cosmology and the detection of the mysterious and so far unseen cold dark matter, which constitutes most of the mass of the universe. They reach into pure particle physics as well, since all the violent creatures just named are basically huge particle accelerators, operating by the same basic principles as the manmade variety here on Earth—including the multi-billion-dollar Large Hadron Collider, which produced evidence for the Higgs boson in 2012—but on a vastly larger scale.

  The neutrino itself has become a focus of particle physics in recent years, since in 1998 it produced the first and still only chink in the armor of the standard model of particle physics. This is the theoretical framework that describes the building blocks of matter, the elementary particles, and how they interact with each other through three of the four fundamental forces: the weak nuclear force, the strong nuclear force, and the electromagnetic force. The standard model, which was constructed in the 1970s, is turning out to be so successful that it’s beginning to feel like a straightjacket. With the discovery of the Higgs, which was the last standard-model particle remaining to be detected, it’s looking as though there’s not much left to discover, and
physicists don’t like things to be tied so neatly with a bow. They’re always looking for something new, and the surprising behavior of the neutrino suggests unknown phenomena yet to be explored. For the heart of physics, and indeed all science, is pure exploration.

  This brings us to the main reason for building this unusual instrument. The newborn field of neutrino astronomy has opened a new window on the universe, and rarely in the history of astronomy has such a new window not led to a discovery that was unimaginable beforehand. Galileo is the classic example.

  The first optical telescopes were developed in Flanders for merchants getting a jump on the market by taking advance inventories of the goods on ships as they approached across the English Channel. Galileo used his superior understanding of optics and math to craft a better one, which he presented to the Venetian Doge as a tool of war. A few months later, he trained another at the Moon on a clear night when Jupiter, the second brightest object in the sky, happened to be floating just above it and to the right. Thus he discovered the four “Medicean stars,” now known as moons, heretically orbiting the planet, and got himself in trouble.

  In 1965, Arno Penzias and Robert Wilson, two physicists at Bell Telephone Laboratories, made an unexpected discovery while they were designing ground-based radio antennae for communications satellites. In order to test a horn-shaped antenna they had designed to be ultra-quiet, they aimed it at what they thought was empty space and were surprised to find that it always picked up a small amount of “noise” no matter how painstaking their design. The noise turned out to be a real signal: the Cosmic Microwave Background Radiation, the afterglow of the Big Bang, the explosion out of nothingness that brought this universe into being about fourteen billion years ago. This discovery transformed the Big Bang and cosmology in general from objects of ridicule into subjects for precise study. It also illustrates another aspect of discovery: the scientist’s mind needs to be prepared in order to interpret what he or she measures or “sees”—or even to be able to see it. Theories of the Big Bang and its microwave afterglow had been gestating for decades by the time Penzias and Wilson made their measurement. They won the Nobel Prize not simply for finding a signal but for interpreting it with the knowledge or “eyes” of their day. This leapfrogging between theory and experiment is what propels science forward. Sometimes theory is out in front, sometimes the accumulated weight of unexplained experimental evidence prompts new theories or even paradigm shifts. And these developments can take decades, as we shall see in this book.

  After the Nuclear Test Ban Treaty was signed in 1963, the U.S. Department of Defense began sending satellites into orbit in order to verify that the Soviets weren’t violating the treaty by testing bombs in space, underwater, or on the Moon. The idea was to sense the gamma rays (invisible light at shorter wavelengths than X-rays) given off by the blasts. The satellites never detected any of those, but they did detect numerous “treaty violations” in deep space: brief and astoundingly intense bursts of gamma rays in the distant cosmos. The scientific community became aware of this discovery a few years later when the data was declassified, and the enigmatic sources of the bursts were given the noncommittal name “gamma ray bursters.” Over the course of one to twenty seconds or so, GRBs give off about as much light as that given off by all the other stars and galaxies in the known universe. Theory holds that they should give off neutrinos, too, so they are of great interest to IceCube.

  The astrophysicist Kenneth Lang observes that “our celestial science seems to be primarily instrument-driven, guided by unanticipated discoveries with unique telescopes and novel detection equipment.… [W]e can be certain that the observed universe is just a modest fraction of what remains to be discovered.”

  * * *

  The dream of making a big discovery is one of the things that drives the working scientist; however, media coverage and prestigious awards like the Nobel give the layperson a distorted sense of its importance, I think. The clichéd emphasis on supposedly earthshattering results is especially pernicious in physics, where it would seem that a discovery that “changes our view of the universe” takes place every few months. Some such over-the-top phrase is almost inevitably employed in any newspaper or magazine article describing even the most insignificant result, and the physicists who have now taken to trumpeting their findings in press conferences before publishing them in the peer-reviewed literature share a good part of the blame. In reality, discoveries on the order of the theory of relativity or Darwinian evolution are exceedingly rare.

  But there is some truth in the noise of science journalism, nevertheless. The fact is that scientists tend to enjoy their work more than most, for the main reason that what really gets them out of bed in the morning is the thrill of the chase. They come to some minor realization, solve some esoteric technical problem, or shine a light into some new dark corner of the territory they’ve been exploring almost every day. More than half the time they’re wrong, but at least they’re on track. And finding out they were wrong—going from confusion to clarity—can be just as thrilling as finding they were right.

  Francis Halzen tells me that the late John Bahcall, a respected neutrino theorist at the Institute for Advanced Study in Princeton, used to say that “physicists have two deep dark secrets that they hide from non-scientists under lock and key. The first is that physics does not progress logically; it’s a series of mishaps.… And the second is that they’re having so much fun that they’d do it even if they weren’t getting paid.”

  My goal is to show you the truth of Bahcall’s secrets by taking you inside an experiment that has provided more than enough of the kind of riches that physicists live for. I’ve had a front-row seat for about twenty years.

  * * *

  I was introduced to IceCube in 1997 by Bruce Koci, the master driller. It happened in a roundabout way.

  One sunny day in June of that year, I received a call at my home near Boston from an editor at Natural History magazine. She asked if I might be free to write an article about a paleoclimatologist named Lonnie Thompson, who retrieves ice cores from high mountain glaciers in order to study past climates and climate change.

  A week later I flew to La Paz, Bolivia, and a week after that I reached base camp below the highest mountain in the country, Nevado Sajama, a dormant 21,500-foot volcano capped by a round snow dome—the perfect shape, I would soon learn, for ice core drilling. Lonnie and his team had been working on the summit for about two weeks at that point, and within the next few days they were planning to use a hot-air balloon to fly the first ice core segments down to a waiting freezer truck on the plain at the base of the mountain. Figuring it was my journalistic responsibility to get to the top in time to see this, I climbed a bit too quickly given the altitude and panted into the drilling camp in golden westerly light on the afternoon before the scheduled liftoff, carrying only a daypack and no sleeping bag.

  It was immediately apparent that I had stumbled upon an extraordinary world—above and beyond the unusual work, the brutal cold, and the breathtaking views all around under a spanking azure sky. The drilling team was blasé about the surroundings. They were there to work, not moon about the beauty of the place, and their dedication was palpable. They knew each other well. They had drilled together for decades in similar locations around the world and had lived on glaciers like this for years all told. Their conversation didn’t stray beyond the tasks at hand. There was a meditative silence on that mountaintop as they used their elegant solar-powered drill to mine ice core segments one meter at a time, log them into a lab notebook, pack them in insulated boxes, and bury them in a snow pit to await the descent to lower altitudes and the ultimate destination of Lonnie’s walk-in freezer at Ohio State University, half a world away.

  Bruce didn’t stand out at first. For one thing, that wasn’t his way. But I will never forget my first interaction with him, which I described in my 2005 book, Thin Ice:

  Soon the sun sank too low to provide power. The pyramidal shadow of the
mountain stretched across the desert to meet the horizon. The sky turned purple then gray. We shoe-horned ourselves into the snow cave, a rectangular hole fifteen feet long and five feet wide—too low for standing—which served as dining room, living room, and lounge. We sat along opposite walls on benches cut in the snow, knee to knee, thigh to thigh, backs and seats against cold white surfaces, sipping tea and soup in near silence.

  After dinner I decided to point out that I had no gear. Bruce Koci [pronounced “ko'-see”] then forced himself slowly to his feet and climbed into the twilight. A few minutes later he called from above, holding four of the six-inch foam pads they use to insulate the ice and two of the fluffiest down sleeping bags I have ever seen—much warmer than my own back at High Camp. He helped me lay out the pads in a tent and pile the bags on top.

  “There,” he said. “Wrap yourself in these like a fox in his tail.”

  This was the first of many acts of generosity, toward others and myself, that I saw Bruce perform in the years that I knew him.

  At that point he was approaching the end of his twenty-year tenure as Lonnie’s lead driller. The two had co-invented the solar-powered drilling technology in the early 1980s and had retrieved the world’s first high-altitude ice cores together on Peru’s Quelccaya Ice Cap, not far to the north of Sajama, in 1983. Bruce was gentle, quiet, and humble, clearly one-of-a-kind, and had a deep spiritual connection to the natural world. Once the expedition was over and my article was complete, I felt a desire to keep in touch, both with him and with Lonnie.

  It wasn’t easy at first, as they spent only two weeks at home—Bruce in Alaska, Lonnie in Ohio—between the expedition to Bolivia and another three-month effort in Tibet. Finally, in mid-November, Bruce sent me an e-mail:

  Mark;