The Uncertainty Principle

Campbell Laird

To see the smallest, most elusive particle in the universe, you need only drive five hours north of the Twin Cities to Soudan, an Iron Range hamlet of around 500 souls located 20 miles from Ely. Follow a winding road up the bluff overlooking the town to the site of an old iron mine, then take a clanking elevator down 2,343 feet to a tunnel full of bats and smelling of incipient mildew, walk through a big green door that looks a bit like the gates of Oz, and into a high-ceilinged cavern roughly the size and shape of an airplane hangar. There, past a bank of fluorescent-lit offices where strange, smart men do inscrutable things with computers, past a huge, gaudy mural of the solar system painted on the cave wall, you will come upon the MINOS Far Detector, a gigantic assemblage of steel and wiring resembling a house-sized loaf of bread.

MINOS, which stands for Main Injector Neutrino Oscillation Search, has two parts. The first, the far detector, is constructed from 486 one-inch-thick octagonal steel plates. Sandwiched between these are half-inch-thick layers of plastic connected by nests of cable to thousands of phototubes. The detector weighs some 6,000 tons, cost around $40 million to build, and contains as much steel as a typical battleship.

The second part of the MINOS experiment is 450 miles away, at Fermi National Accelerator Laboratory in Batavia, Illinois. Sometime early in 2005, Fermi Lab's particle accelerator, the most powerful on Earth, will begin shooting trillions of protons northward in timed bursts. Traveling through a 5,000-foot-long tunnel beneath Fermi Lab's campus, the protons will be winnowed into still smaller particles, which will then fan out toward northern Minnesota. Passing through hundreds of miles of rock beneath the Midwest, these subatomic rockets will reach their destination in about two-thousandths of a second. If MINOS works as planned and if luck holds, one or two of them will rustle the particles of that steel bread-loaf as they whistle past toward the edge of the galaxy.

"We're expecting one interaction every few hours," explains Earl Peterson, manager of the MINOS lab in Soudan. Peterson is a physicist at the University of Minnesota--chief among the 35 institutions from six countries collaborating on the experiment--and he looks very much the part, with a slightly scraggly white beard and a blue cardigan worn through at the elbows. A miasma of cigarette smoke follows Peterson as he shows me around the underground lab where he's spent a good part of the past 20 years designing increasingly sophisticated and ambitious physics experiments. On this particular day in late July, he is overseeing the completion of the far detector, which, as it turns out, has come together well ahead of schedule and long before Peterson's colleagues at Fermi Lab will be ready to begin their subatomic fusillade. "The beam diverges like a flashlight," Peterson explains. "Traveling through 450 miles of rock, you will lose maybe one-one-thousandth of a percent of the neutrinos."

Peterson walks over to a computer station on a catwalk near the loaf's flank. "You don't have a pacemaker, do you?" he asks, noting that the detector produces a magnetic field 10 times that of the Earth's in order to corral wayward neutrinos. He picks up a sheet of paper printed with a spray of colored dots--a simple graphic representation of the wake a neutrino might leave as it slices through the detector's sandwich layers.

The thing about neutrinos is that they're small. Infinitesimally small. So small that they can slip through galaxies unperturbed, passing through stars and planets and human beings without ever touching anything. So small, in fact, that until relatively recently scientists believed that they didn't have any mass at all. Blow your typical hydrogen atom up to 1,000 feet in diameter, and an electron would be about the size of this period. (An ant, by way of comparison, would be 20 million miles long.) The smallest neutrino is 10,000 times smaller still. Blow that hydrogen atom up to the size of the Earth, and the neutrino would be the size of a dust mote. That, as you would expect, makes them an especially elusive quarry for physicists: Imagine trying to fire a baseball at a catcher's mitt 100,000 miles away, and you get some idea of the scale of difficulty involved.

The problem of detecting neutrinos is further complicated by their chameleonic nature. The particles come in three flavors, the electron, tau-, and muon-neutrino. (A 1995 experiment at Los Alamos National Laboratory in New Mexico suggested the possibility of a fourth, a large "sterile" neutrino, but Peterson, like most physicists, remains skeptical of its existence.) As they follow their lonely trajectories through the heavens, neutrinos oscillate from one flavor to another, vibrating like the pitch of a musical instrument from, say, C-sharp to B-flat. Imagine that the neutrinos fired from Fermi Lab are SUVs on a highway; by the time they finish their commute to Soudan, they may have modulated into compact cars or semi-trucks or some mix of the two. If you were to set up a roadblock only for SUVs, the compacts and trucks would simply slip past, and you'd never be the wiser.  

"We don't know two things," Peterson says. "One, we don't know their masses, so you don't know how long it takes for them to change from one flavor to another. The second thing we don't know is what you might call the wavelength--how long it takes for 95 or 20 or 50 percent of the muon-neutrinos to turn into electron-neutrinos. What's a bit mind-boggling is when you get into this probability business with quantum mechanics."

Peterson sits on a desk and draws his legs up behind him. "That what's really weird about this stuff. Those three neutrino kinds are not really basic kinds at all. They're better understood as a set of ingredients. So there's a probability that they'll be one kind or the other. It's the philosophical problem with quantum mechanics: What is this uncertainty shit, anyway?"

T he universe is about 15 billion years old, created, as physicists can best divine, in an eruption of such magnitude that all of space and time unfurled in a single instant. At least in the sliver of a second after that violent birth, the cosmos was a very lively place, with temperatures reaching a trillion trillion times that of the sun's core. A few billion years later, things cooled down enough for matter to clump together as stars and planets, rather like the skin that forms on lukewarm soup.

But, scientists noticed, something was missing--namely, 99 percent of the stuff that ought to be floating around space. This dark matter, so called because it doesn't reflect light and is thus impossible to detect directly, may hold the key to the universe's fate. If this matter is scattered too thinly across space, the universe should continue expanding indefinitely; if not, eventually the force of gravity will cause all of existence to collapse, at the speed of light, back into nothingness. Neutrinos, nearly without mass but infinitely numerous, could account for a considerable part of this missing matter. (Concurrently, another University of Minnesota experiment at Soudan is searching for evidence of a second dark matter suspect, called WIMPs, or weakly interacting massive particles.) Understanding neutrinos may, perhaps, amount to counting angels on the head of a pin; but these particular angels may actually be directing the course of existence.

Peculiar as they are, then, neutrinos are also hugely enticing to scientists seeking to understand the contours of the cosmos. Though billions of neutrinos stream through every inch of space, physicists have no idea how numerous they really are. They may be mere ghostly refugees from the Big Bang. Or they could be the glue that keeps the universe from spinning back into that primordial soup. If the latter, neutrinos may provide a trail of telltale clues to the very nature of the universe--whether it is destined to expand infinitely, or whether, as humans prefer to imagine, it has both beginning and end. Fueling a billion suns without leaving so much as a fingerprint, neutrinos may be a deus ex machina, the tiny variable that gives shape and order to an otherwise entropic cosmos. They may even hint at an answer to the biggest question: why the universe bothers to exist at all. Or, phrased somewhat differently, What is the nature of God?


Tower, a village just down the road from MINOS's underground lair in the Soudan mine, is a singularly unlikely place to plumb the mysteries of time and space. Set against the southern shore of Lake Vermillion, between vast, swampy forests of white pine and the crumbly rust-red hills of the Iron Range, Tower is serenely pretty in an Anytown, USA, sort of way. Along the town's main street there are two gas stations; Zup's grocery store; a hardware store; Erica's Bakery, where, in the morning, you'll find many of Tower's older residents congregating over coffee and doughnuts at the linoleum-topped counter; a funeral home; a few antique stores and knickknack shops catering to seasonal tourists; and a couple of bars. There is a stately old high school with adjacent ball fields, and a Lutheran church. Until last spring, there was a drug store as well, but it has since closed, and townsfolk now drive to Ely to get their prescriptions filled. On summer mornings, the soft chug of lawnmowers breaks the quiet, and a cool, pine-scented breeze blows off the lake. A sign at the edge of town pegs the population at 479, but everyone insists that it is, in point of fact, 502.  

Since its incorporation in 1883, Tower's fortunes have risen and fallen in correlation with America's steel industry. Mostly fallen, actually. In the late 19th century, the area was settled by hardscrabble gold prospectors, who, upon determining that there was no gold, turned instead to mining the rich iron ore deposits just beneath the soil. Lured by the prospect of well paying jobs underground, Cornishmen, Finns, and Swedes streamed into the area. At its most prosperous, around the turn of the 20th century, Tower had more than 5,000 residents.

Mining was from the start a fickle, boom-or-bust business. In the Tower History Museum, located in a derelict ore train, there is, amid the broken phonograph records and yellowed photographs, a Vermillion Iron Journal newspaper clipping from Christmas 1896, detailing a mine closing, mass layoffs, and missed payrolls--a sour foreshadowing of the more recent closings that have devastated the Iron Range economy.

"In 1989 or so, there were 12,000 people employed in mining," explains John Swift, a resort owner in Tower who also happens to be a former commissioner of the Iron Range Resources and Rehabilitation Board, the state agency charged with goosing the area's torpid economy. "There were 5,700 five years ago. There's only around 3,500 today. And you have to remember that the average salary in mining is $65,000, so you'd have to look long and hard to find another job of that kind.

"There's another aspect to it, too," Swift continues. "That mine is what won World War II. Without the iron from that mine to build the ships and tanks, we wouldn't have won." Some years back, Swift wrote a letter to Tom Brokaw suggesting that the newsman hadn't given due credit to Iron Range miners in The Greatest Generation, his popular history of the Second World War. Brokaw never wrote back.

Andy Larson, the president of the Tower-Soudan Historical Society and a lifelong resident, is, like many locals, a third-generation miner. He remembers well when the mine was finally idled, in the winter of 1962. "There was rumors," Larson recalls, "so maybe people felt it was coming. But then they got word from back East to lock 'er up, and that was that. People were pretty upset about it. That was pretty traumatic."

Larson himself worked in a nearby mine until 1986, when, after 25 years of service, he was laid off. "The Eighties were really bad, tougher than now. Now the economy's down. And there's foreign imports from China and Korea. But mining runs in cycles. Things change; they always do." Larson's is a more or less typical attitude among locals: Times are hard on the Range, yes, but things could be worse.

Larson watched with some pride as local iron workers--many of whom were put out of work by the closing of nearby LTV Steel--blasted and quarried MINOS's underground lair. There was, he admits, some initial suspicion about the project's true nature. "When they built the first lab, there was one lady who thought they were going to store atomic energy down there in little glass jars," he says. "There's always a few paranoid people. But those are just the off-the-wall things little old ladies say."

These days, among those locals who register its existence at all, the MINOS project seems to invoke something between civic pride and benign indifference. At the Soudan General Store, which was once the mining company's office, the woman behind the soda fountain offers that the experiment has something to do with neutrons. Other Tower residents occasionally report physicist sightings--"funny-dressed little guys with crazy hair," by one local's description.

"They're not much for drinkers," says Marjorie Lakoskey, who has tended the Iron Ore Bar since 1953. "I've talked to guys from Vietnam and Russia. Not really talked to them, I guess. They all seem pretty nice."

Lakoskey is trim and vigorous for a woman of 83, and it's not so hard to believe that she has occasionally stopped bar fights cold. Her bar is not in as prime condition, however. Located at the edge of town, near a monument hastily constructed to commemorate President McKinley's 1901 assassination, the Iron Ore Bar served as a brewery during Prohibition. Today, its concrete walls are crumbling into ruin.

Though Lakoskey's daughter works as a guide for the DNR, which operates the Soudan mine as a historical site, she herself has never toured the place, largely because of the bats. "I hate them things," she winces. "I had a bat upstairs once, and I had to chase him with a broom." Lakoskey harbors her own private suspicions about the scientists and their experiments--"They're looking for something. I just don't think they're telling us what," she says. But like many townsfolk, she agrees that, on balance, theoretical physics has been good to Tower.  

Still, until a few months ago, it appeared unlikely that physics alone might actually arrest the town's century-long slide toward oblivion.


As much as it is reasonable to say of anyone, Marvin Marshak was probably destined to become an experimental physicist. As a boy in Buffalo, New York, he constructed elaborate science experiments ("mostly things that blew up") in his basement. "We used to fire these rockets made out of steel CO2 cartridges that we'd fill with sulfur and powdered zinc. But then they'd go off and we never knew where they went. We got frustrated with losing them, so one day we tied a string to one. That didn't work, of course. So then we got really frustrated and fired one of them into the side of some kid's house. I think the father discovered it a few days later. Of course, we had no idea where that hole came from."

Today, Marshak, a short, animated man with an agreeable manner and a wisp of hair, is one of the driving forces behind the MINOS experiment. When aboveground, he works out of a tiny University of Minnesota office decorated with a poster from IQ, a romantic comedy about Albert Einstein, and a dry-erase board covered with hieroglyphic-like equations. The idea of setting up shop in the Soudan mine originated with Marshak--or, more precisely, Marshak's wife. At the time, he and his colleagues had been scouring the globe for a suitable location in which to study proton decay, the (so far) theoretical process by which a proton is transmuted into energy. "The idea in the late Seventies was that you could see the individual atom annihilating," he explains. "In order to do this, you'd need to go deep underground because you need a shielded location.

"We just sort of got sucked into this idea that we would go look for this spontaneous decay of matter into energy. And that progressed into practicalities: Can you find a hole in the ground? Just by chance, my wife and I had visited this mine in a state park in Soudan. My recollection of what happened is, one day she said to me, 'Why are you always flying off to wherever? Why don't you just stay home and use this place nearby?'"

After a few abortive attempts at collaboration--physics is a notoriously competitive, ego-driven discipline--Marshak and his U of M partners decided to go it alone. Eventually, in September 1979, Marshak found himself in the Tower high school auditorium, addressing 250 local residents--many of whom believed that he was proposing to store nuclear waste in their backyard. "The reason I remember the date is that my son was born in July," Marshak says. "The university public relations people said I should bring him to the meeting as a prop. I guess me standing there holding this three-month-old baby would make us less scary."

At the time of that first Soudan experiment, Marshak and his fellow scientists were uninterested in neutrinos; if anything, they regarded the particles as cosmic background noise, something to be filtered out. In fact, Marshak explains, top graduate students were usually assigned to study proton decay; the less promising were assigned to neutrinos.

Indeed, the neutrino has always been the problem child of physics. When Wolfgang Pauli first posited the particle's existence in 1930, he did so almost sheepishly. In a now-famous letter, Pauli proposed a solution to the problem of beta-decay, a species of radioactivity that had been troubling scientists in his circle. Among those scientists was a young woman named Lise Meitner, one of the great unsung figures in physics history. Meitner, who had been forced to set up her lab in an abandoned carpenter's workshop because the director of the University of Berlin's Chemistry Institute feared that female students would set their hair afire with Bunsen burners, had noticed an apparent absurdity: In experiments, beta-decay appeared to violate the most sacrosanct law of physics, that of the conservation of energy, by, essentially, suggesting that two plus two equals three. Pauli's "desperate remedy" to this problem was to posit an undetectable particle emitted during radioactive decay that accounted for the missing energy. This strange creature Pauli dubbed a "neutron." Later, the Italian physicist Enrico Fermi renamed it the neutrino.

Fermi, of course, went on to create the first man-made nuclear chain reaction beneath the squash courts at the University of Chicago, an experiment that led directly to the immolation of Hiroshima and Nagasaki and the advent of the Nuclear Age. It's a sad irony that the same dreadful technology also spurred the next major advance in neutrino research. In 1951, Clyde Cowan and Frederick Reines, two young scientists at Los Alamos, where the first atomic bomb had been developed, proposed studying the billions of neutrinos released in an atomic explosion with a detector buried 40 meters from the blast. Determining this impractical--for pretty obvious reasons--they turned instead to the powerful Savannah River nuclear reactor in South Carolina. By mid-1956, they had produced the first evidence that Pauli's ghost particle, in fact, existed.  

Some 10 years later, another researcher, Ray Davis Jr., installed a 380,000-liter tank of perchloroethylene--dry-cleaning fluid, basically--at the bottom of the Homestake Gold Mine near Lead, South Dakota, to study the biggest nuclear reactor of all: the sun. Davis picked Homestake, the deepest gold mine in the western hemisphere, for the same reason the MINOS scientists chose to situate their experiment in Soudan. The thick layer of rock above filters out unwanted solar radiation, while neutrinos, which can pass through a million miles of lead without a worry, are entirely unhindered. The results of Davis's experiment, which ran for 25 years and won him the 2002 Nobel Prize in physics, startled theorists: Far fewer solar electron neutrinos than expected seemed to be reaching the Earth. The best explanation, researchers decided, was that the particles had oscillated from one flavor to another mid-flight. That also meant that the neutrinos must weigh at least something--a conclusion that pitched the entire traditional understanding of physics on its head.

The natural follow-up to Davis's experiment was to study neutrino oscillation using a more controlled source of particles from a powerful accelerator. MINOS was not the first experiment designed to do so. In 1999, a high-energy particle accelerator in Japan began firing a stream of neutrinos at the Super-Kamiokande detector, some 250 km away. Meanwhile, in Italy, a group of researchers at Gran Sasso Laboratory are preparing to catch neutrinos from the CERN accelerator in Switzerland. Yet both experiments have been beset by problems. In Japan, an accident earlier this year smashed thousands of the detector's phototubes. And in June, the entire Gran Sasso lab was closed by court order after a chemical leaked into the local water supply. By chance as much as by design, MINOS became arguably the world's premier neutrino experiment.

Which is, in a roundabout way, why the eyes of the world's physicists are now trained on a tiny village in northern Minnesota. "It is a very important experiment," acknowledges John Bahcall, a collaborator on Davis's Homestake study who is now a researcher at the Institute for Advanced Studies in Princeton, New Jersey, and one of the world's leading theoretical physicists. "All of us are looking over the shoulders of the MINOS scientists to see how well they are doing and what they may learn."

Even as the MINOS experiment gears up, however, Marshak is engaged in another project, which, if successful, could make Tower-Soudan one of the most prestigious addresses in all of science.


The idea of a national underground laboratory started floating around late in 2000, after Homestake Mining Co. announced its intention to close the South Dakota site. The plan, Marshak explains, was to construct a lab for all manner of cutting-edge experiments--high-energy physics as well as chemical and biological studies that needed to be shielded from solar radiation. The lab would be funded by the National Science Foundation, the federal agency that is also the primary benefactor of MINOS. It was an ambitious plan--with a projected initial cost of $280 million, the facility would be one of biggest public science projects in recent history.

In the winter of 2001, Marshak led a committee of scientists considering possible locations for the lab. "We traveled something like 40,000 miles in six weeks," he says. "We were doing things like going to Japan for two days, then going to Italy for two days--the kind of good, fun stuff where, by the time you get home, you have no idea where you've been or what time it is or what you've been doing, other than that your butt hurts."

Homestake was the scientists' favorite from the start. In addition to being the location of Davis's Nobel Prize-winning neutrino study, the mine was, at a mile and a half, much deeper than any other site in the U.S. However, Marshak's committee also considered a site near San Jacinto, which had the not-inconsiderable advantage of being located in southern California rather than in South Dakota; and a federal waste-storage site in New Mexico. According to Marshak, the Soudan site was, at best, an afterthought, a possible backup if all other options collapsed.

South Dakotans were, naturally, eager to attract the project. In 2001, then-Senate Majority Leader Tom Daschle drafted legislation in preparation for turning the mine over to the state. "I am absolutely confident we can get it done this year, probably much sooner than that," he told the press. The people of Lead, South Dakota, a Black Hills town of 3,000 even more economically down-at-heel than Minnesota's Iron Range, also embraced the prospect, proclaiming an annual Neutrino Day and crowning a Miss Neutrino.  

Then things began to get messy. Barrick Gold Corporation, a Toronto company that had purchased the mine in 2001 with the intention of decommissioning it, began to complain about the quarter-million dollars a month it was spending pumping water out of Homestake. The company was willing to turn the property over to the state, but only on the condition that they be released from any future liability for environmental cleanup--a carte blanche indemnification that worried environmentalists.

By early 2003, negotiations between Barrick and the state of South Dakota were dragging on with no end in sight. Wick Haxton, a physicist at the University of Washington and an early proponent of the Homestake site, says that scientists began to have second thoughts. "We'd been told so many times that they were within a few months of a solution," he says. "Nobody really knew what was going on."

In April, a South Dakota judge ordered Barrick to keep Homestake's pumps running. Then, in early June, a group of eminent scientists including Stephen Hawking and a number of Nobel Prize winners sent a letter to Barrick and South Dakota Governor Mike Rounds virtually begging that the mine be kept dry. Scientists even flew in from around the country to picket at the mine's site. All to no avail, however: On June 10, Barrick turned off the pumps, and Homestake began filling, at a rate of 500 gallons per minute, with water. Then, in mid-August, South Dakota Congressman Bill Janklow, one of Homestake's staunchest boosters, was charged with second-degree manslaughter after a fatal traffic accident. Suddenly, the Homestake site began to look like something less than a fait accompli.


The people of Tower are understandably circumspect about the prospect of an enormous underground lab in their backyard--something about geeks bearing gifts, perhaps. Certainly, everyone agrees that a possible half-billion dollars in federal largesse would do wonders for the area. But Iron Rangers have been burned by pie-in-the-sky economic development schemes before. A failed chopsticks factory in Hibbing is, for many, emblematic of such bureaucratic muddling. It doesn't help matters that residents see the immediate utility of the quantum mechanics being explored in their mine as, roughly speaking, zero.

Nevertheless, prodded by recent events in South Dakota, some in Tower have begun to take seriously the possibility of a national lab. One early booster of the idea is Marshall Helmberger, who, for the past 15 years, has edited, published, and written much of the local weekly newspaper The Timberjay from an office on Main Street. In a June 14 editorial, Helmberger called on Minnesota's congressional delegation to get more involved in the effort to bring the project to Minnesota, writing that the lab "could give a much-needed boost to the Iron Range economy."

"The biggest single issue is job creation," says Helmberger. Construction of the lab would likely mean sinking another, deeper mine shaft adjacent to the Soudan site, as well as blasting out more huge underground caverns to house the scientists and their equipment. That, explains Helmberger, would translate into scores of stable, long-term jobs--precisely the sort the Range so desperately needs in order to survive. "There's been some job creation up here. But a lot of it has been in service-type jobs. If this lab were to happen, you're talking about hundreds of good-paying jobs. It would mean Tower would have significant population growth for the first time in decades. And there's a sense of pride in some respects that this cutting-edge science is going on here. It would really put the community on the map, even internationally in a way."

Yet, both Helmberger and Marshak agree that Soudan remains, at best, a dark horse. At present, Marshak says, the future of the project depends mostly on the vagaries of federal pork-barrel politics--compared to which, both iron mining and quantum physics are child's play. "I think there's at least a reasonable chance it will happen," he offers.

Back at the Iron Ore Bar, weak sunlight streams through the smoke-stained venetian blinds. Marjorie Lakoskey is making her afternoon cup of tea. She's heard talk of the proposed lab, too, but, having watched Tower ebb for 50 years, she tends to take a longer view than most. "Business has been quiet. Used to be a box factory down by the lake, but that closed. Then the drugstore went. Every little thing hurts. Now those fellas say they want to put their lab in. Hard tellin'." Lakoskey looks around her empty place and shakes her head. Gravity, it seems, will have its way.

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