Earlier this spring I visited the most nuclear-bombed place in the world. To get there, I traveled one afternoon with a group of Stanford University colleagues to Las Vegas, and early the next morning made my way past the one-armed bandits in the smoke-filled Monte Carlo Resort and Casino, and climbed aboard a charter bus that would drive us 65 miles north to the former Nevada Test Site, a 1,400-square-mile expanse of desert scrub, dry lake beds, and the occasional Joshua Tree. Mountains surround it.
Outside the security gate, there were two uncovered holding areas surrounded by a chain-link fence that was probably 10-feet-high, with a single port-o-potty in each. They're for the protesters that still come around from time to time. We stepped out of the bus, stretched our legs in the cool, thin desert air, showed IDs to security guards and clipped on our dosimeters, a standard precautionary procedure at a nuclear complex. After passing through the gate, a Wackenhut security guard checked us out, and we pulled out onto the main road that traverses the site, which is now known as the Nevada National Security Site.
As we drove north, the valley gave way to the open expanse of Frenchman's Flat, the dry lake bed that served as the site of the first atmospheric test, a one-kiloton device dropped from a B-50 Bomber flying overhead. Within the next decade, they would drop 99 more bombs there and in the surrounding areas.
In his book Nuclear Rites, anthropologist Hugh Gusterson described the enormous sense of anticipation that preceded nuclear blasts. "The most exciting tests were the ones where we had enormous difficulties," a weapons designer from the Lawrence Livermore National Laboratory tells him, "and through some enormous heroic development of solutions to problems we were able to save the test ... And the sense of reward then is just enormous, just fantastic." There's a fair bit of bravado, too. In John McPhee's 1973 book, The Curve of Binding Energy, he described weapons designer Theodore Taylor lighting a Pall Mall off a nuclear detonation of a device called Scorpion in the Nevada desert.
The light came first, and then the waves and waves of heat. Many seconds later came the sound, which varied from a dull thud to a sharp crack. Scorpion, on its day, spread out into the sky in a way that indicated at once a yield in the range its designer wanted--a fantastic hint of how light and compact a nuclear-explosive device could ultimately be. Fifteen seconds after Scorpion flashed, Ted reached down to the parabolic mirror beside him and took from behind it a smoldering Pall Mall. He drew in a long, pleasing draught of smoke. He had lit a cigarette with an atomic bomb.
Perhaps the most staggering remains of large-scale testing are at the Sedan Crater, the result of a 1962 detonation. The test, just months before the Cuban Missile Crisis, was part of a plan called the Plowshare Program, in which U.S. officials wanted to see if there were ways to use nuclear bombs for peaceful purposes like excavating massive areas to build canals or harbors.
According to an official history of the test, the 104-kiloton blast "lifted a huge dome of earth 290 feet in the air, moved 6.5 million cubic yards of earth and rock," and "sent a cloud of radioactivity off in the direction of Salt Lake City," 400 miles away. What remains today is a crater that's 1,200 feet across and 320 feet deep, and a small metal platform installed for tourists like us to see the astonishing damage.
There's so much interest in this site that National Security Technologies LLC, the company that manages it on behalf of the Department of Energy, gives public tours for which tickets must be reserved far in advance. But the guide on our trip, arranged by special invitation, was Stephen Younger, president of the company. A nuclear weapons designer, he studied physics at Catholic University and then the University of Maryland, and now, in addition to his day job, does scholarly anthropological work studying the roots of human violence.
Younger says that when Gene Burke, the fellow who designed the device that detonated for the Sedan test, talked about it, he had a tear in his eye because he was so proud of the technical accomplishment. In one of Younger's books, Endangered Species: How We Can Avoid Mass Destructionand Build A Lasting Peace , he described a crater of particular interest to himself: it "was only about 500 feet across and 50 feet deep; there were certainly bigger ones at the Nevada Test Site. What was special about this one was that it was my crater, made with the first nuclear explosive that I had designed on my own. What had started as a pencil sketch eighteen months before ended in a fireball hotter than the surface of the sun, an energy pulse that vaporized thousands of tons of rock to create a huge bubble over a thousand feet below the desert floor." As he walked up to the edge, he wrote, "there was a sense of accomplishment, of having done something that was important and having done it well." It was also the moment, he wrote, that he understood in his heart as well as his mind, "the magnitude of destruction that could be caused by nuclear explosions."

Younger would be among the last to feel that way. In September 1992, the first President Bush declared a moratorium on nuclear testing. Policymakers have since decided that designing new weapons might lead to more proliferation. As a result, Younger says, the number of people who have designed, built and tested a device, and are actively seeking out new designs can be counted on one hand, if not one finger.
This has all sorts of implications, including the fact that it means the knowledge of how to build a nuclear weapon could risk, in a sense, being unlearned over the next few generations. Riding through the desert, one of my traveling companions, a postdoctoral fellow named John Downer, mentioned his studies of the concept in epistemology known as tacit knowledge. The idea is that certain knowledge cannot easily be transferred through lists of instruction, and is therefore extraordinarily difficult to teach. The most obvious example, Downer says, is trying to explain to someone how to ride a bicycle; a person just has to get a feel for it and learn. Similarly, it is said that the Stradivarius violin is impossible to reproduce. Even though one can find how-to directions for building violins in any number of places, there has always seemed to be something special about these Italian masterpieces that make if difficult for even a master luthier to replicate.
The question, then, is whether the same is true of nuclear weapons: Are they just so complex that at some point explicit directions aren't enough? If the answer is yes, that may be good news from a nonproliferation perspective because it would suggest that concerns about terrorists figuring out how to build a nuclear bomb are overblown. A written list of instructions wouldn't get someone very far with construction if they didn't understand the properties of plutonium -- the most complex of all the elements -- or how the many different components of bomb building fit together. Building a nuclear device just isn't that easy.
Younger observes that the fact that even advanced countries like France initially struggled to build the bomb shows just how difficult it is to bring all of the requisite knowledge together. "On a tour of the French nuclear weapons museum," he wrote in his 2009 book, The Bomb: A New History, "I asked my host, 'Why on earth did you do that?' - referring to certain features of their early designs. His answer was, 'We just didn't know any better.'"
From the standpoint of U.S. strategy, however, there are other potential implications. Younger says other nations, such as Russia, continue to invest in new, modern designs and young nuclear designers. That encourages the passage of knowledge from one generation to the next. But without modernizing or testing in the U.S., scientists are largely involved in mathematical modeling, scaled down versions of testing, or what the University of Chicago anthropologist Joseph Masco calls "an increasingly virtual bomb." "You're never doing the real thing," Younger says.
Younger adds that he has complete confidence in our nuclear stockpile today. But in The Bomb he argues that the only way to truly understand nuclear weapons is to test devices. "Computer simulations are just that -- imitations of the real thing," he writes. "And I know of no way to be sure that a calculation produces an exact rendition of what happens in nature."
This view has its critics, including many of the people now working in the nuclear weapons industry. What's more, even if Younger is correct, a return to testing is a non-starter in the policy world. Many prominent nuclear experts believe the risks of doing so far outweigh any potential benefits. President Obama's vision of a world free of nuclear weapons, outlined two years ago in Prague, included a vow to push forward with Senate ratification of the Comprehensive Test Ban Treaty.
Younger himself says that his belief that the U.S. cannot maintain its nuclear arsenal indefinitely without testing does not mean he advocates a return to it. He argues instead that policymakers' have options, none of them perfect, that include accepting a lower confidence in the U.S. arsenal and trying to compensate for it; introducing a new, more rugged class of nuclear weapon; or accepting "the political fallout resulting from an occasional nuclear test."

With that, down the shaft we went, whisked away in a steel elevator called a Man Cage. We emerged at the bottom into a hallway that was slightly wet to keep the dust down. On a white board, Younger showed us what happens to plutonium as it ages, and explained that it is so complex that even those who understand it best still do not fully comprehend its properties. Thus the need for what are called subcritical experiments: putting tiny bits of plutonium, maybe as little as a few grams, under enormous heat and pressure, and taking an X-Ray snapshot of it to understand the effects of aging. The advantage of doing this underground is that each piece of plutonium can then be secreted away in an alcove called a "zero room" never to be seen from again.
Emerging back into the sunlight, we headed for our next stop: the Nonproliferation Test and Evaluation Complex, otherwise known as the "world's largest facility for open air testing of hazardous toxic materials and biological simulants" (pictured below). One of the things they do there is make homemade explosives of the sort that might be found in conflict zones. One recipe: take 250 pounds of ammonium nitrate and diesel fuel, mix and cook this witches' brew, then dry it. Doing so helps authorities see what the process looks like and understand how to defend against it. When they're done, they blow it all up. "We blow everything up we make," says Michael Horst, facility manager.

Horst and his colleagues also use the vast open spaces to provide customers like DuPont with test beds for practicing their responses to emergencies, like, say, a spill of 450 pounds of chlorosulfonic acid. "We can release any chemical they want," he tells me later, including chlorine and hydrogen cyanide in amounts that are immediately dangerous to human life and health. "We release some really nasty stuff." On one wall, we noticed a sign of the organizational logo that is designed by the facilities manager: a particularly ghoulish skull with beady red eyes and crossbones of lighting and a hammer, all under the slogan, "If it's a kill'r we'll spill'r." In an office near the door, they sold tchotchkes with the logo emblazoned on it. We all bought mugs and t-shirts, climbed back on the bus and settled in for the ride back to Las Vegas.
As we drove away, Younger told me we only visited a fraction of the Rhode Island-sized site. In a way, though, we traveled a great distance: from the early days of the Cold War to the current and more commonplace threats of improvised explosive devices and large-scale accidents. The latter may not be the sublime stuff of the nuclear blast, or the mushroom cloud visible from miles away. But they made questions like whether the bomb can ever be unlearned seem like an abstraction. Whatever the answer, extraordinary dangers remain.