Since that time, "deep geological disposal" has replaced shallow trenches as our preferred nuclear-waste-storage technique. But another, more abstract problem—raised by the Hanford message in a bottle—remains unsolved: not how to store waste but how to label it. Not what container to use or where to bury it but how to explain the long-term dangers of what's inside to a trespasser. This seemingly simple conundrum (just use a radiation hazard symbol!) is complicated by the fact that such a trespass would prove lethal if it took place not only in 60 years but in 10,000 or 100,000. China, the planet's oldest continuous civilization, stretches back, at most, 5,000 years. And the world's oldest inscribed clay tablets—the earliest examples of written communication—date only from 3,000 or 3,500 B.C. It's impossible to say what apocalyptic event might separate 21st-century Americans from our 210th-century successors. Successors, mind you, who could live in a vastly more sophisticated society than we do or a vastly more primitive one.
Communicating the dangers of nuclear waste to unfathomably remote descendents may seem like a topic best left to third-drink philosophers in dorm rooms. It's actually been left to the most humdrum of all Cabinet-level departments after commerce, agriculture, and the interior: the Department of Energy, which oversees the disposal of radioactive trash at the Waste Isolation Pilot Plant near Carlsbad, N.M. According to government guidelines, DoE must plan for the continuing safety of the site over the next 10 millenniums.
So in 1991, the department (through Sandia National Laboratories) hired 13 linguists, scientists, and anthropologists at a cost of about $1 million to devise a conceptual plan for a 10,000-year marker system. DoE has yet to hash out the practical details, and probably won't until just before the pilot plant closes in the 2040s. Yet the summary report, dryly titled "Expert Judgment on Markers To Deter Inadvertent Human Intrusion Into the Waste Isolation Pilot Plant," is a bizarrely fascinating read. Since its publication in 1993, there have been sporadic flurries of media interest in its existence—notably in 2002, after the Senate voted to authorize Yucca Mountain as a permanent waste repository—but few considered assessments. The paper takes seriously the quixotic goal of warning far-off civilizations and ultimately proposes a system as elaborate as it is futile.
The academics dismiss, out of hand, a "Keep Out" sign—a woefully lacking solution, since nuclear waste will remain dangerous much, much longer than such a message would remain intelligible. David Anthony, author of The Horse, the Wheel, and Language, argues that "very few natural languages, those that are learned and spoken at home, remain sufficiently unchanged after a thousand years to be considered the 'same language.' " Case in point: Although modern English grew out of Anglo-Saxon, Americans need either a translation or special expertise to make their way through the Anglo-Saxon epic, Beowulf. Radiation-hazard symbols, as well as other icons immediately recognizable to 21st-century observers, are similarly insufficient. A red circle with a diagonal slash, the report notes, could look like a pictograph of a hamburger if knocked on its side. In a telephone interview, Harvard historian of science Peter Galison—who has lectured on the permanent-markers project—added that a skull-and-crossbones is also too ambiguous: Even today, it connotes danger only to some. Latin Americans may associate it with the Catholic Day of the Dead holiday—during which celebrants wear skull masks and bring sugar skulls to graveyards. An intruder who happens to be familiar with pirate lore might assume the image signifies buried treasure.
Even if future trespassers could understand what keep and out mean when placed side by side, there's no reason to assume they'd follow directions. In "Expert Judgment," the panelists observe that "[m]useums and private collections abound with [keep out signs] removed from burial sites." The tomb of the ancient Egyptian vizier Khentika (also known as Ikhekhi), for example, contains the inscription: "As for all men who shall enter this my tomb … impure … there will be judgment … an end shall be made for him. … I shall seize his neck like a bird. … I shall cast the fear of myself into him." It's possible that the vizier's contemporaries took Khentika at his word. But 20th-century archaeologists with wildly different religious beliefs had no reason to take the neck-cracking threat seriously. Likewise, a scavenger on the Carlsbad site in the year 12,000 C.E. may dismiss the menace of radiation poisoning as mere superstition. ("So I'm supposed to think that if I dig here, invisible energy beams will kill me?") Hence the crux of the problem: Not only must intruders understand the message that nuclear waste is near and dangerous; they must also believe it.
The report's proposed solution is a layered message—one that conveys not only that the site is dangerous but that there's a legitimate (nonsuperstitious) reason to think so. It should also emphasize that there's no buried treasure, just toxic trash. Here's how the authors phrase the essential talking points: "[T]his place is not a place of honor … no highly esteemed deed is commemorated here." Finally, the marker system should communicate that the danger—an emanation of energy—is unleashed only if you disturb the place physically, so it's best left uninhabited.