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Views expressed by guest or resident columnists are entirely their own.

Gregory Benford is a Nebula winner and a former Worldcon Guest of Honor. He is the author of more than thirty novels, six books of non-fiction, and has edited ten anthologies.

A SCIENTIST'S NOTEBOOK:
DEEP TIME

by

Gregory Benford

Modern technology projects our grasp across great distances. Our Voyager space craft glide serenely beyond the solar system, headed out forever. Less obvious is our technology's reach through time.

We peer backward through tree ring dating (good to about 5,000 years), Arctic ice bores (which measures layers of ice, good to about 200,000 years), and nuclear dating methods (good for the Earth's age, about 4.6 billion years). Through the astronomical time machine given by light's finite speed—the so-called "look-back" time—we can look out to several more billion years, culminating in the recent scrutiny of the early universe radiation, we have seen structure as it was about fifteen billion years ago, only perhaps a few million years after the universe began.

We are much less aware of our reach in the other direction, the future. The Voyager probes carry plaques rhapsodizing over our culture, gestures which might be read billions of years from now. Cosmic time capsules. But on Earth, until this century, the Pharaohs were the champions at knowingly reaching down to their posterity—less than 6,000 years.

Nuclear physics changed all that. Now we leave a legacy—on the earth's surface, not gliding serenely though space—through the long half-lives of the radioactive byproducts of nuclear power, weaponry and medicine. These will be around for tens of thousands of years. Chemical wastes may also be as persistent.

In my last column I described my adventures when asked by the Department of Energy, acting for Congress, to estimate the risks of inadvertent disturbance of a projected nuclear waste repository (the Waste Interment Pilot Project) for the next ten thousand years. We estimated the probability at a few percent.

I believe eventually even Not In My Back Yard politics will be unable to stop interment of wastes in the salt flats of southern New Mexico. Whether one regards this as a good idea or not, the political fact is that we have largely run out of time to decide how to store wastes. Holding even low grade radioactive wastes in "swimming pools", as we do now, runs real risks and can't be simply continued for, say, another century. The stuff leaks, gets into ground water. Increasingly, the public wants all sorts of wastes, nuclear or chemical or biological, interred far, far away from them.

 

Given this, how will we protect future generations from such deep-future hazards? How to warn them off the site? A second panel discussed the marker problem in detail, with necessarily science-fictional logic. I found all this to be just about the most fun possible while working for the government.

One illuminating moment came after a day of intense discussion among the so-called Expert Judgment Panel. I was the only science fiction writer there, but the group spanned most sciences, including people like Theodore Taylor, the inventor of the Project Orion idea—spaceships driven by nuclear warhead explosions—in the 1950s. We decided to detour near the Pilot Project site to find the site of Project Gnome, a nuclear test.

In 1961 Project Plowshare exploded a small warhead a thousand feet down in the same salt flat which the Pilot Project wanted to use for nuclear waste storage. The idea was to heat up rock salt and use the molten mass's residual heat to drive steam through electrical generators.

It failed. The blasted-out cavity soon caved in, burying the molten salt. One would think this might have occurred to an engineer before they tried it. But that was in the golden years of nuclear development, when ideas got tried for size right away, rather than spending a decade or so mounting up piles of paper studies.

We all got out of our government-gray cars and the drivers waved vaguely at the flat scrub desert, dust devils stirring among the sage. We spread out, shooing away grazing cattle. A hoot of discovery. A granite slab, tombstone-sized, bearing a copper plaque running green from oxidation. In big letters, PROJECT GNOME, followed by GLEN SEABORG, then Director of the Atomic Energy Commission, and in smaller type the generals and bureaucrats who had overseen this failed effort.

I walked around the slab and saw another plaque, its raised lettering rusted and nearly unreadable.  We could barely make out some technical detail: kilotons, warhead type, purpose, amount of residual radioactivity. At the very bottom,

THIS SITE WILL REMAIN DANGEROUS FOR 24,000 YEARS.

If we hadn't known our quarry, we would not have found it easily out on the dry plain. Drab, small, it did not announce itself.

We could tell, though, that it had been moved. Apparently, cattle needing a rubbing post had in thirty years nudged the slab several meters. How far away would it be in 24,000 years?

Our team, charged with estimating the chances of inadvertent intrusion into the Pilot Project salt flat buried 2,150 feet down, also suggested possible strategies for placing warning markers. We envisioned "miner moles" which would slowly tunnel through deep strata, searching for neglected lodes of valuable minerals. This implied a "spherical strategy"—deploying markers apparent from above, beside and even below the deep repository.

The Pharaohs used one big, obvious marker for their tombs, the pyramid; we suggested as well small, dispersed tags, visible to "eyes" which could see magnetic or acoustic or radioactive signs. Acoustically obvious markers could be made—solid rock unlikely to shatter and lose shape in the salt beds.

Large granite disks or spheres might be easily perceived by acoustic probes. They could be arrayed in two straight lines in the repository hallways, intersecting perpendicularly at the center: X marks the spot. Magnetic markers could produce a clearly artificial pattern, the simplest being a strong, single dipole located at the Pilot Project center. These could be magnetized iron deposits, flagrantly artificial. Specially made high-field permanent magnets could produce a clearly artificial pattern at the hazard's center. (This I stole from 2001: A Space Odyssey; thanks, Arthur.)

Radioactive markers could be left at least some meters outside the bulk of the waste rooms and drifts—say, small samples of common waste isotopes. Like similar weak but telltale markers left on or near the surface, these have the advantage of showing the potential intruder exactly what he is about to get into. No language problem.

All these markers should be detectable from differing distances from the waste itself. Acoustic prospecting in the neighborhood could pick up the granite arrays. Magnetic detectors, perhaps even a pocket compass, could sense the deep iron markers from the surface. Ultra-sensitive particle detectors might detect the waste itself, or small tags with samples of the waste buried a safe distance below ground. (These would be small amounts, of no health risk to the curious—weaker than a radium watch, yet slowly decaying.)

But there's a more basic decision: whether to mark hazardous sites at all. Perhaps the best warning is no warning. The only major inviolate burial site—King Tut's Tomb—provided us with much of the Egyptian legacy; unmarked and forgotten because its entrance was soon buried under the tailings of a grander tomb, it escaped the grave robbers, who may well have included the priests of the time.

Could a hidden or forgotten hazard protect itself from harming future generations best of all? A "soft" surface marker which erodes in a few centuries would cover the short-term possibilities, I argued, and then avoid curiosity seekers in the far future. High technologies would still be able to sense the buried markers, after all.

Of course, this imposes ignorance on our descendants, who may wish to avoid the place but not know quite where it is. Also, low-tech wildcatters drilling for scarce resources in some re-emergent future would have no warning.

Still, I proposed this, mostly for fun. I suggested that standard-issue government concrete would be useful here: it disintegrates in about a century or so, providing everyone with a big, noticeable object for a reassuring lifetime, then erasing it.

Nobody much liked the idea, as I'd guessed. One of the major psychic payoffs in considering markers at all is the Pharaoh effect: the impulse to build a big monument to...well, yourself. Or at least your era. They won't forget us right away! Even better if somebody else (the poor taxpayer) foots the bill.

Considering vast stretches of time tends to bring on lofty sentiments. But the present is mostly ruled by money, so as an example, the panel worked out the costs of erecting a Cheops pyramid, which has lasted 4,600 years. Using square blocks of granite, 9x9x9 feet, one could engrave all six sides with warning messages.

That way, if the exterior faces wear away, lifting one block would uncover a fresh inscription. The pyramid core could hold, not a Pharaoh, but a set of more detailed messages, for those in the future who will dig in out of simple curiosity (archaeologists), or those suspecting that there's a treasure in there somewhere, or else why go to all the trouble?

Making all the blocks of the same material eliminates problems arising from different thermal expansion rates, which can cause cracks. Tapering the pyramid less steeply than the natural slope of a sand pile would avoid much damage from earthquakes. Like the Cheops pyramid, the load bearing stress would be wholly compressive, using only gravity to hold it all together, with no tensile forces which open cracks.

Trouble is, that's expensive. If a single inscribed block costs $5,000, they would cost $62 million, about six percent of the to-date cost of the Pilot Project, though less than one percent of the projected cost over the site's entire active use.

This is no accident. Considering many different markers taught a tough lesson: longevity trades off against cost. There is no simple, good, cheap marker.

Thinking like a cost-conscious Pharaoh, suppose we make the blocks smaller, to ease assembly costs. That makes them easily climbed, increasing vandalism. It also means ordinary sized people can reach all the inscriptions without a ladder.

That opens a larger question: the greatest threat to the Pharaoh's pyramids and to a nuclear marker pyramid is pesky, grasping humans. In historic sites, metals quickly vanished, and buildings were quarried.

Useful, cubic blocks especially might be carted away. The Cheops pyramid lost all its cladding marble skin quite quickly; ancient Greek travelers remarked on how they could be seen as bright white beacons, far across the desert, but no modern observer has found any of that left. (Indeed, it is worth remembering that the Washington Monument was vandalized immediately after it opened in 1886, and the interior stairwell had to be permanently closed. Vandals don't respect greatness.)

One could offset such problems. For example, using interlocking but irregularly shaped blocks would stop their use elsewhere. Making the materials outright obnoxious might help, too—but stones that exude a bad smell steadily evaporate away, destroying the structure.

A better path might be to make the marker hard to take apart. Here the clear winner is reinforced concrete. The Cheops would take much less work to tear down than it was to build up, but the reverse is true, for example, of the Maginot and Siegfried lines of the World Wars. Despite intense political pressure from local communities, the bunkers have proved to be too costly to take away. Contrast the Colosseum in Rome, which has suffered greatly, with most of its building stones 'recycled' into houses.

Probably the ancients understood this principle quite well, since Stonehenge (1500 BC) used blocks of up to 54 tons and English tombs (2000 to 3000 BC) used stones of up to 100 tons. They thought the trouble was worth long-term insurance.

Our experience with concrete goes back 2,000 years; six of the eight Roman bridges built across the Tiber are still in service! We must be a bit cautious here, though, because it is quite possible that Roman concrete was better than ours.

This is because strong concrete demands a low ratio of cement to water, a very stiff mix that is tough and pricey to work with. The Romans used slave labor to ram firm concrete into place, and today's contractors pump a sloppy, muddy mix through pipes. This can make the concrete twenty times less durable than the dry, high-grade sort.

But even such precautions run into a sad lesson of history. Pyramids and other grand structures often mark honored events or people. This might be the primary message a pyramid sends: here's something or somebody important. Why not come see? And surely such a big monument won't miss this little chunk I can pry off here...

This led both panels of experts toward marker systems—different-sized components, relating to each other so that the whole exceeds the sum of the parts. Vandalism doesn't usually take everything, so the message gets through in a holographic sense. (About a third of the Stonehenge stones are missing, yet we can infer the entire design without much dispute. People differ over whether there is evidence of Mycenaean Greek influence in the architectural niceties, or just what the building was truly for, but its layout is clear.)

The best way to insure survival of truly enormous structures against both weather and pilfering is to make them out of dirt. Prehistoric mounds last well. The Romans build a long wall to keep out the Teutonic tribes, stretching from the Danube to the Rhine. Even in that wet climate, while the wood is completely gone, the earth berms survive. Hadrian's Wall in England is a similar case. The record is held by a chambered passage grave which is today a simple mounded earthwork in Ireland, older than 5,000 years.

The panels thought along truly gargantuan lines. A simple berm of, say, thirty-five meters wide and fifteen meters high, completely ringing the Pilot Project area, would demand moving about 12 million cubic meters of earth. The Panama Canal moved 72.6 million cubic meters, and the Great Pyramid occupies 2.4 million cubic meters. So this will be one of the grandest public works in history.

That's initially to greet the tourist, who might mistake even a huge berm for a natural hill, ten thousand years from now. To get their attention, the panels wanted a ring of monoliths, probably of granite, bearing a variety of symbolic, pictographic and linguistic inscriptions.

Stonehenge and other sites have taught us that to keep monoliths upright, more must be buried than is exposed, or else it should be firmly stuck in a rock layer below. They will probably have to be erect, too, because slanted monoliths have a poor track record. They develop tensile stresses at the surface, and in brittle material like granite, once a crack develops, it reaches a critical length—and then the whole monolith splits.

There are good reasons to make none of these from composite materials—thermal stresses, as in the pyramid. This means the monoliths will be imposing, homogeneous rock, arranged in patterns that convey our message of threat.

But prudence suggests that we should also scatter small markers around the site, perhaps slightly buried, which attract attention even if the monoliths somehow fail. The panels considered electrically active markers, reasoning that thermo-electric power (which would use the temperature difference between the surface and 100 feet below) or solar power is available.

The trouble is that even the most reliable electronic components, such as those used in undersea cables, only last a few centuries. More reliably, we could embed contrasting dielectric materials in the site surface, which reflect radar differently. These would give a good, artificial signal to airplanes or even orbiting satellites.

We could also bury time capsules, just a bit below the usual souvenir-hunter's digging zone, made of tough stuff—baked clay, tektite-like glass. These might be tablets, far better than the mud tablets the Babylonians left (inadvertently).

Finally, everyone agreed that there should be some sort of central chamber, where detailed messages are left. It would have a lot of plane surfaces for messages and could be completely buried. It can also include buried magnets, which would be detectable with a good pocket compass even if all surface signs of the site vanish. Their fields could point at the buried waste.

If we elect to put this central room above ground, there are several ways to go. We could use messages chiseled into granite, such as the biography of a Persian king, Darius I, which has lasted over 2,000 years in open, dry weather. It had to contend with blown sand and carbonic acid in rain, but not with the sulfuric acid belched out by coal-fired plants, as now exist within a few hundred miles of the Pilot site.

Beyond 2,000 years, consider a faint carving of a square-hilted dagger on the inner surface of a sarsen stone, which survived in an open field at Stonehenge for perhaps 4,000 years. So expecting detailed messages to last 10,000 years is doubtful.

Probably a buried vault is our best bet—just what the Pharaohs chose. It would be the most interesting and complex marker in the whole site, well hidden, purposely designed to be the world's longest-lasting human artifact. If the above-ground monoliths were strikingly beautiful, maybe the locals will preserve the site because it is pleasing, rather than for its message—thus letting the message travel longer through time, perhaps to a more distant era which needs it more. Saving the striking, obvious structure would leave the vault below undisturbed.

A visitor would meet first the encircling earthworks, then a ring of monoliths—say, as wide as the length of a soccer field—and finally some central marker that would tell (or suggest) the buried chamber. The idea is to draw them in, make them feel psychologically enclosed in the monolith circle, become "involved" with the stone monuments at the center, induced to read the pictographs and messages inscribed.

Maybe it would be smart to convey the general emotional message in some direct way, independent of language. Suppose we erect some aerodynamically streamlined monoliths with gaps between them. These resonate in the wind, sending forth a hollow, mournful note. Most likely, such wailing rocks could establish a legend about the site that transcends language.

There's the rub—getting through to cultures and languages we cannot anticipate. The future may see our scientific age as a passing phenomenon, an idiosyncratic momentary deflection from some One True Path we would not even recognize. So how can we expect them to share our (often unspoken) assumptions, and thus read our warnings?

Generally, we can't. But there are ways of shaping a message so that it has some plausible chance of sailing intact across the great ocean of Deep Time. I'll take up those methods in my next column.

We may not be able to predict the future, but we can reach it nevertheless.  One could characterize nuclear waste containers at WIPP as hazardous time capsules sent into the future, not knowing where they will land or what effect they will have, hoping (perhaps even assuming) that technology will solve the problems they currently represent.

In a sense the Pilot's task runs against powerful human archetypes. We aren't saying, as burial ceremonies do, "Take this child—his name is Klug." or "This mummy of our king we place here, for he needs resurrection." Instead, we're trying to say: We buried this and it's bad.

The only other alternative to this millennia-spanning waste problem is to forswear hazardous technologies in the first place; but we already have plenty of waste, with more accumulating from medical uses alone, so there really is no going back. Besides, how do you get people to give up x-rays and cancer treatments? We are stuck with our largely unrecognized reach into Deep Time. Seemingly minor acts today can amplify through Deep Time, leaving legacies we do not intend and in fact may not even know.

In closing, consider Trinity Site, the spot where the first A-bomb was tested in 1945. At Ground Zero in White Sands, New Mexico, the blast left a glassy crater of fused aluminum silicates a quarter mile across and twenty-five feet deep.

Now there is nothing. Dry winds had filled the crater, tough desert plants had cracked it. Radiation levels are very slightly higher than the background of ordinary scrub desert. Life had reclaimed its territory in a single human generation. The "message" of Trinity is gone.

The easy problem of Deep Time is time's rub. Greater still is the abyss of culture we must cross.

The barren Trinity site recalls Shelley's "Ozymandias":

And on the pedestal these words appear:

"My name is Ozymandias. King of Kings:

Look on my works, ye Mighty, and despair!"

Nothing besides remains. Round the decay

Of that colossal wreck, boundless and bare

The lone and level sands stretch far away.

Deep Time is as much the province of the poet as of the scientist.

Copyright © 1993 by Abbenford Associates

 

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