Such control is tempting. Like most bright promises, it is easy to see possibilities, less simple to see what is probable.

Nanotech borders on biology, a vast field rich in emotional issues and popular misconceptions. Many people, well versed in 1950s B-movies, believe that radiation can mutate you into another life form directly, not merely your descendants -- most probably, indeed, into some giant, ugly, hungry insect.

Not all fiction about nanotech or biotech is like this -- there are good examples of firm thinking in Greg Bear's Queen of Angels and the anthology Nanodreams edited by Elton Eliott, and elsewhere.

All too often, though, in the hands of some science fiction writers, nanotech's promised abilities -- building atom by atom for strength and purity, dramatic new shapes and kinds of substances -- lead to excess. We see stories about quantum, biomolecular brains for s.p.a.ce robots, all set to conquer the stars.

About miraculous, overnight reshaping of our entire physical world -- the final victory of Information over Ma.s.s. Or about accelerated education of our young by nanorobots which coast through their brains, bringing encyclopedias of knowledge disguised in a single mouthful of Koolaid.

Partly this is natural speculative outga.s.sing. One can make at least one safe prediction: such wild dreams will dog nanotech. The real difficulty in thinking about possibilities is that so little seems ruled out. Agog at the horizons, we neglect the limitations -- both physical and social.

Nanotech holds forth so much murky promise that writers can appear to be doing hard sf, while in fact just daydreaming. Not only is the metaphorical net not up on this game of dream tennis, it isn't even visible.

People can tell disciplined speculation from flights of fancy when they deal with something familiar and at hand. Nanotech is neither. Worse, it touches on the edge of quantum mechanical effects, and nothing in modem physics has been belabored more than the inherent uncertainties of the wave-particle duality, and the like. People often take uncertainty as a free ticket to any implausibility, flights of fancy leaving on the hour.

Developing a discipline demands discipline. Dreaming is not enough.

One point we do know must operate in nanotech's development: nothing happens in a vacuum. The explosion of biotech, just one or two orders of magnitude above the nanotech scale, will deeply shape what comes of nanotech.

The transition is gradual. The finer one looks on the scale of biology, the more it looks mechanical in style. The flagella that let bacterium swim work by an arrangement which looks much like a motor, each proton extruded by the motor turns the a.s.sembly a small bit of a full rotation. Above that scale, the "biologic" of events is protean and flexible, compared with mechanical devices. Below it, functions are increasingly more machine-like. The ultimate limit to this would be the nanotech dream of arranging atoms precisely, as when a team at IBM spelled out the company initials on a low temperature substrate. But widespread application of such methods lies probably decades away, perhaps several. The future will be vastly changed by directed biology, before nanotech comes fully on stage.

Consider a field of maize -- corn, to Americans. At its edge a black swarm marches in orderly, incessant columns.

Ants, their long lines carrying a kernel of corn each. Others carry bits of husk; there an entire team coagulates around a chunk of a cob. The streams split, kernel-carriers trooping off to a ceramic tower, climbing a ramp and letting their burdens rattle down into a sunken vault. Each returns dutifully to the field. Another, thicker stream spreads into rivulets which leave their burdens of sc.r.a.p at a series of neatly s.p.a.ced anthills. Dun-colored domes with regularly s.p.a.ced portals, for more workers.

These had once been leaf-cutter ants, content to slice up fodder for their own tribe. They still do, pulping the unneeded cobs and stalks and husks, growing fungus on the pulp deep in their warrens. They are tiny farmers in their own right. But biotech had genetically engineered them to harvest and sort first, processing corn right down to the kernels.

Other talents can be added. Acacia ants already defend their mother trees, weeding out nearby rival plants, attacking other insects which might feast on the acacias. Take that ability and splice it into the corn-harvesters, and you do not need pesticides, or the dredge human labor of clearing the groves. Can the acacia be wedded to these corn ants? We don't know, but it does not seem an immense leap. Ants are closely related and multi-talented. Evolution seems to have given them a wide, adaptable range.

Following chemical cues, they seem the ant.i.thesis of clanky robots, though insects are actually tiny robots engineered by evolution. Why not just co-opt their ingrained programming, then, at the genetic level, and harvest the mechanics from a compliant Nature?

Agriculture is the oldest biotech. But everything else will alter, too.

Mining is the last great industry to be touched by the modem. We still dig up crude ores, extract minerals with great heat or toxic chemicals, and in the act bring to the surface unwanted companion chemicals. All that suggests engineering must be re-thought -- but on what scale? Nanotech is probably too tiny for the fight effects. Instead, consider biomining.

Actually, archaeologists have found that this idea is quite ancient. Romans working the Rio Tinto mine in Spain 2000 years ago noticed fluid runoff of the mine tailings were blue, suggesting dissolved copper salts. Evaporating this in pools gave them copper sheets.

The real work was done by a bacterium, Thiobacillus ferroxidans. It oxidizes copper sulfide, yielding acid and ferric ions, which in turn wash copper out of low grade ores. This process was rediscovered and understood in detail only in this century, with the first patent in 1958. A new smelter can cost a billion dollars. Dumping low quality ore into a sulfuric acid pond lets the microbes chew up the ore, with copper caught downhill in a basin; the sulfuric acid gets recycled. Already a quarter of all copper in the world comes from such bio-processing.

Gold enjoys a similar biological heritage. The latest scheme simply scatters bacteria cultures and fertilizers over open ore heaps, then picks grains out of the runoff. This raises gold recovery rates from 70% to 95%; not much room for improvement. Phosphates for agriculture can be had with a similar, two-bacterium method.

All this, using "natural biotech." Farming began using wild wheat -- a gra.s.s. Immunology first started with unselected strams of Penicillium. We've learned much, mostly by trial and error, since then. The next generation of biomining bacteria are already emerging. A major problem with the natural strains is the heat they produce as they oxidize ore, which can get so high that it kills the bacteria.

To fix that, researchers did not go back to scratch in the lab. Instead, they searched deep-sea volcanic vents, and hot springs such as those in Yellowstone National Park. They reasoned that only truly tough bacteria could survive there, and indeed, found some which appear to do the mining job, but can take near-boiling temperatures.

Bacteria also die from heavy metal poisoning, just like us. To make biomining bugs impervious to mercury, a.r.s.enic and cadmium requires bioengineering, currently under way. One tries varieties of bugs with differing tolerances, then breeds the best to amplify the trait. This can only take you so far. After that, it may be necessary to splice DNA from one variety into that of another, forcibly wedding across species. But the engineering occurs at the membrane level, not more basically --no nanotech needed.

This is a capsule look at how our expectations about basic processes and industries will alter long before nanotech can come on line. What more speculative leaps can we foresee, that will show biotech's limitations? -- and thus, nanotech's necessity.

Consider cryonics. This freezing of the recently dead, to be repaired and revived when technology allows, is a seasoned science fictional idea, with many advocates in the present laboring to make it happen. Neil R. Jones invented it in an sf story in the 1931 Amazing Stories, inspiring Dr. Robert Ettinger to propose the idea eventually in detail in The Prospect of Immortality in 1964.

It has since been explored in Clifford Simak's Why Call Them Back From Heaven? (1967), Fred Pohl's The Age of the p.u.s.s.yfoot (1969), and in innumerable s.p.a.ce flight stories (such as 2001: A s.p.a.ce Odyssey) which use cryonics for long term storage of the crew. Fred Pohl became a strong advocate of cryonics, even appearing on the Johnny Carson show to discuss it. Robert Heinlein used cryonics as part of a time-traveling plot in The Door Into Summer. Larry Niven coined "corpsicle" to describe such "deanimated" folk. Sterling Blake treated the field as it works today in Chiller. Cryonics is real, right now.

About fifty people now lie in liquid nitrogen baths, awaiting resurrection by means which must involve operations below the biotechnical.

Repairing frozen brain cells which have been cross-slashed by shear stresses, in their descent to 77 degrees Absolute, then reheated --well, this is a job nothing in biology has ever dealt with. One must deploy subcellular repair agents to fix freezing damage, and replenish losses from oxygen and nutrient starvation. A solvent for this is tetrafluoromethane -- it stays liquid down to minus 130 degrees Centigrade.

To further repair, one must introduce line-layers, workhorse cells to spool out threads of electrical conductor. These tiny wires could power molecular repair agents -- smart cells, able to break up and sort out ice crystals. Next comes clearing blood vessels, the basic housekeeping, functions which can all be biological in origin.

Then nanotech becomes essential. The electrical power lines could feed a programmed cleanup crew.

They would st.i.tch together gross fractures, like good servants dusting a room, clearing out the dendrite debris and membrane leftovers that the big biological scavenger units missed.

Moving molecular furniture around at 130 degrees below freezing will take weeks, months. One has to be sure the "molyreps" -- molecular repair engineers -- do not work too fast, or else they would heat the patient up all on their own, causing further shear damage.

How do they get the damaged stuff back in place, once they'd fixed it? Special units -- little accountants, really -- would have to record where all your molecular furniture was, what kind of condition it was in. They look over the debris, tag it with special identifying molecules, then anchor it to a nearby cell wall. They file that information all away, like a library. As repair continues, you slowly warm up.

These designer molecules must be hordes of microscopic fanatics, born to sniff out flaws and meticulously patch them up. An army that lived for but one purpose, much as art experts could spend a lifetime restoring a Renaissance painting. But the body is a far vaster canvas than all the art humanity had ever produced, a network of complexity almost beyond comprehension.

Yet the body naturally polices itself with just such mobs of molecules, mending the sc.r.a.pes and insults the rude world inflicted. Biotech simply learns to enlist those tiny throngs. That is true, deep technology --co-opting nature's own evolved mechanisms, guiding them to new purposes. Nanotech goes beyond that, one order of magnitude down in size.

Not necessary to get good circulation in the cells again -- just sluggish is enough. A slow climb to about minus a hundred degrees Centigrade. A third team goes in then, to bond enzymes to cell structures. They read that library the second team had left, and put all furniture back into place.

So goes the Introduction to Molecular Repair For Poets lecture, disguising mere miracles with a.n.a.logies.

Months pa.s.s, fixing the hemorrhaged tissue, mending tom membranes, splicing back together the disrupted cellular connections. Surgeons do this, using tools more than a million times smaller than a scalpel, cutting with chemistry.

Restriction enzymes in bacteria already act like molecular scissors, slicing DNA at extremely specific sites. Nanotech would sharpen this kind of carving, but much of the work could probably be bioengineered, working at larger scales.

With such abilities, surgeons can add serotonin-derived neurotransmitters, from a psychopharmacology far advanced beyond ours. They inhibit the switches in brain chemistry a.s.sociated with emotional states.

A patient reviving may need therapy, cutting off the memories correlated with those emotions that would slow recovery. Such tools imply medicine which can have vast social implications, indeed.

Here is where the future peels away from the foreseeable. Nanotech at this stage will drive qualitative changes in our world, and our world views, which we simply cannot antic.i.p.ate in any detail. All too easily, it looks like magic.

Suppose the next century is primarily driven by biotech, with nanotech coming along as a handmaiden.

Do we have to fear as radical a shift in ideas again, with nanotech?

Biotech looks all-powerful, but remember, evolution is basically a kludge. Organisms are built atop an edifice of earlier adaptations. The long, zigzag evolutionary path often can't take the best, cleanest design route.

Consider our eyes, such marvels. Yet the retina of the vertebrate eye appears to be "installed"

backwards. At the back of the retina lie the light-sensitive cells, so that light must pa.s.s through intervening nerve circuitry, getting weakened. There is a blind spot where the optic nerve pokes through the optical layer.

Apparently, this was how the vertebrate eye first developed, among creatures who could barely tell darkness from light. Nature built on that. The octopus eye evolved from different origins, and has none of these drawbacks.

Could we do better? A long series of mutations could eventually switch our light-receiving cells to the front, and this would be of some small help. But the cost in rearranging would be paid by the intermediate stages, a tangle which would function more poorly than the original design.

So these halfway steps would be selected out by evolutionary pressure. The rival, patched-up job works fairly well, and nature stops there. It works with what it has. We dreaming vertebrates are makeshift constructions, built by random time without foresight. There is a strange beauty in that, but some cost -- as I learned when my appendix burst, some years ago. We work well enough to get along, not perfectly.

The flip side of biology's deft engineering marvels is its kludgy nature, and its interest in its own preservation. We are part of biology, it is seldom our servant, except incidentally. In the long ran, the biosphere favors no single species.

The differences between nanotech and biotech lie in style. Of course functions can blend as we change scales, but there is a distinction in modes.

Cells get their energy by diffusion of gases and liquids; nanotech must be driven by electrical currents on fixed circuits. Cells contain and moderate with spongy membranes; nanoengines must have specific geometries, with little slack allowed. Natural things grow "organically," with parts adjusting to one another, nan.o.builders must stack together identical units, like tinker-toys.

The Natural style vs. the Mechanical style will be the essential battleground of tiny technology.

Mechanicals we must design from scratch. Naturals will and have evolved; their talents we get for free.

Each will have its uses.

Naturals can make things quickly, easily, including copies of themselves--reproduction. They do this by having what Drexler terms "selective stickiness" -- the matching of complementary patterns when large molecules like proteins collide. If they fit, they stick. Thermal agitation makes them smack into each other many millions of times a second, letting the stickiness work to mate the fight molecules.

Naturals build, and as time goes on, they build better -- through evolution. In Naturals, genes diffuse, meeting each other in myriad combinations. Minor facets of our faces change so much from one person to the next that we can tell all our friends apart at a glance {except for identical twins, like me).

These genes collide in the population, making evolutionary change far more rapid because genes can spread through the species, getting tried out in many combinations. Eventually, some do far better, and spread to everyone in later generations.

This diffusion mechanism makes s.e.xually reproduced Naturals change constantly. Mechanicals -- robots of any size, down to nanotech -- have no need of such; they are designed. There is no point in building into nanomachines the array of special talents needed to make them evolve --in fact, it's a hindrance. It could become a danger, too.

We don't want nan.o.bots which adapt to the random forces of their environment, taking off on some unknown selection vector. We want them to do their job. And only their job.

So nanotech must use the Mechanical virtues: rigid, geometric structures; positional a.s.sembly of parts; clear channels of transport for energy, information and materials. Mechanicals should not copy Naturals, especially in aping the ability to evolve.

This simple distinction should lessen many calls of alarm about such invisible, powerful agents. They can't escape into the biosphere and wreck it. Their style and elements are fundamentally alien to our familiar Naturals, born red in tooth and claw.

Nan.o.bots' real problem will be to survive in their working environment, including our bodies. Imagine what your immune system will want to do to an invading band of unsuspecting nan.o.bots, fresh off the farm.

In fact, their first generation will probably have to live in odd chemical soups, energy rich (like, say, hydrogen peroxide or even ozone) and free of Natural predators. Any escaping from their chemical cloister will probably get eaten -- though they might get spat right back out, too, as indigestible.

The "gray goo" problem of nanotech, in which ugly messes consume beautiful flora and fauna, need not occur, precisely because the goo will be gray. It need not have built into it the rugged, hearty defenses which are the down payment for anything which seeks to use sunlight, water and air to propagate itself.

Gray goo will get eaten by green goo -maybe by a slime mold, which has four billion years of survival skills and appet.i.te built in.

So nanotech will not be able to exponentially push its numbers, unless we deliberately design it that way, taking great trouble to do so. Accidental runaway is quite unlikely. Malicious nan.o.bots made to bring havoc, though, through special talents -- say, replacing all the carbon in your body with nitrogen -- could be a catastrophe.

When machines begin to design themselves, we approach the problems of Natural-style evolution. Even so, design is not like genetic diffusion. In principle, it is much faster. Think of how fast cars developed in the last century, versus trees.

That problem lies far beyond the simple advent of nanotech. It will come, but only after decades of intense development one or two levels above, in the hotbed of biotech.

What uses we make of machines at the atomic level will depend utterly on the unforeseeable tools we'll have at the molecular level. That is why thinking about nanotech is undoubtedly fun, but perhaps largely futile. Certainly such notions must be constrained by knowing how very much biology can do, and will do, long before we reach that last frontier of the very, very small.

Eater, May 2000 Skylife : s.p.a.ce Habitats in Story and Science (Editor), 2000 The Martian Race, 1999 Deep Time, 1999 Cosm, 1998 Matter's End, 1995 Sailing Bright Eternity, 1995 Furious Gulf, 1994 Chiller, 1992 (as Sterling Blake) Tides of Light, 1989 Great Sky River, 1987 In Alien Flesh, 1986 A Darker Geometry, with Mark O. Martin Heart of the Comet, 1986, with David Brin Artifact, 1985 Across the Sea of Suns, 1984 Against Infinity, 1983 Timescape, 1980 Nebula Award, Campbell Award, Ditmar Award, British SF Award Shiva Descending, 1980, with Wm. Rotsler Find the Changeling, 1980, with Gordon Eklund In the Ocean of Night, 1977 If the Stars are G.o.ds, 1977, with Gordon Eklund Nebula Award Jupiter Project, 1975 Deeper Than the Darkness, 1970 (ret.i.tled in 1978, The Stars in Shroud)

Deep Time

At its best, science fiction isn't just "fiction about science" -- it is science thinking about itself as a human agenda in the dimension of time. It necessarily speculates, making ranging forays into territories seldom illuminated coherently in our era of intense narrowness.

Any science fiction author hopes he gets the science right enough not to wrinkle the brow of real scientists. I am a professor of physics at the University of California at Irvine, but SF demands a broad knowledge no one can be sure of mastering.

So I hope specialists in the many areas I touch will not find my leaps into the cutting edge of a.s.sorted sciences too rough. Wherever possible, I've cemented my intuitions with travel, visits and detailed consultation. I feel that conclusions won from experience have a solidity that armchair ruminations do not.

Outright speculation is not rare in proper science, but it often arrives well disguised. Sometimes it is a short-term claim to a notion awaiting exploration, as when James Watson and Francis Crick laconically noted in the last sentence of their paper reporting the discovery of DNA's double helix that they saw the implications for reproduction: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material."

Our time can benefit from the vistas made possible by science and science fiction alike. When hatred and technology can slaughter millions in months, such terrors deprive life of that quality made scarce and most precious to the modern mind: meaning. SF gives us perspectives, and so redeems this lack, rendering the human prospect again large and portentous. We gain stature alongside the enormities of both s.p.a.ce and time.

As a physicist, I've learned that the different branches of science lend their followers an intuitive grasp of long scales. Archeologists sense the rise and fall of civilizations by sifting through debris. They are intimately aware of how past societies mismanaged their surroundings and plunged down the slope of collapse, sometimes with startling speed.

Biologists track the extinction of whole genera and, in the random progressions of evolution, apprehend a sweep of time far greater than the whole of human history. Darwinism invokes c.u.mulative changes that can act quickly on insects, while mammals take millions of decades to alter. Our own evolution has tuned our sense of probabilities to work within a narrow lifetime, blinding us to the slow sway of long biological time. This may well be why the theory of evolution came so recently; it conjures up spans beyond our intuition. On the creative scale of the great, slow and blunt Darwinnowings such as we see in the fossil record, no human monument can endure. But our neophyte species can now bring extinction -- which is forever -- to many others.

In their careers, astronomers discern the grand gyre of worlds. But planning, building, flying and a.n.a.lyzing one mission to the outer solar system commands the better part of a professional life. Future technologies beyond the chemical rocket may change this, but there are vaster s.p.a.ces beckoning, which can still consume a career. A mission scientist invests the kernel of his most productive life in a single gesture toward the infinite.

Those who study stars blithely discuss stellar lifetimes encompa.s.sing billions of years. In measuring the phases of stellar mortality, they employ the many examples, young and old, that hang in the sky. We see suns in snapshot, a tiny sliver of their grand and gravid lives caught in our telescopes. Cosmologists peer at distant reddened galaxies and see them as they were before Earth existed. Observers measure the microwave emission that is relic radiation from the earliest detectable signal of the universe's hot birth.

Studying this energetic emergence of all that we can know surely imbues (and perhaps afflicts) astronomers with a perception of how like mayflies we are.

No human enterprise can stand well in the glare of such wild perspectives. Perhaps this is why for some, science comes freighted with coldness, a foreboding implication that we are truly tiny and insignificant on the scale of such eternities. Yet as a species we are young, and promise much. We may come to be true denizens of deep time.

I tried to get at such issues in my novel, Eater. Like the one before it, Cosm, it deals with humanity seen against the huge backdrop of creation itself. In Cosm, a feisty black woman scientist accidentally creates a whole universe. In Eater, we follow astronomers as they confront what could be described as an embodiment of the Old Testament G.o.d -- capricious, strange, with a whim of iron.

That's the sort of startling problem I like to give myself in a novel -- something I haven't seen done before, or at least not to my liking. Such dramas make one think of humanity as it truly is -- one very successful species that hasn't really had enough time to prove whether it will truly last.

I find it amusing to think on truly long time scales; it centers the present, between the vast past and the unknowable future.

For example, though our destiny is forever unclear, surely if we persist for another millennium or two, we shall fracture into several species, as our grasp of our own genome tightens. We will dwell on the scale of a hastening evolution, then, seizing natural mechanisms and turning them to our own tasks. In this sense we will emerge as players in the drama of natural selection, as scriptwriters.

Our ancient migrations over Earth's surfaces have shaped us into "races" which cause no end of cultural trouble and yet are trivial outcomes of local selection. Expansion into our solar system would exert selective pressure upon traits we can scarcely imagine now, adaptations to weightlessness, or lesser gravity, or other ranges of pressure or temperature. In this context, we will need long memories of what we have been, to keep a bedrock of certainty about what it means to be human. This is the work of deep time messages, as well.

The larger astronomical scale, too, will beckon us in such a distant era; for well within a millennium we will be able to launch probes to other stars. To ascend the steps of advanced engineering and enter upon the interstellar stage will portend much, introducing human values and perceptions into the theater of suns and solar systems. The essential dilemma of being human -- the contrast between the stellar near-immortalities we see in our night sky and our own all-too-soon, solitary extinctions -- will be even more dramatically the stuff of everyday experience.

This reminds me of a portion of a favorite poem: Here on the level sand Between the sea and land, What shall I build or write Against the fall of night?

-- A.E. Housman What changes might such perspectives presage? We could lend furious energies to the pursuit of immortality, or something approximating it. If today we eliminated all disease and degeneration, accidents alone would kill us within about 1,500 years. Knowing this, would people who enjoyed such lifetimes none the less strive for risk-free worlds, to further escape the shadow of time's erosions?

On the scale of millennia, threats and prospects alter vastly. Over a few thousand years, the odds that a large asteroid or comet will strike the Earth, obliterating civilization if not humanity, become considerable.

But if we meet something as truly alien as the Eater Of All Things, all bets are off.