How does one begin to describe a process that can replace the industrial system of the world? Physical possibilities, research trends, future technologies, human consequences, political challenges: this is the logical sequence, but none of these makes a satisfactory starting point. The story might begin with research at places like IBM, Du Pont, and the ERATO projects at Tsukuba and RIKEN, but this would begin with molecules, seemingly remote from human concerns. At the core of the story is a kind of technology-"molecular nanotechnology" or "molecular manufacturing"-that appears destined to replace most of technology as we know it today, but it seems best not to begin in the middle. Instead, it seems best to begin with a little of each topic, briefly sketching consequences, technologies, trends, and principles before diving into whole chapters on one aspect or another. This chapter provides those sketches and sets the stage for what follows.

All this can be read as posing a grand "What if?" question: What if molecular manufacturing and its products replace modern technology? If they don't, then the question merely invites an entertaining and mind-stretching exercise. But if they do, then working out good answers in advance may tip the balance in making decisions that determine the fate of the world. Later chapters will show why we see molecular manufacturing as being almost inevitable, yet for now it will suffice if enough people give enough thought to the question "What if?" A Sketch of Technologies

Molecular nanotechnology: Thorough, inexpensive control of the structure of matter based on molecule-by-molecule control of products and byproducts; the products and processes of molecular manufacturing.

Technology-as-we-know-it is a product of industry, of manufacturing and chemical engineering. Industry-as-we-know-it takes things from nature-ore from mountains, trees from forests-and coerces them into forms that someone considers useful. Trees become lumber, then houses. Mountains become rubble, then molten iron, then steel, then cars. Sand becomes a purified gas, then silicon, then chips. And so it goes. Each process is crude, based on cutting, stirring, baking, spraying, etching, grinding, and the like.

Trees, though, are not crude: To make wood and leaves, they neither cut, grind, stir, bake, spray, etch, nor grind. Instead, they gather solar energy using molecular electronic devices, the photosynthetic reaction centers of chloroplasts. They use that energy to drive molecular machines-active devices with moving parts of precise, molecular structure-which process carbon dioxide and water into oxygen and molecular building blocks. They use other molecular machines to join these molecular building blocks to form roots, trunks, branches, twigs, solar collectors, and more molecular machinery. Every tree makes leaves, and each leaf is more sophisticated than a spacecraft, more finely patterned than the latest chip from Silicon Valley. They do all this without noise, heat, toxic fumes, or human labor, and they consume pollutants as they go. Viewed this way, trees are high technology. Chips and rockets aren't.

Trees give a hint of what molecular nanotechnology will be like, but nanotechnology won't be biotechnology because it won't rely on altering life. Biotechnology is a further stage in the domestication of living things. Like selective breeding, it reshapes the genetic heritage of a species to produce varieties more useful to people. Unlike selective breeding, it inserts new genes. Like biotechnology-or ordinary trees-molecular nanotechnology will use molecular machinery, but unlike biotechnology, it will not rely on genetic meddling. It will be not an extension of biotechnology, but an alternative or a replacement.

Molecular nanotechnology could have been conceived and analyzed-though not built-based on scientific knowledge available forty years ago. Even today, as development accelerates, understanding grows slowly because molecular nanotechnology merges fields that have been strangers: the molecular sciences, working at the threshold of the quantum realm, and mechanical engineering, still mired in the grease and crudity of conventional technology. Nanotechnology will be a technology of new molecular machines, of gears and shafts and bearings that move and work with parts shaped in accord with the wave equations at the foundations of natural law. Mechanical engineers don't design molecules. Molecular scientists seldom design machines. Yet a new field will grow-is growing today-in the gap between. That field will replace both chemistry as we know it and mechanical engineering as we know it. And what is manufacturing today, or modern technology itself, but a patchwork of crude chemistry and crude machines?

Nanotechnology will bring new capabilities, giving us new ways to make things, heal our bodies, and care for the environment. It will also bring unwelcome advances in weaponry and give us yet more ways to foul up the world on an enormous scale. It won't automatically solve our problems: even powerful technologies merely give us more power. As usual, we have a lot of work ahead of us and a lot of hard decisions to make if we hope to harness new developments to good ends. The main reason to pay attention to nanotechnology now, before it exists, is to get a head start on understanding it and what to do about it.

Here are a few of today's common assumptions, some so familiar that they are seldom stated:

* Industrial development is the only alternative to poverty.
* Many people must work in factories.
* Greater wealth means greater resource consumption.
* Logging, mining, and fossil-fuel burning must continue.
* Manufacturing means polluting.
* Third World development would doom the environment.

These all depend on a more basic assumption:

* Industry as we know it cannot be replaced.

Some further common assumptions:

* The twenty-first century will basically bring more of the same.
* Today's economic trends will define tomorrow's problems.
* Spaceflight will never be affordable for most people.
* Forests will never grow beyond Earth.
* More advanced medicine will always be more expensive.
* Even highly advanced medicine won't be able to keep people healthy.
* Solar energy will never become really inexpensive.
* Toxic wastes will never be gathered and eliminated.
* Developed land will never be returned to wilderness.
* There will never be weapons worse than nuclear missiles.
* Pollution and resource depletion will eventually bring war or collapse.

These, too, depend on a more basic assumption:

* Technology as we know it will never be replaced.

These commonplace assumptions paint a future full of terrible dilemmas, and the notion that a technological change will let us escape from them smacks of the idea that some technological fix can save the industrial system. The prospect, though, is quite different: The industrial system won't be fixed, it will be junked and recycled. The prospect isn't more industrial wealth ripped from the flesh of the Earth, but green wealth unfolding from processes as clean as a growing tree. Today, our industrial technologies force us to choose better quality or lower cost or greater safety or a cleaner environment. Molecular manufacturing, however, can be used to improve quality and lower costsand increase safety and clean the environment. The coming revolutions in technology will transcend many of the old, familiar dilemmas. And yes, they will bring fresh, equally terrible dilemmas.

Molecular nanotechnology will bring thorough and inexpensive control of the structure of matter. We need to understand molecular nanotechnology in order to understand the future capabilities of the human race. This will help us see the challenges ahead, and help us plan how best to conserve values, traditions, and ecosystems through effective policies and institutions. Likewise, it can help us see what today's events mean, including business opportunities and possibilities for action. We need a vision of where technology is leading because technology is a part of what human beings are, and will affect what we and our societies can become.

The consequences of the coming revolutions will depend on human actions. As always, new abilities will create new possibilities both for good and for ill. We will discuss both, focusing on how political and economic pressures can best be harnessed to achieve good ends. Our answers will not be satisfactory, but they are at least a beginning.