Size matters

For Prince Charles, nanotechnology is a nightmare of grey goo that will devour the world. For around 500 businesses, 300 university departments and investors who have so far gambled around £4bn, nanotechnology is the next big thing - only very, very small.

Nanotechnology is the science of materials and instruments at measurements of a billionth of a metre - the scale of a few atoms or molecules at a time. But, as chemists, physicists and molecular biologists know, everything in the universe happens at the scales of a few atoms or molecules at a time anyway.

The real surprise is that when experts make things at these scales, they get surprising effects. Layers of materials stacked atoms at a time have startling electromagnetic properties: they could become lightweight magnets, or superconductors at room temperature.

Carbon-60 molecules could provide fabrics of astounding strength and lightness. Light emitting diodes at these scales for instance produce light but not heat. Since heat is what makes light bulbs burn out, this discovery alone opens the way to huge savings in materials and energy. Computers are delivering more and more power across ever smaller dimensions. One team this year announced a silicon chip so small that 400 could fit onto the surface of a grain of salt.

The next step is "smart" materials that can think, and work out what to do in changing circumstances: there are bandages that can detect the first whiff of infection, and clothes than can repel stains, fabrics that could soon identify, warn of and even repair their own fractures. There are plans for military camouflage that will change colour according to surroundings: welcome to the almost invisible soldier, and the now-you-see-it, now-you-don't stealth tank.

The challenge is to produce industrial quantities of such materials at such tiny scales. Already, there are millions of bits of sensors - in computer joysticks, in car airbags - fashioned at measures of a millionth of a metre. But to get down to working parts of billionth of a metre, a thousand times finer than a human hair, at a scale invisible to any optical microscope, is a bit tougher.

The dream (and yes, it could also be a nightmare) would be to design tiny bits of machinery that could then replicate themselves. In one scenario, these could replicate exponentially and take over and destroy the world.

In another, tiny machines could benignly cruise the human bloodstream, sweeping away menacing toxins, repairing damaged tissue, cleaning up tumour cells and generally keeping humans alive and healthy indefinitely.

However, nobody yet knows how to do either thing. The technology is still in its infancy.