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Feature - Nanobots - Brian Clegg

In a short extract from his upcoming book Armageddon Science, the Popular Science editor looks at what nanobots are and why some find them very scary.

Imagine the construction of manmade creatures on an even smaller scale than bacteria, an army of self-replicating robots, each invisible to the naked eye. Like bacteria, these “nanobots”, endlessly reproducing devices, could multiply unchecked, forming a grey slime that swamped the world, and destroyed its resources.

Each tiny robot would eat up natural resources in competition with living things, and could reproduce at an inhumanly fast rate. This sounds like science fiction. It is – it’s the premise of Michael Crichton’s thriller, Prey. But the idea of working with constructs on this tiny scale, nanotechnology, is very real. It has a huge potential for applications everywhere from medicine to engineering, from sun block to pottery glaze – but could also be one of the most dangerous technologies human science could engage in, as the so called “grey goo” scenario shows (grey goo because the nanobots are too small to be seen individually, and would collectively appear as a viscous, grey liquid, flowing like a living thing)...

It was the great American physicist Richard Feynman who first suggested that it might become possible to directly manipulate objects at the molecular level in a lecture he gave to the American Physical Society in 1959. Feynman was a trifle optimistic. He said “In the year 2000, when they look back at this age, they will wonder why it was not until the year 1960 that anyone began seriously to move in this direction.” In practice we are only just getting there in the twenty-first century.

There are three huge problems facing anyone attempting to manipulate atoms to produce a new object. First is mapping the structure of an object – having an accurate blueprint to build to. Second is the sheer volume of atoms that have to be worked on. Imagine we wanted to put together something around the size and weight of a human being. That will contain very roughly 7x10²⁷ atoms – 7 with 27 zeroes after it. If you could assemble 1 million atoms a second, it would still take 3x10¹⁴ years to complete. That’s 300 trillion years. Not the kind of time anyone is going to wait for a burger at a drive-thru.

And finally there is the problem of being able to directly manipulate individual atoms, to click them into place, like so many Lego bricks.

Feynman envisaged overcoming the problem of scale by using massively parallel working. It’s like those old problems they used to set in school tests. If it takes one man 10 hours to dig a hole, how long would it take a gang of five men? Feynman envisaged making tiny manipulators, artificial “hands”, perhaps first just one fourth of normal size. He imagined making ten of these. Then each of the little hands would be set to work making ten more hands 1/16th of the original size. So now we have 100 of the smaller hands. Each of those would make ten 1/64th scale – and so on. As the devices got smaller, the number multiplied, until we had billions upon billions of sub-microscopic manipulators ready to take on our challenge.

Twenty-seven years after Feynman’s lecture, author and entrepreneur K. Eric Drexler combined the “nano” prefix with “technology” in his book Engines of Creation to describe his ideas on how it would be possible to work on this scale. He referred to the Feynman-style manipulator as an assembler, a nanomachine that would assemble objects atom by atom, molecule by molecule.

A single assembler working at this scale would take thousands of years to achieve anything. As we have seen, there are just too many molecules in a “normal” scale object. To make anything practical using assembly would require trillions of nanomachines. Drexler speculated that the only practical way to produce such an arm of sub-microscopic workers would be to devise nanomachines that could replicate like a biological creature, leading to the vision of grey goo and the potential devastation portrayed in Crichton’s Prey.

Armageddon Science is published by St Martin's Press in 2011.

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