Myopic Astronomer's Kaleidoscope

BIRDS and bees do it - now machines can reproduce too. The first scalable robot to have built an exact copy of itself could herald a fundamental rethink of how robots may be used to explore other planets.

Hod Lipson and colleagues at Cornell University in Ithaca, New York, built their self-replicating device using small mechanical building blocks that can swivel, and also attach themselves to one another using electromagnets.

Each 10 centimetre cube contains a microprocessor, and they are all equipped with an identical set of instructions that tell the block how to connect and swivel, depending on the way it is linked to other blocks. The instructions are designed to make the blocks work together to self-replicate.

For example, three or four blocks piled on top of each other to form a tower can create an identical tower by swivelling round like a crane to pick up other nearby blocks and pile them on top of each other (Nature, vol 435 p 163). "The instructions aren't complex. In fact, they turn out to be surprisingly simple," Lipson says.

Because the blocks are identical, larger structures can be made by adding more blocks. This scalability is important, Lipson says. Previous work on self-replication has involved only simulations and specially designed machines. "But ours is not a one-off. It proves that there is a whole family of self-replicating machines that can do this." See footage of the process here (Windows Media Video, 5.42MB, courtesy of Hod Lipson, Cornell University).

"It's a neat piece of work. If you could miniaturise these blocks and manufacture them cheaply in large numbers, you could build some interesting structures," says Adrian Bowyer from the University of Bath, UK, who specialises in self-replication. Lipson hopes to do just that by reducing the size of his blocks.

Self-replication could have major implications for how robots are used in remote environments where repairing them is difficult. "Self-replication is the ultimate form of repair," Lipson says. "You can imagine robotic systems on Mars or at the ocean bottom repairing themselves using a mechanism like this."

The team has also come up with a new way of thinking about self-replication that could speed up future work. In the past, self-replication has been thought of as a property that a system either has or does not have. But Lipson and his team suggest that it is more useful to allow for intermediate levels of self-replication. Using this approach, they have developed a mathematical measure of self-replication that depends on the amount of information being copied. "For the first time, we can actually measure self-replication and so understand how to improve it," Lipson says.

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The Nobel Prize in Physics 2006

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