Forbes: The Gecko's Foot

From Scienticity

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Readability:
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Peter Forbes, The Gecko's Foot : Bio-Inspiration : Engineering New Materials from Nature. New York : W.W. Norton & Company, 2005. 272 pages with notes, further reading, and index.

This book is about what Forbes calls the "new science" of "biometrics", sometimes also called "biomimetics"; the latter name is undoubtedly more description but more awkward. Biometric concerns itself with examining nature's engineering in detail to see what can be learned that might enhance modern technologies. Much of the investigation takes place in the nano realm, sizes and lengths too small for optical microscopes to resolve but familiar from the surge of interest in nanotechnology.

The subjects and investigations he describes are all interesting: how lotus leaves manage not to get muddy, how spiders spin their silk, how it is that gecko's can walk up walls and across ceilings, how insects manage to fly, plus some look at nature at macroscopic length scales: building with tension elements, how to get structural rigidity from domes, origami for engineers.

Forbes' writing is casual and engaging, sometimes a bit too casual for my taste. He makes some effort at good scienticity, but his understanding of the scientific concepts surrounding the concepts he's describing is not always as deep as one might like.

Here is an excerpt from early in the chapter discussing light and how animals create iridescence and what implications that might have for the modern physical discipline of photonics. Some of the explanations are not exactly incorrect but lack precision, which I think betrays the somewhat superficial understanding the author has of his subject.

Light is a prime communications medium, in nature and in human technology. And although optical communications in nature might be 500 million years old, the human study and development of natural optical systems is an emerging field. Optical technology is booming, and the big prize is the promise of an all-optical computer. Computers and their silicon chip microprocessors run on electrical pulses, but could they be powered by light? And could nature's optical systems help us to do it?

The electricity in a computer is thee to send pulses through logic devices that make computations and store them on disk. Light can also be pulsed like this and it is 10 times faster than electricity. And light beams can cross without interfering with each other: if electric currents cross they short circuit. (An optical computer would still need to be plugged in – the light pulses are generated by electricity in the first place.)

Light has huge advantages but it is very hard to control. Electricity threads intricate tiny pathways through silicon chips but light does not bend very willingly: it always wants to travel in a straight line. In 1987, two physicists, Eli Yablonovitch, then at Bell Laboratories, and Sajeev John at the University of Toronto, independently realized that a device could be made that would make light as easy to control as electricity. They called it the photonic crystal. it would work like the millions of transistors in a silicon chip by only allowing light of certain wavelengths to pass through: the blocked wavelengths were known as the photonic bandgap. [p. 102]

This next example could be tighter, too. For instance, the light only bends when it meets the interface at an angle; the refractive index of the material is not so simply related just to the velocity of light as one might infer; sometimes light of different color travels at different speeds in different media; and "seriously slowed" could be replaced with a phrase that conveys more information.

Light is a wave motion that travels at different speeds through different media. Its speed through a vacuum is the famous 300 million metres per second and its speed through air is almost the same. But when it meets a solid but transparent medium such as glass, it is seriously slowed and this has the effect of bending the light by an angle characteristic of the medium. This is the phenomenon of refraction and the degree of bending is called the refractive index. Light is 1.5 times as fast in air as it is in glass, so the refractive index is 1.5. The refractive index is one of the keys to the optical tricks of nature and technology alike. [p. 107]

On the other hand, Forbes shows commendable enthusiasm for his subject and his journalism is notably sounder than some of his science. Overall I can recommend the book provided one does not ask too much of the scientific explanations.

-- Notes by JNS