Waves by Mike Goldsmith

Author:Mike Goldsmith [Goldsmith, Mike]
Language: eng
Format: epub
ISBN: 9780192525727
Publisher: Oxford University Press
Published: 2018-09-24T00:00:00+00:00

Patterns

The idea that waves might be involved in the markings of animals is not obvious, and it is greatly to the credit of Alan Turing that he suggested it as long ago as 1952. Turing’s theory was that simple cyclic chemical reactions in identical cells can lead to sinusoidal patterns of pigmentation. Only in this century has this proposal been shown to be broadly correct.

Patterns made by groups of animals can also be illuminated by wave theory. In starling flocks, for example, the distances between birds propagate like sound waves, with successive patterns of compression and rarefaction between birds forming waves of separation. When one bird changes direction, the change propagates through the rest of the flock like a sound wave. Flock sizes can also be predicted through wave theory: the separation waves spread most effectively in larger flocks while the direction-change variety favours smaller groups. So, if the flock is too small, the distances between birds will become very unequal, while if it is too large, the flock will tend to break up when it needs to change direction.

The concept of a flock can loosely be applied to people too, especially people in cars. In a line of traffic, small changes in the velocities of individual cars make no difference to progress overall, but an unexpected event like a sudden lane change by a large vehicle can cause such a sudden and significant slowing by the car immediately behind it that the next car back must also brake, and so must the next, and so on. This can be regarded as a single wave travelling backwards along the line of traffic and explains why traffic may suddenly slow, or even stop, with no visible cause. Cars may continue to stop like this at points many kilometres ‘downstream’ and many minutes after the initial incident. The closer together the cars are the more likely such waves are to occur, and once there are more than about fifteen vehicles per kilometre, the waves travel with very little attenuation. With very close cars, even the usual small changes in speed of individual cars can be communicated easily as backwards-travelling waves, causing the whole system to slow down, and showing that smoothness of traffic flow makes an enormous difference. Hence, the rise of driverless cars may allow for a far greater volume of traffic to be accommodated by roads without causing jams and congestion.

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