13.3.1 - Two-Dimensional Sound

Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization

First Edition

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

One fascinating but little-discussed acoustical sense is the surface wave communication found among a few specialized terrestrial species. There are many insects that have utilized the peculiar two-dimensional quality of their environment to develop a rather exotic mechanism for transmitting and receiving data.

For instance, water striders (Gerris buenoi) are small, stilt-legged insects that skim over quiet ponds, supported by the force of surface tension. Much like the kinesthetic sensors in human bodies which provide continuous positional and velocity data for each limb, water striders can detect the slightest disturbance traveling across the surface of the water. This is highly useful survival-oriented information, because it alerts these organisms to the presence of various dangers such as predators, competitors, and obstacles.

A somewhat more sophisticated surface dweller is the whirligig beetle (Gyrinus), which has devised a kind of "sonar" or echolocation system for use in its peculiar two-dimensional world. This creature senses the vibrations of its own ripples over the water’s surface as they are reflected from the shore or from objects moving within a certain range. Depending upon the exact nature of the return, the clever beetle can determine size, distance, velocity, and even texture of all nearby targets.

Not a few small animals on this planet use surface waves directly for communication. One species of water striders (Rhagadotarsus) is known to conduct its entire courtship display using complex patterns of modulated surface waves:

The sequence begins when a male grasps a floating or fixed object on the water surface and vibrates it in a way that sends out waves at the rate of 17-29 per second. Females nearby respond by moving toward the source. When one approaches to within 5-10 centimeters of the male, he switches to "courtship calling" and finally to pure courtship signals. At 2-3 centimeters the female responds with courtship signals of her own, followed by a series of tactile signals that finally lead to copulation.⁵⁶⁵

Several species of spiders are known to use a form of surface wave communication which involves strumming the webs they weave in specific rhythms and patterns. (This is usually used to pass data between mother and offspring.) Desert scorpions can also detect compressional and surface waves in sand to locate prey.²⁵⁷³

There is no reason why surface-dwelling aliens could not respond to and utilize this exotic 2-D "way of knowing." Because of the peculiar nature of the medium, the universe inhabited by such creatures would be strange indeed. This is due, in part, to the fact that two-dimensional waves are fundamentally and qualitatively different from three-dimensional ones we’re used to hearing.

One striking feature would be the amazing persistence of messages. We know that 3-D acoustical waves pass an observer located at a fixed point in space only one time, never to return again. Except for the single wavefront, the medium is relatively undisturbed. In contrast, oscillations in 2-D media die away only very slowly from frictional forces. The entire surface space is set in motion by such stimuli, and damping is often very weak. The media continues to "wave" for a long time after the emission of the original signal.

ETs speaking by means of surface waves would sound like they were in an echo chamber. Words would have a peculiar drawn out quality, persisting long after they have been spoken. And since the higher frequencies always travel faster than the lower ones, each repetition of the echo will sound distinctly different. The word will stretch itself thin, the higher pitched treble notes bunching together at the beginning of the sound and the progressively lower bass tones trailing behind.