Spring 2010

Two Bubbles, and a Third

All must inevitably burst

D. Graham Burnett

A bottlenose dolphin considers the work of its blowhole. Photo Barry Bland.

In Charon, his wicked little skit about the transience and pathos of human affairs, the second-century satirist Lucian depicts the grizzled boatman of the underworld on holiday in the bright air of the busy earth. Taking some time to mingle with the Olympians, this Stygian tourist looks down from on high in the company of the trickster-god Hermes, and muses aloud concerning the sorry panorama at their feet:

Have you ever stood at the foot of a waterfall, and marked the bubbles rising to the surface and gathering into foam? Some are quite small, and break as soon as they are born. Others last longer; new ones come to join them, and they swell up to a great size: yet in the end they burst, as surely as the rest; it cannot be otherwise. There you have human life. All men are bubbles, great or small, inflated with the breath of life. Some are destined to last for a brief space, others perish in the very moment of birth: but all must inevitably burst.

The text is one of the more elaborate early sources for the classical commonplace that would become a mainstay of European art and literature: homo bulla—“man is a bubble.” As this austere apothegm drifted out of the stern world of the Stoics and into the fervorous sentimentalism of Christiandom, it became the tear-jerking translucency at the center of human vanity: we are beautiful, delicate, and we die too soon.

As with any metaphor, though, everything depends on the vehicle. We are bubbles? Really? But of what sort, exactly? Charon envisioned the froth on the Styx. Okay, but there are more bubbles under those waters than were dreamed of in his ferryman’s philosophy. Let us consider two of them, in the hopes that contemporary fluid dynamics and marine biology can breathe new life into this hollow allegory.

The Alpheidae are a large family of smallish shrimp, more than five hundred different species, the majority of which make their livings creeping around the underside of sponges and corals in the warm, shallow waters of the circumtropical oceans. They are, however, anything but unobtrusive. Known collectively as “snapping shrimp,” these noisy creatures first came to scientific prominence during World War II, when submarine warfare made marine acoustics a matter of life and death at the geopolitical scale. A clutch of new sound technologies—SONAR, SOFAR, SOSUS—took naval surveillance underwater in these years for a cat-and-mouse game of signal detection and spatial interpretation. Or anyway, that was the idea. In practice, if you put a hydrophone offshore anyplace between Brest and Buenos Aires, what came over your headphones was a pervasive roar a little like an out-of-control brushfire. The anti-submarine-warfare guys called in the marine biologists, who fingered the skulking Alpheidae, zillions of which were perpetually clacking away in their burrows with their one oversized claw. Filtering out the racket proved tricky, but not insurmountable, and it was easier than exterminating the little buggers. The physicists moved on to other projects.
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