Head games 

Exploring the long-neglected enigma of foam science

Experts in a given field don’t always make its best teachers or most eloquent explainers. In addition to just being experts, good writers of popular science must also have a knack for taking numbers and concepts that are out of the scope of comprehension for the average reader and rendering them in terms that can be grasped by nearly everyone. Carl Sagan was such a writer. So is Sidney Perkowitz, physicist and author of Universal Foam, an enthusiastic report from the relatively new field of foam science and an irresistibly imaginative look into the prevalence of foam in our lives.

Yes, foam. And yes, there is such a thing as foam science. “For all its frothiness,” Perkowitz writes, “foam is a surprisingly intricate formation that has an impact on astronomy, biology, chemistry, physics and mathematics. Foam is not exclusively a solid, liquid or gas; it is made of bubbles or cells of gas within a liquid or a solid, and it combines characteristics of all three states of matter.”

Harvard physicist David Weitz calls foam the “neglected material.” Neglected, that is, not in its thousands of practical applications but as a field of study unto itself. Historically, foams and foaming substances have been put to use in brewing and baking, in polishing wood, making coffee and champagne, keeping hair moist and pliable for shaving, for sopping up messes and for contraception. Nowadays foams are used in space probes to keep sensitive computer equipment from freezing on the surface of Mars and to capture bits of comet debris for eventual study. On Earth, scientists use models based on foams to determine the optimal stacking arrangement for cells in living tissue, and civic planners study the structure of foam to find out how points on the map can be connected most efficiently with new roads. Much of the Earth itself is made up of foam of one kind or another, and many of the energy systems in the natural world are based around the marvelous properties of foam and bubbles. Bubbles in the sea, for example, dissolve atmospheric gases and solids into seawater and release as much as two trillion pounds of salt into the atmosphere every year. Our lungs work on certain principles of foam physics, as do our livers and kidneys. Everything we see, in fact, and in many cases don’t see, is made up of a super-subatomic foam. In many ways it’s a world of foam—and we just live in it.

A lot is known about foam, but many of the physical principles that govern its behavior remain a mystery. For example, in recent years foam scientists have pressed into service a computer program called a Surface Evolver. This program lets the user assemble triangular tiles to create a three-dimensional surface of any shape and complexity, which the computer then reconfigures to minimize its area. And for all that, the same scientists still don’t know why a soap bubble assumes a certain ideal shape when crowded on all sides by other bubbles in a foam. They don’t even know what this shape is, or which principles determine the shape of new cells formed in a foam when smaller bubbles combine to form bigger ones.

Perkowitz obviously revels in the enigmas of his subject matter. For him foams are both practical and theoretical delights, and he waxes lyrical about the foam on a glass of beer or in a cup of espresso with as much alacrity as he describes the foams that make metals stronger and lighter and such daunting medical adversaries of prions and so-called foamy viruses. Perkowitz sees foam everywhere, and the reader cannot resist his enthusiasm for writing about it.

The writing itself has a complementary foaminess to it. In the same way that a spherical soap bubble represents the optimal shape for the volume it contains, Perkowitz’s wit is bound by the same laws of economy that keep bubbles together in a foam. His mind scampers all over the place but the flow of his sentences keeps the mind-warping breadth of scientific, historical, literary, linguistic and culinary anecdotes together with the bare minimum of surface tension required to hold them. You could charge through the book in an afternoon, but you would be neglecting a careful examination of all the facets joining the anecdotal bubbles in Perkowitz’s foam. The writing, like the substance, is a study in connections.

It can be downright unnerving to read too much about all the things scientists know (or at least hypothesize) about the makeup of the cosmos based on the behavior of particles of matter millions of times too small to be seen through a microscope. Did you know, for example, that in any glass of water minute bubbles of water are collapsing at four times the speed of sound and, in doing so, generating temperatures hotter than the surface of the sun for durations that can be measured in trillionths of seconds? Perkowitz excels at transposing the infinitely large and small of the physical universe into often humorous analogies. The 45 million pounds of polystyrene packing peanuts manufactured every year in the United States, he explains, would be sufficient to cover Manhattan in a layer 3 feet thick. And here’s a strategy for envisioning the Planck length, the smallest unit of measure for subatomic distances, which he gamely pilfers from fellow physicist John Wheeler: A Planck length is dwarfed by a single proton in the same ratio that the proton is dwarfed by the acreage of the whole state of New Jersey. It kind of makes you want to trepan yourself after a while.

Wondering what makes beer foamy? How a woodpecker cost NASA $2 million in custom foam work? Curious about foam research and the unlikely heroes of applied foam science? There may never have a more enjoyable way find out than Universal Foam.

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