Letters from the April 17, 2004, issue of Science News

Sphere criticism

In “Candy Science: M&Ms pack more tightly than spheres” (SN: 2/14/04, p. 102: Candy Science: M&Ms pack more tightly than spheres), I read that an orb of a given size, when slightly flattened, will pack more densely than when perfectly round. No kidding? Do you suppose if we were to crush cars into little cubes we could hurl more into a landfill than we could just by driving them over a cliff? What am I missing?

Marc Gurevitch
Nicholasville, Ky.

Don’t be misled by how many cars might fill a landfill, says Salvatore Torquato of Princeton University. Rather, consider the pile that either whole or crushed cars would form. The M&M team explored what fraction of such a pile is solid material, not air. When deformed spheres such as M&Ms are randomly piled and jostled, their small variations from sphericity boost that fraction unexpectedly high.—P. Weiss

Your story states that “each tight-packed sphere typically has only 6 adjacent neighbors.” However, it is well known that closely packed oranges touch 12 adjacent oranges (cubic closest packing). One is tempted to explain the apparent 2-fold discrepancy by considering that each contact is shared by two particles, but that would be wrong. The number of contacting neighbors actually does decrease to about six in randomly close-packed spheres.

Don Garlick
Humboldt State University
Arcata, Calif.

Myth of sterility

In answer to “Pill Puzzle: Do antibiotics increase breast cancer risk?” (SN: 2/21/04, p. 118: Pill Puzzle: Do antibiotics increase breast cancer risk?), infections elevate activity of the immune system, so they might indirectly suppress tumors of all kinds. If so, antibiotics could increase the incidence of cancer by reducing the duration and degree of infection. The widespread practice of sterilizing our home and work environments could have a similar effect.

Edward P. Tryon
City University
New York, N.Y.

Wave reaction

“Catching Waves: Ocean-surface changes may mark tsunamis” (SN: 2/21/04, p. 116: Catching Waves: Ocean-surface changes may mark tsunamis) says that tsunamis “disrupt winds,” leading to the appearance of dark bands. I propose that upwelling above the crests creates a new surface initially unaffected by the wind and therefore slick. Such bands of slick water formed by tides are a common sight in Puget Sound.

Harry Higgins
Seattle, Wash.