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Does it really take a team of scientists running computer simulations to come up with the common sense that the greater the common surface area of two objects that touch, the more efficient the stacking? The closer objects are to being flat, the more efficiently they will stack. Hence ellipses will, of course, stack more efficiently than spheres.

Howard Zimmerman
New York, N.Y.

“Stacking sheets of paper, cubes, or books [which fill all of a space] is a completely different problem” than stacking curved objects, says Salvatore Torquato of Princeton University. The closest-packed ellipsoids share no surface area, but each touches its neighbors at 14 points, he adds .—P. Weiss The article states that “piles of cubes can occupy every last niche of a space.” True only for rectilinear spaces. Consider the nightly challenge faced by air-cargo carriers such as FedEx and UPS.

Ira Dember
Houston, Texas