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Science Reports M&M Candies Are More Space-Efficient Than Gumballs

By Kenneth Chang

The New York Times -- In possibly the biggest advance in the science of candy since the discovery that Wint-O-Green Life Savers emit faint blue sparks when chewed, scientists are reporting Friday that M&Ms pack more tightly in your mouth than gumballs.

Besides being a publicity boost for Mars Inc., the maker of M&Ms, the research, which appears in the journal Science, could lead to better understanding of glass -- the scientific term for any solid with a random arrangement of atoms or molecules -- and to practical developments like stronger ceramics.

“The questions involved here are really quite deep and quite fundamental,” said Salvatore Torquato, a professor of chemistry at Princeton University and an author of the Science paper.

The research is a more complicated version of a long-studied problem: how tightly identical spheres can be packed together. Neatly stacked, as in a pyramid of oranges at a grocery store, spheres occupy 74 percent of the available volume. Arranged randomly, however, spheres fill only 64 percent of the space.

In the new research, the scientists considered spheroids -- spheres stretched into cigar shapes or squashed into M&M shapes. Stacked neatly, the spheroids still take up 74 percent of the space, just like spheres. But in random arrangements, computer simulations and experiments with M&M’s showed that spheroids could be packed much more densely, filling up to 71 percent of the space.

“You can just randomly pour them and without any effort get something that approaches the densest lattice packing,” Torquato said.

The density increases, he said, because “the particle can move around and rotate to find a more efficient packing.”

If the spheroids are deformed in a second direction, into ellipsoids (in other words, stretched or squashed so the M&M shape is no longer circular when viewed from above -- like, say, an almond M&M), then the maximum packing density increases to 77 percent, more tightly than the simple neat stacks.

With the denser packing, each individual particle is in contact with more neighboring particles. Thus, a ceramic made out of a powder of ellipsoid particles might be stronger than one made of spherical particles.

While the research ended with M&Ms, it started with peas. Paul M. Chaikin, a professor of physics at Princeton, assigned an undergraduate student, Evan A. Variano, to reproduce the work of an 18th-century English clergyman, Stephen Hales, who studied the packing of spheres with peas. Hales soaked the peas, which swelled and deformed, allowing him to see the precise arrangement of each pea with its neighbors.