Glueballs; November 1998; Scientific American Magazine; by Close, Page; 6 Page(s)

There are no atoms of light. That is, photons do not attach to other photons, forming composite entities. But gluons, the particles that bind quarks--the basic units of matter--into objects such as protons, may indeed stick just to one another. Physicists call the resulting glob a glueball.

A glueball is thought to have a radius of 0.5 ¿ 10¿15 meter, less than that of a proton, and live for less time than light takes to cross a hydrogen atom. Ephemeral though these particles may seem, in the past year many physicists have become convinced that glueballs are showing up in experiments.