Number 82 (Story #3), June 2, 1992 by Phillip F. Schewe and Ben Stein HIGH ENERGY PHOTON-PHOTON INTERACTIONS can occur when electrons and positrons, racing past each other at a collider, communicate with each other through a complex web of virtual photons. According to quantum theory, these photons---which cannot be directly observed---can interact in a variety of ways, giving rise to various resonances and jets of particles, which can be detected. A meeting on photon-photon collisions held in San Diego in March revealed that most experimental results, at labs like Tristan and LEP, are in line with the predictions of quantum electrodynamics (QED) and quantum chromodynamics (QCD). At the meeting, V. Telnov of Novosibirsk suggested that a beam of high-energy real photons (virtual photons owe their fleeting existence to the vagaries of the uncertainty principle) could be made by scattering laser light from beams of electrons at a linear collider. (Nature, 28 May.)