Number 170 (Story #1), March 28, 1994 by Phillip F. Schewe and Ben Stein CONTROLLING CHAOS through the use of small perturbations has been possible in a number of systems, such as erratically vibrating metal strips, certain electrical circuits, and mixing in chemical reactions. At the APS Meeting last week in Pittsburgh, Rajarshi Roy of Georgia Tech reported that by using a subtle feedback mechanism he has been able to synchronize two separate chaotic lasers, a development which might be applicable to schemes for encrypting data. Understanding and controlling fibrillating heart tissue may also be possible with chaos-control methods. Mark Spano of the Naval Surface Warfare Center in Whiteoak, Maryland (also speaking at the meeting) has determined that human atrial fibrillation, the massively irregular beating of the atrial chambers of the heart, is chaotic in nature. He also has preliminary evidence that the more life-threatening ventricular fibrillation (erratic behavior in the ventricle chambers) is also chaotic. In studies with rabbit heart tissue, he has been able to control arrhythmia through the application of electrical stimuli. He reported similar work done with rat brain tissue in an effort to control (apparently chaotic) electrical patterns characteristic of epileptic behavior.