Cosmic rays -- particles from heaven or, more prosaically, from outer space -- seem to be responsible for one of the little problems of the computer age. And the little problem could become a big one. Almost everyone who has had extended experience with electronic computers has witnessed unexplained events," say J. F. Zeigler of IBM-Research and W. A. Lanford of the State University of New York at Albany. Events, they say, "in which a single digit of a number appears to change spontaneously, or perhaps the computer itself suddenly stops, and no way can be found for it to repeat the failure." Within the computer industry, they explain in Science magazine, these are known as "soft fails," as distinguished from "hard fails," bad electronic circuits that must be replaced. Well, say the two scientists, cosmic ray nucleons and muons -- elements of the nucleus of the atom -- can and do strike computer circuits and mix up their electronics often enough to be of "marginal significance." Or occasional annoyance. Because computer elements are getting more sensitive, however, and therefore more vulnerable to subatomic particles, "there may be a very significant effect in the next generation of computer circuitry," they warn. In short, a cosmic ray might be likened to a rock hitting a barn door, shaking the door a bit. In the next generation, the rock might wreck the barn.