Simulating Nuclear Testing

CAN SUPERCOMPUTERS REALLY REPLACE NUCLEAR TESTING? Stanford University professor Robert Laughlin, who's worked on bomb-related physics at Lawrence Livermore Lab since 1981, has his doubts about the ability of supercomputers to accurately predict how nuclear weapons will react to aging and storage conditions: "Computer programs can only simulate the stuff you know. Suppose you left a personal computer out in the rain for a year. Is there a program that can tell you whether it will still run? Of course not -- it all depends on what happened to it. Changes happen over time that you are not sure how to measure. Some matter, some don't. The problem is the things you didn't think to put in the simulation." Indeed, past attempts to simulate very complex situations have not always been successful, and the software codes to predict whether bombs will explode or fizzle "are full of adjustable parameters that have been fit to (underground test) data. If the new codes don't match the old ones that correctly predicted experiment results," (and Laughlin bets they won't) "the designers will simply throw them out." (Scientific American Mar 97)