Computing the cosmos

One of the biggest computer simulations ever run is illuminating the deepest mysteries of the universe. To answer the fundamental questions in cosmology, an international group of scientists from Canada, Germany, the United Kingdom, and the United States has been working on an ambitious project whose goal is to simulate on a supercomputer the evolution of the entire universe, from just after the Big Bang until the present. The group, dubbed the Virgo Consortium—a name borrowed from the galaxy cluster closest to our own—is creating the largest and most detailed computer model of the universe ever made. While other groups have simulated chunks of the cosmos, the Virgo simulation is going for the whole thing. The cosmologists' best theories about the universe's matter distribution and galaxy formation will become equations, numbers, variables, and other parameters in simulations running on one of Germany's most powerful supercomputers, an IBM Unix cluster at the Max Planck Society's Computing Center in Garching, near Munich. 4 200 000 000 000: NUMBER OF CALCULATIONS PER SECOND THE VIRGO CONSORTIUM SUPERCOMPUTER CAN PERFORM . The machine specifically designed for simulation, a cluster of powerful IBM Unix computers, has a total of 812 processors and 2 terabytes of memory, for a peak performance of 4.2 teraflops, or trillions of calculations per second. It took 31st place late last year in the Top500 list, a ranking of the world's most powerful computers by Jack Dongarra, a professor of computer science at the University of Tennessee in Knoxville, and other supercomputer experts. But as it turns out, even the most powerful machine on Earth couldn't possibly replicate exactly the matter distribution conditions of the 380 000-year-old universe the Virgo group chose as the simulation's starting point. The number of particles is simply too large, and no computer now or in the foreseeable future could simulate the interaction of so many elements. So the fundamental challenge for the Virgo team is to approximate that reality in a way that is both feasible to compute and fine-grained enough to yield useful insights. The Virgo astrophysicists have tackled it by coming up with a representation of that epoch's distribution of matter using 10 billion mass points, many more than any other simulation has ever attempted to use. In June 2004, the first simulation of our universe was completed. The resulting data, which represents about 20 terabytes, will be available to everyone in the months to come, at least to people with a high-bandwidth connection.