The story of how galaxies were created can be told simply: After the big bang, quantum mechanical gurgling stirred a little unevenness into a swelling ball of matter and energy. Because some regions were denser than their surroundings, their gravitational attraction pulled yet more matter down onto them. Eventually these huge clouds of gas collapsed into galaxies and the stars within.

But this explanation of galaxy formation is no more a satisfying than a definition of weather that simply states that the sun heats the Earth's atmosphere while temperature differences in the air swirl into winds. Although true, it doesn't answer the interesting questions. What causes El Niño? Why does San Francisco average 62 degrees in July? Will it rain this weekend? Similarly, the quantum-fluctuations-collapse -into-galaxies tale doesn't explain why a typical galaxy contains hundreds of billions of stars (as opposed to millions or quadrillions) or why many galaxies clump into clusters and clusters line up into bubblelike structures that span hundreds of millions of light-years with vast voids in between.

For insight into these questions, astrophysicists Thomas Quinn and George Lake, both at Alliance partner University of Washington in Seattle, create universes with computer models to understand how the real one came into being. "We hope to understand how clusters of galaxies form and to define the correct parameters for a cosmological model," Lake says.