If cosmologists were to make a movie of the universe's entire history, the show would start, of course, withthe scorching blast of the Big Bang. The universe--absolutelyevery bit of mass we can detect or even infer today--wouldexpand at unfathomable speeds, going from smaller thana proton to larger than a galaxy in the blink of aneye. As the expansion continued, the universe wouldcool down, and by the time the opening credits of themovie finished scrolling, a superhot soup of elementaryparticles would fill the whole cosmos, ready to cookthe first protons and neutrons.But what would happennext?
The fact is, cosmologists are still working out the restof the plot--what exactly took place during the morethan 13 billion years since that primeval blast. [Forthis article, in keeping with the current trend in internationalscientific publishing, IEEE Spectrum uses thewords "billion" to mean 109 and "trillion" tomean 1012.] A particular piece of the storythat has kept researchers scratching their heads is howgalaxies formed and evolved. How did that amorphous particlesoup transform itself into billions and billions of galaxiesof breathtakingly different shapes and sizes? Why didthese galaxies gather together in clusters, and clustersof clusters, embedded along unimaginably enormous structuresof matter shaped like bubbles, filaments, and sheets?
To answer these and other fundamental questions in cosmology,an international group of scientists from Canada, Germany,the United Kingdom, and the United States has been workingon an ambitious project whose goal is to simulate ona supercomputer the evolution of the entire universe,from just after the Big Bang until the present.
The group, dubbed the Virgo Consortium--a name borrowedfrom the galaxy cluster closest to our own--is creatingthe largest and most detailed computer model of the universeever made. While other groups have simulated chunks ofthe cosmos, the Virgo simulation is going for the wholething. The cosmologists' best theories about the universe'smatter distribution and galaxy formation will becomeequations, numbers, variables, and other parameters insimulations running on one of Germany's most powerfulsupercomputers, an IBM Unix cluster at the Max PlanckSociety's Computing Center in Garching, near Munich.
Late this year, the group plans to begin storing all of itsoutput data in public repositories available to researchers around the world [see "Downloading the Sky" in this issue]. This accessibility, according to Simon D.M. White, a research director at the Max PlanckInstitute for Astrophysics who leads the German participation inthe Virgo Consortium, will allow researchers to compareeach simulated universe to its ultimate benchmark: theuniverse itself, as observed with ground and space telescopes.
If the simulation produces a bizarre universe that doesn'tresemble ours, the assumptions that underpin the simulationare probably flawed or in need of adjustment. On theother hand, if the virtual cosmos is like the one wesee, researchers will know they are on the right track.In this way, they hope to see some of the deepest mysteriesof the cosmos solved on their computer screens.