Is the universe unfolding as it should?

Yes, it is—all around us and on a computer screen near you

by Shannon McCallum

Navarro, in front of an image from the Millennium Run.

Ask University of Victoria astrophysicist Julio Navarro what he did during his recent research sabbatical and he'll fill your head with terms like dark matter, galaxy clusters and black holes.

Oh, and he might mention how he helped create the universe.

A virtual universe, that is. Navarro is a member of the Virgo consortium, an international team of astrophysicists who earlier this year developed the largest computer simulation ever of the structure and growth of the universe. Known as the "Millennium Run," the simulation charts how the cosmos may have evolved since the Big Bang 13.7 billion years ago.

The consortium fed current information on the composition of the universe and the basic laws of physics to one of the largest supercomputers in Europe. One month and 500,000 trillion calculations later, out popped a universe that looks very much like our own.

According to current theory, the universe is a very strange place indeed. The matter we humans are familiar with makes up a scant five per cent of the universe. About a quarter is invisible "cold dark matter," which can only be observed by its gravitational effects on surrounding objects. The remaining 70 per cent is "dark energy," a mysterious force field that is causing the universe to expand at an ever-increasing pace.

"The amazing thing about the Millennium Run is that it shows for the first time that you can cook up a universe like the one we observe with very simple ingredients, even though we don't exactly understand the true nature of those ingredients," says Navarro, who helped conceive and design the simulation.

"For example, if we don't include dark energy, we produce a universe that looks quite different from ours. This tells us our theories are on the right track."

Simulations such as the Millennium Run are crucial for understanding what the universe is made of, where its structure came from, and how it evolved into the galaxies we see today. When combined with observational studies, simulations provide astronomers with powerful tools for probing the mysteries of the universe.

"Our simulation can guide future observational surveys," says Navarro. "For example, it can indicate where and when the earliest black holes would have appeared, so we can tell observational astronomers where to point their instruments.

"Furthermore, we now have a duplicate universe that we can experiment with, instead of passively observing."

The simulation also raises new questions about the Milky Way galaxy, home to our own solar system. This is why Navarro, a world leader in the study of galaxy structure and dynamics, is working with Virgo scientists on a new project—the
Billennium Run—to simulate a single galaxy such as the Milky Way.

The simulation will use one of the world's most powerful academic supercomputers, located in the Netherlands.

"This simulation will enable us to predict with great accuracy the speed, density and direction of the flow of dark matter particles that whiz past Earth—and our own bodies—at any particular time," says Navarro. "This information is invaluable for detecting these subatomic particles, which presumably make up the bulk of the mass of the Milky Way."

Navarro's research is funded by the Natural Sciences and Engineering Research Council, the Canada Foundation for Innovation, the B.C. Knowledge Development Fund, the Canadian Institute for Advanced Research, and UVic.

• The Big Bang is the primeval explosion that most astronomers think gave rise to the universe as we see it today. The age of the universe is calculated by projecting the motion of galaxies backwards through time.
• To see movies and graphics from the Millennium Run simulations, go to www.mpa-garching.mpg.de/galform/press/.