Cosmic Tangle

Did the Big Bang Come with Strings Attached?

by Paul Preuss | The power of supercomputers at the National Energy Research Scientific Computing Center (NERSC) has enabled Julian Borrill of NERSC's Scientific Computing Group to model, in striking detail, a possible state of the universe only a hundred billionth of a trillionth of a trillionth of a second (10-35 second) after the Big Bang.

In 3-D computer movies created by Borrill and Kevin Campbell of NERSC's Visualization Group, objects called "semilocal strings" condense out of interacting quantum fields to form writhing tubes of energy. Some link with other tubes in space-spanning filaments. Some, like the Worm Ourobouros, join head to tail and devour themselves, ultimately popping out of existence. These images, redolent of alchemy but firmly grounded in theoretical physics, may help answer fundamental cosmological questions—such as how our present clumpy universe grew from its smooth initial state.

"Given enough time, gravity can do the job of building stars and galaxies and larger structures," says Borrill, "so long as the right sort of initial perturbations occurred in the density of the very early universe. One candidate for causing those perturbations is the semilocal string." Semilocal strings—not to be confused with the vibrating entities of superstring theory—are related to cosmic strings, a product of the topology of the vacuum. But semilocal strings involve a complex interplay of quantum matter and force fields.

"They are like magnetic tubes with north and south poles," Borrill says. "They originate in a four-dimensional vacuum; it takes eight quantum fields to construct them—four matter fields and four force fields." Unlike cosmic strings, semilocal strings "could answer the question of why there is more matter than antimatter in the universe. One place to look for the generation of this asymmetry is in interactions on the surfaces of these magnetic tubes."

While Borrill and his colleagues Andrew Liddle and Ana Achœcarro had previously calculated many properties of semilocal strings in two dimensions, until Borrill's recent work on the Cray T3E supercomputer the full three dimensional strings were too complex to model, much less understand. "Some people claimed semilocal strings couldn't form," Borrill says. "If only a few formed—if their density was too low—they might just close up on themselves, shrink, and quickly disappear."

The NERSC supercomputer allowed Borrill to specify well over 3 billion initial quantum field values and, with Campbell, to generate 3-D images and movies that allowed a qualitative understanding of the strings' behavior.

"We couldn't have known what we were going to see," Borrill says. "In fact we proved that semilocal strings can exist—enough strings formed that they tended to join onto their neighbors rather than themselves, so that many of them rapidly grew, and the network of strings as a whole persisted."

Having done the initial calculations as a proof of principle, Borrill says, "we can now address more complicated questions," including further studies of matter and antimatter formation, and the implications for patterns of fluctuations in the cosmic microwave background radiation—the earliest moment in the history of the universe which can be directly observed.

"It's a challenge to try to test theories of the early universe when the only observations we can make are billions of years after the fact." Borrill says that machines like the 512-processor Cray T3E at NERSC "are essential to model the initial conditions and see how they evolve, so we can compare the results with what we can observe."

Borrill jokes that the computer-generated strings in his movies are "bigger than the Titanic and a fraction of the cost." Many of these truly cosmic images and movies are available on the web at

Next: A Curvier Form of Carbon

— A Tool for Discovery —
A Tool for Discovery | Seeing It Whole | Climate Modeling | Cosmic Tangle | A Curvier Form of Carbon

Research Review Fall '98 Index | Berkeley Lab