Einstein's general relativity describes gravity, but when applied to the earliest universe or black hole singularities, the equations break down. Cosmologists usually assume the universe is homogeneous and isotropic, simplifying calculations but limiting exploration of more complex scenarios. "Numerical relativity allows you to explore regions away from the lamppost," says Lim, referring to the tendency to stick to solvable but overly simplified conditions.
The technique was originally developed to model black hole collisions and predict the resulting gravitational waves, a task that was solved numerically in 2005. Lim and colleagues propose applying the same methods to cosmic puzzles such as inflation, a rapid expansion in the early universe that explains its large-scale uniformity. Simulations could allow researchers to test different initial conditions or predictions from string theory that give rise to inflation.
Other potential applications include modeling hypothetical cosmic strings and the gravitational waves they might generate, or detecting traces of collisions with other universes if the multiverse exists. Numerical relativity could also explore cyclic models where universes undergo repeated big bangs and crunches, a scenario impossible to test with analytic equations alone.
Because the simulations require supercomputers, progress depends on advancing computational technology. Lim hopes the work will encourage greater collaboration between cosmologists and numerical relativists. "We hope to actually develop that overlap... so that numerical relativists who are interested in using their techniques to explore cosmological problems can go ahead and do it," he says.
Research Report:Cosmology using numerical relativity
Related Links
Foundational Questions Institute, FQXi
Understanding Time and Space
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