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## RELATIVITY GOES DIGITAL

### Einstein's Challenge

In 1916, Albert Einstein published his General
Theory of Relativity, which argues that
gravity is bound up with the curvature
of spacetime by matter (or its equivalent in energy). Expressed mathematically as a set of 10 highly complex, coupled,
nonlinear partial differential equations, the theory
predicts that a sufficiently dense body -- particularly a black hole -- would possess a gravitational field so strong that it would cause space to curve in on itself.

**Ed Seidel, NCSA/Univ. of Illinois, on-camera**

QuickTime Movie (1.2 MB);
Sound File (788K);
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Solving the equations in their full generality (i.e. without restrictions placed on time or geometry) will be essential for understanding what happens when two black holes collide and coalesce, the behavior of a pair of spiraling neutron stars, or the inner collapse of massive stars when they run out of fuel.

For example, any disturbance to a black hole will cause it to oscillate and emit
gravitational
waves. A cataclysmic event, such as the collision of two black holes (theory and observations suggest that there should be a few black hole collisions within a detectable range each year), is predicted by the theory to send gravitational waves rippling through space. The resulting signal, though faint, should be detectable here on Earth by instruments slated for completion by the turn of the century.

### Enter Numerical Relativity

By using Einstein's equations to predict the pattern of gravity waves emitted during the collision of two black holes, or generated in a variety of other cataclysmic events, and comparing the predictions with the observations, an alliance of computational scientists from nine institutions plans to test this as yet unconfirmed prediction of Einstein's famous theory. These scientists belong to a research discipline called **Numerical Relativity**.
**Larry Smarr, NCSA/Univ. of Illinois, on-camera**

QuickTime Movie (1.6 MB);
Sound File (1.0 MB);
Text

**Ed Seidel, NCSA/Univ. of Illinois, on-camera**

QuickTime Movie (856K);
Sound File (579K);
Text

In order to apply the Einstein Equations to "real"
astrophysical phenomena and arrive at meaningful solutions, numerical relativists must employ high performance computers to **crunch the numbers**.
But solving the equations numerically demands another crucial component. Elaborate **computer codes** must be built to enable the machines to crack the problems thrown at them. Relativity researchers also need advanced **visualization** technologies to analyze, explore and interact with the numerical output of their simulations.
**Movies** that distill the time-dependence of all the components of a model into a minutes or seconds of animation can yield profound insights into the complex behavior of model systems, including black holes.

### Digital Relativity: Past, Present and Future

It's no surprise that the history of numerical relativity is bound up with the emergence and development of supercomputers. The ability of numerical relativists to apply the Einstein Equations to more and more complex spacetime geometries continues to depend on the emergence of still more powerful machines. These, in turn, keep spurring scientists to build yet more sophisticated computer codes.

**Larry Smarr, NCSA/Univ. of Illinois, on-camera**

QuickTime Movie (1.8 MB);
Sound File (878K);
Text

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#### Copyright © 1995, The Board of Trustees of the University of
Illinois

*NCSA. Last modified 11/9/95.*