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See Inside February 2007

The Triangular Universe

Instead of string theory, four-dimensional tetrahedrons

Imagine a landscape composed of microscopic triangular structures that constantly rearrange themselves into new patterns. Seen from afar, the landscape looks perfectly smooth, but up close it is a churning cauldron of strange geometries. This deceptively simple model is at the heart of a new theory called causal dynamical triangulation (CDT), which has emerged as a promising approach to solving the most vexing problem in physics--unifying the laws of gravity with those of quantum mechanics.

For more than 20 years, the leading contender in the quest for unification has been string theory, which posits that the fundamental particles and forces are actually minuscule strings of energy. But some scientists say this theory is misguided because it sets the strings against a fixed background; a better model, they argue, would generate not only particles and forces but also the spacetime they inhabit. In the 1980s and 1990s these researchers developed loop quantum gravity, which describes space as a network of tiny volumes only 10-33 centimeter across. Although this approach has achieved some notable successes, such as predicting the properties of black holes, it has yet to pass an essential test: showing that the jumble of volumes always comes together to form the familiar four-dimensional spacetime of our everyday world.

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