# Scientists devise test for string theory

PORTLAND, Ore. — Researchers at the University of Wisconsin at Madison claim that they have found a way to determine the shape of the extra dimensions predicted by string theory.

String theory is a leading candidate in the search to identify a single principle that guides all other forces of nature in the universe—weak and strong nuclear forces as well as electromagnetic and gravitational forces. But until now no one had devised an experiment to test it.

The researchers suggest that they can confirm the unified theory from the effects seen as they peer back into time to observe the most distant astronomical objects, which existed "at the beginning" of the universe.

The postulation of these extra dimensions—up to 10 in all—explains why only the point-like tips of these particles are visible to humans: The rest of each particle could be spread through this multidimensional space. Their interactions in the other dimensions—akin to interference among vibrating "strings"—explains why quantum mechanics requires statistics to describe matter: their tips could be jumping about like the end of a whip.

The theory unifies all forces in nature by modifying the most basic assumption of quantum physics—that particles are point-like objects. String theory maintains instead that we are only observing their point-like appearance because we are perceiving only three physical dimensions.

Engineers have already harnessed derivatives of quantum mechanics' statistical interpretation of matter, such as the Casimir effect. The effect is based on the quantum-mechanical assumption that empty space is not really empty, but at any given moment is composed of particles that wink into and out of existence from previously empty space. Microelectromechanical systems have harnessed the energy of these quantum statistics in experiments conducted by EE Steve Lamoreaux at Los Alamos National Laboratory and professor Ephraim Fischbach at Purdue University.

String theory allows engineers to compute the number of extra dimensions that explain quantum mechanics' statistical interpretation of matter—namely, gauge anomalies. For instance, photons are assumed to have zero mass, but string theory predicts that high-energy string modes could allow photons to exert pressure normally attributed to particles with mass, including the Casimir effect already observed at Los Alamos National Laboratory.

There are tens of thousands of possible shapes for the 10 dimensions of space, according to string theory. By observing their effects in three-dimensional space, we can infer which possible shape best describes our universe. These effects will be easier to see at the beginning of the universe because the tiny dimension of string theory will match the tiny dimensions of space at its birth.

Next, the University of Wisconsin scientists propose to observe the extra dimensions of string theory from their effects on the background of cosmic energy, which has remained virtually unchanged since first being released by the violent birth of the universe.

The National Aeronautics and Space Administration's Wilkinson Microwave Anisotropy Probe, for which the team received a 2006 Nobel Prize, has the most accurate data about the background of cosmic energy in the universe. Unfortunately, that data is not accurate enough to prove the case for string theory.

However, the University of Wisconsin theorists predict that upcoming experiments on the European Space Agency's Planck satellite will have the sensitivity needed to determine the shape of the extra dimensions predicted by string theory.

The National Science Foundation, the Energy Department and the Research Corp. funded the research.