A computer-generated rendering of a multi-dimensional geometry similar to a warped throat. According to U.S. researchers, comparing theoretical models like this to the radiation left over from the early universe may provide a way to test the string theory model of physics.

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SYDNEY: The extra dimensions key to the mind-boggling concept of the universe called string theory might actually be measurable, according to U.S. researchers.

Physicists at the University of Wisconsin, Madison, have demonstrated that it might be possible to ‘see’ the shapes of the extra dimensions by searching for their influence on the still-visible echoes of the Big Bang.

String theory proposes that every object in the universe is made up not of particles, but of tiny, vibrating strings of energy. Each type of fundamental particle is the result of strings vibrating in different ways.

Much of the excitement over string theory stems from its apparent ability to ‘unify’ the four fundamental forces - electromagnetism, gravity, and the strong and weak nuclear forces - into phenomena that can be explained with a single set of equations, thus providing a complete picture of the universe. Creating such a ‘grand unified theory’ of physics, a quest that dominated the careers of many physicists, including Albert Einstein, has so far proved impossible under more conventional models of particle physics.

Although it may have tremendous power to explain the structure of the cosmos, string theory has so far been untestable, partially because it predicts that the universe is made up not only of the four dimensions we can perceive (three spatial dimensions and time), but of another six, 10 in total.

The extra spatial dimensions are hidden inside the ones we can percieve - rolled up into as-yet unknown shapes at every single point in our universe. According to Gary Shiu, the study’s lead author, the physical laws of the universe and the characteristics of elementary particles depend on the geometry of these dimensions. In order to test whether string theory can explain the structure of the universe, he said, scientists must determine whether the extra dimensions exist and what shape they take in our universe.

In today's universe, the shapes created by the extra dimensions are tiny and have been impossible to detect. The team’s new approach, reported in the journal Physical Review Letters, centred on the idea that in the instant after the Big Bang, when the universe was still just a speck, the extra dimensions might have been more apparent. Even, said Shiu, comparable in size to the four we can perceive. In these conditions, the team thought it might be easier to pinpoint the effect of the extra dimensions on the shape of space.

Using two different types of mathematically well-understood multidimensional geometries called warped throats, the team created two different models of hypothetical early universes. When the team compared the two models, they found that the hidden dimensions caused small but significant changes in the structures produced.

"Our results with simple, well-understood shapes give proof of the concept that the geometry of hidden dimensions can be deciphered from the pattern of cosmic energy," he said. "This provides a rare opportunity in which string theory can be tested."

The next step, said Shiu, is to look for the influence of extra dimensions in the energy distribution of our own early universe. Satellites such as the U.S. Cosmic Background Explorer and Wilkinson Microwave Anisotropy Probe have created such maps by observing microwave radiation left over from the Big Bang - radiation has persisted virtually unchanged for the last 13 billion years. But, said Shiu, current data from these satellites are not precise enough to look for the influence of extra dimensions.

Upcoming experiments such as the European Space Agency's Planck satellite should have the sensitivity required to detect subtle variations caused by different geometries, he added.

The implications of such a possibility are profound, said Henry Tye, a physicist at Cornell University in New York. "If this shape can be measured, it would also tell us that string theory is correct."