5 February 2007

Physicists Hope For Glimpse Of Extra Dimensions

by Kate Melville

Looking backward in time to an instant after the big bang, physicists at the University of Wisconsin-Madison have devised a way to unlock the hidden shapes of alternate dimensions of the universe. Their study, in Physical Review Letters, demonstrates that the shapes of extra dimensions can be "seen" by deciphering their influence on cosmic energy released by the violent birth of the universe 13 billion years ago. The method may mean that physicists can use experimental data to discern the nature of these elusive dimensions - the existence of which is a critical but as yet unproven element of string theory, a controversial contender for a "theory of everything."

String theory predicts the existence of six extra spatial dimensions - "hidden" dimensions - curled in tiny geometric shapes at every single point in our universe. The new Wisconsin work may provide a long-sought foundation for measuring this previously immeasurable aspect of string theory. According to string theory mathematics, the extra dimensions could adopt any of tens of thousands of possible shapes, each shape theoretically corresponding to its own universe with its own set of physical laws.

Wisconsin's Gary Shiu says the many-dimensional shapes are far too small to see or measure through any usual means of observation, which makes testing this crucial aspect of string theory very difficult. "You can theorize anything, but you have to be able to show it with experiments," he says. "Now the problem is, how do we test it?"

Shiu's approach is based on the idea that the six tiny dimensions had their strongest influence on the universe when it itself was a tiny speck of highly compressed matter and energy - that is, in the instant just after the big bang. "Our idea was to go back in time and see what happened back then," says Shiu. Lacking the requisite time machine, they used the next-best thing: a map of cosmic energy released from the big bang. The energy, captured by satellites such as NASA's Wilkinson Microwave Anisotropy Probe (WMAP), has persisted virtually unchanged for the last 13 billion years, making the energy map basically "a snapshot of the baby universe," Shiu says.

Much as a shadow can impart the shape of an object, the pattern of cosmic energy in the sky can give an indication of the shape of the other six dimensions present, Shiu believes. To learn how to read telltale signs of the six-dimensional geometry from the cosmic map, Shiu's team worked backward. Starting with two different types of mathematically simple geometries, called warped throats, they calculated the predicted energy map that would be seen in the universe described by each shape. When they compared the two maps, they found small but significant differences between them.

The results indicate that specific patterns of cosmic energy can hold clues to the geometry of the six-dimensional shape. Though the current data are not precise enough to compare their findings to our universe, upcoming experiments such as the European Space Agency's Planck satellite should have the sensitivity to detect subtle variations between different geometries, Shiu believes.

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

Related articles:
String Theory - KNOT!
Physicists Propose Test For String Theory

Source: University of Wisconsin-Madison