Does the expanding and accelerating universe require a mysterious "dark energy" force, accounting for perhaps 70% of the mass-energy budget of the universe, to work? Not according to New York University physicist Georgi Dvali. His theory, presented earlier this month at the annual meeting of the American Association for the Advancement of Science, explains the observations not with some sort of neo-aether, but instead with a modification of gravity itself.

Instead of gravity acting on objects with a predictable and consistent force, Dvali postulates that over vast intergalactic distances gravity "leaks" out of the observed universe:

"The gravitons behave like sound in a metal sheet," says Dvali. "Hitting the sheet with a hammer creates a sound wave that travels along its surface. But the sound propagation is not exactly two-dimensional as part of the energy is lost into the surrounding air. Near the hammer, the loss of energy is small, but further away, it's more significant."

The result? A universe that becomes "self-accelerating" over time, just as we observe now.

The mechanism that "springs the leak"? The extra dimensions predicted in string theory, which postulate as many as seven extra dimensions to the better-known four of conventional spacetime. In fact, the test results predicted by Dvali's theory could end up being an important confirmation of string theory, which to-date has proven stubbornly resistant to such real-world tinkering.