by Marcus Chown

The title of Heinrich Paes' latest paper might not mean much to you. To those who know their theoretical physics, however, "Closed timelike curves in asymmetrically warped brane universes" contains a revelation. It suggests that time machines might be far more common than we ever thought possible.

Forget trawling the universe in search of rotating black holes or exotic wormhole tunnels that could supposedly let us hop from one instant to another. According to Paes, a physicist at the University of Hawaii at Manoa, and his colleagues, the door to a time machine could be anywhere and everywhere in our universe. And unlike most other scenarios for time travel, we can test this one here on Earth. "I think the ideas presented are wonderful and exciting," says Bill Louis, a physicist at Los Alamos National Laboratory in New Mexico and co-spokesperson for the MiniBoone neutrino experiment at Fermilab, near Chicago. "The question is are they true or not."

This has led to the suggestion that our universe may be like a four-dimensional membrane or "brane" adrift in a higher-dimensional space-time. All of the particles and forces in our universe would be trapped in our brane like flies on fly-paper, so we would have no knowledge of any dimensions other than the four we experience, even though our brane might be floating in a 10-dimensional space-time, or "bulk". "If it is, then there is the possibility of short cuts through higher-dimensional space," says Paes. "It’s such short cuts that make time travel possible."