Shortcuts in the fifth dimension

If our Universe is a three-brane embedded in a five-dimensional anti-de Sit ter spacetime, in which matter is confined to the brane and gravity inhabit s an infinite bulk space, then the causal propagation of luminous and gravi tational signals is in general different. A gravitational signal traveling between two points on the brane can take a "shortcut" through the bulk, and appear quicker than a photon traveling between the same two points along a geodesic on the brane. Similarly, in a given time interval, a gravitationa l signal can propagate farther than a luminous signal. We quantify this eff ect, and analyze the impact of these shortcuts through the fifth dimension on cosmology. (C) 2001 Published by Elsevier Science B.V.