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.