GRAVITY:
Brane-Worlds
Gary Gibbons
According to some of the most audacious ideas yet seen in the field of gravity research, our familiar three-dimensional expanding universe can be viewed as a sheet or domain wall, called a "3-brane", that moves in a higher-dimensional space-time which may turn out to be truly gigantic. The jury is still out on whether the idea really works, but some spectacular advances in string theory have made these once apparently preposterous ideas seem quite natural.
The author is currently at the Laboratoire de Physique Theorique de l'Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris Cedex 05, France. He is on leave from the DAMTP, University of Cambridge, UK. E-mail: gwg1{at}damtp.cam.ac.uk