Contents

24 May 2002
Vol 296, Issue 5572

About The Cover

Cover image expansion

COVER In a new "cyclic" model, the Universe consists of two infinite three-dimensional membranes ("branes") that collide and bounce apart every few trillion years (counterclockwise). Our visible world corresponds to the left brane in each frame. Each collision yields new matter and radiation, which cool to form new galaxies and stars. After trillions of years of accelerated expansion, the Universe becomes empty and the cycle begins anew. More information on branes and other multidimensional concepts can be found in the special section in this issue. 1417 [Image: J. Mazeika and P. Steinhardt]