L ooking up at the sky on a clear night, we feel we can see forever. There seems to be no end to the stars and gal- axies; even the darkness in between them is filled with light if only we stare through a sensitive enough telescope. In truth, of course, the volume of space we can observe is limited by the age of the universe and the speed of light. But given enough time, could we not peer ever farther, always encounter- ing new galaxies and phenomena? Maybe not. Like a hall of mirrors, the apparently endless universe might be deluding us. The cosmos could, in fact, be finite. The illusion of infinity would come about as light Is Space Finite? 90 Scientific American April 1999 Is Space Finite? Conventional wisdom says the universe is infinite. But it could be finite, merely giving the illusion of infinity. Upcoming measurements may finally answer this ancient question by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks “INFINITY BOX” evokes a finite cos- mos that looks endless. The box con- tains only three balls, yet the mirrors that line its walls produce an infinite number of images. Of course, in the real universe there is no boundary from which light can reflect. Instead a multiplicity of images could arise as light rays wrap around the universe over and over again. From the pattern of repeated images, one could deduce the universe’s true size and shape. Copyright 1999 Scientific American, Inc.