Number 226 (Story #2), May 15, 1995 by Phillip F. Schewe and Ben Stein IS SPACE DISCONTINUOUS? Several theories attempt to combine quantum mechanics, which reigns supreme in the microcosmic world of atoms, and gravity, which governs the macrocosmos of planets and galaxies. One quantum gravity theory, the superstring model, holds that all substance in the universe consists of the ceaseless quantum interactions of tiny strings. In this theory nothing is said of the background space in which the strings move. In another theory, one introduced by Oxford scientist Roger Penrose, space itself is quantized into discrete volumes (each consisting of a spinning loop) with a characteristic size about the same as that for superstrings, 10**-35 m. Although these theories do not make predictions that will be tested in the lab anytime soon (the energy needed to explore so small a size domain is greater than accelerators can muster) theoretical progress continues. For example, Lee Smolin of Penn State and Carlo Rovelli of the University of Pittsburgh have extended the work of Penrose and others. Without making any assumptions about the nature of space, they discover that space is indeed lumpy. Furthermore, they are able to calculate the range, or "spectrum," of allowable lump sizes. In other words, just as quantum mechanics obliges atoms to exist in only certain energy states, so the combination of quantum mechanics and gravity (at least in this particular theory) results in space itself being quantized. (Nuclear Physics B, 29 May 1995.)