Number 89 (Story #1), July 22, 1992 by Phillip F. Schewe and Ben Stein THE GRAVITATIONAL WAVE BACKGROUND created during the inflationary expansion of the early universe may account for part (perhaps even a large part) of the measured anisotropy in the cosmic microwave background (CMB). This anisotropy is often associated with fluctuations in the density of primordial matter but, according to Lawrence Krauss (303-925-2585) and Martin White of Yale, long-wavelength gravitational waves (with wavelengths as big as the visible universe itself) would result in a CMB quadrupole anisotropy with a value comparable to that actually measured by the Cosmic Background Explorer (COBE). Indeed, the cold dark matter model prediction for the size of the quadrupole, based only on density fluctuations, comes out too low anyway, so, Krauss asserts, it is plausible that some of the quadrupole anisotropy should be due to the gravitational wave background. Future, higher-sensitivity measurements of the CMB, coupled with particle-physics experiments searching for "supersymmetric" particles, may be able to differentiate between the relative influence of gravitational waves and matter-density fluctuations on the CMB. (Article in the 10 August 1992 issue of Physical Review Letters.)