LIMITS TO GLOBAL ROTATION AND SHEAR FROM THE COBE DMR 4-YEAR SKY MAPS

Small departures from a homogeneous isotropic spacetime create observa ble features in the large-scale anisotropy of the cosmic microwave bac kground. We cross correlate the maps of the cosmic microwave backgroun d anisotropy from the Cosmic Background Explorer Differential Microwav e Radiometers four-year data set with template maps from Bianchi type VIIh cosmological models to limit global rotation or shear in the earl y universe. On the largest scales, spacetime is well described by the Friedmann-Robertson-Walker metric, with departures from isotropy about each spatial point limited to shear sigma/H-0<10(-9) and rotation ome ga/H-0<6x10(-8) for 0.1 less than or equal to Omega(0) less than or eq ual to 1.