COSMIC WALLS FROM GRAVITATIONAL COLLAPSE

The formation of plane cosmic walls of negligible thickness from the c ollapse of smooth inhomogeneous plane-symmetric distributions of matte r is considered. Two models with different asymptotic behaviors far fr om the wall in formation are constructed. In the first, the fluid far from the wall is anisotropic, with pressures proportional to density. The second model describes an asymptotically isotropic ideal gas in is entropic flow. Even though both models start from matter distributions with positive density and pressures everywhere, it is found that, dur ing the collapse, negative pressures (tensions) appear within the wall in formation.