A SPHERICAL IMPULSE GRAVITY-WAVE

An exact solution of Einstein's vacuum field equations describing a spherical-fronted impulsive gravity wave is given in a coordinate system in which the metric tensor is continuous across the (future null cone) history of the wave front in Minkowskian space-time. A coordinate transformation is presented which reduces the line element to Minkowskian form in the future of the null cone (it is manifestly in Minkowskian form in the past of the null cone) and enables us to demonstrate how the solution has been constructed using the Penrose procedure of subdividing flat space-time into two halves with the future null cone as boundary and then reattaching the halves with a warp.