Phenomenology of the Gowdy universe on $T^3\times R$

Numerical studies of the plane symmetric, vacuum Gowdy universe on $T^3\times R$ yield strong support for the conjectured asymptotically velocity term dominated (AVTD) behavior of its evolution toward the singularity except, perhaps, at isolated spatial points. A generic solution is characterized by spiky features and apparent “discontinuities” in the wave amplitudes. It is shown that the nonlinear terms in the wave equations drive the system generically to the “small velocity” AVTD regime and that the spiky features are caused by the absence of these terms at isolated spatial points.