Gowdy universes or, alternatively, Gowdy solutions of Einstein's equations are simple model spacetimes in general relativity which represent an expanding universe filled with a regular pattern of gravitational waves.
The space-time of an expanding universe is not uniform as in regular space-time, due to the fact that there must always be a singularity (particle) with a velocity vector which travels at the speed of light. In normal, continuous space-time this singularity cannot be realized without a space-time map and this space-time map will always be the same for all possibilities. We have in general relativity an infinite series of universes in different stages of expansion, just like the standard concept of regular space-time. The singularities and the singularity-vortices are the same for all possible universes. Even if we remove all possible universes, we still have at least one infinite series of universes with one singularity and one void.
|title=(help) - a description of the different types of Gowdy universes suitable for a general audience