Ever since the Hawking-Penrose singularity theorems of the 1960s, it has become clear that physically interesting space-times will generally possess boundaries. This paper reviews various boundary structures, including the g-, c- and b- boundaries, and a recent proposal of Scott and Szekeres called the "abstract boundary" is described in some detail. It is shown that causal and topological properties may be assigned to the abstract boundary. The mathematical formulation fo questions such as the cosmic censorship hypothesis, the Weyl curvature hypothesis and other problems is discussed. The status of these problems is briefly reviewed.

HOME