Indexed on: 01 Dec '74Published on: 01 Dec '74Published in: International Journal of Theoretical Physics
Closed, compact, oriented, Lorentzian four-manifolds are investigated using elementary cobordism theory. The groups of cobordism classes of such manifolds under various cobordism relations are calculated. Oriented vector cobordism classes form an infinite free cyclic group and oriented cobordism classes form a subgroup of index two in the four-dimensional oriented cobordism group. The properties of compact five-manifolds bounded by closed, compact, oriented, Lorentzian four-manifolds are investigated and some speculations made on their possible interpretation.