2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/33694This paper summarizes the contribution presented at the IX Marcel Grossmann Meeting (Rome, July 2000). A simple model of spacetime foam, made by $N$ Schwarzschild wormholes in a semiclassical approximation, is here proposed. The Casimir-like energy of the quantum fluctuation of such a model and its probability of being realized are computed. Implications on the Bekenstein-Hawking entropy and the cosmological constant are considered. A proposal for an alternative foamy model formed by $N$ Schwarzschild-Anti-de Sitter wormholes is here considered.6 pages, RevTex. To be submitted to the on-line proceedings of the Ninth Marcel Grossmann Conference (Rome, 2-8 July 2000); abbreviated version to be submitted to the printed proceedingsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext