Wormholes in spacetime and the constants of nature

The proposal that wormholes in spacetime cause the cosmological constant Λ to vanish is reviewed, and its implications are studied. Wormholes also drive Newton's constant G to the lowest possible value. The requirement that G is at its minimum determines, in principle, all other constants of Nature. In practice, the values of fundamental constants other than Λ cannot be predicted without a detailed knowledge of Planck-scale physics. (orig.)