Adapted from P. Coles, 1999, The Routledge Critical Dictionary of the New Cosmology, Routledge Inc., New York. Reprinted with the author's permission. To order this book click here:

A hypothetical hole or tunnel in the fabric of spacetime. The standard cosmological models are based on the assumption that the Universe has a simple topological structure, like that of a sphere. However, some solutions of the equations of general relativity have been found that correspond to wormholes connecting regions of spacetime in a kind of short-cut. Intriguingly, the two ends of a wormhole might be located at different points in both space and time, and it appears to be possible (at least mathematically) to achieve time travel by moving along the tunnel.