Diagram of a wormhole's topology. Public Domain through Wikimedia Commons

Definition: A wormhole is a theoretical entity allowed by Einstein's theory of general relativity in which spacetime curvature connects two distant locations (or times).

The name wormhole was coined by American theoretical physicist John A. Wheeler in 1957, based on an analogy of how a worm could chew a hole from one end of an apple through the center to the other end, thus creating a "shortcut" through the intervening space.

The picture to the right depicts a simplified model of how this would work in linking two areas of two-dimensional space.

The most common concept of a wormhole is an Einstein-Rosen bridge, first formalized by Albert Einstein and his colleague Nathan Rosen in 1935. In 1962, John A. Wheeler and Robert W. Fuller were able to prove that such a wormhole would collapse instantly upon formation, so not even light would make it through. (A similar proposal was later resurrected by Robert Hjellming in 1971, when he presented a model in which a black hole would draw matter in while being connected to a white hole in a distant location, which expels this same matter.)

In a 1988 paper, physicists Kip Thorne and Mike Morris proposed since that such a wormhole could be made stable by containing some form of negative matter or energy (sometimes called exotic matter). Other types of traversible wormholes have also been proposed as valid solutions to the general relativity field equations.

Some solutions to the general relativity field equations have suggested that wormholes could also be created to connect different times, as well as distant space. Still other possibilities have been proposed of wormholes connecting to whole other universes.

There is still much speculation on whether it is possible for wormholes to actually exist and, if so, what properties they would actually possess.

Also Known As: Einstein-Rosen bridge, Schwarzschild wormhole, Lorentzian wormhole, Morris-Thorne wormhole

Examples: Wormholes are best known for their appearance in science fiction. The television series Star Trek: Deep Space Nine, for example, largely focused on the existence of a stable, traversible wormhole that connected the "Alpha Quadrant" of our galaxy (which contains Earth) with the distant "Gamma Quadrant." Similarly, shows such as Sliders and Stargate have used such wormholes as the means of traveling to other universes or distant galaxies.