A wormhole is a hypothetical physical object that allows space-time to create a shortcut through space and time. According to theories, two very different bodies in the universe can be connected using the curvature of space-time.
An observer passing through a wormhole never exceeds the speed of light, no difference between the start and the finish overcomes a certain way like a light beam flying directly.
The wormhole could connect extremely long distances, such as a billion light-years or more, short distances, such as several meters, different universes, or different time points.
For a better understanding and imagine wormholes is to take a sheet of paper and draw two somewhat distant points on one side of the paper. The sheet of paper represents a plane in the spacetime continuum, and the two points represent a distance to be traveled, but theoretically a wormhole could connect these two points by folding that plane (i.e. the paper) so the points are touching. In this way it would be much easier to traverse the distance since the two points are now touching.
This object was first mentioned in 1935 by Albert Einstein and Nathan Rosen.
The first type of wormhole solution discovered was the Schwarzschild wormhole, which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that it would collapse too quickly for anything to cross from one end to the other. Wormholes that could be crossed in both directions, known as traversable wormholes, would be possible only if exotic matter with negative energy density could be used to stabilize them.
The second type of wormhole is traversable wormholes. The quantum foam hypothesis is sometimes used to suggest that tiny wormholes might appear and disappear spontaneously at the Planck scale, and stable versions of such wormholes have been suggested as dark matter candidates. It has also been proposed that, if a tiny wormhole held open by a negative mass cosmic string had appeared around the time of the Big Bang, it could have been inflated to macroscopic size by cosmic inflation. If traversable wormholes exist, they could allow time travel.
According to current theories on the nature of wormholes, construction of a traversable wormhole would require the existence of a substance with negative energy, often referred to as “exotic matter”. More technically, the wormhole spacetime requires a distribution of energy that violates various energy conditions, such as the null energy condition along with the weak, strong, and dominant energy conditions.
To see why exotic matter is required, consider an incoming light front traveling along geodesics, which then crosses the wormhole and re-expands on the other side. The expansion goes from negative to positive. As the wormhole neck is of finite size, we would not expect caustics to develop, at least within the vicinity of the neck.