Wormholes are known from science finction. They connect two points in space through a kind of tunnel. Instead od traveling through space for years, you can fly with your spaceship into the wormhole and reach your destination within minutes.
In the theory of general relativity wormholes could possibly exist. Our world has four dimensions: three space dimensions and time. Together they form the socalled spacetime. Spacetime can be curved by massive objects like stars or planets. Other stars, planets or spaceships then move along the curved spacetime. Theoretically the spacetime cound be bend and curved without massive object. If two distant points in space are connected in this way, we get a wormhole. This can be shown with the help of mathematics, however, nobody has seen a real wormhole yet.
Furthermore, such a wormhole would be unstable. If a spaceship enters the wormhole, it would collapse to a black hole imedeately. We would need an exotic form of matter to keep the wormhole open, so that a spaceship could traverse it. The exotic matter would be required to weigh less than nothing and exists only theoretically. But there is another solution, an alternative theory of gravity: the Einstein-Gauss-Bonnet-Dilaton theory. Prof. Dr. Jutta Kunz-Drolshagen and Dr. Burkhard Kleihaus from University of Oldenburg, and Prof. Dr. Panagiota Kanti from the Ioannina University in Greece showed in 2011: In this theory stable wormholes exist, which could be used for interstellar travel.
Phys. Rev. Lett. 107, 271101, https://doi.org/10.1103/PhysRevLett.107.271101