Wormholes

One of the problems faced in nearly every story set in space is how to travel astronomical distances without spending years in a spaceship and one leading theory on how this could be done is to use wormholes. Wormholes are simply sections of space that are warped into a shape that creates a shortcut between two widely separated locations. The original theory for these phenomena was proposed in 1935 and called them Einstein-Rosen bridges.

This and other theories exist that allow for various types of wormholes, but they have rather problematic requirements. Any bending of the fabric of space-time requires a massive object, and in order to keep the opening of a wormhole from collapsing into nonexistence it would need to be surrounded by exotic matter with a negative mass. No one has found anything with a negative mass, but some scientists think that the Casimir effect could demonstrate an instance of negative energy, which, by Einstein’s famous equivalence of mass and energy (E=mc²), would prove that exotic matter with negative mass could exist. The existence of negative energy is still quite controversial, but even if it were not there would still be a significant problem creating any of it, since the laws of thermodynamics dictate that you cannot reduce the total energy in a region to less than zero. The Casimir effect only shows a temporary point of negative energy and even that only exists from certain points of view. An additional obstacle to the use of wormholes is the quantity of exotic matter needed: maintaining the opening of even a small traversable wormhole would require a negative mass roughly equivalent to that of a planet.

So wormholes look like a great way to travel to others stars, but only if you happen to have a planet sized lump of a possibly nonexistent material on hand. Oh, and you would also need the same setup on the far end of the wormhole, so you’d better be prepared to spend a few decades or even centuries waiting for someone to get there by other means and arrange the exotic matter at the receiving end.