What's in a wormhole

Wormholes through time and space - without any exotic matter

In many science fiction stories they are an integral part of the universe and often also provide a way of shortening the gigantic distances between the stars. In our physics, wormholes in space-time have so far only been purely hypothetical structures. An international team of researchers has now presented a new theoretical model in which microscopic wormholes play an important role - and may be easier to open than previously thought.

Rubber blanket and tunnel

So far, wormholes have only appeared in the equations of general relativity that Albert Einstein published in 1916. An important assumption of the theory is that the universe has four dimensions - three space dimensions and time as the fourth dimension together form what is known as space-time. It is bent by heavy objects such as stars, similar to a rubber blanket on which a metal ball sinks. The curvature of spacetime determines how objects such as spaceships and planets, but also light, move.

"In theory, space-time could be bent and warped without heavy objects," says Jose Luis Blázquez-Salcedo from the University of Oldenburg, who has meanwhile moved to the Spanish Universidad Complutense de Madrid. A wormhole would be an extremely curved area of ​​space-time that resembles two connected funnels and connects two distant places like a tunnel. "Mathematically speaking, such a shortcut is possible, but no one has ever observed a real wormhole," says the researcher.

Transformation into a black hole

Such a wormhole would also be unstable: if a spaceship were to fly into it, for example, it would immediately collapse into a black hole, i.e. an object in which matter disappears forever. The connection to other places in the universe would be cut. In order to keep the wormhole open, previous models required an exotic, only theoretically conceivable form of matter that has a negative mass - in other words, which, in simple terms, weighs less than nothing.

However, in their study, Blázquez-Salcedo and his colleagues Christian Knoll from the University of Oldenburg and Eugen Radu from the Universidade de Aveiro in Portugal show that wormholes can also be passable without this assumption. The researchers chose a comparatively simple, "semiclassical" approach, as they write in the "Physical Review Letters": They combined elements of relativity theory with elements of quantum theory and the classical theory of electrodynamics.

The Dirac equation makes it possible

They considered certain elementary particles such as electrons and their electrical charge to be the matter that is supposed to pass through the wormhole. As a mathematical description, they chose the Dirac equation, a formula that describes the probability of a particle's location as a so-called Dirac field according to quantum theory and relativity theory.

As the physicists report in their study, it is the consideration of the Dirac field that allows the existence of a wormhole that can be traversed by matter in their model. The prerequisite is that the ratio between the electrical charge and the mass of the wormhole exceeds a certain limit. In addition to matter, signals - such as electromagnetic waves - could also traverse the tiny tunnels in space-time.

Too small to travel

The microscopic wormholes the team envisions would probably not be suitable for interstellar travel. In addition, the model would have to be further refined in order to find out whether the strange structures could actually exist. "We suspect that the wormholes can also exist in a complete model," says Blázquez-Salcedo. (red, March 26, 2021)