## Oldenburg physicists deal with hypothetical tunnels in space-time

Wormholes play an important role in many science fiction films – as a shortcut between two distant places in space. In physics, however, these tunnels in spacetime have so far been purely hypothetical structures. An international team led by Dr. Jose Luis Blázquez-Salcedo from the University of Oldenburg is now presenting a new theoretical model in the journal Physical Review Letters that makes microscopic wormholes appear less exotic than previous theories.

Like black holes, wormholes appear in the equations of general relativity that Albert Einstein established in 1916. An important assumption of the theory is that the universe has four dimensions – three dimensions of space and time as the fourth dimension. Together they form what is known as spacetime. It is curved by heavy objects like stars, similar to a rubber blanket into 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 curved without heavy objects,” explains Blázquez-Salcedo, who has meanwhile moved to the Spanish Universidad Complutense de Madrid. A wormhole would therefore be an extremely strongly curved area of spacetime, which resembles two connected funnels and connects two distant places like a tunnel. “Mathematically speaking, such an abbreviation is possible, but no one has ever observed a real wormhole,” says the researcher.

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 require an exotic, only theoretically conceivable form of matter that has a negative mass, i.e. weighs less than nothing.

Blázquez-Salcedo and his colleagues Dr. Christian Knoll from the University of Oldenburg and Eugen Radu from the Universidade de Aveiro in Portugal now show in their study that wormholes can be passable even without this assumption. The researchers chose a comparatively simple, “semiclassical” approach, as they write: They combined elements of relativity theory with elements of quantum theory and the classical theory of electrodynamics. 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 according to quantum theory and relativity theory as a so-called Dirac field.

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 cross the tiny tunnels in space-time. The microscopic wormholes that 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.

The work was developed within the graduate school “Models of Gravity”, which the Oldenburg physicist Prof. Dr. Jutta Kunz together with Prof. Dr. Claus Lämmerzahl from the Center for Applied Space Technology and Microgravity (ZARM) at the University of Bremen. In addition to the University of Oldenburg, other universities and research centers are also involved.

**Original article***: Jose Luis Blázquez-Salcedo, Christian Knoll and Eugen Radu: “Traversable wormholes in Einstein-Dirac-Maxwell theory”, Physical Review Letters, **journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.101102*

*Provided by **University of Oldenburg** *