A wormhole is a hypothetical shortcut between two distant points in space. Wormholes play a critical role in many science fiction movies—In physics, however, these tunnels in spacetime have remained purely hypothetical.

Two separate teams of scientists have suggested new theories as to how to make wormholes safe enough to be traversable by humans. Both studies were published in the journal *Physical Review Letters*.

Wormholes, similar black holes, appear in the equations of Albert Einstein’s general theory of relativity, published in 1916.

A significant postulate of Einstein’s theory is that the universe has 4 dimensions—3 spatial dimensions and time as the 4th dimension. Together they form what is known as spacetime, and spacetime can be stretched and curved by massive objects like stars, much as a rubber sheet would be curved by a metal ball sinking into it.

The curvature of spacetime determines the way objects like planets and spaceships, but also light, move within it. “In theory, spacetime could also be bent and curved without massive objects,” says Blázquez-Salcedo, the Complutense University of Madrid in Spain. In this situation, a wormhole would be an extremely curved region in spacetime that resembles two interconnected funnels & connects 2 distant points in space, similar to a tunnel.

The physicist explains, “From a mathematical perspective, such a shortcut would be possible, but no one has ever observed a real wormhole.”

Besides, such a wormhole would be unstable. If for example, a spaceship were to fly into one, it would instantly collapse into a black hole—an object in which matter disappears, never to be seen again. The connection is provided to other places in the universe would be cut off. Past models propose that the only way to keep the wormhole open is with an exotic form of matter that has a negative mass, or in other words weighs less than nothing, and which only exists in theory.

Although, Blázquez-Salcedo and his colleagues Dr. Christian Knoll from the University of Oldenburg and Eugen Radu from the Universidade de Aveiro in Portugal show in their model that wormholes could also be traversable without such matter.

The scientists picked a comparatively simple “semiclassical” approach. They combined elements of relativity theory with elements of quantum theory and classic electrodynamics theory. In their model, they consider certain elementary particles such as electrons and their electric charge as the matter that is to pass through the wormhole.

As a mathematical description, they picked the Dirac equation, a formula that describes the probability density function of a particle as per quantum theory and relativity as a so-called Dirac field.

As the physicists report in their study, it is the inclusion of the Dirac field into their model that allows the existence of a wormhole traversable by matter, given that the ratio between the electric charge and the mass of the wormhole exceeds a certain limit.

In addition to matter, signals—for instance, electromagnetic waves—could also traverse the tiny tunnels in spacetime. The microscopic wormholes postulated by the team would probably not be suitable for interstellar travel.

Moreover, the model would need to be further refined to find out whether such unusual structures could actually exist. “We think that wormholes can also exist in a complete model,” says Blázquez-Salcedo.

There’s one issue, however: the proposed wormholes would just be microscopic and far too small for humans to traverse through.

But Juan Maldacena from the Institute for Advanced Study, New Jersey, and Alexey Milekhin from Princeton University may have a solution for a much larger traversable wormhole.

Their 5-dimensional wormhole, as detailed in a separate paper, could theoretically permit a person to travel across an entire galaxy in less than a second, experiencing a force of less than 20 g.

The only trouble is that only the person traversing the wormhole would perceive a second going by. To any outsider, the journey would appear to take 1000s of years.

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