Traveling Through a Wormhole May Be Possible—But It Wouldn't Be a Shortcut

Traversable wormholes may not be a shortcut: It would take longer to go through them than to navigate to the point directly. iStock

Scientists and science-fiction writers alike have long been fascinated by wormholes—theoretical tunnels that link two points in space-time, potentially creating shortcuts for travel through the universe, or indeed, other universes (if they exist.)

Now, Harvard physicist Daniel Jafferis and colleagues have shown that traversable wormholes are theoretically possible. However, they wouldn't be very useful for human travel—even if we had the required technology—as it would take longer to go through them than to navigate to the point directly.

The research was presented at the April 2019 Meeting of the American Physical Society in Denver.

Wormholes—like black holes—were first predicted by Albert Einstein's theory of general relativity in 1916. However, they weren't actually called by this name until 1957, when American theoretical physicist John Wheeler proposed his ideas on the subject.

"Traversable wormholes are possible, consistent with the known laws of physics," Jafferis told Newsweek. "That was something of a surprise: Given that space and time are curved and warped by gravity—as known since 1916 when Einstein figured out general relativity—people long wondered whether there could be a tunnel in space that one can get through connecting two different places."

"The obstruction was that in order to get out of such a tunnel of space, there would have to be an 'anti-focusing' of nearby paths in space-time," he said. "By Einstein's equation, that would require anti-gravity, in other words negative energy."

While the mind-bending physics of quantum mechanics—the physics of the very small—allow for this so-called negative energy, it is hard to have a sufficient amount to make a traversable wormhole possible. In fact, it was thought to be impossible, and some scientists actually ruled it out in many cases.

But using the known laws of physics describing gravity and quantum field theory—a set of principles that combines elements of quantum mechanics and relativity to explain the behavior of subatomic particles—the team showed how wormholes through which matter can travel could exist.

"The new ingredient in our setup is the direct interaction between the two ends of the wormhole," Jafferis said. "Then the required negative energy is consistent with the laws of quantum physics and gravity as we understand them."

Fedor Popov, a scientist at the Moscow Institute of Physics and Technology and Princeton University's Department of Physics, who was not involved in the research, said that one of the main ingredients for creating a traversable wormhole is the violation of what he describes as the "null energy condition."

This condition can be thought of, in some ways, as having enough negative energy to prevent the wormhole from collapsing.

"The naive explanation goes as follows: If one sends a pile of matter through the wormhole, this pile can collapse due to the gravitational attraction and get stuck in the wormhole," Popov told Newsweek. But "ubiquitous negative energy will compensate for the gravitational attraction and hence, will allow matter to pass through the wormhole."

This research shows how to create such negative energy and violate the average null energy condition, he said.

But as far as space travel goes, according to Jafferis, "these wormholes would be not very useful, because it takes longer to go through them than to go directly. Not to mention that it is far, far beyond the present capacity of the human race to make and manipulate [such objects] at all, let alone at the quantum level."

Nevertheless, Jafferis said that the most important implication of the research is related to the so-called "black hole information problem"—which has puzzled scientists since the mid-1970s—and the connections between gravity and quantum mechanics.

"An important conceptual puzzle [in physics] is the so-called black hole information problem," Jafferis said. "Stephen Hawking showed in the 1970s that black holes emit radiation which carried away their energy but seemingly not any trace of the information inside—so that even in principle, information thrown into a black hole would be lost forever. That would contradict the rules of quantum physics."

"Our setup gives an example in which some information that was thrown into a black hole can escape, so it might have hints to resolve this puzzle in general."

According to Popov, the idea of a traversable wormhole came from the work of Wheeler, who proposed a hypothetical tunnel that connects two distinct regions of space-time.

"The first example of such a construction could be an eternal black hole, where the black hole connects two "universes" but is not traversable—meaning that one cannot go to the other universe through the black hole, because this 'tunnel' has 'zero' width," Popov said. "So, we need to somehow widen this tunnel, and the Einstein equations allow us to do this, but they require a quite exotic form of matter."

"The [latest] research is quite interesting for the purposes of theoretical physics because it might help us to understand better the black hole information paradox, quantum gravity and quantum mechanics," he said.

Popov also does not rule out that turning a wormhole into a traversable shortcut across the universe could be possible in the future, although, at present, scientists do not know to how to create the kind of exotic matter that would make this feasible.

"Everything I discussed makes the research of the eternal wormholes a very interesting topic for the physics community," he said. "Moreover, I personally hope that the understanding of wormholes could help humanity in the distant future to shorten interstellar traveling."

"In principle, the shortcut is also not forbidden by the Einstein equations," he said. "Therefore, it might be possible that in five to 10 years, someone might find such a matter and we will have shortcut wormholes."