According to Albert Einstein’s general theory of relativity, which explains how gravity operates in the universe, real-life time travel isn’t just a vague fantasy.
Traveling forward in time is an uncontroversial possibility. In fact, physicists send particles forward in time in accelerators… all the time. That’s not to say the technology for sending humans 100 years into the future will be available anytime soon, though.
Time travel to the past, however, is less understood. Still, astrophysicist Eric W. Davis, of the EarthTech International Institute for Advanced Studies at Austin, argues that it’s possible. All you need, he says, is wormhole, which is a theoretical passageway through space-time that is predicted by relativity. Stephen Hawking says they’re “a mathematical possibility exquisitely difficult to realize.”
“You can go into the future or into the past using traversable wormholes,” Davis said.
Einstein-Rosen Bridge – aka Wormholes
Wormholes have never been seen so far and, if they are going to be ever, they would require an enormous amount of energy—for our standards and present technology— for a person to fit inside, never mind a spaceship.
Davis’ paper, though, published in the American Institute of Aeronautics and Astronautics’ journal, addresses time machines and the possibility that a wormhole could be used as a means for traveling backward in time.
Both general-relativity theory and quantum theory offer several possibilities for traveling along a “closed, timelike curve,” or a path that cuts through time and space—essentially, a time machine. In practical terms, a spaceship reaching a far far away location through a wormhole would travel faster than light, that is it would reach destination faster than the time it would take light to cover the same distance in the Euclidean space. But in reality, through a wormhole there’s no distance, speed, or time as we experience it everyday. So, what gives?
In fact, Davis said, scientists’ current understanding of the laws of physics “are infested with time machines whereby there are numerous space-time geometry solutions that exhibit time travel and/or have the properties of time machines.”
Through the wormhole, the spaceship would not take a fine for violating the universal speed limit because the ship never actually travels at a speed faster than light. We couldn’t actually define a speed for the spaceship within the wormhole.
Theoretically, a wormhole could be used to cut not just through space, but through time as well. ”Time machines are unavoidable in our physical dimensional space-time,” David wrote in his paper. “Traversable wormholes imply time machines, and [the prediction of wormholes] spawned a number of follow-on research efforts on time machines.”
However, Davis adds, turning a wormhole into a time machine won’t be easy. “It would take a Herculean effort to turn a wormhole into a time machine. It’s going to be tough enough to pull off a wormhole,” recent models use quantum field fluctuation that points to—at least—keeping the discussion alive.
Exquisitely difficult to realize
There are several theories for how the laws of physics might work in concert to prevent time travel to the past using wormholes. ”Not only do we assume [time travel into the past] will not be possible in our lifetime, but we assume that the laws of physics, when fully understood, will rule it out entirely,” said Robert Owen, an astrophysicist at Oberlin College in Ohio who specializes in black holes and gravitation theory.
That’s where quantum theory comes in. Like general relativity, quantum theory is a system for explaining the universe, describe exotic properties, and conceptualize improbable scenarios and characteristics. Physicists have used quantum mechanics to assert that traveling through a wormhole would create something called a quantum back reaction. In a quantum back reaction, the act of turning a wormhole into a time machine would cause a massive buildup of energy, ultimately destroying the wormhole just before it could be used as a time machine.
However, the mathematical model used to calculate quantum back reaction only takes into account one dimension of space-time. ”I am confident that, since [general relativity] theory has not failed yet, that its predictions for time machines, warp drives and wormholes remain valid and testable, regardless of what quantum theory has to say about those subjects,” Davis adds.
This illustrates one of the key problems in all these approach to the theory of time travel: physicists have to ground their arguments in either general relativity or quantum theory—both of which are incomplete models—and unable to encompass the entirety of our complex, mysterious universe. Before we can figure out time travel, we need to find a way to reconcile general relativity and quantum theory into a quantum theory of gravity. A Grand Unification Theory might then serve as the basis for further study of time travel.
Therefore, Owen argues that it’s impossible to be certain of whether time travel is possible yet. “The wormhole-based time-machine idea takes into account general relativity, but it leaves out quantum mechanics,” Owen argues. “But including quantum mechanics in the calculations seems to show us that the time machine couldn’t actually work the way we hope.”
Davis, however, believes scientists have discovered all they can about time machines from theory alone, and calls on physicists to focus first on faster-than-light travel. ”Until someone makes a wormhole, there’s no use getting hyped up about a time machine,” Davis concludes.
Accomplishing this will require a universally accepted quantum gravity theory—an immense challenge—but this is exactly where modern theoretical physics studies are marching to.