Time Travel Is Possible Under These Conditions

Time travel has been a subject of interest among scientists and regular people. It's often the theme of TV shows and movies, and traveling back to the past has become a dream many are still trying to achieve. But is it really possible?

Traveling further into the future could be possible if we move at the speed of light or travel in the proximity of a black hole. Time would slow down, and this would enable us to travel arbitrarily far into the future. However, traveling back to the past would be an entirely different matter.

Gaurav Khanna, a physics professor at the University of Massachusetts, Dartmouth, recently wrote in an article for The Conversation that he has always been fascinated with the concept of time travel and has focused his attention on the theory that underlies this concept: Einstein's relativity. He noted that in a paper published in the journal Classical and Quantum Gravity, one of his doctoral students described the process of building a time machine using a simple construction.

Einstein's general theory of relativity allows for the possibility of time loops as a result of the warping and folding of time. The idea is that if you're traveling within this loop, you could end up at a moment in the past and experience the same moments all over again, though you wouldn't notice that it has happened before. This is referred to as closed time-like curves, or what we all know as time machines.

However, studies by well-known physicists like Stephen Hawking and Kip Thorne have shown that nature forbids time loops. In “Chronology Protection Conjecture,” Hawking theorized that nature doesn't allow us to change history, even if time travel were possible. But the work of Caroline Mallary, Khanna's student, may force scientists to review how we look at closed time-like curves.

Exotic material, a matter with negative mass, is believed to be present in order for a time loop to exist, but it is not known to exist in nature. However, Mallary's model doesn't require negative mass exotic material that is believed to be needed for closed time-like curves to develop in physical systems.

Her model of a time machine consists of two super long cars that are made from material that is not exotic and have positive mass. They are parked parallel to each other. One car moves forward rapidly, while the other remains parked. Through the model, Mallary showed that in this setup a time loop can be found in the space between the two cars.

But could this be actually built? The answer is, unfortunately, no. The model the student made requires that the center of each car would have infinite density. This means that they contain singularities with an infinite density, pressure and temperature. In addition, unlike singularities found in the interior of black holes, which makes them completely inaccessible from the outside, the objects in the model can be seen and observed and therefore have true physical effects.

Scientists don't believe this particular object could be found in nature, so it looks like people will not have the ability to travel through time just yet. However, Khanna pointed out that Mallary's model could be evidence that physicists need to look into closed time-like curves a little more.