Mar 4, 20225 min read

Wormholes and Time Travel

As a kid, you would have imagined going on a time machine and meeting Einstein, Napoleon, Shakespeare, Jesus Christ, Aristotle, or even tyrannosaurus. Time travel might sound more like fiction than scientific fact, but the study of physics tells us that time travel is theoretically possible in real life.

Time Travel and the Speed of the Light

Einstein’s theory of relativity states that time is not absolute, but relative. As one moves faster through space, one moves slower through time, and this phenomenon is called time dilation. The time dilation changes significantly according to the speed of an object moving through space. Especially when the speed of light is approached, the time dilation becomes pretty intense. Space and time are not completely separated and neither one is independent of another. Spacetime is a four-dimensional model containing both space and time. Spacetime with rotating blackholes or cosmic strings allows time travel to the past.

As the theory of relativity explains, nothing can be faster than the speed of light. Therefore, if someone were to travel to Alpha Centauri, which is about 4 light-years away, and return to Earth, at least 8 years should be spent. If one decides to travel all the way to the center of our galaxy and return, it takes a hundred thousand years the least. At this point, you might wonder how the traveler can stay alive until the return to the earth. Luckily, as mentioned before, time is relative. Just as in the twin paradox, the travel time felt by the traveler is much shorter than people on earth. During a few years of space travel, hundreds of thousands of years would have passed on the earth.

If one can move faster than the speed of light, time travel is absolutely possible because one moves through time slower while others experience a faster flow of time. However, breaking the speed limit, which is the light speed, seems impossible in real life since the theory of relativity explains that the rocket needs more and more amount of energy as it reaches the speed of light. Modern particle accelerator could accelerate particles until 99.99 percent of light speed, but no matter how much energy was added, the particles could not go any faster than the light speed. If it isn’t possible for particles to move faster than the speed of light, this would also be the case for the rocket.

*Cosmic strings are hypothetical one-dimensional defects formed due to symmetry breaking in the early universe. Cosmic strings have an approximate tension of 1024 tons, which makes them more like a rubber band rather than a string. If the earth sticks to the cosmic string, it would be able to start moving with the speed of 60 miles per hour from rest in 1/30 second.

*In the twin paradox, one of the twins lives at the very top of the mountain, and the other lives at the beach. One living on the mountain would age faster than the other, but the age difference will be unnoticeably small. On the other hand, when one of them goes on space travel for a very long time with a speed of light, the one on the earth would age much faster than the other.

*The speed of light is 3x108 m/s.

Wormholes

Still, there is a possible method for humans to time travel: going through a wormhole. According to Einstein, space and time are flexible, so space-time can be twisted, creating closed time-like curves (CTCs). Wormhole, also known as Einstein-Rosen Bridge, is a portal that works as a “shortcut” between points A and B. In the original space, the distance between the earth and Alpha Centauri is approximately 20 trillion miles, while the wormhole shortens it to a few million miles. When a spacecraft travels through the wormhole, it arrives not only in different spaces but also at different times. As the wormhole is crossed with the speed of light and the actual space traveled is much longer than the wormhole, the time flows much slower in the spacecraft compared to the earth and the spacecraft would eventually arrive at a different point in time. In order to freely travel through time, traversable wormholes, which allow travel in both directions, are needed.

Einstein-Rosen Bridge

What if a black hole doesn’t end at the singularity, but is connected to the other side of the event horizon that looks identical to our universe where everything including time is reversed? An object that fell into the black hole will be pushed out through the white hole in the parallel universe, where time flows in the opposite direction. The tunnel connecting the black hole and the white hole is called the Einstein-Rosen Bridge. However, this bridge cannot be crossed since it takes infinite time to travel through.

Primordial String Theory Wormholes

According to the string theory, small quantum fluctuations, which are random changes in the amount of energy, created numerous traversable wormholes soon after Big Bang. Those small holes are connected by the cosmic strings, which keep the wormhole open. The existence of the wormholes of the string theory, if true, would indicate that our universe is already filled with a number of time travel paths.

Man-Made Wormholes

The most significant requirements that the wormhole should fulfill in order to be both traversable and useful are sizes big enough to cross over, having no event horizon, and staying open. Keeping the wormhole opened is extremely difficult due to the force of gravity. Gravity pinching and cutting the tunnel could result in the formation of the black hole at the end of the wormhole. While cosmic string plays a role in preventing the closure of the wormhole of the string theory, exotic matter, which has a negative mass, should be used in a man-made wormhole. Differently from matters with positive mass that has gravitational force pulling each other, exotic matter pushes things away. As the exotic matter goes against gravity, it can keep the wormhole open.

Time Travel Paradox and Solutions

Grandfather Paradox is a paradox of time travel caused by changing the past. When you kill a young girl’s grandfather before having children with his wife during the travel to the past, there would be an inconsistency between the past and the present. The child of her grandfather should be one of her parents, but if her grandfather is killed before having children, neither the young girl nor her parents would exist. There are several solutions to these kinds of paradoxes.

First, the Novikov self-consistency principle states that the probability of an event resulting in paradox or change in the past is zero. In other words, such an event as killing a young girl’s grandfather before his wife is with a child is impossible to occur. Second, the alternative history hypothesis explains that when the time travelers go to the past, they do not become a part of recorded history, but totally new histories. Therefore, when a young girl’s grandfather is killed in the past, both the original history and the new history with the young girl and her parents unborn would exist.

Future Time Travel

Though wormholes are not yet found and still remain at a theoretical stage, continuous efforts to discover and prove the existence of wormholes and cosmic strings can lead to the foundation of new scientific theories and further development of science technology, and possibly bring a turning point in the history of mankind. Who knows? In the future, you and your descendants might be freely traveling to different periods of time through wormholes.