Is Time-Travel Possible??

           

"Lost time is never found."

                                                                                           ----Benjamin Franklin.

But what if we could find the lost time? They say, Past is gone and nobody knows what the future will bring. But what if we could reverse our mistakes from the past and know what the future will bring well ahead in time? What if time-travel was possible?

            Exciting, Isn't it? The practicability issues of time travel have never once stopped us from getting all whimsical about it. In fact, this is the reason why time travel has been a popular theme concerning science fiction for decades now. Series ranging from Dark to movies like 12 Monkeys and Back to the Future were solely dependent on the concept of time travel.

            If you could, just for a second, put aside the feasibility controversy involving the whole time travel theory, the very idea to go back and forth in time appears incredible and fascinating. An ocean of thoughts just wraps your mind by imagining the things you would be able to do if time travel, was in fact, substantial. 

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             But as you snap out of this wonderful dream, Time travel seems to be just another will-o'-the-wisp. For ages, the concept involving time travel has been controversial. Some think it is unattainable and practically impossible. But few others still have their hopes high. Here are some compelling theories that would spark your curiosity and hopefully someday would open doors to time travel.

  1. Time Dilation 

             A popular theory involving the feasibility of time travel comes from Einstein's theory of special relativity. In 1905, Einstein theoretically proved that time travel is achievable based on his famous equation, E=mc^2 and Time Dilation. Time dilation refers to the passage of time being affected by the laws of nature such as differences in gravity or velocity.

Credit: NASA

The curvature of spacetime is responsible for gravity. Imagine the space-time dimension to be a fabric. If anything that has mass is placed on this fabric, it bends and causes the objects to move in a curved path and this curvature is what we know as gravity. In turn, gravity can also bend time. 
Astrophysicist and science consultant for Star Trek, Dr. Erin Macdonald said,

We think of the bowling ball on the trampoline and that bowling ball dips the trampoline down and that’s what mass does to space-time. This distortion of space-time is what we experience as gravity.

             Time Dilation is closely related to time travel. If the gravitational force/velocity for a particular object is altered, the time would move faster for that particular object while for everything else, it remains at the same pace. So in simple terms, we would say, the object has traveled through time into the future. Thus, Time dilation could be an effective approach to time travel.

2. Black Holes

            According to an article published by NASA as a part of the 'NASA Knows!' series, "A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space." 

             Black holes have always been considered as an implied medium of time travel. It is ascertained that around a black hole, time passes extremely slowly. As a matter of fact, the person standing on the edge of the Blackhole would appear to be frozen for a distant observer. In other words, as you approach a black hole, the time seems to pass really slowly to a point where it stops at the edge of it. Nobody can tell what happens once you are inside it, but it is believed that if a spacecraft, for instance, is made to travel rapidly around a Blackhole, the time spent by the spacecraft would be much lesser than the rest of the universe, which would be like 'traveling into the future'.

In his article "How to build a time machine" Stephen Hawking wrote,

 Imagine they circled the black hole for five of their years. Ten years would pass elsewhere. When they got home, everyone on Earth would have aged five years more than they had.

  3. Tipler Cylinder

             Tipler's cylinder is a hypothetical machine claimed to be a potential mode of time travel. Frank Tipler in his 1974 paper, "Rotating Cylinders and the Possibility of Global Causality Violation" performed an analysis on the unrecognized solutions to the equations of General Relativity discovered by  Willem Stockum and Kornel Lanczos and theoretically proved that it is, in fact, possible to build a black hole-like structure to travel back in time.

             The proposed solution involves an infinitely long cylinder with a mass 10 times the Sun to be rotated at extremely high speed (about a few billion rotations per minute) along its longitudinal axis. This will create a frame-dragging effect. This frame-dragging effect wraps the spacetime continuum in such a way that it creates a closed timelike curvature. If a spaceship is made to travel along a carefully plotted spiral around this rotating cylinder, it will immediately find itself probably billion years back in time and also 'in a galaxy far, far away'(Star Wars reference, but literally). 

  4.  FTL Approach

             Faster-Than-Light(FTL) means traveling faster than the speed of light. Since we had overcome the sound barrier, scientists around the world have been wondering if it's indeed possible to break the light speed barrier too. We have seemingly heard that the speed of light is the speed limit. But what happens when this breaks. The answer is time dilation. When an object travels faster than the speed of light, the passage of time for that object is affected. This can be explained by a famous paradox called 'Twin Paradox.'

             According to Twin Paradox, if one of the twins is sent on a space adventure in a space ship that travels faster than the light and the other one stays on the Earth waiting for his/her sibling, by the time the twin returns, the one who stayed on the Earth would have aged more than the one on the space ship even though they were supposed to be of the same age. This is because when the speed of the light barrier is broken, it affects the time dimension. The time passes slower for the twin on the space ship than for the one who stayed back on the Earth. This seems very strange but it is apparently true.

            There have been hints in the past that NASA has been researching the feasibility of Warp-drive or Faster-Than-Light travel. And finally, in May 2020, an internal feasibility report released by NASA scientist Harold "Sonny" White suggests that something of Warp-Drive kind is definitely on the agency's plate. However, it is assumed that NASA is interested to utilize this technology, if built, to explore deep space, but one might expect time travel to be a hot topic in the future.

  5. Wormholes

            Wormholes are like tunnels that connect two points in space-time. Besides this, they have also been found to lessen the travel time when compared to actually traveling through space. Many theoretical physicists accept that traveling through a wormhole can help us travel through 2 different points in time. 

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            Humans have neither spotted a naturally occurring wormhole yet nor have the technology to produce a huge amount of energy (especially negative energy) to be able to create an artificial one. The problem with wormholes does not end there. Wormholes are highly unstable and extremely small in size. It will again take enormous amounts of energy to stabilize and stretch it to transfer a fully-grown man through it. 

            Though the existence of time travel technology seems far, far away now, I personally believe that it will one day come into existence. And when it does, we would be able to prevent disastrous events like corona-virus outbreaks or casually drop by at Edison's place while he is just about to invent the 'Bulb'. Discover dark secrets from the unknown past or know the mysteries of the Atlantic city. Or simply have a little adventure of your own. The list does not end.