“If time travel is possible, where are the tourists from the future?”
― Stephen Hawking, A Brief History of Time
Have you ever screwed up something so monumentally that you wished you’d go back in time to fix it? Wanted to apologize to someone? Had romantic confession gone cringe? Wanting to punch your 15-year-old self for being an edge lord? We all have had these thoughts or something along the lines of it. Time travel is one of the subject matters of interest for physicists and science enthusiasts alike, it has been a popular trope in pop culture. A lot of science fiction shows and movies use this stimulation in their stories.
The idea of time travel has conversed for centuries even before the advent of modern physics and sci-fi entertainment. This intriguing concept has been a part of classic literature since the 1870s and popularized by H G Wells’ “The Time Machine” in 1881. The whole sci-fi genre in books and movies has popularized the concept among the populace. Stephen Hawking once held a party for time travellers and only passed out the invitations only after the meeting ended, under the presupposition someone would find the invitation in the future and come back in time to attend it, but the experiment failed, no one attended the meeting.
Einstein’s Theory of Relativity
The concept of a time machine isn’t endorsed by physics but the idea of time travel is. Einstein’s theory of relativity employs the idea of time travel by speed of light, the notion is, the closer you travel in the velocity of light (300,000 km/s), the slower time flows around you, and the more time appears to slow down from the point-of-view of a stationary individual. Imagine a vehicle which can travel at the speed of light with people in it, and it travels the earth for 6 months the people viewing the train from outside will experience 6 months but the people in the train would experience a considerably low duration, on paper they would feel as if they travelled to the future. This phenomenon is dubbed the slowing of time due to motion dilation.
Black Hole Propagation
A Black hole is a remnant of a gigantic star after it dies, the gravity is so strong that not even light can escape it. However, time slows down rapidly as you travel across the horizon of a black hole. The fascinating thing about the black hole is time rapidly slows down the closer you inch to the black hole. An object can be travelling really fast around the edge of a black hole but to the viewer from afar, it might appear stationary. Einstein’s theory of gravity explains massive objects bend space and time around them but it is minuscule with reference to the size of earth, the same principle is applied to the gigantic stars, Christopher Nolan’s Interstellar used this theory to explain their “1 hour here is 7 years on Earth” as the planet they were on was in close proximity to a Gargantua (the fictional black hole presented in the movie). Einstein’s theory only explains the black hole, but our understanding of physics fails to explain what happens inside a black hole, since nothing can go inside a black hole and come out, no data can be gathered on the events happening inside it. Theoretically the closer you are to a black hole, the lesser time you experience, does that mean at the epicentre of a black hole you move forward to a whole different future? Or will it redirect you to a new universe which is completely different from our universe? Since no solid inference can be derived from a black hole with our current technology, we can only speculate.
The Einstein-Rosen Bridge
The Einstein-Rosen Bridge, popularly known as wormholes which are a staple in Sci-fi movies with an intergalactic setting can be described as a phenomenon joining 2 different points in space. These “portals” allow an object to travel at extremely high speeds from one point in the universe to another point in the universe, at the speed of light or greater than that. It is speculated some wormholes can transport us to the universe at different points in time. This too is a theory.
However, there are several factors which deem desired time travel as impossible, primarily an object with mass cannot travel at the speed of light due to the immense amount of energy entailed to propel the object at that velocity is practically impossible to achieve. It is like a speed limit set by the universe. Secondly, as we discussed above, the data on the functioning of the inside of a black hole is nonexistent so it harder to carry further studies out.
The Conundrums Associated With Time Travel
Even if by some miracle we carry out in executing a successful time travel, there are a lot of puzzling situations we are dealing with. One is the incident called “The Grandfather Paradox”, what if an individual were to go back in time and kill their grandfather which results in the butterfly effect of them not being born, and if they weren’t born they wouldn’t be able to plot and carry out the event, this creates a lot of inconsistencies in the timeline. The future would be a result of the causality. This will cause a number of events to transpire due to the butterfly effect. This can be observed in the movie “Back to the Future”
The second theory dictates that time is like a river whose flow cannot be interrupted and events will occur irrespective of the changes made to the past, the popular example is the assassination of Adolf Hitler, what if Adolf Hitler was killed as a baby right after he was born and he was replaced with another baby, only to find out that the replaced baby would also turn into a tyrant, what if you go back in time to prevent an accident only to find out you were the cause of the accident, it would result in a lot of complex manoeuvres to retain the original flow of time. This can be observed in “What If….Dr. Strange Lost His Heart Instead of His Hands”.
Another issue is the retention of the future by changing the past. This is a deviation of the grandfather paradox, you can go back in time and kill your grandfather but that event will not result in your present, but it will yield a different timeline where the actual grandfather paradox takes place but you, the one responsible, will not have their existence altered in any way. This is the concept which was employed in “Avengers: Endgame”
Questions to Ponder
I feel that time travel is one method which can be employed to peer into the beginnings of the universe, and understand how it operates and governs, but it gives rise to a lot of questions, why hasn’t anyone come from the future to tell time travel is possible? Why hasn’t anyone from the future warned about the major crisis’ which took place so they could have been prevented? Or what if things once transpired cannot be altered, is this what can be attributed to “The Hand of Fate”? The Universe is a vast ocean filled with the unknown and this phenomenon is just one of them, it just goes to show how little we know of the universe despite centuries of progress.
"The most incomprehensible thing about the universe is that it is comprehensible"
―Albert Einstein, Physics and Reality
