Time Travel and It's Paradoxes
Updated: Feb 6, 2022
One of the most intriguing aspects in all of physics is “TIME TRAVEL”. The idea which has been driving scientists mad for centuries and had them divided in their opinions is time travel possible? Are Back to the Future, Billy and Teds Excellent Adventure and everyone’s favorite Avengers Endgame are in fact containing a dose of reality? Let’s find out!
Is travel through time possible?
The answer is YES! All of us in fact are travelling in time right now. Every living thing in this universe right now is travelling in time at the rate of one second per second. But you may argue that this is not the time travel which we saw in films, books etc. The reason why it’s not the same is because we are not travelling fast enough in time to go to the future or past! While gazing at the stars what do we see? A speck of light in space. But this light which reaches us is actually the one emitted by the stars thousands of years ago. Even though light has a staggering speed of 3x108 m/s it needs to cover about millions of light-years before it reaches us. So, we are actually seeing how the star looked very long time ago. In other words, we are looking back in time. Intriguing right! So, if the star becomes a red giant and dies the next day it will take us another thousand years to notice it
So, can we really ‘time travel”? That is travelling at a rate greater than 1 second per second? Science says it’s possible.
A century earlier Albert Einstein came with his famous creation “The Theory of Relativity”. According to it time is relative. It also says that time and space are linked each other. He also said that the universe has a maximum speed limit-the speed of light. So how does this affect time travel? It tells us that if we are able to move in a greater speed (greater than 1 second per second) time will move relatively slower to us.
Einstein coined the term called space-time which is viewed as a malleable and flowing material able to control time. This theory states that the closer the object is to earth more slower time flows for it. A famous example is that of in Interstellar film. The crew lands in a planet with very high gravitational intensity due to a black hole. Due to this time flows extremely slow for them that when the protagonist reaches earth after the expedition, he finds his daughter has become an old woman but he had remained the same age when he had left initially.
The relativity theory also stated that gravity causes the bending if time and space. This phenomenon is what is experienced by the global positioning satellites (GPS). Due to the very high orbit on which these satellites rotate the time on these satellites runs relatively faster. This error is corrected in order to prevent extreme in accuracy in our GPS systems.
After seeing these examples, one may argue that it’s possible to time travel, we can go into the past and so on. But here comes the catch. In order to go into the past and the future as seen in the books and movies one need to travel at a rate equal to or greater than the speed of light which itself makes time travel impossible. But travelling at the speed of light is only one of the ways in which you can travel in time. So, is another method possible? Let’s find out!
Wormhole Theory
Another possible theory through which time travel is said to be possible is travelling through wormholes. Also called Einstein-Rosen bridges one might be very familiar with this playing a crucial role in the movie Interstellar. The protagonist and his crew travel through a wormhole to research about potential habitable worlds. These are said to be bridges in space time which are said to connect different points in reality with each other. Travelling through these can help us access one particular time in reality other than our present time frame thus making time travel possible.
But lot of scientists have proved that the theory is false as it is not possible for the wormholes to self-sustain themselves. Another anomaly in the existence of black holes is their very small size of their mouth (10^-36 m) making it impossible for us to travel through it. All these facts make time travel not possible even in the distant future through wormhole.
Paradoxes Associated with Time Travel
So, till now we have dwelled upon and pondered over the thought of whether time travel is actually possible. Then let us assume that in the far future, around the year 10,000 a scientist invents a machine travelling in the speed of light and in turn making him come back in past and go to the future. Time travel has become possible! The scientist can go back in time, visit Einstein, may stay there and take credit for the theory of relativity before Einstein does it. But the universe will find a way to disappoint this man.
Lots of scientists have come up with a list of paradoxes which says that time travel is impossible or limited even if we build a time machine. Let us see what are those paradoxes and how do they affect time travel.
1) Bootstrap Paradox
Let’s start right away with an example to understand bootstrap paradox better.
While cleaning the library of his old mansion one day, Antonio found a secret room behind the one of the walls of his library. While checking through it he found out a very old and battered edition of Hamlet. After some research done by some experts, he gets to know that it is the very first edition of Hamlet by Shakespeare. Getting excited he uses his time machine and goes back in time to meet Shakespeare himself. But after meeting him he gets to know that Shakespeare has never heard of it and he hasn’t written it yet.
So, he decides to give the old edition to Shakespeare and urges him to publish the work as his own. He then leaves to his present timeline. Shakespeare then publishes Hamlet and becomes famous. Hundreds of years later one of the very first editions is found by Antonio.
So where did Hamlet actually originate? Shakespeare says he got it from Antonio the time traveler but Antonio says he gave Shakespeare his own edition. So again, we are faced with the question “Where did it originate?”
The book is caught in a time loop or to be more exact a casual loop. It seems to arrive unexpectedly without any cause but it’s the cause for itself. It becomes self-existing. This is what a casual loop means. So, in proper terms the bootstrap paradox is a situation where an object or a person when travelling back in time get stuck up in an endless loop having no particular point of origin. Robert Heinlein gives the perfect example of how the bootstrap paradox affects a living person. It can be accessed here https://en.wikipedia.org/wiki/All_You_Zombies.
2) Grandfather Paradox
One of the most famous paradoxes explained by scientists is the Grandfather paradox. For the sake of argument imagine your grandfather has been abusing you since your childhood. You have been beaten, verbally abused by him leading to you bearing a grudge and deep hatred for him. Nobody could question his authority as he paid for everyone’s bills and food and rules the family with an iron fist. 20 years later you find a time machine. You decide to kill your grandfather and put end to everyone’s suffering. So, you go back in time and meet up with the 10-year-old version of your grandfather and decide to kill him. But whatever method you try to kill him it won’t kill him. How? Is he immortal? Does he know about your plan? The answer is quite different from what we think.
By killing your grandfather, you in turn prevent the birth of your mother or father. Thin in turn prevents your own birth, your reason to travel back in time and so on. In short you are trying to negate the very reason for which you are here and in turn your existence. This is what the grandfather paradox is actually about.
This paradox is not only localized this case but in general talks about those actions that affect the history and through whose results our present is shaped and in turn our future.
Another reasoning to this anomaly is that after killing our grandfather if you go back to the future you will be shocked to know that no will know you. Your identity seems to be surprisingly erased from everyone’s minds. All the things related to you seem to have disappeared. The possible answer is that you are transported to another universe not your original one. A timeline identical to your original one but different from yours. In short terms you are like a Loki variant.
3) Predestination Paradox
Most of us want to change some of our past events in the way we wanted. So, let us say we went back in time to prevent one of the bitter things which happened in our past. But after getting tangled up in a sequence of events we are shocked to know that it was you who caused the past event to ourself inadvertently. That’s what the predestination paradox is all about.
So, in proper terms the predestination paradox is a situation where a person traveling in time in order to change the past event get tangled up in the past events itself and in turn causes the event he tries to prevent.
A famous example occurs that in Harry Potter and the Prisoner of Azkaban. Harry thinks it’s his father who protected him from the Dementors but in the turn of events he realizes it was himself who protected him from dementors by going back in time. Another example is of the movie Predestination.
4) Polchinski Paradox
This paradox was proposed by American physicist Joseph Polchinski in 1990. According to this paradox a billiard ball is dropped into a wormhole and it goes back in time. It then comes out exactly in such a way that it collides with its past self perpendicularly and prevents it from entering the wormhole. Possible solutions to this paradox are that it collides with its past self and causes it to enter the black hole or it doesn’t collide hard enough to prevent the entering.
Lot of these paradoxes pose a challenge while making time travel possibility. Not only these but they are loads of other paradoxes which lands different types of situations while time travelling. Like the Hitler Paradox is nothing more but a generalized situation of the Grandfather Paradox. It’s where we travel back in time to kill Hitler but it won’t happen like we intended to just as explained in the Grandfather Paradox.
In fact, we will create another Hitler and in turn cause WWII.
A lot of scientists have come up with proofs, theories and equations to rule out the paradoxes but not with solid evidence. Most of them solved round only paradox and other paradoxes seem to creep into it every time. Still research is going on how paradox free time travel can be done. But it will be saved to say that time travel won’t happen till then. When will it happen? Only time can tell the answer…
- By N. Pranav
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