3 Most Popular Time Travelling Paradoxes

Universe is a place of unlimited possibilities. And endless possibilities creates endless thoughts. Some of them are absurd whereas some of them make people think. And when many people think of the same idea, the contradiction will be an absolute thing. And these contradictory ideas are called Paradoxes. So, in this article, we’re going to see 5 weird time-travelling paradoxes.

So first let’s know-

When we call something as Paradox?

This is a word that means:

A statement that seems absurd and contradicts itself, but when we deeply think about this, it may prove to be well-founded or true.

For example, see this image on the left. It is a triangle that seems to be impossible. But you can actually make this triangle. This is called the Penrose triangle.

Now there are lots of paradoxes are simply majority of them are so confusing.

One of them that I came to know in my school is Russell’s paradox. It says

Let, R = {S|S∉S} , then R∈R⇔R∉R 

Let R be a set such that it is the set of all sets that do not belong to themselves.

Now observe carefully.

• If R is not in R, then R doesn’t belong to itself. But we said that R only consists those sets which doesn’t belongs to themselves. So R has to be in R.
• If R is in R, then R belongs to itself. But by the definition, R only consists those sets which doesn’t belongs to themselves. So R can’t be in R.

So this is Russell’s paradox.

Now, this is a paradox on set theory that is related to maths. But there are a lot more than this.

Predestination Paradox:

Predestination Paradox basically says us that we never can change history. It simply means that things that already happened are always destined to turn out the same way no matter what happens.

“Whatever happens will happen. It is just a matter of chance and fate.”

So clearly, this paradox occurs when a person tries to change the past by travelling back in time and becoming a part of the event. And ultimately cause the event he is trying to prevent to take place. This results in a ‘temporal causality loop’.

Let’s try to understand this.

Two events are happening here, event 1 and event 2.

Now event 1 happened in past, which is influencing event 2 in future. Now if event 2 is happening, then event 1 has to happen. So, this thing makes a circular loop of events.

Now if someone tries to change event 1 after experiencing event 2, it’s not possible for him/her. Cause the circular loop ensures that history can’t be altered by any time traveller. And if someone attempts to stop something from happening in the past then instead of stopping it, he/she will be the cause of the event.

Example:

Let’s take an example of a boy Rohan who was going for a nice dinner with his girlfriend. But and unfortunate happens and in an accident, he lost his girlfriend. As he was a physicist, he took a pledge that whatever it takes, he will save his girlfriend from this accident.

So he makes a time machine and goes to the time when the accident occurs. He thought that this way he could save his girlfriend. But whenever he tries to save his girlfriend from the accident, she dies in some other way.

After trying so many times the boy understood why it is not possible to save his girlfriend.

Because, if his girlfriend did not die that day, he never tried to make the time machine. Also, all the things he is doing is all because of the death of his girlfriend. So if she didn’t die nothing happens.

This signifies that it was her destiny to die on that day. And no one can change her destiny.

This is the Predestination Paradox.

Bootstrap Paradox:

This is a type of paradox in which an object, person, or piece of information is sent back in time. And it got stuck in an infinite time loop where the object or the information or the person has no apparent origin and exists without ever being created. It is also known as an Ontological Paradox, as ontology is a branch of philosophy concerned with the nature of being or existence.

Example:

Let’s take an example to better understand this.

Let say one day, a random guy gives you a book on the time machine. So you start reading that book and try to make the time machine. After several years of study and hard work you finally make your time machine. Now you want to try whether your time machine works properly or not. Also, you thought to give your younger version motivation to make the machine. So, you set the time when you get that book and go back to that time. You thought that maybe your time machine got damaged or any error occurs after reaching the past. So, you take the book also with you.

After reaching to the past you find out that till now you actually didn’t get the book. So, without thinking much, you give the book to your younger version and motivate him. And then you came back.

Now, think about this incident.

Can you tell me the origin of the book?

The answer is ‘no’.

You can now clearly understand that in this story both the persons are actually you. And the book with you has actually no apparent origin at all.

This means, you and the book are trapped in a loop, which will happen again and again, and you can do nothing.

This is Bootstrap Paradox.

Grandfather Paradox:

It is a paradox of time travel in which inconsistencies occurs by changing the past. It is a quite weird paradox where the paradox says: “a time-traveller travels to the past and kills his/her own grandfather before the conception of his/her father or mother, which prevents his/her own existence.” The paradox does not exclusively consider the contradiction of killing one’s own grandfather to prevent one’s birth. Rather, the paradox actually thinks about the result of an action that alters the past, since there is a contradiction whenever the past becomes different from the way it was.

Explanation:

Not for real, but just think about an event where you wants to kill your grandfather. You make a time machine and go to past. You find your grandfather and kill him before your father was even born.

Now, pause for a moment and think about it carefully. If your grandpa is dead before your dad’s birth. So, how would you come in existence?

Now, there are two possibilities.

1. If your existence is true, then your grandfather’s existence must be true. So, you can’t kill your grandfather.
2. If your grandfather is dead before your father is born, then you can’t exist. So, your time travel also can’t be exist. And so your thinking of killing your grandfather also can’t be exist. That means in this case also you can’t kill your grandfather.

So, this is the Grandfather Paradox.

Why every paradoxes happens for going in past?

To answer this question, first, let’s understand “Time“.

Time is a linear thing, it goes from Past to Present to Future. Now, the point is, the present and the future depend on the past, but neither the present nor the past depends on the future. So, if time travel will ever be possible, then going to future and changing will never be difficult to us. And also it will not violate any theory. But, when we start thinking about going back to the past, all problems start arising. Cause, past has the complete control of the present and the future. So changing something in past becomes more difficult ( or, next to impossible) and controversial, which causes of these kind of paradoxes.

So, if any time traveller somehow go to the past and influence or try to influence anything or any event in past, then it influence the current timeline. Which can even erase the existence of the time traveller.

So, Now the question is-

Is it possible to influence the past events?

Well, it has two answers.

1. No, we can’t change or influence anything in the past. If we do so, then the structure of TIME will not be same. For the time traveller it may become a circular loop or may be something which will be questioning to the existence of the time traveller. And all the 3 paradoxes are the example of this answer actually which clearly says that: “We can’t influence the past“.
2. Yes, we can. But, it is only possible if we consider that parallel universe exists. Means multiverse exists. In that case if we go to the past and change something in past then it will create a new timeline. And our main timline will be as it is, but in the new timeline everthing will be changed. Recently Marvel had released one webseries, LOki. This is all about multiverse and time travelling. So, if you are interested enough, then you can watch it.

Also read:

Tachyon Particles: Are They Really Faster Than Light? • Scientific World (scientyficworld.org)

Reference:

5 Bizarre Paradoxes Of Time Travel Explained (astronomytrek.com)

Books:

Here are some books that you can read toknow more about time travelling.

1. Relativity: The Special and the General Theory
2. A Brief History Of Time: From Big Bang To Black Holes