Introduction:
Hello readers! Welcome back to the second and third instalment of ‘The Paradoxes and Effects of Time Travel.’ If you didn’t already know, this chapter will discuss one theoretical effect/paradox each month. However, this month there is double the content due to our combination of two issues. Anyways, from origins to scientific basis, there’s lots to read! As promised, this month I’ll be discussing a very interesting and classic paradox: the Grandfather Paradox. Although, alongside that, I will also be talking about the very complex and interesting Bootstrap Paradox. Let’s begin!

Introduction to the Grandfather Paradox: 
The Grandfather Paradox is pretty well known, but if you haven’t heard of it yet, you’ve come to the right place! Before I get into the origins, I just wanted to explain how this paradox works. Imagine you went back in time, and managed to kill your grandfather before he met your grandmother. When you did this, you caused your entire reality to change. How? Well, when your grandfather died, he hadn’t met your grandmother. This meant that one of your parents was never born, they never met, and they never had you. Meaning that when you go back to the future, you and your family don’t exist. However, you do exist, because how else did you manage to kill your grandfather? And the cycle goes on. Cool, am I right?

I believe that the first person who ever thought of the Grandfather Paradox was René Barjavel, French author and journalist. He explores the paradox in his 1943 novel: Le Voyageur Imprudent (Future Times Three). This book is about two scientists who discover a substance which allows them to time travel. In the book, there is no actual reference to a grandfather, but an ancestor of the time traveller; nonetheless, the actions of the time traveller continue to have the same effects as the Grandfather Paradox.

Scientific Basis:
The Grandfather paradox relates greatly to relativity, causality, and closed timelike curves. Let’s start off with Einstein’s theory of general relativity! General relativity is the theory that space-time can be warped by mass and energy, which supports the claim that time travel is possible under the right conditions (wormholes can be formed). From general relativity, mathematician Kurt Gödel came up with closed timelike curves (CTCs). They are paths through space-time, which can allow one to travel in a loop, sort of like a circle through time, and return back to their starting point. What’s cool about CTC’s is that they work with Einstein’s theory of relativity, and don’t violate any scientific principles!

Now, I promise this is leading somewhere. CTC’s have two different types, Type 1 and Type 2. A Type 1 CTC allows a time traveller to go back to the past and interfere with past self and life. In theory, this type of CTC is what can allow the Grandfather Paradox to occur. However, we also have Type 2, which follows Nivikov’s self consistency principle. This type forbids paradoxes to be created, and would ensure that causality always followed the correct order. So, no matter how hard they tried, something would always prevent the time traveller from murdering their grandfather, such as a jammed gun. We can observe here how greatly the Grandfather Paradox is linked to time travel through CTCs!

In general, the Grandfather Paradox violates theoretical physics, specifically with causality, because it breaks the natural order of cause and effect. The paradox suggests that the cause (you travelling back in time and killing your grandfather) is eliminated by the effect (you are never born). Simply put, this paradox breaks the rules of causality, and cause and effect aren’t able to occur in the right order. From a scientific point of view, it challenges us to think about our perception of how time works. We are taught that time is linear, and that cause leads to effect in a predictable manner. However time travel, especially this paradox, disrupts those rules of physics.

Examples in Popular Culture:
It’s always fun to see the Grandfather Paradox shown in pop culture! The most popular examples I can think of are Back To The Future and The Umbrella Academy. In Back to the Future, Marty Mcfly is stuck in 1955, far before his birth. He meets his future mother and father, but his existence in the wrong timeline has effects that weren’t in the original timeline he came from. Before getting back to the future, he must make sure his parents fall in love, so that he doesn’t cease to exist. The movie demonstrates this temporal paradox quite well, and even though Marty’s grandfather isn’t literally killed, we can still see the message that comes from the Grandfather Paradox shown clearly.

Now, The Umbrella Academy is a TV show that is largely related to time travel, because the protagonist, Five, has the ability to jump through time. The Grandfather Paradox is shown largely in Season 3 of the show, because the characters are all living in a timeline where their parents don’t exist. Because it’s all merely theoretical, we can’t exactly know what effect this paradox will have, but in The Umbrella Academy, the paradox causes people to start disappearing until there is nothing left of the world. It’s really interesting to watch this interpretation of the paradox! I recommend viewing the third episode of Season 3–  if you can’t really wrap your head around this disastrous concept. The episode starts off with a video titled “Paradox Protocols: The Complete Commission Guide to Temporal Anomalies–Chapter Sixty-Eight: The Grandfather Paradox,” and it shows you exactly why the Grandfather Paradox is so tricky!

Philosophical Implications: 
I haven’t mentioned it before, but one possibility of this paradox involves multiple realities and/or parallel universes. Philosophically, it raises questions about the nature of reality itself. Is time a fixed linear path, or something more flexible and unpredictable? Is reality a single essence, or are there more branches of reality which differentiate from ours? What do you think, dearest readers?

We could also consider free will and control. Do we truly have the free will to change events in the past? The issue with the Grandfather Paradox is that if the time traveller kills their grandfather, their own existence would cease to exist. This raises the question: is it possible to change anything at all? Can we really alter the past, or is everything in our lives predetermined? This ties directly into the concept of determinism. What is truly inevitable, and what is within our power to change?

There is a lot to think about. The Grandfather Paradox not only makes us question the control we hold over our lives, but also the fabric of reality itself. As I consider these questions, it just reminds me that some things can’t be answered, and there is no correct solution.

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Introduction to the Bootstrap Paradox: 
The Bootstrap Paradox, also known as the Ontological Paradox, is quite a tricky little thing. This paradox is one that occurs when an object, piece of information, or even a person exists without any clear origin, essentially forming a causal loop. When the Bootstrap Paradox occurs, it raises the question: Where did it come from?

Unfortunately, it’s hard to pinpoint exactly who thought of this paradox. But, to put it simply, in this paradox something is passed back in time and becomes the very thing that allows itself to exist in the first place. Therefore, a loop is created, and this thing or object is self-sustained, with no definitive point of creation.

Theoretical Perspective:
It all sounds a bit confusing, so here is a hypothetical scenario in which an object has caused the Bootstrap Paradox!

Imagine you are a songwriter, who is unfortunately struggling to write your next song. One day, while rummaging through your old belongings, you find a dusty cassette tape, titled “Greatest Hit of All Time” (terrible name, I know). Anyways, your curiosity overtakes you and you play the song. To your surprise, it’s incredible– the perfect song! So, you decide to copy it, pass it off as your own, and release the song. It blows up, and suddenly, you’ve become rich and famous.

Years later, after a long and successful career, you stumble across a time machine. Feeling nostalgic, you decide to travel back in time to your early days. When you arrive, you realise that your younger self hasn’t yet found the inspiration for your career-building song. Then it hits you: you grab a blank cassette, record the song from memory, title it “Greatest Hit of All Time,” and leave it behind for your younger self to discover.

Now let me ask you this: who actually wrote the song?

The song never had an original creator as it was just passed between your past and future self. So, it essentially “wrote itself,” and exists in a time loop with no clear origin. Interesting…

Scientific Basis:
Just like the Grandfather Paradox, the Bootstrap Paradox once again relates closely to concepts of causality, general relativity, and CTCs. As mentioned before, general relativity suggests that space-time can be warped by mass and energy, potentially allowing for time travel through structures such as wormholes. This theory is the foundation for causality loops, which occur when events are closed in a self-contained loop, with no clear origin or end.

Now, let’s revisit closed timelike curves (CTCs). Just like the Grandfather Paradox, Type 1 CTCs allow for interference in time travel, while Type 2’s follow Novikov’s self consistency principle. The Bootstrap Paradox would fit into a Type 2 CTC (in theory). It’s because it doesn’t directly violate causality, but instead creates a closed loop of existence. In this so-called loop, objects, information, or people exist without a clear point of origin, appearing as though they are "self-created."

This all sounds a little complicated, so I’ll sum it up. From a scientific standpoint, the Bootstrap Paradox doesn’t actually violate any rules of physics, especially not in the way the Grandfather Paradox does. However it does challenge the way we think about cause and effect, since it suggests that events or objects can exist in a self-sustaining loop, defying our typical understanding of linear causality.

It’s quite difficult to find examples of this paradox in the media, so we’re just going to have to skip that for now. If you noticed anything that could suggest time loops in a movie or show however, feel free to let me know!

Conclusion:
Well, I think it’s safe to end it there. To be honest with you readers, my brain is melting and my eyes are sore from all this research. But, I bet you’re wondering what’s up next! Well, funnily enough, my topic of discussion next month is neither a paradox or an effect; it’s a theory. The multiverse theory to be exact! It’s sure to be interesting, and I know I’d love to learn more about it. If you would too, then I’ll see you back here next month. Thanks for reading!

Written by Daphne Clarke.
Edited by Hazel Antler.