When you think about it, everything is just a big ball of wibbly-wobbly . . . timey-wimey stuff.
— The Tenth Doctor, Doctor Who
Time travel is one of the greatest themes found in science fiction. It may seem that science fiction is a modern-day thing, but time travel has been around even in mythology. The story of King Raivarata, found in the Mahabharata, and the Urashima Taro tale from Japan are only a few of the earliest examples.
A lot of great science fiction shows glimpses of the future or allows characters to step back into the past, but some of the most exciting science fiction involves temporal paradoxes—loops in time that don’t make logical sense. Here are some time travel paradoxes in fiction explained, along with how they can be solved according to physics.
Premise: If you go back in time and kill your grandfather, what would happen to you?
Basically, this paradox explores what would happen if something were to happen in the past that could prevent the time travel in the first place. According to physics, the Grandfather Paradox could be solved by two things. The first is through timeline protection; you wouldn’t be able to kill your grandfather no matter how many times (or ways) you try to because you’re alive. The second is through the multiverse theory, where you return to a universe in which you were never alive in the first place after killing your grandfather.
Premise: A person travels back in time and becomes the cause of the event he wants to stop in the first place.
This paradox can be a bit complicated, but here’s an example to help. Imagine if you see a child get into a car accident. You travel back in time to try and save the child, only to find out that the child got into the accident because of you. Just like the name suggests, this paradox implies that things happen just as they are supposed to happen.
Premise: Any object sent backwards in time loses its origin of creation.
In other words, objects (or even people) that are sent back in time lose how and why they were created in the first place. This is also called the Ontological Paradox.
Premise: Any time traveler going back in time and successfully completing their reason for traveling removes the reason they time-traveled in the first place.
A classic example of this paradox is killing Hitler. Compared to killing your own grandfather, which mostly affects just you and your family, killing Hitler affects the future of many more people—the whole world, even. However, if you manage to successfully kill Hitler, you lose your reason for killing him in the first place.
Causal and Time Loop
Premise: A character goes through a series of events over and over until such time that they learn something about themselves and change something, breaking the loop.
This is not necessarily a paradox, but for the character, it is. The causal loop is different from the time loop in that the former does not reset at a specific time or event.
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