How to Time Travel and Not Kill Your Grandfather

If you go back in time, do not kill your grandfather.

In the last few blogs, we explored how people time travel in my science fiction series, The Shadows of Time.

How to Keep Time Travelers out of Your Livingroom

How to Time Travel and Not Lose Your Luggage

How to Make a Computer That Sees the Future

But what dangers await a time traveler in the past?

First, let’s give the time travelers in the series a name. They descend from a group of historians, scientists, and soldiers that came from a nation called Avar. They called themselves Avarians.

The Grandfather Paradox

Let’s say you’re a time traveler. Can you change the past? And if you do, does that change affect the altered past affect you? If it does, it might affect you in a way that alters the way you change the past, and so on. You just created the grandfather paradox, otherwise known as a causality loop. Here’s a short video that explains it if you’ve never heard of it.

Three Theories of Time Travel

This paradox may prevent reverse time travel if the universe has some sort of built-in censorship. Don’t worry. There are theories that work around this paradox depends on the nature of time. Harrison Densmore created an infographic that shows how the nature of the time can prevent changing the past.

Don’t ask me who Harrison Densmore is. I tried finding him to give him credit, but he vanished without a trace. Maybe he’s a time traveler.

“3 Theories of Time Travel” by Harrison Densmore

These three theories are not the only ones out there, but they are the most popular.

Fixed Timeline: Can’t Kill Your Grandfather

In this theory of time, you CANNOT change the past because it has already happened.

Some solutions of general relativity theoretically permit time travel into the past. In the mid-1980s, Russian physicist Igor Dmitriyevich Novikov tried to solve the grandfather paradox. He said that if an event exists, that would give rise to a paradox, or to any “change” to the past whatsoever, then the probability of that event is zero. It would thus be impossible to create time paradoxes. Novikov didn’t invent time travel, but at least someone named the concept after him — the Novikov Self-Consistency Principle.

This idea is nothing new. Oedipus Rex (a Greek tragedy by Sophocles first performed around 429 BC) may not be considered the first time travel story, but Oedipus gets information about the future and tries to change it. In this story, he can’t change his fate because he lives in a fixed timeline. Instead of changing the future foretold, he ends up creating it.

Dynamic Timeline: Can Kill Your Grandfather

In this theory of time, you CAN change the past, and the universe freaks out in some way because it’s caught in a time loop. The hero of the story disappears, or the universe explodes, or the hero is caught in a continuous loop.

One of my favorite Star Trek Next Generation episodes is Cause and Effect, the one where the Enterprise is caught in a causal loop. This episode follows the dynamic timeline theory.

Star Trek Next Generation, Cause and Effect, Paramount StudiosStar Trek Next Generation, Cause and Effect, Paramount StudiosMultiverse Timelines: Grandfather Saved and Killed

If we live in a multiverse, don’t worry. Because if you go back in time in multiverse, you simply spawn off another history or timeline. One timeline contains your past, and another timeline contains the past when you came from the future. Never mind about the law of the conservation of energy.

I base The Shadows of Time series on this theory with a twist. The difference is changing the past comes with a cost. If you change the past and spawn an alternate universe, you create temporal tension. I will expand on this in an upcoming blog. Subscribe to get notified as soon as it’s published.

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