Pair o’ Paradoxes

There are two types of Time Paradox.

Grandfather Paradox

Possibly the most popular. For a competition between two that’s a big win.

The idea here is you go back in time and prevent your own birth and if you were never born then your birth was never prevented.

Explanations of this paradox always look so convoluted and dry, don’t they? Let’s try to fix that.

This is Dorothy, a tornado scientist. She tinkered with cyclone simulation until she accidentally invented an impossible tornado that spun faster than light could travel. It uprooted the entire laboratory and Dorothy had a nice view of the inside of a real life time vortex as she went back in time.

When the winds settled, the lab landed on Dorothy’s grandmother as a young woman. She was as flat as her chance of ever reproducing now. Because she never gave birth, half of Dorothy’s parents never existed and because humans aren’t spores that can reproduce by mitosis, Dorothy was never born either. That means she could never invent a magical tornado that works by rules of the plot to illustrate a theoretical paradox.

But she did and she didn’t. Maybe it depends on your point of view and how optimistic you are.

Possible Outcomes

  1. Time corrects itself like a smart phone keyboard. When things get too out of hand, something is changed to make it more manageable. For instance, it could be changed so that somebody else killed Dorothy’s grandmother, or maybe the lab landed somewhere else, or anything really. After all, if you can change time, there’s no reason for it not to change back again. Perhaps there are Guardians of Time that fix paradoxes, like Time Lords, or Time Cops, or perhaps Time is just an entity that when stretched out-of-place just springs back like a rubber band or a spring.
  2. The paradox is ignored, yet the story uses the Time is Mutable theory instead of Multiple Timelines. If this happens, it’s a sign of poor writing. Or, if you want to be nice, the correction just hasn’t happened yet from our perspectives.
  3. It could cause a chain reaction that would unravel the very fabric of the spacetime continuum and destroy the entire universe! Granted, that’s a worst case scenario. The destruction might in fact be very localized, merely to our own galaxy.

“Well, that’s a relief.”

In Back to the Future, Doc claims that the world will end if a Time Paradox occurs. And yet a Time Paradox happens once, almost twice in the trilogy and nothing bad happens.

The first time, which arguably isn’t a complete paradox, Marty very nearly prevents his own existence. He manages to correct it just in time.

The second time, Biff takes an almanac from 2015, gives it to himself in 1955, and drastically changes his life. That’s fine, sure, way to go, Biff, but if you don’t remember to go back in time in 2015 with the sports almanac to give it to yourself, then that trip will have never happened and you’ll have never gotten the book, and we’ll have a Grandfather Paradox. Except, you don’t even know time travel was involved, because your future self refused to tell you. Not only that, but Doc probably didn’t build a time machine in this reality because you had him committed, so even if you knew, how would you do it? Not only THAT, but a deleted scene shows Future Biff fading from existence after he returns to 2015. According to Bob Gale’s commentary in the DVD and Blu-ray, Lorraine shot Biff in the 90’s. So Biff went to the past and caused his own death. This is a textbook example of a paradox that actually happened! Way to go, Biff.

But then what happens? Nothing. The universe doesn’t explode. Their own galaxy doesn’t explode. Nothing explodes, except perhaps 1.21 jiggawatts of electricity when Doc and Marty go back in time and fix the paradox. You could say that the Ripple Effect used in the series to show changes to Time just hadn’t caught up yet to destroy the universe. That’s possible, but Time was still corrected.

One example of a paradox being ignored is in Looper, but I otherwise enjoyed the movie, so I’m willing to give it the benefit of the doubt and assume it was resolved offscreen during the credits.

Universal destruction has never happened because of a Time Paradox in any story I’ve encountered. I can’t imagine why.

Ontological Paradox

Also known as the Bootstrap Paradox (named after Robert A Heinlein’s short story, By His Bootstraps) or the Reverse Grandfather Paradox, or sometimes a Predestination Paradox, or if you feel like trying to impress someone, an example of the Novikov Self-Consistency Principle, or if you don’t, Wibbly Wobbly Timey Wimey. Pick whatever, I won’t judge you.

This is basically a time loop. Imagine a person or object being sent back in time. The arrival in the past causes a series of events leading to a younger person or newer object sent back in time. It’s then revealed it was the exact same person or object and exact same trip in time. There’s no starting point, no end point. Just a loop.

Conversations and events will happen exactly the same way each time. Occasionally, free will is thwarted, so that even if a person wants to alter the course of Time, it’s impossible to do so. Doctor Who gets around this, so that whenever The Doctor meets himself, his memory becomes cloudy so he doesn’t remember what his past self experienced. (The Universe apparently makes an exception and lets him remember doing something if it involved showing off)

While Grandfather Paradoxes only happen with Mutable Time, Ontological Paradoxes only happen with Immutable Time.

And if Grandfather Paradoxes are the most popular, most talked about, but rarely used, then of course Ontological Paradoxes are the least popular, least talked about, but most used. Several stories that utilize such a paradox will never even reference that a paradox occurred.

And why should they? There are no repercussions, no unwarranted worry that the universe will explode. Due to the nature of Immutable Time, whatever happened has always happened. This paints a picture of Time being more vast than we can comprehend. With Time Travel in the picture, all of these events written in stone in near-eternity can happen more than once, and if you go back in time and cause an Ontological Paradox, why should that one event make the universe explode? It already happened. Time has already passed it by once, your trip won’t make the Universe do a double take.

The only possible problem is entropy. If the exact same object is constantly sent back in time, it will eventually decay, disintegrate, and break the Time Loop. That’s a theory, sure, but it’s another one that never happens. Stories get around this by having the character make a duplicate and never send the exact same copy. In Heinlein’s By His Bootstraps, the main character takes an old worn out piece of paper to the past. He then copies over the contents to newer paper, throws away the original, and years later realizes it was the exact same paper. In the Doctor Who episode, The Big Bang, The Doctor finds a note he wrote in the future. Even though it was still new, he made a copy of the note to send back in time presumably just to prevent entropy getting in the way.

My favorite example of this Paradox is in the Doctor Who episode Blink, when Sally Sparrow is able to have a full conversation with a video of the Doctor recorded 38 years prior. If you’ve never seen Doctor Who, beware you may be spoiled by watching the best scene from one of the best episodes.

More Examples

  • The Terminator
  • Futurama
  • Harry Potter and the Prisoner of Azkaban
  • Bill & Ted’s Excellent Adventure (parodies this paradox to the extreme)

BONUS: Pair o’ Docs

This is when there are two Doctors.


  • Back to the Future
  • Doctor Who
  • Every Doctor Show Ever and Probably Also Inside Hospitals In Real Life
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