Sunday, March 9, 2014


I have become accustomed to using the word "anti-paradox" to describe a particular kind of time travel oddity.  I first encountered this word either on Wikipedia or TVTropes (sometimes it's hard to tell).  Now, despite my constant searching, not only can I not find the original article, but I cannot find any article anywhere on the internet using the word in the way I remembered seeing it.  The definition, as near as I can remember it, is as a follows:

An anti-paradox is a self-supporting, self-validating, tautological statement or situation.

It is a statement that is true precisely because it is true.

One of the examples that the article gave was the Robert A Heinlein book, "All You Zombies".   But that plotline is convoluted, and gross, so let me give a simpler example of a time travel anti-paradox.

A man is sitting in his room.  Suddenly, in a whir of sound and light, a metallic box appears in the room with him, and out steps an elderly gentleman.  The elderly fellow explains that this box is a time machine.  The elder has finished with time travel and wants to end his days as he remembers them before he left; and so, he is giving the machine to the younger man.  The younger man takes the machine and travels up and down the timeline, meeting famous people from history and exploring the technology of the future.  After decades of time travel adventures, saving the world from evil robot kings and stopping the Eiffel Tower from collapsing (he succeeds), the man becomes tired.  All this moving.  He wants to stop, and find some time, and just stay there.  But the only time he really remembers having any attachment to is the time before he left.  And so he returns to that day when he first got in the machine, and hands it off to his younger self, and stays there in his own time until such runs out.

This situation is an anti-paradox.  The man gets the time machine because he has the time machine because he gets the time machine because he has the time machine.  The attainment of the time machine is the cause of its own attainment.

This isn't contradictory, nor does it even offer an apparent contradiction.  It might be more correct to say that it makes too much sense.  The "problem" with it is that it doesn't have any exterior input.  No one builds the time machine.  The man has a time machine because he has a time machine.

I distinctly remember reading this situation as being called an anti-paradox.  Can anyone corroborate this?

If not, then let me propose the word for general use.  Anti-paradox: a self-supporting, self-validating tautology.


  1. I believe what you're describing is known as the bootstrap/ontological paradox:

  2. This blog has got to be the most underread thing on the internet. Thanks and keep it coming.

  3. I've known about this idea for years but never put a name to it. Thank you so much for giving it one!

  4. Never mind who built the time machine. Who built the world? It amounts to the same thing.

  5. So I've found a pretty big problem with this so-called anti-paradox here-

    Say you have this man- We'll call him 'Present Dave', or PD for short.. And to support the Time Machine (or TM), then PD would either have to have built it or have been given the device (let's also assume that Present Dave is a pretty smart dude, so he engineered it).

    Thus we have PD which has just completed a working TM, and at that exact moment the possibility of his future self returning to that time to live out his life has been opened.

    So here are the following events which create the very big problem:

    PD creates TM, then Future Dave (FD) comes into the room to leave (or take his own TM) with him, and PD leaves with his TM only for another FD to return and catch the first FD who returned seconds or minutes earlier right outside the door.

    Herein lies the problem, which I believe has to do with, in a sense, relativity- We can only create this paradox by blinding or observing past or future daves. In the above example, we observe Present Dave who just saw his future self return, and thus he leaves while his own self (PD) returns at the exact moment he leaves. There the paradox ends, because in this timeline we have no more Daves...

    But how did we get 3 from 1? Because we negated to look where this future Dave came from (he came from the exact same dimension). And herein lies the true paradox- To be put simply, PD builds TM, FD "returns", while our PD leaves- Our PD then returns to his original time (finding himself just finishing the TM AND his now present (and older) self just returning from his own time-traveling journey.

    If the paradox is to be continued, you would quickly end up with a very large multitude of 'original' and older daves (each older Dave having to return earlier and earlier). The real issue isn't the paradox, but our poor Dave who is working on a time machine and all of a sudden is inundated with a near infinite amount of his future selfs. Heavy stuff...

    I'm a huge fan of this blog and would love to talk further about this or many other topics, however I'm not sure if this blog is still being maintained or not...

  6. Had to edit my entire post bc I misunderstood the story here- But wouldn't this whole paradox fall apart due to the almost instant and almost infinite exponential growth of time travelers suddenly imported into world?

    If his "future" self stays to live out his life in the same world that he originated, then it would only follow that there would be a constant stream of old guys, exhausted from time travel, exiting (or filling) the room at a constant or almost instant rate.

    I don't think the man having a time machine just because he has a time machine would matter all that much at that point...


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