The Grandfather Paradox

 All my posts are in Reddit or Mastodon these days. Woe is me.

Anyway, someone on Reddit was asking about the Grandfather paradox.

What paradox?

As soon as you go back in time you have created a new "you" out of nothing, there's no need for you to return to your future, you already violated causality and broke physics (conservation of mass-energy) by traveling in time anyway. The "you" in the past who has the memories of "you" in the future is not the "original" you... that one ceased to exist when they went back in time even if they didn't change anything. From the point of view of the physical universe the time machine is a disintegrator.

The whole "we gotta close the loop" business is narratively interesting, I guess, but it doesn't reflect any physical requirement. There is no "continuity".

When the you from the new timeline arrives that doesn't change the arrival of the first time traveler. Both still exist, created from nothing.

And there's no point in trying to restore yourself by stopping you from killing your grandfather. Just by arriving in the past you've kicked off enough butterflies to prevent you from being born no matter what you do. Chaos theory is a bitch.

You will go back into the past and there will be dozens of you who haven't yet realized that there's no point in trying to restore the past. Some will be dead because their time machines arrived close enough to each other that the wall of one machine intersected the body of the time traveler in another. Some of you went back together, so there's all these time machines left behind.

Some of you went off into the future and had adventures before coming back, so some of you will be heavily modified, with implants and artificial immune systems and extra limbs and different species and genders. You have kids with yourself.

Eventually you create a future where there is nobody who isn't a version of you, or your kids, or one of the people who stole one of the time machines you left behind.

Blame Larry Niven (All the Myriad Ways and The Theory and Practice of Time Travel), David Gerrold (The Man who Folded Himself), Douglas Adams (The Hitchiker's Guide to the Galaxy), George R. R. Martin (Unsound Variations), and Charlie Stross (Palimpsest).

Go read all of these, they are all worth it, even the ones that are horribly dated.

Also read Asimov The End of Eternity, Heinlein All You Zombies, Leiber Try to Change the Past, and Niven Rotating Cylinders and the Possibility of Global Causality Violation. Which brings us back to my blog. And now you know the rest of the story.