Comment by AnIdiotOnTheNet | Hacker News Reader

Comment by AnIdiotOnTheNet | Hacker News Reader

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AnIdiotOnTheNet

I've actually thought a lot about this, in particular because I had a dream involving Novikov self-consistency principle. I think the base idea behind self-consistency principle is that it prevents grandfather paradoxes but allows bootstrap paradoxes. In other words, stable time loops are allowed but unstable ones aren't. I submit that it is possible to have meta-stable time loops such that all grandfather paradoxes are ultimately meta-bootstrap paradoxes.

Assume that if time travel is possible, then changing the course of events must be also be possible just as directing future events by our decisions in the present is. If one goes back in time and kills their own grandfather, they have altered the future such that they are never born in order to time travel in the first place, a grandfather paradox. However, since time travel must have existed in order for this situation to occur, then undoubtedly someone else at some future date within this timeline will seek to change history as well. To keep this scenario simple, imagine that this person travels back in order to kill you before you are able to kill your own grandfather, thus restoring your original timeline in which you travel back to kill your own grandfather. This is a meta-stable time loop employing a meta-bootstrap paradox. Each timeline exists and is dependant on time travel from the other. Arbitrarily complex structures are possible involving arbitrarily many timelines, which in an infinite meta-time universe suggests the possibility that all time travel must resolve in this way.

I came up with this years ago, but have only ever seen something like it explored once: in the TV show 'Dark'.

[SPOILERS]

If I remember correctly Dark to some extent relied on time travel to have time travel in the first place, i.e. Claudia Tiedemann needed to go back in time to hand H. G. Tannhaus the blueprints for the time machine that she used to go back in time with. That, in one of the alternate timelines- in the original timeline Tannhaus presumably made a time machine from scratch, or there would be no alternative timelines. In the end Jonas Kahnwald and Martha Nielsen go back in time to alter the course of the original timeline, thus eliminating their own. This is much like you say, except that in the end the original timeline is restored to the point before any time travel could happen, or had a reason to happen. And maybe that's a simpler way to eliminate any paradoxes: no time travel allowed [edit: yeah, sorry, that's Novikov].

Sic mundus creatus est :P

The part I'm referring to specifically is the concept of The Knot, the two timelines that were dependent on time travelers from each other to make the changes that caused them to exist.

Of course the show ended with eliminating The Knott, leaving the only paradox as being where two people suddenly materialized in the middle of the road from to warn about a bridge being out before just as mysteriously ceasing to exist.

> I came up with this years ago, but have only ever seen something like it explored once: in the TV show 'Dark'.

Doraemon, a Japanese children's cartoon (1970s to 1990s), created by Fujiko F Fujio, who is actually very well-versed in physics and science, has used something like this as a plot point in several different chapters/episodes and some movies. It doesn't actively call them "meta-stable time loops", since its target audience is children, but the idea and concept is there. Growing up watching and reading this series, I've learned more and more from it as I rewatch/reread old chapters/episodes, every time. I absolutely love it.

How do meta-stable loops work for time travelers visiting themselves in the past? How is it that moments before entering the time machine they don’t remember ever being visited by a future version of themselves?

Because that happened in a different timeline. If A0 was not visited and later A1 and decides to travel back to A0 and visit, that splits the timeline. Eventually some actor in that timeline (or another created by time travel from that timeline) will alter events such that they prevent A1 from visiting A0, restoring the original timeline and acting as the final piece of the meta-stable structure.

But if traveling back in time forks that timeline you don't have to worry about the self-consistency or bootstrap paradox at all, right?

Well, in this hypothetical cosmology I'm operating under the assumption that timelines can't just fork and continue on indefinitely as that requires energy (in the form of the time traveler) to come from an outside source with no connection to this timeline. From the perspective of the new timeline that event has no origin. By forming a meta-stable loop the two timelines are actually just different parts of the same meta-timeline.

Of course, there's no real reason to believe this is a requirement, it's all just an intellectual exercise.

I think that it would follow you.

Past you would have no advance memory of meeting future you until future you went back in time and met past you, at which point you would have memories from both points being produced at the same time.

That’s a great way to think about it. It reminds me of the Temporal integrity division in the 29th century in Star Trek.

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