Future Man is a super cheap looking show but it's moderately funny and there's like a vacuum of good shows to watch right now so...

I really don't like time travel stories because most of them have flaws. Especially the time travelling hot tub kind.

I am willing to accept time travel only insofar as it acknowledges that each change creates a new future as a sort of alternative reality and there's no "original" future to go back to anymore. This gets rid of the whole fading out of existence nonsense.


Another time travel idea that I found very entertaining is the one from HPMOR (about time turners): you can never *change* the past, there is no separate past/present/future, reality is just computed in one swoop in a self-consistent way.

E.g. the *first* time you encounter this "past", it's *already* changed. There is no "first run-through" that happens differently where you later decide to go back and change it.

@Gargron This is personally the type of time travel I like best, the one where "closed loops" are the only way in which it is possible to time travel.

@Gargron On the note of time travel where the timeline IS changed so that it is impossible to go "back to the original," have you watched Primer? It's the only work in which I've seen time travel done the way they do it and it's extraordinarily interesting.

@AshEaria It is one of my favourite ideas. It can also be super creepy because it can create time loops in which you have to go back in time to do something *only because you know you did it*, but the actions are entirely in character with you except that you never *invented* them

@Gargron If you wanna take that one to the next step, how about doing something wild with the expectation of being helped by a "future" self (example jumping out of a window as your future self puts a trampoline under it), because you know that's exactly what you would do and knowing that eventually you'll have to go back in time to help a bro out and save yourself from the fall, as you'd initially planned? Homestuck plays with this quite a bit. TBH Homestuck has every flavor of time travel.

@Gargron @AshEaria have you encountered "all things devours" or all-night-laundry.com ? Those are two of my favorite time travel narratives, and I think they each establish pretty consistent mechanics in their own ways...

@AshEaria @Gargron in particular, all things devours manages to be a fun and playable game with a convincing time-travel system, which I think is an impressive feat

@dukhovni @Gargron Duly noted for as soon as I have time. I'm a game design student, so games that dabble in time travel (especially if it slides out of the narrative realm and establishes itself as part of the gameplay) are especially interesting to me.

@AshEaria @Gargron Yeah, it's really well-done. The time travel is restricted in certain ways, so there are certain kinds of classic time travel tricks that are just impossible, but it works in a way that makes a lot of sense and happens to be relatively easy to build into a game where players have full agency over their actions at all times

@dukhovni "All Night Laundry was created in the MSPA forums." I don't know how I would have expected otherwise.

@gargron like, if you went back in the past and had to avoid running into yourself

you would have always been there, hiding behind that pillar the first time around?

If I can implore you to read two chapters of text, please read this one and the next one: hpmor.com/chapter/13

I think they might be my favourite, and I think you can probably get away with reading them in a self-contained way.

cc @AshEaria

@Gargron Haha, of course. I love Methods Of Rationality, I just never got very far with it when I started reading it. Will report back on completion.

@AshEaria The quality declines over the course of the story, unfortunately. First chunk is great though!

@varx A pity to hear. I found it hilarious to read back when I first found it and it's still funny as hell now.

@Gargron Done and done. From the previous conversation I'd pretty much figured out how it was going to go, but a wild read nonetheless. What made it super effective against my nerd type is that it also included gamification, which I am unhealthily interested in.

This is how Time-Turners are supposed to work. This, and not the farce that Cursed Child turned out to be.


I'm more into the Primer-style time travel, where you're stacking up duplicate selves in the same time period


it's a complete violation of the whole "matter cannot be created or destroyed" and all, but optics was once a closed science and discovering lasers opened it again

I honestly think "real" time travel would have such flagrant loopholes in order to preserve other aspects of reality

@Gargron That's my favourite personal take, the 4D 'block universe' of General Relativity plus the 'sum over all possible histories' idea from Quantum Mechanics.

If you want to time travel into the past, you can only do so if by doing so you neither contradict your own observed personal past (Grandfather paradox) nor create information that has no source (bootstrap paradox). At the moment you travel, the universe goes 'wibbly wobbly quantum' and decides if you can or not.

@Gargron This could lead to there being whole organizations of 'Time Monks' owing to the universe simply won't let you time travel unless you do so with pure intentions (ie the intention not to create paradox).

The Time Monks will never kill Baby Hitler because they're trained not to want to, because if they want to, the Time Portal simply won't open for them.

@enkiv2 @Gargron Because it's embarrassing to the Cosmic Caretakers if you have causeless self-referential loops in the timestream, that's why.

@enkiv2 @Gargron And that's why the Quantum Time Portal will never open for you, but it opens for the Time Monk next to you. And if you stick your hand in it it's just gonna close immediately and you'll lose your hand.

Stupid infinite quantum wossnames of the n-th dimensional Hilbert Spaces.

On the upside: the Cosmic Caretakers are perfectly happy with us abusing the infinite computation power of Time Portals to create super-fast GPUs, so our VR is really slick

but all our Bitcoins are gone.

@Gargron In the most general form, the point at which you travel backwards must form a fixed point. Any changes are fine as long as they lead to the fixed point, but anything that would create a paradox becomes impossible.

@emc2 I have a problem with this. Even stories that play around with the butterfly effect do not go deep enough. Simply arriving in the past displaces molecules of matter and therefore creates a chain of events that must lead to a different future.

@Gargron Quantum theory provides a possible solution. Causal chains that would cause a paradox have zero probability. (The laws that govern such a phenomenon would necessarily be incomprehensible to any entity experiencing linear time)

@remram44 Paradoxes are simply impossible because an unstable time loop simply doesn't happen - the universe always prefers simpler time loops

@remram44 Worded in a confusing way but suppose you resolve to go back in time and kill your past self. This is too complicated, so something happens to prevent you from going back in time

@Gargron Occam's razor is a subjective idea scientists use. We're talking about an automatic system, a law of nature. Nothing is "simple" or "complex" to the universe

@remram44 This is wrong. For example, a lightning finds the shortest path to the ground. There are things like entropy and complexity

@Gargron Excellent parallel! See, lightning doesn't follow the shortest path that was divined by the universe, it follows a well understood, local, iterative process to the next lowest-resistance region, then the next, and ends up finding a local minimum (that then turns into plasma and produces a flash).

@Gargron Finding a stable loop is finding a fixed point for the function mapping from "what comes from the future" to "what we send to the past". Not only does that mean the universe can find a solution to any complex problem "instantly", it also means that it can *choose* if there are multiple, and of course I'm ignoring the no-solution case that we call "paradox"

@Gargron Also see this paper for an analysis of the consequences of the form of time travel you describe in terms of computation: arxiv.org/abs/1008.1127

@Gargron This is also not what we call Occam's Razor btw

@Gargron There are still an infinite "solution" time loops. How does the universe choose?

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