tl;dr: What adjustments to a "rewind" power allow multiple equally powerful characters?
There are many different models of time travel. Personally I find it easiest to tell stories using the "fixed history" model, where the past is immutable because it has already happened: time travel can cause or provide information about past events, but it cannot change any aspect of history (see 12 Monkeys or the time-turner from HP).
However, it has consistently come up in feedback that people have two problems with this model.
- They do not understand it. ("You can't change anything." "Yeah, but what what if you did this...")
- They feel that it is too restrictive. ("What's the point if you can't change anything?")
So I've decided to write my next story with a model that allows the past to be changed.
In this model, the main character has the ability to rewind time, usually by a limited amount. This power manifests itself to the outside world as precognition.
My internal model of how this works is something like a git repo.
- The state of the universe is continuously stored as time progresses forward.
- At some point, the main character chooses to jump backward to an earlier moment. This can be handled in two ways:
- The character somehow chooses a specific moment, and jumps immediately to that point.
- Upon triggering their power, the character experiences time in reverse (at normal or accelerated speed). They cannot change anything at this point, only choose how far they go back.
- The entire universe undergoes a rollback and is returned to its previous state, with one exception:
- The main character's current mental state is copied into their past body, so that they retain the knowledge they gained in their (current) future.
- Unlike Life is Strange, you cannot hold onto anything that you pick up, and you resume in the location you were at the time you return to.
- Time progresses forward normally again.
There are a few things that I like about this model:
- There is a cost to the rewind. If you rewind one minute sixty times, you'll have wasted an hour of your time: which could be boring at best or mentally exhausting at worst. It probably has a poor effect on your sleep cycle/circadian rhythm as well.
- Making money is nontrivial. If your rewind limit is two minutes (as in Next) you cannot cheat the lottery, which usually must be purchased fifteen minutes or more before the numbers or drawn (I assume a similar rules exist for horse racing and the like). You can't cheat games where the randomness comes after your bet, like craps, roulette, and slot machines (although you can increase your odds by playing multiple times, with the aforementioned time cost). You can cheat games where the randomness happens before your bet, like blackjack and poker; but they are not high-payout games, and a string of wins looks suspicious.
- An outside observer sees no discontinuities. You don't blink out or teleport. The only indication that something has happened is that you are disoriented briefly while your brain readjusts to the sudden change in sensory input. (Although maybe for jumps which "push the limit" concussion-like effects, coma, seizure, etc. may be possible.)
- You can do lots of impressive things in the short-term (like dodge bullets), but can't preexamine the long-term effects of your actions; so most storytelling devices still apply.
However, I don't like the part in the 'rules' that states "main character." The idea that this mechanism is specific to one particular individual is unattractive to me.
Extending the Model
Braid introduces a new feature into the mix: some people in the universe are not affected by your power. In terms of the model above, their mental state is also coped into the past.2 I don't want to use this exact behavior for two reasons:
- The rewind ability is still asymmetric, since the rewind still falls under sole control of the main character.
- Anybody with this 'persistence' property would experience a rewind whenever you initiated one, even if they were on the other side of the planet and never met the 'rewinder.' This would be highly annoying at least!
This is the crux of my question: how can I modify the rules to allow a second character with the rewind power?
Here are my requirements:
- All empowered characters must obey the same set of rules regarding the rewind power.
- Characters must be able to tell when another is using the rewind power against them and counter somehow. ("Going around again? Nice try, but you can't use that trick on me!")
- However, characters must not be forced to relive a moment more than once if they choose not to exercise their power. (Bonus points: two characters can remain unaware of each other's nature or even existence until they interact.)
- Unpowered outside observers must not observe any glitches. If you use a branching-timeline model this includes observers in all timelines.
- If you use a branching-timeline model, at the end of any series of rewinds by both parties there must be only one timeline remaining.
- For example: interpreting the original model as a branching-timeline one, another timeline branches off the current on every rewind. All the "stub" timelines end when the main character chooses to jump. Time only continues forward in the new branch.
- A hard time limit on rewinds is not required.
1 From my understanding, Cage is supposed to be seeing the future, not experiencing and rewinding it; but the story plays the same either way and matches what I'm thinking.
2 The actual game mechanic is that they continue to propagate forward in time as you rewind. This works great for the game, but doesn't make physical sense in the real world.