I'm looking for game mechanics and story telling methods that convey the atmosphere that characters don't just live in one world, but in a multiverse adhering to something similar to the many-worlds interpretation of quantum mechanics. This should in particular imply that if a character's action can lead to interesting stuff both in case of success and in case of failure, both things happen and the game world goes into a superposition of both until one of the options collapse.

In particular, I would like to convey this impression to the players, who should get a bit of an outside view on (a particular part of) that multiverse. It's less of a concern to have this show up on the in-character level (because I don't see how to do that without some traveling or merging of parallel branches, which is not the main feeling I want to convey. If there are good solutions to this, I'm listening.)

Obviously, the mental effort of playing in all the superposed worlds would be excruciatingly high. The main feeling I want to present is that no matter if the actions of a character are successful or not, there is another world out there where the opposite happened, maybe there is even a feeling of a feint echo of this. Furthermore, it would be interesting to under certain circumstances keep parallel branches running and collapse some of them at a time later than the action that lead to the branching, obtaining phenomena such as quantum immortality.

This is somehow the opposite to playing with parallel worlds you can travel to, but which otherwise develop independently from the the world the characters are currently in; Traveling to parallel worlds is not the feeling I'm looking for, but keeping different universe branches after an action alive and selecting one of them at a later point in time (letting the others collapse) is.

Are there any games out there that already implement (something similar to) this premise?

Do you have any suggestions on how to convey this through game mechanics or story techniques?


I had thought this question could stand on its own, but it obviously lacks the context of the setting and stories I want to achieve. (I still appreciate good ideas to this question that have nothing to do with my setting idea, though.)

The world the players live in is a simulation running on a powerful quantum computer. That computer can simulate quite a few parallel branches of the multiverse, but not all of them, so it collapses those that are not significant to the objectives of the simulation. For some reason, the player characters are extremely significant for those objectives, so sometimes a few different branches are allocated to the effects of their actions and only later collapsed when they prove insignificant.

  • \$\begingroup\$ What story do you want to come out of such a game? Characters traveling through such worlds? Independent stories that combine at the end somehow? \$\endgroup\$
    – okeefe
    Commented Nov 22, 2012 at 23:53
  • 2
    \$\begingroup\$ Broken Rooms by Greymalkin Designs touches on this theme tangentially, but in a such a way that the burden of alternate worlds is minimized to a set number. It may offer some ideas that help you pin down your own thoughts. \$\endgroup\$ Commented Nov 23, 2012 at 0:11
  • 1
    \$\begingroup\$ I'm a little confused. What is the purpose of branching universes when the other branches cannot be visited or observed? What your describing sounds like everyday life. \$\endgroup\$ Commented Nov 23, 2012 at 1:47
  • \$\begingroup\$ So, you're looking for a system that allows you to track 'what would have happened' for n parallel worlds, with the ability to bring those worlds (or features thereof) into play under certain circumstances? Given that from a player's perspective, the only time it's meaningful is when the parallel worlds intrude on their own, wouldn't it be easiest just to handle those specific instances by GM fiat and assume that no bookkeeping is necessary, as the phase space of possibilities is broad enough that any parallel world that could reasonably arise under such a system would definitely exist? \$\endgroup\$
    – GMJoe
    Commented Nov 23, 2012 at 5:06
  • 3
    \$\begingroup\$ I'm still not sure what the characters are doing in this nondeterministic spacetime that it matters at all that they're in a simulation. Do they know they're in a simulation? Can they travel between branches? \$\endgroup\$
    – okeefe
    Commented Nov 24, 2012 at 1:03

2 Answers 2


It's quite hard for me to parse exactly what you are looking for here. I think this will fit.

In most RPGs, the random factor is used to create results that you wouldn't pick for the characters. GMs and players are encouraged to make success and failure both interesting situations.

For example, a great thief is trying to get access to blackmail material hidden in a safe. The GM thinks that this is interesting enough to warrant a roll. They agree that success means that he gets the information and failure means that he gets the information but that he leaves a clue behind.

In a normal game, the dice would be rolled and play would proceed from there.

In a game where the players can maintain and collapse superpositions, you can do something different. There is no roll, both the success and failure results happen. The thief both leaves a clue and does not leave a clue.

From then on, any event that would be affected by what happened needs to be treated differently. Some situations would add a bonus or penalty to later actions (persuading someone to lend you money before you go into an auction for instance) and those are easy to narrate.

The difficulty (and your apparent desired outcome) comes when people would change the action they take depending on previous events. When these happen, you'll have to take notes on which previous branching points affect this action and the various decisions that can be taken.

To get the second part of the game let a player collapse the wave at any point and choose which events happened at each branching point. You could also randomly determine them, but that would take away a lot of the point of developing the extra timelines (since you would statistically have had the same timeline all along with much less effort).

To avoid this turning into an exercise in graph theory, you will want to limit the number of timelines that players can hold open. When it comes time for them to make a decision or take an action, if they have no more room for timelines, they have to decide on what has happened and resolve that first. Put another way, if there are more than a certain number of potential different situations then they have to collapse.

My choice of limit is 3. It means that you can have a choice between two different things including not choosing yet. There will still be a lot of complexity, but hopefully it will be manageable.

Finally, let me applaud you for doing something incredibly off the wall.

  • \$\begingroup\$ You also need a way to cope with observer enforced collapse of the timeline. If someone, other then the character witnesses the event then can it be "held"? The thief in your example is fine because he/she is alone. But should the thief be observed by an npc, collapse may be required. The PC could remember an un-collapsed event as having all possible outcomes, that is part of the computer holding that timeline open. Once it collapses the unneeded memories vanish as they are not needed. The computer would seek to minimize that overhead for npc memories. More slots required if witnessed? \$\endgroup\$
    – Leezard
    Commented Nov 23, 2012 at 17:52
  • \$\begingroup\$ @Leezard Based on the setting, the only observer is the supercomputer - it is deciding what timelines to collapse and when. Actions that aren't taken by a player or by an important non player character can be collapsed instantly because they aren't interesting to the simulation. Helpfully, this also reduces the bookkeeping burden. \$\endgroup\$
    – Simon Gill
    Commented Nov 23, 2012 at 17:58
  • \$\begingroup\$ Not enough space in a comment to really get it all out :) I am making an assumption that the simulation is for a bunch of people hooked up to it, Matrix style. Some are, in the scope of the game, npcs yet they are no less flesh and blood than the pcs. From that standpoint, the computer would have to factor in their memories of the event to the overhead of holding a second timeline open. Would that be significant from a computer resource management point of view? I can see arguments for yes and no, no pun intended :) \$\endgroup\$
    – Leezard
    Commented Nov 23, 2012 at 18:11
  • \$\begingroup\$ Also from a game play point of view, if the players get to a place in the game that they are aware of the branching and trying to encourage it, being unobserved could add an extra dimension to the difficulty of making branches happen. I'm really just thinking out loud and enjoying the mental exercise. \$\endgroup\$
    – Leezard
    Commented Nov 23, 2012 at 18:11
  • 2
    \$\begingroup\$ We've got different assumptions on how it all works. I encourage you to build an answer that explains your thinking, since it's an interesting and different perspective. \$\endgroup\$
    – Simon Gill
    Commented Nov 23, 2012 at 18:54

Do you have any suggestions on how to convey this through game mechanics or story techniques?

Before I begin let me say three things:

  1. I do love to talk about quantum mechanics, that does not mean I'm good at it. My understanding is that of a layman. I love to eat tasty pastries too but can't bake for crap.
  2. While my answer is somewhat similar to Simon Gill's it has some base differences that may merit separating them.
  3. I will be focusing on the story techniques with just a bit for mechanics.


I will assume the following things:

  • The PC's are hooked up to a quantum computer and have no knowledge that this is a simulation.
  • They are not the only people hooked up the computer. Every NPC's is another person too, just not one that the computer is "interested" in.
  • While the computer is exceptionally powerful, it is doing something that requires all of that power. In effect resources are limited and the computer must use some form of algorithm to manage resources.
  • The computer is some form of AI, limited or not, it has an "interest" in some of its charges. That is, I think, grounds for it being self aware.

What is a Timeline?

In the normal course of life (simulated or otherwise) all possibilities appear to collapse into a single waveform flow of events. Some of these events lead directly to and impact other events, hence they influence the probability waveform of these later events by making some possibilities more probable than others. The participants in these events have recall of the events. This, more then anything else, gives the timeline a form. What happened is a function of what is remembered nearly as much as what really happened.

Concurrent Multiple Simulated Timelines - Say what?

The world the players live in is a simulation running on a powerful quantum computer. That computer can simulate quite a few parallel branches of the multiverse, but not all of them, so it collapses those that are not significant to the objectives of the simulation.

I will refer to the source of one or more uncollapsed timelines as an "Open Event".

At some point the computer wants to investigate multiple timelines by keeping parallel branches alive. When this happens an Open Event is marked and the fork in the simulation is created spawning two or more parallel timelines. In creating and maintaining these timelines the computer has to invest resources. First are the computational resources required to branch the simulated reality. Second is the memory management of the subjects connected to the simulation. Both of these areas would have an initial cost as well as a running cost as more resources are allocated to feed the on going process.

While it is very tempting for me to get into the hows and whys of this resource management algorithm; it's a trap. Ultimately, that level of detail is not important to the exercise. In keeping this more general all that needs to be said is an event could be classified on a scale by how many people it directly effects and how many events it directly sets in motion. The higher it goes on the scale the more resources it uses and the more memory management is required. Of these two things, I think memory management would force a collapse of timelines more often then a lack of resources. More on that later.

If you want to bring this to the in character level memory management of the PC's is a good place to start. It is an excellent opportunity for adding a game play element. What if the PC remembers the Open Event with some ambiguity, such as they recall each outcome of the Open Event because each of them happened. As more stuff happens in each line they recall the events. This could lead to insanity. Once (If) they figure out what is happening then I see a motivation to make the timeline collapse in favor of the parallel they feel is most desirable. Once the timeline collapses would they lose the memories? Not necessarily but they should know that line ended.

In relation to NPC's it could function differently, I think the computer would be motivated to preserve the integrity the the simulation in respect to those minds experiencing it. While it may justify limited breaks in this for the PC's, NPC's would be a different matter. Having a few people realize reality is not real is one thing, having a few million with the same idea could undermine the purpose of the simulation, rendering it useless.

In light of that line of reasoning, it seems a parallel line may be "forced" to collapse well before computer resources become problematic due to the need to preserve reality integrity for the masses. In some special cases an NPC may get the same treatment as a PC. This could be a vehicle used to create a "Lex Luthor" type and have a main NPC work against the PC's because they want a different timeline to "win".

Pulling it all together

At the end of the day a GM can do what they want with their game. That is the nature of it. So if you want to play fast and loose with this then that is how you should go.

While I could go on and do this complex thing about assigning points to aspects of the Open Event and bookkeeping a number called a Tangent Resource Pool (TReP), I'm not. The more I think about that the more work it would be for the GM and it gets crazy fast. I'll just say that if you want to you could have a thing called TReP (trip) and give it a value to represent "mana" for maintaining parallel timelines. Use up all the points and one or more timelines collapse to free up TReP points.

Alternately, you could simplify things and have one major Open Event and say two or three minor ones running at any given time. That simplifies things greatly and lets you concentrate on story and your PC's.

While I would lean toward designing the TReP (I have a propensity for overkill) I would end up using something more like my second option.

Additional Stuff

Are there any games out there that already implement (something similar to) this premise?

Yes, with what I have state one could work in elements of WoD Mage the Ascension (editions 1 and 2 being what I know) looking at the paradox mechanics for inspiration in regards to memory management and forcing timeline collapse.

Also, check out The Wheel of Time books. There is an RPG based on that as well but I only played it once so I can't say if that will help you at all. The books, however, deal with the concept of Ta'veren extensively. That could be an excellent aid in storytelling shifts in probability. People "feel" the weave of the reality shift around a powerful Ta'veren.

  • \$\begingroup\$ I think there's an erroneous assumption here. As I understand the question, the PCs exist entirely inside the simulated universe. They're not hooked up to it like the Matrix, they are citizens of the simulated reality, so managing their memories isn't necessary. In effect the PCs are copied whole to each branch, and only the later, uncollapsed PCs continue to exist. \$\endgroup\$ Commented Nov 23, 2012 at 21:09
  • \$\begingroup\$ In my personal version of the setting, having a reality outside the simulation is definitely not the default state for any character, it may be a very rare thing at most. However, managing memories is important anyway, because simulated humans need memories, too, and memory overlap is something that could happen if the simulation is buggy... \$\endgroup\$
    – Anaphory
    Commented Nov 23, 2012 at 21:20
  • 1
    \$\begingroup\$ @Anaphory If one accepts the premise that reality is simulatable in the first place, then the essential nature of memories are no different than any other causally-meaningful structure within the simulation, so they'll be as bug-free as the rest of the branching simulation. If memories are buggy, then other reality bugs are possible. \$\endgroup\$ Commented Nov 23, 2012 at 21:24
  • \$\begingroup\$ In the context of this answer, @Leezard is assuming that the essential nature of memories is different from any other causally-meaningful structure. I merely wanted to point out that the question if characters have a reality outside the simulation does not influence this stuff a lot in my opinion. \$\endgroup\$
    – Anaphory
    Commented Nov 23, 2012 at 21:36
  • \$\begingroup\$ @SevenSidedDie Anaphory did say it is "less of a concern to have this show up on the in-character level (because I don't see how to do that without some traveling or merging of parallel branches". I see a way to bring it in game by saying the minds of the people are external to the simulation there by introducing a many-to-one problem. This may not be a high priority but I include it as an assumption because I find it makes things more interesting by allowing it to have an in character effect. I acknowledge it will be of limited value to the OP but others may like it. \$\endgroup\$
    – Leezard
    Commented Nov 23, 2012 at 22:02

Not the answer you're looking for? Browse other questions tagged .