This entry is part 2 in the series Time Travel In RPGs

.| Spiral |. by Clix

The first part of this article looked at two simplistic solutions to the question of how to handle time travel in RPGs, and found that as they stood, neither was satisfactory. A number of readers were kind enough to write in, suggesting additions that could be made to these two solutions to make them more practical for game purposes. This second part will start to examine the metaphysics that I developed for use in my superhero campaign back in the early 1980s, extracting the general requirements of a good solution to the initial problem; when collected, these can be used as a road map to take the work out of creating an interpretation of time travel that is unique to each campaign.

We start by looking at what Time actually IS.

Physical Forces Equivalents

I started out by thinking of time as ‘the fourth dimension,’ and of events as points in motion within that fourth dimension. That let me think about time by way of a more familiar analagy, that of the forces and phenomenta that operate on objects in the physical world – momentum, inertia, accelleration, velocity, etc.

This approach proved very useful as a starting point, so much so that I went further and postulated that time was actually a three-dimensional environment with changes taking place along a given axis of space. This made the analagy even more one-to-one. I named these dimensions Time, Duration, and Extent, though I was never completely satisfied with those names.

What we, in the normal dimensions of space, experience as the passage of time is simply motion along a vector within this three-dimensional time. In the physical universe, energy maifests primarily as matter; in the temporal realm, energy manifests as ‘Events’.

This also made describing the temporal realm far easier – a timeline wasn’t just a convenient graphic device, it was a literal cartoonist’s-sketch of the reality, a diagram representation of what would actually be “percieved” by an observer.

So, that leads to the first requirement: a good time-travel system will make it easy for the GM to visualise and describe the environment, and especially the relationship between events. And to the second: it will provide a metaphor for changes in the succession of events that can be easily understood.

The list of equivalent forces that I derived are:

  • Development is analagous to Entropy
  • Pull is analagous to Gravity
  • Will is analagous to Charge
  • Selection is analagous to the Strong Nuclear Force
  • Affinity is analagous to the Weak Nuclear Force
  • Persistance is analagous to Inertia
  • Option is analagous to Polarity

This ‘force’ parallels Entropy; it is the temporal force that leads to the occurance of all events that can possibly occur at a given instant. As an event is influanced by increasing Development, it becomes possible to alter the configuration of the outcome of the event with greater control and precision, but it becomes harder to make broad, sweeping changes. This is the force that gives different timelines their different histories, and like the Heat-death that is associated with Entropy, eventually, the scope of possible change will become so small that even at a quantum level, nothing is uncertain.

Another way of looking at development is to see it as analagous to time in a physical description of events – you’ll see what I mean a little later.


Gravity holds large chunks of matter together; this force holds clusters of events together. The more closely-related two timelines are, the more Pull holds them together, eventually reaching the point where it becomes more or less meaningless to divide them – for example two timelines in one of which a specific radioactive atom decayed at a given instant and in the other, another within the same chunk of matter. To all intents and purposes, they are identical.


Will provides an uncertainty about the outcome of an event experienced by any specific timeline. Just as Heisenburg’s Uncertainty shows that we can never be sure of exactly where any given subatomic particle actually is – just where it is most likely to be – so we can never be sure of the outcome of any event that is small enough to be subject to Will. And, just as the charge of a single electron is miniscule in the macroscopic world around us, but a lot of them can add up, so Will can accumulate. There’s be more to say later on this subject, under the heading of Free Will.


Selection is a sorting mechanism. Like the strong nuclear force, which arranges subatomic particles into atomic structures, this force sorts small events into chains of compound events, linking outcomes to preceeding events. It is Selection that permits minor events, which are subject to will, to accumulate into larger changes.


Just as selection links changes in the probable outcomes of events, affinity links conditional events. Affinity manifests as Destiny – so, once again, there will be a lot more to say on the subject, later.

Will causes an unlikely outcome to manifest. Affinity forces that cause to have the appropriate effect. Selection links that effect with several others to form a macroscopic event, a Decision. Pull connects that Decision with many other outcomes to make timeline X distinct from timeline Y, in which a Different Decision was made. These will diverge in temporal dimension, ie have different temporal vectors, from the Event as an origin point – in other words, they will slowly spread out with increasing Development of the ramifications and consequences.


While Will defies probability, occasionally selecting for a low-probability result, one small change doesn’t make a very big difference close to the initial event influanced by will. It takes Development for the ripples caused by that event to compound into a more significant change. The tendancy for a timeline to resist change is its Persistance.


Like its equivalent, polarity, this phenomena has little effect except in extremes. Unless a great deal of Option is exerted, the effects are hard to detect. Also like its equivalent, it is probably the hardest to explain.

At its simplest, option is the force that rejects events from outside the space-time continuum, the safeguard of natural law. While that has multiple manifestations in a psuedo-science environment like a superhero campaign, or even in a ‘hard fantasy’ campaign, for the purposes of our discussion, another of its manifestations is more important: it is the force that resists time travel, trying to keep everything in its naturally-allotted temporal place.

This diagram illustrates everything. From condition (1), event A is 100% likely to happen. At event A, there are two possible outcomes, B and C, and both are equally likely. Outcome B inevitably leads to event F, while there is an analagous event, G on the C timeline, because the cause of those events lies before decision A. At event F/G, another cause-and-effect chain, DE interacts with the outcome of decision A to produce three possible outcomes; H and I are the most likely, respectively, but there is a slim chance in both cases that the interaction will result in outcome J. With further development, H becomes L, J becomes M, and I becomes N.

To take a more concrete example, F/G is a meeting, and A is a decision about who will attend to represent one faction.

K represents some external manipulation of the outcomes – enough that J might suddenly become the most likely result. If J represents the possibility of a spontanious explosion during the meeting, killing the participants, K might represent the planting of a bomb by a time-traveller – so that what was a 1% or less chance is suddenly a 99.9% near-certainty.

This diagram also depicts the temporal forces that have been discussed earlier. At A, a condition is set up by Will, that condition being the choice between options B and C. Affinity links events B/C to cause A. Selection keeps them apart. Pull combines cause-effect chain DE with events B & C to produce outcomes F and G, respectively. Persistance keeps the differences between F & G minimal; but those small differences interact with DE to expand those differences, widening the rift in outcomes as events are subject to Development. Exterior influance K can make the unlikely outcome J the most probable outcome, but only by overcoming the force of Option which states that without outside intervention, F will almost certainly become H, which in turn will almost certainly become L, and G will almost certainly become I, which in turn will almost certainly become N.

This model of time permits a rational discussion of time-travel by defining the “landscape” and the way events combine and interact.

The propagation of Consequences

A key question is how consequences progress down the timeline. There are a number of models that can be used as the basis of your description of time, and this criterion is one of the great distinguishing differences between them.

The many-worlds theory of time, in which every possible outcome is equally real, and those outcomes not experienced in a particular world are experienced in a parallel world, is one of the most popular, and it’s the one that I used back in the 80s. There are others – the serial model, which I have to admit I’ve never quite been able to wrap my head around, for example, or the “threaded” one-timeline model of Thrice Apon A Time by James P. Hogan.

When you introduce a change in history, the timeline bends in a new direction. The bigger the change, the bigger the change in direction. It’s simple impact mechanics, the transfer of momentum. You can even see it at work in the diagram above – F&G are virtually indistinguishable because the Decision at A has not yet made any real impact. As soon as it does, the timelines start to diverge.

The same mechanisms also exists within the timeline, and be responsible for the propagation of consequences to events. Think of a timeline as a whole bunch of smaller timelines bouncing around inside a larger hollow tube; most of them will have no effect, but every now and then a whole bunch of them will be pushing in more or less the same direction at the same time, and the direction of the timeline will shift in response. This is the same mechanism that in the physical world translates quantum effects into large-scale effects.

The supposed ‘unified path of history’ is, on closer examination, a large number of possible paths, held together by the force of Persistance, which overcomes the weaker force of Selection which tries to push them apart, just as matter is held together despite atomic structure being basically a set of positively-charged clumps floating in a sea of negatively-charged electrons. You would expect the charges to prevent atoms from forming molecules, but it turns out that molecules are formed by relationships between electrons. You would expect molecules to repel each other (and they do) but gravity is enough to hold a bunch of them together.

So each supposed “Timeline” actually consists of a virtually-infinite number of virtually-identical timelines, distinguished by differences at the quantum level.

Application To Time Travel

So, with our model in place, let’s postulate a theoretical time-traveller from point L. He goes back in time and changes the outcome of event A, so that instead of it being a 50/50 proposition between choices B and C, a third option, D, suddenly results. As soon as he arrives prior to A, his existance creates a new set of alternatives – he’s either there, or he’s not. There can’t be as many time-travellers as there are timelines, because not all timelines will result in his discovery of a mechanism for time-travel.

Immediatly, the timeline at the point of his arrival will do a B/C-style division, between those timelines in which he arrives back in time and those in which he does not. From that point on, he can make any change he likes in the outcome of events and there will be No Paradox that results because his origins will always lie apon the set of otherwise-identical timelines in which he did NOT travel back in time. There is no grandfather paradox because the consequences of killing your own grandfather lie in an alternate world.

That’s not to say that some Other time-traveller can’t go back and change the outcome of events that are experienced by a particular world – the one in which the PCs lie. It does not prevent the PCs from travelling back in time in an attempt to undo that change. And each of these creates a new set of timelines – worlds in which the villain did not change history, worlds in which he did but was stopped by time-travelling PCs, worlds in which he did and the PCs failed to stop him, worlds in which the PCs never found an opportunity to stop him, worlds in which they didn’t try. You can have total ignorance of the outcome of events and still have a deterministic history.

The key to maintaining player satisfaction with the outcome of such time-travel is to ensure that a parallel-world version of the PCs is always at work in the PCs timeline, undoing any change. You pick and choose between these possible worlds as suits the needs of the campaign, and as provides the emotional fulfillment of the PCs. While you could have them go back in time, succeed in their mission to correct history, and return to find that nothing had changed because they weren’t operating in their timeline but in a parallel world, this would be unsatisfying to the players, so we don’t choose that world – it’s fully populated by NPCs. Choose The World That Works for your campaign.

Whenever the PCs attempt to rort the system using time travel, simply have them return not to the world they left, but to one in which the details of their situation are different, possibly worse.

What’s more, since you can switch between parallel worlds at the drop of a hat, this permits any retconning necessary within the campaign – you simply switch the timeline from the pre-retcon background to the post-retcon background.

Next Time: the next (and final) part of this article will expand on some of the implications of this model of time, and on a couple of variations that can be useful as tools for the GM.

Related Posts with Thumbnails
Print Friendly