Firstly: I'd like to note that this post ( and the world it's based in) is partly inspired by the time travel mechanics of the game Achron. If you're confused by my question go watch some videos of that, then you can be confused by them too.

With that out of the way: Let's establish some rules for time-travel.

1: There is one timeline. While parts of the timeline may be affected by effects that no longer exist, there isn't a concept of 'multiple' timelines except in an abstract sense.

2: Any changes to the timeline propagate forwards at the same speed as time. If If I jumped back in time and didn't affect myself at all, there would be a ten year 'epoch' at the front of the timeline in which only one of me existed, but the rest of the timeline would have the history in which I arrived. If I were to jump back ten years and kill myself, it would take ten years before that change reached the point where I jumped.

3: As a consequence of 1 and 2: Paradoxes do not resolve. Instead they form multiple state 'flip flops' in the timeline. Using the example above: I jump back ten years and kill myself. It then takes ten years for me to reach the point where I otherwise would have jumped from. My lack of jumping changes the timeline of ten years ago back to it's original state, which then takes ten years to repeat the process, leading to a paradox with a period of 20 years. These paradoxes never resolve, but will continue to bounce between states forever, sending 'waves' of alternate histories (named 'epochs') down the timeline.

4: Messages can be sent between times. This is equivalent to a jump. If I send a message back to myself saying 'duck', the change it causes will follow the same rules as above. If the changed me also sends the message saying 'duck' this results in a permanent alteration to the timeline. If the changed me does not send the message, a paradox results.

5: It is not possible to detect when a message or traveller has come from (unless the message or traveller tells you), and similarly it is not possible to detect (without prior knowledge) where a message/traveller is going to.

Ok. That's the rules out of the way. Now onto the scenario:

A war has been raging, using time as a battlefield. Nobody knows how long the war has been going, because it's been lost in a haze of paradoxes and time loops. The war is formed into roughly two sides, and at some point these sides have managed to organise themselves with centralised command structures. It can be assumed that any soldier on either side will immediately and implicitly trust any messages they get via the time-communication devices, and that neither side can interfere with the other's time- travel technology directly.

My question is this: Given that the paradox mechanics can result in constantly changing histories, and Epoch boundaries move forward through time constantly, how can either side establish a permanent command structure that won't eventually end up sending orders over itself? So far all I've come up with is jumping back as far as possible and setting up a (very well hidden) command post.

Please note: This isn't actually of vital importance to any plot elements at the moment, but it's been bugging me that I can't think of a decent way to do it, and if I were to expand this world past the current narrative I've got going I'll have to address it.

Addendum: You can assume that this universe is deterministic and ignore the vast majority of quantum level effects. Unless a traveller/message has an actual interaction with a system it can be considered to evolve in exactly the same way. As an example: If a traveller jumps to where a lightning bolt will hit it will route through them. If they jump twenty miles away the bolt will take exactly the same path as it would of without the jump occurring.

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    $\begingroup$ I can't even imagine how confusing and demoralizing this scenario would be for the soldiers on the ground. Fun question, though. $\endgroup$
    – Avernium
    Sep 25, 2015 at 14:10
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    $\begingroup$ Hence the 'you can assume they trust messages implicitly' statement. I've got a couple of monologues around the required mindsets for the various trans-temporal roles, how you can't assume that just because someone is identical to you that they're the same as you, and why as a soldier you have to trust orders implicitly, because the person giving them is probably you. My characters range from being very zen about it all the way to 'how am I going to explain PTSD to my younger self?' $\endgroup$
    – Joe Bloggs
    Sep 25, 2015 at 14:21
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    $\begingroup$ I'm thinking you can steal some techniques that databases use to keep multiple servers synced up. I'll work on it more and try to put a usable answer together. Question: Does every message/event result in some kind of paradox wave? Or could you have the time devices communicate between themselves (keeping up to date) without constantly slightly altering the timelines? $\endgroup$ Sep 25, 2015 at 14:26
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    $\begingroup$ Also, when a paradox event occurs, is randomness "reset"? Mostly concerned about quantum-level events. For example, unstable atoms randomly decay - after a paradox happens will that randomness be new/unique, or will it stay the same? $\endgroup$ Sep 25, 2015 at 14:38
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    $\begingroup$ Have you read any of Robert Heinlein's books involving Time Corps? He dealt with this a lot. He had phrases like "Always be nice to your fellow soldiers when you are the ranking officer. You never know if, next time you meet them, they'll outrank you. Politeness goes a long way in Time Corps." $\endgroup$
    – Cort Ammon
    Sep 25, 2015 at 16:17

3 Answers 3


I am going to use "paradox wave" to refer to changes propagating through the timeline.

This answer also assumes that if you jump through timelines, you're not longer impacted by paradox waves in the timelines you left.

I'm sure this answer isn't perfect, but it outlines a conceptual way to keep things intact, and it's probably just as plausible as time travel is in the first place.

Paradox Detection

Each time communication and travel device will communicate with itself (sending messages back and forth one week apart) in order to detect paradox waves.

To do this, the device will record its own kinetic movements. So being picked up, the user moving around, etc. Presumably a paradox wave that's significant would change these events because the user will taking different actions. Or they could be dead.

This recording and communication is buried in the device and is normally inaccessible to prevent people from accidentally messing with their own timelines.

It will then alert a user in the following scenarios: User+1 week will be alerted if User's kinetic pattern changes. User+1 week will be alerted if User's device stops sending responses/data. User will be alerted if User+1 week's device stops sending responses/data.

This then allows a user to realize their timeline has been altered and take appropriate steps.

Restoring Command Continuity

After a paradox is detected, the command center will then have 2 weeks before the incoming paradox wave to resolve the issue.

Note: I'm assuming 2 weeks because the "propagate at the speed of time" is kind of a really strange concept. Time being relative and only existing within the context of a timeline normally. But in this case, after "1 week" the command center has experienced half a week in their timeline, which means they're "ahead" of the paradox wave by 3.5 days. And at 3.5 days, they'll have another 1.75, and so on. It won't actually catch up to them until double the time of the paradox has passed.

Preventing Circular Paradox Waves

This system could result in additional paradox waves as people are alerted to other waves. In order to keep this from circling, they should observe the following protocols:

Groups shouldn't resolve their own paradoxes. So, establish multiple command bases. If Command A is alerted that they're about to be wiped out, Command B or Command C should be in charge of fixing it.

When a Command is wiped out, they should re-locate to a new location entirely rather than attempt to fix and stay in place.

Stranded Command Groups

Let's use Command A as an example. Say they get hit by a wave, but are just altered and not wiped out. Command A+1 week relocates to preserve command continuity. Now Command A is stranded.

You have two options.

Option 1: "Kill" Command A. You don't necessarily have to literally kill them, you could just mark them as untrusted and out of the war.

Option 2: Re-integrate them as a new command, with a new place in your overall organization structure. You'll want to re-evaluate everyone, check for plants, etc, to keep from being compromised.

  • $\begingroup$ I used 'epochs' for the paradox waves, and the 'speed of time' thing means that the changes won't ever actually catch up to command and control if they're ahead of the change. I very much like the kinetic device synchronisation though. I already had alerts being sent back upon death of the operator, so that's a logical extension to enable epoch tracking. $\endgroup$
    – Joe Bloggs
    Sep 25, 2015 at 16:19

This is only logically consistent only on a small local level. It is actually logically impossible in an attempt to prevent multiple time lines. Though you really DO have multiple time lines here.

If you go back in time and make a change, everything following that change will have a 'different' reality. If I am killed as a child (as a target, not as collateral) none of my friends or family would know anything about me past that point in time and anything I would have done never exists. If I don't exist now, no one would go into the past to 'kill' ME, since I don't exist, but they might go back to kill my younger self. This leads to the 'paradox' in the example.

The big problem is envisioning that 'time' is continuing in this loop over and over. To have any chance for this to happen anything like you are saying, then every time someone goes 'back' in time, time is reset BACK to that exact moment and EVERYTHING that had happened between 'now' and 'then' is 'rewound' and we 'start' over. Meaning there is only one true 'current moment' in time, everything else is the past already set in 'stone' and the future infinitely mutable. And sending someone 'back' erases everything back to that point in time, allowing everything to continue the same as it had before except for any changes that were made by the act.

Anyone growing up in one timeline would never 'know' anything about the other, their lives have 'always' followed this path.

EDT: Taking the idea of each change is a 'wave' of change slowly moving to 'update' the future and doesn't make an instantaneous or updated timeline. (and answer to Joe Bloggs comment)

There is no possible control. If two groups are doing this you don't even have true control of where you are sending anything 'back' to. It could already be changed before they get there. I send a man back to talk to a SGT. but he hits a wave where that SGT was killed 10 minutes previously, so no one in the future would no he's dead. On top of that no one will know HOW any change is actually going to affect the future.

2nd add: If the time change 'waves' move at the same time as regular time, then they will never catch up to 'now'. I send a man back 10 years to do something, that change takes 10 years to reach 'now', but I am now 10 years in my own future when it reaches this point. I will never see the changes I am advocating for unless I have some kind of machine that can 'monitor' the time stream. (I think Star Trek has a group doing that in the far future).

  • $\begingroup$ Rule 2 deals with this. Any change (including something 'resetting') only propagates forward at the same speed as time moves. What you get is not a sudden step from one future to the next, but a series of different histories moving forwards and constantly overwriting each other. You're entirely right that a person in one timeline wouldn't know about another until they'd been there though, but getting from one to the other is a matter of executing the right jump. The problem is how to maintain control, given that this is the case. $\endgroup$
    – Joe Bloggs
    Sep 25, 2015 at 15:34
  • $\begingroup$ @JoeBloggs added more $\endgroup$
    – bowlturner
    Sep 25, 2015 at 15:50
  • $\begingroup$ This is the issue I'm trying to work through. I'm sure there must be a way to co-ordinate messages such that mapping the waves (I refer to them as epochs) is possible, but it gets tricky if the control mechanism is exposed to time travel too (which it is by definition), hence the question! $\endgroup$
    – Joe Bloggs
    Sep 25, 2015 at 15:56
  • $\begingroup$ @JoeBloggs Then you would need some kind of 'timeline' monitor like that have in star trek. another issue, I just thought of. if the 'waves' move at the same speed as the rest of time, then they will NEVER catch up to 'now' thus really once again effectively having multiple time lines, but the lead one is being over written by the following ones. (I'll add this to the answer too!) $\endgroup$
    – bowlturner
    Sep 25, 2015 at 16:02
  • $\begingroup$ Yep. That's addressed in the question when I mention the leading edge of the timeline. I really recommend watching some Achron play through to get an idea of how I envisage the timeline working. They use propagation speeds greater than the speed of time, but it shows the general idea. The 'multiple timelines' only exist in the abstract, with the real timeline being a composite of them all. $\endgroup$
    – Joe Bloggs
    Sep 25, 2015 at 16:14

Have them always follow the orders from the furthest forward orders, also, make sure to send the messages to a time exactly ‘x’ ago, so that orders from different times don’t overlap. As the changes go at the same speed as time, if a specific time back length is made, the changes will overall match up with the orders, meaning that the troops will get the proper orders, from the proper future, at the proper time.

Ex. Jim sends message back 3 minutes, in the version where he gets the message, he doesn’t send it back. 3 min cycle created. By always sending messages back in a timeframe where it will always go with the correct alternations, in this case always 6 minutes ago.


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