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  1. - Top - End - #1
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    FreakyCheeseMan's Avatar

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    Default Rules for Consistent Time Travel

    So, I'm trying to come up with a consistent set of rules for time travel, such that you actually *can* change the past. So, none of the twelve-monkeys, "any change you made would already have been made" stuff. I've yet to come up with a set of rules as to how this works.

    I've come up with two case studies, each of which show the wacko results of different systems.

    In case study #1, Adam and Bob decide they want to kill Hitler. They decide that Adam will leave first, arrive in the past and kill hitler; Bob will leave the day before Adam, arrive shortly after Adam, and help bust Adam out of jail. Adam goes back and kills Hitler. Does Bob show up?

    If so, we have a problem, because the future that Bob came from no longer exists. As such, we have time travelers showing up from no-longer-extant futures, resulting in annoying, probably exponential piles of time clones. If not, we also have a problem; when Bob left, he still had a past to go back to, as Adam had not yet messed it up. So, where does Bob go?

    In case study #2, Adam and Bob get wicked drunk at a party, and Bob dares Adam to jump back in time by two minutes, into the void of space a few miles beyond Earth's atmosphere, and implies that Adam is "a scaredy-cat" if he does not. (Adam's time ship is not airtight.) An inebriated Adam takes the dare. How many Adams show up?

    The sudden appearance and asphyxiation of Adam in the cold void of space is unlikely to make much difference to the party, or to Adam and Bob's unfortunate wager. However, the Adam at the party will still be subtly affected by the added gravitational pull of his time-clone in space. As such, if Adam jumps back again, it would be another, separate Adam that shows up.


    Assuming no one at the party is watching the news, the rapid appearance of a moon-sized mass of drunken, dead time travelers is still unlikely to prevent the bet from taking place, until the gravitational pull becomes great enough to interfere with the celebrations, by which point it's too late anyway; the world ends with not a bang, not with a whimper, but with the sound of six billion voices screaming "What the hell?" and one solitary voice adding "God damnit, Bob."

    So. How do I make a set of logical and consistent rules for time travel, that don't run into either of these problems?

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    WolfInSheepsClothing

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    Default Re: Rules for Consistent Time Travel

    With this you're probably better off going with the multiple universe theory of time travel, as yeah, this stuff breaks down. So, when you go back in time to kill Hitler, you're actually creating a new universe where you kill Hitler. Bob can come along to, and in fact he creates two universes in doing so: one where he came back to help you out, and one where he saw WWII still happened, and figured you failed and his time was better spent making a sandwich. In fact, if Bob does show up, it might not even be the Bob you know. It might be another Bob from a similar but parallel universe, coming at the behest of another, similar but completely different Adam.

    Or you can also go the Doctor Who method and say that time travelers exist outside of time, and therefor are unaffected by the changes (no ball of a billion Adams, and the time stream remains fixed while they are in it, so Bob's post-WWII reality exists until he leaves to join Adam).

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Deophaun View Post
    With this you're probably better off going with the multiple universe theory of time travel, as yeah, this stuff breaks down. So, when you go back in time to kill Hitler, you're actually creating a new universe where you kill Hitler. Bob can come along to, and in fact he creates two universes in doing so: one where he came back to help you out, and one where he saw WWII still happened, and figured you failed and his time was better spent making a sandwich. In fact, if Bob does show up, it might not even be the Bob you know. It might be another Bob from a similar but parallel universe, coming at the behest of another, similar but completely different Adam.

    Or you can also go the Doctor Who method and say that time travelers exist outside of time, and therefor are unaffected by the changes (no ball of a billion Adams, and the time stream remains fixed while they are in it, so Bob's post-WWII reality exists until he leaves to join Adam).
    My problem isn't paradox, but time clones. If we have multiple branching time lines, then time travelers from all of them will end up in the same past, creating a recursive and exponential number of time clones.

    Wait. Why would time travelers being unaffected by the changes prevent the ball of Adams?

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    WolfInSheepsClothing

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by FreakyCheeseMan View Post
    Wait. Why would time travelers being unaffected by the changes prevent the ball of Adams?
    Because they exist outside time, which is author speak for "because I say so."

    You're looking for a solution that, if found, would warrant getting published in a prestigious journal of physics. "Because I say so" is going to have to be the bedrock for your rules, not logic, as the time travel you want throws that out the window (which is why the Doctor practically has a lampshade factory in the TARDIS).

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    Default Re: Rules for Consistent Time Travel

    I like the idea that when you time-travel, you "disconnect" from your original timeline. When you return to the moment you left, the world could be drastically different from the one you know and one in which you never existed, but you still exist with all your memories of your life and your time journey.

    Depending on how far you go back and how much was changed, you might encounter a person similar to you when you return, but only if your time travel changed the timeline in a way so you never left on the time journey. If your past self in the new timeline still went on the time journey, than that was "you" and there would be no duplicate.

    Essentially, you could never return to your own time. There is also no way to "fix" things to how you remember them, as every time journey only creates additional changes and there is way too much randomness involved to recreate the exact circumstances of your timeline of origin.
    Last edited by Yora; 2013-02-14 at 04:00 PM.
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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Yora View Post
    I like the idea that when you time-travel, you "disconnect" from your original timeline. When you return to the moment you left, the world could be drastically different from the one you know and one in which you never existed, but you still exist with all your memories of your life and your time journey.

    Depending on how far you go back and how much was changed, you might encounter a person similar to you when you return, but only if your time travel changed the timeline in a way so you never left on the time journey. If your past self in the new timeline still went on the time journey, than that was "you" and there would be no duplicate.

    Essentially, you could never return to your own time. There is also no way to "fix" things to how you remember them, as every time journey only creates additional changes and there is way too much randomness involved to recreate the exact circumstances of your timeline of origin.
    One of the Fate Core expansions plays with this, I don't remember the name...and I guess it isn't very useful if you haven't backed the Kickstarter...

    It should be available in not too long, though, as part of the expansions bundle.
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    Default Re: Rules for Consistent Time Travel

    Since you're running the show rather than coming up with rules for actual time travel, you can do narrative-based time travel by willfully concealing information about the past until the time travel determines what actually happened.

    Example: Bob is in a building when it suddenly exploded. Steve travels back in time to save him. If he's successful, then he brings Bob to the present immediately, or hides him in a shed in the middle of nowhere until the past catches up, resolving the question of what Bob was up to if he was alive the whole time. If he fails, then Bob was dead all along. If you have a situation like Bob being shot to death in front of dozens of witnesses, then you have to come up with a crazier solution like clones or death-faking pills, but it works all the same.

    This makes absolutely no sense in answering what actually happened in the timeline before time travel was introduced, but it works great for stories, especially ones you're improvising as you go. This way, you can change the past while having main details being fixed in place, and you never have to worry about paradoxes or memories changing.

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Deophaun View Post
    Because they exist outside time, which is author speak for "because I say so."

    You're looking for a solution that, if found, would warrant getting published in a prestigious journal of physics. "Because I say so" is going to have to be the bedrock for your rules, not logic, as the time travel you want throws that out the window (which is why the Doctor practically has a lampshade factory in the TARDIS).
    Well, of course I'm going to have to flub the actual mechanism. But, I want to have a set of rules that will apply in a consistent way to any scenario.

    So, for the Adams-in-Space one... Adam jumps back, but there's still an Adam on earth who's about to make that time jump, and now there's already an Adam in space waiting for him. It would be more difficult, but I could set it up so that each successive Adam arrives an instant later than the last.

    How does Adam being unaffected by the changes alter that?

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Treblain View Post
    Since you're running the show rather than coming up with rules for actual time travel, you can do narrative-based time travel by willfully concealing information about the past until the time travel determines what actually happened.

    Example: Bob is in a building when it suddenly exploded. Steve travels back in time to save him. If he's successful, then he brings Bob to the present immediately, or hides him in a shed in the middle of nowhere until the past catches up, resolving the question of what Bob was up to if he was alive the whole time. If he fails, then Bob was dead all along. If you have a situation like Bob being shot to death in front of dozens of witnesses, then you have to come up with a crazier solution like clones or death-faking pills, but it works all the same.

    This makes absolutely no sense in answering what actually happened in the timeline before time travel was introduced, but it works great for stories, especially ones you're improvising as you go. This way, you can change the past while having main details being fixed in place, and you never have to worry about paradoxes or memories changing.
    I'm not as worried for stories - with stories, I can always do a "The past was always the same way."

    But, I have one particular thing I want to try, with time-traveling Fey trying to save their city (Avalon) from falling to a siege. My own annoying mind makes me want a consistent set of rules, but I've yet to come up with anything that would support that, without time clone singularities.

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    Default Re: Rules for Consistent Time Travel

    If you're looking for something more like a single timeline with rewriteable history, I suggest reading Pastwatch: The Redemption of Christopher Columbus by Orson Scott Card. His solution to sending multiple people back to different points in history was that they all had to leave the present simultaneously, because any change to past events effectively destroys the current timeline. In other words, the new timeline instantaneously overwrites the previous one. I believe it was one-way time travel, though, so maybe not what you're looking for.

    It also happens to be one of the best SF novels I've ever read.
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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by KillianHawkeye View Post
    If you're looking for something more like a single timeline with rewriteable history, I suggest reading Pastwatch: The Redemption of Christopher Columbus by Orson Scott Card. His solution to sending multiple people back to different points in history was that they all had to leave the present simultaneously, because any change to past events effectively destroys the current timeline. In other words, the new timeline instantaneously overwrites the previous one. I believe it was one-way time travel, though, so maybe not what you're looking for.

    It also happens to be one of the best SF novels I've ever read.
    >_> One way time travel can be made into two-way time travel with an endowment and a stand-up freezer.

    That sort of works for the first one, but it has another problem - you can never watch a time-traveler leave, because once he's left, you cease to exist.

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    Default Re: Rules for Consistent Time Travel

    Much to the headache of my player I really like running timetravel games

    I believe the most playable version of time travel is the observer effect. ie a timetraveller cannot change the observed facts from their POV, but they can add new facts.

    A time traveler could not stop JFK being shot.. but they could kidnap him and substitute a cloned replica (and probably find much too late that they have kidnapped someone elses cloned replica).

    The nice thing about this approach is so long as the players play smart they have a lot of opportunity to play fast and loose. but if they try an pull a Bill and Ted and not bother to sent the time machine back to rescue themselves someone else does... much to the determent of the party :->

    One thing when running a time travel game .. a detailed Campaign Chronicle is absolutely vital
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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by FreakyCheeseMan View Post
    Well, of course I'm going to have to flub the actual mechanism. But, I want to have a set of rules that will apply in a consistent way to any scenario.

    So, for the Adams-in-Space one... Adam jumps back, but there's still an Adam on earth who's about to make that time jump, and now there's already an Adam in space waiting for him. It would be more difficult, but I could set it up so that each successive Adam arrives an instant later than the last.

    How does Adam being unaffected by the changes alter that?
    I'm not understanding the problem here. There's only one Adam that jumps back in time. He then dies. No other Adams are available to jump back unless you're allowing alternate universe Adams to jump into the same universe.

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Anxe View Post
    I'm not understanding the problem here. There's only one Adam that jumps back in time. He then dies. No other Adams are available to jump back unless you're allowing alternate universe Adams to jump into the same universe.
    • Adam makes the jump into the past two minutes ago, arriving at the exact point in space he left his own time (i.e. outer space) and asphyxiates.
    • Meanwhile, on Earth, Bob is talking Adam+1 (the second iteration of Adam) into making the jump.

    • Adam+1 makes the jump into the past two minutes ago, arriving at the exact point in space he left his own time (i.e. outer space) and asphyxiates.
    • Meanwhile, on Earth, Bob is talking Adam+2 (the third iteration of Adam) into making the jump.

    • Adam+2 makes the jump into the past two minutes ago, arriving at the exact point in space he left his own time (i.e. outer space) and asphyxiates.
    • Meanwhile, on Earth, Bob is talking Adam+3 (the fourth iteration of Adam) into making the jump.

    • Adam+3 makes the jump into the past two minutes ago, arriving at the exact point in space he left his own time (i.e. outer space) and asphyxiates.
    • Meanwhile, on Earth, Bob is talking Adam+4 (the fifth iteration of Adam) into making the jump.

    • Adam+4 makes the jump into the past two minutes ago, arriving at the exact point in space he left his own time (i.e. outer space) and asphyxiates.
    • Meanwhile, on Earth, Bob is talking Adam+5 (the sixth iteration of Adam) into making the jump.

    • Adam+5 makes the jump into the past two minutes ago, arriving at the exact point in space he left his own time (i.e. outer space) and asphyxiates.
    • Meanwhile, on Earth, Bob is talking Adam+6 (the seventh iteration of Adam) into making the jump.

    • Etc.


    Frankly, I'd be more concerned about the effect of an infinite number of people attempting to occupy the same space at once. It could be quite...explosive.
    Last edited by Grinner; 2013-02-14 at 04:48 PM.

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    Default Re: Rules for Consistent Time Travel

    Uh...no, it doesn't work like that.

    Adam makes the jump into the past, where he then becomes Adam+1 and then dies. He can't jump back into the past again, because he's no longer at the party. He's in the void of space.

    You're thinking of a situation like this...

    Adam jumps into the past, becoming Adam+1. He does not die. Instead, he lives on and now there's two Adams from different points in time.

    Adam+1 jumps back in time, becoming Adam+2, and doesn't die. Unless somehow he transports back to the exact same point in space, then...presumably they tele-frag each other and die, and the universe burps out the remains.

    But if Adam+2 transports back to another point in space, it could theoretically keep going. Except that Adam+2 is older than Adam+1 is older than Adam at the same point in the objective timeline. If Adam keeps looping back, there'll be Adams everywhere, but he'll effectively be living within the same span of years.
    Last edited by CarpeGuitarrem; 2013-02-14 at 05:03 PM.
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    Quote Originally Posted by Saph
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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by CarpeGuitarrem View Post
    Uh...no, it doesn't work like that.

    Adam makes the jump into the past, where he then becomes Adam+1 and then dies.

    You're thinking of a situation like this...

    Adam jumps into the past, becoming Adam+1. He does not die. Instead, he lives on and now there's two Adams from different points in time.

    Adam+1 jumps back in time, becoming Adam+2, and doesn't die. Unless somehow he transports back to the exact same point in space, then...presumably they tele-frag each other and die, and the universe burps out the remains.

    But if Adam+2 transports back to another point in space, it could theoretically keep going. Except that Adam+2 is older than Adam+1 is older than Adam at the same point in the objective timeline. If Adam keeps looping back, there'll be Adams everywhere, but he'll effectively be living within the same span of years.
    No....

    Adam jumps back in time, and into space. From space, he stares at his 2-minutes-ago self, who is now preparing to jump. That 2-minutes-ago self then jumps, but in his timeline, there's already an adam (the first jumper) in the space he's about to occupy. And so on and so on.

    Grinner had it about right.

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    Default Re: Rules for Consistent Time Travel

    Here is a principle of time travel that works with only one timestream and that is 100% paradox free:

    There is only a single linear timestream. When you travel backward in time, you suspend yourself from timespace while the timestream is rewinding. Then you insert yourself back into timespace at the desired moment in the past.
    At that point time continues normally but with the time traveler also interacting with everything else, causing the timestream to play out differently this time.
    If you want to travel to the future, you again remove yourself from timespace and then just wait it out until the timestream has again reached the point you want to go to and then re-enter the timestream.

    Only downside, when you travel back in time, you destroy the future. But it does allow for as many time travelers going through time as you want to, without getting a giant cluster****.
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    Default Re: Rules for Consistent Time Travel

    OK, he's a solution: quantum mechanics.

    You talk about how Adam 1 has a slight gravitational pull on Adam 2, so it's a new history. That means that you also get an entirely new set of quantum fluctuations occurring throughout the entire universe (they're random, so there's no reason for them to be the same quantum fluctuations the origin timeline experienced). If you subscribe to the idea that the brain is a quantum computer (which will help you out here), Adam 2 now has a different set of significant inputs that will influence his decision. He can choose not to go back in time simply because reality changed, not because of any recognizable physical phenomena.

    This, by the way, means that if you go back in time to an empty corner of the universe and do absolutely nothing, you will have completely altered the course of history and the future will be utterly unrecognizable, because everyone would have made different choices just by the fact that you changed the universe's random number seed.

    Now, the question is, what do we do with all the dead catgirls that this is going to generate?

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Deophaun View Post
    OK, he's a solution: quantum mechanics.

    You talk about how Adam 1 has a slight gravitational pull on Adam 2, so it's a new history. That means that you also get an entirely new set of quantum fluctuations occurring throughout the entire universe (they're random, so there's no reason for them to be the same quantum fluctuations the origin timeline experienced). If you subscribe to the idea that the brain is a quantum computer (which will help you out here), Adam 2 now has a different set of significant inputs that will influence his decision. He can choose not to go back in time simply because reality changed, not because of any recognizable physical phenomena.

    This, by the way, means that if you go back in time to an empty corner of the universe and do absolutely nothing, you will have completely altered the course of history and the future will be utterly unrecognizable, because everyone would have made different choices just by the fact that you changed the universe's random number seed.
    That's a fascinating take. I'll have to read up on quantum mechanics.

    Quote Originally Posted by Deophaun View Post
    Now, the question is, what do we do with all the dead catgirls that this is going to generate?
    Meat is meat.
    Last edited by Grinner; 2013-02-14 at 05:18 PM.

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    Default Re: Rules for Consistent Time Travel

    You're making less sense than Zero Escape. And that's saying something.

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by Yora View Post
    Here is a principle of time travel that works with only one timestream and that is 100% paradox free:

    There is only a single linear timestream. When you travel backward in time, you suspend yourself from timespace while the timestream is rewinding. Then you insert yourself back into timespace at the desired moment in the past.
    At that point time continues normally but with the time traveler also interacting with everything else, causing the timestream to play out differently this time.
    If you want to travel to the future, you again remove yourself from timespace and then just wait it out until the timestream has again reached the point you want to go to and then re-enter the timestream.

    Only downside, when you travel back in time, you destroy the future. But it does allow for as many time travelers going through time as you want to, without getting a giant cluster****.
    It seems like it only allows for one, at least going backward. Time traveling forward isn't interesting, cause that's what happens by default.

    It also imposes some pretty heavy narrative problems. First, you can never, ever remember seeing a time ship having left; when it left, it destroyed the universe, to you can't have seen it.

    Secondly, nomatter how long you wait, no time ship will ever arrive, since the arrival of a time ship is essentially creating a universe. You can *remember* time ships arriving, though.

    But, yeah, it is consistent.

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    Default Re: Rules for Consistent Time Travel

    There is one idea that I liked, in that any change you make has to be such that the observed result doesn't change. That is, you can kill Hitler, but you have to replace him with a double who hangs around for people to see until Hitler's recorded demise. Alternately, if you don't put a double in place, someone from further up the timestream gets hit by the paradox, and comes back to resuscitate Hitler after you leave.

    It rules out the "kill Hitler" time-travel plot, but it lets you do others like "save the scrolls from the Library of Alexandria," "steal the Hope Diamond and replace it with a fake" or "rescue Abraham Lincoln from his assassination."

    It also lets you do some fun things with time. Example: You're locked in a prison cell. So, naturally, you decide that some time after you get out, you'll come back in time to help yourself get out. You then look under the mattress and find the key to the door. You then have to arrange things so that this becomes a stable time loop: You need to obtain the key from some point along the timeline, put it under the mattress, and replace it with the version you found in the cell, all without being caught. It's complicated, but it quickly becomes hilarious when you start doing it with cruise ships. In one of my games, the players needed so many ships that they single-handedly caused the Bermuda Triangle.

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by kieza View Post
    There is one idea that I liked, in that any change you make has to be such that the observed result doesn't change. That is, you can kill Hitler, but you have to replace him with a double who hangs around for people to see until Hitler's recorded demise. Alternately, if you don't put a double in place, someone from further up the timestream gets hit by the paradox, and comes back to resuscitate Hitler after you leave.

    It rules out the "kill Hitler" time-travel plot, but it lets you do others like "save the scrolls from the Library of Alexandria," "steal the Hope Diamond and replace it with a fake" or "rescue Abraham Lincoln from his assassination."

    It also lets you do some fun things with time. Example: You're locked in a prison cell. So, naturally, you decide that some time after you get out, you'll come back in time to help yourself get out. You then look under the mattress and find the key to the door. You then have to arrange things so that this becomes a stable time loop: You need to obtain the key from some point along the timeline, put it under the mattress, and replace it with the version you found in the cell, all without being caught. It's complicated, but it quickly becomes hilarious when you start doing it with cruise ships. In one of my games, the players needed so many ships that they single-handedly caused the Bermuda Triangle.
    That works in terms of paradox, but it doesn't really solve the second listed problem. Plus, there's the whole issue of "What is observation" and "What about things that could become observed later?".

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    Default Re: Rules for Consistent Time Travel

    Multiple futures is definitely the way to go. In the case of the Darwin-Award nominee Adam, let's say that Adam is in Universe A, and call this Adam-A. Adam then jumps back in time. This causes an alteration in the universe as it would have played out, meaning that a new universe splits off. This is universe B, which has an Adam B in it. No Adam shows up in universe A. Adam A does show up in universe B, and asphyxiates. If this does have any effect on Adam B, and his time-travelling, that will in turn create universe C, which Adam-B shows up in. In short, each universe either gets 1 Adam, or none.

    The tricky part is the first scenario, wherein someone attempts to travel back in time from a universe which has had a previous time traveler travel back in time. You need to watch out for two things. First, that your arrival time is exactly the same as the previously-departing time traveler. If you're too early, you spawn a new universe, which your buddy doesn't land in, and if you're too late, your buddy spawns a new universe which you don't land in. Either way, you're separated. And second, you can expect a bunch of time travelers coming back from futures that you never would have dreamt would happen, altering the course of events, and thus ensuring that those futures didn't happen. This, of course, would introduce time travel devices before they're invented.

    You might be able to hand-wave a lot of this away with the idea of multiple pasts. Just as it might be possible for the present to split off into multiple possible futures, it might also be possible for multiple pasts to combine into a single present. For example, in one past, Oswald shoots Kennedy and there are conspiracy claims that it was some CIA plot gunman on the grassy knoll etc. In a DIFFERENT past, the conspiracy actually exists, there is a second gunman, but the truth gets generally dismissed as conspiracy fiction. Because both scenarios result in pretty much the same present, we can say those timelines merged together. You can use this as a device for reconnecting time-split parties.

    Though your players might have fun with, "Okay, you now have a new background wherein your character is much the same, but because your buddy changed time you instead spent the past fifteen years in a zombie post-appocalypse. I'll give you five minutes to figure out the changes in your personality, history, and stats. GO."

    Quote Originally Posted by Deophaun View Post
    Now, the question is, what do we do with all the dead catgirls that this is going to generate?
    Sweep them under the rug and trust anorexia to keep the bulge inconspicuous, of course. Same as always.
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    Default Re: Rules for Consistent Time Travel

    So, my problem with multiple futures is that, if they share a single past (or a smaller number of pasts than futures), then you get *lots* of futures feeding time travelers into a single past, which causes problems quickly - you'll get a lot of time clones, and each of them spawns another time line, so you get even more, and then the universe collapses in a black whole of confused time-travelers.

    Multiple pasts is... an interesting idea, but conceptually, hard to work. For it to solve the problem, we have to have roughly as many pasts as futures; that, however, strains imagination.

    We can imagine a future in which the machines rise against us, or do not. But, we can't really imagine a past (our past) in which WWII didn't happen. So, instinctively, it seems like there'd be more futures.

    Now, I know more about orders of infinity than the average bear, so I know that isn't exactly the same as impossible to overcome, but it's still tricky. A hotel with every room full can still give a room to a new guest, so long as there are infinite rooms, but I have trouble coming up with the narrative mechanisms for such to happen in a game universe.

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by FreakyCheeseMan View Post
    No....

    Adam jumps back in time, and into space. From space, he stares at his 2-minutes-ago self, who is now preparing to jump. That 2-minutes-ago self then jumps, but in his timeline, there's already an adam (the first jumper) in the space he's about to occupy. And so on and so on.

    Grinner had it about right.
    That's because...they're one and the same.

    From Adam's chronology, this is how it looks.

    Five Minutes Ago
    Adam is getting talked into the bet

    Two Minutes Ago
    Adam is still getting talked into the bet
    Future!Adam dies in space, watching Adam getting talked into the bet

    Zero Hour
    Adam jumps into the past, and now becomes Future!Adam from its point of view. He is witnessed by Adam.

    There is only one Adam. I only refer to him as Adam and Future!Adam to avoid confusion. Because, really, it goes like this...

    Adam jumps 2 minutes into the past, and dies in the void of space...while he watches himself from 2 minutes ago getting talked into the jump. If he survives for the full two minutes, he sees himself disappear from the present. The loop closes.

    His personal timeline runs right alongside the objective timeframe, but it's as if it's been snipped and pushed back some so that the end of one and the beginning of the other overlap.
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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by FreakyCheeseMan View Post
    So, my problem with multiple futures is that, if they share a single past (or a smaller number of pasts than futures), then you get *lots* of futures feeding time travelers into a single past, which causes problems quickly - you'll get a lot of time clones, and each of them spawns another time line, so you get even more, and then the universe collapses in a black whole of confused time-travelers.

    Multiple pasts is... an interesting idea, but conceptually, hard to work. For it to solve the problem, we have to have roughly as many pasts as futures; that, however, strains imagination.

    We can imagine a future in which the machines rise against us, or do not. But, we can't really imagine a past (our past) in which WWII didn't happen. So, instinctively, it seems like there'd be more futures.

    Now, I know more about orders of infinity than the average bear, so I know that isn't exactly the same as impossible to overcome, but it's still tricky. A hotel with every room full can still give a room to a new guest, so long as there are infinite rooms, but I have trouble coming up with the narrative mechanisms for such to happen in a game universe.
    Warning: Semi-intense maths follow.

    I've played around with this some from the mathematical side, too. Instead of thinking of a fixed universe and a changing state, consider instead a set of possible states, and time-flow as a function or Markhov chain defined on this set of states. There's too many states to count, so we'll use a sigma-algebra (probably defined in terms of observable variables) to break these states into workable subsets. We'll call these smallest subsets universes. There are infinite possible states for each universe, but we have no mechanism for distinguishing between them, so they all fall into the same element of the sigma algebra. For extra fun, the sigma-algebra can be defined in terms of variables that we, personally, can observe, rather than can be observed from anywhere in the universe. So our present universe "A" will combine the possibility that the sun just went nova with the possibility that it didn't, because we won't be able to discern the difference for over 8 minutes.

    Arbitrarily, let's say that many of these sigma algebras are measurable, especially in a conditioned-probability sense. GIVEN that we're in universe B, there is a calculable probability that we WERE in universe C, D, E, or F twenty minutes ago, and similarly twenty minutes ahead of time. There are likely infinite options, but let's stick with those four past universes as examples.

    This brings us back to the two subsets of universe A (sun goes splody, versus sun doesn't go.... well, okay, it does go splody, but it's just the usual trillions of fusion bombs per second splody rather than something bad). These are NOT distinguishable in the moment. They ARE distinguishable 9 minutes later. In short, we can distinguish between lots and lots more universes in the past, than we can in the present. Hindsight really IS better. This means that there are actually MORE universes in the past than in the present, because we have the tools to break them down better. (Actually, there's only one universe in the present, and the number of universes increases the further into the past we look.)

    Now, let's go back in time. The probability dictates WHICH of C, D, E, or F we end up in. Let's say we randomly end up in F. We're immediately shunted into universe G, which is what would happen to F if we had a bunch of particles randomly assemble themselves under the rules of quantum mechanics into a random group of people (us) with the appropriate physical condition and memories. This is extremely low-probability from F, but given that we started in B, which has us pushing the button on our time-travel machine, it's pretty high odds for us.

    Now here's the interesting part. Every substate in B has some version of us going back in time, appearing in C, D, E, or F, and getting shunted into the appropriate offshoot. If C, D, E, and F make up every possible past for universe B, then their measure is IDENTICAL to universe B. That means we've got exactly the same order of infinity of time travelers and destination universes, AND the same sense of weighting (it's not exactly a number) of time travelers and destinations.

    In other words, it could work. ... you know, if we could actually build a time machine.
    Last edited by Reltzik; 2013-02-14 at 06:35 PM.
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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by CarpeGuitarrem View Post
    *snip*
    I think that makes sense...Time still advances, leaving room at that point in space-time for the next Adam?
    Last edited by Grinner; 2013-02-14 at 06:52 PM.

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    Default Re: Rules for Consistent Time Travel

    Math math math ma-mathy-math-math. Math!

    It's been a few years since I flunked out of my math major, but I think I followed most of that. So, you're combining the notion of a time cone into this - not only is there only one present, but that present has a very narrow spatial definition, because things just a little ways aware are unknowable?

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    Default Re: Rules for Consistent Time Travel

    Quote Originally Posted by CarpeGuitarrem View Post
    That's because...they're one and the same.

    From Adam's chronology, this is how it looks.

    Five Minutes Ago
    Adam is getting talked into the bet

    Two Minutes Ago
    Adam is still getting talked into the bet
    Future!Adam dies in space, watching Adam getting talked into the bet

    Zero Hour
    Adam jumps into the past, and now becomes Future!Adam from its point of view. He is witnessed by Adam.

    There is only one Adam. I only refer to him as Adam and Future!Adam to avoid confusion. Because, really, it goes like this...

    Adam jumps 2 minutes into the past, and dies in the void of space...while he watches himself from 2 minutes ago getting talked into the jump. If he survives for the full two minutes, he sees himself disappear from the present. The loop closes.

    His personal timeline runs right alongside the objective timeframe, but it's as if it's been snipped and pushed back some so that the end of one and the beginning of the other overlap.
    So, that's just a "You can't change the past, cause you already would have" case - already mentioned I was trying to avoid those, cause they so limit what you can do with time travel.

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