Time Travel, Part 2

Can the past be changed?

If you can travel through time, can you make changes?  There are many scientific theories that deal with this very question from the standpoint of paradoxes not being possible.  The Novikov self-consistency principle for example states that if an event has the chance to create a paradox, the probability of that event occurring will be 0.  Essentially this theory proposes that if you try to change the past something will happen to prevent you from making the change.

This can be interpreted two ways.  One would be that the universe will not allow the paradox to happen.  I personally discount this entirely, because it would require the universe to have desires and intervene.  The other concept is that the past has already occurred, so if someone goes back to try to change it, they obviously have failed because here in the present that change did not occurred.  This is a far more acceptable theory, but leads to a boring story.  If your time traveler cannot make changes, then what is the point of the trip.  It could be a trip of discovery, but following this theory puts many limitations on your story.

The only theories scientists seem to take seriously in regard to making changes revolve around alternate realities.  If a person makes a change they are then creating an alternate reality.  Their original reality still exists, but they are now cut off from it and there is the potential for a temporal clone to exist.

Alternate realities provide many options, but they also present one major issue.  Any time traveler from the future — by the nature of just being there — has cut themselves off from their own time.  How big of a change would need to be made before a temporal clone situation arises?   Because decisions have not yet been made and time travelers can change things, then any trip to the future would have to be only a potential future.  By seeing that future you are then ensuring that at least minor changes will occur because of your knowledge.  You also then have to deal with many potential futures for every universe.  If time travel occurs after the split why wouldn’t multiple versions of you from different alternate realities run into each other when they go back to a time before the split occurred?  This methodology can be interesting, but tends to just be too convoluted for my tastes.  A paradox cannot occur because there are an infinite number of realities.

Another method that allows for changes to be made is similar to the previous method.  In this case an alternate reality is created by the change, but the original one now no longer exists.  There is only one timeline and any change causes it to readjust itself.  This is my preferred method of dealing with time travel.  It allows for changes, paradoxes, and can provide the largest sense of drama.  If your actions can risk your own existence, it makes everything you do that much more important.  If you subscribe to the butterfly effect this method also has the most potential for suspenseful stories.

The down side is that this method also doesn’t attempt to answer paradoxes at all.  Your characters typically have to find a way to avoid changes themselves and are thus combating paradoxes.  The real question is that if they change their world enough for them to have never time traveled to begin with, if they were to return to their own time would it have to be a temporal clone?  Also since the characters are typically trying to fix what they have changed, you generally don’t see what would happen to the world if the character that made the change had suddenly never been born and thus could not have traveled back in time.  The way comic books typically deal with this concept is to say that while the person may not exist anymore in the future, they did exist at a point before the change was made since they were the one making the change.  Thus a character may fade, but their actions did occur because they were there before the timeline diverged.

However you want to handle time travel in your story or game, you have to decide in the beginning if the past can be changed, and if so what method you will be using to show these changes.  While I’m sure it is possible to make it work, I just don’t personally see a way to make a game work if you are traveling through time but cannot change it.  That would likely just lead to frustration from your players.

Comments (8)

DanOctober 26th, 2009 at 4:00 pm

The other concept is that the past has already occurred, so if someone goes back to try to change it, they obviously have failed because here in the present that change did not occurred. This is a far more acceptable theory, but leads to a boring story.

There was a sci-fi game I ran several years ago. Chad was playing a time traveler from the future. His character had developed a time travel machine, but in lab tests, they’d found they simply couldn’t change the past. For example, he’d have an empty file cabinet, travel back in time, put something in there, and return. But by the time he’d gotten back, some lab tech had coincidentally found the errant object and put it away, leaving the cabinet empty again.

As his life goes on, a particular alien race closes in like a noose around the other races of the galaxy, wiping them out. Chad’s character is in one of the last strongholds of humanity with his machine. Seeing the end of all life, his bosses send him back in time to the point when the game occurs (and everyone else’s character was residing normally) with the objective of stopping this reality from occurring.

His character knew it was impossible. It couldn’t be done. But there was no other option, so they forced him to try. This sense of desperation and futility added a lot of really neat RP to the game. He had to convince the other characters of who he was, where he was from, and the coming future he knew to be true — and then set about doing something his character knew to be impossible.

I did eventually allow him an “out” through which he could give mankind a future. I won’t tell you how I did it, because I may use that plot again in a future game. But let me give you a possible outcome. What if his character had a limited understanding of his own present? Maybe his character couldn’t go back in time and stop this alien race’s progress, but he might be able to send some humans to colonize another galaxy, using a one-way gate such that Milky Way humans don’t even know the colony is out there when their doom comes.

That’s not how I resolved the plot, but it’s an example of how you can have a really neat game — that’s still winnable — using the “unchangeable past” model.

TJPOctober 26th, 2009 at 4:20 pm

This site – http://www.mjyoung.net/time/index.htm – is a goldmine for all things time-travel. It’s a fun idea to have in your games and Joseph Young has a neat take on it.

BurrowowlOctober 26th, 2009 at 9:36 pm

From Continuum:

The Beer Crisis of William and Edward

William and Edward are spanner buddies with their own place. They’re both sitting in the living room watching football. William has a cold beer, which makes Ed thirsty. Ed span levelly into the kitchen, and discovers there is no cold beer in the fridge. Be spans Down ten minutes, finds one cold beer, and opens it, and span back Up to enjoy the game.

“Hey!” growls WIll, pointing to his beer. “Is that my beer? You just fragged me!”

“Oh crap,” grumbled Ed, coming off the first sip. “Guess I gotta fix that.”

“Yes you do, and before halftime.”

Ed carefully puts the beer down in the living room, walks back to the kitchen. He puts another six pack of the same brand into the fridge. As a caution, he attaches a post-it note to one saying “Don’t touch!! -Ed” He spans Up an hour (to let it get cold), finds it to be the only one remaining, then takes the cold beer back Down one hour and nine minutes, and replaces it in the fridge for Will to find in the next few seconds.

He tosses the post-it note away, and spans back Up eleven minutes — to avoid a Gemini — and return to the football game.

“How’s that? Unfragged?” he asks Will.

Will gives him the thumbs up.

“Just don’t touch the one I marked for the next hour, okay?”


OrwellianOctober 27th, 2009 at 4:36 pm

another problem with time travel in the first method is breaking a fundamental law. you would be adding matter and energy to a universe, your body is made up of atoms, the same atoms that existed in the past you go and visit. That is not just a time machine, but also a machine that can add mass and energy to the universe. Even if its just your consciousness, i would assume there would have to be some movement of energy from the present to the past.

I can only jive with the multiple universe time travel stories.

Chris MOctober 27th, 2009 at 8:25 pm

Reminds me of M theory if I am not mistaken. Once a time traveler goes back to a certain point in time say 1955 AD. Then by his presence alone he causes a divergence in tghe space time continuum that rippling outward across the universe. Meaning a time traveler’s relative displacement in time also effects space changing the universe creating a divergent universe separate and unique from our own, Thus if you were a time traveler you would be unsuspectingly or knowingly changing the universe and splitting it off from the root universe say Universe Prime into sub universes split off from the main one based on each event and incidence of travel that took place. It also would mean that the further back or forward in time you went and each time you acted the ratio of impossibility or rather improbability of you as a time traveler would exponentially diminish with every jump in time made. Because the model of the universe and space time is quite possibly fluid in n dimensions and sub dimensions and always in motion with black holes drinking in dark matter and light, galactic collisions and stars millions of years old are dying and stellar nurseries wink into being as galaxies themselves separate and the universe as a canvas is expanding outward from the Big Bang.

WayneOctober 28th, 2009 at 2:05 am

Great comments guys. You are actually hitting on topics of future installments in some cases. Particularly there are some physics concepts for much later down the line. Next up is retrocausality followed by the effects of time travel on a civilization.

FreemageOctober 28th, 2009 at 4:31 pm

One way to cope with the paradox issue is destructive time-travel. This is the single-timeline model, with an added concept of someplace “outside” of the timestream, through which you travel to reach a different point in the timeline and re-enter.

The moment you step outside, you have an existence that completely ignores paradox–you cannot be affected by any changes to the timeline. Thus, if you travel to the past and happen to erase your own existence, you-the-time-traveler still exist, but you can no longer find yourself in the timestream. Furthermore, your memory always remains the same, no matter what you do to your timeline. As you and other travelers change history, then, you become less and less connected to the timeline–eventually, you don’t really know anything about the world beyond what you learn during visits.

A variant of this is that when you use whatever method you use to time-travel, you don’t actually travel at all–you simply create a clone of yourself in that “outside” realm. This clone can enter and exit the time-stream at will, and can interact with you without paradox. This is probably the most altruistic form of time-travel, since T-you will not actually be the one to enjoy any alterations in your personal history.

Whether going with timeclones or destructive time-travel, depending on the setting, stepping “outside” could be accomplished through one specific method, or could have a dozen possible means of occuring, ranging from naturally occuring ‘breaches’, to specific events (such as attempting FTL), to sorcery and the like.

DAVIDOctober 29th, 2009 at 6:47 am

i don’t think this was mentioned, but one thing that has always fascinated me about time travel is the unknown that we are in essence trying to answer. i am considering adding an element of time travel to a game i will be running, and the way they interact with this is up to them. but essentially, what happens is that the events that lead you to want to time travel must be satisfied in some way. for example, the new time machine remake movie that came out a while back now is what gave me the idea. since he is back in time, she couldn’t be saved because she was the catalyst for him creating the machine. so i always wondered why he never just gave his previous self either the plans themselves, creating a paradox star treck has used a lot, or gave himself a new motivation. what that is would be up to the story teller, but i think this idea at the very least can give a good playable model for using it. what do you think?

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