Some of you may remember this post, https://vazor222.livejournal.com/4582.html, from more than 10 years ago, where I sought to understand the Replacement Theory of Time Travel by M.J. Young which can be found here: http://www.mjyoung.net/time/theory.html
I had a couple of topics left unexplored there which I would like to present now.
The first one is that I wanted to state my guess about the Replacement Theory of Time Travel and "fading" in time travel stories. Under the replacement theory, Marty McFly would have never started fading — the current timeline was always going to end with George intervening. Even if it was not, Marty would not have been there in the first place, having never existed to be sent back to the past.
There are lots of possibilities in the time travel theory realm, including a version of a time travel mechanic that allows for such dramatic "fading" effects — here I imagine a sort of fog machine ripple effect from the time travel machine, but such a device would have to be displayed carefully to show that it gets input from the "new" timeline (for some reason), and to explain how memories are preserved in what is effectively two timelines, one of which is "fading".
Another undeveloped theory is the Two-Dimensional Time Travel Theory http://www.mjyoung.net/time/2DTime.html which is an exciting prospect. In its article, the author presents its exciting possibilities, but also some irreconcilable problems. I feel like it is a step closer to what some people think of when they say parallel dimension theory.
The other topic I felt like I had more to explain was the multidimensional time travel theory I had when developing timeplotter. I feel like some people say "parallel dimension" and think of the common explanation: every time you do something, two dimensions are created, one where you did it and one where you did not. I think this explanation was probably not meant to be taken literally, but just as an illustration to explain what the different dimensions are. In my understanding of parallel dimension theory, all the universes all already exist. There are an infinite number of them only if space is infinite. Let's zoom in on one.
In our first example parallel dimension B, under my understanding, this is not a complete universe with a full timeline or anything. It is one configuration of atoms, paused in time. If you search around in it, you can see that all of these objects and planets and matter exist, still and silent, as a single moment, in a particular unique configuration of atoms and particles. This dimension, this configuration, is one of the (potentially) infinite dimensions or versions of reality.
One more thing to note before we move on to our second example parallel dimension Q in this theory. The first example dimension has particles and objects that are paused, yes, but they have more information than that, as you might expect. They have potential energy, heat, and history. Some devices and creatures in that dimension have memories. Some of them are even in the middle of replaying those memories. Even a stone has a "history" of sorts — every nick and crack and even its composition is there or not there because of all the history of that stone. This is a history we assume exists because of cause and effect and our observations of the real world.
Now, on to the second example parallel dimension C. Let us say that this is the instant _after_ the first example. It has all the same properties, being a still silent moment in time, a configuration of all the atoms and particles in the universe, but with one key difference: it is a single step forward into the future. Under my theory of parallel dimensions, we are all traveling through these dimensions all the time. Normal life is simply where you change from a being with certain memories in one moment, to a being with new, but very similar, memories in the next. You change from being the person that read this word, to the person that read this next word.
Of course you may presume that if you can find a dimension that logically follows the laws of cause and effect to get from dimension B to C, then you can assume that there was a dimension A where B came from. Thus you get a normal timeline, traveling through dimensions as we all do every day, going from dimension A where you existed starting to read this, to dimensions B and C as you read the words above.
Now, let us explore an example dimension β (beta) which is an entirely different configuration of the universe. This may be more what people expect when you talk of jumping to a new dimension. There may be alien life forms, the laws of physics might be different, the history of objects are different, but it is presumed that there are still cause and effect and a natural "timeline" for this unique dimension to follow. This is like the "sideways time travel" discussed 2DTime article linked above.
Let us say that example dimension β happens to be a dimension where the history of one special person — a "time" traveler — is exactly like the history of that person from example dimension B, but they are otherwise in a dimension that was exactly like dimension A. They then "continue" on into the future of the new timeline.
Hopefully now you can see how someone with this viewpoint might ask what happens in the future of example dimension C, or why more travelers could not come into the story in the same way.
Of course, this theory has many problems. Is it really time travel if all of these dimensions already exist? Is it even a theory worth considering, if every possible story has already been told (since every possible configuration of the universe already exists, that means every history already exists)? Did you murder the version of yourself that existed in the example dimension that came before β?
It is more like considering timelines as paths that tread their way through the multiverse, and seeing cause and effect lines as a law (as in gravity) that holds given timelines on their course. It is like 2DTime but with every possible timeline already existing at once.
With those followups out of the way, I wanted to discuss more thoughts and questions about the Replacement Theory of Time Travel.
I really only have one big question left. How does an infinity loop get created? Why does the fact that the young Traveler will not travel back, destroy the future of the C-D timeline? Won't Traveler and younger Traveler just live on in peace following the future of the C-D timeline? In my original post I asked this question, but it was never answered.
I suppose it is just one of the core propositions of the theory. The moment the traveler jumps to the past, if they arrive in such a way as to create a timeline that will result in the original traveler not jumping, time proceeds forward, and then when it is no longer possible to create the _cause_ that created the adult Traveler appearing _effect_ in the C-D timeline, that cause is now gone and so the effect must disappear and so time must suddenly revert.
While this is a fine proposal, for me it brings up questions.
Why does the C-D timeline need to exist? With the way the rest of the theory treats timelines, the timeline is determined from the moment of the Traveler's arrival. So wouldn't it be at that moment that the cause is no longer found and the adult Traveler must cease to exist? I suppose this is equivalent to saying that time travel is not possible, unless the traveler jumps with the planning and preparation that will ensure that an N-jump will happen.
But let us assume time travel is possible regardless of where the new timeline will go. In that case, my question is, why does the C-D timeline need to revert at that particular time? You might say "because that is the point at which it is now certain that the young Traveler cannot recreate the events of the C-D timeline." However I posit that you could be certain of that at different times. Perhaps the point at which the Traveler changes the younger Traveler's mind should be the revert point? No, the young Traveler could change their minds. Perhaps the young Traveler is delayed a little but would have left from the C-D timeline at a little bit later point in time than D and successfully recreated the events at point C? I can see that you need to resolve the cause and effect somewhere, but wouldn't it be simpler if it happened at the moment of the jump back to C?
"Logically, once he reaches the past, everything he does in the past ought to become part of the future, in some sense "immediately", because from the perspective of the future his entire time in the past is, plainly, in the past. It is thus at the moment of his departure from the future that all history changes; his moment of return to the future is irrelevant."
How does replacement theory explain the conservation of matter problem? I've heard one physicist say time travel to the past is dangerous because it would mean a huge energy explosion to try to put matter from the future on top of matter in the past.
All that said, I really like the replacement theory and it has inspired several story ideas. I wonder which of these would work under the theory?
Could you tell the story of a "Time Battle" where the hero tries to save time but the villain jumps first so they win?
Could you tell the story of a "Time Fighter" who is able to travel to the new future that exists after an N-jump, get information about the potential Infinity Loop, and then jump back to the right place to prevent it?
Could you have a villain that uses a saw tooth snap to create a flood of evil robots? Could they build one evil robot and one time machine and then send themselves the evil robot until they have lots of copies?
Could you have a story where the time machine can both send the traveler to the past and can also be used to make yourself younger? If he left himself a note, could the Traveler then replace himself at the end of the C-D timeline?
Thank you for reading and if you have comments feel free to leave them below!