Time Travel Theory 101
"Good afternoon, Class," said Professor Vector as the students filed into the classroom and took their seats, "and welcome to Time Travel Theory 101. I'll be handing out a Syllabus to describe our course objectives for this quarter, along with my grading and examination policies. It's succinct enough on its own, so I don't believe we'll be needing to go over it during class time that could otherwise be used for valuable class discussion. Any questions may be addressed after class is over. Please be seated."
The bespectacled woman that stood at the front of the classroom spoke in a quiet, understated tone that nonetheless commanded respect from the students present. She cleared her throat and began.
"Since Time Travel is a specialized field that is not available to the general public, I expect most of you don't have any advanced knowledge about it. There are also many myths and rumors that tend to fly about regarding it, and I intend to dispel those by the end of the course. Now, since I believe an open discussion is the best stimulant to intellectual development, I'll open the floor for any questions that you may have."
The class sat in an awkward silence for several seconds.
"I'm perfectly content waiting until someone speaks up. It's your tuition going down the drain, not mine."
A hand rose.
"Yes, you in the corner?"
A blond-haired boy of about 20, in a shale-gray hoodie, lowered his hand and spoke.
"How would you explain the Grandfather Paradox?" he asked.
Professor Vector nodded. "This question usually does come up, in one form or another, on the first day of class. Before I give a detailed answer, can anybody explain the Grandfather Paradox?"
A girl in the middle of the front row with short, red-brown hair raised her hand. "Yes, you?"
"Isn't that the one where a guy goes back in time and kills his own grandfather? So his dad's never born, and neither is he?"
"Exactly. And can you tell me why this is a problem?"
"Well," she said, "if he never existed, then he couldn't have killed his grandfather."
"Exactly. The Grandfather Paradox is what we call a Causal Loop; a chain of events with no definitive cause."
The air filled with the sound of scratching pens and shuffling paper as the students wrote down each new piece of information.
"The Grandfather Paradox, however, is not a situation that a Time Traveller will ever encounter. Can anyone tell me why?"
A girl with large, round-framed glasses and shoulder-length black hair raised her hand.
"Yes, you in the back?"
"The Grandfather Paradox, as well as all other paradoxes, is a logical impossibility by definition. An event in which the Time Traveller pre-empts his own existence cannot happen in any internally consistent system used to describe Time Travel," she spoke, then took a breath. "Therefore, Causal Loops are purely theoretical events, and cannot happen in any real-life situation."
"Exactly," Professor Vector said, beaming. She eyed the other students, and the scratching of pens continued again.
"This effectively describes the first concept which you need to know for this course, known as the First Causal Theorem. It states that no event may be without a cause."
The blond-haired boy raised his hand again. "Yes?" Vector asked.
"That doesn't really answer my question, though. If I were to go back in time and try to kill my own grandfather, I don't see what would stop me."
"Well," Vector said, "familial violence aside, this happens to be what I wanted to explain next. The short answer is, nothing would stop you. However, no paradox would occur, and you would not cease to exist."
She approached the board and drew a horizontal line across it.
"This line," she said, "in all its glory, represents the Timeline."
She marked it in four spots and scribbled a number 1 beside it.
------------------------------- 1
A B C D
(NOTE: From here on out, "Point D" will refer to the moment of an original departure to the past or future, "Point A" will refer to the point of arrival, and "Point C" will refer to the time of the cause of an event being examined. Point B is used for only this example.)
"Point C denotes the birth of the Time Traveller, point D denotes the time of his departure to the past, point A denotes his time of arrival, and point B denotes the time that the Time Traveller's grandfather concieved his father."
The students hurriedly copied the diagram down as she continued to explain.
"Now, let's see what happens when the Traveller actually arrives."
She made a new addition to the diagram.
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/
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A B C D
"When the Time Traveller arrives in the past, a new timeline splits off from the old, creating two separate timelines; one in which the Time Traveller arrived and made alterations, and the original, in which he didn't. This phenomenon is called Timeline Bifurcation. When many such bifurcations have happened, we may refer to the result as the Time Web."
She adjusted her glasses, then turned back to the diagram. "Let us say," she continued, "that the Time Traveller then kills his own grandfather, then returns to point D. He will arrive at point D on timeline 2, in which his alterations have taken place, and therefore he will have never existed in this timeline."
A spiky-haired boy in the second row raised his hand. "Yes?" Vector asked.
"But... if nothing can be without a cause, then how can the Time Traveller still exist if he was never born?"
"An excellent question," Vector said. "However, our nameless Time Traveller is not without a cause." She indicated the C at the bottom of the diagram. "His origin is right here, point C on timeline 1, where he was originally born. This is an example of the Second Causal Theorem, also known as the Precept of Time Traveller's Immunity. It states that the cause for a given event may lie on a separate timeline from the event itself. In order for Mr. Time Traveller to stop existing, someone would have to find a way to make a direct alteration to timeline 1 itself, which thankfully nobody has figured out how to do. No alteration to a timeline may occur without causing the timeline to bifurcate. Therefore, a Time Traveller may not cause himself to cease to exist, even by preventing his own birth."
She turned back to the class. "I take it, Mr., er," She checked the attendance sheet, "Rodney, that this satisfactorily answers your question?"
The blond-haired boy silently nodded.
"Good. Now, one good question deserves another; are there any others?"
Another moment of silence went by. "Yes, how about you, Ms. Blake?" She said to the Black-haired girl in the back, who had raised her hand again.
"I'm interested in knowing the outcome of another theoretical situation," she said. "Say the Time Traveller's alterations didn't prevent him from being born. If he were to make another sort of high-impact alteration, such as assasinating the president, this would dramatically change the progression of that timeline, but wouldn't prevent the Traveller's birth. Another version of himself would be born at point C on timeline 2, one who grew up experiencing the changed timeline. But if the Traveller then returned to point D, that would mean that there would be two versions of him, himself and the one who originated in timeline 2, with the altered political atmosphere that came of the President's assasination being all he remembered. But that would break the law of Conservation of Energy, since, having two copies of the same person, it would increase the net amount of matter in the universe, wouldn't it?"
Vector nodded in comprehension, if not in agreement. "There is a particularly mysterious side to some phenomena that occur in Time Travel, since as a field of science it is young and not yet fully understood. To summarize, no, assuming that the Time Traveller returned exactly to his point of departure, or to any point afterwards, he would not find another version of himself. This is because of a phenomenon that is not as yet fully understood, known as Time Bastard."
There were some chuckles from the other students, but Vector silenced them with a meaningful glare, then continued.
"In essence, when any entity, be it an object or a living being, departs for the past at a specific point D, then causes alterations that do not pre-empt his, her, or its existence, an alternate version will indeed come into existance on that timeline. However, when the new version of this entity reaches an age equal to that of the original entity when he, she, or it originally departed for the past, the alternate version will cease to exist."
The class sat in an awed silence for a few moments.
"So, when the Time Traveller arrived at point D, his alternate would cease existing at exactly that moment?" The girl asked.
"Yes," Vector said, "But this can get a little more complicated if the alternate version of the entity does any time-travelling itself."
She cleared her throat before continuing. "Say a time traveller, before departing, picked up an object, such as a rock, and took it with him when he traveled about thirty minutes into the past. He then picks up the version of that same rock that existed thirty minutes previously, then immediately took it with him back to the present."
"There would, essentially, be two copies of that same rock, though they exist in two separate contexts of time and therefore do not break the Conservation of Energy. However, as soon as thirty minutes pass, the rock from the past would cease to exist. This is because the rock aged to exactly the same age as the original rock was when it departed with the Time Traveller for the past, causing the phenomenon of Time Bastard. Nobody knows precisely how or why this happens, nor what TRULY happens to the rock after it disappears. However, it is an observed fact that has been reproduced in laboratory tests countless times, and can therefore be considered a concrete and predictable phenomenon."
"Before I continue," Vector said, "How many of you have seen the movie 'Back to the Future'?"
Most of the hands in the classroom went up.
"Good. Rife though it is with inconsistencies and contradictions, the plot of this movie contains a very clear-cut example of Time Bastard. Consider the main character Marty's trip to the past. He goes back and makes a number of alterations, which have a profound effect on his family's history, but do not, in the end, prevent him from being born. He then returns to the present to find a drastically changed version of the present he once knew. Presumably, somewhere in the new timeline he created, at a point corresponding to the original Marty's birth, another version of Marty is born on the new timeline, one who grew up experiencing the effects of the original Marty's trip through time. However, when Marty arrives back in the present, his parents clearly remember this alternate Marty, yet no duplicate version of Marty can be found. Time Bastard has occured, and this alternate version of Marty has ceased to exist."
"Before Time Bastard was discovered," Vector continued, "Time Travel scientists talked about what is called 'The Problem of Feedback Loops'. The idea goes that if a person or object is sent back in time, if they do not prevent their original trip through time from happening again on the resulting timeline, it would set off a feedback loop, since their counterpart would then go back in time, creating a new timeline in which the trip happens again, creating yet ANOTHER timeline in which the trip happens AGAIN, etc. ad infinitum. However, in the same way that it eliminated the Problem of Duplicates that Ms. Blake has just described for us, Time Bastard neatly eliminates the Problem of Feedback Loops. Consider a Time Traveller that goes from point D back in time about five minutes; recently enough to immediately witness his past self on the new timeline making the trip again. When point D arrives and the Traveller's alternate makes the trip, he will appear to have disappeared on his way back to the past. However, in actuality, Time Bastard has occured, and the alternate has ceased to exist. Therefore, no new timeline is created, and no feedback loop occurs."
"That, I think, is enough on the subject of Time Bastard for our purposes. Are there any other questions?"
The spiky-haired boy raised his hand again. "We've been talking about travel to the past so far, but what about travel to the future? Does it work the same way?"
"That is a very good question, and with a very important answer," She said. "Travel to future destinations does indeed differ at a few critical points from travel to the past."
"I'll admit to having glossed over this particular point in our previous examples, for the sake of simplicity," she began, "but when one arrives at a point that is LATER in time than their departure, a timeline splits off at the point of arrival in the same way that it does when one arrives in the past. It is VERY important to note that NOTHING, not even the Time Traveller's return trip, is written in stone. If you travel one year into the future, you will find yourself in a future in which you have been missing for one year's time. You will NOT meet your future self by travelling to the future. In fact, I think it fair to say that you should hope you NEVER see your future selves, since if you do, in all likelihood you will be subject to Time Bastard in the near future, since you may only meet your future self if THEY travel back FROM the future."
"Time Bastard, however, is a phenomenon that only occurs as a result of a trip backwards in time. It does not even come into the equation of you travel to the future. You will not, after all, create any alternate versions of yourself by travelling to the future."
"A diagram of a complete round trip to the future will look like this," she began, then drew a horizontal line as before, marking it at four points, and numbering it.
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D R A d
"In this case, R represents the planned point of return, when it differs from the point of arrival, while the small d represents the point of departure from the future to return to the present time. D and A, as before, represent the original points of departure and arrival. Now, our theoretical traveller will depart from point D for point A."
She made an addition to the diagram.
-------------- 2
/
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D R A d
"Now, we are making the implicit assumption that the traveller will remain alive and in a condition in which he is able to return to his home time. Now we'll examine what happens when he does, departing from point d and arriving slightly after his original departure, at point R."
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/ -------------- 2
/ /
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D R A d
"As the diagram demonstrates, no matter what sort of alterations are made after his arrival, once he returns, the Time Traveller will never see the effects of them again, so long as he chooses a point of return that is chronologically before point A. Also note that, on timeline 1, the Time Traveller will not exist at any point between points D and A. In fact, it's fair to assume that even AFTER point A, on timeline 1 he probably will continue to be missing, though nobody has been able to directly observe this to confirm such."
Sensing that this topic was done, the red-brown-haired girl raised her hand for another question. "Yes?" Vector asked.
"Has anybody gone back to see what the beginning of time is like? Or IS there a beginning of time?"
She nodded. "Time does, in fact, have a beginning. There is a point at the very beginning of the Time Web as we know it, where all timelines converge with the Mother Timeline, and time begins to flow. This point is referred to as Origin. One, incidentally, cannot travel back TO Origin, since all points are either BEFORE or AFTER Origin."
"Before? How is it possible to travel back BEFORE the beginning of time? Shouldn't there be no such thing?"
"One would think so," Vector said, "But it is, in fact, possible to travel back to before Origin. However, since time does not flow before Origin, there is nothing that one could call a timeline before it. Time before Origin is referred to as the Suboriginal Void."
"What would you find if you went back there?"
"Well," she began, "There is plenty of speculation, but since nobody has returned from the Suboriginal Void since travelling there, nothing can be confirmed through direct observation. However, there are a few things that we are fairly certain of. Since the universe itself did not come into being until Origin, things do not exist, in the sense of the term we normally use, before Origin. Let me draw an analogy to explain this."
"Say, for example, that you had a computer. Say you installed a program on this computer, such as Photoshop, or some other program that has its own specific file format, which only that program can read. Say you then created a file with this program, then saved it onto a floppy disk or some other form of removable memory. Then, you take the disk with you back in time to a point before you had originally installed the program, then inserted the disk. What would you find?"
"The file would still be there; but it would just be a 'file'. A nothing. A string of information that the computer cannot recognize or display as anything meaningful. This, we think, is what happens to people and things that are sent back in time to the Suboriginal Void. Things like protons, neutrons, and electrons that make up matter cannot be properly expressed without a flow of time, so they do not cease to exist, they simply... cease being 'somethings' and become 'nothings'."
"But then," said the girl, "wouldn't they start existing normally once Origin had passed?"
Vector smiled. "Let me remind you that there is no flow of time before Origin, so it cannot 'pass' like another point in time can. Things that go to the Suboriginal Void, stay there."
There weren't any further questions on this subject.
"Now, now! We still have class time left, so there must be some more questions to keep such a good discussion going!"
The bespectacled girl raised her hand again. "Yes?"
"You mentioned something called the Mother Timeline; can you tell us about that?"
"Very good. This is a subject that doesn't normally come up on the first day of class, but I think we've covered enough material to introduce it. It's actually a simple enough idea to grasp, since it follows logically from all the material we've covered so far. Since every timeline that has seen the effects of Time Travel branched off from another timeline-- and I can assure you, our timeline has seen the effects of Time Travel-- it follows logically that, if one regresses far enough on the Time Web, one will find an 'original timeline', from which all other timelines branch, which is untouched by the effects of Time Travel-- perhaps other than the disappearance of would-be Time Travelers as they depart and create other timelines. This timeline is referred to as the Mother Timeline, and it is represented on diagrams and in formulas as 'á'. Nobody can say exactly how much our timeline differs from the Mother Timeline, or if it differs at all. A given person may have an alternate on this timeline, or perhaps nobody does. It is nearly impossible to say, since the Mother Timeline is purely theoretical, and cannot, in theory, be observed."
"I may as well end this subject now, for we have pretty much left the realm of confirmed fact and flown off into the world of pure conjecture. Are there other questions?"
The boy named Rodney raised his hand again. "Yes?"
"Something's been bothering me," he said. "How can anyone know about alternate timelines if one timeline can't interfere with another?"
Vector smiled. "That's a very good question. However, I never stated that one timeline can't interfere with another."
This got surprised looks from everyone in the class.
"It so happens that every once in a while, due to miscalculation, or in a fit of daring, a Time Traveller makes a trip forward in time so far that we lack the means to measure the trip. Now, as you might recall, the further back in time one goes, the fewer timelines there are. This works in reverse; the further forward in time one goes, the more timelines there are, since trips through time happen constantly on the Time Web."
"Most Time Travel scientists now believe that, at an indeterminate point in the future, the Time Web accumulates so many timelines that it literally collapses under the stress. This is referred to as The Collapse. After this point, there is no distinction between one timeline and the next. However, time still flows, so one is still able to arrive at this point, and travel back. However, since there is no distinction between timelines, and causality has therefore broken down, the Time Traveller will very likely not end up back on the timeline he came from. He will end up on a timeline that is most likely very far-flung from his own; our timeline has in fact received such visitors. This phenomenon is referred to as Post-Collapse Displacement."
"The flow of time after the Collapse is most likely rogue and irregular, and it's fairly safe to say that it eventually stops. This would create conditions similar to those of the Suboriginal Void, this called the Post-Temporal Void."
The glasses-wearing girl raised her hand again. "Yes?"
"Speaking of travelling to alternate timelines, I wanted to know something else. Say a Time Traveller departs for the future, but there's a timeline branch between his departure and arrival points. What prevents him from going up that branch and into a different timeline?"
"A good question," Vector said, "but allow me to assure you that not all timelines are equal. One timeline can very definitively be said to be a branch FROM another, hence why they are displayed as such on Time Web diagrams. There isn't currently any way to travel 'up' a branch like you just described; however, experimental 'Rail Switch mechanisms' are being developed that will eventually allow Time Travellers to control which timelines they travel through. In fact, if one were to combine a sufficiently advanced Rail Switch mechanism with Post-Collapse Displacement, it may be possible to travel to ANY timeline that one wishes. However, this is once again in the realm of wild conjecture, and so I'm obligated to remind you that no promises may be made on that front before further developments."
Vector glanced up at the clock, and her eyes widened. "My, but how the time flies! It seems we're out of time for this class session. I hope to see you all again tomorrow, and I thank you, as always, for an engaging discussion. Have a nice day!"
CLASS NOTES
Causal Loop: A chain of events with no definitive cause. (THEORETICAL)
The Grandfather Paradox: Scenario in which a Time Traveller prevents his/her own birth. Logical impossibility.
First Causal Theorem: All events have a cause.
Second Causal Theorem: Cause of an event may lie on a separate timeline from the event itself. Also known as the Precept of Time Traveller's Immunity.
Past Travel - Paradoxes will not occur as the result of alterations. When the traveller returns to the present, it will be in the new timeline.
Timeline Bifurcation: Splitting/branching of a timeline caused by the presence of a Time Traveller. Splits directly at the point of arrival.
The Problem of Duplicates: Idea that trips to the past should create duplicates of the Time Traveller. Debunked by Time Bastard.
The Problem of Feedback Loops: Idea that going to the past without preventing the original trip from happening again will set off a feedback loop of new timelines. Debunked by Time Bastard.
Time Bastard: When a duplicate of a Time-Travelling entity on the new timeline reaches the point in time/age of departure of the original entity, the duplicate will cease to exist. Applies only to Past Travel.
Future Travel - Meeting future self is NOT possible in a trip to the future (only when future self travels back). Future the traveller arrives in is one where he/she has not been seen since departure. Alterations will not be seen again once the Traveller returns to the present.
Origin: The point in time where Time begins to flow. All points are either before or after Origin.
Suboriginal Void: Time before Origin. No flow of time; matter/energy cannot be properly expressed here. Impossible to leave by normal means after entering.
Mother Timeline: Theoretical Base/Original timeline from which all other timelines branch. Untouched by the effects of Time Travel.
The Collapse: Indeterminate point in the future where Time Web reaches critical mass due to large number of timelines, and collapses. There is no causality, and no distinction between one timeline and the next.
Post-Collapse Displacement: Phenomenon in which the Time Traveller travels to a point in time after the Collapse, then attempts to return. Since timelines are not distinguished, the Traveller will usually end up on a timeline different from his/her original timeline.
Post-Temporal Void: Theoretical time after the Collapse where irregularities in time flow result in a complete stoppage of the flow of time. Similar to the Suboriginal Void.
Rail Switch mechanisms: Experimental mechanisms that would allow the Time Traveller to choose which timeline he/she travels through when moving forward in time. Sufficiently advanced versions combined with Post-Collapse Displacement may allow controlled dimensional travel.
