The Effects of Time Travel on History in a Single Time Stream Universe
by Lee Canaday
1) Time travel is possible and therefore there is no problem with identical particles of matter or energy existing at the same time in different places. If time itself is a property of particles of energy and matter, then particles from different times could not be identical. Also, part of time travel being possible means that the past still "exists" and the actions of beings in the past are constantly being replayed. My fictional time machine used for the purpose of illustration can hop into any miniscule point of time along the way.
2) There is but one time stream. Since the idea of one's actions altering the past and somehow creating "parallel universes" puts the time traveler nearly on par with God, I will ignore the possibility.
When I discuss "events" and "history" and such and their alterations, I am implying no change in the fundamental particles of time. The particles of time are part of the basic structure of the universe. What man does within those particles matters naught to the universe. Anything could be written there, like molecules of chalk caught in the texture of a slate. This slate, however, is impervious and could not be altered by the chalk in even the smallest way no matter how much was ever written or erased on it. The history of man and trillions of alien life forms could be changed an infinite number of times and still the universe would go plodding on in the same manner as before. Therefore, one should keep in mind that there will be two separate concepts addressed here: 1) the physical nature of time and 2) the course of human events and how they may be changed by a time traveler.
I am not a scientist and will keep things in layman's terms though the concepts may be a little confusing on the first reading. I am proceeding from pure suppositions with the most parsimonious explanations I believe are possible based on what I've read in the field of science and science fiction. I am using my common sense and logic to come up with a satisfactory concept of the manner in which time travel may affect human (and, analogously, other species') history. This concept is in opposition to the many convoluted dramatic contrivances that have been dealt us by science fiction authors over the years. In my idea of time travel, there'd be little dramatic tension, I'm afraid. There'd be no disappearing images in photographs, no bullet holes magically appearing even when the gun was unloaded by the time traveler, no "predestination paradoxes," no whatever else they may shovel our way. It would, however, make sense.
Very few of the ideas put forth by authors over the years have made sense regarding the most basic paradox encountered in time travel. This, the most often discussed problem of time travel, is the "grandfather paradox" wherein one inexplicably goes back in time, presumably before the time traveler's parent is born, and kills his grandfather. In such a case, the time traveler is never born and could never have gone back in time to kill his grandfather and so on. In most sci-fi stories, there seems to be some similar paradoxical problems and the effects of one's actions in the past have disastrous and instantaneous results traveling forward from that point in time throughout the time continuum. The problem with this is that we are all really time travelers and our actions have results. The effects, many of them easily observable, do not spread instantaneously into the future. How could they? Is the time traveler of these stories actually some god with supernatural powers? If not, then how do his actions spread forward into the far distant future instantaneously? It does not make sense.
If I, a modest time traveler like the rest of us, do something on the order of, say, blowing up the Lincoln Memorial, at what rate do the effects of my actions travel forward into the future? The answer is that the effects travel forward at the same rate that I and everyone else are traveling into the future: the speed of the present (P). The present, as the comedian, George Carlin once pointed out is hard to pin down. When is now? When we are right now (P) is constantly moving into the future. The moment we've just experienced is constantly moving further into the past. There's no way to pin it down except to say we're always in the present and that the present is always moving forward.
We all, therefore, know how to travel into the future. Some of us seem to do it a little more quickly or slowly than others relative to our perception of time itself, but in physical reality there is only one rate at which we travel: the speed of the present (P). If we were to travel faster than P into the future, it seems unlikely that we could create any paradoxes until we came back home which would have the same effect as traveling into the past.
Traveling into the past opens a whole can of worms. One's mere presence in the past can set off an entire chain of events that changes life on earth as we know it. It is unlikely that such an earth shattering metamorphosis of history would occur except by design. However, it has to be acknowledged that once a modern person ("modern" to whatever era he is from) goes back into the past, the past era he is visiting is "contaminated" by his very presence. This must be presumed since it can't be known what effects he has had if he has interacted with or has been seen by anyone of that era, or perhaps has accidentally left some mutated disease germs behind. We will call this contaminated past P'.
The particle theory of time states that extremely small moments of time are connected in a linear fashion like pearls on a necklace. We travel through these incredibly small particles of time within the "present" as it moves forward at a certain "speed".
For the purposes of this article, I will also assume that we are at P, the very edge of the necklace where pearls are being created and added, lengthening the necklace, perhaps to infinity. There is no "future" in existence yet. It is being created as a natural function of the universe it as we go along. This may or may not be the case, but it helps to illustrate our concept of time and the existence of the past.
Of course, from any point back along the necklace it would appear that people, through their actions, are slowly "creating the future" of human events by laying the groundwork for later generations' actions and existences. As part of the history of mankind, they have, merely through living their lives and taking whatever actions, big or small, made life for us what it is. For that reason, I will also refer to the time "stream" since it is apparent that wherever you hop into past with your time machine, you are slipping into a stream, which like a wave, is constantly moving forward. Once you are in the stream, you are moving along with it in whatever past "present" you landed.
It could be that, like light, time exhibits properties of both particles and waves. I will use the necklace analogy for statically demonstrating the status of particles along the time line in relationship to each other after time travel has occurred. To demonstrate the fluid, or wave-like, ever-moving nature of time, I will use the stream analogy in my explanation. When using these and other analogies, we will be looking at time from an objective distance as if on the banks of the stream or as if holding the necklace. Such perspectives will be outside of normal space and time so that we can graph any changes that might occur and see any relationships that link one moment in history to another through the effects of the time traveler.
Now, back to the grandfather paradox. Let's say I'm really mad at my grandfather and, in a fit of anger, wished that he'd never been born. This seems a little more humane than killing him and still insures that he does not come to exist in the past. Of course I have a time machine and am literally able to make sure he is never born. I hop into the machine in the year 2000, set the dials to a date in 1889, several years before my grandfather is conceived. I then encounter his mother, my great-grandmother, and kidnap her and take her off to Australia where she meets the grandfather of Crocodile Dundee and falls in love with him and stays forever. I did it! No worrisome grandfather will ever be born!
But wait! How can I still exist? I'm still me, genetically intact with the same personality. I'm still there in the past. Nothing has happened to me. I'm not slowly fading out of existence nor mutating into a different being. But my lineage has been interrupted! There should be no way, according to most sci-fi stories and movies that I could be standing there. How could my grandfather not exist, yet there I am in the past, the same person who descended from that man? Once I destroyed the existence of my grandfather, shouldn't I have disappeared? Of course, if I had disappeared, then I couldn't have gone into the past to stop my grandfather from being born, so I then would have been born and then gone into the past and so on.
Since, as I pointed out earlier, the effects of our actions in the present (P) only travel forward into time at the speed of the present, then the effects of my actions in the contaminated past (P') will only go forward into the future at the same rate. The chain of events that brought me there still exist, still have occurred along the pearls that still exist on the necklace, though not in the normal order except from my perspective. In the stream, P' is a boat 111 units (years) behind another boat P. They travel at the same speed along the stream. P' can therefore never catch up with P. That is, the new events that have now occurred in the contaminated past, will never catch up with the present since they are both moving forward in the stream at the same rate. (Or, if the rate is ever different, it is different at the same points along the time stream and therefore consistent for each of them and the effect is the same as both moving into the future at the same rate.) The past cannot overtake or even catch up with the present! Now, allow me to momentarily combine the analogies by placing a drop of red stain on the necklace. The red stain represents the contaminated past. I put it on the pearl representing the exact moment in 1889 that I arrived and hold the necklace at an angle so that the stain flows forward along the necklace. The stain is a viscous mixture that spreads out from the pearl representing the particle I arrived on in 1889 to the pearls in 1890 and then on into the 20th century. It is soon smeared from pearls in 1889 to pearls in 2000. Then something happens. The contaminated period of time, P', has reached a limit. It has caught up to the very pearl where I jumped into my time machine and went into the past to destroy my lineage. At that pearl, the stain encompassing the period of time that contains a history where I never existed cuts off my trip to the past. It has destroyed a link that has been forged between pearls in the two years, 1889 and 2000. At each moment of time in the minuscule particle where I left from the year 2000, I am constantly leaving, over and over again, to travel to the year 1899. There is a link of sorts that is forged. It constantly "refreshes" the contamination of the past as events rush through the particles over and over again like water in a stream. (The number of "presents" or "nows" would presumably depend on the minuteness of the time particles. The smaller the particles, the greater the number.)
The link is the trip in that very particle of time that is constantly occurring. That is, if you looked at the stream from the bank, a fish is constantly jumping upstream. When the boat, P' reaches the fish as he jumps out of the water again, he is unable to jump out of the water due to the boat, P' blocking its way.
When P' reaches the particle of time in which I leave to go to the past, it changes the course of human events that made that trip possible. Like a tape recording that is being recorded over with something new, my trip to the past is wiped out by the new recording of the contaminated past (P'). There is no way I can continue in the year 2000 to go to 1889. The point I arrive in1889 is therefore "clean" or "pure" again. As the months pass, the red stain slips off the pearls in 1889 and slowly moves forward along the pearls spanning a length of 111 years but no more. In other words, the human events of 1889 are once again only formed from genuine occurrences in the time leading up to that period rather than having been influenced in the least bit by an interloper from the future.
However, this "clean" time, P2, is starting at the point in 1889 where I don't arrive in my time machine and itself only moves at the creeping pace of the present. At that speed it slowly wipes out the red stain upon the pearls of the necklace. The particles of time are restored. The original chain of events is once again in place. And we all know where that chain of events leads. Yes! I once again am able to hop in my time machine after another 111 years have passed and once again contaminate time.
What, you may ask, has happened to P', the contaminated period of years? Nothing. It still exists. An altered span of 111 years, where my grandfather and his descendants do not exist, that spreads forward through the years like a ripple on a lake. Behind that wave, there is another span of 111 years of uncontaminated time. Behind that one, another span of 111 years of contaminated time, identical in every respect to the original. A definite pattern of interrelated altered and unaltered periods of human history has been created.
As you may probably guess, time travel could wind up creating quite a mess out of human history as written on the particles of time. One wave of altered history would follow another wave after another. Waves could be created within waves and this could cause further problems. If a historian were to go back into time, he might land in a wave of history that has already been changed significantly by someone else and might not offer any insight to his period of study. The permutations of such a theory are endless. The end result, however, is that going back in time cannot alter the particular present that one leaves since any changes could never catch up with that present since the present, and all of time, are constantly moving forward.