And the bell rings for the next round....
I'm glad you like the Boston Vacation concept. It usually makes it very clear that a trip into the future has no effect on the timeline, unless it is paired with a trip to the past which does.
Obviously, there are changes to the past which will be noticed, and these may create more severe anomalies than those which are not noticed--although even here we can't be certain. If someone from the future had planted an ordinary 1940's style bomb in Hitler's bunker and succeeded in killing him, they would have drastically altered history in a way which would create a major anomaly--but no one would be the wiser! On the other hand, the dropped gun on the airplane in Millennium should have been left behind. Probably no one would ever have figured out what it was, nor guessed that it came from the future. The first theory would have been that it belonged to one of the passengers, and was some new gadget which would have been patented sooner or later; if they concluded that that was not the case, it is most likely that a theory involving military secrets would be replaced by one involving aliens--the idea of time travelers might never occur to them. Just because history is changed in a drastic way doesn't mean that anyone is aware of it.
I do have trouble with the many worlds theory; most of my thoughts revolve around the notion that everything that might happen does happen in some world. Let us suppose, as an example, that you have developed a theory of time travel technology, and built a machine which should enable you to travel through time if your theory is correct. You set the parameters and step into the machine. Now if the many worlds theory is correct, and everything that happens in one world also specifically doesn't happen in another, then in one of those worlds your time machine will send you back, and in another it won't. (We could also suppose that in another it will kill you, and in another it will send you somewhere else--there are many possible outcomes; but these two will suffice.) But that means that in two worlds where you used the same theory to create the same design and built exactly the same machine, it worked in one world, and didn't work in the other. But if that's so, then it must also be true of every technological device ever invented, and the concept of science in every world is so convoluted and unpredictable that it ceases to be science.
Let us press it another step. I doubt there is anyone who has never had a car break down unexpectedly. Belts break, water pumps fail, alternators die, batteries go dead, hoses burst, fuel lines clog, fuel pumps malfunction--the number of things which can go wrong with your car at any instant is legion. Yet generally our cars prove to be rather dependable. For every moment you operate your car, there must be worlds created in which each of those things goes wrong, singly and in every possible combination. Why would the vehicle run so well in the world we experience? Of course, the answer that would be given for this is that such breakdowns, although unexpected and unpredicted by us, occur because of natural laws--the belt wears out, the battery gets old, the impurities in the fuel collect in the lines, the pressure of expanding hot gasses in the hoses becomes too great. The fact is that these things don't happen at random: they happen because of the convergence of many factors which bring about an outcome 100% likely based on those factors, but incalculable to us because we can't collect all of the information on those factors. Were we able to duplicate the exact conditions on a million identical cars, we would have the same breakdown at the same moment--this borne out by computer models which demonstrate what would happen to a vehicle in precisely defined circumstances.
But what is true of cars is also true of people. If everything that "might" happen "does" happen in some universe, then for every choice we make there is a version of us which chose each other option. But the choices we make are based on our individual psychological makeups, our abilities to gather and evaluate information, the information actually available to us, and other specific factors which together lead us inexorably to the paths we follow. We believe that our free will makes it possible for us to do anything--and in a sense it does. I am one who finds the smug attitude of so many sociologists annoying: many of these people believe that everyone is locked into their predictable choices except them. But they're only partly right. Everyone is locked into their predictable choices including them. Their choices are less predictable because one of the psychological factors which controls them is their ability to recognize which would be the predictable choice for someone in their social group, and include that information in their decisions. But that doesn't mean that their decisions are not fixed; it only means that it is not as easy to identify the weight of the various factors which control their decisions.
I'll try to put it simply. If you have the ability to gather and evaluate information, and to determine which path most fits with your own values, and to implement that path, your choice is free; it is not less so merely because someone could predict which path you would take were they smart enough and had enough information about you and your available information. I think we all have friends and loved ones who would dare to say that we are predictable at some level, that they know what we're going to say or do in certain situations. The fact that they are not always right doesn't mean that we aren't predictable--only that they do not have complete information.
Almost 30 years ago, a very wise (Presbyterian) pastor of my acquaintance gave me an interesting notion. He said that when you approach the gates of heaven, carved above the pearly gates are the words, "Come unto me all who labor and are heavy laden, and I will give you rest." You consider this for some time; perhaps you turn away. Perhaps you enter. If you enter, and look back over your shoulder, you will see the words, "Many are called, but few are chosen." To us looking forward through time, there are choices without number; but looking back, we can see that only one path could bring us here, and that many of the things we imagined we might have done we never would have done.
If indeed our choices would be predictable given sufficient information and intellect, and our science is fixed (that is, the rules which determine whether that time machine works are such if it works in this world it doesn't also not work in another world), then the imagined worlds in which all the things did happen which didn't happen here are no more than imagined.
Thus Dr. Who and Quinn Mallory are both mistaken: there are no divergent worlds based on changes in the events of the past. What happened in this universe was at some level inevitable, despite our abilities individually and collectively to choose and form that destiny. Of course, sliding technology does seem to require the many worlds theory, and therefore would seem to be precluded.
However, under my theories, there is one circumstance in which sideways time would exist: if someone has traveled back from the future to the past, they will have created a divergent timeline from that past, and someone in that divergent timeline might be able to move sideways to reach the original timeline. For example, in Back to the Future 2 (as I examine it), while Doc and Marty are in the future, Bif returns to 1955 and alters the intervening history such that when they return to 1985 everything has changed. But the other timeline must still exist, because the time machine still exists, and because Doc and Marty remember the other timeline. Now, BTTF2 is a disaster in its treatment of temporal anomalies; but in that circumstance it must be the case that a sideways time machine--the sliding machine of recent interest--could take you from the new history to old history.
I'm aware that those far ahead of me in quantum physics believe that at the subatomic level there are events occurring at random; Einstein would not accept this notion, and I, too, find it difficult. We are both aware that radioactive decay (a subatomic process, but not one involved in quantum physics' theory) is a process which appears random; but it is not random. A subatomic particle from a decaying atom will break off at the moment it becomes unstable and in the direction it is driven by internal forces; it will collide with another atom in its path. We cannot predict these events due to insufficient information. Were we able to create a model which would duplicate these activities on a larger scale and at a slower rate, probably our teenagers could predict the individual events just by watching. In "Jurassic Park", Jeff Goldblum's character attempts to demonstrate "chaos theory" by dripping drops of water on the back of someone's hand, and observing that each takes a different path. But he has not demonstrated that the path of the water is random--rather, what we learn is that the physical factors which control the path of the water are outside our ability to identify and predict under those circumstances. We are able to predict the path of water down a mountain, largely because the relevant information is stable long enough for us to identify it. I fully expect that the quantum activity which is currently thought to be random will eventually be determined to be controlled by specific factors outside our knowledge. Remember, our ability to observe events at the subatomic level is extremely limited: just because we cannot see any difference between the conditions precipitating two dissimilar events doesn't mean that there are no differences.
I've done quite a bit on clairvoyance and precognition for the Multiverser game system. Clairvoyance--remote sight--would not be involved here; precognition (with retrocognition) might be connected. Theoretically, information from the future (or the past) could be gathered by technological/scientific, psionic/mental, or supernatural/magical means. I believe in magic; as the Bishop of Aquilla said, it's part of my job. But if there are magical means of gaining information about the future, my best guess is that they involve beings of the supernatural realm viewing our timeline (not being constrained within it as we are) and telling us what they see. That means that we have little control of what we learn, and great difficulty evaluating its veracity (that is, not knowing the identities or motivations of such beings, we cannot be certain why they would give us this information or whether they would provide false information when it suited their purposes).
A technological alternate time viewer is not what you are suggesting; but it could be possible to create such a device, and the effects of it would be similar to any other means of acquiring information from a different point in the timeline.
The type of precognition in which most people believe would be psionic--untapped mental powers gathering information about the future. I'm afraid James Randi is right to doubt the existence of such powers: his organization has offered a substantial monetary prize to anyone who can prove such powers or phenomena, and in over a decade no one has even attempted to claim it. That in itself is very telling--it isn't that no one has succeeded in convincing them, but that no one has tried. I have already mentioned his comments on precognitive dreams; the evidence for information coming from the future is unconvincing.
But were we to assume that by any one of these methods information was conveyed from the future to the past, that would have the same effect as if someone were to have traveled back in time. That is, there can be no information from a future which doesn't exist. Therefore, time must progress from the present to the point in the future from which the information emanates--there must be an AB timeline in which that information is not known. Then the transfer of information from the future to the past changes the past: something is known which could not have been known before. This creates the CD timeline. However, if the actions taken due to the information are such that the information is now false, that information cannot now be known in the past, and cannot have been discovered by precognitive means--an infinity loop is created.
Incidentally, the Multiverser game system deals with this problem in several ways. With magical precognition, the referee is given the task of keeping the information regarding the future somewhat limited, and assuring that through the actions of other characters the predicted future comes to pass in some form. With psionic precognition, we assume that precognitive information comes from the most probable future, but that action can be taken to choose a less probable future world, accepting the idea that the most probable world and the most absurd world will both become reality, along with every other possible world. Thus, in that reasoning, the events which brought about the undesirable future did occur, creating that other universe from which it was possible precognitively to gather information, but the choices made by us carried us into the desirable future (although our divergent selves are suffering through the future we foresaw). If the multi-universe theory is true, then the only type of precognition which can reasonably exist is one which views the most likely of many futures at that moment; the precognitive information may change which future is most likely thereafter without affecting the precognitive event itself.
The timeline is not subjective. If John A changes history, he changes it for himself and everyone else. However, one thing that is extremely risky is the idea of going back in time to change something specific: if you succeed, you undo the reason for making the trip, and so undo your success, and recreate the reason for the trip, the classic infinity loop. When John goes back to intentionally change the past, he erases the version of himself who decided to make that trip; the new version of himself doesn't know what things were like before he made the change, and so doesn't know what change he would want to make. If we succeed in killing Hitler before he commits his atrocities, we save the world from those atrocities, but in the process destroy the information upon which our decision to kill him was based--and why then would we have done it? We are only able to change the past by our actions from the future if 1) the changes are accidental or incidental to an effort to achieve another objective, or 2) a secondary reason for us to enter the past and perform actions which will have that effect is created.
We may eventually discover that time is not mutable--that our discussions of time travel shall be forever moot. "You can't change the past" may be more than wise advice to live in the present. What I have created is a theory which is a satisfactory approach to the effects of time travel if indeed you can change the past--and if you can move through the time line out of sequence, you can change the past. I shall try to present the logic of it.
If John A leaves 2000 (point B) and moves to 1980 (point A), he intrinsically alters his own history. The history he knows--the AB timeline--has been eliminated. No future can stem from that history, because it no longer exists. The 1980 he reaches is not really point A, but point C, distinct from point A by his presence. However, the cause of the change in 1980 is located in 2000, at point B; therefore the events which led to point B must exist in order to create the cause at point C. If I am wrong--if the AB timeline does not exist in some sense parallel to (actually, divergent from) the CD timeline, then the CD timeline becomes impossible (the cause has ceased to exist), and all of time is destroyed by the attempt to move backwards through it--and time travel is thus intrinsically impossible. However, if we assume that time travel is possible, we must have another explanation--and the only one which survives this is to assume that upon the activation of the machine, time itself snaps back from 2000 to 1980, and everyone relives those moments, changed by whatever effects the presence of John from 2000 would have on them. However, in the AB timeline, 2001 is never reached: that timeline is destroyed, and the cause of that destruction is John's trip backward through time. The timeline has run 1998, 1999, 2000, 1980b, 1981b. We have a divergent history, and the only year 2001 which can arrive now is the one in which the history is the CD time segment.
Now it gets complicated. (NOW it gets complicated?!?) John A also ceases to exist. We must suppose that the CD time segment ends in 2000, at which time John B either will or will not go back in time. If the changes to the timeline initiated by John A have not in any way changed John B's identity or circumstances, then John B will make the trip originally made by John A, and will perform the same actions at the same points resulting in the same consequences; the CD timeline will in essence repeat itself, confirming itself as history, and the year 2001 will arrive with John B living to see it. (John C will also go back in time, as will John D, John E, John F; but as these persons are all identical to John B, they will not change history.) But let us suppose that John B has been changed by John A. The John who makes this trip (assuming that he makes it) will be a different person, and so a different history will be created--the EF timeline, in which John B is present and affecting his surroundings. Time must snap back to 1980 with each successful trip until John N and John N+1 are the same person.
Now let us assume that that never happens. In theory, the universe could be trapped in a "cycling causality" (a term I borrowed from Tim Fox) perpetually, never stabilizing. I consider that unlikely. Eventually one of two outcomes will result. The desired outcome--suggested above--is that John N will be identical to John N+1, and 2001 will arrive. The undesired outcome is the infinity loop, which must be understood separately.
If John A goes back in time, he creates the CD timeline. In order for John A to do that, certain things had to be true. John A had to have the ability to make the trip, and he had to have the reason to make the trip. If either of those two things are absent due to John A's trip, then John B will not make the trip. However, the CD timeline was created by a cause in 2000 (at point B) having an effect in 1980 (at point C). If John B does not repeat the actions of John A, then the cause of the CD timeline is not repeated, and the CD timeline cannot support its own existence. Thus, at point D, at the moment at which John B fails to return to 1980, time must snap back again to 1980 to play out the newly altered history, the history in which John from 2000 does not intervene in the events of 1980--in fact, the original AB timeline. Yet we know that the consequence of the events of this timeline is that John does go back in time, creating the CD timeline. Time is now perpetually trapped--it moves naturally from A to B, snaps back to C, moves to D, snaps back to A, and never reaches 2001 for anyone.
It is undoubtedly the case that PLR suggest a pragmatic consideration of at least the short-term consequences of short-term actions, and for those with any wisdom an additional consideration of long-term consequences. The ability to consider long-term consequences is apparently not shared by everyone. I have been informed that cigarette smoking over the long term dries, yellows, cracks, and generally ages skin (one more detriment to a nasty habit). It strikes me as ironic that so many teenagers start smoking in order to look older--because in perhaps 30 years, they get their wish. But of course adolescents are less able to consider long-term consequences than adults (or perhaps it would be better to say that we hope adults are more able to consider these things than adolescents--I am not convinced it is always so). In all, it is likely that people choose the reasonable approach precisely because they are less motivated by instant gratification than we might suppose; and if we accept that most people will pick a reasonable approach most of the time, the multiple universe theory goes out the window, because it is dependent on the notion that for every choice made there is another universe for every alternate choice which might have been made. The fact that we can predict that people will choose particular options demonstrates my point, that these other universes are fantastic.
I think that's everything to date; have I left any gaps you'd like filled? As always, I enjoy the discussion.
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