That may be Anderson’s real theory: what can I write that plays mind games with temporal mechanics? I think a lot of writers in the time travel business give no thought at all to a theory of time, and instead create stories that have a feel of plausibility so they can challenge theoreticians like me to explain how they could or why they could not ever happen.

–M. J. Young

You wrote:

I am afraid, *no* time travel theory can do that. Even in the replacement theory the time traveler does not impact ‘his own’ life but that of his younger self, who by that very action grows into a different person. When the traveler returns he faces this alter ego, who is the *true* kid brother’s brother. And well, he is a stranger, and he will always be a stranger. This is the outcome of the two-dimensional theory. The replacement theory is even worse: if I am not mistaken, it predicts an infinity loop here. The alter ego does not build the time machine, his kid brother being cured, and the traveler has nowhere to return, the time being trapped between 2000 and 2030.

That may be a matter of perspective.

If we consider my construction of Back to the Future Part I, I maintain that the original Marty McFly whom we have followed through the film ceases ever to have existed at the moment that the altered Marty McFly leaves the parking lot. If we assume that that altered Marty manages to disrupt his parents’ meeting and bring them back together sufficiently like the original Marty did, leading to his own departure from 1985, then the Marty who awakens the next day finds the affluent McFly home, but is not at all surprised by it because he has always known about it. Yet this is the same Marty, son of Fred and Lorraine, with many of the same interests. Marty really has changed his own life; he just does not know what it was before he intervened. In any case, there is no alternate Marty running around his universe; he is the only one.

The points raised in The Two Brothers: Why Parallel Dimension Theory Is Not Time Travel focus on the fact that there would now be two Martys in that world, one of whom came from the other world and the other who grew up in this one. Conveniently for parallel dimension theory, one of those Martys decided to run off and start another universe, and we do not know where he is now. However, there is this sense of displacement, that the Marty who awakens in the affluent McFly house does not really belong there, and it seems just a matter of time before he is identified as an imposter. He probably does not know his own financial position or any of his passwords (and yes, the wealthy had that technology in 1985).

Indeed, under the replacement theory the two brothers story does create an infinity loop; but it is real time travel, and not movement to another universe.

You further wrote:

In fact, there is no difference between the parallel words and the two-dimensional theory predictions except for a purely metaphysical question of whether the old history is preserved or erased. It may seem important that if the old history is there you only compounded the net misery, but if it is erased you took one for your brother and stayed alive. But is it really a *moral* achievement that you erased an entire world full of people to create a new ‘less miserable’ one? This sounds like something the god of gnostics would do.

I see your point, but I’m not sure it’s entirely correct.

Mind, this draft is an effort to explore whether such a theory is plausible; it is, to my mind, full of holes I cannot plug. Your efforts with supertime are fascinating, but that is not the discussion here. I am in no way committed to defending two-dimensional time; I think it inadequate for time travel. I do not, however, think that lateral movement in two-dimensional time is destroying people.

Thinking strictly in terms of linear time, I was recently declined representation by a well-known literary agent. Had he undertaken to represent me, it is possible that my next book would have made a significant impact to my immediate financial situation and my long-term future. In that sense, his choice “erased” a possible future and “replaced” it with one I find less promising. Yet I have no memories of either future at this point, and will only remember the one in which he declined to represent me.

There are those who suggest that at any given now all possible futures exist, but there is only one past; that by making our choices moment by moment we eliminate most possible futures and create a single past. Based on that perception, that agent destroyed the bright future that has me collecting royalties on books and doing speaking engagements, and created the one in which I remain a lesser-known celebrity still struggling to get on the D-list, as it were. Yet we would not say that he destroyed anything; he simply made a choice which caused changes which formed a future different from some other possible future.

If we accept lateral time, then choices made which involve time travel do exactly that, but do so across all of history. Thus if someone from the future travels back and tells that agent, “You’re making a mistake, you really need to represent this guy,” the step laterally unmakes the future in which I am not represented and replaces it with the future in which I am. That is not different from what the man (I am very tempted to use his name or agency, but I think that would be inappropriate) did initially, choosing one of the many possible futures by his initial choice. The lateral change is not different from what we now think the linear change is.

Again, thank you for your comments and insights. I hope my responses have been helpful.

–M. J. Young

“I’m inclined to think that time travelers under your theory face the problems I address in The Two Brothers: Why Parallel Dimension Theory Is Not Time Travel…”

I am cautiously optimistic that it does not face the egregious ones (see below). To the extent that it does, the replacement theory (and indeed, any time travel theory) has the same problems. But I understand where you are coming from. To me, the prime motive was to save room for chance and free will. I fancy my model to be the most conservative alteration of the replacement theory, provided the free will is taken seriously and played out to its logical conclusions. There is still a tint of dissatisfaction that one can not erase one’s own life and replay it better, probably the most powerful emotion behind seeking time travel. But hey, there is a price to pay for making choices: what is done is done, time travel or not. ‘Tomorrow never comes until it’s too late’.

“Until it has been demonstrated that a block of pure carbon can be reliably moved from the present to the past, no one is going to allow a human being, nor even an earthworm, to make a trip in any such machine… The ultimate problem with parallel dimension theory is that if it works it can’t be demonstrated. Thus time travel dead-ends under this theory, as no one can know whether those who vanish are in another physical world, or have merely had their atoms scattered across the cosmos.”

In short, ‘it will never get this far’ problem is obviated in any parallel dimension theory, where one can return to both the left and the created branches. In my model this is achieved by their segments sharing the same spacetime.

Suppose researchers test a time machine by sending a carbon cube one minute back. They may be discouraged by the fact that it did not pop out of nowhere one minute prior to the experiment. But they proceed anyway. The cube does pop out of nowhere in front of almost identical group of researchers that are one minute behind the original group along the highway. They proceed with their experiment and conclude that time travel works. They may notice that the returned cube is not exactly identical to the one sent, but this can be attributed to any number of effects of the trip. As long as travel times remain small their experiments will be mostly successful and will attract lavish funding.

Of course, eventually they will be shocked by receiving a tapeworm right before sending a rainworm. I trust that my hypothetical colleagues will figure out what happened. With any luck, they will confirm their hunch by having one of their own converse with their future counterparts, and come back to resolve the tapeworm paradox. It is also possible that they will first come up with a contraption that automatically returns objects back to them after a short time trip. In that case, they can perform a disappearing-reappearing act in their lab in front of senators and generals without any anomalies.

“Yet he is not your brother; or perhaps more precisely, you are not his brother… Meanwhile, back in your own world, your brother died. You did not save your brother; you saved someone else’s brother… It isn’t time travel unless the traveler arrives in his own past. That means he can impact his own life; and that means we need a theory that addresses what happens when someone impacts his own life. The theory of this site does that…”

I am afraid, *no* time travel theory can do that. Even in the replacement theory the time traveler does not impact ‘his own’ life but that of his younger self, who by that very action grows into a different person. When the traveler returns he faces this alter ego, who is the *true* kid brother’s brother. And well, he is a stranger, and he will always be a stranger. This is the outcome of the two-dimensional theory. The replacement theory is even worse: if I am not mistaken, it predicts an infinity loop here. The alter ego does not build the time machine, his kid brother being cured, and the traveler has nowhere to return, the time being trapped between 2000 and 2030.

In fact, there is no difference between the parallel words and the two-dimensional theory predictions except for a purely metaphysical question of whether the old history is preserved or erased. It may seem important that if the old history is there you only compounded the net misery, but if it is erased you took one for your brother and stayed alive. But is it really a *moral* achievement that you erased an entire world full of people to create a new ‘less miserable’ one? This sounds like something the god of gnostics would do.

For time travel to impact ‘own self’ it would have to transmute the time traveler into his younger self after he made the changes. Somehow the memories of the time travel have to be preserved but not affect this new person. Perhaps, they only resurface at the time when the jump originally occurred, etc. I am sceptical as to logical consistency of such a theory. The replacement theory, the two-dimensional theory and even the parallel worlds do the next best thing. They duplicate a person into a changer and a changee, cause and effect. This duplication destroys the possibility of changing *own* past even if you start with exactly the same past. The only difference with my theory is that I replace ‘exactly’ with ‘more or less’ simply because ‘exactly’ leaves no room to chance.

As for me, I have trouble with non-linear realities. Things are or are not. I do not think it possible that my years in college have been erased but I still remember them and my name appears in their alumni records. If those years have vanished, then everything subsequent to them must also have vanished. I’m a stickler for chain of causality, which is what drives the replacement theory more than any other single factor.

I do thank you for your input, though. Your notions do seem closer to Anderson’s stories, although I think he would insist on instant change of all history, protecting only those who have traveled from one point of time to another.

–M. J. Young

I do not believe that there is such a strict dichotomy. One can think of driving along the highway of time with past ceasing to be and present being created, instead of moving along a static landscape. The question is if there is a single car (the Now) driving, or a neverending chain of cars (nows) in rapid succession. Our experience being restricted to a single now we do not know one way or the other. But believing that our now is the only Now is akin to placing the Earth into the center of the universe, so I opted for the pluralistic view. It still makes sense to talk about time travel with our car extending wings, flying away and landing on a different part of the highway. Since there are multiple and co-equal nows there is no need to switch from one to another or erase anything.

Perhaps you meant that in such a model time is not really time anymore, but just another dimension of space. I am inclined to agree, but any theory of time travel casts time as a dimension of space in some sense. And one does not get to create a landscape while moving along other space dimensions, so time is still special. But if you are saying that time travel is only meaningful if all new causes are instantly played to their effects then we disagree on the definition. This links directly to a philosophical position on chance and free will so I will not expand on it here.

“Your problem in connection with this two-dimensional time theory is you fail to grasp that the linear time we experience is, by this theory, entirely atemporal, and the perpendicular lateral time is temporal.”

Actually, I have no problem with the two-dimensional theory, and I agree that it has no problem with relativity unlike the replacement theory. I suggested a different theory of lateral time for the Anderson’s stories since your model does not work for them very well. Relativity is only an analogy here: we have gradual propagation of changes in space, so why not also in time since we are treating it as something like a space dimension? This does require a correlation between linear and lateral time and a new fundamental constant analogous to the speed of light, the maximum speed of temporal shock waves. Your two-dimensional theory emerges as a classical limit when the maximum speed goes to infinity. My theory sets the maximum speed equal to the natural rate of living through time.

“By this reasoning, it seems not merely possible but entirely likely that my birth has been erased but I do not yet know it, and the parents with whom I conversed earlier today have false memories of me being their son, but history has not yet caught up with any of us.”

Your description of events surrounding your birth is entirely accurate, but I would change the tonality. Your birth might have been erased and you will never know it under normal conditions (no shock waves). Your parents’ memories are not false, metaphysically and causally you are *their* rightful offspring, but the moment of *your* birth is no longer along the highway. Instead, somewhere up the road there is a couple of people, much like your parents, that do not have a son. And that history will never catch up with any of you, again under normal conditions. Causality moves not along time, which is like space, but along lateral time, exactly because it is the truly temporal dimension. Due to the correlation however, there is a simultaneous shift along the time highway.

“It is possible that your theory might work for the Time Patrol stories; at least, Anderson might have something like your theory in mind. It is still a very shaky notion.”

Is time travel ‘really’ time travel under the above circumstances? People may disagree, but my model is as descriptive and logically consistent as the replacement theory. Shock waves spoil the sport though. Why should changes made by a time traveler propagate any faster than changes made by other drivers? Let me offer an interpretation of Anderson’s story that does not require any shock waves.

Suppose the universe of the Founders in the distant future faces imminent doom at time X. It has nothing to do with time travel, could be the Big Crunch or the Big Reap that some astrophysicists are prophecising. They are working to avert it or to live through it, but they need time. Time travel technology being available to them, they go back to an earlier time, share their research with their ancestors and collaborate to find a solution. They repeated it multiple times but did not succeed yet. They can not go too far back since the people are not ready to comprehend their science, etc. If somebody in the past makes changes that prevent certain key discoveries from being made, their operational time segment will eventually start shrinking even without shock waves. Its forward end keeps rolling into time X, and its backward end is being rewritten into unusable wasteland. Since the Founders do not know when they will find a solution they need to keep this segment as intact as possible for as long (in lateral time) as possible. Hence the Time Patrol.

P.S. It has been a while since I read Time Patrol (15+ years), but I seem to recall that Anderson explicitly adopts a version of parallel worlds with return to the branch one creates. He only allows one active branch at a ‘time’ though, the rest remaining mere possibilities. There was one story with 20th century looking like brushed up 19th and the Founders erased. The character had to travel to the branch point to fix it.

You wrote

In fact, relativity tells us nothing is affected at all beyond the boundary that light can reach within elapsed time. Similarly, changes made at a particular instant of time do not spread across the entire timeline in one lateral click.

This is very similar to the objection you expressed (via e-mail) to the Spreadsheet Illustration of Time Travel; but the answer is not exactly the same, as that replacement theory and this two-dimensional time theory are distinct in critical ways related to this point. However, perhaps I can address the concept here.

There are two ways to consider linear time. One way is that it is as it appears to us, that as we move from instant to instant the past ceases to be and the present is created, the future not existing until it, in turn, is created. The other is that it is more like a highway, the entirety of it existing in static form but we moving along it at a fixed rate. The odd part is, if the former theory is correct then time travel probably is impossible, because only the present actually exists. Time travel would have to change the entire universe, in essence by making “now” a different time, causing everything after “now” to have never existed and restoring the universe to a previous “now” from which to move forward–and leaving the presence of the time traveler as an inexpicable anomaly. Only if the latter view is true does it make any sense at all to speak of traveling in time. We can go to “then” because “then” exists as its own temporal “place”.

Under the replacement theory, when you change “then”, if it is in the past, every effect that flows from that moment must also change. In most of the discussions on the Temporal Anomalies site, time is treated as if it is progressing from one “now” to another; only in the Spreadsheet Illustration is this larger view presented, mostly for those whose understanding of time allows perceiving the entirety of time as a single highway.

You state that change cannot happen faster than the speed of light. That has one impact on the replacement theory, which I will address by e-mail; but it has a different impact here. Your problem in connection with this two-dimensional time theory is you fail to grasp that the linear time we experience is, by this theory, entirely atemporal, and the perpendicular lateral time is temporal.

What that means is that if there is a time travel event at year 1000 in linear time, it does not matter if it takes all of time for the effects of that event to reach the entire universe, because “all of time” is static, and thus instantaneous from a meta-temporal perspective. Certainly it might take a hundred years for the information related to the time traveler’s arrival to travel a hundred light years, and it might take a billion years for that information to travel a billion light years; but the time it takes for the information to travel is irrelevant, because from the lateral time perspective everything in linear time has already happened, all in the same instant of lateral time. Whether we believe time has a beginning and an end, or whether we believe it is infinite in one or both directions, the entire point of lateral time is that it is a step from one complete history of the universe to the next. Regardless of how long it takes for information to travel through the entire universe, it will have done so within the confines of the linear time that constitutes one “tick” on lateral time, because lateral time is by definition the movement from one complete history of the universe to the next.

I agree that lateral clicks could happen without time travel; I disagree, though, that there is any correlation between linear elapsed time and lateral elapsed time. The entire point is that there is no such correlation, that lateral time represents the medium against which the entire history of the universe can be changed from one complete history to the next.

This is also why your suggestion that it takes thirty “lateral” years for a change in history to propagate forward thirty “linear” years fails. A lateral tick is the replacement of the entire history of the world, all causes played to their effects.

Your belief that there are random events (which I do not share, but that is a discussion for our e-mail) gives some validity to the progression of lateral time without time travel. It suggests that those random events would be different in each progressive version of the universe. However, I find it difficult to accept. By this reasoning, it seems not merely possible but entirely likely that my birth has been erased but I do not yet know it, and the parents with whom I conversed earlier today have false memories of me being their son, but history has not yet caught up with any of us. If such random events can be changing the universe from tick to tick, then the universe has changed untold times. It is even possible (although somewhat unlikely) that my birth has been undone, that the propagation of that fact is working its way forward through time toward me, but that my birth has since been restored, and that I am alive now and alive then but do not exist for some time between.

Unless I badly misunderstand what you are proposing, that seems an inescapable conclusion of your position.

It is possible that your theory might work for the Time Patrol stories; at least, Anderson might have something like your theory in mind. It is still a very shaky notion.

Thanks again for your thoughts.

–M. J. Young

As a consequence, chronological history does not exist ‘simultaneously’ but is created at a fixed rate (one year of time per one unit of lateral time equal to say 10^30 clicks). There is no single present, each instant of time is recreated at each click of lateral time across the entire timeline. Once that instant is recreated its previous version is lost ‘forever’, but not before it creates a latter (in time) instant of a latter (in lateral time) timeline. Both the past and the future are mutable due to random events with changing outcomes, or due to deliberate changes made by time travelers.

But changes do not spread across the entire timeline ‘instantly’, they propagate through time at the same rate as we live through it. For example, changes made in 2000 would only spread up to 2030 after 30 units of lateral time. In particular, without time travel we would never become aware of changes made to our past or, for that matter, to our future. Also, there is a detectable moment at which the changes are made, they do not happen to all history ‘simultaneously’.

In this picture, Anderson’s future time travelers have nothing to worry about. Even if their past is erased they will never be affected by changes spreading at the natural rate. They should only be concerned if they are vain enough to want to preserve the entire history that led to their appearence. To accomodate Time Patrol stories one has to assume that it is possible for time jump effects to spread faster than the natural rate. Only such temporal shock waves could threaten the founders of Time Patrol.

Still, even the shock waves do not spread instantly and the founders will have time, lateral time, to eliminate the cause of the shock wave before it reaches them. The shock wave might still erase them but the new one, the correction wave, would recreate them again. Such a theory makes Time Patrol meaningful, and placing it into a distant past makes sense assuming the shock waves only spread forward in time. From the dinosaur past Time Patrol is able to correct the alteration even after its founders were completely erased. Of course, what a clever time criminal should do is destroy their base in the past, and then make changes that would erase them from the future.

Did you know that Schroedinger created that particular thought experiment to demonstrate that the multiple dimensions theory was utter nonsense, and now it is cited to explain how the multiple dimensions theory works? If the explanation means what the person who wrote the explanation meant by it, then the explanation is that it doesn’t work.

But this is fiction, of course, so it’s allowed to work in some universes.

What I have most trouble with, I think, is the notion that just because a theory of time is complete irrational nonsense doesn’t mean it can’t be true in some universe.

What I’m trying to do here, though, is devise a theory that is not complete irrational nonsense which makes possible some kinds of time travel stories that are not possible under the existing theories. I don’t believe I have as yet suceeded, though.

–M. J. Young