In discussing temporal anomalies caused by time travel, the infinity loop garners the most attention of all those occurring under replacement theory. This decribes any scenario in which actions in one history cause a second history, but actions in the second history cause the first. It has been called a bow tie loop, or a Mobius time loop; sometimes the term cycling causality is used for anomalies similar to infinity loops, but the use of that term is not consistent, and will be discussed in our next article.
Image © E. R. Jones and M. Joseph Young. Used courtesy Valdron Inc
A simple example of an infinity loop is a case in which a time traveler attempts to prove that he is a time traveler by telling someone, "I know what you are going to have for lunch," and then reporting what he remembered from his own history, only to have the person "prove him wrong" by having something else. Thus in one history, the skeptic has a hamburger, and in the second history the traveler tells him he is going to have a hamburger, so the skeptic decides instead to have pizza in the second history; but this changes the information available to the traveler who now tells the skeptic in the third history that he will have pizza, and the skeptic instead has the hamburger he originally preferred. Since having the hamburger in one timeline will cause him to have the pizza in the next, and having the pizza in that timeline will cause him to have the hamburger in the next, history is forever trapped between these two timelines.
According to strict replacement theory, when this occurs time itself becomes trapped, and cannot progress to the next day, because the causal chain requires that the skeptic have eaten either the hamburger or the pizza, and it is impossible for either to be the final answer. Thus this is the end of time, because there can be no history beyond that point.
The theory also holds that an infinity loop occurs if a time traveler somehow prevents his own trip to the past, such as by "fixing" what he wanted to fix. Supposing that the time traveler wished to kill Stalin before the man came to power, and in traveling to the past managed to do so, his counterpart born in the world in which Stalin never came to power will have no reason to make that trip. Yet if he never leaves from the future, he never arrives in the past, and so never kills Stalin.
The fixed time theory resolves this by saying that it is impossible: you cannot kill Stalin because it is established that he survived, and thus that you already failed. Parallel and divergent dimension theories resolve the problem by saying that you did kill Stalin, not in your own world but in another universe indistinguishable from your own world. In essence, the past you changed was someone else's past, someone who never knew that Stalin mattered, and since you came from a different universe, the fact that your counterpart never makes that trip does not alter the fact that you arrived. Thus the infinity loop is connected strictly to replacement theory.
This aspect of time reverting to its original form because of the failure of the traveler to depart from the future raises the strongest objections to replacement theory. Efforts to resolve it in a manner in which the traveler's failure to depart does not undo his arrival have led to such theories as two-dimensional time and supertime. Yet under strict replacement theory, the outcome is unavoidable based on causal chains, that if the cause is removed, the effect is removed in sequence, regardless of the temporal relationship.
Next time we will consider the sawtooth snap and cycling causality.
Comments
Why does the time traveler have to go back after the slice of pizza? and the entire universe stops time just because some guy ate pizza instead of a hamburger? Is this suppose to be logical or just tom-foolery?
Thanks for your question, Jeff. A lot of people get hung up on that, particularly with "little" examples. Let's try a big example.
Al decides to prevent the Holocaust by killing Hitler. He travels to 1920, finds the unknown potential despot, and kills him. The history of the universe changes; Hitler never comes to power. Instead, Mussolini takes the lead in Fascism, and Italy launches WW2 and its own pogrom against Jews. The Al of this world has never heard of Hitler, but he decides to prevent the pogrom by killing Mussolini, and so travels to 1920 to kill the popular politician.
You must answer these questions: Are there two Als in 1920, or only one? If one, did he kill Hitler or Mussolini? If two, where did the other originate? In either case, what now is the history of the world?
Replacement theory says that Al killed Hitler in history 2, Mussolini (not Hitler) in history 3. That also means that if Al does not travel to the past, he kills nobody, and no one is de
If you go back and kill Hitler before he comes to power, that means you never read about him in the history books. If you never read about him in the history books, how can you go back to kill him? If you don't go back to kill him, he comes to power. So you go back and kill him. So you don't read about him, so you don't kill him, so you do, so you don't, so you do, so you don't.
Same basic concept with the hamburger and pizza, just on a much smaller scale. You were going to eat pizza, and ate a hamburger instead, so you eat the pizza, so you eat the hamburger, so you eat the pizza, etc. Don't feel bad, it took me about 10 years to wrap my head around this concept.
Thanks for your explanatory comment, John; that's exactly right.
Sorry my response was cut short last time; I thought I had three more characters, but it took a few off the end. I must remember not to take the counter down so close to 0.
In any case, if there is only one universe the final form of history has to contain all causes and all effects within it, and so if a cause undoes itself history cannot stabilize unless a second cause intervenes.
I hope that helps.
--M. J. Young
Couldn't be more wrong John. I would grow up in a world where Hitler came to power and was assassinated by someone unknown. I would never go back and 'unkill Hitler'.
Jeff, this is the part I do not understand. You agree that it is possible to "undo" the cause of the holocaust by traveling to the past and killing Hitler, but you fail to see that the same principle is at stake here.
Suppose that you traveled back from 2009 to 1920 to kill him, but did not kill him until 1921; and then in 2008 someone decided that Hitler should not be killed, so they traveled to 1920 and killed you. Would that mean Hitler was never killed? So then, why could they not kill you in 2008, and prevent you from traveling back to kill Hitler in the past?
If it is possible to travel to the past to change it, it must be possible to change it back by stopping someone from traveling to the past to change it.
Or is your "unknown" person the god Nature's way of preventing paradox, causing someone else to do it when you do not?
I hope this helps.
--M. J. Young
Nonsense. If I killed Hitler, only someone who came from the future 2010 could kill me, but by then Hitler would already be dead. Yes, they could punish me by killing me but Hitler can not come back to life. I did not realize that God was controlling paradox in your theories. You should have been more clear about that as it isn't in any time travel flics that I know of. So he controls all the weird stuff in your theory? That's odd.
Jeff, I don't understand where your temporal immunity originates. By your theory, you can kill Hitler and prevent him from rising to power, but I cannot then kill you and prevent you from killing Hitler. You would have it that the acts of a time traveler can change the past, but they cannot change the acts of another time traveler.
Let me attempt to focus this. If you traveled to the past and stopped Hitler, but I perceived that you "had done" this so I stopped you before you stopped him, that would not undo what you had already done in the past. In that case, it seems to me, if you traveled to the past and killed Hitler, that would not prevent his rise to power, and although he died in 1921, he still lived to lead the Third Reich.
Breaking a causal chain either undoes what flows from it or it does not. If it does, it does so for every causal chain, even those which are temporally non-sequential.
--M. J. Young
No Jeff, you could not be more wrong. Under this theory, that's what would happen. Whatever theory you're using isn't this theory. It's akin to playing Chess under the rules of Monopoly. It doesn't work.
Under this theory, if you went back to kill Hitler, you would then grow up in a world where Hitler never came to power. If Hitler never came to power, how could you know to go back to kill him? If you don't go back to kill him, then he comes to power. So you go back to kill him, so you don't know that he comes to power. It's really simple. Whatever theory you're using isn't this theory, so you are wrong. We're trying to explain this theory to you. This is how this theory works. You're trying to tell us that we're wrong about how this theory works. Well, since this IS how this theory works, we're not wrong.
That's a bit harsh, John.
Jeff, infinity loops do not happen under every theory of time; they happen under a strict causal replacement theory. They are probably the primary reason some reject replacement theory in favor of other models (already discussed in previous articles, q.v.). Under a strict causal chain replacement theory model, infinity loops are inevitable, because the effect requires the cause, and erasing the cause automatically erases the effect, regardless of their relationship it time.
I hope that helps.
--M. J. Young
What do you call the 'self-correcting theory'?, which basically states that if I kill Hitler, someone else will still take over in his place and essentially commit the same crimes killing millions of people. Or, the 'made worse theory' where if I kill Hitler, events turn out much worse like Germany rules the world, which makes me go back and restore events as we now know them. And the 'made better theory' where the changes all lead to some sickly sweet, everything is perfect theory, like McFly and LakeHouse, Kate and Leopold,etc.
Jeff, the short answer is that they are replacement theory variants with irrational elements incorporated; the long answer is more than will fit in a comment field with a one thousand character limit, so I'm going to save your question for a future article looking at each of those variants in detail.
Thanks much for asking, and sorry for putting off the answer like this, but there's only so much I can do via comments.
--M. J. Young
Jeff, I saw a movie many, many moons ago which was exactly what you are talking about. Someone went back to kill Hitler, and when the time traveler returned, he found that one of the Jews who had previously been killed in the Holocaust had grown up to become a dictator which made Hitler look like a pansy. The time traveler had to go back and restore the original time line, as it was the lesser of the two evils. I wish I could remember the name of that movie.
Sorry for getting snappy with you in my other comment, BTW. I keep forgetting, this isn't as obvious to everyone as it is to me.
to a1nut: It's ok to be snappy, it's just that you are not only wrong, you act like an idiot. And your opinion was not requested.
It doesn't have to make sense, as long as I believe it.
It's amusing to see these heated arguments over the "right" and "wrong" of time travel theories. As far as I'm concerned, what is "right" is that time travel, in any way, shape or form, is simply impossible. But where's the fun in that, when it comes to analyzing fictional time travel stories? Can't we be civil here?
I leave you with this:
abyssandapex.com/200710-wikihistory.html
Kane Magus--I believe and hope that time travel will prove to be impossible; it has not yet been excluded from possibility by physicists, as the discussions above temporally displaced wormholes demonstrates. It may be that Clarke's (other) Law applies here, that if an elderly distinguished scientist says something is possible he is certainly right, but if he says it is impossible he is probably wrong. Matter transmission is thought to be impossible because of Heisenberg, but it may be that quantum non-locality will permit an end-run of Heisenberg and make the process possible within the next century or so.
So I'm betting time travel will never be developed, but trying to determine what would happen if it were.
That's what's at issue.
--M. J. Young
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