Time Loops Are Impossible
0:01 [Applause] [Music] [Applause]
When it comes to time travel, there's generally two types of people: the dreamers that want to argue that there's many, multiple timelines and universes and dimensions, and that going back in time and changing something changes the timeline and skews it away so that you can get many different paradoxes and alternate futures and a bunch of, you know, crazy [ __ ] like that. Then there's the pragmatist that got burned out arguing about all that, and they say, "Well, there's probably only one timeline, and if anyone went to the past, they probably were in the past to begin with. So when they end up going to the past, they actually just helped create the future that they came from."
And that's not right either. It seems like the logical, consistent solution into time-travel: the past can't be changed, and if you try to change it, you just end up creating the future you wanted to avoid. And that's cool, but it doesn't really make much sense. The Greeks tried to explain it away through the gods, and they essentially came to the conclusion
1:01 that the gods don't like you too bad so don't bother trying that was the moral of Sophocles play Oedipus Rex Oedipus was told by a fortune teller that he would [ __ ] his mom and kill his dad and then he went did it despite his parents taking precautions to avoid it the gods wrote it in his fate there was nothing that could be done to stop it but it's still a loop the events wouldn't have taken place had the fortune tellers in this story not told people about the events that would happen there's no causality either it's just the way things are because the gods willed them that way and it's a kind of naive way to look at the world there are two kinds of things that really exist possible things that are caused by other things and necessary things that are their own cause the idea has its origins in the Middle Eastern philosopher --boom Sinha and it leads us to think of time like a set of dominoes neat clean causality Oedipus Rex says no time is just what the gods want it to be like a giant hand that can just smash the dominoes any which way it wants thankfully neasha killed the gods for us so we
2:01 don't have them intervening on our behalf anymore but now that leaves us with a serious question can a time loop like that even exist according to modern-day fatalists yes so if it does just sit back and watch your life crumble because you don't really have a shot of fixing it and that's pretty much how things go in 12 monkeys after seeing his future self while he was a child James Cole goes back in time and eventually dies thus causing the vision that he saw as a child he sent back in time to help find a cure for a plague that wipes out most of humanity but in doing so is pretty much one of the causes of the plague itself but by that point he doesn't even care he's [ __ ] going to the Florida Keys with a woman he kidnapped he just gives up but regardless as Cole's going back in time he inevitably causes specific events of the future to take place [Music] there's a phone call he needs to make to tell the future about his findings and he eventually tells that woman he kidnapped dr. Railly about the call and
3:02 she's the one who makes it earlier in the film we heard that very call this kind of fatalistic logic means that the past present and future don't exist because any moment has to be some past and some future to some other moment Cole causes the call causing Cole to go back in time and cause the call there is no cause and in the East they represent that idea through what's called endures net so in Buddhism it is taught that everything in this universe depends on everything else that we have a kind of a huge Network and this is called the doctrine of mutual interdependence all of it hangs on you and you hang on all of it and this is conveyed in a symbol which is called indras net imagine a multi-dimensional spider's web in the early morning covered with dew drops and every dew drop contains the reflection of all the other dew drops and in each reflected dew drop the reflections of all the other dew drops in that reflection and so ad infinitum
4:03 The doctrine holds that cause and effect are mere fabrications, productions of the ego's presumed separateness from all other things or, in other words, time is light. But that's kind of a cop-out excuse of an answer.
For something better, we need to look at possible and necessary things again, but not in the way that medievals looked at him. Today, in metaphysics, we say a thing is possible when we can speculate about some theoretical world where it doesn't exist. Garfield is a possible thing because we can conceive of a world where Garfield, thankfully, does not exist. But a necessary thing is a thing whose non-existence would create a world so different from ours that we say its existence must be in every possible world. Numbers, for example — not their representations in text, but rather countable quantities — are likely to be necessary things.
Saul Kripke came up with most of that when he was still in high school, and he condensed a lot of it into a simple logical axiom, and
5:04 essentially all it means is that if you have two things and their relationship is necessary (indicated by that arrow), then both things need to be necessary. So if I have a mug and I drop it, and we say that it is a necessary relationship, the mug then had to be necessary, and the drop had to be necessary.
And this is typically the way we conceive of these time loops: they have to happen. We can't think of a world like the ones in fiction without assuming that this time loop exists, because without the time loop in 12 Monkeys, there is no virus, no time travel, nothing that makes that possible world what it is. And yet, there is no time loop in our world. There's no James Cole in our world. None of the characters exists in our world, so what gives?
If we say that C is Cole's going back in time and E is his younger self viewing his death, Crypt Keys' axiom means that both things could not have failed to happen. But in the movie, there are times when Cole realizes that what he's doing is leading to that vision he had
6:05 when he was a kid and in that way C and E are converging on the same event Cole's going back in time is the thing that his younger self sees and this vision is Cole's going back in time and if C equals E then this reverse statement is true to which like we said means the time loop has to exist everywhere and can't be changed but it doesn't exist everywhere believe it or not you can't prove Cole's going back in time caused himself to see his death you can't prove that he caused the virus and you can't prove that he caused the phone call either you can't prove with pure logic that anything caused anything else if I drop my mug and it falls we don't know that it's because I dropped it maybe it just got heavier at that moment maybe magnets grow in the ground we assume that those things don't happen because ten times out of ten they don't the mug just falls but someone who hasn't seen that like a baby they don't know that and they're pretty amazed when things happen around them for that reason it's an idea that comes to us from David Hume and because of it two events can't be one in the same because
7:06 one event can't logically lead from another. This statement then, regardless of necessity, is a logical considering cause and effect, but that's also kind of a cop-out. You can't have a time loop because you can't logically know causes? I mean, if I drop my mug and see it, I can be pretty sure I dropped it. If we see James Cole go back in time, we can see the things he does, even if some of them don't really make sense.
Another issue with this statement is the arrow called the material implication. It's not meant to describe causes, because all it takes for it to be true is for E not to be false. So if we say C equals me dropping my mug and we say E is the grass is green, then the statement means, "If I drop my mug, then the grass is green." Yeah, they're both true statements: I did drop my mug, the grass is green, so technically "if C, then E" is true, but that doesn't make sense causally.
If we make use of possible worlds to explain causes, we get something a bit more logical. Let's go back to me dropping my mug. I drop it; it falls. We could say that my letting go of
8:08 it maximize the probability that it would drop it maximized the number of possible worlds where it did drop me dropping my mug doesn't maximize the number of possible worlds where the grass is brain the two are completely independent things where as as soon as I let go of my mug it does begin to fall we can see that it is falling so it's possibility is likely 100% because it fell the theory was proposed in the book the facts of causation and it makes use of this symbol to indicate the idea of cause it also says that event probabilities need to be independent in 12 monkeys there are times when Cole seemingly goes along with the time loop for no reason at all he's seen the moment where he's shot and he knows he's going to wear a Hawaiian shirt but when Raley picks it out he just stands there he could say no he could say he won't go to the Airport but he doesn't he just goes along with it and while he might be inclined to say oh the future already happened so he has to go along with it there's nothing he can do that's not
9:08 true it's a logical fallacy called affirming the consequent and going back to my mug once again say that if I drop it it falls now let's just say it Falls we can't go back and say therefore I dropped it because we don't know if I dropped it we know that it falls it could have been knocked off my desk as she should be on my head we don't know the same applies to the future and the present given some present we can't go back and say they're for the future it's a fallacy so events in the present don't have to lead to the future coal doesn't have to agree to go to the airport doesn't have to agree to put on this [ __ ] wig but he does in the movie predestination the exact same logic applies but it takes place so frequently that it becomes absurd again spoilers here in 12 monkeys Cole kind of exists outside of the time loop he's born to regular parents and lives a regular life up until the point he's sent back in time but in predestination that's not how it works at all our main character Jane physically cannot exist without
10:10 time-travel and the time loop that is her life she is at different points in her life a woman and a man so she falls in love with herself and gets pregnant with herself in her womb so she then can give birth to herself but then in the future she as a guy kidnaps herself and sends her back in time as an orphan so all that can happen in the first place but then she again has a guy needs to stop her future self from bombing New York eventually leading to her him killing herself himself it is probably one of the most complex time loops in the entirety of fiction and because we can't affirm consequence and must have independent probabilities it all falls apart Jane doesn't need to fall in love with her future self and her future self doesn't need to get her pregnant she doesn't need to give birth even though it is the 1940s and she doesn't need to transition into becoming a guy the exact way she does she as a guy doesn't need to choose to go back in time and then doesn't need to choose to return to the future he doesn't need
11:10 to stop the bomber, and he doesn't need to kill himself. It's all only probable. The same is true for 12 Monkeys, Harry Potter, and to some extent, Primer.
Many of us want to think that time is set in stone and that fate determines our future, while while many others of us just want to think that anything can happen at any time. But when it comes to time travel, there's generally two types of people: the dreamers that want to argue that there's many, multiple timelines and universes and dimensions, and that going back in time and changing something changes the timeline and skew... [Applause] [Music] [Applause] [Music]
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