Is Time Travel Possible?

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Speaker 1: Hi, I'm Daniel and I'm Jrrie, and we're here to explain the universe. Dude came in so late there. Oh, I'm sorry. I travel back in time and get that right. I guess I was out of time. Hi. I'm Daniel and I'm Jrrie, and we're here to explain the universe. I'm Horri. I'm a cartoonist the creator of PhD Comics. And I'm Daniel. I'm a particle physicist, and together were the authors of the book We Have No Idea, which tries to tackle some of the biggest questions of the universe and doesn't answer any of them. That's right. Like, for example, today's topic, which is which movies get time travel? Right? Are there any science fiction movies that actually get time travel scientifically correct? Any that could really plausibly happen given some technology in the future that we could invent. That's the question we're going to tackle today. We went out in the street and we asked people what they thought. What do you think? Here's what people in the street had to say. Do you think time travel is possible? Um? I think theoretically yes, like based on math and everything, but I don't think we as humans will be able to I hope so, but I don't know if it is, because everyone in movies always says you need infinite energy, and I don't think that's possible. Probably. I mean, there's so much out there that we don't know about that I don't think I could really rule it out. What's your favorite time of a movie, Daniel Man, I gotta tell you, I don't think I like any time travel movies. What do you mean you can't enjoy any of them? Right? The problem for me is that when I watched science fiction, I really wanted to make sense. I mean, you can invent whatever rules you want, you come up with your own universe, with your own physics, whatever, but then it has to follow those rules, because if you don't follow the rules, then anything can happen, and then you're not really invested because at any point the plot could just shift and twist and spike, and you know, you could save the universe with crazy glowing bananas or something. So you have to have some rules. What do you think it's it's so appealing about time travel, right, there's so many movies about it books. Why do you think humans love to think about time travel? Or wish they could do it. I think there's a lot of reasons. I think one is just fascination, Like I'd like to go back and see what dinosaurs really look like, or I'd like to know who really killed JFK. Or I'd like to travel to the future and like learn the secrets of the universe that humans will one day reveal. Right, this feeling that we're like trapped in the present. We could travel somewhere else, We could we could see and learn something new. And some of these things are facts, like there is a real story about how the dinosaurs died, or how the moon was made or all this kind of stuff. It really happened, and in some cases the clues for it are just gone. And if you could travel back in time, you could you could learn those things for real. The other big thing is that people wish they could change things they've done in the past. Right, of course, who doesn't try. Yeah, like regret, you have regret about things you did. You wish you could go back and like, um, I don't know, we'd been more bold with a certain person or been more said something differently than before. So that feeling of regret, like oh, I can't go back, that's right, and we're trained like in video games, you know you have another life, or you can save the game and go back and try it again. Right, it's a really tempting idea. Or you remember an argument you had and then you wish you had gone back and said something different, like when you've had time later to come up with a really juicy zinger and you could go back and deliver it and embarrass somebody. We've all fantasized about that. And then in the future, we worry about the future. Right, it's like an unknown that makes us concern, so we somebody's wish we could see what would happen, what's going to happen? Yeah, yeah, Or even steal secrets from the future. Right. Imagine you could go forward in a hundred years, scoop up a bunch of inventions, bring them back, and then you know, get rich and famous. Rights steal steal ideas from from people who haven't even been born yet. Right, it's like almost a victimless crime because the victims are not even yet. Fetus is right, so you could again, but again it's I guess it's also again this idea of um the past and the future being inaccessible to us. Like you said, we're trapped in the present, and the president itself is a weird idea, like what is the present? You know, if you imagine like time is like a line, the president is like a moment an instant along that line. But weirdly, it's not static, right, It's not a place like in space. It like moves forward at one second per secon And we could spend a whole podcast diving into the mysteries and the science of time, and probably we should. We don't have time time today, but I think it's it's worth thinking about what time is so we can understand what aspects of time travel are scientifically problematic, um, so that we're prepared when we dig into all these deeply flawed time travel movies. Yeah, well then that makes sense why there's so many movies and and and stories about it. It's like it's a great fantasy to be able to travel through time. Absolutely, I'd love to be able to do it. I mean, if somebody built a real working time machine, I would be first in line to use it to answer deep questions about the universe and go forwards and backwards and you know, buy different pair of socks and all sorts of stuff. We just wrote down a little sentence here that I think I will help us, uh drive home the point of what time is, which is by saying what time is not? Right? Absolutely, that's a great way to find a long list of what time isn't time, it's not rather berries, I'm clouds. Yeah. Well, but an interesting one we wrote down was time is not like space? Right? What does that mean? Well, we're all fascinated with space, right, And the idea of space travel is fun, and even just in terms of space, like is in your environment, like where you are on Earth. We get in our car, we drive somewhere. We have this agency, right, we can go where we want. We can move forward and backwards, we can move up and down a little bit, we can move side to side. We have this freedom to move in space. And I think that's where this notion of travel comes from. And we'd love to apply that same notion to time. And in fact, it's very scientifically titilating to think of time as a fourth dimension of space. And it's true that in Einstein's relativity he binds time and space together into this one concept called space time. The two things get part of the same kind of space, right, All kinds of all part of the same mathematical construct. It's a four dimensional mathematical construct that has three dimensions of space and one dimension of time. And we kind of wish we could travel through time the way we travel around in space, like skipping around or doing loops or going back to the same spot, but we can't do that with time. It's like it's a one directional and it's always moving forward. That's right. And in any science fiction universe, you're gonna have a theory of physics. You're gonna have some science in that universe, and that theory is going to have time in it. Right. If it's a story where something happens, right, and if it has time and it then it has to have cause and effect, and that's causality. Right, A happens then be if a cause to B, then A have to happen before B. In science fiction, we typically give people free reign to come up with their own new laws of physics and then create a story in that universe. Right, that's the creative element of it. But they have to come up with a consistent set and for it to be consistent, it has to follow causality and causality rules out of time travel, right, So that's basically screwed. That's the big bummer. That's the big bummer then, because everything has to be linked from A to B, B two s by the laws of physics. You can't just kind of jump around, that's right. And you also can't even really avoid it by trying to make little changes. You know. There's this famous story, uh one of the earlier time travel stories. Ray Bradberry think that the story is called the Butterfly Effect. Guy goes back in time and he goes he's like hunting t rex is or something pretty awesome. There's some company and they tell them you can't touch anything but the t rex They find t rexes which were already gonna die, so it doesn't affect anything else in the future. But he accidentally steps on a butterfly and he kills that butterfly, and killing that butterfly has some effect. You know, some lizard which was going to eat that butterfly now doesn't and then dies, and then the thing that was going to eat that lizard dies, and then the thing that was going to eat that right, and then dot dot dot fifty million years later. Who knows how big the effects are. The world is a chaotic system. Any tiny little change that crushing a butterfly could lead to enormous changes, like humans don't evolve, you know, or the world is completely different. So any change to the past can have enormous cataclysmic effects in the future, which might affect the human going back in time in the first place, right exactly. Think about it, like everything that happened in the past is a partial cause of you, because the system is so complicated and interconnected that anything in the past can conceivably play a role in your creation. So if you're the time traveler and you go back and do anything, even just breathe air molecules and warm them up a little bit, you're changing some of the things that caused you. And so then you as a physical object and the science based universe no longer really exist. Right, So it's an immediate paradox. Even if you just go back in time and take a breath, right, and it's like going around molecules that might have somehow is in influence to you being there, that's right. Yeah, Okay, so causing effect is a big bummer. It means that you can't mess around with the ordering of things. You can't miss with logic and that and even small changes will snowball into large effects. I remember now the name of that story is the Sound of Thunder. It's a Ray Bradberry story. It's a really awesome story. Cool alright. So, um, so you're saying time travel is impossible. Now we should clarify time travel backwards backwards, right, That would reorder causing effect. Right, because we're always travling forward, we're always traveling forward to time. That's not a problem. We're all time travelers. We're all time travelers. It's not a very exciting ride, but you're on it. And some, I mean technicate, some could even travel forwards faster than others, right, like if I cop in a spaceship, because with speed of light come back, I traveled uh through time differently than you. That's right. Now that we're done with the bummer part that time travel backwards is not possible, let's talk about the exciting part, which is you're absolutely right time travel forward. There's no thing preventing that. And and you could build a machine, which you know just I mean, it's very simple actually technologically, you just like cryogenics. If I freeze you, the h popsicle stays in place for a million years, as long as we have technology, as long as we have technology to dethaw you and revive you in five million years, then you have traveled forward five million years and the reason will have taken a break popped out in a future time. That's right, Yeah, And I mean there's lots of moral and biological problems with that, but from a physics point of view, you're just stretching cause and effect. You're not breaking it. May if that's later it okay. Yeah. Backwards potentorial backwards is I'm possible, And that's kind of the basis of most fun movies. Right, It's like going back and changing something. And I want to talk about that some more, but first let's take a quick break. So, time travel backwards and possible, that's the basis of most fun movies. And so, um, how do most movies get around is like impossibility of breaking calosality and logic? Yeah, so I think that most movies are just banking on the fact that nobody's really paying super close attention and it's just there for the ride and doesn't care as much as I do about movies being logically they assume most people are not trained physicists. That's right, And I think a lot of science fiction fans probably more relaxed about whether the universe follows its rules. And so if you're willing to break the rules, then you know you can do anything you like. Um, but they at least put up the appearance usually of trying to follow some rules. And so how do they do it? Well? One classic way is the split universe. They say, okay, you go back in time to see your grandfather, for example, and then when you arrive back in time, you split the universe is the original universe in which you didn't go back in time, and this is new universe where you've gone back in time. To talk about timelines, right, yeah, and so you're a product of the original timeline called timeline zero, and that you have inserted yourself into another universe called timeline one. And if you make changes in timeline one, it doesn't affect timeline zero, which is what caused you, what created you, where you came from. That you're freedom uck up timeline one. You can kill your grandfather, for example, and he can be dead, and in timeline one you're never even born. Right. Well, there's a famous scene, that famous scene and Back to the Future where Doc Brown played by Christopher Lloyd explains basically like he whips out of chalkboard and explains time travel to Marty and so he like draws online. It says like, this is the time that you're in and then you travel back in time and you split off a different timeline. Man, that movie has so many problems because, yeah, they try to go in that movie, they try to go for the altar a timeline right right theory, right, But it doesn't even really make sense because in that movie, he has what broken up his parents, so his parents won't get together, so they won't make him right, so he won't exist anymore. So problem number one is if they're in this split timeline theory, then it shouldn't matter. Right, he's in a new timeline, but he's disappearing, you know, just like fading from the photographs and his hand is becoming transparent. Why is that happening If he's from the original and changed timeline, the new timeline can affect the old timeline, Yeah, which in which case you're not really in a split timeline at all. The other. The other thing, this is the thing that really irks me about that whole approach, is that why does he fade slowly? Right? It takes him, like, you know, two hours of movie time for his hand to gradually disappear and then bloated right away. No, if he doesn't exist anymore, then boom, he just doesn't exist. It makes no sense. You're you're killing it. A childhood favorite movie here, it's a great movie. Everybody, I love the movie, Go and watch it. I showed it to my kids. They loved it. But from a time perspective, it just makes no sense. And that's the part that that drives me bonkers. And then like I can imagine you jointed your kids. Okay the movie ended, then you whip out a chalkburn and then launch it to it when I would like your how this movie was bunking? Right? All right? Kids, I hope you enjoyed that it's all wrong. Well, in comparison, let's compare this out to other ways in which other movies have sort of trying to get around this impossibility of time trouble. So what are other ways movies try it? So? Other ways people do it? Is to imagine one consistent universe where you go back in time and then do you change the future, but the future has already been affected by your going back in time, which just like you can't change the future future, well you can't. The past always can change the future. Right, that's the way it works, right, causality A causes B. You change A, it changes B. But in the these stories, they try to make us so that the future comes back to affect the past, and that that past has already even taken new account into the future. So an example of that is the movie like Looper or Primer is sort of similar where the Harry Potter is one of my favorite time termin movies, the third Harry Potters. Have you seen Harry Potter movies. Yeah, he goes back in time and tries to change thing, but it turns out he was there all along. That's right. He was there all along, and that's right. And so they avoid the split universe thing right where it happens one way once then happens another way later, Like that makes any sense for it happen later. We're talking about time travel, right, um, And so in the Harry Potter example, he loops back and he's there there's sort of two of him for a while, right, is the one that's come back to to change this, and the one the original one um, so the A version in the B version UM. And so the way they try to avoid that any inconsistencies there is that the second time through, when he's looped back and he's observing the same events from now, having already seen it once, he somehow feels obligated to follow the rules, right because he could break them. If Harry goes back in time and doesn't save his life, what would happen, Well, we don't know, right, because then he would die, and then he wouldn't be there in the future to come back, and and and he wouldn't be there anymore, right, he would he would blow up the universe. It suddenly wouldn't make sense logically. So if he saves him, if future Harry saves him and then he becomes future Harry and doesn't save himself, is a logically inconsistency. But I mean that's the separate question of like, is there free will in the universe and all that? But you know that I feel like there's a separate conversation. No, that's totally connected because it doesn't cause and effect. Right, we have the freedom. We have the free will to change causes. That's how we have an effect on the future goods. We could launch the whole thing about free will, but like as an idea of like a single timeline in which the future in which the present already took into account, you going back in time. What's wrong with that idea? From a physics point of view, everybody has to play nice, right, so everybody has to agree we're going to follow this dance card and do exactly what we know we have to do to to create the future that we came from. It only works if there's a very tightly constructed loop there where the things you did in the past cause your future self exactly the person who then came back to the past, right, right, If that's happen, well do you said that it's the way you said it has we finally constructed? Right, So writer is really good and finally constructed. Then it's logically consistent, isn't it all? Right? So there's two possibilities. Right, if you believe in free will, this is all bunk because there's no way to control what people do, and people have the options to do whatever they like, including screwing up the future. If you don't believe in free will, if you think that people are just a product of their experiences and their situations, and then there's still a problem. Even if you're a brilliant writer, you're having to solve an enormously chaotic problem, right, which is somehow cause a past, a create a past which exquisitely causes the future, which will then come back and cause that same past. Like even in the Harry Potter example, he can't just decide what he's gonna do. He's got to follow a dance card and to be told exactly what to do, and and other food. Other movies have the same idea. For example, one of my favorites that I mentioned earlier, primer Um. In primer they climb into a box and the box moves them back in time um and then they get out of the box right and they then there's two of them, So there's two of them that that overlap in the same time period. So but before they get in the box, they have to isolate themselves. Because there's two of them at the same time, one of them has to isolate itself so that doesn't interact and doesn't do anything to mess up the future. So the way they've handled it there, as they've said, well, one of them is going to be a good citizen. It's gonna go sit in a basement and not interact, not create any time and problems. Right. And you see this a lot in time travel movies where they say they travel back in time. They say, oh, don't touch that or you can't kiss that girl because you'll cause a problem. Right, But it's impossible because the world is so complicated and so interconnected. As we were saying earlier, anything you do, even just being there, is going to cause these problems. Right over millions of years, though that's more likely, right, Yeah, small changes over millions of years, that's a problem. But you know, maybe like small changes over a couple of hours. Yeah, you're right. If we destroy the universe in a million years, who cares, right, as long as we get to make money in the stock market. Okay, Yeah, I see where you're going. Well, this is a perfect point to take a break. Okay. So that those are two great devices, multiple timelines, one exclusitely constructed, logically consistent timeline in which there's no free will. Are there any other ways that people do time travel. Well, there's a whole other approach which is trying to think of time as a dimension of space, right, And that's sort of the original idea we had earlier, like why can't we move through time the way we moved through space? Can you see this in some movies, for example, very famously an Interstellar I saw this movie. It involves a guy going into a black hole, which has its own problems. We can talk about in another episode, but I have a whole episode just on how Interstellar um has has problems. And Interstellar a great movie. Lots of the physics is correct, but this part of it is is total is total gibberish. He goes inside of a black hole, and inside the black hole he can move through time as if it was space, Like he could say, oh, I'm at this time. I'm gonna walk over to the left by ten feet. That's going to take me back twenty years. He needs like right like this kind of like claytoscope type of reality where like moving sideways moves you sideway backwards and time or something exactly. And he uses that to talk to his daughter and to send her a message and give her the secret physics that a knowledge that means that they can get off the planet, etcetera, ETCETERA. Problem with that is he's moving through time as if it was space, right, So like he's here and then he was there, So they've they've created another dimension of time on top of it. Right, what is moving through time mean? Moving his motion over time? It just doesn't make any sense. And and the reason is that stories have time, right. Stories are a narrative. I'm sitting down, I'm telling you a story by the fire where caveman. There's a narrative. It starts and it finishes. It has to have time through it. So if you're going to create this new idea of time being able to move through time like it was space, you can't tell that story without adding another new dimension of time to it. So an interstellar they create time as if it was a dimension of space. But then they bolt on this new dimension of time without telling extra which doesn't make extra time moving a time time. Well, it's interesting that we can't like, uh, And that's kind of the magic of movies, right, is that you can make fantasies and story and books and stories can like violate the laws of physics. And still senhow come up with a fun story? Yeah? Absolutely absolutely, and and you know that that's part of that movie is forgiven. I personally liked Interstill a lot. I thought it was a lot of fun. I rolled my eyes and grin and did that one scene, you know, but I like get the theater and he was like, you're like grown. I try to grow quietly and I save it for this, I save it for talking to you or he that resentment. Remember, I remember I went to see Contact. Remember the movie Contact, of course, one of my favorite movies of all time. It's about this woman who receives a signal from space and she it's her search for like what the meaning of life? And it's a main using movie, really great where the scientist is the hero, right right people scientists not a bad sign, just not a mad sign, just not a selfie crazy selfish crazy scientists, but the hero. Yeah, awesome movie. Go see if Robert Semeg has directed it. But I happened to go to see that movie when it first came out. With a bunch of signal processing PhD s, like four of them. These are like Stanford PhDs and like signal, and they came out and I was like, that was amazing, and they were just laughing at like all the ways they try to boost the signal or like let's invert the phase whatever, and they thought that was all bonkers. It's probably like going to see It's like probably probably like watching you know cs I with a bunch of actual friends and scientists like enhanced that image, you know. So, But I try to be a good citizen in the movie theater, I grown internally and I'm trying to to spoil everybody else's experience. You keep it in, bottle it up U. Another one in that same category is the movie Arrival, which is based on a short story called The Story of Your Life. And it's a nice story. Yeah, it's it's very well written. It's beautifully written. Um, and it has the same idea. Aliens come, and these aliens have a different perception of time. They can move through time as if it was a dimension of space. And the cool thing is that the author has thought about what would that mean for their language. So in the short story at least and a little bit in a movie, it changes the linguistics of the aliens, which makes it hard initially for humans to figure out what they're doing because they write their sentences all at once, not like we're starting now and I'm ending there. They have this different kind of language where they I think it is that the consciousness of the aliens are spread through time like it like like their brains are spread through space, their consciousness is spread through time, and so they can reference facts from the future and from the present and from the past. Um. And that's cool. But that the canstality thing, right, like their consciousness in the future can't possibly affect the consciousness in the past. Right, there's that problem. But I don't even have to get into that to take a part that movie, which is they have this nice idea, but they don't even really follow through because, for example, the aliens have a conversation with us back and forth. I say this, you say that, I say this, You say that. A conversation has time in it, right, So if they were going to be consistent about it, then there should just be one blob of a conversation. Here's everything I'm going to ever say to you all at once, right, there shouldn't be any back and forth in their linguistic structure at all. The talk you down to us. So that was the problem, right, They needed to find out how to talk down to us humans who only got it literally forwards. Yeah, we're too stupid to understand their language, right, or were too stupid to find the potholes in the story. It's the same idea that they want to liberate us from time, because that's a really appealing idea. But they need to tell a story, and in the story, time has to move forward. There has to be dramatic elements and something that we can't really affect something in the past, like you can't reverse right. All right, well, I think we're out of time. Daniel. Let's time travel back to the beginning this podcast. You do it all over again and start over. How do you know he didn't? Maybe we did this time? Yeah, yeah, the second thing. We went back and we made this podcast so funny. You should have seen the first time we have recorded with and the first time we listened to this podcast. Oh my god, you're groaning out loud like Daniel in the theater. Do you have a question you wish we would cover. Send it to us. We'd love to hear from you. You can find us on Facebook, Twitter, and Instagram at Daniel and Jorge One word or email us to feedback at Daniel and Jorge dot com.