How does relativity affect our perception of time?

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Speaker 1: Ay, Daniel, what's the most mind blowing thing that physics has taught us about the universe? Wow? It is hard to pick just one. Could I do a top five? Maybe? No? I want your single all time one thing that you think is the most bonkers that we've learned about Who had to challenge? All Right? I got one. There is one thing about the universe that, to me is the most brain scrambling thing I've ever learned. The hardest thing for me to get my brain around is that people can disagree about the order in which events happened. We don't all see the same things happening sometimes in the universe. Yeah, you can see things happening in one order, and then I can see things happening in a totally different order, and we can both be correct. Hi'm poor hammade cartoonists and the creator of PhD Commics. Hi. I'm Daniel. I'm a particle physicist, sometimes in a podcast host other times, and everybody disagrees about when I do what. Welcome to our podcast. Daniel and Jorge agree to disagree about the universe, in which we explained to you the craziest, the most amazing but true things about our universe. Yeah, and this is again a production of I Heart Radio, and in our podcast we try to take you to the forefront of science to talk about the craziest things that scientists are thinking about today, and also delve into the history of science to tell you why we think the universe is so nuts and how we figured that out. Is there a history of science, Daniel, or is that also open for this agreement people disagree about in what order we discover things, or what was the most important, or how we change people's minds. Yeah. I think in our podcast we also not just talk about scientific discoveries or scientific theories, but also a little bit about how that affects how we see the universe, you know, and how it challenges what we believe about how the universe works. Yeah. Absolutely. I think a lot of the deepest questions in physics come from a sort of a philosophical motivation. We want to know how the universe works because it matters to us that we can make sense of the universe. And when we ask the universe questions and it gives us answers that force us to totally change the way we think about the universe. That has pretty deep philosophical implications, and so that's sometimes the most fun topic. Yeah, And so basically, we're just trying to blow your mind in the gentlest, most podcasts friendly way possible. Or we're trying to share with you how the minds of physics this have been blown, and we want your mind to be blown just as much. But yeah, a little bit more gently. Yes, please, I'm not sure my brain can handle this much mind blowing is in in one hour. But you know, when I was learning physics as an undergrad, I remember these moments when I finally really deeply understood a concept, and that concept would force me to relax or destroy or get rid of some assumption I had about the universe, and I realized that that just wasn't true, that the way I'd been thinking about the world was just fundamentally wrong. Yeah, it's amazing. And so today we'll be talking about one such topic that honestly gives me a headache every time we talked about it, Daniel. We've written about it in actually a couple of chapters in our book We Have No Idea, A Guide to the Unknown Universe, And I have to admit I never really got my head around it. I authored the book, but didn't actually understood what was in it. Yeah, and this is a topic that people email us about, they ask us about, they listen to some of our podcasts about it, and still right in with questions. I think there's a lot of popular misconceptions about how this works and some consequences that I think a lot of people have not really realized. There's some really deep philosophical implications to these ideas that I don't think have been widely enough appreciated. Yeah, So to the on the podcast, we'll be talking about how does relativity affect our understanding of time? Time? Or I guess the short title is is there a consistent order of events in the universe? Yeah, and spoiler alert, the answer might be it's relatively surprising that the answer is not what you expect. We've talked to this podcast before about time dilation, the effect of speed on the rate of which clocks move forward, and that's weird and that's hard for people to get their mind around, and there's some misconceptions there. But you know, time and relativity is even weirder than that. It's more than just making things run slowly or making things run quickly. It's about how things happen here versus how things happen there. Do you think age also affects how you perceive time? Like I feel like my kids, I have no patients at all, and that the world just moves at a snail's pace for them, whereas for me, as I get older, things he's moved fast. Well, I mean I moved slower, but the world seems to move fast. Yeah, And I think that Actually you raise an interesting point, because we are all imperfect observers if you just sort of watch something and describe it later. There's all these studies about how people give terrible accounts, you know, even eyewitnesses give different accounts of the same events, And so that's certainly one problem. It's like people are unreliable observers. But even in the case when everybody was a perfect observer, everybody had a video camera, I've already had, you know, perfect measuring devices, and everybody accounted for transmission of light and all that stuff. Even in those cases, it's hard to make sense of the universe. Like if we were all robots but the exact same you know, clock in our chips, and we were all measuring things exactly, we it would still be kind of a weird universe where not everyone would agree maybe on the order of events, Yeah, precisely. And you have to separate those because we're interested not in the question of our people good eyewitnesses, because we already know the answer to that is no um, but the question of how does the universe actually work, because we want to know the answer to the question, not just for humanity, but in general, you know, the deep fundamental questions, so that when the aliens come, when we talk to them about physics, we can make sense of what they've learned. And we don't want to learn human physics, we want to learn fundamental physics. And so this idea of time dilation, this idea that time move slowly depending on maybe how fast you're going or or where you are, is kind of weird and pretty mind blowing. And so we were wondering out there how many people really sort of understood what it means and what the ramification, what it means for our basic understanding of time. So I walked around campus that use the irvine, and I asked folks, not people in the physics department, not people who have taken my class on special relativity, just random people on campus, willing to answer questions from a scrafty looking physicist. So I think for a moment, what do you know about how relativity affects our understanding of time? Here's what people had to say. Do you know how relativity affects our understanding of time? No? I do not. Actually, no, I'm not share Newton's theory of relativity. I'm sorry, I don't. Is this physics like a physics question, I'm not. I don't know much about physics. Okay, I don't know how to answer that. I'm an English Ready, if there was a whole like demonstration of that, where if like you go at like in a spaceship, like near the speed of light or something, and then you can come back and then like some amount of time has changed on Earth while like no, really time has changed for you or somewhere about and thinking Planet of the Apes when they're in the spaceship and then by the time they come back, they've only aged a couple of years, but timeline Earth has passed a lot because they're traveling at a different speed. Remain Planet Apes is a well known physics documentary. Right, yes, yes, I believe relativity. That's from Einstein is the idea that like time doesn't flow at the same rate like across the universe. I think something like I think gravity or something affects like how it flows in other places. All Right, a couple of knows, but a couple of people did have a lot of pretty good ideas, or at least they said a lot of physics terms. And I mean like Newton's theory of relativity, like the Planet of the Apes. You know, I've seen that movie. Yeah, Planet of the Apes. That's a that's a documentary about physics. Yeah, there you go. Now, you're right. People had the people who knew anything about it definitely knew that relativity and time connected and that relativity changes have time moves. And I think already that's a big success, right, the idea that time is not universal, that we don't have clocks everywhere in the universe ticking forward at the same rate. That's a big step forward to to break that assumption. You don't think you didn't have a theory of relativity. I mean he could have had one about his relatives or something, but just not not the one that caught up right. His theory relativity was don't bring up politics at Christmas dinner. Yeah, also also useful things to live by. But yeah, I think it seems like maybe there is a general sense right that relativity effects our understanding of time and makes things weird, but maybe a lot of people don't know how or what. Yeah. And I think also there's a lot of misunderstandings based on the emails that we get from listeners who are asking us questions about relativity and tweets and stuff that people have posted. I have the feeling that people think that if you move fast and your clock will slow down, which is not the right way to think about time and relativity. That's how I thought time and relativity works. So we're in for a long conversation. So, um, so people have been writing with questions about time. Yeah, a lot of people ask the questions like what is it like to be a photon? Or how does a photon move at the speed of light? If moving at the speed of light means that it's time is frozen, they're asking what would be the human experience of moving at these velocities where physics gets really weird. Yeah, and so let's clear that up. First of all, the key thing to understand about relativity and time and clocks. Is that the speed at which o'clock moves depends on its relative velocity to you. Now, these things are always relative. So if you're holding a clock and it's not moving relative to you, it's just going to go forward at one second per second. Like you always experience time the same way because you're not moving relative to yourself. Right, it's all the relative motion that distorts time. If you see a clock moving fast, and you're watching the face of that clock, then it runs slowly, but only according to you. I think maybe we need to step back a little bit paint the picture of Like I'm standing here and I'm holding a clock in front of me. You're saying that because the clock is not moving relative to me, I'm not going to see or feel anything strange about that. That's right. Like it's it's gonna I'm gonna hear it ticking, and I'm gonna it's gonna sound like it's taking at one second. That's right. And you always experience time the same way, Like you don't experience time going slowly or going quickly. But if I'm zipping past you at half the speed of light and I look at your clock, that it looks to me like your clock is running slowly. Now, according to you, the clock is not moving. You're holding it, so the clock runs at the normal pace one second per second like usual. You don't experience time slowing down just because I'm moving past you and I see your time slowing down. But again, if i'm is it being passed you at half the speed of light, then it looks to me like your clock is running slowly. Well, first of all, how would you look at my clock if you were moving back? Remember would you have time? Daniel? Really, I'm super robot observer. Remember I can observe anything accurately. Oh, I see you're running at a basilian giga hurt. I am super physics scratched. No, you have to imagine I have like some awesome telescope and I'm watching the face of your clock or something. All right, So I'm in my little space here and I have my clock, and it's taking away and you're zooming bye. And as you're zooming by, we're going to go into super matrix slow motion and you'r and so you're looking at my clock, and my clock is moving relative to you like you're seeing it go by. And if you were to measure its ticks you, it would to you it would seem like it's ticking slower like tick take right, is that kind of what you mean by that? My clock seems slower to you precisely, and your clock seems slow to me, But it doesn't seem slow to you. Right, It looks to me like you are aging slowly because your time is running slowly. In a year, for me, less time will have passed for you, and I will see you aging slowly. But for you time just moves forward because again, you're not moving relative to you. The thing to remember is moving clocks run slowly, so you're not moving relative to yourself, So your clock doesn't run anymore slowly, but they only move slowly relative to the person who's not moving. Yeah, everybody has a frame of reference that's centered at them, and things are moving or not moving in their frame. And if they're moving fast, then their clocks run slowly. If they're not moving, then their clocks run normally, all right, And that's that's basic general relativity is that time seems to slow down in a pocket of space that's moving fast relative to you. So that's special relativity or relativity has to do with how space is bent by mass. Special relativity is all these effects of light speed and clocks and stuff. And it's not just that it appears to go slowly, like your time really does move slowly according to me. And that's the crux is that I have a story about the universe that I'm telling based on my perfect observations, and that's a true story. And you're telling a different story about the order in which things happened, in the rate at which time flowed, and that's your story. And your story is different because you're in a different place and moving in a different speed relative to me. But both our stories can be correct, meaning, um, I can experience my clock taking it one second per second, but you would say that my clock is not taking it one second per second precisely. And it's not just that it appears that way, it actually is. I guess it depends on what the deffer nition of is. Thank you, Bill. And so you know a lot of people write in they say things like, you know, a photon is moving at the speed of light, which is true. And if a photon had a clock on it, somehow, I don't know how you could have a photon with a clock on it. But imagine you could then wouldn't that clock be frozen? Yes? True, because something moving at the speed of light, it's time slows down to an effective rate of zero. But that doesn't mean that photon is not experiencing time. It's experiencing time maybe normally, but by the time it blinks, it's made it across the whole length of the universe. Yeah, because from the point of view the photon, I guess the whole universe is moving past it at the speed of light, and so the whole universe is like length contracted down to zero. We'll have to do a whole other episode about the effect of relativity on length and distances and crazy stuff like that. But the idea is that moving clocks runs slowly. That's the thing to keep in mind, because all these statements have to be made in a relative sense. You can't say I'm moving really fast, and therefore my clock has run slowly. You have to say I'm moving with fast relative to what. And it's for that observer that your clock is running slowly, not for you, right, Because I'm sitting here in my pocket of space and I'm watching you sit by and if I look at your clock, I would say that your clock is moving slowly, and you would be correct. And I would look at your clock and say your clock is moving slowly and I would be correct. Well, it would be a really short conversation. Then if you're moving past, have dispeeded, like, hey, that well he's gone already, forget it. If this podcast was in stereo, we could do some cool effects. They're resooming back and forth. Make it happen, engineers, you started to treat engineers the same way I have now. Just engineers are just people out there to make things happen. I think people who make things happen are awesome. By the way, my caveat to day engineers. All right, So that's that's special relativity. That's the general idea that, uh, time seems to move totally depending on how fast you're going relative to other people who might be watching your clock. Yeah, I would say time moves slowly for people that are moving fast relative to you. I think that's pretty close to what it's just said. I'm sure it's not. We can disagree on that, all right. So that's special relativity, and it's it creates a weird situation for arguments about what happened and in what order things happen, and just in general um about time and in the universe. So let's get into that, but first let's take a quick break, all right, Daniel, Let's maybe get into the details here of how time or how special relativity messes with our understanding of time. So what what's them? Are we going to paint a picture for people? Are are were gonn to be on trains on rockets? Or Alice and Bob going to be involved? Or yeah, let's let's mix it up a little bit, because usually special relativity is like people on trains, because when they invented special relativity, trains are like the fastest thing around. But that's old and usually quantum mechanics thought experiments involved two experimenters named Alice and Bob. But let's pick it up. Let's use Alice and Bob for a special relativity thought experiment. Let's use Alicia Andrew berta perfect though, just to mix it up, all right, So if um, Alicia and Roberto are having a race, say, it's like some family events right there there with their relatives, so it's all about relativity and they've all had their you know, Christmas Ham or whatever, and now they're going to go out and make an ill advised hundred yard dash in the backyard. And they're both really fast, and people are watching the race, and then afterwards, of course they're going to argue about who one. But let's say that everybody who's watching the race is a perfect observer. Everybody has um a clock that they can start and stop, and everybody's really paying attention and knows what they're doing. Then the question is who wins the race? So they're both at the starting line, you know, we said go, they start running towards the finish line, and I'm sitting there at the finish line waiting to see who gets there first, precisely and all right. The amazing thing is that there is no one, single correct answer for who wins this race. Now, if you're sitting at the finish line, and my money is on Alicia, to be honest, you've always liked her more than Roberto, and frankly, Roberto is pissed about it. Well, she's my cousin, So it's Roberto, man, what's wrong with you? Anyway? Um, if you are sitting at the finish line, so you have um no velocity relative to the ground. Then you might see Alice. You might see Alicia beat Roberto in the race. Cool, and might think, well, that's it, that's the answer, right, she won time to celebrate. So so I'm sitting in a chair by the finish line, and to me, Alicia was running faster than Bob, so she got to the finish line first, precisely, And you might think, well, that's it, right. Other people might see from another angle, or other people might be sitting somewhere differently, or you know, maybe even if somebody is driving by in a car, they might see the velocity of Alicia and Roberto be different. But everybody should agree about the basic facts because there's a single thing that happened. That's the way you grew up thinking about the universe. That's what sort of makes intuitive sense to you. It's true, right, Like if there's somebody sitting on the opposite side of the finish line, sitting in a chair as well, you're saying that they could also see a different result, even if they're not moving like me. Actually, the other observer would have to have a different velocity and you not just be separated in distance. But you're right, The order of events that you see depends on two things. Your location relative to Alicia and Roberto and your speed relative to them. So if you are in a to make it simple, if you are in a car, and your car is super fast and you're going at like half the speed of light or something, then you could see the race differently and you could see you have a different outcome. You could see Roberto cross the finish line before Alicia. This is not some trick where like the life from you takes longer to get there or anything like that. But if you have a different relative distance to Alicia and Roberto, and you're moving at a certain velocity, then you can actually see the events happen in a different order. I am sitting in my chair, I'm going to measure who wins. But if you're moving, driving by at really fast velocities, you might see something totally different than what I see. Yeah, I could see Roberto across the finish line before Alicia, and I would also be right. But do you have to drive towards them perpendicular to them? You know what I mean? Like what's actually happening there to make you see something different? Now, let's imagine It's pretty simple. Let's say I'm moving in the same direction as Alicia and Roberto. Right, you started way before them and or way back, and by the time they cross the finish line, you're crossing the finish line too, but you're going really fast. Right, I started on the moon or something like that, so that I'm passing the race at exactly the same moment that Alicia and Roberto are actually running, so that I'm parallel with them but moving at some very high velocity. Then I can see the order of events differently. I can see the race start, and then I can see Roberto finish the race before Alicia. Even if you sitting on your plastic chair eating leftovers while you're watching sees Alicia passed the finish line first. Yeah, no, I understand that what is maybe happening, But I guess I'm trying to just understand maybe for the people listening to this is why, like, is there any way that we can understand with this example, like how special relativity makes it so that we see different things? Well, special relativity tells you that the flow of time is dependent on velocity, right, and also on distance, So the way the clocks work depends on how far away they are and how fast they are moving. So we talked earlier about how the speed that a clock will move depends on how far how fast it's moving relative to you. That's true, but there's another factor we didn't get into, which is that it also depends on where the clocks are. And so if you see two clocks moving at the same speed relative to you, but there's a distance between them, then you see a different effect on the two clocks. It's not just dependent on the velocity, it's also dependent on the distance to the clocks. Because fundamentally, what's happening is that the universe has sort of like a clock at every location and those and the way those clocks flow depends on your velocity rel tipped to them. Okay, so now you're talking about like a third person. The key thing is this separation between Roberto and Alicia. If Roberto and Alicia are like literally on top of each other, then you don't get this effect. But if there's a gap between that's a different that's a different picture there that that doesn't happen in family gatherings. But if there's a gap between them, right, if there's a their meter apart, five ms apart or something. Then their clocks are going to run differently. But how does that affect who I see getting to the finish line first? Like, like, it shouldn't mattered to me that their clocks are running slower. How does that affect how I see them and how you would see? Well, if you see if you see Alicia's clock running more slowly than Roberto's, then she's got not going to be running as fast. I only know that they're clocks are running slower because they're moving relative to me. So how why imagine that there's a clock floating in space next to Alicia and Roberto? Right, So some drone robot clock that hangs out right next to them, and it can perfectly synchronize it's motion and location relative to them to which one one for each of them. Then you would see Alicia's clock running at a different rate than you see Roberto's clock, because not only do they have a velocity relative to you, but there's a distance between them. You have a different location, and so the way at which time flows depends not just on your relative velocity but also where you are relative to that observer. All right, So you're saying that I'm going to measure. I might measure Alicia or Roberto winning sitting by the finish line, but as somebody else you on your car, running towards the race at an at an angle maybe, or going at a certain speed closest speed of light, you might see something different than what I see. Precisely, if you are sitting there and you have no velocity relative to the ground, maybe you see them tie because they've been training forever and they've been working on this, and they're both really really fast. But then if I am zipping past in a car or moving really fast, then I could see Alicia reached the finish line before Bob. Reach is the finish line. And you know, it's tricky when you're thinking about special relativity. It's really easy to get yourself confused. But the most the cleanest way to think about it is in terms of events and when those events happen. And so you see Alicia reached the finish line before Roberto. Now you might think, how is that possible, Like they're running at the same speed. Well, you know, it's there's also a question of did you see them leave the starting point at the same moment? Right, because if you're moving at a high speed relative to the race, then time is distorted for you, your your view of their time is distorted. So you're saying that it has to do a little bit with the idea that time for Alicia and Roberta are going to be moving differently relative to me and to you, and so that's going to affect kind of how what we see who we see crossing the line. First, precisely, if you are sitting there in a plastic chair, finishing your dinner and watching Alicia and Roberto across the finish line at the same moment, and you see their clocks moving at the same speed, and you see them also starting their race at the same moment, right, I think maybe that's the key insight, whereas you maybe saw them start at different times. Yeah, I see Roberto win, but might also look to me like Roberto cheated, like he left the starting point at a different moment. Right. This concept of simultaneity of things happening at the same moment depends on your relative speed to those events and your distance from them. So like in the Jorge Olympics Backyard Olympics um, Alicia would win, but in the Daniel moving at the really in a really fast car Olympics, somebody else, not only would they, somebody else would win, but somebody else would have cheated. Yeah, but you know, according to me, they've cheated it. According to you they haven't. And then we have a third cousin, you know, um, and she is driving her even faster car the other direction, right than that, different religio velocity can cause a different distortion of how time works from her perspective, and she could see Alicia totally blow Roberto away instead of just winning by little bit. Well, I think at the end of the day, you know, you're going to be by the time they finished, you're going to be, you know, hundreds of thousands of miles away, And so who cares? What do you think? And if you think they cheated, it's how I would put it. Whereas I'm right there with the metals ready to hand them out, you know, precisely, yea. So in the end, your point of view is most important because you're handing out the trophies. But the point is that the folks in the car driving past on high speeds, they see different order of events, and they're not wrong. It's not like they messed it. Up because they're moving fast, or it took light more time to get to them, or any sort of trick like that. If we're assuming perfect robotic observers, they just see the order of events differently because time is moving differently according to them, and their account doesn't have to be wrong. It's just different, just like the astronaut or the or just like the photon. It's not like the photon is wrong. It's just that they experience things differently because they're moving at a different speed. Right, And you know, we as humans grew up in a world where things move pretty slowly, and so we can in the end reconcile usually a single series of events like this happened, then that happened, then this other thing happened. And sometimes it's hard to disentangle people's emotions and they're bad eyewitnesses. But you know, if we had video cameras that everybody's location, usually we can disentangle this stuff. But as you get next to the speed of light, as you get things moving really quickly, then that breaks down and time flows differently in such a way that it could actually change this order, which means that people have a different account of what happened first, and what happened second? And I remember the moment in my you know, junior special relativity class when I learned this. It just blew my mind that there's not like a universally agreed upon order of events for stuff happening. But mostly we would be all right, we would be or I don't, I don't want to say disagreeing, but we would be seeing different things. But that usually sort of happens more prominently when you get closer to the speed of light. Yeah, you can't notice these effects at slow speeds, even for the Examp Bowl of Alicia Roberto. If they're running at fairly low speeds, you know, ten per second, which actually pretty fast, and they're running only a hundred you'd have to be going really fast to change the order of events by even nano seconds. So these effects are very small unless you're approaching the speed of light. Yeah, okay, Yeah, it's not like Roberto can argue that he should have gone in the metal, because the likelihood that there's an observer going to near the speed of light near my backyard is um maybe not zero, but unlikely. Well, it depends on who's listening to his argument. I might be more sympathetic to it. I might be like, you know, you're right, Roberto, there is some universe in which you did win this and you were jilted from getting the metal. Yeah, but really you would be like, yes, Robert, but I think you're and then you'd be gone. Daniel thinks you won and he's your medal, but he's now by Alpha centauri, so you're out of yea, So so go catch up if you want your your metal. All right, that's pretty mine, bend sing um that so many things can be happening in my in my backyard, or that I have new cousins called Alicia and Roberto. But let's talk about now whether you know how that makes any sense or how physicists are able to wrap their heads around these kinds of things. But first let's take a quick break, all right, Daniel, So according to physics, my backyard Olympics are totally arbitrary, meaning that to me they the outcome might be one thing, but to you, moving at close to the speed of light, the outcome might be different. And you're saying that this really throws into question this idea of simultaneity in the universe, Like things happening at the same time, because things happening at the same time might depend on who's measuring whether they happen at the same time. And it's a kind of thing that we have to do in physics all the time, is we think the universe works a certain way, and then the universe shows us the Nope, it doesn't, and that momentarily throws us for a loop thing. What you know, um, you could do the same experiment twice and get different outcomes because quantum mechanics is really probabilistic, or you know, time doesn't work the same way for everybody. But we don't give it up. We don't say the universe therefore makes no sense. What we do is we sort of retreat to a looser sense of what sense means. We said, all right, we can't make those assumptions. What assumptions can we make? What can we say about the universe, and we find another way for it to make sense. They sort of don't make sense in the sort of like Newtonian you know, high school physics or you know what we learned as babies how the world works. It doesn't make sense in that way, just like maybe quantum mechanics doesn't make sense to us, but it does make sense if you sort of expand and you understand the sort of the equations that are happening. Yeah, Like in quantum mechanics, you can't say that the universe is deterministic. You can't say that if you do, if you shoot an electron at the same atom in exactly the same way, you'll get the same outcome every time. You won't because there's a randomness there. But what you can do is you can say that there are still laws of physics, and those laws of physics determine which random outcomes are more likely or less likely. So you've sort of taken a step backwards. You said, well, I can determine a specific outcome, but I can say something about the distribution of outcomes, and you can do something sort of similar for relativity. You can take a step back and you can say, well, I can't say that everybody has to agree about the order in which things happen in the universe. Okay, what can I say instead? Well, you can say that everybody sees things happening according to the same laws. So you know, you sitting in your plastic chair at the edge of the finish line, you see things happening according to a certain laws, set of laws of physics. Me and my high speed Lamborghini, I see things happening according to the same laws of physics. Now I see different things happening, but they're following the same laws. Right, You're basically saying that the laws of the universe account for this difference of point of view in order of events, and so then it makes sense. It's like you're saying the laws of physics don't make sense, and that makes sense. They make a different sense. They don't make common sense, but they make mathematically, they certainly don't make common sense. Now it means that you can use the same laws to predict what's going to happen. Is I can use in my frames. So no matter how fast you're going and where you are in the universe, you should be able to use the same laws to describe what you see and to predict what's going to happen, and those laws should work. So we can still make that requirement. The events can be different from place to place. In the description of what happened can be different from place to place, but each one follows the same set of rules. Right, there's nothing inconsistent about the universe. It's just that the rules of the universe allow for this kind of of different points of view depending on your speed precisely, and that your point of your direction precisely. And I think it's a tiny bit deeper than that. It's not just that we understand how to translate what you see to what someone else going at high speeds will see. We do understand that, and that's cool. But the deeper bit is that the same rules apply no matter how fast you are going, So you can use the same laws of physics. Now, you and I can disagree about the order that we saw the race be run and who won and who cheated, but we agree on the rules of physics that describe what we saw, not just how it translates from what I saw to what you saw. We see them follow the same rules. And I think that's pretty deep. And then there's one more thing that we can still cling to. We can say that even though things can happen in a different order, sometimes there are some rules about that, you can't arbitrarily re order the universe. Oh, I see, Yeah, this is what you're saying earlier. There's a difference between simultaneity and cold. That's right, they're both impossible to pronounce words yeah and clug cool. Obviously, if I can reverse the order there of events, I would say causality, correct. Yeah. The key thing is that you can use velocity and distance and all these crazy relativistic effects to reverse the order of some events, events that are not causally connected, events where one didn't cause the other one. But some things you can't. Mean, we can see different outcomes of a race between Alicia and Roberta, but we probably wouldn't disagree on a relay raise with Alicia. Er yeah, yeah, Or for example, there's no speed at which you can go in order to see Alicia finish the race before she starts, and that order events definitely happens. She starts the race, and then later she finishes. Now when she finishes relative to Roberto, that's a different question. We can zoom around our spaceships to get whatever answer we want, But there's no But you'd have to go faster than the speed of light in order to reverse two events that are causally connected where one caused the other one. So that's why you can't, for example, make the Big Bang happened at the end of the universe, or you know, all sorts of other crazy stuff. There's some freedom here to move around the order of events, but it's not pure total freedom. Don't go crazy people. Meaning is not that the whole universe is open to interpretation, because you know, like, um, the Big Bang happened and Earth formed, and it's not like moving at any speed will change anything about that. But maybe small things, like small things that might some people might say happen or not happen simultaneously. Then people moving at different speed might have a different point of view. Yeah, And the size of these things depends on sort of how far away they are, like things that are in another galaxy, they are really really far away. Nothing over there is causally dependent on anything we do, because nothing we do here can acted for a long long time, because you know, there's because of the speed of light. So things happening on the other side of the universe, you know, the order in which those events happen is almost irrelevant for us. So we could change those are events by a billion years, probably because it makes no difference to the causal connections, because nothing that happens here affects that for a very long time. Things that are close together, right, it's much more sensitive. You can causally affect the things close to you. You can touch things, you can push things over, You can shine a flashlight and affect things nearby. So you're saying that that a raise in the backyard in another galaxy could have happened before or after my race, maybe because there's a long separation between them. But because they don't affect each other, then it's it's okay to sort of move them around in terms of our perception of when they happen. Yeah, And we talked about this thing called the light cone, which is this cone of in space that that opens up at the speed of light around you. You can only affect things that are in your light cone. Things that are sort of downstream from you, you can affect them. Those things are causally dependent on what you do. Things that are not in your light cone that they're too far away from you for you to affect them now or in the near future, there's no way for you to have any influence over them. So their relativity can go crazy and it can change the order events without breaking anything. Right, But we're still all in the same universe, right, we are all in the same universe. Yeah. Yeah, it's not like I'm disconnected from that galaxy or things that are not in my light cone. Something in my light cone might be in that other things like cone, and so I'm sort of still connected to the rest of the universe. Yeah, And your light cone goes on forever and so eventually will encompass the entire universe. Right, things you do now could affect things fifteen billion light years away, but it's going to take fifteen billion years. So your light cone is growing, and eventually everything is like cone overlaps, right, So things do come into contact. And I think my ego needs any more feeding, Daniel, just to think that I can affect the entire universe eventually. That's pretty big step up from handing out medals from the backyard backyard Olympics to expecting the entire universe. Small steps, my friend, backyard Olympics today, galaxy collisions tomorrow. No, I think the thing to understand is that we are all living the same universe, and that universe has a certain set of rules. But those rules are not necessarily the rules you thought they were, and it allows for some fudging and some flexibility and for some weird stuff to happen. But it's not throwing everything out the window. It has to be consistent with the you know, the the universe we've lived and the things we've observed. You don't get to go really fast and go back in time. You don't get to go really fast and you know, change your order from a chicken sandwich to a burger or whatever. Right. There are still rules to the universe. They're just not as hard and fast as you thought. And fundamentally it means that the universe is different from the one we thought it was. You know, the way quantum mechanics has deep implications for the way the universe works, but doesn't really change your day to day. Right. You if you don't go to work, you still lose your job. Right. There are some things that are deterministic. We don't fix climate change. The planet might get too hot. Right, It's not like we can disagree about that. No, And this is not an excuse to say that you can have just whatever facts you want, right, It's just that the facts are sort of local. Right, depending on where you are and how fast you're going. Your account of what happened in the universe is different, but it's always just blown my mind that people can have correct but different accounts of the order in which things happened. Although I think one thing that never changes is I think Roberto is a cheater. I think he cheats in any universe, in any galaxy, and no matter who you're looking, I think the question in my mind and in listeners minds is do you actually have a cousin named Roberto? And if so, does he listen to the podcast? Oh my god, I justly do have a cousin named Roberto. That's what happened. I don't need to say you're a cheater talking about our other cousins. Cousin Roberto Prime, and do you have a cousin named Alicia, because now she's going to be your favorite. Let me think I don't have a cousin name. Let me think who has to say? Let me think, like dozens of cousins, so one of the thirty six cousins needs a little bit of a second there to think about, where were you last night? Honey? Let me think? You know? Never a very inspiring answer, especially in Latin American culture, where everyone has a nickname that is totally unrelated to their actual name. You have to think a little bit. Oh, so when you're talking about Roberto, that's actually a nickname for your other cousin, Nicholas or something. Yes, that's right, something like that. That is how it goes. It sounds like a Russian novel. All right. Well, I hope that sufficiently altered or bent your mind there for at least at the time of this podcast. And remember that the university is crazy. The university's bonkers, but it's our universe and we love it, and eventually we hope it will make sense to us. That's right, just like we love that crazy cousin we all have who we now have to apologize to after this podcast. Well, nobody listens to this podcast, I think so. All right, Thanks everyone for listening and for asking us crazy questions. And if you still don't understand special relativity in the flow of time, don't worry. Nobody else really does either. Thanks for listening. See you next time. Before you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us on Facebook, Twitter, and Instagram at Daniel and Jorge. That's one word or email us at feedback at Daniel and Jorge dot com. Thanks for listening, and remember that Daniel and Jorge explained. The Universe is a production of I Heart Radio. From more podcast from my heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.