Daniel and Kelly’s Extraordinary Universe - Does the Universe need cause and effect?

Episode Date: September 23, 2021

Daniel and Jorge talk about whether things have to happen in a definite order, or not! Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate.

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Listen to Culture raises us on the iHeart radio app, Apple Podcasts, or wherever you get your podcasts. What are we doing today for the opening of the podcast? You know, actually, I thought maybe we would invert the usual process. We have a usual process? Yeah. First, we have an idea and then we record it. So you want to flip it today?

So what does that mean? We're going to start recording and then hope we get an idea? Isn't that like putting cause after effect? Yeah, you know, just a little causality inversion to start your day. What could go wrong? It's never a good time when a physicist says, what could go wrong? Well, you know, we haven't destroyed the universe yet. But what if we blow up?

up the universe with this inverted opening. Oh, and that gives me an idea for a perfect opening. Hopefully people laugh before they listen to that. Hi, I'm Jorge. I'm a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a physics professor at UC Earth. Vine, and I usually don't know what I'm going to say before I say it. Isn't that part of the job description for a professor, not knowing what you're talking about? Exactly, but making it sound like you do.

That's where the PhD comes from, I guess. Years of training. Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I-Hard Radio. In which we're not afraid to admit what we don't know about the universe because we love to embrace that ignorance. We dive deep into everything that we don't understand. about the universe, the very nature of space and time, the context of the reality around us, all of the squishy and beautiful and incredible matter that fills it and wiggles around inside of it. We are desperate to understand the deep nature of the universe and we are here to explore it and

explain it to you. Yeah, because there is a lot we don't know about the universe and I'm not just talking about myself a cartoonist, but there's a lot that even physicists don't know about, not just things hidden inside of black holes or neutron stars or inside of particles, there is some very fundamental questions we still have about this wild and wacky universe. Yeah, exactly. Like, where did I put my phone and how come I can never find an even number of socks at the same time?

I think maybe you put the phone in your socks. That would solve two mysteries. If I could just have like digital socks so I could have them on my phone, that would be so much more convenient. Well, I know you like to wear a sandals, so I'm pretty sure you already have virtual socks. Yeah, exactly. this way I could just delete all the socks in one fell swoop. But it's not really just socks that we are curious about.

We really do want to understand the deep nature of reality around us. What is this universe? How did it come to be? Why is it this way and not another way? And most importantly, are there things about it that we're getting basically wrong? Yeah, because I feel like you can ask questions about the universe and the stuff in the universe, you know, like black holes and stars and particles. But you can also kind of ask deep kind of philosophical questions about it.

You know, it's sort of like about the nature of it or what can break the universe even. Yeah, because we know that in human history, we've made a lot of basic mistakes about the way we thought the universe worked because we've only seen it work in one particular way or in one set of circumstances. And we imagined that must be true forever. It must be a deep truth about the universe. And it turns out not so much, which means that what lies ahead of us is more discoveries that basically. basic assumptions about the nature of the universe are probably wrong. And it might just be that we need to hammer at these things forever or wait till the aliens arrive

and give us some other context for looking at the nature of the universe. But that's cheating, Daniel. Are they also going to tell you where your socks are? Are you going to be that irresponsible? They're going to email us, socks. That's going to be nice. Digital socks. That's not cheating at all. I think the first galactic physics conference will be, you know, a great melding of minds.

If you think that's cheating, then, you know, physicists shouldn't work together. at all. We should all be trying to figure out the universe on our own. Well, do you think it'd be a two-way conference with us and the aliens? Do you think we have anything to teach them? Are we joking? Are we being serious? I don't know. I mean, if they can travel through the stars and, you know, invent warp drives, do you think we have anything to teach them? Or do you think we know something they don't at this point? I think it's very likely that everything we've learned in our human sciences is probably corrupted by human bias and totally useless to aliens, not just because we haven't made advances

is far enough, but probably just the questions we ask and the nature of the way we answer them is probably deeply inherently human in ways we can't even imagine. You know, we don't even really know where the edge of the box is. We just know that we're in this sort of like human constructed box about ways to think about the universe. And it isn't until the aliens come that we'll even figure out like where the edge of that box is. Yeah, I guess because we've been trying to figure everything out with the human brain.

And, you know, what if you have a totally different brain? Maybe you get to see things in a very different way. Yeah, or different sensory organs, right? What if you can see x-rays or you can smell photons or you can taste electrons or something like that, right? You might have figured out totally different ways to think about the universe in a completely different order. Maybe quantum mechanics is intuitive to them because, you know, they've seen this stuff

happening in front of them every single day. Or maybe they can see neutrinos. And so the universe is like totally opaque and very weird to them. It's going to be a challenge to map from human brains to aliens. in brains. Sometimes it's hard to even map from human brain to human brain. Yeah. So I think what you're saying is that sometimes there are revolutions in human thought where we thought that the universe worked one way and then it turns out it worked another way. Right. Like maybe quantum physics is one of those big revolutions or relativity.

Exactly. Those two are the best examples of moments when we realize that fundamentally the universe is very different from the way we imagined. And I think we put those on the scale of other kinds of realizations like discovering that the Earth is not the center of the solar system or even the cosmos or discovering that our galaxy is one of trillions of galaxies instead of the entire cosmos. You know, these kinds of things help us understand not just the nature of the universe around us, but our place in it in the context of our very existence. So these are pretty deep potential revolutions in our understanding of the nature of the

universe. Yeah. And do you think that has made physicists a little bit paranoid almost in a way? Like now you doubt everything, like even the basic, you know, logic of the universe, right? No, it makes us excited because it means that around every corner is a potential explosion of ideas. You could tug on any random thread and pull the whole thing apart. Paranoid makes it sound like we're afraid to pull the whole thing apart. We are desperate to pull it apart because it will reveal something else, something new that we can chew on,

where we can make new progress and ask new questions. That's a dream come true. I think being afraid of explosions at every corner, It's sort of the definition of being paranoid. But you're saying you're paranoid in a good way. You're like a good paranoid. A good kind of paranoid. Yeah, somehow you walked me into that corner,

but yes, I am now admitting I'm a good kind of paranoid. But yeah, you can ask pretty deep questions about the universe. And so today we're asking a pretty challenging question, I mean, in the sense that it challenges something very deep and sort of, I don't know, logical and basic about the universe that, you know, maybe a lot of people don't even think you can even ask. That's right. It's something that's so fundamental to the universe that even is incorporated in how we explain the universe itself.

It's something inherent, I think, in the way humans think, in the way we tell stories and think about what makes sense and what doesn't make sense. Yeah, so today on the program, we'll be asking the question. Does the universe need cause and effect? Whoa, Daniel, this kind of blew my mind. I mean, how can you question cause and effect and causality in the universe? Are you saying there's some effects to questioning causes? Yeah, the effect of asking this question is, it's got me really confused. I know.

I think it's so fundamental to the way we think. You know, the way we explain things to ourselves is that we tell stories and stories go like, A, happened and then B happened and then C happened. That's the way we thought. That's the way we think. That's the way we organize our minds. And so it's pretty hard to imagine that you could have a universe without cause and effect. On the other hand, just because it's part of our minds doesn't mean it has to be part of the universe, right? The whole goal of physics is to break out of that box and understand something universal instead of something human.

Now, Daniel, is this related to like the idea of the arrow of time or is this sort of like a basic kind of thing about the universe where like things can happen without being connected to other things? Do you know what I mean? Yeah, definitely it's connected. to the question of time because cause and effect orders things. And we'll talk about this in more detail later. You know, there's this concept of like a light cone which organizes the order of events. Things have to happen in the universe. But that's only true if you have causality.

If things have to happen in a certain order, things don't have to happen in a certain order, that whole picture might go out the window. Whoa. And that's, you know, totally opposite from our everyday experience, right? Like our everyday experience is that effects do follow causes, right? Absolutely. You know, your friends don't like arrive for dinner before you invite them. You should meet my friends.

Introverts don't have guests arrive for dinner before you invite them. You know, it's like if you send somebody a message, they can't read the message before you send it. Right. That kind of thing would violate causality. It's definitely connected with the flow of time because it has to do with like, you know, sending messages back in. time. One of the reasons we always say that you can't travel back in time is that it would violate causality. You would have effects that influence their own causes, right? It's like very basic to the way we think about the universe stepping forwards in time, flowing from now to the

future. All right. Well, then the question is, do we actually need causality? Do we need cause and effect in the universe to make it work? Or are you saying it's sort of maybe like an illusion or something that's apparent but not really needed in the universe? What are we actually asking? here. I think the question is whether it's always needed. You know, this is the kind of thing that we observe in the universe. It's definitely part of the universe. But just like with relativity and quantum mechanics, there are some places where it seems like it might not hold together, some like little threads where it doesn't really work and it isn't really consistent with some other basic principles. And that gives us a clue that maybe it's not always required. Maybe like it comes

together in certain circumstances. It's a nice way to describe what often happens in the universe, but it's not actually a fundamental principle and we can find some places where it's tossed out the window. So who would be the one we toss out? Cause or effect? Which one do you like better? I prefer horses to cow, so let's throw out cowsality. Is it cost or effect? Well, anyways, we were as usual wondering how many people out there had thought about this crazy deep fundamental question and how many people think they might have an answer to this strange query? So Daniel went out there to the internet to ask people, do we need cause and effect? So thank you everybody out there on the internet who is willing to answer these funny, crazy questions without having a chance to think about it or Google it.

If you'd like to do that, it sounds fun to you. Please write to us to questions at Danielanhorpe.com. We want your voice. So think about it for a second. Do you think the universe needs cause and effect? Here's what people had to say. I think that we as human beings probably need it. Whether the universe needs it or existence, probably not.

I can imagine a crazy universe where everything was upside down and happened of its own volition. But as people, I think we wouldn't do very well in such a place. I don't know much about this. It makes me think of the Matrix when the Merovingian is talking about cause and causality or something like that. I understood that about as much as I understood most of that movie. But without honestly really knowing much about it, I'm going to say no. I know things can kind of happen what seems to be randomly in the universe. And with things, the statistical chances that some of the things that do happen,

the statistical chances are so low that it just doesn't seem like there could be a cause for every single thing that can happen because there's so many different things that can happen. So do we need causality? I'm going with no on that one. I think we need causality, because if we didn't have cause and effect, everything would just be chaos because, like, there would be no reason for anything to happen. Things would, stepping on a butterfly would cause something completely crazy to happen,

not just, like, butterfly effect, but like completely bananas. Well, let's, I'm thinking of this. You eat, you get fat, cause and effect. And I think we don't need it. And it should be voted out. So we don't need it. We can start a petition. Sure, if we need cause out of use.

But I mean, if you want to know the path, cause an effect, obviously play a role in knowing what that one part was. But if we didn't have it, we didn't need it, that would mean the possibility of multiverses, and that'd be exciting, and maybe we don't want causality. No, I don't think we need causality. You can have two things that are correlated, like in, you know, economics or statistics,

You know, they look for correlations, and correlations provide information in and of themselves. Maybe it's nice to know causality, but I don't think you necessarily need causality to get information. All right. Some pretty definitive answers here. Nobody seemed to sort of stumble a lot. I know. And some people who really think like, nah, we could do without causality. That really surprised me.

Oh, really? Wow. Do you think that's human hubris? Maybe physics has just been so successful in, like, knocking down basic pillars of reality that people are ready for, like, physics to undermine everything. You're seeing it as a positive. I'm seeing it as a positive. People are open-minded to unraveling the basic nature of their very existence.

That's great. Well, I think maybe this goes back to what I asked earlier about what exactly do we mean by causality and not having causality. Like, does it mean that you can't have A without B or does it mean that, you can't have A without B? or does it mean that, you know, A's always have to be connected to B's. You know what I mean? Like, can things appear out of nowhere without a cause? Or are we saying that A always has to come before B.

You can't have B before A. Do you know what I mean? Do you know the difference? Yeah, it's about the ordering of events, right? I mean, you still can't break random laws of physics. You can't just, like, create energy from nothing. It's not like it's a free for all out there. We think the universe still does have laws and does follow those laws.

We're just not sure that those laws require that A always happens before B. So we're pretty clear that you can't just have B without like B pop out of nowhere, right? The laws of physics says no. Yeah, well, it depends on exactly what B is, right? Like quantum mechanics says you can have particles pop out of the vacuum, but there are rules for that, right? There are ways that it can happen. So we still think that the universe does follow laws. But hey, maybe when the aliens show up, they're like physics, we gave up on that a million years ago

because we discover the universe is totally arbitrary deep down. But yes, we still think that the universe follows laws. And so you're saying that what we're asking today is whether or not those laws sort of prescribe a specific order that things have to happen in the universe. Yeah, but not everything in the universe is connected by causal order, remember. Because there's a finite speed of information, there's some things that you can't have an effect on, right? Like events that are happening right now in Andromeda, you can't have any effect on

with decisions you make right now because the information from your decision right now to like send a beam of light or whatever won't affect Andromeda for millions of years. So even with causality, there are some parts of the universe that are not causally connected to other parts. All right. Well, let's maybe break it down for people. What exactly do you mean by causality? How do you define causality or cause and effect?

Yeah. So take two points in space and time, call them A and B for lack of more. creative labels. And here we mean a point in space and in time. Right. So we mean like A is at your house at 8 a.m. in the morning and B as you've arrived at work at 9 a.m. So the events have a space and a time in them. All right. And so these two things are causally connected. They have a definite order of events if something that happens at B relies on information from A. Right. So maybe for example, you brought something with you from home to work. So for example, you brought your breakfast or you forgot your breakfast when you left the house.

So something you did at A affects what you do at B. You then need to buy breakfast or steal your co-workers breakfast or something. So those two events are connected causally because something that happens at A influences what happens at B. Meaning like if I want to have breakfast at my office, I need to have packed it or left the house with that breakfast. Otherwise, there's no way that I could have that breakfast from home, right? Exactly. And once you get to work and you have breakfast with you or don't, there's nothing you can do to affect A, right? So this is one directional. A can affect B, but B cannot affect A. So that's what we mean by a definite order of events. If A can have influence on B, then B cannot have influence on A. If your decision to leave the house with or without breakfast affects what you do for breakfast at work, then what you do for breakfast at work cannot affect whether or not you leave the house with your breakfast. It can't go backwards. Right.

I think you're just saying you can't go back in time, but the two are sort of connected, right? Like if I don't have breakfast in my office, then that means I didn't leave my home with it, right? So they're sort of connected, aren't they? But you're saying like one of them affects the other and not the other way around. Yes, exactly. Information flow is only in one direction here. And here B is part of the sort of the light cone of A, right? We talked about how decisions you make can only influence things.

things around you that are nearby and in your future. And we talked about in a previous podcast how to formalize that. You think about a light cone, which is all the things in your future that you can influence. And you can influence things that are nearby in your immediate future or things that are far away in the deep future because it's time for information to get there. All right. So I think you're saying that I didn't leave my house with my breakfast.

Therefore, I don't have it in my office. That's the cause and that's the effect. Yeah, exactly. And there's no way to go the opposite direction. What would that even mean? Like, I'm at my office first and then I left the house without the breakfast? It would mean that somehow once you get to your office with it without your breakfast, you could still influence whether you left your house with or without your breakfast.

That you could like somehow go back and change what happened at 8 a.m. And change your decision based on whether or not you had it with you in your office at 9 a.m. So, you know, making a decision at 9 a.m. can't influence what happened at 8 a.m. That's all we're saying with cause and effect. all right so then that's cause and effect and that seems pretty important for the universe to make sense right because otherwise things would be what inconsistent like i can always you know create paradoxes and time loops and things like that it does seem pretty basic right it's the way that we think about physics when i first got into physics i thought it was amazing because it could predict the future and it predicts the future based on the conditions of the present you know if you are shooting a cannon ball at a castle you can predict its trajectory if you know its direction and its velocity, right? Those are the causes and the effect is like, oh, it hits the castle wall or it goes over the castle wall.

And so physics seems to me to be like all about using causes to predict effects. You know, that's what the laws of physics are. They take the current description in the universe and sort of step it forwards in time to the next description. So it seems pretty basic. All right. Well, it seems basic, which I think is probably a cue that we're going to challenge that. and it might turn out to be wrong.

So let's get into that and how we can maybe test it or find out the true answer. But first, let's take a quick break. Ah, come on. Why is this taking so long? This thing is ancient. Still using yesterday's tech, upgrade to the ThinkPad X1 Carbon,

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all on one device. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the okay story time podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Now hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. It's even more likely that they're cheating. He insists

there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. that's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System

on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. A foot washed up a shoe with some bones in it. They had no idea who it was. Most everything was burned up pretty good from the fire that not a whole lot was salvageable. These are the coldest of cold cases. But everything is about to change. Every case that is a cold case that has DNA right now in a backlog will be identified in our lifetime. A small lab in Texas is cracking the code on DNA.

Using new scientific tools, they're finding clues in evidence so tiny you might just miss it. He never thought he was going to get caught. And I just looked at my computer screen. I was just like, ah, got you. On America's crime lab, we'll learn about victims and survivors. And you'll meet the team behind the scenes at Othrum, the Houston Lab that takes on the most hopeless cases to finally solve the unsolvable. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. We're talking about cause and effect and whether you actually need it to make a happy.

universe, I guess, right? A functioning universe? Yeah, exactly. Whether we can make sense of our universe without causality or whether it's actually absolutely fundamentally required for anything to make sense to us. Okay. So then we define causality as like I shoot an arrow and an apple and it hits the apple, but I can't do it the other way around. Like I can't have hit the apple before shooting the arrow. Exactly. Because if you hit the apple before you shoot the arrow, you could like change your mind and not shoot the arrow and then oops, you already hit it. How can you change your mind? It seems to like automatically make no sense.

It seems like a paradox, as you said. And it seems to be sort of connected to the arrow of time, right? Like time only flows one way. But there's a little bit more to it than that, right? There's a little bit more to it than that. And of course, the thing that makes things weird and twist your brain and maybe give us an escape from causality is going to end up being quantum mechanics, of course. Of course.

Quantum mechanics. It's always scrambling your brain. So that seems, I think, I'm guessing it's going to add some sort of uncertainty or randomness to causality. Yeah. And before we get to quantum mechanics, I think it's important that you have in your mind a clear picture of the part of the universe that you can affect with your causes. This is, again, this concept of a light cone, right? If you send out a flash of light right now, you like turn on a really bright light, then who can tell that you have done that? people who are really far away from you cannot see that right now.

They have to wait until the future. And people that are even further away have to wait to the deeper future to see that flash of light. Because light travels at the fastest speed of information, people who haven't seen that flash of light can't be influenced by it yet, right? So we think about that as a light cone. In two dimensions, you can imagine yourself sort of at the tip of a triangle that's opening up as time goes on and you can influence more and more of the future based on your decisions of the present.

In 3D is sort of like, you know, you're at the tip of a cone right now and it's opening up. Right. I guess maybe I wonder if you can talk about the breakfast cone of my breakfast that I took out when I left my home. Like you're saying like there's a sort of a limited number of time and places that I can be at with my breakfast

if I chose to leave my house with my breakfast, right? Like I can't instantly be at my work with breakfast because I can't get there in time. And also I can't be in like China in an hour with my breakfast, right? Because I'm limited to how fast I can move. Exactly. And so if you're going to your office pretty close by, then you can bring your breakfast with you. And that can influence your coworkers. Are they going to try to steal your breakfast?

Do they forget their own breakfast? Are they influenced by the smell of your breakfast, this kind of stuff? But the, you know, podcast headquarters in Shanghai, for example, can't be influenced by. that decision until later, until your light cone has grown to expand and include all of those things. So there are things that you cannot influence right now in the universe just because of this finite speed of light. And so everything you can influence, we call that part of your light cone. Right. Or breakfast cone, which by the way sounds like a great breakfast idea for McDonald's or one of these fast food chains. Breakfast cone, that sounds like scrambled egg

flavored ice cream. That does not sound a cueing to me. Or scrambled eggs. eggs on a cone. Scrammeled eggs on a cone. Actually, that might be a great food truck. You know, that's the kind of thing you would see in L.A. with like a huge line of hipsters, you know? Right. Yeah.

Breakfast cones. Let's make it happen. All right. So then how do these light cones affect our sense of cause and effect? Well, the interesting thing about light cones is that they're pretty simple if the universe is not bent, right? If space is flat, if light moves in straight lines like it does out in deep space, then they're just like we talked about them. They're triangles.

in two dimensions or their cones in 3D. But they get more complicated when space bends. You know that gravity is not just a force. It's also a description of the way that the universe bends, that space itself bends when we are near heavy objects. So the reason, for example, the Earth goes around the sun is not because there's a force of gravity pulling on it, but because the sun bends space.

And so the Earth is moving in a path, which is actually quite natural for an object under no force. It's moving in a circle. And so the same thing happens to light cones. If you are near something massive like a black hole or a star or whatever, your light cone bends because the path that light takes also bends. So the things you can influence change. Now you're making me think of bugles. You know the snack with the curved cones?

I think maybe I should have some breakfast before recording these podcasts. But this is important for our food truck. We can't have curd cones because then the eggs will all fall out, right? Wait, what? This is why physicists shouldn't be cooked. But anyways, going back to our topic, you're saying space can bend and that can bend or light cones and that can somehow affect cause and effect?

Like you can break cause and effect by bending space? Yeah, it doesn't break cause and effect yet. It just changes what you can affect. For example, say you are inside a black hole and you make your breakfast. You cannot influence what people eat or who gets breakfast outside of the black hole, right? this concept of a light cone

inside a black hole it gets twisted the light cone only points towards the center of the black hole if you're near a black hole your light cone is distorted if you send out a flash of light or shoot a bunch of breakfasts at your friends they don't all just travel in straight paths and so there are some people who are actually near you

who you cannot influence because of the bending of space the point is the bending of space determines which causes line up with which effects I see so it's not you're saying cause and effect is flexible in a way. Yeah, exactly. As you're near some heavy mass,

then which causes and which effects line up depends exactly on the curvature of space because it depends on how information travels. If you can't send a light pulse to somebody, then you can't send them information, then your causes cannot influence their effects. All right, so we can limit cause and effect, but I guess the question is,

can we break it or do we need it? And you're saying that things start to get weird when you add quantum mechanics. Yeah, exactly. So now we've done special relativity with light cones. We went to general relativity by bending those light cones through space. Now we're going to add in the final ingredient, which is quantum mechanics, right? Say we're near this black hole so our light cone is all twisted and bent and who we can influence

and talk about breakfast with depends on the curvature of space. But what if the curvature of space itself was uncertain? Like what if we didn't know exactly where that black hole was because it was like created from some quantum process. So I had a probability to be here and a probability to be over there. Then we would have like two possible light cones, which would mean like two possible portions of the universe that we could influence. But I wonder, do you actually need the black hole to get those two possible light cones?

Like, you know, isn't there quantum uncertainty in everything, right? Like if I leave my house, there's maybe a 50% chance that I took a right and a 50% chance I took it left. And so there's two possible breakfast cones. Two possible breakfast cones. Yes, the black hole is just the extreme example because it's easy to think about how the black hole changes the shape of your light cone is very dramatic. But every time there's quantum uncertainty and that uncertainty leads to uncertainty in where stuff is in the universe, that means this uncertainty about the curvature of space, which means this uncertainty about the causality, right? If I don't know where the black hole is or where Jorge's breakfast went, then I can't necessarily predict which part of the universe.

I can influence. Okay. So then there's some uncertainty in the light cones and two possible futures. So then how does that break causality? Well, you can imagine some experiments, right? Like, let's say, for example, we have two people doing experiments. And in quantum mechanics, thought experiments, people always use Alice and Bob because they're, you know, A and B.

Maybe we can mix it up a little bit. You can think up more clever names. But we have two people doing experiments somewhere out in space. And their experiments depend, for example, on how close they're. are to the Earth, right? Because the Earth is going to bend space. And you know that, for example, if you are near the Earth, then your time slows down because gravitational time dilation makes clocks run slower, like clocks closer to the Earth run more slowly than clocks further from the Earth. So now we have these two experimenters. They're out in space. One of them is closer

to the Earth than the other one, right? But if the Earth's location is uncertain, we don't know which one it is. So now one of them has had their time slowed down more than the other one. So one of them can influence the other because their time has been slowed down. So for example, if Alice has had her time slowed more, then she hasn't gotten as far in her experiment and Bob can send her a message influencing her experiment. But if Bob has had his time slowed down more, then Alice can influence his experiment. So we don't know necessarily which way causality goes from Alice to Bob or from Bob to Alice because we don't know

where Earth is and that determines where these light cones flow. Okay, well, first of all, I'm a little worried we can't find the Earth. It's a little concerning.

I think you're saying like Alice and Bob are doing the same experiment, right? Like you're trying to figure out what inside of a box and they have maybe the same box and you're saying

if one of them is moving at a different time rate then like if one of them has time moving faster for them they could finish the experiment and then run over and tell the other one what's in the box. Exactly.

Or maybe they're like trying to unlock somebody's phone and they're trying to guess codes or something. And if Alice's time runs more slowly, then Bob can try a bunch of codes. And if he finds one, he can send Alice a message saying, oh, try this one. Or don't try these. I already try them.

That's if Alice's time is running more slowly. If it's the opposite, like the earth happens to be in another situation where it slows down Bob's time, then Alice can finish her experiment first. So who finishes the experiment first and who can send a message to the other one about their results depends on who is closer to the gravitational object that's slowing down time. And you know, it sounds weird to say like, well, how do we not know where the Earth is? It's a crazy thought experiment where we've like put the Earth in some sort of crazy quantum mechanical

superposition so we don't know where it is. That's pretty hard to imagine. But this is what we do when we try to understand like the extremes of the universe. We come up with these crazy experiments to understand whether the rules are broken. in extreme situations. I wonder if you can simplify by just talking about like Shorottinger's box, right? Like you're saying, let's put the earth, Alice and Bob, inside of a box. And we sort of don't know where the earth is.

And so from us sitting outside of the box, we don't know who told who about the results of the experiment. Yeah, this sounds like Schrodinger's prisoner's dilemma. Sounds catastrophic. Exactly. So we don't know then what has happened inside the box. Was it Alice and then Bob or was it Bob and then Alice? And so in this situation, because the position of the light cones is uncertain, causality is uncertain.

And so in this kind of experiment, it's like, well, which happened? Was it A before B or B before A? So now causality has become uncertain. Remember, at the very beginning, we defined causality saying, well, if A can influence B, you know, A causes B, that means it's impossible for B to cause A. So in this experiment, like we have two events and we can't say which one happens. happen first, and they do influence each other. One is definitely inside the light cone of the other. We just don't know which. Right. But that's just sort of, isn't that sort of regular quantum mechanics? Like, we don't really know whether the cat is alive or dead anyways, right? That's right. We

don't know quantum mechanics whether the cat is alive or dead, but we've added in another element here, which is causality, because now quantum mechanics is influencing the very shape of space, which determines which events can happen in what order. In this classical Schrodinger's box example, you know, the causality is clear, like, you know, the radioactive element decays and either kills the cat or it does not. The order of events is clear, even though which events happens is not, right? It's not like the cat can escape and then rebuild the box or something. You can't have anything going backwards in that experiment.

Here, we might have things happening in an indefinite order because we've made the shape of space itself uncertain, and it's that shape of space that determines what can influence what, because it controls the shape of the light cone. All right. So then the causality of what happened inside the box is uncertain. There's a quantum uncertainty about it. But does that really mean that causality broke or it's not needed or it's false? Do you know what I mean?

Like it's just that we don't know, right? How does that sort of break things about the universe? Yeah, well, it means that maybe causality is not always needed. You know, it seems like it's the kind of thing that happens a lot. most of the time in most circumstances you don't get huge uncertain bending of space that makes causality uncertain so causality is probably like a very effective principle but you know we want to understand the deep nature of the universe not just like hey this mostly works let's move on we want to understand how things actually work and right now we have

these two really key ideas about the way the universe works quantum mechanics which tells us things are fundamentally uncertain and general relativity which tells us how space bends around mass, and we'd like to merge those two. We'd like to have a theory of quantum gravity that tells us, you know, how quantum mechanics and gravity play well together. Well, this suggests that, you know, we might have to give up causality if we want to merge them. That if we want to bring quantum mechanics and general relativity together, then these two concepts might not play well together. You know, they seem to create these situations with uncertain causality. And so maybe the key to binding a theory of quantum gravity and revealing the deep nature of the universe is

to give up on causality, say it happens a lot, it's convenient, it's nice, but it's not actually always required. I guess maybe it's hard to see sort of the stakes here with Bob and Alice because, you know, like whether one of them tells the other first or the second maybe doesn't, you know, sort of affect my reality that much. But can you think of an example of where like this uncertainty in causality would sort of have more, I don't know, sort of like deeper repercussions? You know, I think that physicists are still struggling to get their minds around the consequences here. And we'll talk in a minute about like experiments people are doing to try to use this. We're developing ideas for like how to improve computation or, you know, make information,

transmission, actually more efficient or change the very nature of thermodynamics. But it's something that's so basic and fundamental to our thinking that we're having trouble even like contemplating what physics would look like without causality. and so it's hard to get your mind around how that would actually influence the universe. All right, well, I think basically what you're saying, though, is that there are situations where quantum mechanics can throw uncertainty about the order of things, right?

Like, there can be situations where we don't know if A came before B or B came before A. And so because there are situations where we don't know, maybe the question is, do we actually need it, right? I think that's what you're getting at. It's like maybe since it's not something that has to, be known. Maybe it's something we don't even need in the universe. Yeah. And maybe it's not something the universe demands. You know, the same way when you have quantum entanglement, you might have like

two particles that are far away in uncertain states about, you know, what direction their spin is. And we like to think, oh man, but there has to be a real truth there. It has to either be this or that. You know, there has to be some deep hidden knowledge. And we discovered actually the universe doesn't care. The universe is happy to have that be uncertain, the true nature of these particles. And now we're taking that a step further and saying, look, maybe the universe doesn't really care always whether A happened before B or B happened before A. Maybe it's happy to have that be uncertain for it to be undetermined, which is pretty hard for us to consider. All right. Well, maybe we don't need causality, but we definitely need to pay for this podcast. So that's the one cost and effect we can't ignore.

So let's talk about how you might test whether or not this theory is right or whether or not you actually do need causality in the universe. But first, let's take a quick break. Ah, come on. Why is this taking so long? This thing is ancient. Still using yesterday's tech, upgrade to the ThinkPad X1 Carbon, ultra-light, ultra-powerful, and built for serious productivity with Intel core ultra-processors, blazing speed, and AI-powered performance.

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so you can work, create, and boost productivity all on one device. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week

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Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not?

To hear the explosive finale, listen to the O.K. Storytime Podcasts on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually. impelled metal, glass.

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Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right, so Daniel, apparently maybe the universe doesn't need causality, or maybe the, I think what you're saying is that maybe the universe doesn't really care that much about causality,

like it could go either way. Exactly. It's like effect before cause, cog before effect, whatever. As long as I get my breakfast cone, I'm fine. Yeah, whatever, as long as I got bacon in my scrambled egg cone. Yeah, and again, let me just reiterate. This doesn't mean that anything goes, that you should just like go out there and steal jewelry and whatever. There are no consequences for your actions, right? You're still going to prison if you steal money from your local grocery store. It just means that sometimes in scenarios where there are two possible orders for events, the universe

might not pick between them. Right. Yeah, it might leave things undecided and go about its happy way. Yeah, exactly. Physicists call this indefinite causality. So not like a complete overthrow of a causality, but like an important weakening, you know,

to say like, oh, there's a crack in causality. There are cases when you don't have to know what happens first. What if you just call it causality-ish? Diet causality. Yeah, there you go. All right, so that's a possibility. and it seems like the universe, you know, it's kind of fuzzy about causality.

And so are there experiments to sort of test this or to figure out what the right answer is in physics? Yeah, there are some really cool experiments. People came up with these ideas in the 2000s and sort of playing with them as they were trying to stitch together quantum mechanics and general relativity to think about quantum gravity

and realized maybe this is the stumbling block. Maybe this is the piece we need to get rid of so that everything else clicks together nicely. And so they tried to make some experiments And then, you know, it's hard to have black holes or to put the Earth in a quantum superposition. So they came up with a totally different set of experiments. And it's mostly folks who were working on things like quantum information, where, you know, they are like splitting photon beams and polarizing them and capturing the information in them and not in them and this kind of stuff. They were able to do experiments that probe this kind of thing.

All right. So then how does the experiment work? What's going on? Yeah. So what you do is you take a beam of photons. These are just, you know, like it's a laser beam essentially. and you have these particles flying out, and then you split them. You use this one of these beam splitters, so like half the photons go one way, and half the photons go the other way.

And then you send the photons through two different paths. Along one path, you do A to the photons and then B, and along the other path you do B, and then you do A. And what does that mean to do A or do B? It's like you perform some operation, you change the photons a little bit. In this case, what they did is they polarized the photons. photons are more than just like packs of light. They have like little spins to them. You can change the way those spins are pointed.

And so along one path, they like flip the spins one way and then another way. Along the other path, they do it in the opposite order. Right. They sort of run it through some filters, right? Yeah, exactly. You can think about it like that, running it through some filters. And the key thing is that the order matters. Like the photons look different if you do A and then B versus B and then A.

And, you know, this can happen because sometimes these. There's things are conceptually the same as like rotations where, you know, it matters what order do you do them. It's like if you turn around and then you turn left, it's different than if you turn left and then turn around. All right. So then I have a laser beam. I split it. And in one half of it, I do A and B. And the other side, I do B and then A.

And then what? I compare them to see if something different happened. And then you bring them back together, right? You rejoin them. And now you have photons and you don't know which path they took. Do they do the A-B path or the B-A path? And what you see when it comes out is a really interesting interference pattern between photons that went through A-B and the photons that went through B-A. And just like in sort of the double slit experiment where particles could have gone through one slit or the other and the probability to have gone through one or the other interferes with the first ones, then you get these interference patterns.

So this interference patterns means that you really do have photons from both in your beam. and that for any given photon, you don't know whether it went through A-B or whether it went through B-A. So what you're seeing is this interference pattern between the probabilities, which means that both possibilities exist for any given photon. Each photon has a possibility to have gone through one side or the other. Oh, I see. It's like you take those two beams and then you join them again and then you look at the photons that come out. And when you get a photon out of that joined beam, you don't know whether it went through A-B or B-A,

but it looks like it went through both at the same time, sort of like the cat alive and death. Exactly. And so here these photons have had an experience that has indefinite causality, right? We don't know what the order of events was for these photons. And it matters, right? A, B has different photons than B.A.

And so an individual photon is a probability of one or probability of the other. And that leads to this really interesting interference pattern so you can see that this is actually happening. It's not like you have just two different groups of photons, ones that are AB and ones that are B.A. Every photon now has a probability of having one order or the other. Right.

But I guess, you know, it's looking at this skeptically, it's not like you did the same thing, A and B in different orders, but they went through different filters, kind of, right? They took a different path through space. So it's sort of not, like, I'm not really changing the order of events. I'm changing the path.

That's right. But in this case, the path determines, the order of events. And you're right, it's not exactly analogous to what we're talking about before with light cones and the bending of space. It's a different way to try to construct indefinite causality.

You're right, they're not exactly physically the same filters. Right. It's sort of like a standing for having done the same thing in a different order. Yes, exactly. Because you can't do that.

You can't like reverse time and do the experiment again in the other order and then rejoin it. That would be super awesome if you could do that. But here we separate them in space instead. That would be a dessert cone for sure. But I think what you're saying is that they did this experiment and it confirmed that, you know, it's sort of like you can have two different orders at the same time happening quantum mechanically.

Exactly. And what they do are really cool things with correlations. It's just like with Bell's inequality, you know, the example of having two quantum entangled particles where, you know, if one is spin up, the other one has to be spin down. And to prove that they're not determined until you open one box, even if they're really far apart, you have to do these really subtle. little experiments called probing Bell's Inequality that show that you can get like correlations between the two boxes that you can't have otherwise. In the same way, they do that here. They like change what A and B are.

They rotate them. And they get these correlations between one side and the other that you can't have if causality was definite. So you have to have indefinite causality to see the specific results of these experiments. The patterns, the numbers that they get out cannot be reproduced if causality is definite. If every photon actually went to one side or the other and then merges, that does not explain the results of the experiment. It has to be indefinite to get the interference patterns and the correlations that they see.

Right. All right. So then it sort of confirms that the universe is causally-ish, definitely causal. So then what does that mean for us? Like, does that mean that we can now break the rules and do cool things? Or does it mean that, you know, it's just another sort of step in our sort of befudlement with quantum mechanics? Is there some rule in particular you're hoping to get to break? Is you looking for permission?

Yeah, you know, I want to eat the breakfast cone and not gain weight. Can we sort of reverse the cost and effect there? Exactly. Or you can eat breakfast any time of day. No, there are some potential applications to this. You know, any time you gain some new insight to the way the universe works, you can come up with some ways to take advantage of that insight to do something you couldn't do before. And so people are thinking carefully about what this means. And there's some

cool things that you can do. Like you can send more information over noisy channels by using indefinite causality to encode some of that extra information. Or people have come up with like weird quantum computers where two halves of the computer are not linked by causality. And so they can like both do their calculation before the other one and send the results to the other one. And so you can sort of like skip steps there and sort of like cheat in time, which is pretty cool. So there's some ways people are thinking about using this. For me, it's not about the applications. It's about making progress to this ultimate theory.

You know, we want a deep picture of the universe and we want to understand how the bending of space is consistent with quantum mechanics and all this crazy stuff. And so it might just be that this very way we think about the universe, causality isn't always required. It's like it usually happens. It's most of the time a good way to describe things, but not something that you have to have at the basic core

in all the deep equations. And so that would, you think, maybe give us some insight into merging these two theories together, quantum mechanics and general relativity? Yeah, exactly. This is a stumbling block, right? As we talked about before, if you have general relativity, which bends space and you have quantum mechanics, which makes that bending uncertain, then causality is no longer clear. And that's been a problem for quantum gravity.

So maybe the answer is like, well, just act like it's not a problem. Maybe it's actually okay. you know, maybe this wasn't a wall in our progress. We just need to sort of like not worry about it so much. Yeah, that's my favorite way to deal with problems, Daniel. Just ignore them. Just don't look at the scale when you weigh yourself. And then you don't have to worry about causing it.

Well, it is an important lesson in the way we think about things. You know, we put up mental barriers sometimes. We imagine like, oh, well, that's impossible. Oh, they can't be. And then later people come along and they're like, well, actually, why not? Or, you know, why are we following this rule? Is this really actually important? and then they discover this is a whole rich area of exploration.

You know, think about like imaginary numbers. People for a long time thought, well, that's ridiculous. It's nonsense. But it turns out to be really important branch of mathematics for understanding the way the universe works. And so sometimes you've got to like knock on these mental walls and discover that there's actually lots of interesting territory on the other side. Yeah, I think that should be your new slogan for physics, you know, physics, colon, why not? You know, Nike has just do it. You should have, why not?

haven't destroyed the universe yet. Why not put scrambled eggs in that cone? Seriously, that's a great idea. All right, well, we hope you enjoyed that and, you know, got you to think a little bit about what we think is certain in this universe. Maybe things are not as certain as we think they are, even the basic logic of how and when things happen. And that goes to show you that there are still really deep and basic questions out there

that people are struggling with about the nature of the universe. and maybe what we're missing is one really cool flash of insight and maybe you will have that flash of insight and revolutionize the way everybody thinks about the universe. Why not? Well, we hope you enjoyed that. Thanks for joining us.

See you next time. Thanks for listening. And remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. For more podcasts from IHeartRadio, for more podcasts from IHeart. Heart Radio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. processors, blazing speed, and AI-powered performance.

It keeps up with your business, not the other way around. Whoa, this thing moves. Stop hitting snooze on new tech. Win the tech search at Lenovo.com. Lenovo, Lenovo. Unlock AI experiences with the ThinkPad X1 Carbon, powered by Intel Core Ultra processors so you can work, create, and boost productivity all on one device. December 29th, 1975.

LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged. Terrorism. Listen to the new season of Law and Order Criminal Justice System on the iHeart

Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate.

Maybe. Find out how it ends by listening to the OK Storytime podcast. and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.