Daniel and Jorge Explain the UniverseDaniel 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.com
See omnystudio.com/listener for privacy information.
If you love iPhone, you'll love Apple Card. It's the credit card designed for iPhone. It gives you unlimited daily cash back that can earn four point four zero percent annual percentage yield. When you open a high Yield savings account through Apple Card, apply for Applecard in the wallet app subject to credit approval. Savings is available to Apple Card owners subject to eligibility. Apple Card and Savings by Goldman Sachs Bank USA, Salt Lake City Branch, Member FDIC terms and more at applecard dot Com. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is US Dairy tackling greenhouse gases? Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit us dairy dot COM's Last Sustainability to learn more.
Hi.
I'm David Ego from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I mean neuroscientists at Stanford and I've spent my career exploring the three pound universe in our heads.
Join me weekly to explore the relationship.
Between your brain and your life, because the more we know about what's running under the hood be or we can steer our lives. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple podcasts, or wherever you get your podcasts.
I'm doctor Laurie Santos, host of the Happiness Lab podcast.
As the US.
Elections approach, it can feel like we're angrier and more divided than ever.
But in a new hopeful season of.
My podcast, I'll Share with the Science Really shows that was surprisingly more united than most people think.
We all know something is wrong in our culture and our politics and that we need to do better, and that we can.
Listen on the iHeartRadio app, Apple podcasts or wherever you listen to podcasts.
Hey, Daniel, 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 gonna start recording and then hope we get an idea. Isn't that like putting costs after effect?
Yeah, you know, just a little causality inversion to start your day. What could go wrong?
It's never a good sign when a physicist says, what could go wrong?
Well, you know, we haven't destroyed the universe yet, but.
What if we blow 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 Jorgem, cartoonist and the creator of PhD comics.
Hi.
I'm Daniel. I'm a particle physicist and a physics professor at UC Irvine, 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.
And 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 iHeartRadio.
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 to mystery.
If I could just have like digital socks, I could have them on my phone. That would be so much more convenient.
Well, I know you like to wear sandals, so I'm pretty sure you already have virtual socks.
Yeah, exactly. That's why I could just delete all the socks and one fell through. 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 you know, 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 deep truth about the universe, and it turns out not so much, which means that what lies ahead of us is more discoveries that 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, so it'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 mind. And if you think that's cheating, then you know physics 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 the two way conference with us and the aliens? Do you think we have anything to teach them?
Are we joking or we're 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 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 will 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 we 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 alien 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 and 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 physics is a little bit paranoid almost in a way like now you doubt everything, like even the basics, 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 is sort of the definition of me of being paranoid. What you're saying, you're paranoid in a good way. You're like a good paranoid.
A good kind of paranoid is 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 and the way we tell stories and think about what makes sense and what doesn't make sense.
Yeah.
So today own 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 questions and causes?
Yeah? Yeah. The effect of asking this question is it's got to be 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 talk, 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 era 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 detailed 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, if 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 costality? Do we need cost 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, and 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 cause out? Cause or effect? Which one do you like better?
I prefer horses to cows, So let's throw out cowsality.
Is it cost or effect? Well, anyways, we were, as usual, were 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. Do you please write to us to questions at Danielandjorge dot 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, 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 about 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 chao, 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 an 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 causally, but I mean, if you want to know the part cause an effect, obviously play role in knowing what that one part was.
But if we didn't have it and we didn't need it, that would mean the possibility is multi versus, and that'd be so maybe we don't want 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 no causality, but I don't think you necessarily need causality, to get information.
All right, some pretty definitive answers here. Nobody seem 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 humans?
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, 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 know, as always have to be connected to bs? Do 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 have B before A? Do you know what I mean? Do you me all 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 the pop out of nowhere. Right, the laws of physics says no.
Yeah, well depends on exactly what B is, right, Like quantum mechanics says, you can 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 give up on that a million years ago because we discovered 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 a 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 eight am in the morning, and B as you've arrived at work at nine am. 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 coworker's 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 and 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 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 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 to 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 or 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 eight am and change your decision based on whether or not you had it with you in your office at nine am. So you know, making a decision at nine am can't influence what happened at eight am. 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 that you use 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 queue that we're going to challenge that it might turn out to be wrong. So let's get into that and what how we can maybe test it or find out the true answer. But first, let's take a quick break.
With big wireless providers, what you see is never what you get. Somewhere between the store and your first month's bill, the price you thought you were paying magically skyrockets. With mint Mobile, you'll never have to worry about gotcha's ever again. When mint Mobile says fifteen dollars a month for a three month plan, they really mean it. I've used mint Mobile and the call quality is always so crisp and so clear I can recommend it to you. So say bye bye to your overpriced wireless plans, jaw dropping monthly bills and unexpected overages. You can use your own phone with any mint Mobile plan and bring your phone number along with your existing contacts. So dit your overpriced wireless with Mint Mobiles deal and get three months a premium wireless service for fifteen bucks a month. To get this new customer offer in your new three month premium wireless plan for just fifteen bucks a month, go to mintmobile dot com slash universe. That's mintmobile dot com slash universe. Cut your wireless build a fifteen bucks a month at mintmobile dot com slash universe. Forty five dollars upfront payment required equivalent to fifteen dollars per month new customers on first three month plan only. Speeds slower about forty gigabytes on unlimited plan. Additional taxi spees and restrictions apply. See mint Mobile for details.
AI might be the most important new computer technology ever. It's storming every industry and literally billions of dollars are being invested, so buckle up. The problem is that AI needs a lot of speed and processing power, So how do you compete without cost spiraling out of control? It's time to upgrade to the next generation of the cloud. Oracle Cloud Infrastructure or OCI. OCI is a single platform for your infrastructure, database, application development, and AI needs. OCI has four to eight times the bandwidth of other clouds, offers one consistent price instead of variable regional pricing, and of course nobody does data better than Oracle. So now you can train your AI models at twice the speed and less than half the cost of other clouds. If you want to do more and spend less, like Uber eight by eight and Data Bricks Mosaic, take a free test drive of OCI at Oracle dot com slash strategic. That's Oracle dot com slash Strategic Oracle dot com slash Strategic.
If you love iPhone, you'll love Apple Card. It's the credit card designed for iPhone. It gives you unlimited daily cash back that can earn four point four zero percent annual percentage yield. When you open a high Yield savings account through Applecard, apply for Applecard in the wallet app, subject to credit approval. Savings is available to Applecard owners subject to eligibility. Apple Card and Savings by Goldman Sachs Bank USA Salt Lake City Branch Member FDIC terms and more at applecard dot com. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt. You're probably not thinking about the environmental impact of each and every bite, but the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US Dairy tackling greenhouse gases. Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more.
All right, we're talking about cause and effect and whether you actually need it to make a happy universe. I guess, right, a functioning the.
Universe, Yeah, exactly, whether we can make sense of our universe without causality, or whether it's actually absolutely fundamentally required for anything that makes 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, 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.
Course, of course, want the mechanics always your brain. So that seems that 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 are 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 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 three D it's 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 Okay, took out when I left my home, Like you're saying, like there's this 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 by 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 acurian to.
Mean, or scrambled eggs on a cone.
Scrambled eggs on a cone. Actually, that might be a great food truck. You know, that's the kind of thing you would see in La with like a huge line of hipsters, you know.
Right, yeah, breakfast cones. It's making 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 my light moves in straight lines like it does out in deep space, then they're just like we talked about them. They're triangles and two dimensions, or they're cones in three D. 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, but 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 curve cones because then the eggs will all fall out, right.
What this is why physicists shouldn't be cooks. But anyways, going back to our topic, you're saying, as you know, space can bend, and that can bend or light cones, and that can somehow effect cause and effect. That you can break cost 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're 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 you know, 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 lineup with which effects I see.
So it's not that you're saying cost and effect is flexible in a way.
Yeah, exactly. As you're near some heavy mass, then which cause in which effects lineup depends exactly on the curvature of space, because it depends on how information travels. You know, 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 a maybe a fifty percent chance that I took a right and a fifty percent 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. It's very dramatic. But every time there's quantum uncertainty, and that uncertainty leads to uncertainty in where stuff is in the universe. That means it's 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 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 of more clever names. But we have two people doing experiments somewhere out in space, and their experiments depend, for example, on how close they 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 slow 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. That'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've been simplify by just talking about like shrod Inger'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 their experiment.
Yeah, this sounds like Shortinger'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 the very beginning, we define causality saying, well, if A can influence B, you know A causes B to 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 happened first, and they do influence each other. One is definitely inside the light cone or 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 kata is alive or dead anyways?
Right, that's right, we don't know quantum mechanics whether the cat is or live 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 Schutinger's box example, you know, the causality is clear, like you know, the radioactive element decays and it 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 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 that 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 in 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 finding a theory of quantum gravity and revealing the deep nature of the universe is to give up on causality, to 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, uh, it 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 or dynamics. 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 like how that would actually influence the universe.
All right, well, I think basically what you're saying though, is that you know, 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? That's 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 happen 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 in 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 caustality in the universe. But first, let's take a quick break.
When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are us. Dairy has set themselves some ambitious sustainability goals, including being green how gas neutral by twenty to fifty That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more.
Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America.
I mean neuroscientists at Stanford, and.
I've spent my career exploring the three pound universe in our heads. We're looking at a whole new series of episodes this season to understan and why and how our lives look the way they do. Why does your memory drift so much? Why is it so hard to keep a secret, When should you not trust your intuition? Why do brains so easily fall for magic tricks? And why do they love conspiracy theories? I'm hitting these questions and hundreds more, because the more we know about what's running under the hood, better we can steer our lives.
Join me weekly to explore the relationship.
Between your brain and your life by digging into unexpected questions. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
Parents, are you looking for a screen free, engaging way to teach your kids the Bible, one that's easy to understand and enjoyable for multiple ages. Kids Bible Stories Podcast is here to help. I created this for my own children and it's now a favorite among thousands of Families love the vivid imagery, scriptures, and sound effects, while parents appreciate the apply section for meaningful conversations. We have hundreds and hundreds of beautiful episodes that bring the Bible to life when you simply press play. It's a sound and practical resource that walks alongside you as you teach your kids. We want kids to see how incredible God's word is in an engaging and memorable way with Kids Bible Stories Podcast. Listen to Kids Bible Stories Podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
My name is Sadiete. I moved to the US at nineteen. I spoke no English, and I struggle finding job opportunities. Everything I have I owe to the Adult Littlecy Center and getting my high school diploma at age twenty two.
It was an honor helping you achieve your greatness. Now you're helping others achieve theirs.
It inspires me.
When you graduate, they graduate, find free and supportive adult education centers near you at finish yoururdiploma dot org brought to you by Dollar General Literacy Foundation and the AD Council.
All Right, So, Daniel, apparently maybe the universe doesn't need causality, you know, 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, cause before effect. Whatever. As long as I got my breakfast cone, I'm.
Fine, Yeah, whatever, as long as I got bacon and 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 causality, but like an important wakening, you know, to say like, ooh, this a cracking 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 two thousands 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. 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 are 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 beams 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 then 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 polarize 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 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 are things that are conceptually the same as like rotations, where you know it matters what order 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 happens.
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 AB path or the BA path? And what you see when it comes out is a really interesting interference pattern between photons that went through AB and then photons that went through B A. And it's 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 AB or whether it went through BA. 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 the photons that come out, and when you get a photon out of that joint beam. You don't know whether it went through AB or BA, but it sort of 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, AB has different photons than BA, and sort an individual photon, there's 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 BA. Every photon now has a probability of having one order or the other.
Right, But I guess, you know, 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 the 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 bells 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 spinned down, and to prove that they are not determined until you open one box, even if they're really far apart. You have to do these really subtle experiments called probing bells 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 br 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 definitely 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 constally ish definitely causal. So then what does that mean for us, Like, does that mean that we can now break the rules to do cool things or does it mean that, you know, it's just another sort of step in our sort of befuddlement with quantum mechanics.
Is there some rule in particular you're hoping to get to break you're looking for permission.
Yeah, you know, I want to eat the breakfast cone and not gain weight. Can we sort of reverse the cause and effect there exactly?
Or you can eat breakfast any time of day. No, there are some potential applications to this. You know, anytime 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 causativefect 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 and it 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 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 a code?
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 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, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases many farms use anaerobic digestors to turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's last Sustainability to learn more.
Now's the time to start your next adventure behind the wheel of an exciting new Toyota Hybrid. With the largest lineup of hybrid, plug in, hybrid and electrified vehicles to choose from, Toyota has the one for you. Every new Toyota Hybrid comes with Toyota Care, two year complimentary scheduled maintenance, an exclusive hybrid battery warranty, and Toyota's legendary quality and reliability. Visit your local Toyota dealer today. Toyota Let's go Places. See your local Toyota dealer for hybrid battery warranty details.
Hi.
I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I'm I mean neuroscientists at Stanford and I've spent my career exploring the three pound universe in our heads.
Join me weekly to explore the relationship.
Between your brain and your life. Because the more we know about what's running under the hood, better we can steer our lives. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
