WEBVTT - Does the Universe need cause and effect? 0:00:08.240 --> 0:00:10.719 Hey, Daniel, what are we doing today for the opening 0:00:10.720 --> 0:00:13.079 of the podcast? You know, actually I thought maybe we 0:00:13.119 --> 0:00:17.479 would invert the usual process. We have a usual process. Yeah, 0:00:17.720 --> 0:00:20.400 first we have an idea and then we record it. 0:00:20.480 --> 0:00:22.800 So you want to flip it today? So what does 0:00:22.840 --> 0:00:25.160 that mean? We're gonna start recording and then hope we 0:00:25.239 --> 0:00:28.400 get an idea. Isn't that like putting costs after effect? Yeah, 0:00:28.440 --> 0:00:31.320 you know, just a little causality inversion to start your day? 0:00:31.480 --> 0:00:33.440 What could go wrong? It's never a good sign when 0:00:33.440 --> 0:00:35.760 the physicist says what could go wrong? Well, you know, 0:00:35.840 --> 0:00:38.320 we haven't destroyed the universe yet, but what if we 0:00:38.400 --> 0:00:41.280 blow up the universe with this inverted opening? Oh, and 0:00:41.400 --> 0:00:44.199 that gives me an idea for a perfect opening. Hopefully 0:00:44.200 --> 0:01:02.160 people laughed before they listen to that. Hi am Jorgemming, 0:01:02.200 --> 0:01:05.240 cartoonists and the creator of PhD comics. Hi. I'm Daniel. 0:01:05.240 --> 0:01:08.120 I'm a particle physicist and a physics professor at u 0:01:08.240 --> 0:01:10.520 C Irvine, and I usually don't know what I'm going 0:01:10.560 --> 0:01:12.720 to say before I say it. Isn't that part of 0:01:12.760 --> 0:01:15.679 the job description for a professor not knowing what you're 0:01:15.680 --> 0:01:18.920 talking about exactly, but making it sound like you do, 0:01:19.160 --> 0:01:22.319 and that's where the PhD comes from. I guess years 0:01:22.319 --> 0:01:26.479 of training. Welcome to our podcast, Daniel and Jorge Explain 0:01:26.560 --> 0:01:29.240 the Universe, a production of My Heart Radio in which 0:01:29.280 --> 0:01:31.680 we are not afraid to admit what we don't know 0:01:31.760 --> 0:01:35.240 about the universe because we love to embrace that ignorance. 0:01:35.520 --> 0:01:38.959 We dive deep into everything that we don't understand about 0:01:39.000 --> 0:01:41.959 the universe, the very nature of space and time, the 0:01:42.040 --> 0:01:45.200 context of the reality around us, all of the squishy 0:01:45.280 --> 0:01:49.200 and beautiful and incredible matter that fills it and wiggles 0:01:49.240 --> 0:01:51.920 around inside of it. We are desperate to understand the 0:01:51.960 --> 0:01:54.200 deep nature of the universe, and we are here to 0:01:54.400 --> 0:01:57.400 explore it and explain it to you. Yeah, because there 0:01:57.520 --> 0:01:59.320 is a lot we don't know about the universe. And 0:01:59.320 --> 0:02:01.800 I'm not just talking about myself a cartoonist, but there's 0:02:01.800 --> 0:02:05.040 a lot that even physicists don't know about, not just 0:02:05.120 --> 0:02:07.840 things hidden inside of black holes or neutron stars or 0:02:07.880 --> 0:02:11.960 inside of particles. There's some very fundamental questions we still 0:02:12.000 --> 0:02:15.160 have about this wild and wacky universe. Yeah, exactly, like 0:02:15.440 --> 0:02:17.560 where did I put my phone? And how come I 0:02:17.560 --> 0:02:19.840 can never find an even number of socks at the 0:02:19.880 --> 0:02:22.440 same time, I think maybe you put the phone in 0:02:22.480 --> 0:02:25.560 your socks. That would solve if I could just have 0:02:25.639 --> 0:02:28.040 like digital socks so I could have them on my phone, 0:02:28.320 --> 0:02:31.040 that would be so much more convenient. Well, I know 0:02:31.080 --> 0:02:32.880 you like to wear sandals, so I'm pretty sure you 0:02:32.880 --> 0:02:35.480 already have virtual socks. Yeah, exactly. That's why I could 0:02:35.520 --> 0:02:38.400 just delete all the socks in one film. But it's 0:02:38.400 --> 0:02:40.760 not really just sucks that we are curious about. We 0:02:40.840 --> 0:02:44.200 really do want to understand the deep nature of reality 0:02:44.240 --> 0:02:47.079 around us. What is this universe? How did it come 0:02:47.080 --> 0:02:49.680 to me? Why is it this way and not another way? 0:02:49.880 --> 0:02:53.040 And most importantly, are there things about it that we're 0:02:53.040 --> 0:02:55.840 getting basically wrong? Yeah, because you know, I feel like 0:02:55.840 --> 0:02:59.320 you can ask questions about the universe and the stuff 0:02:59.360 --> 0:03:01.440 in the universe us, you know, like black holes and 0:03:01.840 --> 0:03:05.200 stars and particles, but you can also kind of ask deep, 0:03:05.320 --> 0:03:08.160 kind of philosophical questions about it. You know, it's sort 0:03:08.200 --> 0:03:10.919 of like about the nature of it or what can 0:03:11.000 --> 0:03:13.400 break the universe even Yeah, because we know that in 0:03:13.520 --> 0:03:16.440 human history we've made a lot of basic mistakes about 0:03:16.440 --> 0:03:19.040 the way we thought the universe worked, because we've only 0:03:19.080 --> 0:03:21.799 seen it work in one particular way or in one 0:03:21.840 --> 0:03:25.480 set of circumstances, and we imagined that must be true forever, 0:03:25.560 --> 0:03:27.600 it must be a deep truth about the universe, and 0:03:27.600 --> 0:03:30.520 it turns out not so much, which means that what 0:03:30.639 --> 0:03:33.959 lies ahead of us is more discoveries that basic assumptions 0:03:34.000 --> 0:03:36.520 about the nature of the universe are probably wrong, and 0:03:36.560 --> 0:03:38.600 it might just be that we need to hammer at 0:03:38.600 --> 0:03:41.480 these things forever, or wait till the aliens arrive and 0:03:41.520 --> 0:03:43.920 give us some other context for looking at the nature 0:03:43.960 --> 0:03:46.760 of the universe. But that's cheating, Daniel. Are they also 0:03:46.800 --> 0:03:48.440 going to tell you where your socks are? Are you 0:03:48.480 --> 0:03:52.400 gonna be that irresponsible? They're gonna email us socks. It's 0:03:52.400 --> 0:03:55.280 gonna be nice digital socks. That's not cheating at all. 0:03:55.320 --> 0:03:58.560 I think the first Galactic physics conference will be, you know, 0:03:58.840 --> 0:04:01.320 a great melding of lines. If you think that's cheating, 0:04:01.640 --> 0:04:03.760 then you know physicist shouldn't work together at all. We 0:04:03.760 --> 0:04:05.560 should all be trying to figure out the universe on 0:04:05.600 --> 0:04:07.640 our own. Well, but do you think it'd be the 0:04:07.680 --> 0:04:09.760 two way conference with us and the aliens? Do you 0:04:09.760 --> 0:04:12.400 think we have anything to teach them? Are we joking 0:04:12.400 --> 0:04:14.640 over being serious? I don't know. I mean, if they 0:04:14.640 --> 0:04:18.200 can travel through the stars, and you know, invent warp drives. 0:04:18.240 --> 0:04:20.120 Do you think we have anything to teach them or 0:04:20.600 --> 0:04:22.599 do you think we know something they don't? At this point, 0:04:22.680 --> 0:04:24.839 I think it's very likely that everything we've learned in 0:04:24.839 --> 0:04:27.960 our human sciences is probably corrupted by human bias and 0:04:28.080 --> 0:04:31.360 totally useless to aliens, not just because we haven't made 0:04:31.440 --> 0:04:34.919 advances far enough, but probably just the questions we ask 0:04:35.000 --> 0:04:37.320 in the nature of the way we answer them is 0:04:37.360 --> 0:04:41.320 probably deeply inherently human in ways we can't even imagine. 0:04:41.600 --> 0:04:43.720 You know, we don't even really know where the edge 0:04:43.760 --> 0:04:45.640 of the box is. We just know that we're in 0:04:45.680 --> 0:04:48.560 this sort of like human constructed box about ways to 0:04:48.640 --> 0:04:51.359 think about the universe. And it isn't until the aliens 0:04:51.360 --> 0:04:53.520 come that will even figure out like where the edge 0:04:53.520 --> 0:04:56.080 of that box is. Yeah, I guess because we we've 0:04:56.120 --> 0:04:58.119 been trying to figure everything out with the human brain. 0:04:58.160 --> 0:04:59.880 And you know what if you have a totally different 0:05:00.200 --> 0:05:03.200 maybe you get to see things in a very different way, yeah, 0:05:03.320 --> 0:05:06.000 or different sensory organs. Right, what if you can see 0:05:06.279 --> 0:05:09.520 X rays, or you can smell photons, or you can 0:05:09.560 --> 0:05:12.479 taste electrons or something like that, Right, you might have 0:05:12.520 --> 0:05:14.920 figured out totally different ways to think about the universe 0:05:14.960 --> 0:05:18.039 in a completely different order. Maybe quantum mechanics is intuitive 0:05:18.040 --> 0:05:21.040 to them because you know, they've seen this stuff happening 0:05:21.040 --> 0:05:23.400 in front of them every single day. Or maybe they 0:05:23.400 --> 0:05:26.120 can see neutrinos and so the universe is like totally 0:05:26.160 --> 0:05:28.320 opaque and very weird to them. It's going to be 0:05:28.360 --> 0:05:30.760 a challenge to map from human brains to alien brains. 0:05:30.800 --> 0:05:33.200 Sometimes it's hard to even map from human brain to 0:05:33.320 --> 0:05:36.640 human brain. Yeah, So I think what you're saying is 0:05:36.680 --> 0:05:39.640 that sometimes there are revolutions and human thought where we 0:05:40.200 --> 0:05:42.320 thought that the universe worked one way and then it 0:05:42.360 --> 0:05:45.799 turns out it worked another way, right, Like maybe quantum 0:05:45.800 --> 0:05:48.880 physics is one of those big revolutions, or relativity exactly. 0:05:49.200 --> 0:05:52.000 Those two are the best examples of moments when we 0:05:52.040 --> 0:05:55.360 realized that fundamentally the universe is very different from the 0:05:55.400 --> 0:05:57.839 way we imagined. And I think we put those on 0:05:57.880 --> 0:06:01.200 the scale of other kinds of realizations, like discovering that 0:06:01.279 --> 0:06:03.360 the Earth is not the center of the Solar System 0:06:03.560 --> 0:06:06.479 or even the cosmos, or discovering that our galaxy is 0:06:06.560 --> 0:06:10.480 one of trillions of galaxies instead of the entire cosmos. 0:06:10.800 --> 0:06:13.400 You know, these kinds of things help us understand not 0:06:13.600 --> 0:06:15.960 just the nature of the universe around us, but our 0:06:16.040 --> 0:06:18.720 place in it, in the context of our very existence. 0:06:19.080 --> 0:06:22.359 So these are pretty deep potential revolutions in our understanding 0:06:22.360 --> 0:06:24.320 of the nature of the universe. Yeah, and do you 0:06:24.320 --> 0:06:26.680 think that has made fits This is a little bit 0:06:27.000 --> 0:06:29.719 paranoid almost in a way like now you doubt everything, 0:06:29.800 --> 0:06:33.560 like even the basics, you know, logic of the universe. Right. No, 0:06:33.720 --> 0:06:36.640 it makes this excited because it means that around every 0:06:36.680 --> 0:06:41.119 corner is a potential explosion of ideas. You can tug 0:06:41.120 --> 0:06:43.920 on any random thread and pull the whole thing apart. 0:06:44.120 --> 0:06:46.479 Paranoid makes it sound like we're afraid to pull the 0:06:46.480 --> 0:06:49.000 whole thing apart. We are desperate to pull it apart 0:06:49.080 --> 0:06:51.520 because it will reveal something else, something new that we 0:06:51.560 --> 0:06:53.800 can chew on, where we can make new progress and 0:06:53.839 --> 0:06:56.400 ask new questions. That's the dream come true. I think 0:06:56.400 --> 0:06:58.760 being afraid of explosions at every corner is sort of 0:06:58.760 --> 0:07:01.960 the definition of making being paranoid. But you're saying, and 0:07:02.240 --> 0:07:04.800 you're paranoid in a good way. You're like a good paranoid, 0:07:05.600 --> 0:07:08.240 a good kind of parentig is somehow you walk me 0:07:08.240 --> 0:07:10.320 into that corner. But yes, I am now admitting I'm 0:07:10.320 --> 0:07:13.760 a good kind of paranoid. But yeah, you can ask 0:07:13.760 --> 0:07:16.240 pretty deep questions about the universe, and so today we're 0:07:16.280 --> 0:07:19.760 asking a pretty challenging question. I mean in the sense 0:07:19.800 --> 0:07:23.240 that it challenges something very deep and sort of I 0:07:23.280 --> 0:07:26.560 don't know, logical and basic about the universe that you know, 0:07:26.880 --> 0:07:28.880 maybe a lot of people don't even think you can 0:07:28.960 --> 0:07:31.600 even ask. That's right. It's something that's so fundamental to 0:07:31.600 --> 0:07:34.640 the universe that even is incorporated in how we explain 0:07:34.720 --> 0:07:38.040 the universe itself. It's something inherent I think in the 0:07:38.080 --> 0:07:40.960 way humans think and the way we tell stories and 0:07:41.000 --> 0:07:44.080 think about what makes sense and what doesn't make sense. Yeah, 0:07:44.120 --> 0:07:45.880 So to be on the program, we'll be asking the 0:07:45.960 --> 0:07:56.280 question does the universe need cause and effect? WHOA Daniel? 0:07:56.640 --> 0:07:58.080 This kind of blew my mind. I mean, how can 0:07:58.120 --> 0:08:00.840 you how can you question cause and effect and causality 0:08:00.840 --> 0:08:02.760 in the universe? Are you saying there's some effects to 0:08:02.880 --> 0:08:07.160 question and causes? Yeah? Yeah. The effect of asking this 0:08:07.240 --> 0:08:10.200 question is it's gott me really confused. I know. I 0:08:10.200 --> 0:08:12.800 think it's so fundamental to the way we think, you know, 0:08:12.880 --> 0:08:15.520 we the way we explain things to ourselves, as we 0:08:15.600 --> 0:08:18.280 tell stories and stories go like a happened, and then 0:08:18.320 --> 0:08:21.160 be happened, and then see happened. That's the way we talk, 0:08:21.280 --> 0:08:23.520 that's the way we think, that's the way we organize 0:08:23.560 --> 0:08:27.080 our minds, and so it's pretty hard to imagine that 0:08:27.120 --> 0:08:29.880 you could have a universe without cause and effect. On 0:08:29.960 --> 0:08:32.160 the other hand, just because it's part of our minds 0:08:32.240 --> 0:08:34.800 doesn't mean it has to be part of the universe, right. 0:08:35.160 --> 0:08:37.360 The whole goal of physics is to break out of 0:08:37.360 --> 0:08:41.280 that box and understand something universal instead of something human. Now, Daniel, 0:08:41.360 --> 0:08:43.760 is this related to like the idea of the arrow 0:08:43.880 --> 0:08:46.120 of time or is this sort of like a basic 0:08:46.400 --> 0:08:48.920 kind of thing about the universe where like things can 0:08:49.000 --> 0:08:52.120 happen without being connected to other things. Do you know 0:08:52.160 --> 0:08:55.120 what I mean? Yeah, definitely it's connected to the question 0:08:55.120 --> 0:08:58.240 of time, because cause and effect orders things. And we'll 0:08:58.240 --> 0:09:00.600 talk about this in more detailed later. You know, there's 0:09:00.600 --> 0:09:03.760 this concept of like a light cone, which organizes the 0:09:03.880 --> 0:09:06.360 order of events. Things have to happen in the universe, 0:09:06.559 --> 0:09:10.520 But that's only true if you have causality. If things 0:09:10.559 --> 0:09:13.440 have to happen in a certain order. Things don't have 0:09:13.480 --> 0:09:16.480 to happen in a certain order. That whole picture might 0:09:16.520 --> 0:09:19.840 go out the window. Whoa, And that's you know, totally 0:09:19.840 --> 0:09:24.319 opposite from our everyday experience, right, Like our everyday experience 0:09:24.400 --> 0:09:27.880 is that effects do follow causes, right absolutely. You know, 0:09:28.280 --> 0:09:31.160 if your friends don't like, arrive for dinner before you 0:09:31.200 --> 0:09:37.640 invite them, you should meet my friends. Introverts don't have 0:09:37.760 --> 0:09:40.760 guests rorive for dinner before you invite them. You know. 0:09:40.840 --> 0:09:43.000 It's like if you send somebody a message, they can't 0:09:43.040 --> 0:09:45.760 read the message before you send it. Right, the kind 0:09:45.760 --> 0:09:48.880 of thing would violate causality. It's definitely connected with the 0:09:48.880 --> 0:09:50.520 flow of time because it has to do with like, 0:09:50.760 --> 0:09:53.240 you know, sending messages back in time. One of the 0:09:53.280 --> 0:09:55.760 reasons we always say that you can't travel back in 0:09:55.800 --> 0:09:58.520 time is that it would violate causality. You would have 0:09:58.559 --> 0:10:01.560 effects that influence the our own causes. Right. It's like 0:10:01.840 --> 0:10:04.200 very basic to the way we think about the universe, 0:10:04.280 --> 0:10:07.720 stepping forwards in time, flowing from now to the future. 0:10:07.880 --> 0:10:10.280 All right, Well, then the question is do we actually 0:10:10.360 --> 0:10:13.160 need causality? Do we do we need costs and effect 0:10:13.200 --> 0:10:15.360 in the universe to make it work or are you 0:10:15.360 --> 0:10:18.520 saying it's sort of maybe like an illusion or something 0:10:18.559 --> 0:10:21.160 that's apparent, but not really needed in the universe. What 0:10:21.240 --> 0:10:24.199 are we actually asking here? I think the question is 0:10:24.480 --> 0:10:27.079 whether it's always needed? You know, this is the kind 0:10:27.120 --> 0:10:28.839 of thing that we observe in the universe. It is 0:10:28.880 --> 0:10:32.000 definitely part of the universe. But just like with relativity 0:10:32.000 --> 0:10:35.120 and quantum mechanics, there are some places where it seems 0:10:35.160 --> 0:10:38.520 like it might not hold together, some like little threads 0:10:38.600 --> 0:10:41.559 where it doesn't really work and it isn't really consistent 0:10:41.800 --> 0:10:44.280 with some other basic principles, And that gives us a 0:10:44.360 --> 0:10:48.280 clue that maybe it's not always required, and maybe like 0:10:48.320 --> 0:10:51.080 it comes together in certain circumstances. It's a nice way 0:10:51.120 --> 0:10:53.880 to describe what often happens in the universe, but it's 0:10:53.920 --> 0:10:56.320 not actually a fundamental principle, and we can find some 0:10:56.400 --> 0:10:59.240 places where it's tossed out the window. So I who 0:10:59.240 --> 0:11:01.600 would be the one we cause out? Cause or effect? 0:11:01.800 --> 0:11:04.120 Which one do you like better? I prefer horses to cow, 0:11:04.240 --> 0:11:09.559 so let's throw out cowsality is it cost or effect? Well? Anyways, 0:11:09.559 --> 0:11:11.839 we were, as usual, wondering how many people out there 0:11:11.840 --> 0:11:15.560 had thought about this crazy, deep, fundamental question, and how 0:11:15.559 --> 0:11:17.600 many people think they might have an answer to this 0:11:17.800 --> 0:11:20.480 strange query. So Daniel went out there to the internet 0:11:20.520 --> 0:11:23.920 to ask people do we need cause and effect? So 0:11:24.040 --> 0:11:26.440 thank you everybody out there on the Internet who is 0:11:26.440 --> 0:11:29.760 willing to answer these funny, crazy questions without having a 0:11:29.840 --> 0:11:32.680 chance to think about it or google it. If you'd 0:11:32.679 --> 0:11:34.520 like to do then it sounds fun. Do you please 0:11:34.520 --> 0:11:37.600 write to us two questions at Daniel and Jorge dot com. 0:11:37.800 --> 0:11:40.120 We want your voice, so think about it for a second. 0:11:40.160 --> 0:11:43.640 Do you think the universe needs cause and effect? Here's 0:11:43.679 --> 0:11:46.000 what people had to say. I think that we as 0:11:46.520 --> 0:11:50.800 human beings probably need it. Whether the universe needs it 0:11:51.360 --> 0:11:55.600 or existence, probably not. I can imagine a crazy universe 0:11:55.640 --> 0:12:00.440 where everything was upside down and happened of its own coalition, 0:12:00.600 --> 0:12:03.400 But as people, I think we wouldn't do very well 0:12:03.440 --> 0:12:07.320 in such a place. I don't know much about this. 0:12:07.880 --> 0:12:10.280 That makes me think of the Matrix when the marrow 0:12:10.360 --> 0:12:15.320 Vingian is talking about cause and causality or something like that. Um, 0:12:15.360 --> 0:12:18.000 I understood about that about as much as I understood 0:12:18.000 --> 0:12:22.079 most of that movie. But without honestly really knowing much 0:12:22.080 --> 0:12:25.160 about it, I'm gonna say no. I know things can 0:12:25.320 --> 0:12:30.240 kind of happen what seems to be randomly in the universe, 0:12:30.520 --> 0:12:37.040 and with things the statistical chances that some of the 0:12:37.120 --> 0:12:40.600 things that do happen, the statistical chances are so low 0:12:40.679 --> 0:12:42.760 that it just doesn't seem like there could be a 0:12:42.800 --> 0:12:45.720 cause for every single thing that can happen, because there's 0:12:45.800 --> 0:12:49.600 so many different things that can happen. So do we 0:12:49.640 --> 0:12:53.760 need causality? I'm going with no on that one. I 0:12:53.800 --> 0:12:57.280 think we need causality because if we didn't have cause 0:12:57.320 --> 0:13:04.000 and effect, everything would just be us because like there 0:13:04.040 --> 0:13:07.640 would be no reason for anything to happen. Things would 0:13:08.880 --> 0:13:12.760 stepping on a butterfly would cause something completely crazy to happen, 0:13:13.800 --> 0:13:18.840 not just like butterfly effect, but like completely bananas. Well, 0:13:19.040 --> 0:13:24.360 let's I'm thinking of this. You eat, you get fat, 0:13:25.600 --> 0:13:32.040 cause an effect, and I think we don't need it, 0:13:32.440 --> 0:13:38.520 and they should be voted out so we don't need it. 0:13:40.160 --> 0:13:43.040 We can start a petition, I'm sure if we need 0:13:43.120 --> 0:13:45.120 called out, But I mean, if you want to know 0:13:45.200 --> 0:13:48.640 the past, cause an effect obviously play a role in 0:13:48.960 --> 0:13:54.160 knowing what that one part was. But if we didn't happen, 0:13:54.200 --> 0:13:57.880 if we didn't need it, that would mean possibility is multiverse, 0:13:58.880 --> 0:14:01.640 and that would be though. I think maybe we don't 0:14:01.720 --> 0:14:08.080 want No. I don't think we need causality. You can 0:14:08.200 --> 0:14:12.840 have two things that are correlated, like in you know, 0:14:13.040 --> 0:14:18.760 economics or statistics. You know, they look for correlations, and 0:14:18.840 --> 0:14:24.600 correlations provide information in and of themselves. Maybe it's nice 0:14:24.640 --> 0:14:28.520 to no causality, but I don't think you necessarily need 0:14:29.320 --> 0:14:35.120 causality to get information, all right, some pretty definitive answers here. 0:14:35.280 --> 0:14:37.920 Nobody seem to sort of stumble a lot, I know, 0:14:38.360 --> 0:14:40.400 and some people who really think, like, yeah, we could 0:14:40.440 --> 0:14:45.200 do without causality. That really surprised me. Really, wow, do 0:14:45.240 --> 0:14:48.880 you think that's human humors? Maybe physics has just been 0:14:48.920 --> 0:14:52.560 so successful in like knocking down basic pillars of reality 0:14:52.560 --> 0:14:55.160 that people are ready for, like physics to undermine everything. 0:14:55.360 --> 0:14:58.000 You're seeing it as a positive, seeing it as a 0:14:58.040 --> 0:15:01.880 positive people are open minded to unraveling the basic nature 0:15:01.920 --> 0:15:04.360 of their very existence. That's great. Well, I think maybe 0:15:04.400 --> 0:15:06.760 this goes back to what I asked earlier about what 0:15:06.880 --> 0:15:10.160 exactly do we mean by causality and not having causality? 0:15:10.440 --> 0:15:13.680 Like does it mean that you can't have a without 0:15:13.720 --> 0:15:16.800 B or does it mean that you know, as always 0:15:16.840 --> 0:15:19.200 have to be connected to bees? You know what I mean? 0:15:19.240 --> 0:15:21.440 Like can things appear out of nowhere without a cause? 0:15:21.640 --> 0:15:24.240 Or are we saying that it always has to come 0:15:24.280 --> 0:15:26.680 before B. You cant have be before A, you know 0:15:26.720 --> 0:15:29.240 what I mean? The difference. Yeah, it's about the ordering 0:15:29.360 --> 0:15:32.840 of events, right, I mean, you still can't break random 0:15:32.880 --> 0:15:36.160 laws of physics. You can't just like create energy from nothing. 0:15:36.480 --> 0:15:38.400 It's not like it's a free for all out there. 0:15:38.560 --> 0:15:42.000 We think the universe still does have laws and does 0:15:42.040 --> 0:15:44.360 follow those laws. We're just not sure that those laws 0:15:44.400 --> 0:15:48.280 require that A always happens before B. So we're pretty 0:15:48.320 --> 0:15:51.680 clear that you can't just have B without like the 0:15:51.960 --> 0:15:56.520 pop out of nowhere. Right the laws of physics says no, Yeah, 0:15:56.560 --> 0:15:59.120 well depends on exactly what B is, right, Like quantum 0:15:59.120 --> 0:16:01.880 mechanics says, you and have particles pop out of the vacuum. 0:16:01.920 --> 0:16:04.240 But there are rules for that, right, There are ways 0:16:04.280 --> 0:16:06.040 that it can happen. So we still think that the 0:16:06.120 --> 0:16:09.080 universe does follow laws. But hey, maybe when the aliens 0:16:09.080 --> 0:16:11.160 show up, they're like physics, we gave up on that 0:16:11.200 --> 0:16:13.680 a million years ago because we discover the universe is 0:16:13.760 --> 0:16:16.720 totally arbitrary deep down. But yes, we still think that 0:16:16.760 --> 0:16:19.200 if the universe follows laws, And so you're saying that 0:16:19.240 --> 0:16:22.920 what we're asking today is whether or not. Those laws 0:16:23.560 --> 0:16:26.440 sort of prescribe a specific order that things have to 0:16:26.520 --> 0:16:28.560 happen in the universe. Yeah, but not everything in the 0:16:28.640 --> 0:16:32.160 universe is connected by causal order. Remember, because there's a 0:16:32.240 --> 0:16:35.680 finite speed of information, there's some things that you can't 0:16:35.720 --> 0:16:39.120 have an effect on, right Like events that are happening 0:16:39.240 --> 0:16:42.120 right now in Andromeda. You can't have any effect on 0:16:42.160 --> 0:16:45.120 with decisions you make right now, because the information from 0:16:45.160 --> 0:16:47.440 your decision right now to like send a beam of 0:16:47.520 --> 0:16:51.720 light or whatever won't affect Andromeda for millions of years. 0:16:52.080 --> 0:16:55.120 So even with causality, there's some parts of the universe 0:16:55.280 --> 0:16:58.320 that are not causally connected to other parts. All right, Well, 0:16:58.440 --> 0:17:02.000 let's maybe break it down for people. What exactly do 0:17:02.040 --> 0:17:05.080 you mean by causality? How do you define causality or 0:17:05.160 --> 0:17:09.520 causing effect? Yeah, so take two points in space and time, 0:17:09.640 --> 0:17:13.000 call them A and B for lack of more creative labels. 0:17:13.359 --> 0:17:16.520 And here we meet a point in space and in time. Right, 0:17:16.560 --> 0:17:19.600 So we mean like A is at your house at 0:17:19.720 --> 0:17:21.920 eight a m. In the morning, and B as you've 0:17:21.960 --> 0:17:24.919 arrived at work at nine am. So the events have 0:17:24.960 --> 0:17:27.480 a space and a time in them, all right, And 0:17:27.520 --> 0:17:30.520 so these two things are causally connected to have a 0:17:30.560 --> 0:17:34.200 definite order of events if something that happens at B 0:17:34.600 --> 0:17:38.120 relies on information from A. Right. So maybe, for example, 0:17:38.359 --> 0:17:41.679 you brought something with you from home to work, so 0:17:41.760 --> 0:17:44.919 for example, you brought your breakfast or you forgot your 0:17:44.920 --> 0:17:47.880 breakfast when you left the house. So something you did 0:17:47.880 --> 0:17:50.600 it A affects what you do. Would be you then 0:17:50.640 --> 0:17:53.760 need to buy breakfast or steal your coworkers breakfast or something. 0:17:54.040 --> 0:17:57.359 So those two events are connected causally because something that 0:17:57.440 --> 0:18:00.840 happens at A influences what happens at B, meaning like 0:18:00.880 --> 0:18:04.199 if I want to have breakfast at my office, I 0:18:04.240 --> 0:18:06.600 need to have packed it or left the house with 0:18:06.640 --> 0:18:09.880 that breakfast otherwise there's no way that I could have 0:18:09.920 --> 0:18:12.680 that breakfast from home, right exactly. And once you get 0:18:12.680 --> 0:18:15.280 to work and you have breakfast with you or don't, 0:18:15.320 --> 0:18:17.760 there's nothing you can do to affect A, right, So 0:18:17.800 --> 0:18:21.159 this is one directional. A can affect B, but B 0:18:21.440 --> 0:18:24.119 cannot affect A. So that's what we mean by a 0:18:24.200 --> 0:18:27.399 definite order of events. If A can have influence on B, 0:18:27.640 --> 0:18:31.240 then B cannot have influence on A. If your decision 0:18:31.480 --> 0:18:34.560 to leave the house with or without breakfast affects what 0:18:34.640 --> 0:18:36.679 you do for breakfast at work, then what you do 0:18:36.680 --> 0:18:39.359 for breakfast at work cannot affect whether or not you 0:18:39.440 --> 0:18:42.680 leave the house with your breakfast. It can't go backwards, right. 0:18:42.880 --> 0:18:44.760 I think you're just saying you can't go back in time. 0:18:44.800 --> 0:18:46.879 But the two are sort of connected, right, Like if 0:18:46.920 --> 0:18:49.240 I don't have breakfast in my office, then that means 0:18:49.240 --> 0:18:52.280 I didn't I didn't leave my home with it. Right. 0:18:52.320 --> 0:18:54.520 So they're sort of connected, aren't they. But you're saying 0:18:54.600 --> 0:18:57.760 like one of them affects the other and not the 0:18:57.800 --> 0:19:00.760 other way around. Yes, exactly. Information flow is only in 0:19:00.880 --> 0:19:04.600 one direction here and here B is part of the 0:19:04.640 --> 0:19:07.880 sort of the light cone of a Right. We talked 0:19:07.880 --> 0:19:11.800 about how decisions you make can only influence things around 0:19:11.840 --> 0:19:14.560 you that are nearby and in your future, and we 0:19:14.600 --> 0:19:17.119 talked about in a previous podcast how to formalize that. 0:19:17.359 --> 0:19:19.359 You think about a light cone, which is all the 0:19:19.440 --> 0:19:22.280 things in your future that you can influence, and you 0:19:22.280 --> 0:19:25.760 can influence things that are nearby in your immediate future 0:19:26.040 --> 0:19:28.320 or things that are far away in the deep future, 0:19:28.600 --> 0:19:31.199 because it's time for information to get there, all right. 0:19:31.240 --> 0:19:33.119 So I think you're saying that I didn't leave my 0:19:33.200 --> 0:19:35.359 house with my breakfast, and therefore I don't have it 0:19:35.400 --> 0:19:38.720 in my office. That's the cause and that's the effect. Yeah, exactly, 0:19:39.000 --> 0:19:40.879 And there's no way to go to the opposite direction. 0:19:41.000 --> 0:19:43.000 What would that even mean? Like I'm at my office 0:19:43.280 --> 0:19:46.440 first and then I left the house without the breakfast. 0:19:46.560 --> 0:19:49.560 It would mean that somehow, once you get to your 0:19:49.600 --> 0:19:52.640 office with or without your breakfast, you could still influence 0:19:52.920 --> 0:19:55.280 whether you left your house with or without your breakfast. 0:19:55.520 --> 0:19:57.840 That you could like somehow go back and change what 0:19:58.000 --> 0:20:01.080 happened at eight am and change a decision based on 0:20:01.520 --> 0:20:03.200 whether or not you had it with you in your 0:20:03.200 --> 0:20:06.119 office at nine am. So you know, making a decision 0:20:06.119 --> 0:20:08.840 at nine am can't influence what happened at eight am. 0:20:08.920 --> 0:20:11.120 That's all we're saying with cause and effect, all right, 0:20:11.320 --> 0:20:13.720 So then that's cause and effect and that that seems 0:20:13.800 --> 0:20:17.440 pretty important for the universe to make sense, right, because 0:20:17.480 --> 0:20:22.320 otherwise things would be what inconsistent, Like I can always 0:20:22.480 --> 0:20:25.400 you know, create paradoxes and time loops and things like that. 0:20:25.520 --> 0:20:27.760 It does seem pretty basic, right. It's the way that 0:20:27.840 --> 0:20:30.840 we think about physics. When I first got into physics, 0:20:30.840 --> 0:20:33.600 I thought it was amazing because it could predict the future, 0:20:33.960 --> 0:20:36.439 and it predicts the future based on the conditions of 0:20:36.480 --> 0:20:39.240 the present. You know, if you are shooting a cannonball 0:20:39.320 --> 0:20:42.760 at a castle, you can predict its trajectory if you 0:20:42.800 --> 0:20:47.080 know it's direction and its velocity, right, those are the causes, 0:20:47.160 --> 0:20:49.240 and the effect is like, oh, it hits the castle 0:20:49.280 --> 0:20:51.919 wall or it goes over the castle wall. And so 0:20:52.040 --> 0:20:54.879 physics seems to me to be like all about using 0:20:54.920 --> 0:20:57.440 causes to predict effects. You know, that's what the laws 0:20:57.480 --> 0:21:00.479 of physics are. They take the current description the universe 0:21:00.480 --> 0:21:02.679 and sort of step it forwards in time to the 0:21:02.720 --> 0:21:06.080 next description. So it seems pretty basic. All right, Well, 0:21:06.400 --> 0:21:08.960 it seems basic, which I think is probably a queue 0:21:09.000 --> 0:21:11.400 that we're going to challenge that and it might turn 0:21:11.400 --> 0:21:13.800 out to be wrong. So let's get into that and 0:21:13.880 --> 0:21:17.040 what how we can maybe tested or find out the 0:21:17.080 --> 0:21:32.239 true answer. But first let's take a quick break. All right, 0:21:32.280 --> 0:21:34.800 we're talking about cause and effect and whether you actually 0:21:34.840 --> 0:21:38.480 needed to make a happy universe I guess right, a 0:21:38.560 --> 0:21:42.199 functioning universe. Yeah, exactly whether we can make sense of 0:21:42.240 --> 0:21:47.160 our universe without causality, or whether it's actually absolutely fundamentally 0:21:47.200 --> 0:21:50.000 required for anything to make sense to us. Okay, So 0:21:50.040 --> 0:21:53.240 then we define causality as like I shoot an arrow 0:21:53.400 --> 0:21:56.280 and an apple and it hits the apple, but I 0:21:56.280 --> 0:21:58.080 can't do it the other way around. I like, I 0:21:58.119 --> 0:22:01.880 can't have hit the apple before shooting the arrow exactly, 0:22:01.920 --> 0:22:03.960 because if you hit the apple before you shoot the arrow, 0:22:04.240 --> 0:22:06.600 you could like change your mind and not shoot the arrow, 0:22:06.640 --> 0:22:08.760 and then oops, you already hit it. How can you 0:22:08.840 --> 0:22:11.760 change your mind? It seems to like automatically make no sense. 0:22:11.800 --> 0:22:13.639 It seems like a paradox, as you said, And it 0:22:13.640 --> 0:22:17.120 seems to be sort of connected to the arrow of time, right, 0:22:17.400 --> 0:22:19.760 like time only flows one way. But there's a little 0:22:19.760 --> 0:22:21.639 bit more to it than that, right, there's a little 0:22:21.640 --> 0:22:23.920 bit more to it than that. And of course the 0:22:24.040 --> 0:22:26.719 thing that makes things weird and twist your brain and 0:22:26.760 --> 0:22:29.359 maybe give us an escape from causality is going to 0:22:29.480 --> 0:22:33.520 end up being quantum mechanics. Of course. Of course, quantum 0:22:33.520 --> 0:22:37.520 mechanics always scrambling your brain. So that seems that I 0:22:37.600 --> 0:22:39.760 think I'm guessing it's going to add some sort of 0:22:39.840 --> 0:22:43.240 uncertainty or randomness to causality. Yeah, And before we get 0:22:43.240 --> 0:22:45.080 to quantum mechanics, I think it's important that you have 0:22:45.160 --> 0:22:48.080 in your mind a clear picture of the part of 0:22:48.119 --> 0:22:52.239 the universe that you can affect with your causes. This 0:22:52.280 --> 0:22:55.400 is again this concept of a light cone. Right if 0:22:55.440 --> 0:22:58.199 you send out a flash of light right now, you like, 0:22:58.280 --> 0:23:01.040 turn on a really bright light, then who can tell 0:23:01.080 --> 0:23:03.560 that you have done that? People who are really far 0:23:03.640 --> 0:23:06.040 away from you cannot see that right now. They have 0:23:06.080 --> 0:23:08.720 to wait until the future, and people that are even 0:23:08.720 --> 0:23:11.159 further away have to wait till the deeper future to 0:23:11.200 --> 0:23:14.159 see that flash of light. Because light travels are the 0:23:14.240 --> 0:23:18.040 fastest speed of information, people who haven't seen that flash 0:23:18.040 --> 0:23:21.320 of light can't be influenced by it yet, right, So 0:23:21.359 --> 0:23:24.639 we think about that as a light cone. In two dimensions, 0:23:24.640 --> 0:23:26.840 you can imagine yourself sort of the tip of a 0:23:26.920 --> 0:23:30.639 triangle that's opening up as time goes on, and you 0:23:30.680 --> 0:23:33.119 can influence more and more of the future based on 0:23:33.200 --> 0:23:35.960 your decisions of the present. In three D is sort 0:23:36.000 --> 0:23:37.679 of like you know, you're at the tip of a 0:23:37.680 --> 0:23:40.760 cone right now and it's opening up, right. I guess 0:23:40.760 --> 0:23:43.240 maybe I wonder if we can talk about the breakfast 0:23:43.280 --> 0:23:47.080 cone of my breakfast Okay, when I left my home, 0:23:47.480 --> 0:23:49.400 like you're saying, like, there's this sort of a limited 0:23:49.560 --> 0:23:52.840 number of time and places that I can be at 0:23:52.920 --> 0:23:56.760 with my breakfast if I chose to leave my house 0:23:56.800 --> 0:23:59.760 with my breakfast right, like, I can instantly be at 0:23:59.800 --> 0:24:02.480 my work with breakfast, because I can't get there in time. 0:24:03.400 --> 0:24:06.320 And also I can't be in like China in an 0:24:06.320 --> 0:24:09.320 hour with my breakfast right because I'm limited to by 0:24:09.400 --> 0:24:12.360 how fast I can move exactly. And so if you're 0:24:12.359 --> 0:24:14.959 going to your office pretty close by, then you can 0:24:14.960 --> 0:24:17.600 bring your breakfast with you, and that can influence your coworkers. 0:24:17.640 --> 0:24:19.280 Are they going to try to steal your breakfast? Did 0:24:19.320 --> 0:24:21.639 they forget their own breakfast? Are they influenced by the 0:24:21.680 --> 0:24:23.679 smell of your breakfast? This kind of stuff. But the 0:24:23.760 --> 0:24:27.119 you know, podcast headquarters in Shanghai, for example, can't be 0:24:27.160 --> 0:24:30.800 influenced by that decision until later, until your light cone 0:24:30.800 --> 0:24:34.439 has grown to expand and include all of those things. 0:24:34.960 --> 0:24:37.240 So there are things that you cannot influence right now 0:24:37.280 --> 0:24:39.960 in the universe just because of this finite speed of light, 0:24:40.359 --> 0:24:42.760 and so everything you can influence, we call that part 0:24:42.760 --> 0:24:45.560 of your light cone, right or breakfast cone, which, by 0:24:45.560 --> 0:24:48.520 the way, it sounds like a great breakfast idea for 0:24:48.640 --> 0:24:52.120 McDonald or one of these fast food chains. Breakfast cone 0:24:52.119 --> 0:24:54.800 that sounds like scrambled egg flavored ice cream that does 0:24:54.840 --> 0:24:59.879 not sound, or scrambled eggs on a cone. Scrambled eggs 0:25:00.000 --> 0:25:03.160 on a cone. Actually, that might be a great food truck, 0:25:03.160 --> 0:25:04.400 you know, that's the kind of thing you would see 0:25:04.400 --> 0:25:06.600 in l a with like a huge line of hipsters, 0:25:06.640 --> 0:25:12.040 you know, right, yeah, breakfast cones happen alright, So then 0:25:12.080 --> 0:25:14.480 how do these light cones affect our our sense of 0:25:14.520 --> 0:25:17.040 cause and effect? Well, the interesting thing about light cones 0:25:17.200 --> 0:25:20.800 is that they're pretty simple if the universe is not bent, right, 0:25:20.800 --> 0:25:23.280 if if space is flat, if light moves in straight 0:25:23.320 --> 0:25:25.760 lines like it does out in deep space, then they're 0:25:25.800 --> 0:25:27.960 just like we talked about them their triangles and two 0:25:27.960 --> 0:25:30.640 dimensions or their cones and three D. But they get 0:25:30.640 --> 0:25:35.159 more complicated when space bends. You know that gravity is 0:25:35.160 --> 0:25:37.639 not just a force, it's also a description of the 0:25:37.680 --> 0:25:41.560 way that the universe bends, that space itself bends when 0:25:41.560 --> 0:25:44.640 we are near heavy objects. So the reason, for example, 0:25:44.680 --> 0:25:47.040 the Earth goes around the Sun is not because there's 0:25:47.080 --> 0:25:49.840 a force of gravity pulling on it, but because the 0:25:49.880 --> 0:25:52.840 Sun bends space, and so the Earth is moving in 0:25:52.880 --> 0:25:55.520 a path which is actually quite natural for an object 0:25:55.720 --> 0:25:58.840 under no force. It's moving in a circle. And so 0:25:59.080 --> 0:26:02.040 the same thing how happens to light cones. If you 0:26:02.080 --> 0:26:05.000 are near something massive like a black hole or a 0:26:05.000 --> 0:26:08.080 star or whatever, your light cone bends because the path 0:26:08.200 --> 0:26:11.240 that light takes also bends. So the things you can 0:26:11.280 --> 0:26:14.480 influence change. Now you're making me think of bugles, you know, 0:26:14.560 --> 0:26:18.720 the snack, but the curved cones. I think maybe I 0:26:18.720 --> 0:26:21.560 should have some breakfast before recording these podcasts. But this 0:26:21.640 --> 0:26:24.119 is important for our food truck. We can't have curved 0:26:24.119 --> 0:26:26.560 cones because then the eggs will all fall out, right 0:26:26.800 --> 0:26:31.440 wit what this is why physicists shouldn't be cooked. But anyway, 0:26:31.480 --> 0:26:33.520 it's going back to our topic. You're saying, as you know, 0:26:33.600 --> 0:26:36.280 space can bend, and that can bend or light cones, 0:26:36.320 --> 0:26:38.640 and that can somehow affect causing effect like you can 0:26:38.680 --> 0:26:41.520 break calls in effect by bending space. It doesn't break 0:26:41.520 --> 0:26:45.000 causing effect yet, it just changes what you can affect. 0:26:45.080 --> 0:26:47.679 For example, say you are inside a black hole and 0:26:47.760 --> 0:26:51.400 you make your breakfast. You cannot influence what people eat 0:26:51.600 --> 0:26:54.400 or who gets breakfast outside of the black hole. Right, 0:26:54.840 --> 0:26:57.400 this concept of a light cone inside a black hole, 0:26:57.480 --> 0:27:00.280 it gets twisted. The light cone only points to towards 0:27:00.359 --> 0:27:02.560 the center of the black hole. If you're near a 0:27:02.560 --> 0:27:05.160 black hole, your light colne is distorted. If you send 0:27:05.160 --> 0:27:07.119 out a flash of light or you know, shoot a 0:27:07.200 --> 0:27:09.320 bunch of breakfasts at your friends, they don't all just 0:27:09.359 --> 0:27:12.359 travel in straight paths. And so there are some people 0:27:12.359 --> 0:27:16.159 who are actually near you who you cannot influence because 0:27:16.200 --> 0:27:18.960 of the bending of space. The point is the bending 0:27:18.960 --> 0:27:22.480 of space determines which causes line up with which effects 0:27:23.359 --> 0:27:26.040 I see. So it's not that you're saying cause and 0:27:26.080 --> 0:27:29.000 effect is flexible in a way. Yeah exactly. As you're 0:27:29.040 --> 0:27:31.719 near some heavy mass, then which causes in which effects 0:27:31.760 --> 0:27:34.919 line up depends exactly on the curvature space because it 0:27:34.960 --> 0:27:38.040 depends on how information travels. You know, if you can't 0:27:38.080 --> 0:27:40.760 send a light pulse to somebody, then you can't send 0:27:40.800 --> 0:27:45.080 them information. Then your causes cannot influence their effects. All right, 0:27:45.160 --> 0:27:47.320 So we can limit cause and effect. But I guess 0:27:47.320 --> 0:27:49.080 the question is can we break it or do we 0:27:49.119 --> 0:27:51.439 need it? And you're saying that things start to get 0:27:51.480 --> 0:27:54.680 weird when you add quantum mechanics, Yeah, exactly. So now 0:27:54.760 --> 0:27:57.560 we've done special relativity with light cones, we went to 0:27:57.680 --> 0:28:01.760 general relativity by bending those light cones through space. Now 0:28:01.840 --> 0:28:04.320 we're going to add in the final ingredient, which is 0:28:04.400 --> 0:28:07.480 quantum mechanics. Right, say we're near this black hole, so 0:28:07.520 --> 0:28:09.680 a light cone is all twisted and bent, and who 0:28:09.680 --> 0:28:13.119 we can influence and talk about breakfast with depends on 0:28:13.200 --> 0:28:15.800 the curvature of space. But what if the curvature of 0:28:15.800 --> 0:28:19.800 space itself was uncertain? Like what if we didn't know 0:28:19.920 --> 0:28:23.280 exactly where that black hole was because it was like 0:28:23.600 --> 0:28:26.960 created from some quantum process, So I had a probability 0:28:26.960 --> 0:28:29.920 to be here and a probability be over there, then 0:28:29.920 --> 0:28:33.600 we would have like two possible light cones, which would 0:28:33.600 --> 0:28:36.520 mean like two possible portions of the universe that we 0:28:36.560 --> 0:28:38.960 could influence. But I wonder, do you actually need the 0:28:39.000 --> 0:28:41.360 black hole to get those two possible light cones? Like, 0:28:41.600 --> 0:28:45.440 you know, isn't there quantum uncertainty in everything? Right? Like 0:28:45.600 --> 0:28:48.120 if I leave my house, there's maybe a fifty percent 0:28:48.160 --> 0:28:50.400 chance that I took a rite in a fifty percent 0:28:50.440 --> 0:28:52.640 chance I took at left, And so there's two possible 0:28:52.680 --> 0:28:56.560 breakfast cones, two possible breakfast cones. Yes, the black hole 0:28:56.640 --> 0:28:59.160 is just the extreme example because it's easy to think 0:28:59.200 --> 0:29:01.920 about how the black hole changes the shape of your 0:29:02.000 --> 0:29:05.640 light cone is very dramatic. But every time this quantum uncertainty, 0:29:05.840 --> 0:29:09.400 and that uncertainty leads to uncertainty and where stuff is 0:29:09.520 --> 0:29:12.840 in the universe. That means this uncertainty about the curvature 0:29:12.880 --> 0:29:17.080 of space, which means this uncertainty about the causality. Right, 0:29:17.120 --> 0:29:18.840 if I don't know where the black hole is or 0:29:18.840 --> 0:29:22.160 where Jorhees Breakfast went, that I can't necessarily predict which 0:29:22.240 --> 0:29:25.920 part of the universe I can influence. Okay, so then, um, 0:29:25.960 --> 0:29:29.920 there's some uncertainty in the light cones and two possible futures. 0:29:30.040 --> 0:29:32.400 So then how does that break causality? Well, you can 0:29:32.440 --> 0:29:35.320 imagine some experiments, right, Like let's say, for example, we 0:29:35.400 --> 0:29:39.480 have two people doing experiments, and in quantum mechanics thought experiments, 0:29:39.480 --> 0:29:42.719 people always use Alice and Bob because there you know 0:29:42.800 --> 0:29:44.800 A and b. Maybe we can mix it up a 0:29:44.840 --> 0:29:47.160 little bit, you can think of more clever names. But 0:29:47.240 --> 0:29:50.280 we have two people doing experiments somewhere out in space, 0:29:50.440 --> 0:29:53.440 and their experiments depend, for example, on how close they 0:29:53.440 --> 0:29:56.160 are to the Earth, right, because the Earth is going 0:29:56.240 --> 0:29:59.000 to bend space and you know that for example, if 0:29:59.040 --> 0:30:02.280 you are near the Earth, then your time slows down 0:30:02.440 --> 0:30:06.800 because gravitational time dilation makes clocks run slower like Clocks 0:30:06.840 --> 0:30:09.400 closer to the Earth run more slowly than clocks further 0:30:09.480 --> 0:30:12.680 from the Earth. So now we have these two experimenters. 0:30:12.680 --> 0:30:15.560 They're out in space. One of them is closer to 0:30:15.600 --> 0:30:18.000 the Earth than the other one, right, but if the 0:30:18.040 --> 0:30:21.160 Earth's location is uncertain, we don't know which one it is. 0:30:21.480 --> 0:30:24.280 So now one of them has had their time slowed 0:30:24.280 --> 0:30:26.479 down more than the other one. So one of them 0:30:26.560 --> 0:30:30.680 can influence the other because their time has been slowed down. So, 0:30:30.720 --> 0:30:33.400 for example, if Alice has had her time slowed more, 0:30:33.720 --> 0:30:36.240 then she hasn't gotten as far in her experiment, and 0:30:36.320 --> 0:30:39.560 Bob can send her a message influencing her experiment. But 0:30:39.640 --> 0:30:42.320 if Bob has had his time slowed down more, then 0:30:42.360 --> 0:30:46.040 Alice can influence his experiment. So we don't know necessarily 0:30:46.440 --> 0:30:49.560 which way causality goes from Alice to Bob or from 0:30:49.640 --> 0:30:53.200 Bob to Alice, because we don't know where Earth is, 0:30:53.320 --> 0:30:57.160 and that determines where these light cones flow. Okay, well, um, 0:30:57.200 --> 0:30:59.440 first of all, I'm a little worried we can't find Earth. 0:31:00.120 --> 0:31:03.080 It's a little concerning. I think you're saying, like the 0:31:03.120 --> 0:31:05.560 Alice and Bob are doing the same experiment right, Like 0:31:05.600 --> 0:31:07.840 you're trying to figure out whats inside of a box 0:31:08.080 --> 0:31:10.560 and they have maybe the same box, and you're saying 0:31:10.600 --> 0:31:12.479 that if one of them is moving at a different 0:31:12.480 --> 0:31:15.560 time rate than like, if one of them has time 0:31:15.600 --> 0:31:18.040 moving faster for them, they could finish the experiment and 0:31:18.080 --> 0:31:20.600 then run over until the other one what's in the 0:31:20.640 --> 0:31:23.920 box exactly? Or maybe they're like trying to unlock somebody's 0:31:23.920 --> 0:31:26.520 phone and they're trying to guess codes or something. And 0:31:26.560 --> 0:31:30.600 if Alice's time runs more slowly, then Bob can try 0:31:30.600 --> 0:31:32.480 a bunch of codes, and if he finds one, he 0:31:32.480 --> 0:31:34.960 can send Alice a message saying, oh, try this one, 0:31:35.040 --> 0:31:37.400 or don't try these, I already try them. That's if 0:31:37.440 --> 0:31:40.920 Alice's time is running more slowly. If it's the opposite, 0:31:41.000 --> 0:31:43.680 like the Earth happens to be in another situation where 0:31:43.680 --> 0:31:46.720 it slows down Bob's time, then Alice can finish her 0:31:46.720 --> 0:31:50.200 experiment first. So who finishes the experiment first and who 0:31:50.200 --> 0:31:52.240 can send a message to the other one about their 0:31:52.280 --> 0:31:56.400 results depends on who is closer to the gravitational object 0:31:56.480 --> 0:31:59.160 that's slowing down time. And you know it sounds weird 0:31:59.240 --> 0:32:00.680 to say, like, well, how do we not know where 0:32:00.680 --> 0:32:03.320 the Earth is? It's a crazy thought experiment where we've 0:32:03.400 --> 0:32:05.800 like put the Earth in some sort of crazy quantum 0:32:05.800 --> 0:32:08.560 mechanical superpositions, so we don't know where it is. That's 0:32:08.600 --> 0:32:10.560 pretty hard to imagine. But this is what we do 0:32:10.560 --> 0:32:13.200 when we try to understand like the extremes of the universe. 0:32:13.240 --> 0:32:16.600 We come up with these crazy experiments to understand whether 0:32:16.640 --> 0:32:19.479 the rules are broken in extreme situations. I wonder if 0:32:19.480 --> 0:32:23.000 you can simplify by just talking about like short Dinger's box, right, 0:32:23.040 --> 0:32:25.080 Like you're saying, let's put the Earth, Alice and Bob 0:32:25.120 --> 0:32:27.400 inside of a box, and we sort of don't know 0:32:27.400 --> 0:32:30.400 where the Earth is, and so from us sitting outside 0:32:30.400 --> 0:32:33.240 of the box, we don't know who told who about 0:32:33.240 --> 0:32:37.360 the results of their experiment. It sounds like Shortingers prisoners dilemma, 0:32:38.160 --> 0:32:43.000 sounds catastrophic exactly. So we don't know then what has 0:32:43.040 --> 0:32:45.760 happened inside the box. Was it Alice and then Bob, 0:32:46.040 --> 0:32:48.880 or was it Bob and then Alice? And so in 0:32:48.920 --> 0:32:53.240 this situation, because the position of the light cones is uncertain, 0:32:53.600 --> 0:32:57.440 causality is uncertain, and so in this kind of experiment, 0:32:57.480 --> 0:32:59.840 it's like, well, which happened Was it A before B 0:33:00.160 --> 0:33:03.880 or B before A. So now causality has become uncertain. 0:33:04.120 --> 0:33:07.280 Remember the very beginning, we define causality saying, well, if 0:33:07.320 --> 0:33:10.440 A can influence B, you know A causees B. That 0:33:10.440 --> 0:33:13.440 that means it's impossible for B to cause A. So 0:33:13.480 --> 0:33:16.160 in this experiment, like we have two events and we 0:33:16.280 --> 0:33:19.440 can't say which one happened first, and they do influence 0:33:19.480 --> 0:33:21.840 each other. One is definitely inside the light cone of 0:33:21.880 --> 0:33:24.760 the other. We just don't know which, right, And and 0:33:24.840 --> 0:33:27.800 that's just sort of isn't that sort of regular quantum mechanics, 0:33:27.840 --> 0:33:30.040 Like we don't really know whether the cat is alive 0:33:30.120 --> 0:33:32.440 or dead anyways, right, that's right, we don't know quantum 0:33:32.440 --> 0:33:34.440 mechanics whether the cat is are live or dead. But 0:33:34.520 --> 0:33:38.240 we've added in another element here, which is causality, because 0:33:38.280 --> 0:33:41.640 now quantum mechanics is influencing the very shape of space, 0:33:41.880 --> 0:33:45.440 which determines which events can happen in what order. In 0:33:45.440 --> 0:33:49.520 this classical shortingers box example, you know, the causality is clear, 0:33:49.920 --> 0:33:52.920 like you know, the radioactive element decays and either kills 0:33:52.960 --> 0:33:55.440 the cat or it does not. The order of events 0:33:55.560 --> 0:33:58.719 is clear, even though which events happens is not right, 0:33:58.760 --> 0:34:01.200 it's not like the cat can scape and then rebuild 0:34:01.200 --> 0:34:04.600 the box or something. You can't have anything going backwards 0:34:04.600 --> 0:34:07.360 in that experiment. Here, we might have things happening in 0:34:07.400 --> 0:34:10.760 an indefinite order because we've made the shape of space 0:34:10.840 --> 0:34:14.360 itself uncertain, and it's that shape of space that determines 0:34:14.680 --> 0:34:17.719 what can influence what because it controls the shape of 0:34:17.719 --> 0:34:20.640 the light cone. All right, So then the causality of 0:34:20.640 --> 0:34:23.800 what happened inside the box is uncertain. There's a quantum 0:34:23.880 --> 0:34:27.359 uncertainty about it. But does that really mean that causality 0:34:27.880 --> 0:34:31.279 broke or it's it's not needed or it's false, do 0:34:31.320 --> 0:34:33.040 you know what I mean? Like, it's just it's just 0:34:33.080 --> 0:34:35.520 that we don't know, right, How does that sort of 0:34:35.560 --> 0:34:38.200 break things about the universe. Yeah, well, it means that 0:34:38.239 --> 0:34:41.280 maybe causality is not always needed. You know, it seems 0:34:41.320 --> 0:34:43.400 like it's the kind of thing that happens a lot 0:34:43.840 --> 0:34:46.520 most of the time. In most circumstances, you don't get 0:34:47.000 --> 0:34:51.400 huge uncertain bending of space that makes causality uncertain. So 0:34:51.480 --> 0:34:54.759 causality is probably like a very effective principle. But you know, 0:34:54.840 --> 0:34:57.320 we want to understand the deep nature of the universe, 0:34:57.400 --> 0:35:00.160 not just like hey, this mostly works. Let's move on. 0:35:00.600 --> 0:35:03.400 We want to understand how things actually work. And right 0:35:03.440 --> 0:35:06.799 now we have these two really key ideas about the 0:35:06.800 --> 0:35:09.480 way the universe works, quantum mechanics, which tells us things 0:35:09.520 --> 0:35:13.399 are fundamentally uncertain, and general relativity, which tells us how 0:35:13.480 --> 0:35:16.960 space bends around mass. And we'd like to emerge those two. 0:35:17.000 --> 0:35:19.040 We would like to have a theory of quantum gravity 0:35:19.080 --> 0:35:21.680 that tells us, you know, how quantum mechanics and gravity 0:35:21.680 --> 0:35:24.520 play well together. Well, this suggests that, you know, we 0:35:24.640 --> 0:35:27.200 might have to give up causality if we want to 0:35:27.200 --> 0:35:29.360 emerge them. That if we want to bring quantum mechanics 0:35:29.400 --> 0:35:32.719 and general relativity together, then these two concepts might not 0:35:32.800 --> 0:35:35.279 play well together. You know, they seem to create these 0:35:35.320 --> 0:35:38.759 situations with uncertain causality. And so maybe the key to 0:35:39.280 --> 0:35:41.640 finding a theory of quantum gravity and revealing the deep 0:35:41.719 --> 0:35:44.719 nature of the universe is to give up on causality. 0:35:44.760 --> 0:35:48.120 To say, it happens a lot, it's convenient, it's nice, 0:35:48.280 --> 0:35:51.319 but it's not actually always required. I guess maybe it's 0:35:51.360 --> 0:35:53.400 hard to see sort of the stakes here with Bob 0:35:53.400 --> 0:35:56.319 and ell is because you know, like whether one of 0:35:56.320 --> 0:36:00.480 them tells the other first or the second, maybe it doesn't, 0:36:00.560 --> 0:36:02.920 you know, sort of affect my reality that much. But 0:36:03.080 --> 0:36:04.880 can you think of an example of where like this 0:36:05.000 --> 0:36:09.279 uncertainty in causality would sort of have more, I don't know, 0:36:09.520 --> 0:36:12.120 sort of like deeper repercussions. You know. I think that 0:36:12.200 --> 0:36:15.040 physicists are still struggling to get their minds around the 0:36:15.200 --> 0:36:18.000 consequences here. And we'll talk in a minute about like 0:36:18.080 --> 0:36:20.879 experiments people are doing to try to use this. We're 0:36:20.920 --> 0:36:25.520 developing ideas for like how to improve computation or you know, 0:36:25.719 --> 0:36:30.440 make information transmission actually more efficient, or change the very 0:36:30.520 --> 0:36:33.440 nature of thermodynamics. But it's something that's so basic and 0:36:33.480 --> 0:36:36.400 fundamental to our thinking that we're having trouble even like 0:36:36.560 --> 0:36:40.080 contemplating what physics would look like without causality, and so 0:36:40.160 --> 0:36:42.320 it's hard to get your mind around like how that 0:36:42.360 --> 0:36:45.040 would actually influence the universe. All right, Well, I think 0:36:45.040 --> 0:36:47.640 basically what you're saying though, is that you know, there 0:36:47.640 --> 0:36:52.520 are situations where quantum mechanics can throw uncertainty about the 0:36:53.160 --> 0:36:55.600 order of things, right, Like there can be situations where 0:36:55.640 --> 0:36:57.480 we don't know if A came before B or B 0:36:57.640 --> 0:37:01.040 came before A. And so because there our situations where 0:37:01.440 --> 0:37:04.320 we don't know. Maybe the question is do we actually 0:37:04.320 --> 0:37:06.440 need it? Right? That's I think that's what you're getting at. 0:37:06.480 --> 0:37:09.279 It's like, maybe since it's not something that has to 0:37:09.520 --> 0:37:11.680 be known, maybe it's something we don't even need in 0:37:11.719 --> 0:37:14.960 the universe. Yeah, and maybe it's not something the universe demands, 0:37:15.400 --> 0:37:18.000 you know, the same way when you have quantum entanglement. 0:37:18.239 --> 0:37:21.319 You might have like two particles that are far away 0:37:21.360 --> 0:37:24.600 in uncertain states about you know, what direction their spin is, 0:37:25.080 --> 0:37:27.000 and we like to think, oh man, but there has 0:37:27.040 --> 0:37:28.959 to be a real truth there. It has to either 0:37:29.000 --> 0:37:31.239 be this or that. You know, there has to be 0:37:31.280 --> 0:37:34.200 some deep hidden knowledge. And we discovered actually the universe 0:37:34.239 --> 0:37:36.920 doesn't care the universes happen to have that be uncertain, 0:37:37.160 --> 0:37:40.239 the true nature of these particles. And now we're taking 0:37:40.239 --> 0:37:42.400 that a step further and saying, look, maybe the universe 0:37:42.440 --> 0:37:45.560 doesn't really care always whether A happen before B or 0:37:45.600 --> 0:37:48.200 B happened before A. Maybe it's happy to have that 0:37:48.280 --> 0:37:51.560 be uncertain, for it to be undetermined, which is pretty 0:37:51.600 --> 0:37:54.040 hard for us to consider. All Right, Well, maybe we 0:37:54.080 --> 0:37:57.000 don't need causality, but we definitely need to pay for 0:37:57.040 --> 0:38:00.279 this podcast. So that's the one cost and of we 0:38:00.320 --> 0:38:03.640 can't ignore. So let's talk about how you might test 0:38:03.680 --> 0:38:06.200 whether or not this theory is right, or whether or 0:38:06.200 --> 0:38:09.080 not you actually do need castality in the universe. But 0:38:09.160 --> 0:38:24.200 first let's take a quick break. All right, So, Daniel, 0:38:24.239 --> 0:38:27.000 apparently maybe the universe doesn't need causality, you know, or 0:38:27.080 --> 0:38:28.719 maybe I think what you're saying is that maybe the 0:38:28.800 --> 0:38:31.880 universe doesn't really care that much about castality, Like it 0:38:31.920 --> 0:38:35.799 could go either way. Exactly. It's like effect before cause, 0:38:35.880 --> 0:38:38.080 caused before effect, whatever. As long as I got my 0:38:38.120 --> 0:38:41.560 breakfast cone, I'm fine, you know, whatever, as long as 0:38:41.600 --> 0:38:45.000 I got taken in my scrambled cone. Yeah, and again, 0:38:45.080 --> 0:38:48.439 let me just reiterate. This doesn't mean that anything goes 0:38:48.760 --> 0:38:51.200 that you should just like go out there and steal 0:38:51.280 --> 0:38:54.359 jewelry and whatever. There are no consequences for your actions, right, 0:38:54.360 --> 0:38:56.600 You're still going to prison if you steal money from 0:38:56.640 --> 0:38:59.400 your local grocery store. It just means that sometimes in 0:38:59.440 --> 0:39:02.440 scenarios are there are two possible orders for events, the 0:39:02.520 --> 0:39:06.040 universe might not pick between them, right. Yeah, it might 0:39:06.239 --> 0:39:11.480 leave things undecided and go about its happy way. Yeah, exactly. 0:39:11.640 --> 0:39:15.600 Physicists called this indefinite causality, so not like a complete 0:39:15.640 --> 0:39:19.080 overthrow of causality, but like an important weakening, you know, 0:39:19.160 --> 0:39:21.440 to say like, oh, these are cracking causality. There are 0:39:21.440 --> 0:39:25.000 cases when you don't have to know what happens first. 0:39:25.120 --> 0:39:29.880 What if you just call it causality is diet causality? 0:39:30.239 --> 0:39:33.080 There you go, all right, so that's a possibility. And 0:39:33.120 --> 0:39:35.520 it seems like the universe, you know, it's kind of 0:39:35.520 --> 0:39:38.319 fuzzy about causality, And so are there experiments to sort 0:39:38.320 --> 0:39:40.200 of test this or to figure out what the right 0:39:40.239 --> 0:39:43.839 answer is in physics, Yeah, there are some really cool experiments. 0:39:44.120 --> 0:39:46.800 People came up with these ideas in the two thousands 0:39:46.840 --> 0:39:48.640 and sort of playing with them. Is as they were 0:39:48.680 --> 0:39:52.080 trying to stitch together quantum mechanics and general relativity to 0:39:52.120 --> 0:39:55.080 think about quantum gravity, and realized maybe this is the 0:39:55.120 --> 0:39:57.480 stumbling block, Maybe this is the piece we need to 0:39:57.480 --> 0:40:00.320 get rid of so that everything else clicks together nicely, 0:40:00.880 --> 0:40:03.239 And so they tried to make some experiments. Then you know, 0:40:03.280 --> 0:40:06.080 it's hard to have black holes or to put the 0:40:06.120 --> 0:40:08.759 Earth in a quantum superposition, so they came up with 0:40:08.800 --> 0:40:11.239 a totally different set of experiments. And it's mostly folks 0:40:11.280 --> 0:40:14.239 who are working on things like quantum information. Whether you know, 0:40:14.280 --> 0:40:18.000 they are like splitting photon beams and polarizing them and 0:40:18.040 --> 0:40:20.440 capturing the information in them and not in them, and 0:40:20.480 --> 0:40:22.480 this kind of stuff. They were able to do experiments 0:40:22.480 --> 0:40:25.359 that probe this kind of thing. All right, So then 0:40:25.440 --> 0:40:27.759 how does the experiment work? What's going on? Yeah, So 0:40:27.800 --> 0:40:29.880 what you do is you take a beam of photons. 0:40:29.920 --> 0:40:32.480 These are just you know, like it's a laser beam essentially, 0:40:32.560 --> 0:40:34.839 and you have these particles flying out and then you 0:40:34.880 --> 0:40:37.320 split them use this one of these beams splitters, so 0:40:37.400 --> 0:40:39.440 like half the photons go one way and half the 0:40:39.440 --> 0:40:42.200 photons go the other way. And then you send the 0:40:42.239 --> 0:40:46.239 photons through two different paths. Along one path you do 0:40:46.360 --> 0:40:48.919 A to the photons and then B. And then along 0:40:48.960 --> 0:40:50.920 the other path you do B. And then you do A. 0:40:51.480 --> 0:40:53.080 What does that mean to do A or do B. 0:40:53.480 --> 0:40:56.280 It's like you perform some operation you change the photons 0:40:56.320 --> 0:40:58.719 a little bit. In this case, what they did is 0:40:58.760 --> 0:41:01.839 they polarize the photo potons. Photons are more than just 0:41:01.920 --> 0:41:04.600 like packs of light. They have like little spins to them. 0:41:04.880 --> 0:41:07.839 You can change the way those spins are pointed, and 0:41:07.920 --> 0:41:10.600 so along one path they like flip the spins one 0:41:10.640 --> 0:41:12.960 way and then another way. Along the other path. They 0:41:12.960 --> 0:41:15.120 do it in the opposite order, right, they sort of 0:41:15.200 --> 0:41:17.400 run it through some filters, right, yeah, exactly. You can 0:41:17.440 --> 0:41:19.280 think about it like that, running it through some filters. 0:41:19.480 --> 0:41:22.520 And the key thing is that the order matters, Like 0:41:22.600 --> 0:41:25.279 the photons look different if you do A and then 0:41:25.320 --> 0:41:28.440 B versus B and then A, and you know this 0:41:28.560 --> 0:41:31.719 could happen because sometimes these are things are conceptually the 0:41:31.760 --> 0:41:34.799 same as like rotations, where you know it matters what 0:41:34.960 --> 0:41:37.480 order you do them. It's like if you turn around 0:41:37.640 --> 0:41:39.440 and then you turn left, it's different than if you 0:41:39.480 --> 0:41:41.719 turn left and then turn around. All right, So then 0:41:41.760 --> 0:41:44.080 I have a laser beam. I split it and in 0:41:44.280 --> 0:41:46.520 one half of it I do A and B and 0:41:46.600 --> 0:41:48.920 the other side I do B and then A, And 0:41:48.960 --> 0:41:51.799 then what I compare them to see if they if 0:41:51.800 --> 0:41:54.759 something different happen, And then you bring them back together, right, 0:41:55.040 --> 0:41:57.560 you rejoin them, and now you have photons and you 0:41:57.600 --> 0:41:59.840 don't know which path they took. Do they do the 0:42:00.000 --> 0:42:02.719 A B path or the B A path? And what 0:42:02.880 --> 0:42:05.440 you see when it comes out is a really interesting 0:42:05.480 --> 0:42:09.279 interference pattern between photons that went through A B and 0:42:09.320 --> 0:42:11.680 then photons that went through B A And just like 0:42:11.719 --> 0:42:14.759 in sort of the double slit experiment where particles could 0:42:14.760 --> 0:42:16.920 have gone through one slit or the other, and the 0:42:16.960 --> 0:42:19.920 probability to have gone through one or the other interferes 0:42:20.120 --> 0:42:23.279 with the first ones. Then you get these interference patterns. 0:42:23.280 --> 0:42:25.920 So this interference patterns means that you really do have 0:42:25.960 --> 0:42:29.239 photons from both in your beam, and that for any 0:42:29.280 --> 0:42:31.360 given photon, you don't know whether it went through A 0:42:31.480 --> 0:42:33.920 B or whether it went through B A. So what 0:42:33.960 --> 0:42:38.040 you're seeing is this interference pattern between the probabilities, which 0:42:38.040 --> 0:42:41.959 means that both possibilities exist for any given photon. Each 0:42:41.960 --> 0:42:44.680 photon has a possibility to have gone through one side 0:42:44.840 --> 0:42:47.080 or the other. Oh, I see, it's like you take 0:42:47.120 --> 0:42:49.319 those two beams and then you join them again, and 0:42:49.320 --> 0:42:51.920 then you look the photons that come out, and when 0:42:51.920 --> 0:42:54.080 you get a photon out of that joint beam, you 0:42:54.120 --> 0:42:56.920 don't know whether it went through A B or B A, 0:42:57.920 --> 0:43:00.399 but it's sort of it looks like it went through 0:43:00.440 --> 0:43:02.600 both at the same time, sort of like the cat 0:43:02.840 --> 0:43:06.520 alive and death exactly. And so here these photons have 0:43:06.680 --> 0:43:10.799 had an experience that has indefinite causality. Right, we don't 0:43:10.840 --> 0:43:13.960 know what the order of events was for these photons, 0:43:14.000 --> 0:43:17.200 and it matters, right, A B has different photons than 0:43:17.360 --> 0:43:21.160 BE at an individual photon, there's a probability of one 0:43:21.400 --> 0:43:24.239 or probability of the other, and that leads to this 0:43:24.520 --> 0:43:27.040 really interesting interference pattern. So you can see that this 0:43:27.120 --> 0:43:29.640 is actually happening. It's not like you have just two 0:43:29.719 --> 0:43:32.040 different groups of photons, ones that are A B and 0:43:32.080 --> 0:43:34.960 ones that are B A. Every photon now has a 0:43:34.960 --> 0:43:38.160 probability of having one order or the other. Right, But 0:43:38.239 --> 0:43:41.040 I guess you know it's looking at this skeptically. It's 0:43:41.040 --> 0:43:42.920 not like you did the same thing A and B 0:43:43.080 --> 0:43:46.120 in different orders, but they went through different filters kind 0:43:46.120 --> 0:43:49.160 of right, They took a different path through space. So 0:43:49.160 --> 0:43:51.960 it's sort of not like I'm not really changing the 0:43:52.080 --> 0:43:54.400 order of events. I'm changing the path, that's right. But 0:43:54.440 --> 0:43:56.880 in this case, the path determines the order of events. 0:43:56.960 --> 0:43:59.080 And you're right, it's not exactly analogous to what we're 0:43:59.080 --> 0:44:02.320 talking about before with light cones and the bending of space. 0:44:02.600 --> 0:44:05.640 It's a different way to try to construct indefinite causality, 0:44:05.960 --> 0:44:09.759 right there, not exactly physically the same filters, right, it's 0:44:09.760 --> 0:44:12.279 sort of like a standing for having done the same 0:44:12.320 --> 0:44:15.319 thing in a different order. Yes, exactly, because you can't 0:44:15.360 --> 0:44:17.799 do that. You can't like reverse time and do the 0:44:17.840 --> 0:44:20.719 experiment again in the other order and then rejoin it. 0:44:20.760 --> 0:44:22.440 That would be super awesome if you could do that, 0:44:22.520 --> 0:44:25.600 but here we separate them in space instead. That would 0:44:25.600 --> 0:44:28.080 be a dessert cone for sure. But I think what 0:44:28.080 --> 0:44:30.160 you're saying is that they did this this experiment and 0:44:30.200 --> 0:44:32.880 it confirmed that. You know, it's sort of like you 0:44:32.920 --> 0:44:35.760 can have two different orders at the same time happening 0:44:36.120 --> 0:44:38.839 quantum mechanically exactly. And what they do are really cool 0:44:38.880 --> 0:44:42.480 things with correlations. It's just like with bells inequality. You know, 0:44:42.520 --> 0:44:45.799 the example of having two quantum entangled particles, where you 0:44:45.840 --> 0:44:47.279 know if one is spin up, the other one has 0:44:47.320 --> 0:44:50.799 to be spinned down. And to prove that they're not 0:44:50.920 --> 0:44:53.399 determined until you open one box, even if they're really 0:44:53.400 --> 0:44:56.120 far apart, you have to do these really subtle experiments 0:44:56.200 --> 0:44:59.480 called probing bells inequality that showed that you can get 0:44:59.520 --> 0:45:02.560 like or relations between the two boxes that you can't 0:45:02.600 --> 0:45:05.399 have otherwise. In the same way they do that. Here, 0:45:05.600 --> 0:45:08.120 they like change what A and B are, they rotate them, 0:45:08.160 --> 0:45:10.239 and they get these correlations between one side and the 0:45:10.280 --> 0:45:14.000 other that you can't have if causality was definite. So 0:45:14.080 --> 0:45:17.520 you have to have indefinite causality to see the specific 0:45:17.560 --> 0:45:20.560 results of these experiments. The patterns, the numbers that they 0:45:20.600 --> 0:45:24.279 get out cannot be reproduced if causality is definitely If 0:45:24.320 --> 0:45:27.000 every photon actually went to one side or the other 0:45:27.320 --> 0:45:29.920 and then merges, that does not explain the results of 0:45:29.960 --> 0:45:32.480 the experiment. It has to be indefinite to get the 0:45:32.600 --> 0:45:36.439 interference patterns and the correlations that they see, right, all right, 0:45:36.480 --> 0:45:39.080 So then it's sort of confirms that the universe is 0:45:39.160 --> 0:45:45.239 CAUSALI ish and definitely causal. So then what does that 0:45:45.320 --> 0:45:47.799 mean for us? Like, does that mean that we can 0:45:47.840 --> 0:45:51.880 now break the rules and then to do cool things 0:45:52.080 --> 0:45:54.680 or does it mean that, you know, it's just another 0:45:54.719 --> 0:45:57.920 sort of step in our sort of befuddlement with quantum mechanics. 0:45:58.160 --> 0:46:00.319 Is there some rule in particular your hope to get 0:46:00.360 --> 0:46:03.359 to break looking for permission? Yeah, you know, I want 0:46:03.360 --> 0:46:06.200 to eat the breakfast coding and not gain weight, reverse 0:46:06.840 --> 0:46:10.560 cause and effect. They're exactly, or you can eat breakfast 0:46:10.640 --> 0:46:13.759 any time of day. No, there are some potential applications 0:46:13.800 --> 0:46:15.839 to this. You know, any time you gain some new 0:46:15.960 --> 0:46:18.640 insight to the way the universe works, you can come 0:46:18.719 --> 0:46:20.920 up with some ways to take advantage of that insight 0:46:21.080 --> 0:46:23.719 to do something you couldn't do before. And so people 0:46:23.719 --> 0:46:25.839 are thinking carefully about what this means, and there's some 0:46:25.880 --> 0:46:28.280 cool things that you can do, like you can send 0:46:28.320 --> 0:46:32.440 more information over noisy channels by using indefinite causality to 0:46:32.600 --> 0:46:35.520 encode some of that extra information, or people have come 0:46:35.600 --> 0:46:38.759 up with like weird quantum computers where two halves the 0:46:38.760 --> 0:46:41.560 computer are not linked by causality, and so they can 0:46:41.800 --> 0:46:45.240 both do their calculation before the other one and send 0:46:45.280 --> 0:46:47.279 the results to the other one, and so you can 0:46:47.320 --> 0:46:49.960 sort of like skip steps there and sort of like 0:46:50.080 --> 0:46:52.440 cheat in time, which is pretty cool. So there's some 0:46:52.480 --> 0:46:55.279 ways people are thinking about using this. For me, it's 0:46:55.280 --> 0:46:58.680 not about the applications, it's about making progress to this 0:46:58.800 --> 0:47:01.520 ultimate theory. You know, we want a deep picture of 0:47:01.560 --> 0:47:04.440 the universe, and we want to understand how the bending 0:47:04.480 --> 0:47:07.319 of space is consistent with quantum mechanics and all this 0:47:07.400 --> 0:47:10.360 crazy stuff. And so it might just be that this 0:47:10.719 --> 0:47:14.360 very way we think about the universe, causality isn't always required. 0:47:14.400 --> 0:47:16.879 It's like it usually happens. It's most of the time 0:47:16.920 --> 0:47:19.319 a good way to describe things, but not something that 0:47:19.360 --> 0:47:22.200 you have to have at the basic core in all 0:47:22.280 --> 0:47:24.960 the deep equations, and so that would you think maybe 0:47:25.239 --> 0:47:27.800 give us some insight into merging these two theories together 0:47:28.160 --> 0:47:32.200 quantum mechanics and general relativity. Yeah, exactly. This is a 0:47:32.239 --> 0:47:35.080 stumbling block, right, as we talked about before. If you 0:47:35.200 --> 0:47:38.640 have general relativity, which bend space, and you have quantum mechanics, 0:47:38.760 --> 0:47:43.160 which makes that bending uncertain, then causality is no longer clear. 0:47:43.280 --> 0:47:46.040 And that's been a problem for quantum gravity. So maybe 0:47:46.040 --> 0:47:48.400 the answer is like, well, just act like it's not 0:47:48.440 --> 0:47:51.560 a problem. Maybe it's actually okay, you know, maybe this 0:47:51.719 --> 0:47:53.920 wasn't a wall in our progress. We just need to 0:47:53.920 --> 0:47:56.359 so like not worry about it so much. Yeah, that's 0:47:56.400 --> 0:48:00.000 my favorite way to deal with problems, Daniel, Just tocore them. 0:48:00.360 --> 0:48:02.560 Just don't look at the scale when you weigh yourself, 0:48:02.920 --> 0:48:04.919 and then you don't have to worry about causing it. Well, 0:48:04.960 --> 0:48:06.640 it is an important lesson and the way we think 0:48:06.680 --> 0:48:09.040 about things, you know, we put up mental barriers. Sometimes 0:48:09.120 --> 0:48:12.319 we imagine like, oh, well that's impossible, they can't be 0:48:12.480 --> 0:48:14.239 and then later people come along and they're like, well, 0:48:14.280 --> 0:48:17.800 actually why not, or you know, why are we following? 0:48:17.840 --> 0:48:20.520 This rule? Is there's really actually important. And then they 0:48:20.560 --> 0:48:23.960 discovered this is a whole rich area of exploration, you know, 0:48:24.200 --> 0:48:27.640 think about like imaginary numbers. People for a long time thought, well, 0:48:27.680 --> 0:48:29.800 that's ridiculous, it's nonsense, but it turns out to be 0:48:29.880 --> 0:48:32.759 really important branch of mathematics for understanding the way the 0:48:32.840 --> 0:48:36.200 universe works. And so sometimes you've got to like knock 0:48:36.239 --> 0:48:39.200 on these mental walls and discover that there's actually lots 0:48:39.200 --> 0:48:41.440 of interesting territory on the other side. Yeah, I think 0:48:41.440 --> 0:48:44.040 that should be your new slogan for physics. You know, 0:48:44.239 --> 0:48:48.080 physics colon. Why not? You know, Nike has just do it? 0:48:48.239 --> 0:48:51.080 You should have Why not haven't destroyed the universe yet? 0:48:52.600 --> 0:48:55.480 Why not put scrambled eggs in that cone? Seriously, that's 0:48:55.480 --> 0:48:58.000 a great idea. All right, Well, we hope you enjoyed that, 0:48:58.200 --> 0:49:00.160 and you know, got you to think a little bit 0:49:00.160 --> 0:49:02.959 about what we think is certain in this universe. Maybe 0:49:03.200 --> 0:49:04.880 things are not as certain as we think they are, 0:49:04.960 --> 0:49:08.919 even the basic logic of how and when things happen. 0:49:09.200 --> 0:49:11.200 And that goes to show you that there are still 0:49:11.360 --> 0:49:14.680 really deep end basic questions out there that people are 0:49:14.719 --> 0:49:18.120 struggling with about the nature of the universe. And maybe 0:49:18.160 --> 0:49:21.080 what we're missing is one really cool flash of insight. 0:49:21.560 --> 0:49:24.080 And maybe you will have that flash of insight and 0:49:24.120 --> 0:49:28.399 revolutionize the way everybody thinks about the universe. Why not, Well, 0:49:28.440 --> 0:49:31.200 we hope you enjoyed that. Thanks for joining us, see 0:49:31.200 --> 0:49:41.600 you next time. Thanks for listening, and remember that Daniel 0:49:41.600 --> 0:49:44.120 and Jorge explained the universe is a production of I 0:49:44.360 --> 0:49:47.799 Heart Radio or more podcast from my heart Radio, visit 0:49:47.840 --> 0:49:51.319 the I heart Radio app, Apple Podcasts, or wherever you 0:49:51.440 --> 0:49:58.680 listen to your favorite shows. Yeah,