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

• 0:08
  Speaker 1: Hey, Daniel, what are we doing today for the opening
• 0:10
  Speaker 1: of the podcast? You know, actually I thought maybe we
• 0:13
  Speaker 1: would invert the usual process. We have a usual process. Yeah,
• 0:17
  Speaker 1: first we have an idea and then we record it.
• 0:20
  Speaker 1: So you want to flip it today? So what does
• 0:22
  Speaker 1: that mean? We're gonna start recording and then hope we
• 0:25
  Speaker 1: get an idea. Isn't that like putting costs after effect? Yeah,
• 0:28
  Speaker 1: you know, just a little causality inversion to start your day?
• 0:31
  Speaker 1: What could go wrong? It's never a good sign when
• 0:33
  Speaker 1: the physicist says what could go wrong? Well, you know,
• 0:35
  Speaker 1: we haven't destroyed the universe yet, but what if we
• 0:38
  Speaker 1: blow up the universe with this inverted opening? Oh, and
• 0:41
  Speaker 1: that gives me an idea for a perfect opening. Hopefully
• 0:44
  Speaker 1: people laughed before they listen to that. Hi am Jorgemming,
• 1:02
  Speaker 1: cartoonists and the creator of PhD comics. Hi. I'm Daniel.
• 1:05
  Speaker 1: I'm a particle physicist and a physics professor at u
• 1:08
  Speaker 1: C Irvine, and I usually don't know what I'm going
• 1:10
  Speaker 1: to say before I say it. Isn't that part of
• 1:12
  Speaker 1: the job description for a professor not knowing what you're
• 1:15
  Speaker 1: talking about exactly, but making it sound like you do,
• 1:19
  Speaker 1: and that's where the PhD comes from. I guess years
• 1:22
  Speaker 1: of training. Welcome to our podcast, Daniel and Jorge Explain
• 1:26
  Speaker 1: the Universe, a production of My Heart Radio in which
• 1:29
  Speaker 1: we are not afraid to admit what we don't know
• 1:31
  Speaker 1: about the universe because we love to embrace that ignorance.
• 1:35
  Speaker 1: We dive deep into everything that we don't understand about
• 1:39
  Speaker 1: the universe, the very nature of space and time, the
• 1:42
  Speaker 1: context of the reality around us, all of the squishy
• 1:45
  Speaker 1: and beautiful and incredible matter that fills it and wiggles
• 1:49
  Speaker 1: around inside of it. We are desperate to understand the
• 1:51
  Speaker 1: deep nature of the universe, and we are here to
• 1:54
  Speaker 1: explore it and explain it to you. Yeah, because there
• 1:57
  Speaker 1: is a lot we don't know about the universe. And
• 1:59
  Speaker 1: I'm not just talking about myself a cartoonist, but there's
• 2:01
  Speaker 1: a lot that even physicists don't know about, not just
• 2:05
  Speaker 1: things hidden inside of black holes or neutron stars or
• 2:07
  Speaker 1: inside of particles. There's some very fundamental questions we still
• 2:12
  Speaker 1: have about this wild and wacky universe. Yeah, exactly, like
• 2:15
  Speaker 1: where did I put my phone? And how come I
• 2:17
  Speaker 1: can never find an even number of socks at the
• 2:19
  Speaker 1: same time, I think maybe you put the phone in
• 2:22
  Speaker 1: your socks. That would solve if I could just have
• 2:25
  Speaker 1: like digital socks so I could have them on my phone,
• 2:28
  Speaker 1: that would be so much more convenient. Well, I know
• 2:31
  Speaker 1: you like to wear sandals, so I'm pretty sure you
• 2:32
  Speaker 1: already have virtual socks. Yeah, exactly. That's why I could
• 2:35
  Speaker 1: just delete all the socks in one film. But it's
• 2:38
  Speaker 1: not really just sucks that we are curious about. We
• 2:40
  Speaker 1: really do want to understand the deep nature of reality
• 2:44
  Speaker 1: around us. What is this universe? How did it come
• 2:47
  Speaker 1: to me? Why is it this way and not another way?
• 2:49
  Speaker 1: And most importantly, are there things about it that we're
• 2:53
  Speaker 1: getting basically wrong? Yeah, because you know, I feel like
• 2:55
  Speaker 1: you can ask questions about the universe and the stuff
• 2:59
  Speaker 1: in the universe us, you know, like black holes and
• 3:01
  Speaker 1: stars and particles, but you can also kind of ask deep,
• 3:05
  Speaker 1: kind of philosophical questions about it. You know, it's sort
• 3:08
  Speaker 1: of like about the nature of it or what can
• 3:11
  Speaker 1: break the universe even Yeah, because we know that in
• 3:13
  Speaker 1: human history we've made a lot of basic mistakes about
• 3:16
  Speaker 1: the way we thought the universe worked, because we've only
• 3:19
  Speaker 1: seen it work in one particular way or in one
• 3:21
  Speaker 1: set of circumstances, and we imagined that must be true forever,
• 3:25
  Speaker 1: it must be a deep truth about the universe, and
• 3:27
  Speaker 1: it turns out not so much, which means that what
• 3:30
  Speaker 1: lies ahead of us is more discoveries that basic assumptions
• 3:34
  Speaker 1: about the nature of the universe are probably wrong, and
• 3:36
  Speaker 1: it might just be that we need to hammer at
• 3:38
  Speaker 1: these things forever, or wait till the aliens arrive and
• 3:41
  Speaker 1: give us some other context for looking at the nature
• 3:43
  Speaker 1: of the universe. But that's cheating, Daniel. Are they also
• 3:46
  Speaker 1: going to tell you where your socks are? Are you
• 3:48
  Speaker 1: gonna be that irresponsible? They're gonna email us socks. It's
• 3:52
  Speaker 1: gonna be nice digital socks. That's not cheating at all.
• 3:55
  Speaker 1: I think the first Galactic physics conference will be, you know,
• 3:58
  Speaker 1: a great melding of lines. If you think that's cheating,
• 4:01
  Speaker 1: then you know physicist shouldn't work together at all. We
• 4:03
  Speaker 1: should all be trying to figure out the universe on
• 4:05
  Speaker 1: our own. Well, but do you think it'd be the
• 4:07
  Speaker 1: two way conference with us and the aliens? Do you
• 4:09
  Speaker 1: think we have anything to teach them? Are we joking
• 4:12
  Speaker 1: over being serious? I don't know. I mean, if they
• 4:14
  Speaker 1: can travel through the stars, and you know, invent warp drives.
• 4:18
  Speaker 1: Do you think we have anything to teach them or
• 4:20
  Speaker 1: do you think we know something they don't? At this point,
• 4:22
  Speaker 1: I think it's very likely that everything we've learned in
• 4:24
  Speaker 1: our human sciences is probably corrupted by human bias and
• 4:28
  Speaker 1: totally useless to aliens, not just because we haven't made
• 4:31
  Speaker 1: advances far enough, but probably just the questions we ask
• 4:35
  Speaker 1: in the nature of the way we answer them is
• 4:37
  Speaker 1: probably deeply inherently human in ways we can't even imagine.
• 4:41
  Speaker 1: You know, we don't even really know where the edge
• 4:43
  Speaker 1: of the box is. We just know that we're in
• 4:45
  Speaker 1: this sort of like human constructed box about ways to
• 4:48
  Speaker 1: think about the universe. And it isn't until the aliens
• 4:51
  Speaker 1: come that will even figure out like where the edge
• 4:53
  Speaker 1: of that box is. Yeah, I guess because we we've
• 4:56
  Speaker 1: been trying to figure everything out with the human brain.
• 4:58
  Speaker 1: And you know what if you have a totally different
• 5:00
  Speaker 1: maybe you get to see things in a very different way, yeah,
• 5:03
  Speaker 1: or different sensory organs. Right, what if you can see
• 5:06
  Speaker 1: X rays, or you can smell photons, or you can
• 5:09
  Speaker 1: taste electrons or something like that, Right, you might have
• 5:12
  Speaker 1: figured out totally different ways to think about the universe
• 5:14
  Speaker 1: in a completely different order. Maybe quantum mechanics is intuitive
• 5:18
  Speaker 1: to them because you know, they've seen this stuff happening
• 5:21
  Speaker 1: in front of them every single day. Or maybe they
• 5:23
  Speaker 1: can see neutrinos and so the universe is like totally
• 5:26
  Speaker 1: opaque and very weird to them. It's going to be
• 5:28
  Speaker 1: a challenge to map from human brains to alien brains.
• 5:30
  Speaker 1: Sometimes it's hard to even map from human brain to
• 5:33
  Speaker 1: human brain. Yeah, So I think what you're saying is
• 5:36
  Speaker 1: that sometimes there are revolutions and human thought where we
• 5:40
  Speaker 1: thought that the universe worked one way and then it
• 5:42
  Speaker 1: turns out it worked another way, right, Like maybe quantum
• 5:45
  Speaker 1: physics is one of those big revolutions, or relativity exactly.
• 5:49
  Speaker 1: Those two are the best examples of moments when we
• 5:52
  Speaker 1: realized that fundamentally the universe is very different from the
• 5:55
  Speaker 1: way we imagined. And I think we put those on
• 5:57
  Speaker 1: the scale of other kinds of realizations, like discovering that
• 6:01
  Speaker 1: the Earth is not the center of the Solar System
• 6:03
  Speaker 1: or even the cosmos, or discovering that our galaxy is
• 6:06
  Speaker 1: one of trillions of galaxies instead of the entire cosmos.
• 6:10
  Speaker 1: You know, these kinds of things help us understand not
• 6:13
  Speaker 1: just the nature of the universe around us, but our
• 6:16
  Speaker 1: place in it, in the context of our very existence.
• 6:19
  Speaker 1: So these are pretty deep potential revolutions in our understanding
• 6:22
  Speaker 1: of the nature of the universe. Yeah, and do you
• 6:24
  Speaker 1: think that has made fits This is a little bit
• 6:27
  Speaker 1: paranoid almost in a way like now you doubt everything,
• 6:29
  Speaker 1: like even the basics, you know, logic of the universe. Right. No,
• 6:33
  Speaker 1: it makes this excited because it means that around every
• 6:36
  Speaker 1: corner is a potential explosion of ideas. You can tug
• 6:41
  Speaker 1: on any random thread and pull the whole thing apart.
• 6:44
  Speaker 1: Paranoid makes it sound like we're afraid to pull the
• 6:46
  Speaker 1: whole thing apart. We are desperate to pull it apart
• 6:49
  Speaker 1: because it will reveal something else, something new that we
• 6:51
  Speaker 1: can chew on, where we can make new progress and
• 6:53
  Speaker 1: ask new questions. That's the dream come true. I think
• 6:56
  Speaker 1: being afraid of explosions at every corner is sort of
• 6:58
  Speaker 1: the definition of making being paranoid. But you're saying, and
• 7:02
  Speaker 1: you're paranoid in a good way. You're like a good paranoid,
• 7:05
  Speaker 1: a good kind of parentig is somehow you walk me
• 7:08
  Speaker 1: into that corner. But yes, I am now admitting I'm
• 7:10
  Speaker 1: a good kind of paranoid. But yeah, you can ask
• 7:13
  Speaker 1: pretty deep questions about the universe, and so today we're
• 7:16
  Speaker 1: asking a pretty challenging question. I mean in the sense
• 7:19
  Speaker 1: that it challenges something very deep and sort of I
• 7:23
  Speaker 1: don't know, logical and basic about the universe that you know,
• 7:26
  Speaker 1: maybe a lot of people don't even think you can
• 7:28
  Speaker 1: even ask. That's right. It's something that's so fundamental to
• 7:31
  Speaker 1: the universe that even is incorporated in how we explain
• 7:34
  Speaker 1: the universe itself. It's something inherent I think in the
• 7:38
  Speaker 1: way humans think and the way we tell stories and
• 7:41
  Speaker 1: think about what makes sense and what doesn't make sense. Yeah,
• 7:44
  Speaker 1: So to be on the program, we'll be asking the
• 7:45
  Speaker 1: question does the universe need cause and effect? WHOA Daniel?
• 7:56
  Speaker 1: This kind of blew my mind. I mean, how can
• 7:58
  Speaker 1: you how can you question cause and effect and causality
• 8:00
  Speaker 1: in the universe? Are you saying there's some effects to
• 8:02
  Speaker 1: question and causes? Yeah? Yeah. The effect of asking this
• 8:07
  Speaker 1: question is it's gott me really confused. I know. I
• 8:10
  Speaker 1: think it's so fundamental to the way we think, you know,
• 8:12
  Speaker 1: we the way we explain things to ourselves, as we
• 8:15
  Speaker 1: tell stories and stories go like a happened, and then
• 8:18
  Speaker 1: be happened, and then see happened. That's the way we talk,
• 8:21
  Speaker 1: that's the way we think, that's the way we organize
• 8:23
  Speaker 1: our minds, and so it's pretty hard to imagine that
• 8:27
  Speaker 1: you could have a universe without cause and effect. On
• 8:29
  Speaker 1: the other hand, just because it's part of our minds
• 8:32
  Speaker 1: doesn't mean it has to be part of the universe, right.
• 8:35
  Speaker 1: The whole goal of physics is to break out of
• 8:37
  Speaker 1: that box and understand something universal instead of something human. Now, Daniel,
• 8:41
  Speaker 1: is this related to like the idea of the arrow
• 8:43
  Speaker 1: of time or is this sort of like a basic
• 8:46
  Speaker 1: kind of thing about the universe where like things can
• 8:49
  Speaker 1: happen without being connected to other things. Do you know
• 8:52
  Speaker 1: what I mean? Yeah, definitely it's connected to the question
• 8:55
  Speaker 1: of time, because cause and effect orders things. And we'll
• 8:58
  Speaker 1: talk about this in more detailed later. You know, there's
• 9:00
  Speaker 1: this concept of like a light cone, which organizes the
• 9:03
  Speaker 1: order of events. Things have to happen in the universe,
• 9:06
  Speaker 1: But that's only true if you have causality. If things
• 9:10
  Speaker 1: have to happen in a certain order. Things don't have
• 9:13
  Speaker 1: to happen in a certain order. That whole picture might
• 9:16
  Speaker 1: go out the window. Whoa, And that's you know, totally
• 9:19
  Speaker 1: opposite from our everyday experience, right, Like our everyday experience
• 9:24
  Speaker 1: is that effects do follow causes, right absolutely. You know,
• 9:28
  Speaker 1: if your friends don't like, arrive for dinner before you
• 9:31
  Speaker 1: invite them, you should meet my friends. Introverts don't have
• 9:37
  Speaker 1: guests rorive for dinner before you invite them. You know.
• 9:40
  Speaker 1: It's like if you send somebody a message, they can't
• 9:43
  Speaker 1: read the message before you send it. Right, the kind
• 9:45
  Speaker 1: of thing would violate causality. It's definitely connected with the
• 9:48
  Speaker 1: flow of time because it has to do with like,
• 9:50
  Speaker 1: you know, sending messages back in time. One of the
• 9:53
  Speaker 1: reasons we always say that you can't travel back in
• 9:55
  Speaker 1: time is that it would violate causality. You would have
• 9:58
  Speaker 1: effects that influence the our own causes. Right. It's like
• 10:01
  Speaker 1: very basic to the way we think about the universe,
• 10:04
  Speaker 1: stepping forwards in time, flowing from now to the future.
• 10:07
  Speaker 1: All right, Well, then the question is do we actually
• 10:10
  Speaker 1: need causality? Do we do we need costs and effect
• 10:13
  Speaker 1: in the universe to make it work or are you
• 10:15
  Speaker 1: saying it's sort of maybe like an illusion or something
• 10:18
  Speaker 1: that's apparent, but not really needed in the universe. What
• 10:21
  Speaker 1: are we actually asking here? I think the question is
• 10:24
  Speaker 1: whether it's always needed? You know, this is the kind
• 10:27
  Speaker 1: of thing that we observe in the universe. It is
• 10:28
  Speaker 1: definitely part of the universe. But just like with relativity
• 10:32
  Speaker 1: and quantum mechanics, there are some places where it seems
• 10:35
  Speaker 1: like it might not hold together, some like little threads
• 10:38
  Speaker 1: where it doesn't really work and it isn't really consistent
• 10:41
  Speaker 1: with some other basic principles, And that gives us a
• 10:44
  Speaker 1: clue that maybe it's not always required, and maybe like
• 10:48
  Speaker 1: it comes together in certain circumstances. It's a nice way
• 10:51
  Speaker 1: to describe what often happens in the universe, but it's
• 10:53
  Speaker 1: not actually a fundamental principle, and we can find some
• 10:56
  Speaker 1: places where it's tossed out the window. So I who
• 10:59
  Speaker 1: would be the one we cause out? Cause or effect?
• 11:01
  Speaker 1: Which one do you like better? I prefer horses to cow,
• 11:04
  Speaker 1: so let's throw out cowsality is it cost or effect? Well? Anyways,
• 11:09
  Speaker 1: we were, as usual, wondering how many people out there
• 11:11
  Speaker 1: had thought about this crazy, deep, fundamental question, and how
• 11:15
  Speaker 1: many people think they might have an answer to this
• 11:17
  Speaker 1: strange query. So Daniel went out there to the internet
• 11:20
  Speaker 1: to ask people do we need cause and effect? So
• 11:24
  Speaker 1: thank you everybody out there on the Internet who is
• 11:26
  Speaker 1: willing to answer these funny, crazy questions without having a
• 11:29
  Speaker 1: chance to think about it or google it. If you'd
• 11:32
  Speaker 1: like to do then it sounds fun. Do you please
• 11:34
  Speaker 1: write to us two questions at Daniel and Jorge dot com.
• 11:37
  Speaker 1: We want your voice, so think about it for a second.
• 11:40
  Speaker 1: Do you think the universe needs cause and effect? Here's
• 11:43
  Speaker 1: what people had to say. I think that we as
• 11:46
  Speaker 1: human beings probably need it. Whether the universe needs it
• 11:51
  Speaker 1: or existence, probably not. I can imagine a crazy universe
• 11:55
  Speaker 1: where everything was upside down and happened of its own coalition,
• 12:00
  Speaker 1: But as people, I think we wouldn't do very well
• 12:03
  Speaker 1: in such a place. I don't know much about this.
• 12:07
  Speaker 1: That makes me think of the Matrix when the marrow
• 12:10
  Speaker 1: Vingian is talking about cause and causality or something like that. Um,
• 12:15
  Speaker 1: I understood about that about as much as I understood
• 12:18
  Speaker 1: most of that movie. But without honestly really knowing much
• 12:22
  Speaker 1: about it, I'm gonna say no. I know things can
• 12:25
  Speaker 1: kind of happen what seems to be randomly in the universe,
• 12:30
  Speaker 1: and with things the statistical chances that some of the
• 12:37
  Speaker 1: things that do happen, the statistical chances are so low
• 12:40
  Speaker 1: that it just doesn't seem like there could be a
• 12:42
  Speaker 1: cause for every single thing that can happen, because there's
• 12:45
  Speaker 1: so many different things that can happen. So do we
• 12:49
  Speaker 1: need causality? I'm going with no on that one. I
• 12:53
  Speaker 1: think we need causality because if we didn't have cause
• 12:57
  Speaker 1: and effect, everything would just be us because like there
• 13:04
  Speaker 1: would be no reason for anything to happen. Things would
• 13:08
  Speaker 1: stepping on a butterfly would cause something completely crazy to happen,
• 13:13
  Speaker 1: not just like butterfly effect, but like completely bananas. Well,
• 13:19
  Speaker 1: let's I'm thinking of this. You eat, you get fat,
• 13:25
  Speaker 1: cause an effect, and I think we don't need it,
• 13:32
  Speaker 1: and they should be voted out so we don't need it.
• 13:40
  Speaker 1: We can start a petition, I'm sure if we need
• 13:43
  Speaker 1: called out, But I mean, if you want to know
• 13:45
  Speaker 1: the past, cause an effect obviously play a role in
• 13:48
  Speaker 1: knowing what that one part was. But if we didn't happen,
• 13:54
  Speaker 1: if we didn't need it, that would mean possibility is multiverse,
• 13:58
  Speaker 1: and that would be though. I think maybe we don't
• 14:01
  Speaker 1: want No. I don't think we need causality. You can
• 14:08
  Speaker 1: have two things that are correlated, like in you know,
• 14:13
  Speaker 1: economics or statistics. You know, they look for correlations, and
• 14:18
  Speaker 1: correlations provide information in and of themselves. Maybe it's nice
• 14:24
  Speaker 1: to no causality, but I don't think you necessarily need
• 14:29
  Speaker 1: causality to get information, all right, some pretty definitive answers here.
• 14:35
  Speaker 1: Nobody seem to sort of stumble a lot, I know,
• 14:38
  Speaker 1: and some people who really think, like, yeah, we could
• 14:40
  Speaker 1: do without causality. That really surprised me. Really, wow, do
• 14:45
  Speaker 1: you think that's human humors? Maybe physics has just been
• 14:48
  Speaker 1: so successful in like knocking down basic pillars of reality
• 14:52
  Speaker 1: that people are ready for, like physics to undermine everything.
• 14:55
  Speaker 1: You're seeing it as a positive, seeing it as a
• 14:58
  Speaker 1: positive people are open minded to unraveling the basic nature
• 15:01
  Speaker 1: of their very existence. That's great. Well, I think maybe
• 15:04
  Speaker 1: this goes back to what I asked earlier about what
• 15:06
  Speaker 1: exactly do we mean by causality and not having causality?
• 15:10
  Speaker 1: Like does it mean that you can't have a without
• 15:13
  Speaker 1: B or does it mean that you know, as always
• 15:16
  Speaker 1: have to be connected to bees? You know what I mean?
• 15:19
  Speaker 1: Like can things appear out of nowhere without a cause?
• 15:21
  Speaker 1: Or are we saying that it always has to come
• 15:24
  Speaker 1: before B. You cant have be before A, you know
• 15:26
  Speaker 1: what I mean? The difference. Yeah, it's about the ordering
• 15:29
  Speaker 1: of events, right, I mean, you still can't break random
• 15:32
  Speaker 1: laws of physics. You can't just like create energy from nothing.
• 15:36
  Speaker 1: It's not like it's a free for all out there.
• 15:38
  Speaker 1: We think the universe still does have laws and does
• 15:42
  Speaker 1: follow those laws. We're just not sure that those laws
• 15:44
  Speaker 1: require that A always happens before B. So we're pretty
• 15:48
  Speaker 1: clear that you can't just have B without like the
• 15:51
  Speaker 1: pop out of nowhere. Right the laws of physics says no, Yeah,
• 15:56
  Speaker 1: well depends on exactly what B is, right, Like quantum
• 15:59
  Speaker 1: mechanics says, you and have particles pop out of the vacuum.
• 16:01
  Speaker 1: But there are rules for that, right, There are ways
• 16:04
  Speaker 1: that it can happen. So we still think that the
• 16:06
  Speaker 1: universe does follow laws. But hey, maybe when the aliens
• 16:09
  Speaker 1: show up, they're like physics, we gave up on that
• 16:11
  Speaker 1: a million years ago because we discover the universe is
• 16:13
  Speaker 1: totally arbitrary deep down. But yes, we still think that
• 16:16
  Speaker 1: if the universe follows laws, And so you're saying that
• 16:19
  Speaker 1: what we're asking today is whether or not. Those laws
• 16:23
  Speaker 1: sort of prescribe a specific order that things have to
• 16:26
  Speaker 1: happen in the universe. Yeah, but not everything in the
• 16:28
  Speaker 1: universe is connected by causal order. Remember, because there's a
• 16:32
  Speaker 1: finite speed of information, there's some things that you can't
• 16:35
  Speaker 1: have an effect on, right Like events that are happening
• 16:39
  Speaker 1: right now in Andromeda. You can't have any effect on
• 16:42
  Speaker 1: with decisions you make right now, because the information from
• 16:45
  Speaker 1: your decision right now to like send a beam of
• 16:47
  Speaker 1: light or whatever won't affect Andromeda for millions of years.
• 16:52
  Speaker 1: So even with causality, there's some parts of the universe
• 16:55
  Speaker 1: that are not causally connected to other parts. All right, Well,
• 16:58
  Speaker 1: let's maybe break it down for people. What exactly do
• 17:02
  Speaker 1: you mean by causality? How do you define causality or
• 17:05
  Speaker 1: causing effect? Yeah, so take two points in space and time,
• 17:09
  Speaker 1: call them A and B for lack of more creative labels.
• 17:13
  Speaker 1: And here we meet a point in space and in time. Right,
• 17:16
  Speaker 1: So we mean like A is at your house at
• 17:19
  Speaker 1: eight a m. In the morning, and B as you've
• 17:21
  Speaker 1: arrived at work at nine am. So the events have
• 17:24
  Speaker 1: a space and a time in them, all right, And
• 17:27
  Speaker 1: so these two things are causally connected to have a
• 17:30
  Speaker 1: definite order of events if something that happens at B
• 17:34
  Speaker 1: relies on information from A. Right. So maybe, for example,
• 17:38
  Speaker 1: you brought something with you from home to work, so
• 17:41
  Speaker 1: for example, you brought your breakfast or you forgot your
• 17:44
  Speaker 1: breakfast when you left the house. So something you did
• 17:47
  Speaker 1: it A affects what you do. Would be you then
• 17:50
  Speaker 1: need to buy breakfast or steal your coworkers breakfast or something.
• 17:54
  Speaker 1: So those two events are connected causally because something that
• 17:57
  Speaker 1: happens at A influences what happens at B, meaning like
• 18:00
  Speaker 1: if I want to have breakfast at my office, I
• 18:04
  Speaker 1: need to have packed it or left the house with
• 18:06
  Speaker 1: that breakfast otherwise there's no way that I could have
• 18:09
  Speaker 1: that breakfast from home, right exactly. And once you get
• 18:12
  Speaker 1: to work and you have breakfast with you or don't,
• 18:15
  Speaker 1: there's nothing you can do to affect A, right, So
• 18:17
  Speaker 1: this is one directional. A can affect B, but B
• 18:21
  Speaker 1: cannot affect A. So that's what we mean by a
• 18:24
  Speaker 1: definite order of events. If A can have influence on B,
• 18:27
  Speaker 1: then B cannot have influence on A. If your decision
• 18:31
  Speaker 1: to leave the house with or without breakfast affects what
• 18:34
  Speaker 1: you do for breakfast at work, then what you do
• 18:36
  Speaker 1: for breakfast at work cannot affect whether or not you
• 18:39
  Speaker 1: leave the house with your breakfast. It can't go backwards, right.
• 18:42
  Speaker 1: I think you're just saying you can't go back in time.
• 18:44
  Speaker 1: But the two are sort of connected, right, Like if
• 18:46
  Speaker 1: I don't have breakfast in my office, then that means
• 18:49
  Speaker 1: I didn't I didn't leave my home with it. Right.
• 18:52
  Speaker 1: So they're sort of connected, aren't they. But you're saying
• 18:54
  Speaker 1: like one of them affects the other and not the
• 18:57
  Speaker 1: other way around. Yes, exactly. Information flow is only in
• 19:00
  Speaker 1: one direction here and here B is part of the
• 19:04
  Speaker 1: sort of the light cone of a Right. We talked
• 19:07
  Speaker 1: about how decisions you make can only influence things around
• 19:11
  Speaker 1: you that are nearby and in your future, and we
• 19:14
  Speaker 1: talked about in a previous podcast how to formalize that.
• 19:17
  Speaker 1: You think about a light cone, which is all the
• 19:19
  Speaker 1: things in your future that you can influence, and you
• 19:22
  Speaker 1: can influence things that are nearby in your immediate future
• 19:26
  Speaker 1: or things that are far away in the deep future,
• 19:28
  Speaker 1: because it's time for information to get there, all right.
• 19:31
  Speaker 1: So I think you're saying that I didn't leave my
• 19:33
  Speaker 1: house with my breakfast, and therefore I don't have it
• 19:35
  Speaker 1: in my office. That's the cause and that's the effect. Yeah, exactly,
• 19:39
  Speaker 1: And there's no way to go to the opposite direction.
• 19:41
  Speaker 1: What would that even mean? Like I'm at my office
• 19:43
  Speaker 1: first and then I left the house without the breakfast.
• 19:46
  Speaker 1: It would mean that somehow, once you get to your
• 19:49
  Speaker 1: office with or without your breakfast, you could still influence
• 19:52
  Speaker 1: whether you left your house with or without your breakfast.
• 19:55
  Speaker 1: That you could like somehow go back and change what
• 19:58
  Speaker 1: happened at eight am and change a decision based on
• 20:01
  Speaker 1: whether or not you had it with you in your
• 20:03
  Speaker 1: office at nine am. So you know, making a decision
• 20:06
  Speaker 1: at nine am can't influence what happened at eight am.
• 20:08
  Speaker 1: That's all we're saying with cause and effect, all right,
• 20:11
  Speaker 1: So then that's cause and effect and that that seems
• 20:13
  Speaker 1: pretty important for the universe to make sense, right, because
• 20:17
  Speaker 1: otherwise things would be what inconsistent, Like I can always
• 20:22
  Speaker 1: you know, create paradoxes and time loops and things like that.
• 20:25
  Speaker 1: It does seem pretty basic, right. It's the way that
• 20:27
  Speaker 1: we think about physics. When I first got into physics,
• 20:30
  Speaker 1: I thought it was amazing because it could predict the future,
• 20:33
  Speaker 1: and it predicts the future based on the conditions of
• 20:36
  Speaker 1: the present. You know, if you are shooting a cannonball
• 20:39
  Speaker 1: at a castle, you can predict its trajectory if you
• 20:42
  Speaker 1: know it's direction and its velocity, right, those are the causes,
• 20:47
  Speaker 1: and the effect is like, oh, it hits the castle
• 20:49
  Speaker 1: wall or it goes over the castle wall. And so
• 20:52
  Speaker 1: physics seems to me to be like all about using
• 20:54
  Speaker 1: causes to predict effects. You know, that's what the laws
• 20:57
  Speaker 1: of physics are. They take the current description the universe
• 21:00
  Speaker 1: and sort of step it forwards in time to the
• 21:02
  Speaker 1: next description. So it seems pretty basic. All right, Well,
• 21:06
  Speaker 1: it seems basic, which I think is probably a queue
• 21:09
  Speaker 1: that we're going to challenge that and it might turn
• 21:11
  Speaker 1: out to be wrong. So let's get into that and
• 21:13
  Speaker 1: what how we can maybe tested or find out the
• 21:17
  Speaker 1: true answer. But first let's take a quick break. All right,
• 21:32
  Speaker 1: we're talking about cause and effect and whether you actually
• 21:34
  Speaker 1: needed to make a happy universe I guess right, a
• 21:38
  Speaker 1: functioning universe. Yeah, exactly whether we can make sense of
• 21:42
  Speaker 1: our universe without causality, or whether it's actually absolutely fundamentally
• 21:47
  Speaker 1: required for anything to make sense to us. Okay, So
• 21:50
  Speaker 1: then we define causality as like I shoot an arrow
• 21:53
  Speaker 1: and an apple and it hits the apple, but I
• 21:56
  Speaker 1: can't do it the other way around. I like, I
• 21:58
  Speaker 1: can't have hit the apple before shooting the arrow exactly,
• 22:01
  Speaker 1: because if you hit the apple before you shoot the arrow,
• 22:04
  Speaker 1: you could like change your mind and not shoot the arrow,
• 22:06
  Speaker 1: and then oops, you already hit it. How can you
• 22:08
  Speaker 1: change your mind? It seems to like automatically make no sense.
• 22:11
  Speaker 1: It seems like a paradox, as you said, And it
• 22:13
  Speaker 1: seems to be sort of connected to the arrow of time, right,
• 22:17
  Speaker 1: like time only flows one way. But there's a little
• 22:19
  Speaker 1: bit more to it than that, right, there's a little
• 22:21
  Speaker 1: bit more to it than that. And of course the
• 22:24
  Speaker 1: thing that makes things weird and twist your brain and
• 22:26
  Speaker 1: maybe give us an escape from causality is going to
• 22:29
  Speaker 1: end up being quantum mechanics. Of course. Of course, quantum
• 22:33
  Speaker 1: mechanics always scrambling your brain. So that seems that I
• 22:37
  Speaker 1: think I'm guessing it's going to add some sort of
• 22:39
  Speaker 1: uncertainty or randomness to causality. Yeah, And before we get
• 22:43
  Speaker 1: to quantum mechanics, I think it's important that you have
• 22:45
  Speaker 1: in your mind a clear picture of the part of
• 22:48
  Speaker 1: the universe that you can affect with your causes. This
• 22:52
  Speaker 1: is again this concept of a light cone. Right if
• 22:55
  Speaker 1: you send out a flash of light right now, you like,
• 22:58
  Speaker 1: turn on a really bright light, then who can tell
• 23:01
  Speaker 1: that you have done that? People who are really far
• 23:03
  Speaker 1: away from you cannot see that right now. They have
• 23:06
  Speaker 1: to wait until the future, and people that are even
• 23:08
  Speaker 1: further away have to wait till the deeper future to
• 23:11
  Speaker 1: see that flash of light. Because light travels are the
• 23:14
  Speaker 1: fastest speed of information, people who haven't seen that flash
• 23:18
  Speaker 1: of light can't be influenced by it yet, right, So
• 23:21
  Speaker 1: we think about that as a light cone. In two dimensions,
• 23:24
  Speaker 1: you can imagine yourself sort of the tip of a
• 23:26
  Speaker 1: triangle that's opening up as time goes on, and you
• 23:30
  Speaker 1: can influence more and more of the future based on
• 23:33
  Speaker 1: your decisions of the present. In three D is sort
• 23:36
  Speaker 1: of like you know, you're at the tip of a
• 23:37
  Speaker 1: cone right now and it's opening up, right. I guess
• 23:40
  Speaker 1: maybe I wonder if we can talk about the breakfast
• 23:43
  Speaker 1: cone of my breakfast Okay, when I left my home,
• 23:47
  Speaker 1: like you're saying, like, there's this sort of a limited
• 23:49
  Speaker 1: number of time and places that I can be at
• 23:52
  Speaker 1: with my breakfast if I chose to leave my house
• 23:56
  Speaker 1: with my breakfast right, like, I can instantly be at
• 23:59
  Speaker 1: my work with breakfast, because I can't get there in time.
• 24:03
  Speaker 1: And also I can't be in like China in an
• 24:06
  Speaker 1: hour with my breakfast right because I'm limited to by
• 24:09
  Speaker 1: how fast I can move exactly. And so if you're
• 24:12
  Speaker 1: going to your office pretty close by, then you can
• 24:14
  Speaker 1: bring your breakfast with you, and that can influence your coworkers.
• 24:17
  Speaker 1: Are they going to try to steal your breakfast? Did
• 24:19
  Speaker 1: they forget their own breakfast? Are they influenced by the
• 24:21
  Speaker 1: smell of your breakfast? This kind of stuff. But the
• 24:23
  Speaker 1: you know, podcast headquarters in Shanghai, for example, can't be
• 24:27
  Speaker 1: influenced by that decision until later, until your light cone
• 24:30
  Speaker 1: has grown to expand and include all of those things.
• 24:34
  Speaker 1: So there are things that you cannot influence right now
• 24:37
  Speaker 1: in the universe just because of this finite speed of light,
• 24:40
  Speaker 1: and so everything you can influence, we call that part
• 24:42
  Speaker 1: of your light cone, right or breakfast cone, which, by
• 24:45
  Speaker 1: the way, it sounds like a great breakfast idea for
• 24:48
  Speaker 1: McDonald or one of these fast food chains. Breakfast cone
• 24:52
  Speaker 1: that sounds like scrambled egg flavored ice cream that does
• 24:54
  Speaker 1: not sound, or scrambled eggs on a cone. Scrambled eggs
• 25:00
  Speaker 1: on a cone. Actually, that might be a great food truck,
• 25:03
  Speaker 1: you know, that's the kind of thing you would see
• 25:04
  Speaker 1: in l a with like a huge line of hipsters,
• 25:06
  Speaker 1: you know, right, yeah, breakfast cones happen alright, So then
• 25:12
  Speaker 1: how do these light cones affect our our sense of
• 25:14
  Speaker 1: cause and effect? Well, the interesting thing about light cones
• 25:17
  Speaker 1: is that they're pretty simple if the universe is not bent, right,
• 25:20
  Speaker 1: if if space is flat, if light moves in straight
• 25:23
  Speaker 1: lines like it does out in deep space, then they're
• 25:25
  Speaker 1: just like we talked about them their triangles and two
• 25:27
  Speaker 1: dimensions or their cones and three D. But they get
• 25:30
  Speaker 1: more complicated when space bends. You know that gravity is
• 25:35
  Speaker 1: not just a force, it's also a description of the
• 25:37
  Speaker 1: way that the universe bends, that space itself bends when
• 25:41
  Speaker 1: we are near heavy objects. So the reason, for example,
• 25:44
  Speaker 1: the Earth goes around the Sun is not because there's
• 25:47
  Speaker 1: a force of gravity pulling on it, but because the
• 25:49
  Speaker 1: Sun bends space, and so the Earth is moving in
• 25:52
  Speaker 1: a path which is actually quite natural for an object
• 25:55
  Speaker 1: under no force. It's moving in a circle. And so
• 25:59
  Speaker 1: the same thing how happens to light cones. If you
• 26:02
  Speaker 1: are near something massive like a black hole or a
• 26:05
  Speaker 1: star or whatever, your light cone bends because the path
• 26:08
  Speaker 1: that light takes also bends. So the things you can
• 26:11
  Speaker 1: influence change. Now you're making me think of bugles, you know,
• 26:14
  Speaker 1: the snack, but the curved cones. I think maybe I
• 26:18
  Speaker 1: should have some breakfast before recording these podcasts. But this
• 26:21
  Speaker 1: is important for our food truck. We can't have curved
• 26:24
  Speaker 1: cones because then the eggs will all fall out, right
• 26:26
  Speaker 1: wit what this is why physicists shouldn't be cooked. But anyway,
• 26:31
  Speaker 1: it's going back to our topic. You're saying, as you know,
• 26:33
  Speaker 1: space can bend, and that can bend or light cones,
• 26:36
  Speaker 1: and that can somehow affect causing effect like you can
• 26:38
  Speaker 1: break calls in effect by bending space. It doesn't break
• 26:41
  Speaker 1: causing effect yet, it just changes what you can affect.
• 26:45
  Speaker 1: For example, say you are inside a black hole and
• 26:47
  Speaker 1: you make your breakfast. You cannot influence what people eat
• 26:51
  Speaker 1: or who gets breakfast outside of the black hole. Right,
• 26:54
  Speaker 1: this concept of a light cone inside a black hole,
• 26:57
  Speaker 1: it gets twisted. The light cone only points to towards
• 27:00
  Speaker 1: the center of the black hole. If you're near a
• 27:02
  Speaker 1: black hole, your light colne is distorted. If you send
• 27:05
  Speaker 1: out a flash of light or you know, shoot a
• 27:07
  Speaker 1: bunch of breakfasts at your friends, they don't all just
• 27:09
  Speaker 1: travel in straight paths. And so there are some people
• 27:12
  Speaker 1: who are actually near you who you cannot influence because
• 27:16
  Speaker 1: of the bending of space. The point is the bending
• 27:18
  Speaker 1: of space determines which causes line up with which effects
• 27:23
  Speaker 1: I see. So it's not that you're saying cause and
• 27:26
  Speaker 1: effect is flexible in a way. Yeah exactly. As you're
• 27:29
  Speaker 1: near some heavy mass, then which causes in which effects
• 27:31
  Speaker 1: line up depends exactly on the curvature space because it
• 27:34
  Speaker 1: depends on how information travels. You know, if you can't
• 27:38
  Speaker 1: send a light pulse to somebody, then you can't send
• 27:40
  Speaker 1: them information. Then your causes cannot influence their effects. All right,
• 27:45
  Speaker 1: So we can limit cause and effect. But I guess
• 27:47
  Speaker 1: the question is can we break it or do we
• 27:49
  Speaker 1: need it? And you're saying that things start to get
• 27:51
  Speaker 1: weird when you add quantum mechanics, Yeah, exactly. So now
• 27:54
  Speaker 1: we've done special relativity with light cones, we went to
• 27:57
  Speaker 1: general relativity by bending those light cones through space. Now
• 28:01
  Speaker 1: we're going to add in the final ingredient, which is
• 28:04
  Speaker 1: quantum mechanics. Right, say we're near this black hole, so
• 28:07
  Speaker 1: a light cone is all twisted and bent, and who
• 28:09
  Speaker 1: we can influence and talk about breakfast with depends on
• 28:13
  Speaker 1: the curvature of space. But what if the curvature of
• 28:15
  Speaker 1: space itself was uncertain? Like what if we didn't know
• 28:19
  Speaker 1: exactly where that black hole was because it was like
• 28:23
  Speaker 1: created from some quantum process, So I had a probability
• 28:26
  Speaker 1: to be here and a probability be over there, then
• 28:29
  Speaker 1: we would have like two possible light cones, which would
• 28:33
  Speaker 1: mean like two possible portions of the universe that we
• 28:36
  Speaker 1: could influence. But I wonder, do you actually need the
• 28:39
  Speaker 1: black hole to get those two possible light cones? Like,
• 28:41
  Speaker 1: you know, isn't there quantum uncertainty in everything? Right? Like
• 28:45
  Speaker 1: if I leave my house, there's maybe a fifty percent
• 28:48
  Speaker 1: chance that I took a rite in a fifty percent
• 28:50
  Speaker 1: chance I took at left, And so there's two possible
• 28:52
  Speaker 1: breakfast cones, two possible breakfast cones. Yes, the black hole
• 28:56
  Speaker 1: is just the extreme example because it's easy to think
• 28:59
  Speaker 1: about how the black hole changes the shape of your
• 29:02
  Speaker 1: light cone is very dramatic. But every time this quantum uncertainty,
• 29:05
  Speaker 1: and that uncertainty leads to uncertainty and where stuff is
• 29:09
  Speaker 1: in the universe. That means this uncertainty about the curvature
• 29:12
  Speaker 1: of space, which means this uncertainty about the causality. Right,
• 29:17
  Speaker 1: if I don't know where the black hole is or
• 29:18
  Speaker 1: where Jorhees Breakfast went, that I can't necessarily predict which
• 29:22
  Speaker 1: part of the universe I can influence. Okay, so then, um,
• 29:25
  Speaker 1: there's some uncertainty in the light cones and two possible futures.
• 29:30
  Speaker 1: So then how does that break causality? Well, you can
• 29:32
  Speaker 1: imagine some experiments, right, Like let's say, for example, we
• 29:35
  Speaker 1: have two people doing experiments, and in quantum mechanics thought experiments,
• 29:39
  Speaker 1: people always use Alice and Bob because there you know
• 29:42
  Speaker 1: A and b. Maybe we can mix it up a
• 29:44
  Speaker 1: little bit, you can think of more clever names. But
• 29:47
  Speaker 1: we have two people doing experiments somewhere out in space,
• 29:50
  Speaker 1: and their experiments depend, for example, on how close they
• 29:53
  Speaker 1: are to the Earth, right, because the Earth is going
• 29:56
  Speaker 1: to bend space and you know that for example, if
• 29:59
  Speaker 1: you are near the Earth, then your time slows down
• 30:02
  Speaker 1: because gravitational time dilation makes clocks run slower like Clocks
• 30:06
  Speaker 1: closer to the Earth run more slowly than clocks further
• 30:09
  Speaker 1: from the Earth. So now we have these two experimenters.
• 30:12
  Speaker 1: They're out in space. One of them is closer to
• 30:15
  Speaker 1: the Earth than the other one, right, but if the
• 30:18
  Speaker 1: Earth's location is uncertain, we don't know which one it is.
• 30:21
  Speaker 1: So now one of them has had their time slowed
• 30:24
  Speaker 1: down more than the other one. So one of them
• 30:26
  Speaker 1: can influence the other because their time has been slowed down. So,
• 30:30
  Speaker 1: for example, if Alice has had her time slowed more,
• 30:33
  Speaker 1: then she hasn't gotten as far in her experiment, and
• 30:36
  Speaker 1: Bob can send her a message influencing her experiment. But
• 30:39
  Speaker 1: if Bob has had his time slowed down more, then
• 30:42
  Speaker 1: Alice can influence his experiment. So we don't know necessarily
• 30:46
  Speaker 1: which way causality goes from Alice to Bob or from
• 30:49
  Speaker 1: Bob to Alice, because we don't know where Earth is,
• 30:53
  Speaker 1: and that determines where these light cones flow. Okay, well, um,
• 30:57
  Speaker 1: first of all, I'm a little worried we can't find Earth.
• 31:00
  Speaker 1: It's a little concerning. I think you're saying, like the
• 31:03
  Speaker 1: Alice and Bob are doing the same experiment right, Like
• 31:05
  Speaker 1: you're trying to figure out whats inside of a box
• 31:08
  Speaker 1: and they have maybe the same box, and you're saying
• 31:10
  Speaker 1: that if one of them is moving at a different
• 31:12
  Speaker 1: time rate than like, if one of them has time
• 31:15
  Speaker 1: moving faster for them, they could finish the experiment and
• 31:18
  Speaker 1: then run over until the other one what's in the
• 31:20
  Speaker 1: box exactly? Or maybe they're like trying to unlock somebody's
• 31:23
  Speaker 1: phone and they're trying to guess codes or something. And
• 31:26
  Speaker 1: if Alice's time runs more slowly, then Bob can try
• 31:30
  Speaker 1: a bunch of codes, and if he finds one, he
• 31:32
  Speaker 1: can send Alice a message saying, oh, try this one,
• 31:35
  Speaker 1: or don't try these, I already try them. That's if
• 31:37
  Speaker 1: Alice's time is running more slowly. If it's the opposite,
• 31:41
  Speaker 1: like the Earth happens to be in another situation where
• 31:43
  Speaker 1: it slows down Bob's time, then Alice can finish her
• 31:46
  Speaker 1: experiment first. So who finishes the experiment first and who
• 31:50
  Speaker 1: can send a message to the other one about their
• 31:52
  Speaker 1: results depends on who is closer to the gravitational object
• 31:56
  Speaker 1: that's slowing down time. And you know it sounds weird
• 31:59
  Speaker 1: to say, like, well, how do we not know where
• 32:00
  Speaker 1: the Earth is? It's a crazy thought experiment where we've
• 32:03
  Speaker 1: like put the Earth in some sort of crazy quantum
• 32:05
  Speaker 1: mechanical superpositions, so we don't know where it is. That's
• 32:08
  Speaker 1: pretty hard to imagine. But this is what we do
• 32:10
  Speaker 1: when we try to understand like the extremes of the universe.
• 32:13
  Speaker 1: We come up with these crazy experiments to understand whether
• 32:16
  Speaker 1: the rules are broken in extreme situations. I wonder if
• 32:19
  Speaker 1: you can simplify by just talking about like short Dinger's box, right,
• 32:23
  Speaker 1: Like you're saying, let's put the Earth, Alice and Bob
• 32:25
  Speaker 1: inside of a box, and we sort of don't know
• 32:27
  Speaker 1: where the Earth is, and so from us sitting outside
• 32:30
  Speaker 1: of the box, we don't know who told who about
• 32:33
  Speaker 1: the results of their experiment. It sounds like Shortingers prisoners dilemma,
• 32:38
  Speaker 1: sounds catastrophic exactly. So we don't know then what has
• 32:43
  Speaker 1: happened inside the box. Was it Alice and then Bob,
• 32:46
  Speaker 1: or was it Bob and then Alice? And so in
• 32:48
  Speaker 1: this situation, because the position of the light cones is uncertain,
• 32:53
  Speaker 1: causality is uncertain, and so in this kind of experiment,
• 32:57
  Speaker 1: it's like, well, which happened Was it A before B
• 33:00
  Speaker 1: or B before A. So now causality has become uncertain.
• 33:04
  Speaker 1: Remember the very beginning, we define causality saying, well, if
• 33:07
  Speaker 1: A can influence B, you know A causees B. That
• 33:10
  Speaker 1: that means it's impossible for B to cause A. So
• 33:13
  Speaker 1: in this experiment, like we have two events and we
• 33:16
  Speaker 1: can't say which one happened first, and they do influence
• 33:19
  Speaker 1: each other. One is definitely inside the light cone of
• 33:21
  Speaker 1: the other. We just don't know which, right, And and
• 33:24
  Speaker 1: that's just sort of isn't that sort of regular quantum mechanics,
• 33:27
  Speaker 1: Like we don't really know whether the cat is alive
• 33:30
  Speaker 1: or dead anyways, right, that's right, we don't know quantum
• 33:32
  Speaker 1: mechanics whether the cat is are live or dead. But
• 33:34
  Speaker 1: we've added in another element here, which is causality, because
• 33:38
  Speaker 1: now quantum mechanics is influencing the very shape of space,
• 33:41
  Speaker 1: which determines which events can happen in what order. In
• 33:45
  Speaker 1: this classical shortingers box example, you know, the causality is clear,
• 33:49
  Speaker 1: like you know, the radioactive element decays and either kills
• 33:52
  Speaker 1: the cat or it does not. The order of events
• 33:55
  Speaker 1: is clear, even though which events happens is not right,
• 33:58
  Speaker 1: it's not like the cat can scape and then rebuild
• 34:01
  Speaker 1: the box or something. You can't have anything going backwards
• 34:04
  Speaker 1: in that experiment. Here, we might have things happening in
• 34:07
  Speaker 1: an indefinite order because we've made the shape of space
• 34:10
  Speaker 1: itself uncertain, and it's that shape of space that determines
• 34:14
  Speaker 1: what can influence what because it controls the shape of
• 34:17
  Speaker 1: the light cone. All right, So then the causality of
• 34:20
  Speaker 1: what happened inside the box is uncertain. There's a quantum
• 34:23
  Speaker 1: uncertainty about it. But does that really mean that causality
• 34:27
  Speaker 1: broke or it's it's not needed or it's false, do
• 34:31
  Speaker 1: you know what I mean? Like, it's just it's just
• 34:33
  Speaker 1: that we don't know, right, How does that sort of
• 34:35
  Speaker 1: break things about the universe. Yeah, well, it means that
• 34:38
  Speaker 1: maybe causality is not always needed. You know, it seems
• 34:41
  Speaker 1: like it's the kind of thing that happens a lot
• 34:43
  Speaker 1: most of the time. In most circumstances, you don't get
• 34:47
  Speaker 1: huge uncertain bending of space that makes causality uncertain. So
• 34:51
  Speaker 1: causality is probably like a very effective principle. But you know,
• 34:54
  Speaker 1: we want to understand the deep nature of the universe,
• 34:57
  Speaker 1: not just like hey, this mostly works. Let's move on.
• 35:00
  Speaker 1: We want to understand how things actually work. And right
• 35:03
  Speaker 1: now we have these two really key ideas about the
• 35:06
  Speaker 1: way the universe works, quantum mechanics, which tells us things
• 35:09
  Speaker 1: are fundamentally uncertain, and general relativity, which tells us how
• 35:13
  Speaker 1: space bends around mass. And we'd like to emerge those two.
• 35:17
  Speaker 1: We would like to have a theory of quantum gravity
• 35:19
  Speaker 1: that tells us, you know, how quantum mechanics and gravity
• 35:21
  Speaker 1: play well together. Well, this suggests that, you know, we
• 35:24
  Speaker 1: might have to give up causality if we want to
• 35:27
  Speaker 1: emerge them. That if we want to bring quantum mechanics
• 35:29
  Speaker 1: and general relativity together, then these two concepts might not
• 35:32
  Speaker 1: play well together. You know, they seem to create these
• 35:35
  Speaker 1: situations with uncertain causality. And so maybe the key to
• 35:39
  Speaker 1: finding a theory of quantum gravity and revealing the deep
• 35:41
  Speaker 1: nature of the universe is to give up on causality.
• 35:44
  Speaker 1: To say, it happens a lot, it's convenient, it's nice,
• 35:48
  Speaker 1: but it's not actually always required. I guess maybe it's
• 35:51
  Speaker 1: hard to see sort of the stakes here with Bob
• 35:53
  Speaker 1: and ell is because you know, like whether one of
• 35:56
  Speaker 1: them tells the other first or the second, maybe it doesn't,
• 36:00
  Speaker 1: you know, sort of affect my reality that much. But
• 36:03
  Speaker 1: can you think of an example of where like this
• 36:05
  Speaker 1: uncertainty in causality would sort of have more, I don't know,
• 36:09
  Speaker 1: sort of like deeper repercussions. You know. I think that
• 36:12
  Speaker 1: physicists are still struggling to get their minds around the
• 36:15
  Speaker 1: consequences here. And we'll talk in a minute about like
• 36:18
  Speaker 1: experiments people are doing to try to use this. We're
• 36:20
  Speaker 1: developing ideas for like how to improve computation or you know,
• 36:25
  Speaker 1: make information transmission actually more efficient, or change the very
• 36:30
  Speaker 1: nature of thermodynamics. But it's something that's so basic and
• 36:33
  Speaker 1: fundamental to our thinking that we're having trouble even like
• 36:36
  Speaker 1: contemplating what physics would look like without causality, and so
• 36:40
  Speaker 1: it's hard to get your mind around like how that
• 36:42
  Speaker 1: would actually influence the universe. All right, Well, I think
• 36:45
  Speaker 1: basically what you're saying though, is that you know, there
• 36:47
  Speaker 1: are situations where quantum mechanics can throw uncertainty about the
• 36:53
  Speaker 1: order of things, right, Like there can be situations where
• 36:55
  Speaker 1: we don't know if A came before B or B
• 36:57
  Speaker 1: came before A. And so because there our situations where
• 37:01
  Speaker 1: we don't know. Maybe the question is do we actually
• 37:04
  Speaker 1: need it? Right? That's I think that's what you're getting at.
• 37:06
  Speaker 1: It's like, maybe since it's not something that has to
• 37:09
  Speaker 1: be known, maybe it's something we don't even need in
• 37:11
  Speaker 1: the universe. Yeah, and maybe it's not something the universe demands,
• 37:15
  Speaker 1: you know, the same way when you have quantum entanglement.
• 37:18
  Speaker 1: You might have like two particles that are far away
• 37:21
  Speaker 1: in uncertain states about you know, what direction their spin is,
• 37:25
  Speaker 1: and we like to think, oh man, but there has
• 37:27
  Speaker 1: to be a real truth there. It has to either
• 37:29
  Speaker 1: be this or that. You know, there has to be
• 37:31
  Speaker 1: some deep hidden knowledge. And we discovered actually the universe
• 37:34
  Speaker 1: doesn't care the universes happen to have that be uncertain,
• 37:37
  Speaker 1: the true nature of these particles. And now we're taking
• 37:40
  Speaker 1: that a step further and saying, look, maybe the universe
• 37:42
  Speaker 1: doesn't really care always whether A happen before B or
• 37:45
  Speaker 1: B happened before A. Maybe it's happy to have that
• 37:48
  Speaker 1: be uncertain, for it to be undetermined, which is pretty
• 37:51
  Speaker 1: hard for us to consider. All Right, Well, maybe we
• 37:54
  Speaker 1: don't need causality, but we definitely need to pay for
• 37:57
  Speaker 1: this podcast. So that's the one cost and of we
• 38:00
  Speaker 1: can't ignore. So let's talk about how you might test
• 38:03
  Speaker 1: whether or not this theory is right, or whether or
• 38:06
  Speaker 1: not you actually do need castality in the universe. But
• 38:09
  Speaker 1: first let's take a quick break. All right, So, Daniel,
• 38:24
  Speaker 1: apparently maybe the universe doesn't need causality, you know, or
• 38:27
  Speaker 1: maybe I think what you're saying is that maybe the
• 38:28
  Speaker 1: universe doesn't really care that much about castality, Like it
• 38:31
  Speaker 1: could go either way. Exactly. It's like effect before cause,
• 38:35
  Speaker 1: caused before effect, whatever. As long as I got my
• 38:38
  Speaker 1: breakfast cone, I'm fine, you know, whatever, as long as
• 38:41
  Speaker 1: I got taken in my scrambled cone. Yeah, and again,
• 38:45
  Speaker 1: let me just reiterate. This doesn't mean that anything goes
• 38:48
  Speaker 1: that you should just like go out there and steal
• 38:51
  Speaker 1: jewelry and whatever. There are no consequences for your actions, right,
• 38:54
  Speaker 1: You're still going to prison if you steal money from
• 38:56
  Speaker 1: your local grocery store. It just means that sometimes in
• 38:59
  Speaker 1: scenarios are there are two possible orders for events, the
• 39:02
  Speaker 1: universe might not pick between them, right. Yeah, it might
• 39:06
  Speaker 1: leave things undecided and go about its happy way. Yeah, exactly.
• 39:11
  Speaker 1: Physicists called this indefinite causality, so not like a complete
• 39:15
  Speaker 1: overthrow of causality, but like an important weakening, you know,
• 39:19
  Speaker 1: to say like, oh, these are cracking causality. There are
• 39:21
  Speaker 1: cases when you don't have to know what happens first.
• 39:25
  Speaker 1: What if you just call it causality is diet causality?
• 39:30
  Speaker 1: There you go, all right, so that's a possibility. And
• 39:33
  Speaker 1: it seems like the universe, you know, it's kind of
• 39:35
  Speaker 1: fuzzy about causality, And so are there experiments to sort
• 39:38
  Speaker 1: of test this or to figure out what the right
• 39:40
  Speaker 1: answer is in physics, Yeah, there are some really cool experiments.
• 39:44
  Speaker 1: People came up with these ideas in the two thousands
• 39:46
  Speaker 1: and sort of playing with them. Is as they were
• 39:48
  Speaker 1: trying to stitch together quantum mechanics and general relativity to
• 39:52
  Speaker 1: think about quantum gravity, and realized maybe this is the
• 39:55
  Speaker 1: stumbling block, Maybe this is the piece we need to
• 39:57
  Speaker 1: get rid of so that everything else clicks together nicely,
• 40:00
  Speaker 1: And so they tried to make some experiments. Then you know,
• 40:03
  Speaker 1: it's hard to have black holes or to put the
• 40:06
  Speaker 1: Earth in a quantum superposition, so they came up with
• 40:08
  Speaker 1: a totally different set of experiments. And it's mostly folks
• 40:11
  Speaker 1: who are working on things like quantum information. Whether you know,
• 40:14
  Speaker 1: they are like splitting photon beams and polarizing them and
• 40:18
  Speaker 1: capturing the information in them and not in them, and
• 40:20
  Speaker 1: this kind of stuff. They were able to do experiments
• 40:22
  Speaker 1: that probe this kind of thing. All right, So then
• 40:25
  Speaker 1: how does the experiment work? What's going on? Yeah, So
• 40:27
  Speaker 1: what you do is you take a beam of photons.
• 40:29
  Speaker 1: These are just you know, like it's a laser beam essentially,
• 40:32
  Speaker 1: and you have these particles flying out and then you
• 40:34
  Speaker 1: split them use this one of these beams splitters, so
• 40:37
  Speaker 1: like half the photons go one way and half the
• 40:39
  Speaker 1: photons go the other way. And then you send the
• 40:42
  Speaker 1: photons through two different paths. Along one path you do
• 40:46
  Speaker 1: A to the photons and then B. And then along
• 40:48
  Speaker 1: the other path you do B. And then you do A.
• 40:51
  Speaker 1: What does that mean to do A or do B.
• 40:53
  Speaker 1: It's like you perform some operation you change the photons
• 40:56
  Speaker 1: a little bit. In this case, what they did is
• 40:58
  Speaker 1: they polarize the photo potons. Photons are more than just
• 41:01
  Speaker 1: like packs of light. They have like little spins to them.
• 41:04
  Speaker 1: You can change the way those spins are pointed, and
• 41:07
  Speaker 1: so along one path they like flip the spins one
• 41:10
  Speaker 1: way and then another way. Along the other path. They
• 41:12
  Speaker 1: do it in the opposite order, right, they sort of
• 41:15
  Speaker 1: run it through some filters, right, yeah, exactly. You can
• 41:17
  Speaker 1: think about it like that, running it through some filters.
• 41:19
  Speaker 1: And the key thing is that the order matters, Like
• 41:22
  Speaker 1: the photons look different if you do A and then
• 41:25
  Speaker 1: B versus B and then A, and you know this
• 41:28
  Speaker 1: could happen because sometimes these are things are conceptually the
• 41:31
  Speaker 1: same as like rotations, where you know it matters what
• 41:34
  Speaker 1: order you do them. It's like if you turn around
• 41:37
  Speaker 1: and then you turn left, it's different than if you
• 41:39
  Speaker 1: turn left and then turn around. All right, So then
• 41:41
  Speaker 1: I have a laser beam. I split it and in
• 41:44
  Speaker 1: one half of it I do A and B and
• 41:46
  Speaker 1: the other side I do B and then A, And
• 41:48
  Speaker 1: then what I compare them to see if they if
• 41:51
  Speaker 1: something different happen, And then you bring them back together, right,
• 41:55
  Speaker 1: you rejoin them, and now you have photons and you
• 41:57
  Speaker 1: don't know which path they took. Do they do the
• 42:00
  Speaker 1: A B path or the B A path? And what
• 42:02
  Speaker 1: you see when it comes out is a really interesting
• 42:05
  Speaker 1: interference pattern between photons that went through A B and
• 42:09
  Speaker 1: then photons that went through B A And just like
• 42:11
  Speaker 1: in sort of the double slit experiment where particles could
• 42:14
  Speaker 1: have gone through one slit or the other, and the
• 42:16
  Speaker 1: probability to have gone through one or the other interferes
• 42:20
  Speaker 1: with the first ones. Then you get these interference patterns.
• 42:23
  Speaker 1: So this interference patterns means that you really do have
• 42:25
  Speaker 1: photons from both in your beam, and that for any
• 42:29
  Speaker 1: given photon, you don't know whether it went through A
• 42:31
  Speaker 1: B or whether it went through B A. So what
• 42:33
  Speaker 1: you're seeing is this interference pattern between the probabilities, which
• 42:38
  Speaker 1: means that both possibilities exist for any given photon. Each
• 42:41
  Speaker 1: photon has a possibility to have gone through one side
• 42:44
  Speaker 1: or the other. Oh, I see, it's like you take
• 42:47
  Speaker 1: those two beams and then you join them again, and
• 42:49
  Speaker 1: then you look the photons that come out, and when
• 42:51
  Speaker 1: you get a photon out of that joint beam, you
• 42:54
  Speaker 1: don't know whether it went through A B or B A,
• 42:57
  Speaker 1: but it's sort of it looks like it went through
• 43:00
  Speaker 1: both at the same time, sort of like the cat
• 43:02
  Speaker 1: alive and death exactly. And so here these photons have
• 43:06
  Speaker 1: had an experience that has indefinite causality. Right, we don't
• 43:10
  Speaker 1: know what the order of events was for these photons,
• 43:14
  Speaker 1: and it matters, right, A B has different photons than
• 43:17
  Speaker 1: BE at an individual photon, there's a probability of one
• 43:21
  Speaker 1: or probability of the other, and that leads to this
• 43:24
  Speaker 1: really interesting interference pattern. So you can see that this
• 43:27
  Speaker 1: is actually happening. It's not like you have just two
• 43:29
  Speaker 1: different groups of photons, ones that are A B and
• 43:32
  Speaker 1: ones that are B A. Every photon now has a
• 43:34
  Speaker 1: probability of having one order or the other. Right, But
• 43:38
  Speaker 1: I guess you know it's looking at this skeptically. It's
• 43:41
  Speaker 1: not like you did the same thing A and B
• 43:43
  Speaker 1: in different orders, but they went through different filters kind
• 43:46
  Speaker 1: of right, They took a different path through space. So
• 43:49
  Speaker 1: it's sort of not like I'm not really changing the
• 43:52
  Speaker 1: order of events. I'm changing the path, that's right. But
• 43:54
  Speaker 1: in this case, the path determines the order of events.
• 43:56
  Speaker 1: And you're right, it's not exactly analogous to what we're
• 43:59
  Speaker 1: talking about before with light cones and the bending of space.
• 44:02
  Speaker 1: It's a different way to try to construct indefinite causality,
• 44:05
  Speaker 1: right there, not exactly physically the same filters, right, it's
• 44:09
  Speaker 1: sort of like a standing for having done the same
• 44:12
  Speaker 1: thing in a different order. Yes, exactly, because you can't
• 44:15
  Speaker 1: do that. You can't like reverse time and do the
• 44:17
  Speaker 1: experiment again in the other order and then rejoin it.
• 44:20
  Speaker 1: That would be super awesome if you could do that,
• 44:22
  Speaker 1: but here we separate them in space instead. That would
• 44:25
  Speaker 1: be a dessert cone for sure. But I think what
• 44:28
  Speaker 1: you're saying is that they did this this experiment and
• 44:30
  Speaker 1: it confirmed that. You know, it's sort of like you
• 44:32
  Speaker 1: can have two different orders at the same time happening
• 44:36
  Speaker 1: quantum mechanically exactly. And what they do are really cool
• 44:38
  Speaker 1: things with correlations. It's just like with bells inequality. You know,
• 44:42
  Speaker 1: the example of having two quantum entangled particles, where you
• 44:45
  Speaker 1: know if one is spin up, the other one has
• 44:47
  Speaker 1: to be spinned down. And to prove that they're not
• 44:50
  Speaker 1: determined until you open one box, even if they're really
• 44:53
  Speaker 1: far apart, you have to do these really subtle experiments
• 44:56
  Speaker 1: called probing bells inequality that showed that you can get
• 44:59
  Speaker 1: like or relations between the two boxes that you can't
• 45:02
  Speaker 1: have otherwise. In the same way they do that. Here,
• 45:05
  Speaker 1: they like change what A and B are, they rotate them,
• 45:08
  Speaker 1: and they get these correlations between one side and the
• 45:10
  Speaker 1: other that you can't have if causality was definite. So
• 45:14
  Speaker 1: you have to have indefinite causality to see the specific
• 45:17
  Speaker 1: results of these experiments. The patterns, the numbers that they
• 45:20
  Speaker 1: get out cannot be reproduced if causality is definitely If
• 45:24
  Speaker 1: every photon actually went to one side or the other
• 45:27
  Speaker 1: and then merges, that does not explain the results of
• 45:29
  Speaker 1: the experiment. It has to be indefinite to get the
• 45:32
  Speaker 1: interference patterns and the correlations that they see, right, all right,
• 45:36
  Speaker 1: So then it's sort of confirms that the universe is
• 45:39
  Speaker 1: CAUSALI ish and definitely causal. So then what does that
• 45:45
  Speaker 1: mean for us? Like, does that mean that we can
• 45:47
  Speaker 1: now break the rules and then to do cool things
• 45:52
  Speaker 1: or does it mean that, you know, it's just another
• 45:54
  Speaker 1: sort of step in our sort of befuddlement with quantum mechanics.
• 45:58
  Speaker 1: Is there some rule in particular your hope to get
• 46:00
  Speaker 1: to break looking for permission? Yeah, you know, I want
• 46:03
  Speaker 1: to eat the breakfast coding and not gain weight, reverse
• 46:06
  Speaker 1: cause and effect. They're exactly, or you can eat breakfast
• 46:10
  Speaker 1: any time of day. No, there are some potential applications
• 46:13
  Speaker 1: to this. You know, any time you gain some new
• 46:15
  Speaker 1: insight to the way the universe works, you can come
• 46:18
  Speaker 1: up with some ways to take advantage of that insight
• 46:21
  Speaker 1: to do something you couldn't do before. And so people
• 46:23
  Speaker 1: are thinking carefully about what this means, and there's some
• 46:25
  Speaker 1: cool things that you can do, like you can send
• 46:28
  Speaker 1: more information over noisy channels by using indefinite causality to
• 46:32
  Speaker 1: encode some of that extra information, or people have come
• 46:35
  Speaker 1: up with like weird quantum computers where two halves the
• 46:38
  Speaker 1: computer are not linked by causality, and so they can
• 46:41
  Speaker 1: both do their calculation before the other one and send
• 46:45
  Speaker 1: the results to the other one, and so you can
• 46:47
  Speaker 1: sort of like skip steps there and sort of like
• 46:50
  Speaker 1: cheat in time, which is pretty cool. So there's some
• 46:52
  Speaker 1: ways people are thinking about using this. For me, it's
• 46:55
  Speaker 1: not about the applications, it's about making progress to this
• 46:58
  Speaker 1: ultimate theory. You know, we want a deep picture of
• 47:01
  Speaker 1: the universe, and we want to understand how the bending
• 47:04
  Speaker 1: of space is consistent with quantum mechanics and all this
• 47:07
  Speaker 1: crazy stuff. And so it might just be that this
• 47:10
  Speaker 1: very way we think about the universe, causality isn't always required.
• 47:14
  Speaker 1: It's like it usually happens. It's most of the time
• 47:16
  Speaker 1: a good way to describe things, but not something that
• 47:19
  Speaker 1: you have to have at the basic core in all
• 47:22
  Speaker 1: the deep equations, and so that would you think maybe
• 47:25
  Speaker 1: give us some insight into merging these two theories together
• 47:28
  Speaker 1: quantum mechanics and general relativity. Yeah, exactly. This is a
• 47:32
  Speaker 1: stumbling block, right, as we talked about before. If you
• 47:35
  Speaker 1: have general relativity, which bend space, and you have quantum mechanics,
• 47:38
  Speaker 1: which makes that bending uncertain, then causality is no longer clear.
• 47:43
  Speaker 1: And that's been a problem for quantum gravity. So maybe
• 47:46
  Speaker 1: the answer is like, well, just act like it's not
• 47:48
  Speaker 1: a problem. Maybe it's actually okay, you know, maybe this
• 47:51
  Speaker 1: wasn't a wall in our progress. We just need to
• 47:53
  Speaker 1: so like not worry about it so much. Yeah, that's
• 47:56
  Speaker 1: my favorite way to deal with problems, Daniel, Just tocore them.
• 48:00
  Speaker 1: Just don't look at the scale when you weigh yourself,
• 48:02
  Speaker 1: and then you don't have to worry about causing it. Well,
• 48:04
  Speaker 1: it is an important lesson and the way we think
• 48:06
  Speaker 1: about things, you know, we put up mental barriers. Sometimes
• 48:09
  Speaker 1: we imagine like, oh, well that's impossible, they can't be
• 48:12
  Speaker 1: and then later people come along and they're like, well,
• 48:14
  Speaker 1: actually why not, or you know, why are we following?
• 48:17
  Speaker 1: This rule? Is there's really actually important. And then they
• 48:20
  Speaker 1: discovered this is a whole rich area of exploration, you know,
• 48:24
  Speaker 1: think about like imaginary numbers. People for a long time thought, well,
• 48:27
  Speaker 1: that's ridiculous, it's nonsense, but it turns out to be
• 48:29
  Speaker 1: really important branch of mathematics for understanding the way the
• 48:32
  Speaker 1: universe works. And so sometimes you've got to like knock
• 48:36
  Speaker 1: on these mental walls and discover that there's actually lots
• 48:39
  Speaker 1: of interesting territory on the other side. Yeah, I think
• 48:41
  Speaker 1: that should be your new slogan for physics. You know,
• 48:44
  Speaker 1: physics colon. Why not? You know, Nike has just do it?
• 48:48
  Speaker 1: You should have Why not haven't destroyed the universe yet?
• 48:52
  Speaker 1: Why not put scrambled eggs in that cone? Seriously, that's
• 48:55
  Speaker 1: a great idea. All right, Well, we hope you enjoyed that,
• 48:58
  Speaker 1: and you know, got you to think a little bit
• 49:00
  Speaker 1: about what we think is certain in this universe. Maybe
• 49:03
  Speaker 1: things are not as certain as we think they are,
• 49:04
  Speaker 1: even the basic logic of how and when things happen.
• 49:09
  Speaker 1: And that goes to show you that there are still
• 49:11
  Speaker 1: really deep end basic questions out there that people are
• 49:14
  Speaker 1: struggling with about the nature of the universe. And maybe
• 49:18
  Speaker 1: what we're missing is one really cool flash of insight.
• 49:21
  Speaker 1: And maybe you will have that flash of insight and
• 49:24
  Speaker 1: revolutionize the way everybody thinks about the universe. Why not, Well,
• 49:28
  Speaker 1: we hope you enjoyed that. Thanks for joining us, see
• 49:31
  Speaker 1: you next time. Thanks for listening, and remember that Daniel
• 49:41
  Speaker 1: and Jorge explained the universe is a production of I
• 49:44
  Speaker 1: Heart Radio or more podcast from my heart Radio, visit
• 49:47
  Speaker 1: the I heart Radio app, Apple Podcasts, or wherever you
• 49:51
  Speaker 1: listen to your favorite shows. Yeah,