Latest / Daniel and Kelly’s Extraordinary Universe / Could a grand unified theory of physics be impossible?

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Could a grand unified theory of physics be impossible? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: The long arc of physics bends towards what exactly. Over
0:13
Speaker 1: the centuries, we have developed theories to explain the universe,
0:16
Speaker 1: and then seeing them overturned replaced by something new. Einstein's
0:20
Speaker 1: gravity replaces Newton, quantum mechanics up ends a deterministic universe.
0:25
Speaker 1: It feels like progress, but is it. We imagine that
0:28
Speaker 1: there is a single, beautiful, simpol set of laws that
0:31
Speaker 1: control how the universe works, and that with each new
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Speaker 1: idea we are getting closer to the deep truth. But
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Speaker 1: what if there is no single deep truth? Then what
0:42
Speaker 1: is it that we are learning anyway? I'm Daniel, I'm
1:01
Speaker 1: a particle physicist and a professor at UC Irvine, and
1:04
Speaker 1: I'm spending my life chasing the truth of the universe.
1:08
Speaker 1: And Welcome to the podcast Daniel and Jorge Explain the Universe,
1:11
Speaker 1: a production of I Heart Radio in which we don't
1:14
Speaker 1: shy away from trying to discover the truth of the universe,
1:17
Speaker 1: as blindingly bright as it may be. We bring you
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Speaker 1: as close as possible to our current understanding of what's
1:24
Speaker 1: out there in the universe, from particles two galaxies, what
1:28
Speaker 1: we do and do not understand. My friend and co
1:31
Speaker 1: host Jorge is on a break, so I've invited a
1:34
Speaker 1: guest to chat with us today about this journey to
1:36
Speaker 1: understand the universe. I personally see our cosmos as if
1:40
Speaker 1: it was a giant detective novel. We gather clues and
1:43
Speaker 1: try to figure out what is going on. What story
1:46
Speaker 1: out there explains everything that we see. As we collect
1:50
Speaker 1: more information, we can rule out ideas that we had initially.
1:53
Speaker 1: Sometimes we get a clue that provides a huge plot twist.
1:57
Speaker 1: What the universe is fundamentally random? What gravity isn't the
2:01
Speaker 1: force after all? Mind blown? Those are my favorite moments
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Speaker 1: in science because they make me feel like we are
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Speaker 1: taking steps towards the truth, like we're on a road
2:12
Speaker 1: towards figuring out what the story of the universe is.
2:16
Speaker 1: Because any good detective novel has to be just one
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Speaker 1: simple requirement. It absolutely positively, without any deviation, has to
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Speaker 1: follow its own rules. No cheating, no magic, no sudden
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Speaker 1: changing of the rules to reveal the murderer. If the
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Speaker 1: reader is going to have a fair chance that puzzling
2:36
Speaker 1: out the answer, then the clues have to make sense.
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Speaker 1: They have to be real hints about the actual underlying story.
2:44
Speaker 1: There has to be a coherent story, one that's self consistent,
2:47
Speaker 1: and we expect that to be true about the universe
2:50
Speaker 1: as well. Most of us who are not philosophers or
2:53
Speaker 1: super skeptics, think that the universe is real, that it's
2:57
Speaker 1: out there, that it's following some set of laws, and
3:01
Speaker 1: that by paying attention we could figure out what those
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Speaker 1: laws are. We feel like we're chipping away at it
3:06
Speaker 1: from different angles chemistry, biology, physics, but in the end
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Speaker 1: we're all working towards revealing a single, larger truth. We're
3:14
Speaker 1: each turning on our own lampposts and shining light on
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Speaker 1: what's under them, with the idea that more light means
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Speaker 1: a better view and that eventually we will be able
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Speaker 1: to see the whole picture. But how do we know
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Speaker 1: that's true. Is it possible that there isn't a single
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Speaker 1: coherent story of the universe, that laws in different contexts
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Speaker 1: and different situations could be incompatible with each other, That
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Speaker 1: each field of science might be its own separate patch,
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Speaker 1: not part of a larger quills. So today on the podcast,
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Speaker 1: we'll be asking the question, could a grand unified theory
3:55
Speaker 1: of physics be impossible? To help me tackle this grand
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Speaker 1: as dopequest? I've invited a philosopher of physics who spends
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Speaker 1: all of her days thinking about this particular question. So
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Speaker 1: it's my pleasure to welcome to the podcast, Dr Katie Robertson.
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Speaker 1: Katie has degrees in physics and philosophy, including a PhD
4:14
Speaker 1: in philosophy from Cambridge. She's now a fellow at the
4:17
Speaker 1: University of Birmingham, where she thinks about how the microscopic
4:20
Speaker 1: laws of physics weave themselves together to form the world
4:23
Speaker 1: we experience, from thermodynamics to the arrow of time and
4:26
Speaker 1: black holes. Katie, Welcome to the podcast, and thank you
4:29
Speaker 1: very much for joining us. Thank you so much for
4:32
Speaker 1: having me. So let's get started by getting to know
4:34
Speaker 1: you and your interests a little bit. Obviously, black holes
4:37
Speaker 1: and the deep mysteries of physics are fascinating, but I'm
4:39
Speaker 1: sure there were many directions open to you, from experimental
4:42
Speaker 1: physics to theoretical all the way to philosophy. What made
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Speaker 1: you choose this path? Why do philosophy rather than theoretical
4:49
Speaker 1: physics or experimental physics? Um well, I think I was
4:52
Speaker 1: always interested in the conceptual questions in physics. Ravans are
4:55
Speaker 1: getting really confused in high school physics and asking my
4:58
Speaker 1: teacher like of what isn't then electron Who's like, well,
5:01
Speaker 1: that's kind of a philosophical question. And so then having
5:06
Speaker 1: studied physics and philosophy together, it was kind of like
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Speaker 1: the philosophy of physics, which was the thing that really
5:11
Speaker 1: kind of grabbed me. And I was really bad at experiments.
5:14
Speaker 1: I managed in my first year labs to get the
5:18
Speaker 1: gravitational constant to be a thousand, So I think that
5:21
Speaker 1: was never going to be an avenue for me. Unfortunately,
5:24
Speaker 1: what's for the orders of magnitude between friends? Anyways? So
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Speaker 1: do you take that's a philosophical question to be an
5:32
Speaker 1: encouragement or like a discouragement from the physicist? That might
5:36
Speaker 1: seem like, you know, that's not really territory we want
5:38
Speaker 1: you to be asking, But it sounds like you took
5:40
Speaker 1: it as like, yeah, go dig deeper into that. I
5:42
Speaker 1: guess the sociological thing, isn't it whether you think it's
5:45
Speaker 1: a good question or not. I mean, I guess in
5:47
Speaker 1: some ways it's not an encouraging thing. Like if you
5:50
Speaker 1: think something is purely philosophical, you might think that means
5:53
Speaker 1: that it's out of the reach of empirical support, and
5:57
Speaker 1: that's normally seen as a bad thing, right. The key
6:00
Speaker 1: feature of sciences that we can do experiments and get
6:02
Speaker 1: evidence in that way. But I think there's kind of
6:04
Speaker 1: like a continuum between the two, between physics and philosophy,
6:07
Speaker 1: and often in the history of physics, lots of physicists
6:10
Speaker 1: have had certain like philosophical convictions that have led them
6:14
Speaker 1: to their results. So I think it's quite interesting seeing
6:16
Speaker 1: how the two kind of mixed together, So, you know,
6:19
Speaker 1: I I find it quite interesting. But yeah, so some
6:21
Speaker 1: might find it discouraging to find out it's it's a
6:23
Speaker 1: philosophical question. I think that a lot of the questions
6:27
Speaker 1: we do in physics are philosophical, and a lot of
6:29
Speaker 1: physicists have strong philosophical positions, which is usually I don't
6:34
Speaker 1: do philosophy, which is actually, of course a strong philosophical position, right, Yeah,
6:39
Speaker 1: I mean something like Ironstein, right, with his worries about
6:42
Speaker 1: quantum mechanics, were really driven by like philosophical views of
6:46
Speaker 1: what the world should be like. So yeah, I guess
6:48
Speaker 1: it's one of those things. You know, you've got philosophical views,
6:50
Speaker 1: it's just whether you've explicitly stated them and come to
6:54
Speaker 1: terms with them. Or whether they're kind of hiding buried
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Speaker 1: in new somewhere. So, then, of all the questions in
7:00
Speaker 1: physics and philosophy, what's the one that keeps you up
7:03
Speaker 1: at night? I'm often describing science to our listeners is
7:06
Speaker 1: like just a bunch of people who are curious about
7:08
Speaker 1: the world. Everybody's chosen their one question to devote their
7:12
Speaker 1: life too. So what's the question you would ask like
7:14
Speaker 1: the oracle or super advanced aliens if you had the opportunity.
7:19
Speaker 1: So one question that I have the maybe it's like
7:23
Speaker 1: one of those sort of questions that doesn't have a
7:25
Speaker 1: clear empirical answer that maybe the aliens wouldn't be any
7:28
Speaker 1: better off with. But one question I find really interesting
7:30
Speaker 1: is this question about what the relationship is between like
7:33
Speaker 1: what our theories tell us the world is like and
7:35
Speaker 1: what the world is like. So is it going to
7:38
Speaker 1: be that our um theories, you know, miss out some
7:41
Speaker 1: stuff or are we like using you know, often we
7:44
Speaker 1: have like kind of extra mathematical structure more than what
7:47
Speaker 1: we need in our theories. And sometimes we can know that,
7:50
Speaker 1: we can know there's extra kind of descriptive fluff fur um,
7:55
Speaker 1: and sometimes we don't. So I yeah, I guess I'm
7:57
Speaker 1: interested in, like, you know, how what we should read
7:59
Speaker 1: off from our theories? You know, which bit should we
8:01
Speaker 1: take to be true and really about the world, which
8:04
Speaker 1: bits are kind of just kind of extra stuff that
8:08
Speaker 1: doesn't really correspond to one of them? Wonderful? Well. I
8:10
Speaker 1: love how philosophy lets us ask like profound questions about
8:14
Speaker 1: things that seem ordinary, right, like is our science teaching
8:17
Speaker 1: us anything at all? Or whatever? And one question that
8:20
Speaker 1: I really struggle with is like, why can I watch
8:23
Speaker 1: a ball fly through the air and describe it using
8:27
Speaker 1: fairly simple equations? You know, why is it possible for
8:31
Speaker 1: me to do that? And the naive answer and maybe
8:33
Speaker 1: the listener out there is thinking, well, because the universe
8:35
Speaker 1: follows laws, and we can deduce those laws, no big deal.
8:38
Speaker 1: But I think as a particle physicist that probably those laws,
8:41
Speaker 1: if they exist, they operate at the microscopic level right
8:44
Speaker 1: on particles or strings or whatever the basic bits are.
8:47
Speaker 1: So if I'm watching those basic bits themselves, I can
8:49
Speaker 1: use those laws to describe them. But I'm not right.
8:51
Speaker 1: I'm massively zoomed out. If I'm watching a baseball, it
8:54
Speaker 1: has like ten to the twenty nine particles in it. Why,
8:57
Speaker 1: if I'm looking at ten to the twenty nine basic bits,
9:00
Speaker 1: do I see anything that makes sense? Why isn't it
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Speaker 1: all just fuzz and chaos? I mean, I don't have
9:04
Speaker 1: a simple rule that predicts the role of a die
9:07
Speaker 1: or the movement of the stock market because it's so
9:09
Speaker 1: sensitive to those turned details. Why isn't it always like that?
9:12
Speaker 1: Why when you zoom out in the world, does any
9:15
Speaker 1: sort of simplicity seem to emerge? Can you help us
9:18
Speaker 1: get a grasp on that kind of question? Yeah, I
9:20
Speaker 1: mean there's been a lot of different responses that people
9:23
Speaker 1: have given, So, I mean there's a kind of defeatist response, right,
9:26
Speaker 1: which is, well, it's very complicated, but we've got to
9:29
Speaker 1: do what we can to make sense of it. And
9:31
Speaker 1: so even though it appears that things are simple, that's
9:35
Speaker 1: just how we have to approach it, you know, in
9:37
Speaker 1: the same way you might think, well, the reason that
9:39
Speaker 1: we have to I don't know, use Newtonian mechanics or
9:44
Speaker 1: do biology and chemistry is just because we're really bad
9:47
Speaker 1: at solving the rod in an equation for complicated systems,
9:50
Speaker 1: and that's why we have these kind of other theories.
9:53
Speaker 1: So that's the kind of like defeatist option, which is
9:56
Speaker 1: that we're just not good enough at solving the really
9:59
Speaker 1: tough things. If we could, maybe we would use those
10:01
Speaker 1: instead to understandable going across the room. So is that
10:04
Speaker 1: saying that the universe really is complicated and that we're
10:07
Speaker 1: just making like a weak approximation of it by describing
10:09
Speaker 1: it simply. It's sort of like it's part of the
10:12
Speaker 1: fact that we're you know, in the same way that
10:14
Speaker 1: if a child doesn't know very much language, then they're
10:18
Speaker 1: going to describe the world in a kind of much
10:20
Speaker 1: less colorful way perhaps than an adult would describe the world.
10:24
Speaker 1: And so that makes it seem like the reason we
10:26
Speaker 1: see any simplicity is like, well, we're just a bit simple,
10:29
Speaker 1: so we have to be able to see things that way,
10:31
Speaker 1: which I find a bit well, it's defeatus. But also
10:34
Speaker 1: I think it would be kind of amazing, right if
10:36
Speaker 1: we were just not very good at describing the world,
10:38
Speaker 1: and the ways in which we did describe the world
10:41
Speaker 1: was so successful, right, Like, it seems like it's not
10:45
Speaker 1: just um, sometimes people have this distinction between the way
10:49
Speaker 1: the world really is versus like what's our perspective on it? So,
10:52
Speaker 1: you know, we see the flowers in the garden in
10:54
Speaker 1: a really different way from how bees see flowers, because
10:58
Speaker 1: our eyes are sensitive different parts of the electromanity spectrum.
11:00
Speaker 1: So you might think, well, maybe some of the simplicity
11:03
Speaker 1: is a bit like the kind of color of the flowers.
11:05
Speaker 1: It's just like how we see things rather than how
11:07
Speaker 1: they really are. But I don't really like that way
11:08
Speaker 1: of thinking about it, because I think we're getting something
11:10
Speaker 1: really right. You know. It's not just that we're using
11:13
Speaker 1: simple laws because we're simple people. Is that there is
11:17
Speaker 1: this kind of macroscopic simplicity out of this kind of microscopic,
11:22
Speaker 1: kind of incredibly complicated stuff going on. Nonetheless, this kind
11:26
Speaker 1: of higher or emergent level, you get this kind of simplicity, right,
11:30
Speaker 1: Like to use your analogy of a child, maybe a
11:32
Speaker 1: child doesn't use flowery language, but when they say me
11:35
Speaker 1: want candy, you understand right, it works. It's successful. And
11:39
Speaker 1: when I'm taking an approximation of something, because they can
11:41
Speaker 1: to the full calculation and taking the first second third
11:43
Speaker 1: order of perturbation theory, I mostly get the answer right
11:46
Speaker 1: and I can ignore the other details. And if the
11:49
Speaker 1: universe was just chaos and fuzz then that wouldn't work right,
11:52
Speaker 1: and it doesn't. For example, when I try to predict
11:54
Speaker 1: the stock market, trust me, I've tried. You know, it
11:57
Speaker 1: doesn't work. So I feel like the defeatist answer seems
12:00
Speaker 1: to totally fail at explaining why simplicity emergence. And also
12:04
Speaker 1: do the defeatists call themselves the defeatists? I guess maybe
12:07
Speaker 1: the more correct way of labeling them it might might
12:12
Speaker 1: be somebody who would say something like, there's just a
12:14
Speaker 1: kind of methodological autonomy. Like the reason we have this
12:18
Speaker 1: methodology where there's all these different scientific disciplines that's focused
12:22
Speaker 1: on different things. They have their own conferences, but in
12:24
Speaker 1: large they just talk to each other rather than you know,
12:27
Speaker 1: sometimes talk between each other. But you know that the
12:29
Speaker 1: reason we have science kind of like hived into these
12:32
Speaker 1: different kind of institutions is just because that's how we
12:34
Speaker 1: go about doing it. So you can think about as
12:35
Speaker 1: being the kind of methodological autonomy. It's like, perhaps the
12:39
Speaker 1: answer isn't just that it's you know, it's simpler to
12:41
Speaker 1: use Newtonian physics for calculating what's going to happen with
12:46
Speaker 1: the ball across the park. It's not just that. Is
12:48
Speaker 1: also that that's the kind of right laws to be
12:50
Speaker 1: using at that level. So that would be a kind
12:53
Speaker 1: of different way of thinking about it, where it's not
12:55
Speaker 1: just that we're not very good at solving the Stronian
12:57
Speaker 1: equation for complicated systems, it's it's actually these other laws
13:02
Speaker 1: and equations are kind of more suited. In the same
13:06
Speaker 1: way that if I ask you what the weather is
13:08
Speaker 1: going to be tomorrow because I want to go to
13:11
Speaker 1: the park, the kind of right grain of answer is like,
13:14
Speaker 1: you know, it'll be sunny, it'll be raining. It won't
13:16
Speaker 1: be like to give me a kind of complete survey
13:20
Speaker 1: of what the weather across the whole world's gonna be like.
13:22
Speaker 1: So one alternative answer to just saying well, we've got
13:25
Speaker 1: to do things that way in the kind of defeatist
13:27
Speaker 1: or kind of methodological approach, would be to say, well, actually,
13:30
Speaker 1: there's kind of different laws are appropriate for different things
13:34
Speaker 1: in the same way different tools are appropriate for different
13:36
Speaker 1: tasks or something like that. But does that reject like reductionism,
13:40
Speaker 1: Does that say that those laws ethicals are made for example,
13:43
Speaker 1: doesn't arise somehow from like the too ing and throwing
13:47
Speaker 1: of the basic bits that they emerge at their own level,
13:49
Speaker 1: or you suggesting that they do emerge, that they're just
13:52
Speaker 1: are naturally these different scales which the universe coalesces into simplicity. Right.
13:57
Speaker 1: So I think reductionism is very for debate because lots
14:01
Speaker 1: of people mean different things by it, right, Like some
14:03
Speaker 1: people mean by it again a kind of methodology, like, hey,
14:07
Speaker 1: you want to understand something, look at its component parts.
14:10
Speaker 1: That's the best way to go about doing it. If
14:11
Speaker 1: I want to understand this thing, I want to understand
14:13
Speaker 1: all of its parts, and that's how I'll understand it.
14:15
Speaker 1: That's what a particle physicists would do, for example. And
14:18
Speaker 1: you know that also goes across other sciences. For instance,
14:21
Speaker 1: you know, if you want to understand disease, some people think,
14:23
Speaker 1: really the crucial thing to understand is the kind of
14:25
Speaker 1: genetic factors that lead to that disease. Other people might think, oh,
14:29
Speaker 1: perhaps there's a kind of the environment plays a large role.
14:32
Speaker 1: So there's kind of this kind of theme of understanding
14:35
Speaker 1: things in terms of their parts kind of goes across
14:37
Speaker 1: all the different sciences. I think that's one form of reductionism.
14:40
Speaker 1: Another form of productionism would be to kind of be
14:43
Speaker 1: a kind of more meaty claim about the way the
14:46
Speaker 1: world is, so to say, really, all that exists is
14:50
Speaker 1: the very fundamental particles, whatever they turn out to be
14:53
Speaker 1: in the end, they're going to be all that there
14:55
Speaker 1: really is. Everything else is just the kind of different
14:58
Speaker 1: way of talking about those things, a very complicated different way.
15:01
Speaker 1: But I think that the kind of probably the most
15:04
Speaker 1: useful way of talking about reductionism is to talk about
15:07
Speaker 1: how we understand, like how one theory is related to another.
15:10
Speaker 1: So the kind of obvious example of this is, you know,
15:13
Speaker 1: Newtonian mechanics was very successful. Ultimately we think that it's
15:16
Speaker 1: not quite right, and if things are either very heavy
15:19
Speaker 1: or very moving, very fast or very small, then it
15:21
Speaker 1: doesn't work. But we can show how in certain limits,
15:25
Speaker 1: if your football is being kicked by human rather than
15:30
Speaker 1: a kind of incredibly strong alien, then it's going to
15:32
Speaker 1: be traveling at speeds when Newtonian mechanics is so really good.
15:35
Speaker 1: So we can understand how those theories are related to
15:37
Speaker 1: each other. In particular, we can understand how to construct
15:39
Speaker 1: one theory out of another, you know, in a particular
15:42
Speaker 1: limits you get back your one theory from another. And
15:44
Speaker 1: I think that relationship is really useful for seeing which
15:48
Speaker 1: scales you think different theories will work out, because if
15:51
Speaker 1: you can show that you're going to get back Newtonian
15:54
Speaker 1: mechanics in the low velocity limits, then that kind of
15:56
Speaker 1: explains why Neuchinian mechanics was really good there. And I
15:59
Speaker 1: think that's a way of being that as a kind
16:00
Speaker 1: of one pattern emerging out of another more fundamental pattern
16:06
Speaker 1: in a certain regime. So I think reduction is really
16:08
Speaker 1: helpful for understanding how the different kind of theories and
16:13
Speaker 1: laws that we have all fit together. You asked whether
16:16
Speaker 1: that's compatible with thinking there are laws at different levels,
16:19
Speaker 1: So some people have said no, if you've got kind
16:21
Speaker 1: of emergent laws, emergence, you know, it's one of those words,
16:25
Speaker 1: it's like so controversial what you mean by it. But
16:28
Speaker 1: for some people, emergence just means the failure of reduction.
16:31
Speaker 1: So for those people that story about getting theories back
16:34
Speaker 1: in different limits or whatever, that's going to be a
16:37
Speaker 1: case of reduction. And if there's reduction, then there's no emergence.
16:40
Speaker 1: So there aren't these kind of there's a kind of
16:43
Speaker 1: no meaty sense in which there's these kind of new
16:45
Speaker 1: things at higher levels. Really it's all just the fundamental things,
16:49
Speaker 1: and you can show why you thought there were other things.
16:52
Speaker 1: You can show why you thought there were Newtonian forces,
16:54
Speaker 1: but really there isn't. That was just a kind of
16:56
Speaker 1: old way of speaking. I kind of prefer the view
16:59
Speaker 1: where you think different laws is emerging and they're all
17:02
Speaker 1: kind of on a part with each other in the
17:04
Speaker 1: sense of like some laws are more fundamental than other laws,
17:07
Speaker 1: but none of them are like kind of second grade citizens.
17:10
Speaker 1: You know, they're like you get the laws of Newtonian
17:14
Speaker 1: mechanics emerging house of relativistic laws, but that you know,
17:18
Speaker 1: that's just the right laws have in that domain when
17:20
Speaker 1: things are going nice and slow. Then that's kind of
17:24
Speaker 1: the way to the kind of laws to use. I
17:27
Speaker 1: like your organization of the topics there in terms of complexity,
17:30
Speaker 1: like the idea that maybe Einstein's view of gravity is
17:34
Speaker 1: more complete, but it's too complicated. Like if I wanted
17:38
Speaker 1: to solve the question of like what is the Earth's
17:40
Speaker 1: orbit going to be, and you gave me Einstein's gravity,
17:42
Speaker 1: I'll be like, well, I'll be here for a while,
17:45
Speaker 1: Whereas Newtonian mechanics is going to give me the answer
17:47
Speaker 1: straight away, and it's also going to give me a
17:50
Speaker 1: story that I can tell that I understand. And maybe
17:54
Speaker 1: this is also the argument you're making that some of
17:56
Speaker 1: these laws are just more useful in their explanation. Like
18:00
Speaker 1: if I want to tell you what happened to the
18:02
Speaker 1: ball this afternoon, and then I give you a description
18:04
Speaker 1: of all ten of the twenty nine particles and what
18:06
Speaker 1: each of them did, doesn't really answer your question. But
18:08
Speaker 1: if I say, oh, it flew in a parabola and
18:11
Speaker 1: landed feet from home base or whatever, that's sort of
18:15
Speaker 1: the story the explanation that we're looking for. So does
18:18
Speaker 1: that mean that it sort of depends on the question
18:20
Speaker 1: we're asking, that there are no more fundamental rules. They're
18:23
Speaker 1: just sort of like laws that answer the questions we're asking.
18:26
Speaker 1: So I guess the worry with that is that if
18:28
Speaker 1: it just depends on what question we're asking, you might
18:31
Speaker 1: then think, well, that just depends on what you care about,
18:34
Speaker 1: and so it's really just tied into your interests, and
18:38
Speaker 1: then that kind of starts to look like it's dragging
18:40
Speaker 1: us in the defeatist direction, where it is all connected
18:43
Speaker 1: to what we understand about the world rather than how
18:46
Speaker 1: the world really is. So I think that helpful way
18:50
Speaker 1: to go is to think of what sense is Newtonian
18:53
Speaker 1: mechanics better for describing the trajectory of the ball? And
18:58
Speaker 1: I think that the kind of right answer for that is, well,
19:01
Speaker 1: when somebody asks you a question, you need to give
19:03
Speaker 1: them the right amount of details. It's not just that
19:06
Speaker 1: that's more useful, like that's the better explanation. And so
19:11
Speaker 1: that would then mean the kind of structures and laws
19:13
Speaker 1: associated to the kind of less fundamental theory are doing
19:17
Speaker 1: the kind of best explanation. And normally people think if
19:22
Speaker 1: something's giving you the best explanation, that's the thing we
19:25
Speaker 1: should take to be true. So this is sometimes called
19:27
Speaker 1: inference to the best explanation. What's the reason why the
19:30
Speaker 1: apple fell to the ground? Is it because the fairies
19:33
Speaker 1: pushed it? Or is it because Newtonian mechanics, or is
19:35
Speaker 1: it because I look the wrong way? You know, you
19:38
Speaker 1: can think of all the different possible explanations, and the
19:40
Speaker 1: kind of best explanation is the one that we normally
19:42
Speaker 1: take to be true. So if you can kind of
19:44
Speaker 1: give a reason why these non fundamental theories, you know,
19:48
Speaker 1: we think they're less complete, they're missing some of the
19:50
Speaker 1: details about the world, but nonetheless we think that they're
19:54
Speaker 1: perhaps giving the best explanations. Then we can still be
19:57
Speaker 1: committed to all of this kind of emergent structure, and
20:00
Speaker 1: we don't have to relegate it to just kind of
20:02
Speaker 1: useful stories that we tell. We can really say that
20:05
Speaker 1: it's getting at what the world's like. We're lucky that
20:07
Speaker 1: there's some simplicity, and that's kind of useful for us,
20:09
Speaker 1: we want to say, and that's really this interesting fact
20:11
Speaker 1: about the world. This is kind of deep thing that
20:13
Speaker 1: despite all this kind of fundamental complexity, there's some kind
20:17
Speaker 1: of relative simplicity at the kind of less fundamental or
20:20
Speaker 1: macroscopic level. Okay, I can't wait to dive deeper into
20:23
Speaker 1: that topic, but first we have to take a quick break. Okay,
20:39
Speaker 1: we're back and we're talking with philosopher Katie Robertson about
20:43
Speaker 1: whether the universe makes sense, whether there is a single
20:47
Speaker 1: theory of physics out there. And it certainly seems convenient
20:51
Speaker 1: that there are sometimes simple stories that you can tell,
20:55
Speaker 1: and I certainly get the argument that, like, sometimes those
20:57
Speaker 1: simple stories really are the answer. You don't necessarily want
21:01
Speaker 1: the totally microscopic picture in every sense. But the thing
21:04
Speaker 1: that still puzzles me is why that's possible, And the
21:07
Speaker 1: thing I can't get over is the fact that sometimes
21:09
Speaker 1: it's not. You know, sometimes we look at systems and
21:11
Speaker 1: they are complex, and our approximations fail, and we can't
21:14
Speaker 1: find a simple story to describe the path of hurricanes
21:17
Speaker 1: or the fluctuations of the stock market. So it can
21:20
Speaker 1: just be that we're looking at the universe and we're
21:22
Speaker 1: asking these questions, we're always able to find some simple
21:25
Speaker 1: story because we are not. So it makes me wonder
21:28
Speaker 1: why they emerge in some cases and not in others,
21:31
Speaker 1: and specifically why they seem to emerge at various scales, right,
21:35
Speaker 1: Like you say, we organize ourselves into physics and biology
21:38
Speaker 1: and chemistry conferences. Is that because of some human interest
21:42
Speaker 1: in the way the universe works at these levels? Or
21:44
Speaker 1: is because the universe itself, you know, reveals itself and
21:47
Speaker 1: simple stories only at some scales and not at some
21:50
Speaker 1: other scales. If aliens are doing science on some other planet,
21:53
Speaker 1: are they also doing physics and biology and chemistry and
21:55
Speaker 1: having separate conferences the way they don't talk to each
21:57
Speaker 1: other or do they have like a different ladder of
22:00
Speaker 1: science is completely because of their own history. Is there
22:03
Speaker 1: any way to grapple with those questions to try to
22:06
Speaker 1: get the sense for why science seems to be simple
22:08
Speaker 1: at some skills and not at others. I mean, it's
22:10
Speaker 1: a really interesting question, right. The philosopher jerryford Or, I think,
22:14
Speaker 1: said something. I'm want to fudge the quote a bit,
22:16
Speaker 1: but it's something like, I expect to find out the
22:19
Speaker 1: answer to why we have something other than physics. Why
22:23
Speaker 1: isn't it just that we only have to do physics
22:25
Speaker 1: and we don't have all these kind of different scales
22:27
Speaker 1: and levels of which we talk about the world. He
22:29
Speaker 1: said something like, I expect to find out the answer
22:31
Speaker 1: to that question the day after I find out why
22:33
Speaker 1: there's something rather than nothing, you know. He kind of said,
22:36
Speaker 1: this is a bit of a million dollar question. To
22:39
Speaker 1: my mind, I think there's going to be lots of
22:40
Speaker 1: different answers to that, rather than one answer that fits
22:43
Speaker 1: the relations between all different scales. So I think, as
22:46
Speaker 1: is often the case in understanding how different scientific theories
22:49
Speaker 1: are related to each other, the devil's going to be
22:51
Speaker 1: in the details. So I think, in the case of
22:53
Speaker 1: thinking about how we get kind of directed processes like
22:57
Speaker 1: a cup of coffee cooling down or glass smashing the floor.
23:00
Speaker 1: You know, these processes that we think of as being
23:02
Speaker 1: directed in time, how we get that kind of macroscopic
23:05
Speaker 1: pattern out of the microscopic pattern in so, how we
23:09
Speaker 1: get that from the microdynamics, and how we get to
23:11
Speaker 1: statistical mechanics. That's one area where I think we can
23:14
Speaker 1: see how that happens, how we get that emergence. So
23:18
Speaker 1: what we have in that case is that we have
23:20
Speaker 1: a description that's really kind of detailed at the lower level. Right,
23:24
Speaker 1: there's ten of the twenty three molecules and a gas.
23:26
Speaker 1: That's a very complicated description. We can instead of talking
23:29
Speaker 1: about exactly where molecule five and fifty three is, we
23:33
Speaker 1: can talk about some kind of average properties of the gas.
23:36
Speaker 1: So we can talk about kind of what's sometimes called
23:39
Speaker 1: a kind of coarse grain probability distribution. Instead of following
23:42
Speaker 1: exactly where every single passicle is, we just say on average,
23:45
Speaker 1: there's a kind of an even smearing of them across
23:47
Speaker 1: the box, for instance. And this kind of course graining
23:50
Speaker 1: type procedure is a bit like averaging. You know, you
23:53
Speaker 1: throw away some of the details, and sometimes when we
23:55
Speaker 1: do this we can kind of uncover new patterns. We
23:58
Speaker 1: can see that oh, actually, there's kind of a rule
24:01
Speaker 1: about how this kind of new variable that we've defined works.
24:05
Speaker 1: And sometimes when we do that, when we kind of abstract,
24:08
Speaker 1: sometimes you might think of it as being, you know,
24:10
Speaker 1: you're kind of throwing away some details like abstracting to
24:13
Speaker 1: a new variable. Sometimes then we find a new law
24:16
Speaker 1: in terms of that variable. So in the case of
24:18
Speaker 1: statistical mechanics, we can throw away information about the correlations,
24:22
Speaker 1: the kind of three or more practical correlations. Gas molecules
24:26
Speaker 1: are all bump into one another and getting correlated with
24:28
Speaker 1: each other. You can throw away the kind of three
24:30
Speaker 1: or more partical correlations in such a way that you
24:33
Speaker 1: can find a kind of new dynamics at the higher level,
24:36
Speaker 1: where you've kind of got this course grain dynamics, or
24:38
Speaker 1: something like the Boltzmann equation, which tells you how quickly
24:40
Speaker 1: gases relax the equilibrium. That is kind of an example
24:43
Speaker 1: of these coarse grained error of usal dynamics. So in
24:45
Speaker 1: that case you've got kind of like a detailed story
24:48
Speaker 1: about how you've got this higher level emergent kind of
24:51
Speaker 1: description and structure in those specific cases. But you know,
24:55
Speaker 1: there's also other cases where you might use something a
24:57
Speaker 1: bit like course graining to kind of throw away the
24:59
Speaker 1: details that you're going to be able to follow. And
25:01
Speaker 1: sometimes that's good and you can find an equation. Sometimes
25:03
Speaker 1: you can't, Like there's those really bad ways to average
25:05
Speaker 1: or course grain, and that you get nothing out of him, right,
25:08
Speaker 1: Like it's there's this nice quote by this I think
25:11
Speaker 1: he's a historian of physics Van camp And who says
25:13
Speaker 1: it's kind of the art of the physicists to find
25:16
Speaker 1: the right variables rather than a kind of science of
25:19
Speaker 1: like exactly how should we treat choose to course grain.
25:22
Speaker 1: There's the kind of a lot of bad choices you
25:24
Speaker 1: can make, but in some cases you can find a
25:26
Speaker 1: kind of close form dynamics. And that's the case where
25:29
Speaker 1: we think we found like a new pattern. But you
25:30
Speaker 1: make it sound like a discovery, like you're stumbling over something.
25:33
Speaker 1: You're like, ah, look, the universe is doing this thing right,
25:36
Speaker 1: like we're coming into it. We don't necessarily understand why
25:39
Speaker 1: it's possible to go from statistical mechanics description of all
25:43
Speaker 1: those tiny little particles to like you know, thermodynamics of
25:47
Speaker 1: gases and all this kind of stuff. And you use
25:49
Speaker 1: the word abstraction, which I find really interesting because it
25:51
Speaker 1: tells me that we're like summing up a lot of details,
25:54
Speaker 1: were saying, forget all the details of what's in here,
25:56
Speaker 1: I'm just going to call this thing a ball and
25:58
Speaker 1: treat it like a point, right, where like dracting away
26:00
Speaker 1: a lot of the details. And how do we know
26:03
Speaker 1: that that kind of abstraction isn't sort of arbitrary or cultural? Right?
26:07
Speaker 1: Is that us imposing our view on the world, like, oh,
26:10
Speaker 1: this is interesting, that's not interesting, I want to tell
26:13
Speaker 1: a story about this, Or is it the universe coalescing
26:16
Speaker 1: around something like Again, I wonder whether that's us forcing
26:20
Speaker 1: our sort of mental structure on the universe because we
26:22
Speaker 1: can't possibly process all the details, or if it's really
26:25
Speaker 1: that we're discovering this in the universe. How could we
26:27
Speaker 1: possibly know the difference between those two scenarios without, of course,
26:31
Speaker 1: talking to aliens about their science. How phony we can
26:34
Speaker 1: meet those aliens. So people used to think that it
26:37
Speaker 1: really was due to like our not being able to
26:40
Speaker 1: kind of keep ahold of all of the details that
26:42
Speaker 1: we use the kind of course graining procedure in statistical mechanics.
26:46
Speaker 1: So people thought that the way we chose the kind
26:48
Speaker 1: of averaging technique was according to what we could measure.
26:51
Speaker 1: You know, we can't precisely know exactly where each molecule
26:55
Speaker 1: is in the in the box of gas. Then they
26:57
Speaker 1: use that as a kind of motivation for why you
27:00
Speaker 1: could then course grain and throw away some of the
27:01
Speaker 1: details because we couldn't measure it. But I actually think
27:03
Speaker 1: that's a really bad explanation of why we cause grain,
27:06
Speaker 1: because it's not like, as we've got better at measuring things,
27:09
Speaker 1: we use different course graining schemes in statistical mechanics, right,
27:13
Speaker 1: So it's not really linked to what we can see
27:17
Speaker 1: in inverted commerce because if it were, then as what
27:20
Speaker 1: we see can change, we would change kind of averaging
27:23
Speaker 1: or course graining technique. So I think that for that reason,
27:26
Speaker 1: it's more like the kind of discovering new patterns way
27:29
Speaker 1: of thinking about it rather than it being kind of
27:31
Speaker 1: connected to us, because if it was connected to us
27:33
Speaker 1: and we change, would expect to see a change connected
27:36
Speaker 1: to that. So yeah, in the in the staff Met case,
27:38
Speaker 1: they really did think that. You know, there's some amazing
27:41
Speaker 1: quotes about the time asymmetry that comes out of it.
27:43
Speaker 1: I think somebody described it. I think Pritage and Stayer
27:45
Speaker 1: subscribed it as allusory kind of resulted kind of entropic
27:49
Speaker 1: asymmetry that you get. Somebody else says it's kind of
27:52
Speaker 1: just anthropocentric, you know, it's a feature of us. But
27:54
Speaker 1: I think that once we understand that these techniques that
27:56
Speaker 1: we have of abstracting and throwing away details, they're not
27:59
Speaker 1: necessar seratly connected to what we know about the world
28:03
Speaker 1: in any kind of detailed way. It might be that
28:05
Speaker 1: we're kind of attending to certain features of the world
28:08
Speaker 1: rather than other bits. You know, we're not focusing on
28:10
Speaker 1: all the kind of what's this particle doing over here,
28:12
Speaker 1: and what's this one doing over here? And I'm going
28:14
Speaker 1: to keep a track of what every single particle and
28:16
Speaker 1: the gas is doing. I'm just gonna be interested in
28:18
Speaker 1: a bit more of a zoomed out way. But that
28:20
Speaker 1: zooming out isn't I think connected to kind of our
28:24
Speaker 1: perspective on the world. This is interesting sort of second
28:27
Speaker 1: class nature to things that emerge that we talked about
28:30
Speaker 1: all the time in particle physics. So I never really
28:32
Speaker 1: thought of it as like, you know, derogatory. But you know,
28:35
Speaker 1: there's recent ideas about how space itself and maybe even
28:39
Speaker 1: time are not fundamental to the universe they emerge, meaning
28:43
Speaker 1: that you could have a universe without space before the
28:46
Speaker 1: quantum bits of woven themselves together into reality, or you
28:49
Speaker 1: could have a universe without time. And it's sort of
28:51
Speaker 1: like demotes those things and says they're not essential, they're
28:55
Speaker 1: not fundamental, And it seems to me like you're making
28:57
Speaker 1: the argument that they shouldn't be a demotion, that there's
28:59
Speaker 1: just you know, there's a set of these ideas and
29:02
Speaker 1: different ones are applicable in different places, in different contexts,
29:05
Speaker 1: but we shouldn't think of the most fundamental is necessarily
29:09
Speaker 1: the most primary or the most true. Is that fair?
29:12
Speaker 1: And yeah, I think so. There's a kind of tendency
29:14
Speaker 1: sometimes in philosophy to really only focus on the fundamental.
29:18
Speaker 1: I mean, I guess Um Anderson and his famous more
29:21
Speaker 1: is more as different paper right, was kind of pointing
29:24
Speaker 1: to a similar tendency within physics. He were saying, Look,
29:26
Speaker 1: it's really important to look at these other areas of physics,
29:28
Speaker 1: not just fundamental physics. And yeah, I think it's right
29:31
Speaker 1: to think of these non fundamental things as not kind
29:36
Speaker 1: of second class in that way, not just because you know,
29:41
Speaker 1: condensed matter physicists want funding to um but because they're
29:44
Speaker 1: also telling it's true things about the world. And it's
29:46
Speaker 1: kind of an interesting conundrum I think connected to the
29:49
Speaker 1: one that you mentioned at the outset about you know
29:51
Speaker 1: why is why is it all not just kind of
29:53
Speaker 1: buzzing confusion? Why do we get the simplicity? I think
29:55
Speaker 1: an interesting question is, you know, even if we were
29:58
Speaker 1: to understand the very kind of fundamental nature of the world,
30:01
Speaker 1: that'd still be so much we didn't know, right, Like
30:03
Speaker 1: we wouldn't understand stereotype threat in psychology or something, you know,
30:08
Speaker 1: Like it's not like just knowing about the fundamental is
30:10
Speaker 1: enough to give for you the kind of knowledge of
30:12
Speaker 1: all these other levels. So I think, yeah, understanding these
30:15
Speaker 1: levels is really important as well. Yeah, I think you're right.
30:18
Speaker 1: And obviously, even if we had like string theory or
30:21
Speaker 1: the most fundamental theory, it wouldn't tell us, you know,
30:23
Speaker 1: how do you raise your children, or how do you
30:25
Speaker 1: make chicken soup? You know, or even where is the
30:28
Speaker 1: ball going to fly when somebody hits it with a bat.
30:30
Speaker 1: And I think maybe the primacy comes because some people,
30:33
Speaker 1: not everybody, are interested in the most fundamental questions. They
30:36
Speaker 1: want to know what is the most fundamental picture of
30:38
Speaker 1: the universe, even if that is not relevant to our
30:40
Speaker 1: everyday lives and too important questions like how can we
30:43
Speaker 1: build a faster computer? You know, etcetera, etcetera. Something that
30:46
Speaker 1: confuses me about these non fundamental theories, these effective theories,
30:51
Speaker 1: you know, the ones that work so well fluid dynamics
30:53
Speaker 1: and galaxy in formation, is that they feel sometimes inconsistent,
30:57
Speaker 1: you know, like, for example, the basic equation of fluid dynamics,
31:00
Speaker 1: because the Naviti Stokes equation makes this assumption that the
31:03
Speaker 1: fluids you're describing is continuous, that it's explicitly not made
31:07
Speaker 1: of tiny little bits like like of saying, but of
31:10
Speaker 1: course we know that they are right. So shouldn't theories
31:13
Speaker 1: like fit together more smoothly? I mean, I love how
31:16
Speaker 1: Newtonian theory is an extreme case of Einsteinian theory, but
31:20
Speaker 1: that seems like is that maybe an exception because in
31:23
Speaker 1: other cases, you know, the assumptions you have to make
31:25
Speaker 1: at different levels are incompatible. It gives me a sense
31:28
Speaker 1: of science is more like you know, a disjoint patchwork
31:31
Speaker 1: than really like a smooth idea that you're like shining
31:35
Speaker 1: a lamp post on at different scales. Yeah, that's a
31:38
Speaker 1: really interesting question because you know, one way to get
31:41
Speaker 1: around the fact that the navious equation says that everything
31:44
Speaker 1: is continuous is to say, well, instead of it's saying
31:46
Speaker 1: this false thing, we're just gonna say that it shouldn't
31:50
Speaker 1: say anything about that. You know, we should just reinterpret
31:52
Speaker 1: it as like not committing either way. And so you
31:55
Speaker 1: can kind of think of a kind of selective approach
31:57
Speaker 1: to your theories, you know, like some bits of the
31:59
Speaker 1: we shouldn't take too seriously. And that's often what people
32:01
Speaker 1: have thought about old theories, right, which is they got
32:03
Speaker 1: some bits right and they've got some bits wrong. And
32:06
Speaker 1: one way that sometimes people like to think about the worlds,
32:08
Speaker 1: which comes back to this question of how our theories
32:10
Speaker 1: relate to the world, is that not everything they say
32:14
Speaker 1: is correct. So some people want to say that the
32:17
Speaker 1: really important thing that's kind of continuous between the different
32:20
Speaker 1: scales and continuous across and theory change is the kind
32:23
Speaker 1: of mathematical structure, the kind of extra details about what
32:27
Speaker 1: the kind of furniture of the world is, like whether
32:30
Speaker 1: fluids are continuous or not. That's the kind of thing
32:32
Speaker 1: where historically they've got it a bit wrong, but normally
32:34
Speaker 1: the mathematical equations are at least approximately the right thing.
32:39
Speaker 1: So this is sometimes called like structural realism, And the
32:41
Speaker 1: idea is that instead of kind of taking your scientific
32:45
Speaker 1: theory at its word, you should really only be committed
32:47
Speaker 1: to the kind of mathematical structure of the theory. But
32:50
Speaker 1: doesn't the math come out of these assumptions that you
32:52
Speaker 1: start from these assumptions and then you can build the
32:54
Speaker 1: math on top of them and like the axiomatic foundations
32:57
Speaker 1: of the theory, right, how can you have the math
32:59
Speaker 1: without foundations? Well, this is a kind of a tricky
33:02
Speaker 1: question for the structural realists, right, they want to say
33:04
Speaker 1: the laws, we're getting those right, But what the kind
33:07
Speaker 1: of objects in that those laws are we're not quite
33:11
Speaker 1: social about. I mean, quantum mechanics is are kind of
33:13
Speaker 1: clear case for this, right, Like we're really confident about
33:16
Speaker 1: the strouding your equation exactly what quanstant particles are? Like,
33:21
Speaker 1: you know you're gonna end up whether a big disagreement
33:24
Speaker 1: when you have a group of this discussing it. So
33:26
Speaker 1: the idea is that it's kind of like epistemic security.
33:28
Speaker 1: You know, you don't want to put your neck over
33:30
Speaker 1: the parapet too much. You've got to just commit to
33:32
Speaker 1: the bits of your theory that you think are really
33:34
Speaker 1: kind of secure and good. And maybe these are these
33:37
Speaker 1: assumptions about, for instance, fluids being continuous are kind of
33:40
Speaker 1: the kind of ladder or scaffolding that helps you get
33:43
Speaker 1: to your theory. But you can kind of kick away
33:45
Speaker 1: afterwards and say, the thing I'm really confident about and
33:48
Speaker 1: I think is getting at the nature of the world
33:52
Speaker 1: is the kind of equations and the math. But everything
33:55
Speaker 1: else I'm going to just not commit too much. Too well.
33:58
Speaker 1: I can't be too critical of that kind of strategy,
34:01
Speaker 1: since as a particle physicist, I couldn't even really tell you, like,
34:03
Speaker 1: what is a particle? After all? Right, And you're right,
34:06
Speaker 1: we certainly do a lot of particle physics, and we
34:08
Speaker 1: collide them and we describe them, and we have excellent
34:10
Speaker 1: descriptions of them without even really knowing what it is
34:12
Speaker 1: we're talking about. So I definitely have very little ground
34:16
Speaker 1: to stand on there. Okay, I have a lot more
34:18
Speaker 1: questions for you, Katie, but first we have to pause
34:21
Speaker 1: for another quick break. All right, we're back and we're
34:36
Speaker 1: talking to Dr Katie Robertson, a philosopher of physics, about
34:40
Speaker 1: whether it's possible to understand everything in the universe with
34:44
Speaker 1: a single theory. I want to take us in another direction,
34:46
Speaker 1: which is sort of further down this skeptical road. You know,
34:49
Speaker 1: if each science is helping us understand a part of
34:51
Speaker 1: the world, and if we say, you know, each one
34:54
Speaker 1: has our own area of validity, is it possible that
34:56
Speaker 1: we can eventually stitch them together to get a whole
34:59
Speaker 1: list day understanding of the underlying truth. The idea being
35:03
Speaker 1: like the more lamp posts you turn on, the more
35:05
Speaker 1: ground truth you're revealing. And I'm reading this book by
35:08
Speaker 1: Nancy Cartwright who has this school of thought. Her book
35:11
Speaker 1: is called The Dappled World, and she seems to be
35:13
Speaker 1: arguing that there might not be unity to science, that
35:16
Speaker 1: there isn't a whole truth underneath it, that we're revealing,
35:20
Speaker 1: that each piece could actually be separate and not link
35:23
Speaker 1: up into a coherent picture. Frankly, as a somebody who's
35:26
Speaker 1: born and bred as a particle physicist, I struggle to
35:29
Speaker 1: comprehend this argument. What is the argument here? Can you
35:32
Speaker 1: walk us through how to get to that sort of
35:33
Speaker 1: state of mind? So I guess you can think of
35:37
Speaker 1: there's being kind of two issues. The first is we
35:41
Speaker 1: seem to go about doing science in this very kind
35:44
Speaker 1: of institutional each in this kind of patchworkboy, right, the
35:48
Speaker 1: kind of I think she describes it as like, you know,
35:50
Speaker 1: some of the edges line up neatly, others are kind
35:52
Speaker 1: of afraid and they don't quite connect. You know, some
35:54
Speaker 1: disciplines really do kind of fit together with each other
35:57
Speaker 1: in a nice way, and other ones that's a bit
35:59
Speaker 1: more complicated. But we seem to get away with doing
36:01
Speaker 1: things like that. So there's kind of one question which
36:04
Speaker 1: is like, how can we do that if really everything
36:09
Speaker 1: is made up of whatever the most fundamental stuff is
36:12
Speaker 1: why did we get away with ignoring those details? Which
36:15
Speaker 1: is kind of the question that we started with um.
36:17
Speaker 1: And then the question on the kind of other side
36:21
Speaker 1: is if you think that all these patches don't line up,
36:24
Speaker 1: they're not unified, then how come we sometimes have processes
36:28
Speaker 1: like kind of you can think of like a causal
36:30
Speaker 1: process is leaping across patches. And when we have, for instance,
36:33
Speaker 1: m R I scans for the detection of disease, for instance,
36:36
Speaker 1: that seems like a case where we can't say or
36:39
Speaker 1: biology is just about something like totally different from physics,
36:42
Speaker 1: Because if that were the case, why would physics be
36:44
Speaker 1: so useful in understanding things in biology? So I kind
36:48
Speaker 1: of see the patchwork view as giving you an easy
36:51
Speaker 1: answer to the first problem. Why is that all these
36:54
Speaker 1: different things at different levels, Well, there's just different things
36:57
Speaker 1: going on at different levels. There isn't this kind of
37:00
Speaker 1: unified picture. So it kind of gives you an easy
37:02
Speaker 1: answer to that question. But then you have a hard answer,
37:06
Speaker 1: which is, well, if these patches are kind of insulated
37:10
Speaker 1: from each other in this different way, why is it
37:13
Speaker 1: that there's these kind of it looks like kind of
37:15
Speaker 1: causal processes going between them, or kind of threads running
37:18
Speaker 1: through different sciences. So I think that's part of the motivation.
37:23
Speaker 1: But another key part of Cartwright's picture is that she
37:27
Speaker 1: has a I think it was the book before the
37:28
Speaker 1: daff Wled World, a book with the title how the
37:32
Speaker 1: Laws of Physics Lie clickbaid, clickbaid. It's from the eighties,
37:36
Speaker 1: but definitely you know the original philosophy physics clickbait where
37:40
Speaker 1: she argues that you know, our laws are so abstract
37:44
Speaker 1: and they apply in such tightly controlled situations and the
37:47
Speaker 1: lab that we're used to kind of screening off the
37:50
Speaker 1: kind of noise from the environment, but really kind of
37:53
Speaker 1: out in the wild. The laws is kind of a
37:55
Speaker 1: lawless land, you know, the laws that we're used to having,
37:59
Speaker 1: we have no have good reason for thinking that they
38:01
Speaker 1: would carry across, which is a view I find hard
38:04
Speaker 1: to stomach. And like you, I like the idea of
38:06
Speaker 1: there being kind of the different things happening at different scales,
38:10
Speaker 1: but I still like thinking that it's kind of all
38:12
Speaker 1: connected in there's these kind of links between them. Things
38:16
Speaker 1: emerge out of other things, And I'm they're fan of
38:19
Speaker 1: the more emergentist type view than the patch Bork view,
38:22
Speaker 1: but that's that's the motivation. I think. Well, I'm sort
38:24
Speaker 1: of shocked that you describe the picture of there are
38:27
Speaker 1: just different rules for different situations. It's sort of like
38:30
Speaker 1: the easy answer, because that like rocks me to the core.
38:33
Speaker 1: I have a hard time understanding, like with then what
38:35
Speaker 1: is the universe right? Like how does it decide when
38:38
Speaker 1: to use one set of laws and another set of laws?
38:41
Speaker 1: In carent writes books, she has this quote which when
38:43
Speaker 1: I've read this, I'd like dropped the book. I couldn't
38:45
Speaker 1: believe it. She says laws of nature are limited in
38:48
Speaker 1: their range and regions that seem to overlap. There may
38:51
Speaker 1: be no rules at all for composing the separate effects,
38:55
Speaker 1: and some situations may not be subject to law at all.
39:00
Speaker 1: It happens happens by hap, which is like, is the
39:03
Speaker 1: universe whimsical? Is it just like making stuff up as
39:06
Speaker 1: it goes along? I mean, that's certainly not my experience
39:09
Speaker 1: of the universe and the experience of experimental physics for
39:12
Speaker 1: hundreds of years. Is this sort of like a an
39:15
Speaker 1: exercise and skepticism by Cartwright? Like, how do we really
39:18
Speaker 1: know that the laws that we isolate in the laboratory
39:22
Speaker 1: also apply out on the wind blown streets? Or do
39:25
Speaker 1: you think is really a coherent philosophical position and one
39:28
Speaker 1: that's revealing our blinders? Are you know, the assumptions we've
39:32
Speaker 1: been making about the universe because of the way our
39:35
Speaker 1: minds work. It's an interesting question because I think that
39:38
Speaker 1: I kind of have the same gut feeling as you
39:40
Speaker 1: in that when you think about describing a bigger and
39:43
Speaker 1: bigger system, there's no point where you're told, no, don't
39:46
Speaker 1: take the tensive product of those two systems together. The
39:48
Speaker 1: shortening equation, it will stop working. So it doesn't seem
39:51
Speaker 1: to really go with what our experience of doing physics
39:54
Speaker 1: is like. But Cartwright is very sensitive, I think, to
39:58
Speaker 1: the kind of details of the practice of physics in
40:01
Speaker 1: a way that sometimes philosophers have just assumed, well, there'll
40:05
Speaker 1: be a theory that applies to everything, and they've sort
40:07
Speaker 1: of just taken it as this kind of brute fact
40:09
Speaker 1: about the way the world is. And I guess I
40:12
Speaker 1: see her as sort of like poking at that assumption
40:14
Speaker 1: and saying, well, how well justified is that? I think that, Yeah,
40:19
Speaker 1: my my hunch is that I think that we can
40:22
Speaker 1: say that it's a world just assumption and that it
40:25
Speaker 1: hasn't not worked so far. But equally, I guess I
40:29
Speaker 1: think her emphasis on just how tightly controlled certain experimental
40:34
Speaker 1: contexts are and being careful about kind of exporting that
40:38
Speaker 1: to other cases, I think it is an important thing,
40:41
Speaker 1: And I think at the beginning of her book she
40:42
Speaker 1: has this kind of way of casting what she's doing
40:45
Speaker 1: is a slightly different approach. So she says there's kind
40:50
Speaker 1: of two enterprises that science is involved in representing the
40:54
Speaker 1: way the world is, and then intervening on the world,
40:58
Speaker 1: and obviously others answers, like medical sciences obviously really interested
41:03
Speaker 1: in the intervening parts in medicine. Sometimes we know exactly
41:06
Speaker 1: what to do to help something, we don't necessarily know
41:08
Speaker 1: the mechanisms behind it that mean that that works, but
41:11
Speaker 1: we know how to intervene on the world sometimes at least.
41:14
Speaker 1: And she kind of puts herself in the camp of saying,
41:18
Speaker 1: I'm not as interested in the project of representing the world.
41:22
Speaker 1: I'm more interested in the project of intervening on the world.
41:25
Speaker 1: But she worries that the by not thinking about how
41:29
Speaker 1: we want to intervene on the world, the fact that
41:31
Speaker 1: that's what she's interested in. She has these kind of
41:33
Speaker 1: lovely pictures where she shows like that maybe you remember
41:36
Speaker 1: them from the beginning of the book, where it's like
41:38
Speaker 1: kind of like the messy house and then the tidy house,
41:40
Speaker 1: and she kind of says, we need to understand that
41:42
Speaker 1: the world is kind of messier than we think that
41:44
Speaker 1: it sometimes is, because then when we want to intervene
41:47
Speaker 1: on the world, we're going to be more successful in
41:49
Speaker 1: doing so because we've got a kind of better idea
41:52
Speaker 1: of what things are like. And so I think that's
41:54
Speaker 1: part of her motivation. But I think at the end
41:56
Speaker 1: of the day, I still come down on there. I
41:59
Speaker 1: think that it is much more connected. I don't think
42:02
Speaker 1: there's these kind of lawless lands between the patterns of laws.
42:06
Speaker 1: So yeah, I think I'm with you on that one. Well.
42:09
Speaker 1: One of her examples that I found really interesting was
42:12
Speaker 1: thinking about how to apply physics in the real world. Right,
42:15
Speaker 1: And so you take a coin, for example, and it drops,
42:18
Speaker 1: and you can say, well, coin is mostly described by
42:21
Speaker 1: F equals I may, it's mostly just dominated by gravity.
42:23
Speaker 1: Is fairly simple situation, And I guess this is the
42:25
Speaker 1: kind of thing she would say, is essentially screened off
42:28
Speaker 1: from the other details. But if instead of dropping a coin,
42:31
Speaker 1: you drop like a bank note and it's a windy day,
42:34
Speaker 1: then could you possibly ever describe the motion of that
42:36
Speaker 1: bank note using ff equals I may it's like this
42:38
Speaker 1: bit of wind, in that bit of wind, and the
42:40
Speaker 1: other bit of wind, and in that situation, like you know,
42:42
Speaker 1: one might ask, is it just too complicated and it's
42:45
Speaker 1: a lot of different sums, or is it really not
42:48
Speaker 1: described by any physics at all? And I guess her
42:51
Speaker 1: point is you can't ever really tell, right, you know,
42:55
Speaker 1: in the absence of a model that yields accurate predictions,
42:57
Speaker 1: we have no grounds for thinking that any particular law applies.
43:01
Speaker 1: Is another quote from her book, And I guess I
43:03
Speaker 1: find that useful as like a warning, like keep in mind,
43:06
Speaker 1: you don't really know how to solve most of the
43:08
Speaker 1: situations in the world outside of your well controlled experiments.
43:11
Speaker 1: But you know, we also have this history and physics
43:14
Speaker 1: of success. You know, we build the transistors in the laboratory,
43:18
Speaker 1: and then they fly airplanes that mostly don't crash right
43:21
Speaker 1: out in the complicated world. And in the history of
43:23
Speaker 1: physics we see this like unification, where electricity and magnetism
43:28
Speaker 1: come together, we add the weak force. Maybe in the
43:30
Speaker 1: future we'll be able to combine that with the strong
43:32
Speaker 1: force and gravity. It seems to me like argument of
43:35
Speaker 1: history at least is against her. Is that the view
43:38
Speaker 1: mostly in mainstream philosophy, or is there a camp of
43:40
Speaker 1: people who are continuing this work. So there are a
43:42
Speaker 1: camp of people that are continuing in the kind of
43:45
Speaker 1: car right line of thinking. I think you're completely right
43:47
Speaker 1: to kind of characterize it as a kind of kind
43:50
Speaker 1: of epistemic humility warning, you know, like you don't have
43:53
Speaker 1: a warrant to say that it's definitely gonna work. So
43:57
Speaker 1: I think that's a really important part of the project
44:00
Speaker 1: xt And but then on the other hands, you kind
44:01
Speaker 1: of a tone in the other direction, which is, well,
44:04
Speaker 1: we've we've not yet found a situation where that doesn't
44:07
Speaker 1: you know, for for objects of the size of a banknote,
44:10
Speaker 1: just summing up all the forces on it doesn't work
44:13
Speaker 1: as a way of predicting what happens. Okay, maybe we
44:16
Speaker 1: won't ever be able to do it in the case
44:17
Speaker 1: of the banknotes. It's just too complicate it. But I
44:20
Speaker 1: guess that's that's the kind of warrant that we have,
44:23
Speaker 1: kind of holding onto the idea that maybe we can't
44:25
Speaker 1: predict it, but it is like predictable in principle. Maybe
44:28
Speaker 1: aliens with their supercomputers have totally solved that problem, all right.
44:32
Speaker 1: So then my last question for you is, aside from
44:34
Speaker 1: meeting aliens with super advanced answers to questions in physics
44:38
Speaker 1: and philosophy, what do you think are prospects from making
44:41
Speaker 1: progress on these questions. I mean, we can't ever really
44:44
Speaker 1: understand how a banknote flutters in the wind. Are we
44:47
Speaker 1: going to be able to figure out if there is
44:49
Speaker 1: a grand, unified theory out there for us to work towards,
44:53
Speaker 1: or if the universe is really just a patchwork. How
44:55
Speaker 1: do we understand these things? Our philosopher is gonna be
44:58
Speaker 1: arguing about this for a thousand years, or we actually
45:00
Speaker 1: to figure this out. I guess we don't. I don't know, really,
45:02
Speaker 1: because I think that it comes back to like whether
45:05
Speaker 1: we think that even if it's going to be a patchwork,
45:08
Speaker 1: even if you know, sometimes people say it's kind of
45:11
Speaker 1: turtles all the way down. You know, we could just
45:13
Speaker 1: keep smashing particles together and finding new particles forever and ever.
45:18
Speaker 1: You know, you make that sound like a bad thing,
45:19
Speaker 1: That sounds like job security for me. In that case,
45:23
Speaker 1: then we would expect kind of you know, that there
45:25
Speaker 1: isn't a fundamental level. That would be a bit like
45:27
Speaker 1: saying perhaps I'm tempted to think that even if we
45:31
Speaker 1: that could be the case, or it could be a patchwork,
45:33
Speaker 1: we still the best methodology that we would have is
45:37
Speaker 1: to keep looking for kind of more fundamental theories and
45:41
Speaker 1: I think working out how everything kind of patches together,
45:45
Speaker 1: you know, is it going to be that we always
45:47
Speaker 1: have a kind of effective theory that works within a
45:50
Speaker 1: certain domain, and then a more fundamental theory underlying that.
45:54
Speaker 1: Um it would be really interest I mean, there's, particularly
45:57
Speaker 1: for the case of things like black holes as fast
46:00
Speaker 1: anating questions of how things will turn out. So I'm
46:03
Speaker 1: tempted to think whilst at the moment I placed my
46:05
Speaker 1: bets on it not being a patchwork in the sense
46:07
Speaker 1: of there's lawless kind of lands between the patches, will
46:11
Speaker 1: be interesting to find out. Well. I like the way
46:14
Speaker 1: you describe the arc of science there were like discovering.
46:16
Speaker 1: We're letting the universe tell us its story, and I
46:20
Speaker 1: just hope that we're not too biased by the way
46:22
Speaker 1: we're listening to the story, to the story we want
46:24
Speaker 1: to hear that we are able to absorb, you know,
46:27
Speaker 1: the shocking truth of the universe, because it sometimes takes us,
46:30
Speaker 1: you know, decades or centuries to really come to grips
46:33
Speaker 1: with what the experiments are telling us. It's it's hard
46:36
Speaker 1: to deviate sometimes from sort of like the historical path
46:39
Speaker 1: of science. And you know, I'm metor I can pronounce
46:42
Speaker 1: that phrase epistemical humility. We should try to maintain that
46:45
Speaker 1: as much as possible, but also make progress on the
46:47
Speaker 1: science at the same time. Well, thanks very much for
46:49
Speaker 1: joining us today on the podcast and for talking about
46:52
Speaker 1: these really important but also very abstract questions about the
46:55
Speaker 1: way we do science. Thanks for having me, Thanks everyone
46:58
Speaker 1: for listening. Tune in next time. Yeah, thanks for listening,
47:08
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
47:11
Speaker 1: a production of I Heart Radio. For more podcast from
47:14
Speaker 1: my heart Radio, visit the i heart Radio app, Apple Podcasts,
47:18
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