Latest / Daniel and Kelly’s Extraordinary Universe / Could there be more than one theory of everything?

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Could there be more than one theory of everything? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: As I sit down to record today's episode, the beams
• 0:12
  Speaker 1: of the Large Hadron Collider are powering up. Today will
• 0:15
  Speaker 1: be the first day of collisions in twenty twenty three,
• 0:18
  Speaker 1: after a long shutdown to rebuild and upgrade our equipment.
• 0:22
  Speaker 1: We hope to see some new particles, to discover some
• 0:25
  Speaker 1: new forces, to reveal new truths about the nature of
• 0:29
  Speaker 1: space and time and matter and energy. But what if
• 0:33
  Speaker 1: everything we're learning is not really the truth? What if
• 0:37
  Speaker 1: it's just a story we tell ourselves. What if there
• 0:40
  Speaker 1: are other possible stories that could also explain what we
• 0:44
  Speaker 1: see in our experiments? How would we ever even know?
• 1:04
  Speaker 2: Hi?
• 1:04
  Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
• 1:07
  Speaker 1: UC Irvine and something of an amateur philosopher of science.
• 1:12
  Speaker 1: Welcome to the podcast Daniel and Jorge Explain the Universe,
• 1:16
  Speaker 1: a production of iHeartRadio in which normally we dig into
• 1:19
  Speaker 1: questions about how the universe works, what's going on the
• 1:22
  Speaker 1: tiny quantum level, what's at the heart of black holes?
• 1:26
  Speaker 1: How does everything work, and how does it weave itself
• 1:28
  Speaker 1: together to make the incredible, beautiful, mysterious reality that we experience.
• 1:35
  Speaker 1: My normal co host and friend Jorge can't be with
• 1:37
  Speaker 1: us today. So I'm going to take the opportunity to
• 1:39
  Speaker 1: do something a tiny bit different and do a bit
• 1:41
  Speaker 1: of a dive into some questions in the philosophy of science,
• 1:45
  Speaker 1: because I really want to understand not just what's happening
• 1:48
  Speaker 1: in the universe, but why it's happening. What are we
• 1:52
  Speaker 1: really learning about the universe when we do particle physics,
• 1:56
  Speaker 1: or when we do any kind of science. Let's make
• 1:58
  Speaker 1: it concrete. Example, when we build the Large Hadron Collider,
• 2:02
  Speaker 1: we did it because we wanted to uncover how the
• 2:05
  Speaker 1: universe works. We want to know answers to questions like
• 2:09
  Speaker 1: is space filled with quantum fields that buzz and wiggle
• 2:12
  Speaker 1: to make particles? How many of those fields are there?
• 2:15
  Speaker 1: And what are the rules of their interactions? Is there
• 2:18
  Speaker 1: a field for a dark matter? Are there other fields
• 2:21
  Speaker 1: that we never even imagined? Are all of the fields
• 2:23
  Speaker 1: really part of one superfield in a way we haven't
• 2:27
  Speaker 1: ever thought of. These are the kind of questions we
• 2:30
  Speaker 1: think about, and the language of physics these days is
• 2:32
  Speaker 1: always the language of these fields. We imagine that space
• 2:36
  Speaker 1: is filled with these quantum fields, and we've been very
• 2:38
  Speaker 1: successful at using these quantum fields to describe everything we've
• 2:42
  Speaker 1: seen so far in particle physics. But there's always a butt.
• 2:47
  Speaker 1: But nobody has ever actually seen a field. What we
• 2:51
  Speaker 1: see in the collider are sprays of particles that are
• 2:54
  Speaker 1: the debris of collisions. The collision itself happens too quickly
• 2:57
  Speaker 1: and is too small to actually look at, and even
• 3:01
  Speaker 1: the particles that we do see don't prove that fields
• 3:04
  Speaker 1: themselves actually exists. When a particle bends in a magnetic field,
• 3:09
  Speaker 1: what we see is the particle bending, not the field itself.
• 3:15
  Speaker 1: There's always this part of the story where the field
• 3:18
  Speaker 1: hides behind a curtain. It's an unobservable part of our
• 3:22
  Speaker 1: science that helps explain what we do see, but is
• 3:25
  Speaker 1: never itself directly observable, And that unobservable part, in my opinion,
• 3:30
  Speaker 1: is really important. It's the juicy bit. It's the real
• 3:33
  Speaker 1: explanation for what's happening out there in the universe. It's
• 3:37
  Speaker 1: how we think about physics. We hope, or we wonder,
• 3:40
  Speaker 1: at least, whether the universe is also doing its calculations
• 3:44
  Speaker 1: to decide whether a particle goes this way or that
• 3:46
  Speaker 1: way using fields. I mean, are those fields really out
• 3:50
  Speaker 1: there pushing and pulling on stuff when we're not looking.
• 3:53
  Speaker 1: Or are those fields just our description? Are they part
• 3:57
  Speaker 1: of the story we are telling ourselves about the particles?
• 4:02
  Speaker 1: Are those fields just part of our minds? Are they
• 4:05
  Speaker 1: really deep elements of the universe itself? One really fun
• 4:08
  Speaker 1: way to probe this famous question is to wonder, could
• 4:12
  Speaker 1: there be another explanation that's just as good? Is there
• 4:15
  Speaker 1: another way to describe the universe that doesn't need fields,
• 4:19
  Speaker 1: that tells a different story about what's happening out there
• 4:22
  Speaker 1: in the universe. So today on the podcast, we'll be
• 4:26
  Speaker 1: asking the question could there be more than one theory
• 4:34
  Speaker 1: of everything? To help me dive into these thorny questions
• 4:37
  Speaker 1: of philosophy, I've invited a guest expert, a philosopher of
• 4:41
  Speaker 1: science who specializes in this very topic. Okay, so then
• 4:50
  Speaker 1: it's my great pleasure to welcome to the podcast Professor
• 4:54
  Speaker 1: Thomas William Barrett. He's professor at the University of California
• 4:57
  Speaker 1: at Santa Barbara in the Department of f Philosophy, and
• 5:01
  Speaker 1: he works mostly on philosophy of science and logic, and
• 5:04
  Speaker 1: on his homepage he has a picture of himself as
• 5:07
  Speaker 1: an infant in front of a Philosophy Building. Welcome to
• 5:09
  Speaker 1: the podcast.
• 5:10
  Speaker 2: Thanks very much, thanks for having me. It's a pleasure
• 5:12
  Speaker 2: to be here.
• 5:13
  Speaker 1: So does that picture mean that you've been doing philosophy
• 5:16
  Speaker 1: since you were a little baby?
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  Speaker 2: In a sense, I guess. I mean everyone tries not to,
• 5:21
  Speaker 2: but it's, you know, unavoidable. We've all been doing philosophy
• 5:25
  Speaker 2: since we've been little babies. Well.
• 5:27
  Speaker 1: I know people like to say that babies are scientists
• 5:30
  Speaker 1: because they're all exploring the world and trying to figure
• 5:32
  Speaker 1: out how things work. But I'd be fascinating if babies
• 5:34
  Speaker 1: were also philosophers of science at the same time.
• 5:37
  Speaker 2: Yeah, I mean, honestly, in that picture, if you look closely,
• 5:40
  Speaker 2: I have my little truck in my hand. At the time,
• 5:43
  Speaker 2: I was probably more interested in the truck than in philosophy.
• 5:47
  Speaker 2: Some days now feel the same.
• 5:49
  Speaker 1: All right, Well, before we dig into the topic of
• 5:51
  Speaker 1: the day, we'd like to get to know you a
• 5:53
  Speaker 1: little bit about where you stand in the sort of
• 5:55
  Speaker 1: big questions of philosophy. So let me ask you what
• 5:58
  Speaker 1: I think is maybe the most important question in philosophy
• 6:00
  Speaker 1: of science, which is, in your opinion, does a star
• 6:04
  Speaker 1: Trek transporter actually move your molecules from one place to
• 6:08
  Speaker 1: another or does it kill you and reassemble you somewhere else?
• 6:12
  Speaker 1: Is it a murder machine or a teleportation device?
• 6:14
  Speaker 2: I don't know, man, your guess is as good as mine.
• 6:16
  Speaker 2: I'm more of a Star Wars guy than a Star
• 6:20
  Speaker 2: Trek guy. I honestly, I think I've only seen like
• 6:24
  Speaker 2: maybe one or two Star Trek episodes. I saw one
• 6:27
  Speaker 2: of the movies when I was a kid, But I'm
• 6:30
  Speaker 2: not a Star Trek guy. It's been Star Wars all
• 6:33
  Speaker 2: the day.
• 6:34
  Speaker 1: All right, Well, then, what's the deepest question in philosophy
• 6:37
  Speaker 1: raised by Star Wars? Is it whether the force actually
• 6:41
  Speaker 1: has a scientific explanation or if it's just magic?
• 6:45
  Speaker 2: Yeah? Science versus religion questions? Yeah, that's good stuff, Way
• 6:51
  Speaker 2: above my pay grade though.
• 6:54
  Speaker 1: All right, Well, we'll try to talk about something a
• 6:57
  Speaker 1: little bit easier here on the podcast today. What I
• 6:59
  Speaker 1: want to talk about drills into the question of, like
• 7:02
  Speaker 1: what are we learning when we are building our theories
• 7:05
  Speaker 1: of the universe. You know, I'm a particle physicist, and
• 7:08
  Speaker 1: here in our department we try to or we imagine
• 7:11
  Speaker 1: that we're trying to build a description of what's happening
• 7:14
  Speaker 1: in the universe that when we draw a little finement diagrams.
• 7:17
  Speaker 1: We're describing what we think the universe is actually doing
• 7:20
  Speaker 1: when electrons fly through the universe. But you know, most
• 7:24
  Speaker 1: people who think about science, who are in philosophers naturally
• 7:28
  Speaker 1: imagine that that's what's happening, you know. They think that
• 7:31
  Speaker 1: what we see is real, that the electron is real,
• 7:33
  Speaker 1: not just something that we use to do calculations. If
• 7:36
  Speaker 1: you tell most people out there, like, look, we don't
• 7:38
  Speaker 1: know if an electron is actually real, or if the
• 7:41
  Speaker 1: theories that we use to describe them are just things
• 7:43
  Speaker 1: in our head. In your view, what's the sort of
• 7:45
  Speaker 1: easy way to understand or to approach the question of like,
• 7:48
  Speaker 1: what are we learning? Does it represent what's actually out
• 7:51
  Speaker 1: there or just things that we are imagining, you know,
• 7:53
  Speaker 1: without going full matrix sort of theory on you, what's
• 7:57
  Speaker 1: an easy way to access this question?
• 7:58
  Speaker 2: In your view, the question is something like the extent
• 8:01
  Speaker 2: to which our theories should be taken as literally true
• 8:07
  Speaker 2: in their description of the world, and whether our evidence
• 8:11
  Speaker 2: for you know, taking our theories is literally true, whether
• 8:15
  Speaker 2: the success of our theories gives us good reason to
• 8:19
  Speaker 2: think that they are true in all their aspects, not
• 8:23
  Speaker 2: just like the stuff that they say about what we
• 8:26
  Speaker 2: can see, but the stuff that they say about what
• 8:28
  Speaker 2: we can't see. So some folks in philosophy think that
• 8:33
  Speaker 2: the empirical success of our theories, and they are like,
• 8:39
  Speaker 2: incredibly empirically successful, our best theories, gives us good reason
• 8:43
  Speaker 2: to just take them literally as true in all their aspects.
• 8:51
  Speaker 2: Other folks in philosophy think that the proper conclusion is
• 8:55
  Speaker 2: something more modest, like, you know, it isn't an anti
• 8:58
  Speaker 2: science stance or anything, but sugg just the empirical success
• 9:01
  Speaker 2: of our theories doesn't tell us that we should take
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  Speaker 2: them as literally true both in describing stuff that's observable
• 9:08
  Speaker 2: and in describing stuff that's not observable. It just tells
• 9:13
  Speaker 2: you that theories are successful, and they were designed in
• 9:15
  Speaker 2: such a way to be successful. But are they uncovering
• 9:19
  Speaker 2: deep truths about the unobservable structure of the universe? Maybe not.
• 9:25
  Speaker 1: Yeah, that's a great way to think about it, the
• 9:26
  Speaker 1: observable versus the unobservable. And I imagine people might be thinking, like,
• 9:31
  Speaker 1: what do you mean unobservable? We do experiments, we see stuff,
• 9:34
  Speaker 1: we know electrons are out there. What's a good way
• 9:36
  Speaker 1: to think about the unobservable sort of side of science.
• 9:40
  Speaker 1: One thing I sometimes imagine is like the fields themselves.
• 9:44
  Speaker 1: We talk about on this podcast a lot how space
• 9:46
  Speaker 1: is filled with fields, and sometimes those fields ripple to
• 9:49
  Speaker 1: make particles, or they ripple to make photons, et cetera.
• 9:52
  Speaker 1: But those fields aren't something we ever directly interact with. Right,
• 9:56
  Speaker 1: Is that an example of something that's unobservable but a
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  Speaker 1: part of our theory.
• 9:59
  Speaker 2: Yeah, that's right. So, like another good example comes from
• 10:03
  Speaker 2: the history of classical space time theories. So you can
• 10:08
  Speaker 2: think about Newton's old theory of gravitation. So, according to
• 10:14
  Speaker 2: Newton's old theory of gravitation, space time is flat. So
• 10:19
  Speaker 2: like the arenea in which events take place is flat,
• 10:23
  Speaker 2: it doesn't have interesting geometrical features. And according to this theory,
• 10:27
  Speaker 2: gravity is best described as a force, So it's a
• 10:30
  Speaker 2: field on your flat space time. And Newton's old law
• 10:35
  Speaker 2: of universal gravitation then dictates how particles massive bodies will
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  Speaker 2: move around depending on what this force is at different
• 10:42
  Speaker 2: points in space time. It turns out that you can
• 10:45
  Speaker 2: do this theory. This was discovered by folks in the
• 10:48
  Speaker 2: early twentieth century. You can do Newton's theory, but on
• 10:51
  Speaker 2: a space time that's curved. So, in this alternative formulation
• 10:57
  Speaker 2: of Newtonian gravitation, space time is curved. Gravity manifests itself
• 11:02
  Speaker 2: and in terms of the curvature of space time rather
• 11:06
  Speaker 2: than force. And so now this raises an interesting question.
• 11:10
  Speaker 2: You can't observe you're not observing the structure of space time, right,
• 11:15
  Speaker 2: what you're observing is how stuff is moving around in
• 11:18
  Speaker 2: space time. And so now we have this question. It's
• 11:21
  Speaker 2: space time curved or is it flat? According to Newton's theory,
• 11:25
  Speaker 2: there are ways to do the theory according to which
• 11:27
  Speaker 2: it's curved, ways to do theory according to which it's flat.
• 11:30
  Speaker 2: They result in the same empirical prediction.
• 11:31
  Speaker 1: But way, But how does the curved space Newton's theory
• 11:34
  Speaker 1: different from Einsteini in general relativity.
• 11:37
  Speaker 2: It is the same basic concept as Einsteini in general relativity,
• 11:42
  Speaker 2: but it yields the same predictions as Newton's theory yields.
• 11:48
  Speaker 2: I see. So Einstein's theory and Newton's theory disagree about
• 11:51
  Speaker 2: like for example, the famous cases, they disagree about how
• 11:55
  Speaker 2: mercury would orbit the Sun. Right, this was the evidence
• 11:58
  Speaker 2: that led us to Einstein's theory was Newton's theory was
• 12:02
  Speaker 2: getting Mercury's orbit wrong. So the Newtonian gravitation theory set
• 12:09
  Speaker 2: on a curve space time, which folks will call newton
• 12:11
  Speaker 2: kartong theory, sometimes yields the same empirical predictions as Newton's theory,
• 12:17
  Speaker 2: not as Einstein's theory, but it agrees with Einstein's theory
• 12:20
  Speaker 2: on the status of the curvature of space time.
• 12:23
  Speaker 1: I see, Okay, So you're saying that you could have
• 12:26
  Speaker 1: two theories. Newton's original theory of gravity is a force
• 12:29
  Speaker 1: and this other weird variation where gravity comes from the
• 12:33
  Speaker 1: curvature of space time, but it gives the same predictions
• 12:36
  Speaker 1: as Newton's original theory rather than the predictions of Einstein's theory.
• 12:40
  Speaker 1: And so then you're saying, this's an unobserved part of
• 12:43
  Speaker 1: the universe, the actual predictions of how things are going
• 12:46
  Speaker 1: to move. And then there's the sort of behind the
• 12:48
  Speaker 1: scenes mechanism. Is it a force or is it the
• 12:50
  Speaker 1: curvature of space time? What's sort of happening behind the
• 12:52
  Speaker 1: scenes to make that happen. So you're saying, there we
• 12:55
  Speaker 1: have like two theories with different descriptions for what's unobserved.
• 12:58
  Speaker 2: That's right, There is different descriptions for what's un observed,
• 13:03
  Speaker 2: but the same exact description of observable stuff.
• 13:08
  Speaker 1: That's really interesting and that touches on the topic I
• 13:11
  Speaker 1: wanted to dig into today, which is this underdeterminism, this
• 13:14
  Speaker 1: concept in philosophy that we might never actually reveal what's
• 13:19
  Speaker 1: happening in the unobserved section of the universe, that there
• 13:23
  Speaker 1: might be multiple ways to describe what's sort of happening
• 13:26
  Speaker 1: behind the scenes that give the same exact empirical predictions
• 13:31
  Speaker 1: that you could never distinguish in experiment, but be described
• 13:34
  Speaker 1: by different ideas. And you know, in the example you
• 13:37
  Speaker 1: just described, we know that both of those are actually wrong, right,
• 13:39
  Speaker 1: Newton's theory of forces in Newton's theory of kurt space
• 13:42
  Speaker 1: are both give the same predictions, but they're wrong. But
• 13:44
  Speaker 1: let's imagine some other scenario where we have a theory
• 13:47
  Speaker 1: of quantum fields and some independent group of scientists have
• 13:51
  Speaker 1: been working for a thousand years and they have a
• 13:53
  Speaker 1: theory of quantum shmields or something, and they're you know,
• 13:56
  Speaker 1: fundamentally different. They're not conceptually the same, but they give
• 13:59
  Speaker 1: the same prediction. So I think it's fascinating to think about.
• 14:04
  Speaker 1: You know, is it possible to have two really different
• 14:07
  Speaker 1: descriptions of what's happening in the universe that predict the
• 14:09
  Speaker 1: same thing that we would observe. Is that the sort
• 14:12
  Speaker 1: of the fundamental question of underdeterminism and philosophy.
• 14:15
  Speaker 2: Yeah, that's exactly right, Like the underlying concept is simple
• 14:19
  Speaker 2: and will be familiar to all sorts of folks, Like
• 14:22
  Speaker 2: we find ourselves in situations just in our day to
• 14:26
  Speaker 2: day lives, where the body of evidence that we've gathered
• 14:30
  Speaker 2: doesn't help us adjudicate between two theories. So imagine like
• 14:36
  Speaker 2: you come home and I've been to the grocery store.
• 14:39
  Speaker 2: You're wondering what I bought at the grocery store. You
• 14:42
  Speaker 2: see the receipt sitting on the dining room table, and
• 14:45
  Speaker 2: you look at it, and all it says on the
• 14:46
  Speaker 2: receipt is that I spent eighteen bucks at the grocery store.
• 14:49
  Speaker 2: You know that apples they're like two dollars, oranges are
• 14:53
  Speaker 2: three dollars. And now you're faced with a kind of
• 14:57
  Speaker 2: underdetermination problem. You don't know how many apples I bought,
• 15:02
  Speaker 2: how many oranges I bought. The data gap doesn't help
• 15:04
  Speaker 2: me discriminate between the two theories. The data doesn't tell
• 15:09
  Speaker 2: you which one is correct, whether I bought six apples
• 15:13
  Speaker 2: or nine oranges or some combination. And that's exactly the
• 15:18
  Speaker 2: issue that the problem of underdetermination. That's exactly the issue
• 15:24
  Speaker 2: that the problem of underdetermination alleges we often face in
• 15:30
  Speaker 2: science where we have two theories and the data doesn't
• 15:36
  Speaker 2: help us decide which one is correct. The two theories
• 15:40
  Speaker 2: are compatible with precisely the same data, And so what
• 15:43
  Speaker 2: do we do in a case like that? What do
• 15:45
  Speaker 2: we believe right?
• 15:46
  Speaker 1: And in that scenario it makes me feel uncomfortable that
• 15:50
  Speaker 1: I'm being so nosy about your grocery store purchases. But
• 15:53
  Speaker 1: you know, in the case of the universe, I don't
• 15:54
  Speaker 1: think the universe deserves any privacy. I think, you know,
• 15:57
  Speaker 1: we are entitled to peak behind the curtain as much
• 16:00
  Speaker 1: as we can and trying to figure out what's going
• 16:03
  Speaker 1: on and what the universe bought at the grocery store.
• 16:05
  Speaker 1: But what is the motivation for this? Is this just
• 16:08
  Speaker 1: like you know, philosophical meandering, Oh what if? What could
• 16:11
  Speaker 1: it be possible? Some sort of deep skepticism that maybe
• 16:14
  Speaker 1: will never figure things out, or do we have like
• 16:17
  Speaker 1: any sort of concrete examples of scenarios where we really
• 16:21
  Speaker 1: had two excellent theories that gave exactly the same predictions
• 16:26
  Speaker 1: but had different scenarios behind the scenes.
• 16:28
  Speaker 2: Yeah, so let me give a couple of examples. The
• 16:31
  Speaker 2: example we were discussing earlier of Newton's standard theory of gravity,
• 16:36
  Speaker 2: in which gravity is a force versus this geometrized version
• 16:41
  Speaker 2: of theorem gravity. That's a famous historical case. Of course,
• 16:47
  Speaker 2: as you say, like, we know that neither of those
• 16:50
  Speaker 2: theories is correct. They make bad predictions, but the existence
• 16:58
  Speaker 2: of an example like this should give one pause. It
• 17:02
  Speaker 2: gives us read think that maybe the same thing can
• 17:05
  Speaker 2: happen with our current best theories. So there are other
• 17:09
  Speaker 2: examples from the history of physics. Another famous one is
• 17:13
  Speaker 2: the case of Hamiltonian and Lagrangian mechanics. Okay, suppose you
• 17:18
  Speaker 2: formulate your theory of classical mechanics. Newton's old theory how
• 17:23
  Speaker 2: stuff will move around in space by taking positions and
• 17:28
  Speaker 2: velocities is fundamental. Okay, So you think that we should
• 17:33
  Speaker 2: specify the energy conditions of a system by laying down
• 17:37
  Speaker 2: something that you call a Lagrangian So kind of a
• 17:42
  Speaker 2: function on possible configurations of positions and velocities that dictates
• 17:47
  Speaker 2: how active or lively these configurations are. Hell me how
• 17:54
  Speaker 2: these properties of the system, the positions and velocities of
• 17:58
  Speaker 2: particles in your system, will evolve over time by laying
• 18:01
  Speaker 2: down a set of equations that you call the Euler
• 18:04
  Speaker 2: Legronge equations. Okay, so call your theory Lagrangian mechanics. On
• 18:09
  Speaker 2: the other hand, for whatever reason, don't like velocity, Okay,
• 18:15
  Speaker 2: I find momentum to be much more elegant. You know,
• 18:17
  Speaker 2: it's conserved, and so I formulate my theory by specifying
• 18:22
  Speaker 2: energy conditions to the system laying down a Hamiltonian. I
• 18:26
  Speaker 2: take positions in momentum as the fundamental properties that a
• 18:32
  Speaker 2: system has, and I can tell you how the system
• 18:37
  Speaker 2: will evolve over time by laying down a different set
• 18:40
  Speaker 2: of equations. So call these Hamilton's equations, and they take
• 18:43
  Speaker 2: in the Hamiltonian of the system. So the Hamiltonian describes
• 18:47
  Speaker 2: something like the total energy of the system, rather than
• 18:50
  Speaker 2: its activity or liveliness, just total energy. I call my
• 18:53
  Speaker 2: theory Hamiltonian mechanics. So it turns out that our theories
• 18:57
  Speaker 2: are empirically equivalent. So what do we mean by that?
• 19:01
  Speaker 2: We mean, there's no possible evidence that is compatible with
• 19:07
  Speaker 2: my theory but incompatible with yours, or vice versa.
• 19:11
  Speaker 1: So first, like some set of balls or squirrels on
• 19:14
  Speaker 1: roller coasters, they always give the same predictions for what's
• 19:17
  Speaker 1: going to happen exactly.
• 19:18
  Speaker 2: Your theory gives the same prediction as my theory. But
• 19:21
  Speaker 2: it seems like we've done things differently, right, You care
• 19:25
  Speaker 2: about positions and velocities. I care about positions and momentums.
• 19:30
  Speaker 2: The laws of nature, one might say, according to your theory,
• 19:34
  Speaker 2: or different than the ones according to my theory, Like
• 19:37
  Speaker 2: we laid down different equations when we were saying how
• 19:42
  Speaker 2: the stuff was going to behave And so one might
• 19:45
  Speaker 2: think that we have a choice to be made here
• 19:48
  Speaker 2: between these two theories. But the evidence won't make the
• 19:52
  Speaker 2: choice for us. So that's another example of a possible
• 19:59
  Speaker 2: case of under termination, where two theories compatible with the
• 20:02
  Speaker 2: same body of evidence, but it seems like we might
• 20:05
  Speaker 2: have a choice to make between them. In cases like this,
• 20:09
  Speaker 2: the standard conclusion to draw is kind of a skeptical thing.
• 20:16
  Speaker 2: The things about which these two theories disagree. We now
• 20:21
  Speaker 2: don't have answers to these questions unless we can decide
• 20:24
  Speaker 2: which one of the two theories is correct, and how
• 20:27
  Speaker 2: do we make that decision. The evidence isn't going to
• 20:29
  Speaker 2: make the decision for us, so we have to come
• 20:33
  Speaker 2: to a decision by some other means.
• 20:35
  Speaker 1: So we have two different sets of equations that give
• 20:38
  Speaker 1: the same predictions for what happens to squirrels on roller
• 20:41
  Speaker 1: coasters or billiar tables and these kinds of things, and
• 20:43
  Speaker 1: you're saying that they really are different in some way,
• 20:46
  Speaker 1: And because they always give the same predictions, there's no
• 20:49
  Speaker 1: way to do this sort of famous scientific test of say, well,
• 20:52
  Speaker 1: let's do an experiment and figure out the different hypotheses
• 20:55
  Speaker 1: and the different predictions, because they're always the same. But
• 20:58
  Speaker 1: if they're always the same, how do we know that
• 21:00
  Speaker 1: they really are different theories? I mean, I can take
• 21:03
  Speaker 1: any arbitrary theory and say I'm going to multiply everything
• 21:05
  Speaker 1: by two, and then at the end I'm going to
• 21:06
  Speaker 1: divide by two, and superficially, the equations might look a
• 21:09
  Speaker 1: little bit different, but it gives exactly the same predictions.
• 21:12
  Speaker 1: But not for an interesting reason, not because I'm really
• 21:15
  Speaker 1: saying this different stuff happening behind the scenes of the universe.
• 21:18
  Speaker 1: So in the case of Hamiltonian versus Lagrangeen mechanics, or
• 21:21
  Speaker 1: really in the case of fields versus Shmields, or any comparison,
• 21:25
  Speaker 1: what does it mean to say that they're different? How
• 21:27
  Speaker 1: do we know that they're different? Or is there some
• 21:29
  Speaker 1: standard we apply to say, like, this theory is telling
• 21:32
  Speaker 1: a different story about what's happening in the universe than
• 21:35
  Speaker 1: that theory. How do we do that?
• 21:36
  Speaker 2: Yeah, good question. So, like the suggestion is something like,
• 21:39
  Speaker 2: maybe in some of these worrying cases of underdetermination, you
• 21:44
  Speaker 2: don't actually have two genuine rivals. They're the same theory,
• 21:49
  Speaker 2: just presented to you in different guises, And so like
• 21:53
  Speaker 2: you don't have a real choice to make. It's the
• 21:55
  Speaker 2: choice between one theory and itself, just presented to you differently.
• 22:00
  Speaker 2: So maybe let me tell a story. The most famous
• 22:04
  Speaker 2: case of this happened in the early years of quantum mechanics. Okay,
• 22:09
  Speaker 2: so in brief, Heisenberg had his matrix mechanics, Schrodinger had
• 22:15
  Speaker 2: his wave mechanics, and these guys like did not vibe
• 22:22
  Speaker 2: on the base of it. Their theories seemed incompatible. So
• 22:27
  Speaker 2: they made the same predictions, but they used like radically
• 22:30
  Speaker 2: different mathematical apparatus. To do so. So Schrodinger at one
• 22:35
  Speaker 2: point equipped that Heisenberg's theory lacked visualizability, into which Heisenberg
• 22:41
  Speaker 2: shot back, I quote what Schrodinger writes about visualizability as crap.
• 22:50
  Speaker 2: We eventually, like, we realized that there's a way to
• 22:52
  Speaker 2: translate between the Heisenberg picture and the Schrodinger picture and
• 22:57
  Speaker 2: vice versa. And so there's a sense in which there
• 23:01
  Speaker 2: are two ways of doing quantum mechanics were not that different.
• 23:04
  Speaker 2: After all. The disputes between the two theories, like the
• 23:08
  Speaker 2: stuff that they disagreed about is just verbal. It was
• 23:13
  Speaker 2: like we were having a verbal dispute. It was the
• 23:16
  Speaker 2: same theory presenting in two different ways. And so we
• 23:21
  Speaker 2: don't have a trouble in case of underdetermination. There a
• 23:23
  Speaker 2: trouble in case of underdetermination was avoided because you didn't
• 23:26
  Speaker 2: have a genuine decision to be made between these two
• 23:32
  Speaker 2: Between these two theories, the two theories were actually one.
• 23:34
  Speaker 1: So it turns out that they were really just the
• 23:36
  Speaker 1: same theory dressed in different clothes, right.
• 23:38
  Speaker 2: Yeah, yeah, And so this is something that one might
• 23:41
  Speaker 2: be tempted to say in the case of Hamiltonian and
• 23:44
  Speaker 2: lagrondgy mechanics too, you know, you pick position and velocity
• 23:48
  Speaker 2: to do your theory. I pick position and momentum to
• 23:52
  Speaker 2: do my theory. But we can translate back and forth
• 23:55
  Speaker 2: between these two descriptions. It's not like when you talk
• 23:59
  Speaker 2: about position in the law, I can't do that in
• 24:02
  Speaker 2: my theory. I would do it, you know, a little differently.
• 24:05
  Speaker 2: I'd use a little bit of different language to do so.
• 24:08
  Speaker 2: But am I saying a genuinely different thing about the
• 24:11
  Speaker 2: world when I decide to say it in position and
• 24:14
  Speaker 2: momentum language versus when you say it in position and
• 24:19
  Speaker 2: philosophy language. So in general, this is a kind of
• 24:22
  Speaker 2: response one can give to underdetermination worries. It's like, look
• 24:28
  Speaker 2: in a lot of the problematic cases of underdetermination that
• 24:31
  Speaker 2: we see, so cases where you have two theories that
• 24:35
  Speaker 2: can't be discriminated between on the basis of the evidence
• 24:38
  Speaker 2: we've gathered. In a lot of these cases, you don't
• 24:41
  Speaker 2: actually have genuine rivals. The two theories can't be discriminated
• 24:45
  Speaker 2: between on the basis of the evidence we've gathered, but
• 24:47
  Speaker 2: they're the same theory.
• 24:48
  Speaker 1: Yeah, and so what about the case of later sort
• 24:52
  Speaker 1: of quantum mechanical interpretations. You know, we have various descriptions
• 24:56
  Speaker 1: of what's going on with particles. Is the way function
• 24:59
  Speaker 1: call colapsing, or is the universe splitting into multiple universes
• 25:03
  Speaker 1: or is the collapse relative? You know, like in relational
• 25:07
  Speaker 1: quantum mechanics. Are those examples of true underdetermination where we
• 25:11
  Speaker 1: have really different stories, genuinely different accounts of the physical world,
• 25:15
  Speaker 1: but that make effectively the same predictions for what we
• 25:18
  Speaker 1: could see in experiments, like we can't distinguish between the
• 25:21
  Speaker 1: many world hypothesis or the Copenhagen interpretation using experiments. Is
• 25:26
  Speaker 1: that an example?
• 25:27
  Speaker 2: That is an example where it becomes harder for one
• 25:30
  Speaker 2: to say that the theories are genuinely the same, and
• 25:34
  Speaker 2: yet they have the same experiments supporting both of them.
• 25:40
  Speaker 2: So some folks at this point will say that there's
• 25:44
  Speaker 2: another natural way to respond to problems of underdetermination. So
• 25:48
  Speaker 2: the empirical evidence doesn't help us decide which theory is correct,
• 25:52
  Speaker 2: But we have some stuff that we can use to
• 25:54
  Speaker 2: make these decisions not using empirical evidence, and we do
• 25:58
  Speaker 2: this all the time. We appear to other virtues that
• 26:01
  Speaker 2: a theory might exhibit.
• 26:02
  Speaker 1: Like simplicity or exact money.
• 26:05
  Speaker 2: Okay, yeah, simplicity, fruitfulness, I don't know something like this,
• 26:11
  Speaker 2: And scientists do this all the time. We all do this.
• 26:15
  Speaker 1: Well, I was having a conversation with a theoretical physicist
• 26:18
  Speaker 1: who's quite well known in particle physics, but I won't
• 26:21
  Speaker 1: name him, and I describe this problem to him, and
• 26:23
  Speaker 1: he said, well, look, if the theories predict the same
• 26:26
  Speaker 1: things but are different, then they're different only in the metaphysics, right,
• 26:30
  Speaker 1: only in the irrelevant details, which I think is another
• 26:32
  Speaker 1: way to say, like, well, maybe who cares? Right, Like,
• 26:35
  Speaker 1: we have two different descriptions of the universe, but they
• 26:37
  Speaker 1: give the same predictions. What does it matter? And to
• 26:40
  Speaker 1: me this is sort of shocking coming from a theorist
• 26:42
  Speaker 1: who you know, I think their job essentially is to
• 26:45
  Speaker 1: uncover the mechanisms of the universe, not just to produce
• 26:50
  Speaker 1: calculational tools that will get us to the next step,
• 26:52
  Speaker 1: but like reveal the nature of reality man. And so
• 26:56
  Speaker 1: to hear somebody be like, well, maybe it doesn't matter
• 26:57
  Speaker 1: if it's fields or shmields as lung as the numbers
• 27:01
  Speaker 1: are right.
• 27:01
  Speaker 2: How does that strike you, as sort of.
• 27:03
  Speaker 1: A philosopher of science, do you think that that sort
• 27:05
  Speaker 1: of instrumental approach is a solution to this problem, or
• 27:08
  Speaker 1: are we just avoiding the question.
• 27:10
  Speaker 2: It's not an attitude that's uncommon among philosophers. Also, I
• 27:16
  Speaker 2: do think it's kind of avoiding sidestepping the question rather
• 27:20
  Speaker 2: than taking it on head on. One thing that I
• 27:23
  Speaker 2: should say, though, is notice that this kind of attitude.
• 27:28
  Speaker 2: So we have two theories, the evidence doesn't distinguish between them,
• 27:32
  Speaker 2: so they're the same in all important aspects. There's a
• 27:36
  Speaker 2: sense in which that attitude lands oneself in the same
• 27:41
  Speaker 2: place as taking the problem of underdetermination seriously ends oneself in.
• 27:47
  Speaker 2: The idea is, if you don't think that the theories
• 27:49
  Speaker 2: are telling you anything about the non empirical stuff, the
• 27:54
  Speaker 2: unobservable stuff, there's a sense in which you're not taking
• 27:57
  Speaker 2: your theories all that serious right, which is very close
• 28:04
  Speaker 2: to the place that the problem of underdetermination would lead
• 28:08
  Speaker 2: us in both cases, So, say you don't take the
• 28:11
  Speaker 2: metaphysics of your theory seriously, and there are some unanswered
• 28:14
  Speaker 2: questions like is space flat or is it curved? Suppose
• 28:18
  Speaker 2: you take the problem of underdetermination seriously, then you end
• 28:22
  Speaker 2: up with unanswered questions for a slightly different reason, but
• 28:25
  Speaker 2: in both cases you're ending with questions that are not
• 28:28
  Speaker 2: being answered by your physics.
• 28:31
  Speaker 1: Okay, I have a lot more questions about how this
• 28:33
  Speaker 1: all works and how we can make sense of it,
• 28:35
  Speaker 1: but first let's take a quick break. All right, we're
• 28:51
  Speaker 1: back and we're talking to Professor Thomas Barrett about the
• 28:53
  Speaker 1: question of underdeterminism in philosophy of science, whether it's possible
• 28:58
  Speaker 1: to have multiple theories that describe the universe and make
• 29:01
  Speaker 1: exactly the same predictions but are in themselves fundamentally different. Well,
• 29:07
  Speaker 1: in almost every example, we've considered various versions of Newtonon theory.
• 29:11
  Speaker 2: Et cetera.
• 29:12
  Speaker 1: One can sometimes imagine that maybe in the future or
• 29:15
  Speaker 1: somebody will come up with an experiment to help us distinguish,
• 29:18
  Speaker 1: or somebody will be the next generation's John Bell will
• 29:20
  Speaker 1: come up with a super clever quantum experiment to help
• 29:22
  Speaker 1: us reveal multiple universes or something, even in the face
• 29:26
  Speaker 1: of like infinite data. Is the argument for underdetermination really
• 29:31
  Speaker 1: that it's impossible that, you know, even in a million years,
• 29:33
  Speaker 1: a billion years of super Einstein's could never come up
• 29:37
  Speaker 1: with a way to distinguish that. It might literally be impossible,
• 29:41
  Speaker 1: not just we haven't figured it out yet.
• 29:43
  Speaker 2: Yeah, So think back. This is a good question think
• 29:46
  Speaker 2: back to the apples and oranges example. The natural thing
• 29:51
  Speaker 2: to say in that example is like, look, dude, you've
• 29:54
  Speaker 2: just looked at the receed on the table. You want
• 29:57
  Speaker 2: to know how many apples and oranges there are? Like,
• 29:58
  Speaker 2: go open up the pa entry, right, Like gather more data?
• 30:03
  Speaker 2: So problematic, like truly problematic cases of underdetermination, you know,
• 30:08
  Speaker 2: the ones that will keep you up at night. Our
• 30:11
  Speaker 2: cases where even gathering the more data won't help you
• 30:15
  Speaker 2: distinguish between the two theories. Just the two theories are
• 30:21
  Speaker 2: provably compatible with precisely the same collection of evidence. So
• 30:27
  Speaker 2: maybe one example, one further example will be helpful here.
• 30:31
  Speaker 2: So this comes from our recent work my good friend
• 30:36
  Speaker 2: and your colleague, get Irvine JB. Mancheck has done in
• 30:42
  Speaker 2: general relativity. So what Manchik proves is that in the
• 30:47
  Speaker 2: context of Einstein's theory of general relativity, we encounter a
• 30:53
  Speaker 2: very pernicious kind of underdetermination. So here's the gist. In
• 30:58
  Speaker 2: general relativity. Intuitively, like and signals can't travel faster than
• 31:03
  Speaker 2: the speed of light, you can only know at most
• 31:08
  Speaker 2: everything that goes on in your past light cone. So
• 31:11
  Speaker 2: all the evidence that's available to you at some time
• 31:14
  Speaker 2: will have arrived to you via some trajectory that's contained
• 31:18
  Speaker 2: in your past, like Cone. Right, like picture the stuff
• 31:22
  Speaker 2: that you see, Well, that's arriving to you via photons
• 31:26
  Speaker 2: that are reflecting off the surface of the thing. They're
• 31:29
  Speaker 2: all contained in your past like Cone. Your colleagues reporting
• 31:32
  Speaker 2: to you their evidence, well they came to you in
• 31:35
  Speaker 2: your past, like Cone. So Manchik proves now that given
• 31:39
  Speaker 2: this information, there's always more than one model of the
• 31:44
  Speaker 2: universe according to Einstein's theory that's compatible with the data
• 31:49
  Speaker 2: you could have possibly gathered.
• 31:51
  Speaker 1: Meaning that there's always part of the universe sort of
• 31:53
  Speaker 1: shrouded in darkness because it could be just like so
• 31:56
  Speaker 1: far away given the age of the universe, that there
• 31:59
  Speaker 1: hasn't been time for light from it to arrive here,
• 32:01
  Speaker 1: And so there could be huge purple dragons beyond the
• 32:04
  Speaker 1: ende of the universe, or not huge purple dragons beyond
• 32:06
  Speaker 1: the edge of the universe.
• 32:07
  Speaker 2: Yeah, exactly. I mean, they don't even have to be
• 32:09
  Speaker 2: that far from you. They just have to be not
• 32:11
  Speaker 2: in your backward like Cone. So the idea is, if
• 32:14
  Speaker 2: general relativity is true, if Einstein's theory is true, that
• 32:19
  Speaker 2: it itself implies that we can't know the global structure
• 32:25
  Speaker 2: of the universe because of the limitations that the theory
• 32:29
  Speaker 2: places on how evidence must work. It has to be
• 32:34
  Speaker 2: contained in your backward like cone, we have a case
• 32:37
  Speaker 2: where no matter how much data you gather, you're going
• 32:41
  Speaker 2: to have different possibilities for what the universe is. Like
• 32:47
  Speaker 2: that the data doesn't distinguish between well.
• 32:49
  Speaker 1: It seems to me in the end to come down
• 32:51
  Speaker 1: to a form of skepticism to say, like, look, there
• 32:54
  Speaker 1: could always be some other theory out there that makes
• 32:58
  Speaker 1: the same predictions but has a different story about the universe,
• 33:02
  Speaker 1: and so is the conclusion then, I mean, what does
• 33:04
  Speaker 1: that mean about our understanding of the universe? As you say,
• 33:08
  Speaker 1: does that mean we shouldn't take too seriously the story
• 33:11
  Speaker 1: about what's happening When we write Fineman diagrams there are
• 33:14
  Speaker 1: a great little trick for making calculations. But does that
• 33:17
  Speaker 1: mean that we can't really believe that the universe is
• 33:20
  Speaker 1: doing its own finement calculations that fields are real because
• 33:24
  Speaker 1: there could be schmields instead. Does that mean we can
• 33:26
  Speaker 1: never really know what's happening out there in the universe.
• 33:30
  Speaker 2: Yeah, So it all turns on how seriously you take
• 33:35
  Speaker 2: this possibility of alternative theories that have the same empirical
• 33:42
  Speaker 2: consequences as are current theories. So notice all we've done
• 33:47
  Speaker 2: here is I've given a bunch of examples of pairs
• 33:51
  Speaker 2: of theories where the evidence can't tell you which one
• 33:55
  Speaker 2: is rund. I haven't given you a general prison siezure
• 34:00
  Speaker 2: that you can use to construct from our best physical
• 34:04
  Speaker 2: theory arrival that agrees with it in all of its predictions,
• 34:10
  Speaker 2: but it's different. So that would be the gold standard,
• 34:13
  Speaker 2: right If we could do that, then I would be
• 34:17
  Speaker 2: very disturbed. We would have a mechanism for generating pairs
• 34:21
  Speaker 2: of theories where the evidence doesn't hell which one is right,
• 34:25
  Speaker 2: but they're different, and then we're kind of we're sunk.
• 34:28
  Speaker 2: I don't know how to answer our questions about the
• 34:31
  Speaker 2: unobservable anymore. We don't have that. All we have is
• 34:34
  Speaker 2: a bunch of examples. So what's the right conclusion to draws?
• 34:38
  Speaker 2: We do have a lot of examples. I mean, I've
• 34:40
  Speaker 2: talked to you as well. I don't know, depends on
• 34:42
  Speaker 2: how many you think is a lot. I think I've
• 34:43
  Speaker 2: talked about four.
• 34:44
  Speaker 1: Let me just make sure I understand what you're saying
• 34:46
  Speaker 1: you're trying to be careful not to overstate your conclusions.
• 34:49
  Speaker 1: You're saying, we have some examples that suggest that it
• 34:51
  Speaker 1: might be possible to have two theories that explain the
• 34:55
  Speaker 1: universe equally well but have different stories, But we don't
• 34:58
  Speaker 1: have a general proof that that's all we possible. They
• 35:00
  Speaker 1: don't have like a procedure that says, if you have
• 35:03
  Speaker 1: a great theory, I can always use it to generate
• 35:05
  Speaker 1: an alternative theory that works just as well. So you're
• 35:08
  Speaker 1: saying there'd be a little bit of skepticism about our skepticism.
• 35:12
  Speaker 2: Yeah, that's right, or we should be modest about our skepticism. Right.
• 35:16
  Speaker 1: I was reading this article of by Philip Kitchener, and
• 35:18
  Speaker 1: he says, give us a rival explanation, and we'll consider
• 35:21
  Speaker 1: whether it is sufficiently serious to threaten our confidence, which
• 35:25
  Speaker 1: is basically like saying, maybe this is a problem in theory,
• 35:29
  Speaker 1: but right now it's not one that's facing us, so
• 35:32
  Speaker 1: maybe it won't.
• 35:33
  Speaker 2: Yeah. I think that's right. So now philosophers have attempted
• 35:38
  Speaker 2: through the years to give kind of algorithmic procedures for
• 35:42
  Speaker 2: generating rival theories that are equally compatible with our data.
• 35:48
  Speaker 2: The kind of algorithmic procedures they give, though, result in
• 35:52
  Speaker 2: theories that most folks would not take seriously. So let
• 35:55
  Speaker 2: me give one example. So you have the theory of
• 35:58
  Speaker 2: the universe. I have a rival theory, like we'll call
• 36:02
  Speaker 2: it the when you turn your back theory. My theory
• 36:05
  Speaker 2: says that the universe behaves exactly like your theory says
• 36:09
  Speaker 2: it does when it's being observed, but when it's not
• 36:11
  Speaker 2: being observed, it behaves in some completely other, specific and
• 36:16
  Speaker 2: compatible Why our theories are equally compatible with the evidence.
• 36:20
  Speaker 2: My theory says exactly the same thing about how universe
• 36:23
  Speaker 2: will behave when it's being observed, as your theory does
• 36:25
  Speaker 2: by construction. But my theory is different from your theory. Okay,
• 36:29
  Speaker 2: So I mean, like take this over to the physics
• 36:30
  Speaker 2: department and tell a physicist. I mean, you can tell
• 36:33
  Speaker 2: me no one would take this theory seriously. Right, this
• 36:36
  Speaker 2: is ad hoc. It's totally gerrymandered, it's not interesting. It's
• 36:40
  Speaker 2: not a scientifically compelling theory. My theory that is. And
• 36:44
  Speaker 2: so it's like easy to dismiss this. It's not a
• 36:47
  Speaker 2: genuine case of underdetermination.
• 36:50
  Speaker 1: Yeah, that's right, that's not something I would take seriously.
• 36:52
  Speaker 1: I mean, it's essentially equivalent in all the important bits. Right,
• 36:56
  Speaker 1: It's using the same calculational machinery to make predictions for
• 37:00
  Speaker 1: actual observations. Is just adding some bells and whistles to
• 37:04
  Speaker 1: the non observed side of things. It doesn't really seem
• 37:08
  Speaker 1: to me to count as a compellingly different explanation for
• 37:11
  Speaker 1: what's happening in the universe.
• 37:13
  Speaker 2: Yeah, and going back to something you said earlier, like,
• 37:16
  Speaker 2: we have other means by which we can choose what
• 37:20
  Speaker 2: theory to believe. So our theories are equally compatible with
• 37:25
  Speaker 2: the evidence, but your theory is much simpler than mine, right,
• 37:29
  Speaker 2: Yours has a kind of elegance that mine lacks. So
• 37:33
  Speaker 2: we might think that that gives us better reason to
• 37:34
  Speaker 2: believe your theory than mine.
• 37:37
  Speaker 1: And so is that the strongest argument against underdeterminism to say, like, look,
• 37:42
  Speaker 1: we don't have a perfect example, and we can't arbitrarily
• 37:46
  Speaker 1: generate one, so we don't really know that this is
• 37:49
  Speaker 1: a problem.
• 37:50
  Speaker 2: Yeah, I would say there are two kinds of arguments
• 37:54
  Speaker 2: against the problem of under determination. So one is this
• 37:58
  Speaker 2: one that you just mentioned, Like how common are genuine
• 38:01
  Speaker 2: cases of underdetermination in order for this to be a
• 38:04
  Speaker 2: troubling problem. They had better be really common. The other
• 38:08
  Speaker 2: route is the thing that we were just talking about,
• 38:10
  Speaker 2: so appealing to what folks will call theoretical virtues that
• 38:17
  Speaker 2: are non empirical, so simplicity or fruitfulness or elegance, in
• 38:23
  Speaker 2: order to decide between rival theories that are equally compatible
• 38:28
  Speaker 2: with the evidence. So just because two theories are equally
• 38:32
  Speaker 2: compatible with the evidence, doesn't mean that we don't have
• 38:34
  Speaker 2: better reason to believe this one than we have reason
• 38:38
  Speaker 2: to believe this one. That opens a whole can of worms. Though, like,
• 38:41
  Speaker 2: these are philosophy questions. What are the non empirical reasons
• 38:45
  Speaker 2: for believing something? What are the reasons that are not
• 38:49
  Speaker 2: exhausted by just looking at the evidence for believing one
• 38:51
  Speaker 2: hypothesis over another. That's philosophy, right.
• 38:57
  Speaker 1: Right, And you say that in a way that makes
• 38:59
  Speaker 1: it to like it's philosophy, it's not science. But I
• 39:02
  Speaker 1: wonder sometimes if we're too crisp about, you know, making
• 39:05
  Speaker 1: a delineation between those two things, because, as you say,
• 39:08
  Speaker 1: often we're using philosophy to make decisions in science, we
• 39:11
  Speaker 1: prefer this theory to that theory because it's simpler. Those
• 39:14
  Speaker 1: are choices influenced by our philosophy of science. We're doing
• 39:18
  Speaker 1: that kind of stuff all the time. The thing I
• 39:19
  Speaker 1: find fascinating is that most people in particle physics have
• 39:22
  Speaker 1: very strong opinions about philosophical questions, but they also often
• 39:27
  Speaker 1: think philosophical questions are a waste of time, you know,
• 39:31
  Speaker 1: like if I go around, sir and ask people like,
• 39:33
  Speaker 1: do you think the top quark or the Higgs boson
• 39:35
  Speaker 1: is real? It's there when we're not looking, or it's
• 39:38
  Speaker 1: just a tool in our calculations that are like, dude,
• 39:41
  Speaker 1: we discovered the Higgs boson. Here, we know it's real.
• 39:43
  Speaker 1: We found it, there's a Nobel prize for it. You're crazy.
• 39:48
  Speaker 1: You have to take them on a pretty long walk
• 39:49
  Speaker 1: to get them to the place where you're like, Okay,
• 39:51
  Speaker 1: that's true. It's not directly observed and therefore we don't
• 39:54
  Speaker 1: really know if it's there and there could be another explanation, etcetera, etc.
• 39:57
  Speaker 1: All right, I want to hear more about that, but
• 39:59
  Speaker 1: first we have to take another quick break. All right,
• 40:14
  Speaker 1: this is Daniel and we are doing an episode on
• 40:17
  Speaker 1: underdeterminism in science, wondering whether it's possible to explain the
• 40:21
  Speaker 1: universe in two different but equivalent ways. Well, my question
• 40:26
  Speaker 1: to you is, what do you think are the prospects
• 40:28
  Speaker 1: for making progress? Like is this something we can ever
• 40:32
  Speaker 1: really resolve? I mean, could it be that in a
• 40:34
  Speaker 1: million years we're doing science and we're still worrying about
• 40:37
  Speaker 1: this kind of thing, Like maybe somebody's going to come
• 40:40
  Speaker 1: up with another theory that explains what's going on. Or
• 40:43
  Speaker 1: do you think philosophers can like resolve questions like this,
• 40:46
  Speaker 1: that they can come up with a proof that two
• 40:48
  Speaker 1: theories that give the same predictions are fundamentally categorically the same,
• 40:52
  Speaker 1: or that you could develop the kind of algorithm you're
• 40:54
  Speaker 1: talking about earlier to generate an alternative theory that's realistic
• 40:59
  Speaker 1: from an existing theory. What do you think are the
• 41:01
  Speaker 1: prospects for making progress on this question?
• 41:03
  Speaker 2: One thing I think is important to say is like,
• 41:06
  Speaker 2: in terms of progress, like setting aside under determination stuff
• 41:10
  Speaker 2: like science is always making progress. Right, taking the problem
• 41:13
  Speaker 2: of determination seriously doesn't imply that it isn't like progress
• 41:17
  Speaker 2: that's made when we moved from Newton's theory of gravity
• 41:20
  Speaker 2: to Einstein's, like, our theories get more and more predictively successful,
• 41:23
  Speaker 2: and that is definitely progress. So even if we still
• 41:27
  Speaker 2: take the problem of underdetermination seriously. Science is making a
• 41:31
  Speaker 2: kind of progress, So what about making progress on the
• 41:36
  Speaker 2: problem of underdetermination itself? I wish I knew. Note that
• 41:40
  Speaker 2: one of the routes that we were talking about in
• 41:44
  Speaker 2: responding to the problem just in fact, all of them
• 41:47
  Speaker 2: involve one doing like philosophy taking seriously the kinds of
• 41:54
  Speaker 2: questions that philosophers of science takes seriously. We have to
• 41:58
  Speaker 2: identify what the theoretical virtues are, so like what the
• 42:04
  Speaker 2: reasons are we have to believe one theory rather than another,
• 42:08
  Speaker 2: and then we have to argue that these help us
• 42:11
  Speaker 2: make good decisions, like in terms of which theory we
• 42:15
  Speaker 2: should believe. We also have to, as you were mentioning,
• 42:18
  Speaker 2: like come to some kind of agreement on win two
• 42:20
  Speaker 2: theories or saying the same thing, or when their genuine
• 42:23
  Speaker 2: rivals to one another. And these are hard philosophy questions.
• 42:30
  Speaker 2: So I mean, going back to something that you said earlier,
• 42:33
  Speaker 2: I think there's this famous Fineman quote. So he once
• 42:37
  Speaker 2: said that philosophy of sciences is useful to science or
• 42:42
  Speaker 2: to scientists, as ornithology is to birds. Oh man, I mean,
• 42:46
  Speaker 2: it's a great quote. Makes me chuckle. Every time, but
• 42:49
  Speaker 2: man like, look, birds are doing some ornithology here, right,
• 42:53
  Speaker 2: or or implicitly at least, or we have to in
• 42:57
  Speaker 2: order to make progress on this kind of stuff.
• 42:59
  Speaker 1: Yeah, it's true, it's a great zinger, but I think
• 43:01
  Speaker 1: it's it's not necessarily very productive. Well, let me make
• 43:04
  Speaker 1: the question a little bit more sort of vivid and concrete.
• 43:07
  Speaker 1: Let's imagine a hypothetical scenario, say far in the future,
• 43:10
  Speaker 1: or maybe not that far in the future. Aliens arrive
• 43:13
  Speaker 1: and they are you know, scientific, and they use mathematics,
• 43:18
  Speaker 1: and they do physics, and they have also been pursuing
• 43:22
  Speaker 1: the project of revealing the fundamental nature of the universe,
• 43:25
  Speaker 1: matter and energy and particles in space and time and
• 43:27
  Speaker 1: all that stuff. And we get to sit down across
• 43:30
  Speaker 1: the table from them and compare notes. So here we
• 43:32
  Speaker 1: have like a completely independent scientific tradition, but you know,
• 43:36
  Speaker 1: undimently pointing at the same thing. So we can avoid
• 43:38
  Speaker 1: questions of like, what aliens do science? And could we
• 43:41
  Speaker 1: communicate with them? What do you think the chances are
• 43:44
  Speaker 1: that their theory is compatible with ours, that it's the
• 43:48
  Speaker 1: same theory, but you know, written with different kind of squiggles,
• 43:51
  Speaker 1: dressed in different clothing, or the chances that they really
• 43:54
  Speaker 1: have come up with a completely different mechanism to describe
• 43:58
  Speaker 1: the universe. What do you think the chances are in
• 44:00
  Speaker 1: that scenario that our two theories are compatible or incompatible.
• 44:04
  Speaker 2: Yeah, I don't know, man, Your guess is as good
• 44:06
  Speaker 2: as mine. If I had to guess, I'd say it's
• 44:11
  Speaker 2: pretty unlikely that anyone else does science and exactly the
• 44:16
  Speaker 2: way we do it, you know, like so much of
• 44:19
  Speaker 2: the way that we do science is grounded in accidental
• 44:22
  Speaker 2: things about what humans are, like, you know, we're medium sized,
• 44:27
  Speaker 2: we travel pretty slowly. It's grounded and the kinds of
• 44:33
  Speaker 2: things that we care about what we want to do
• 44:35
  Speaker 2: with our science, how our particular perceptual apparatus works, like
• 44:39
  Speaker 2: how you know, our eyes work, stuff like that, and
• 44:43
  Speaker 2: the way that we do science is grounded in accidental
• 44:46
  Speaker 2: facts about history too. Given all this, it's hard for
• 44:50
  Speaker 2: me to imagine that anyone else would do it exactly
• 44:53
  Speaker 2: in the way that we do well.
• 44:56
  Speaker 1: That's one of the things that makes me excited to
• 44:57
  Speaker 1: talk to aliens about science, because you know, if they're
• 45:01
  Speaker 1: doing science the same way we are, then hey, we
• 45:03
  Speaker 1: might learn some cool science. And if they're not, we
• 45:05
  Speaker 1: might learn some cool things about ourselves and the way
• 45:08
  Speaker 1: that we explore the universe and the way like being
• 45:10
  Speaker 1: human colors how we are seeing the universe, and it's
• 45:14
  Speaker 1: so hard to sort of get out of our own heads,
• 45:16
  Speaker 1: and that's like maybe one way to do it.
• 45:18
  Speaker 2: So, yeah, when you hear from them, let me know.
• 45:23
  Speaker 1: I think when they do arrive, we should send the
• 45:25
  Speaker 1: philosophers first before we send the physicists, you know, in
• 45:28
  Speaker 1: case they're not so friendly. All right, Well, thanks very
• 45:30
  Speaker 1: much for chatting with me about this really fascinating question
• 45:33
  Speaker 1: in philosophy and in science, and in philosophy and science.
• 45:36
  Speaker 1: I really enjoyed it. Thanks very much for your time.
• 45:38
  Speaker 2: Yeah, thanks for having me on, Danielle. It was a pleasure.
• 45:48
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
• 45:51
  Speaker 1: the Universe is a production of iHeart Radio. For more
• 45:54
  Speaker 1: podcasts from iHeart Radio, visit the iHeartRadio app, Apple Podcasts,
• 45:59
  Speaker 1: or where where you listened to your favorite shows.
• 46:07
  Speaker 2: H