1 00:00:08,600 --> 00:00:11,960 Speaker 1: As I sit down to record today's episode, the beams 2 00:00:12,000 --> 00:00:15,400 Speaker 1: of the Large Hadron Collider are powering up. Today will 3 00:00:15,440 --> 00:00:18,720 Speaker 1: be the first day of collisions in twenty twenty three, 4 00:00:18,800 --> 00:00:22,680 Speaker 1: after a long shutdown to rebuild and upgrade our equipment. 5 00:00:22,800 --> 00:00:25,680 Speaker 1: We hope to see some new particles, to discover some 6 00:00:25,800 --> 00:00:29,080 Speaker 1: new forces, to reveal new truths about the nature of 7 00:00:29,160 --> 00:00:32,839 Speaker 1: space and time and matter and energy. But what if 8 00:00:33,040 --> 00:00:37,199 Speaker 1: everything we're learning is not really the truth? What if 9 00:00:37,200 --> 00:00:40,400 Speaker 1: it's just a story we tell ourselves. What if there 10 00:00:40,440 --> 00:00:44,720 Speaker 1: are other possible stories that could also explain what we 11 00:00:44,800 --> 00:00:48,559 Speaker 1: see in our experiments? How would we ever even know? 12 00:01:04,240 --> 00:01:04,440 Speaker 2: Hi? 13 00:01:04,600 --> 00:01:07,640 Speaker 1: I'm Daniel. I'm a particle physicist and a professor at 14 00:01:07,720 --> 00:01:11,960 Speaker 1: UC Irvine and something of an amateur philosopher of science. 15 00:01:12,600 --> 00:01:16,240 Speaker 1: Welcome to the podcast Daniel and Jorge Explain the Universe, 16 00:01:16,360 --> 00:01:19,560 Speaker 1: a production of iHeartRadio in which normally we dig into 17 00:01:19,640 --> 00:01:22,840 Speaker 1: questions about how the universe works, what's going on the 18 00:01:22,920 --> 00:01:26,200 Speaker 1: tiny quantum level, what's at the heart of black holes? 19 00:01:26,240 --> 00:01:28,720 Speaker 1: How does everything work, and how does it weave itself 20 00:01:28,760 --> 00:01:34,760 Speaker 1: together to make the incredible, beautiful, mysterious reality that we experience. 21 00:01:35,080 --> 00:01:37,720 Speaker 1: My normal co host and friend Jorge can't be with 22 00:01:37,800 --> 00:01:39,720 Speaker 1: us today. So I'm going to take the opportunity to 23 00:01:39,760 --> 00:01:41,600 Speaker 1: do something a tiny bit different and do a bit 24 00:01:41,600 --> 00:01:44,759 Speaker 1: of a dive into some questions in the philosophy of science, 25 00:01:45,200 --> 00:01:48,640 Speaker 1: because I really want to understand not just what's happening 26 00:01:48,760 --> 00:01:52,000 Speaker 1: in the universe, but why it's happening. What are we 27 00:01:52,160 --> 00:01:55,720 Speaker 1: really learning about the universe when we do particle physics, 28 00:01:56,000 --> 00:01:58,760 Speaker 1: or when we do any kind of science. Let's make 29 00:01:58,800 --> 00:02:02,560 Speaker 1: it concrete. Example, when we build the Large Hadron Collider, 30 00:02:02,920 --> 00:02:05,520 Speaker 1: we did it because we wanted to uncover how the 31 00:02:05,680 --> 00:02:08,920 Speaker 1: universe works. We want to know answers to questions like 32 00:02:09,360 --> 00:02:12,680 Speaker 1: is space filled with quantum fields that buzz and wiggle 33 00:02:12,760 --> 00:02:15,840 Speaker 1: to make particles? How many of those fields are there? 34 00:02:15,880 --> 00:02:18,440 Speaker 1: And what are the rules of their interactions? Is there 35 00:02:18,440 --> 00:02:21,120 Speaker 1: a field for a dark matter? Are there other fields 36 00:02:21,120 --> 00:02:23,639 Speaker 1: that we never even imagined? Are all of the fields 37 00:02:23,680 --> 00:02:27,200 Speaker 1: really part of one superfield in a way we haven't 38 00:02:27,280 --> 00:02:30,040 Speaker 1: ever thought of. These are the kind of questions we 39 00:02:30,080 --> 00:02:32,680 Speaker 1: think about, and the language of physics these days is 40 00:02:32,720 --> 00:02:36,080 Speaker 1: always the language of these fields. We imagine that space 41 00:02:36,200 --> 00:02:38,640 Speaker 1: is filled with these quantum fields, and we've been very 42 00:02:38,680 --> 00:02:42,480 Speaker 1: successful at using these quantum fields to describe everything we've 43 00:02:42,520 --> 00:02:47,040 Speaker 1: seen so far in particle physics. But there's always a butt. 44 00:02:47,120 --> 00:02:51,080 Speaker 1: But nobody has ever actually seen a field. What we 45 00:02:51,120 --> 00:02:54,079 Speaker 1: see in the collider are sprays of particles that are 46 00:02:54,080 --> 00:02:57,920 Speaker 1: the debris of collisions. The collision itself happens too quickly 47 00:02:57,960 --> 00:03:00,960 Speaker 1: and is too small to actually look at, and even 48 00:03:01,000 --> 00:03:04,679 Speaker 1: the particles that we do see don't prove that fields 49 00:03:04,720 --> 00:03:09,760 Speaker 1: themselves actually exists. When a particle bends in a magnetic field, 50 00:03:09,840 --> 00:03:14,639 Speaker 1: what we see is the particle bending, not the field itself. 51 00:03:15,120 --> 00:03:18,040 Speaker 1: There's always this part of the story where the field 52 00:03:18,160 --> 00:03:21,959 Speaker 1: hides behind a curtain. It's an unobservable part of our 53 00:03:22,080 --> 00:03:25,160 Speaker 1: science that helps explain what we do see, but is 54 00:03:25,240 --> 00:03:30,079 Speaker 1: never itself directly observable, And that unobservable part, in my opinion, 55 00:03:30,240 --> 00:03:33,440 Speaker 1: is really important. It's the juicy bit. It's the real 56 00:03:33,520 --> 00:03:37,160 Speaker 1: explanation for what's happening out there in the universe. It's 57 00:03:37,160 --> 00:03:40,040 Speaker 1: how we think about physics. We hope, or we wonder, 58 00:03:40,080 --> 00:03:44,160 Speaker 1: at least, whether the universe is also doing its calculations 59 00:03:44,200 --> 00:03:46,400 Speaker 1: to decide whether a particle goes this way or that 60 00:03:46,480 --> 00:03:50,400 Speaker 1: way using fields. I mean, are those fields really out 61 00:03:50,400 --> 00:03:52,960 Speaker 1: there pushing and pulling on stuff when we're not looking. 62 00:03:53,840 --> 00:03:57,600 Speaker 1: Or are those fields just our description? Are they part 63 00:03:57,600 --> 00:04:01,720 Speaker 1: of the story we are telling ourselves about the particles? 64 00:04:02,280 --> 00:04:04,960 Speaker 1: Are those fields just part of our minds? Are they 65 00:04:05,000 --> 00:04:08,800 Speaker 1: really deep elements of the universe itself? One really fun 66 00:04:08,880 --> 00:04:12,120 Speaker 1: way to probe this famous question is to wonder, could 67 00:04:12,120 --> 00:04:15,080 Speaker 1: there be another explanation that's just as good? Is there 68 00:04:15,120 --> 00:04:19,080 Speaker 1: another way to describe the universe that doesn't need fields, 69 00:04:19,080 --> 00:04:22,880 Speaker 1: that tells a different story about what's happening out there 70 00:04:22,920 --> 00:04:26,080 Speaker 1: in the universe. So today on the podcast, we'll be 71 00:04:26,080 --> 00:04:34,200 Speaker 1: asking the question could there be more than one theory 72 00:04:34,400 --> 00:04:37,840 Speaker 1: of everything? To help me dive into these thorny questions 73 00:04:37,839 --> 00:04:41,240 Speaker 1: of philosophy, I've invited a guest expert, a philosopher of 74 00:04:41,320 --> 00:04:50,760 Speaker 1: science who specializes in this very topic. Okay, so then 75 00:04:50,920 --> 00:04:54,440 Speaker 1: it's my great pleasure to welcome to the podcast Professor 76 00:04:54,480 --> 00:04:57,680 Speaker 1: Thomas William Barrett. He's professor at the University of California 77 00:04:57,720 --> 00:05:01,000 Speaker 1: at Santa Barbara in the Department of f Philosophy, and 78 00:05:01,040 --> 00:05:04,760 Speaker 1: he works mostly on philosophy of science and logic, and 79 00:05:04,880 --> 00:05:06,960 Speaker 1: on his homepage he has a picture of himself as 80 00:05:07,000 --> 00:05:09,880 Speaker 1: an infant in front of a Philosophy Building. Welcome to 81 00:05:09,920 --> 00:05:10,440 Speaker 1: the podcast. 82 00:05:10,480 --> 00:05:12,880 Speaker 2: Thanks very much, thanks for having me. It's a pleasure 83 00:05:12,920 --> 00:05:13,480 Speaker 2: to be here. 84 00:05:13,680 --> 00:05:16,279 Speaker 1: So does that picture mean that you've been doing philosophy 85 00:05:16,360 --> 00:05:17,479 Speaker 1: since you were a little baby? 86 00:05:17,720 --> 00:05:21,240 Speaker 2: In a sense, I guess. I mean everyone tries not to, 87 00:05:21,440 --> 00:05:25,320 Speaker 2: but it's, you know, unavoidable. We've all been doing philosophy 88 00:05:25,320 --> 00:05:27,880 Speaker 2: since we've been little babies. Well. 89 00:05:27,880 --> 00:05:30,839 Speaker 1: I know people like to say that babies are scientists 90 00:05:30,880 --> 00:05:32,640 Speaker 1: because they're all exploring the world and trying to figure 91 00:05:32,640 --> 00:05:34,960 Speaker 1: out how things work. But I'd be fascinating if babies 92 00:05:34,960 --> 00:05:37,320 Speaker 1: were also philosophers of science at the same time. 93 00:05:37,520 --> 00:05:40,040 Speaker 2: Yeah, I mean, honestly, in that picture, if you look closely, 94 00:05:40,080 --> 00:05:43,920 Speaker 2: I have my little truck in my hand. At the time, 95 00:05:43,960 --> 00:05:46,960 Speaker 2: I was probably more interested in the truck than in philosophy. 96 00:05:47,080 --> 00:05:48,920 Speaker 2: Some days now feel the same. 97 00:05:49,240 --> 00:05:51,360 Speaker 1: All right, Well, before we dig into the topic of 98 00:05:51,400 --> 00:05:53,440 Speaker 1: the day, we'd like to get to know you a 99 00:05:53,480 --> 00:05:55,479 Speaker 1: little bit about where you stand in the sort of 100 00:05:55,800 --> 00:05:58,560 Speaker 1: big questions of philosophy. So let me ask you what 101 00:05:58,600 --> 00:06:00,920 Speaker 1: I think is maybe the most important question in philosophy 102 00:06:00,960 --> 00:06:04,280 Speaker 1: of science, which is, in your opinion, does a star 103 00:06:04,320 --> 00:06:08,000 Speaker 1: Trek transporter actually move your molecules from one place to 104 00:06:08,040 --> 00:06:11,520 Speaker 1: another or does it kill you and reassemble you somewhere else? 105 00:06:12,000 --> 00:06:14,440 Speaker 1: Is it a murder machine or a teleportation device? 106 00:06:14,640 --> 00:06:16,640 Speaker 2: I don't know, man, your guess is as good as mine. 107 00:06:16,680 --> 00:06:20,120 Speaker 2: I'm more of a Star Wars guy than a Star 108 00:06:20,200 --> 00:06:23,080 Speaker 2: Trek guy. I honestly, I think I've only seen like 109 00:06:24,080 --> 00:06:27,840 Speaker 2: maybe one or two Star Trek episodes. I saw one 110 00:06:27,880 --> 00:06:30,360 Speaker 2: of the movies when I was a kid, But I'm 111 00:06:30,360 --> 00:06:33,000 Speaker 2: not a Star Trek guy. It's been Star Wars all 112 00:06:33,080 --> 00:06:33,400 Speaker 2: the day. 113 00:06:34,560 --> 00:06:37,280 Speaker 1: All right, Well, then, what's the deepest question in philosophy 114 00:06:37,360 --> 00:06:41,120 Speaker 1: raised by Star Wars? Is it whether the force actually 115 00:06:41,160 --> 00:06:44,799 Speaker 1: has a scientific explanation or if it's just magic? 116 00:06:45,160 --> 00:06:51,960 Speaker 2: Yeah? Science versus religion questions? Yeah, that's good stuff, Way 117 00:06:51,960 --> 00:06:53,440 Speaker 2: above my pay grade though. 118 00:06:54,839 --> 00:06:57,040 Speaker 1: All right, Well, we'll try to talk about something a 119 00:06:57,080 --> 00:06:59,680 Speaker 1: little bit easier here on the podcast today. What I 120 00:06:59,680 --> 00:07:02,000 Speaker 1: want to talk about drills into the question of, like 121 00:07:02,120 --> 00:07:05,440 Speaker 1: what are we learning when we are building our theories 122 00:07:05,440 --> 00:07:08,080 Speaker 1: of the universe. You know, I'm a particle physicist, and 123 00:07:08,120 --> 00:07:11,000 Speaker 1: here in our department we try to or we imagine 124 00:07:11,000 --> 00:07:14,200 Speaker 1: that we're trying to build a description of what's happening 125 00:07:14,200 --> 00:07:17,280 Speaker 1: in the universe that when we draw a little finement diagrams. 126 00:07:17,320 --> 00:07:20,440 Speaker 1: We're describing what we think the universe is actually doing 127 00:07:20,760 --> 00:07:24,640 Speaker 1: when electrons fly through the universe. But you know, most 128 00:07:24,640 --> 00:07:28,440 Speaker 1: people who think about science, who are in philosophers naturally 129 00:07:28,480 --> 00:07:31,120 Speaker 1: imagine that that's what's happening, you know. They think that 130 00:07:31,160 --> 00:07:33,360 Speaker 1: what we see is real, that the electron is real, 131 00:07:33,480 --> 00:07:36,520 Speaker 1: not just something that we use to do calculations. If 132 00:07:36,560 --> 00:07:38,640 Speaker 1: you tell most people out there, like, look, we don't 133 00:07:38,640 --> 00:07:41,200 Speaker 1: know if an electron is actually real, or if the 134 00:07:41,200 --> 00:07:43,640 Speaker 1: theories that we use to describe them are just things 135 00:07:43,640 --> 00:07:45,400 Speaker 1: in our head. In your view, what's the sort of 136 00:07:45,440 --> 00:07:48,720 Speaker 1: easy way to understand or to approach the question of like, 137 00:07:48,960 --> 00:07:51,520 Speaker 1: what are we learning? Does it represent what's actually out 138 00:07:51,520 --> 00:07:53,840 Speaker 1: there or just things that we are imagining, you know, 139 00:07:53,880 --> 00:07:56,960 Speaker 1: without going full matrix sort of theory on you, what's 140 00:07:57,000 --> 00:07:58,880 Speaker 1: an easy way to access this question? 141 00:07:58,920 --> 00:08:01,360 Speaker 2: In your view, the question is something like the extent 142 00:08:01,400 --> 00:08:06,480 Speaker 2: to which our theories should be taken as literally true 143 00:08:07,760 --> 00:08:11,560 Speaker 2: in their description of the world, and whether our evidence 144 00:08:11,840 --> 00:08:15,480 Speaker 2: for you know, taking our theories is literally true, whether 145 00:08:15,560 --> 00:08:19,120 Speaker 2: the success of our theories gives us good reason to 146 00:08:19,240 --> 00:08:23,800 Speaker 2: think that they are true in all their aspects, not 147 00:08:23,920 --> 00:08:25,920 Speaker 2: just like the stuff that they say about what we 148 00:08:26,000 --> 00:08:28,000 Speaker 2: can see, but the stuff that they say about what 149 00:08:28,040 --> 00:08:32,680 Speaker 2: we can't see. So some folks in philosophy think that 150 00:08:33,679 --> 00:08:38,520 Speaker 2: the empirical success of our theories, and they are like, 151 00:08:39,200 --> 00:08:43,760 Speaker 2: incredibly empirically successful, our best theories, gives us good reason 152 00:08:43,880 --> 00:08:50,280 Speaker 2: to just take them literally as true in all their aspects. 153 00:08:51,720 --> 00:08:55,120 Speaker 2: Other folks in philosophy think that the proper conclusion is 154 00:08:55,160 --> 00:08:58,360 Speaker 2: something more modest, like, you know, it isn't an anti 155 00:08:58,440 --> 00:09:01,800 Speaker 2: science stance or anything, but sugg just the empirical success 156 00:09:01,800 --> 00:09:03,719 Speaker 2: of our theories doesn't tell us that we should take 157 00:09:03,760 --> 00:09:08,319 Speaker 2: them as literally true both in describing stuff that's observable 158 00:09:08,880 --> 00:09:13,199 Speaker 2: and in describing stuff that's not observable. It just tells 159 00:09:13,200 --> 00:09:15,440 Speaker 2: you that theories are successful, and they were designed in 160 00:09:15,480 --> 00:09:18,840 Speaker 2: such a way to be successful. But are they uncovering 161 00:09:19,120 --> 00:09:24,480 Speaker 2: deep truths about the unobservable structure of the universe? Maybe not. 162 00:09:25,000 --> 00:09:26,920 Speaker 1: Yeah, that's a great way to think about it, the 163 00:09:26,960 --> 00:09:31,280 Speaker 1: observable versus the unobservable. And I imagine people might be thinking, like, 164 00:09:31,320 --> 00:09:34,080 Speaker 1: what do you mean unobservable? We do experiments, we see stuff, 165 00:09:34,080 --> 00:09:36,600 Speaker 1: we know electrons are out there. What's a good way 166 00:09:36,640 --> 00:09:40,200 Speaker 1: to think about the unobservable sort of side of science. 167 00:09:40,559 --> 00:09:44,000 Speaker 1: One thing I sometimes imagine is like the fields themselves. 168 00:09:44,040 --> 00:09:46,480 Speaker 1: We talk about on this podcast a lot how space 169 00:09:46,559 --> 00:09:49,160 Speaker 1: is filled with fields, and sometimes those fields ripple to 170 00:09:49,160 --> 00:09:52,280 Speaker 1: make particles, or they ripple to make photons, et cetera. 171 00:09:52,760 --> 00:09:56,679 Speaker 1: But those fields aren't something we ever directly interact with. Right, 172 00:09:56,720 --> 00:09:58,920 Speaker 1: Is that an example of something that's unobservable but a 173 00:09:58,960 --> 00:09:59,680 Speaker 1: part of our theory. 174 00:09:59,800 --> 00:10:02,880 Speaker 2: Yeah, that's right. So, like another good example comes from 175 00:10:03,240 --> 00:10:07,640 Speaker 2: the history of classical space time theories. So you can 176 00:10:08,000 --> 00:10:14,520 Speaker 2: think about Newton's old theory of gravitation. So, according to 177 00:10:14,720 --> 00:10:19,240 Speaker 2: Newton's old theory of gravitation, space time is flat. So 178 00:10:19,320 --> 00:10:23,560 Speaker 2: like the arenea in which events take place is flat, 179 00:10:23,600 --> 00:10:27,400 Speaker 2: it doesn't have interesting geometrical features. And according to this theory, 180 00:10:27,640 --> 00:10:30,480 Speaker 2: gravity is best described as a force, So it's a 181 00:10:30,520 --> 00:10:35,120 Speaker 2: field on your flat space time. And Newton's old law 182 00:10:35,120 --> 00:10:38,920 Speaker 2: of universal gravitation then dictates how particles massive bodies will 183 00:10:38,920 --> 00:10:42,600 Speaker 2: move around depending on what this force is at different 184 00:10:42,640 --> 00:10:45,199 Speaker 2: points in space time. It turns out that you can 185 00:10:45,240 --> 00:10:47,679 Speaker 2: do this theory. This was discovered by folks in the 186 00:10:48,320 --> 00:10:51,600 Speaker 2: early twentieth century. You can do Newton's theory, but on 187 00:10:51,720 --> 00:10:57,160 Speaker 2: a space time that's curved. So, in this alternative formulation 188 00:10:57,240 --> 00:11:02,040 Speaker 2: of Newtonian gravitation, space time is curved. Gravity manifests itself 189 00:11:02,840 --> 00:11:06,040 Speaker 2: and in terms of the curvature of space time rather 190 00:11:06,160 --> 00:11:10,240 Speaker 2: than force. And so now this raises an interesting question. 191 00:11:10,360 --> 00:11:15,160 Speaker 2: You can't observe you're not observing the structure of space time, right, 192 00:11:15,200 --> 00:11:17,960 Speaker 2: what you're observing is how stuff is moving around in 193 00:11:18,040 --> 00:11:21,320 Speaker 2: space time. And so now we have this question. It's 194 00:11:21,720 --> 00:11:25,720 Speaker 2: space time curved or is it flat? According to Newton's theory, 195 00:11:25,760 --> 00:11:27,400 Speaker 2: there are ways to do the theory according to which 196 00:11:27,440 --> 00:11:29,800 Speaker 2: it's curved, ways to do theory according to which it's flat. 197 00:11:30,000 --> 00:11:31,760 Speaker 2: They result in the same empirical prediction. 198 00:11:31,920 --> 00:11:34,760 Speaker 1: But way, But how does the curved space Newton's theory 199 00:11:34,800 --> 00:11:37,199 Speaker 1: different from Einsteini in general relativity. 200 00:11:37,400 --> 00:11:42,280 Speaker 2: It is the same basic concept as Einsteini in general relativity, 201 00:11:42,679 --> 00:11:47,400 Speaker 2: but it yields the same predictions as Newton's theory yields. 202 00:11:48,040 --> 00:11:51,640 Speaker 2: I see. So Einstein's theory and Newton's theory disagree about 203 00:11:51,679 --> 00:11:55,440 Speaker 2: like for example, the famous cases, they disagree about how 204 00:11:55,520 --> 00:11:58,800 Speaker 2: mercury would orbit the Sun. Right, this was the evidence 205 00:11:58,800 --> 00:12:02,160 Speaker 2: that led us to Einstein's theory was Newton's theory was 206 00:12:02,200 --> 00:12:09,320 Speaker 2: getting Mercury's orbit wrong. So the Newtonian gravitation theory set 207 00:12:09,360 --> 00:12:11,600 Speaker 2: on a curve space time, which folks will call newton 208 00:12:11,640 --> 00:12:17,160 Speaker 2: kartong theory, sometimes yields the same empirical predictions as Newton's theory, 209 00:12:17,240 --> 00:12:20,439 Speaker 2: not as Einstein's theory, but it agrees with Einstein's theory 210 00:12:20,480 --> 00:12:23,600 Speaker 2: on the status of the curvature of space time. 211 00:12:23,880 --> 00:12:26,080 Speaker 1: I see, Okay, So you're saying that you could have 212 00:12:26,120 --> 00:12:29,400 Speaker 1: two theories. Newton's original theory of gravity is a force 213 00:12:29,600 --> 00:12:33,680 Speaker 1: and this other weird variation where gravity comes from the 214 00:12:33,720 --> 00:12:36,160 Speaker 1: curvature of space time, but it gives the same predictions 215 00:12:36,200 --> 00:12:40,080 Speaker 1: as Newton's original theory rather than the predictions of Einstein's theory. 216 00:12:40,600 --> 00:12:43,080 Speaker 1: And so then you're saying, this's an unobserved part of 217 00:12:43,120 --> 00:12:46,000 Speaker 1: the universe, the actual predictions of how things are going 218 00:12:46,040 --> 00:12:48,000 Speaker 1: to move. And then there's the sort of behind the 219 00:12:48,000 --> 00:12:50,000 Speaker 1: scenes mechanism. Is it a force or is it the 220 00:12:50,000 --> 00:12:52,839 Speaker 1: curvature of space time? What's sort of happening behind the 221 00:12:52,880 --> 00:12:55,040 Speaker 1: scenes to make that happen. So you're saying, there we 222 00:12:55,080 --> 00:12:58,559 Speaker 1: have like two theories with different descriptions for what's unobserved. 223 00:12:58,800 --> 00:13:02,920 Speaker 2: That's right, There is different descriptions for what's un observed, 224 00:13:03,240 --> 00:13:08,680 Speaker 2: but the same exact description of observable stuff. 225 00:13:08,720 --> 00:13:11,480 Speaker 1: That's really interesting and that touches on the topic I 226 00:13:11,480 --> 00:13:14,760 Speaker 1: wanted to dig into today, which is this underdeterminism, this 227 00:13:14,880 --> 00:13:19,360 Speaker 1: concept in philosophy that we might never actually reveal what's 228 00:13:19,400 --> 00:13:23,120 Speaker 1: happening in the unobserved section of the universe, that there 229 00:13:23,200 --> 00:13:26,520 Speaker 1: might be multiple ways to describe what's sort of happening 230 00:13:26,559 --> 00:13:30,880 Speaker 1: behind the scenes that give the same exact empirical predictions 231 00:13:31,120 --> 00:13:34,120 Speaker 1: that you could never distinguish in experiment, but be described 232 00:13:34,120 --> 00:13:36,960 Speaker 1: by different ideas. And you know, in the example you 233 00:13:37,080 --> 00:13:39,480 Speaker 1: just described, we know that both of those are actually wrong, right, 234 00:13:39,559 --> 00:13:42,319 Speaker 1: Newton's theory of forces in Newton's theory of kurt space 235 00:13:42,360 --> 00:13:44,560 Speaker 1: are both give the same predictions, but they're wrong. But 236 00:13:44,840 --> 00:13:47,480 Speaker 1: let's imagine some other scenario where we have a theory 237 00:13:47,520 --> 00:13:51,280 Speaker 1: of quantum fields and some independent group of scientists have 238 00:13:51,280 --> 00:13:53,360 Speaker 1: been working for a thousand years and they have a 239 00:13:53,400 --> 00:13:56,280 Speaker 1: theory of quantum shmields or something, and they're you know, 240 00:13:56,320 --> 00:13:59,120 Speaker 1: fundamentally different. They're not conceptually the same, but they give 241 00:13:59,160 --> 00:14:03,640 Speaker 1: the same prediction. So I think it's fascinating to think about. 242 00:14:04,200 --> 00:14:07,400 Speaker 1: You know, is it possible to have two really different 243 00:14:07,400 --> 00:14:09,640 Speaker 1: descriptions of what's happening in the universe that predict the 244 00:14:09,640 --> 00:14:12,199 Speaker 1: same thing that we would observe. Is that the sort 245 00:14:12,240 --> 00:14:15,280 Speaker 1: of the fundamental question of underdeterminism and philosophy. 246 00:14:15,520 --> 00:14:19,840 Speaker 2: Yeah, that's exactly right, Like the underlying concept is simple 247 00:14:19,920 --> 00:14:22,480 Speaker 2: and will be familiar to all sorts of folks, Like 248 00:14:22,560 --> 00:14:25,920 Speaker 2: we find ourselves in situations just in our day to 249 00:14:26,000 --> 00:14:30,200 Speaker 2: day lives, where the body of evidence that we've gathered 250 00:14:30,560 --> 00:14:36,000 Speaker 2: doesn't help us adjudicate between two theories. So imagine like 251 00:14:36,120 --> 00:14:39,160 Speaker 2: you come home and I've been to the grocery store. 252 00:14:39,360 --> 00:14:42,160 Speaker 2: You're wondering what I bought at the grocery store. You 253 00:14:42,200 --> 00:14:44,920 Speaker 2: see the receipt sitting on the dining room table, and 254 00:14:45,000 --> 00:14:46,680 Speaker 2: you look at it, and all it says on the 255 00:14:46,720 --> 00:14:49,360 Speaker 2: receipt is that I spent eighteen bucks at the grocery store. 256 00:14:49,880 --> 00:14:53,200 Speaker 2: You know that apples they're like two dollars, oranges are 257 00:14:53,240 --> 00:14:57,760 Speaker 2: three dollars. And now you're faced with a kind of 258 00:14:57,840 --> 00:15:02,080 Speaker 2: underdetermination problem. You don't know how many apples I bought, 259 00:15:02,080 --> 00:15:04,920 Speaker 2: how many oranges I bought. The data gap doesn't help 260 00:15:04,960 --> 00:15:08,920 Speaker 2: me discriminate between the two theories. The data doesn't tell 261 00:15:09,000 --> 00:15:13,800 Speaker 2: you which one is correct, whether I bought six apples 262 00:15:13,960 --> 00:15:18,720 Speaker 2: or nine oranges or some combination. And that's exactly the 263 00:15:18,720 --> 00:15:24,360 Speaker 2: issue that the problem of underdetermination. That's exactly the issue 264 00:15:24,360 --> 00:15:30,280 Speaker 2: that the problem of underdetermination alleges we often face in 265 00:15:30,520 --> 00:15:36,040 Speaker 2: science where we have two theories and the data doesn't 266 00:15:36,080 --> 00:15:40,360 Speaker 2: help us decide which one is correct. The two theories 267 00:15:40,400 --> 00:15:43,760 Speaker 2: are compatible with precisely the same data, And so what 268 00:15:43,800 --> 00:15:45,440 Speaker 2: do we do in a case like that? What do 269 00:15:45,480 --> 00:15:46,760 Speaker 2: we believe right? 270 00:15:46,840 --> 00:15:50,680 Speaker 1: And in that scenario it makes me feel uncomfortable that 271 00:15:50,720 --> 00:15:53,360 Speaker 1: I'm being so nosy about your grocery store purchases. But 272 00:15:53,440 --> 00:15:54,800 Speaker 1: you know, in the case of the universe, I don't 273 00:15:54,800 --> 00:15:57,400 Speaker 1: think the universe deserves any privacy. I think, you know, 274 00:15:57,480 --> 00:16:00,840 Speaker 1: we are entitled to peak behind the curtain as much 275 00:16:00,920 --> 00:16:03,200 Speaker 1: as we can and trying to figure out what's going 276 00:16:03,240 --> 00:16:05,600 Speaker 1: on and what the universe bought at the grocery store. 277 00:16:05,680 --> 00:16:07,920 Speaker 1: But what is the motivation for this? Is this just 278 00:16:08,080 --> 00:16:11,760 Speaker 1: like you know, philosophical meandering, Oh what if? What could 279 00:16:11,760 --> 00:16:14,920 Speaker 1: it be possible? Some sort of deep skepticism that maybe 280 00:16:14,960 --> 00:16:17,600 Speaker 1: will never figure things out, or do we have like 281 00:16:17,880 --> 00:16:21,160 Speaker 1: any sort of concrete examples of scenarios where we really 282 00:16:21,200 --> 00:16:26,000 Speaker 1: had two excellent theories that gave exactly the same predictions 283 00:16:26,480 --> 00:16:28,680 Speaker 1: but had different scenarios behind the scenes. 284 00:16:28,920 --> 00:16:31,520 Speaker 2: Yeah, so let me give a couple of examples. The 285 00:16:31,560 --> 00:16:36,720 Speaker 2: example we were discussing earlier of Newton's standard theory of gravity, 286 00:16:36,840 --> 00:16:41,320 Speaker 2: in which gravity is a force versus this geometrized version 287 00:16:41,440 --> 00:16:47,200 Speaker 2: of theorem gravity. That's a famous historical case. Of course, 288 00:16:47,280 --> 00:16:50,680 Speaker 2: as you say, like, we know that neither of those 289 00:16:50,720 --> 00:16:58,320 Speaker 2: theories is correct. They make bad predictions, but the existence 290 00:16:58,520 --> 00:17:02,160 Speaker 2: of an example like this should give one pause. It 291 00:17:02,200 --> 00:17:05,520 Speaker 2: gives us read think that maybe the same thing can 292 00:17:05,560 --> 00:17:09,239 Speaker 2: happen with our current best theories. So there are other 293 00:17:09,280 --> 00:17:13,440 Speaker 2: examples from the history of physics. Another famous one is 294 00:17:13,920 --> 00:17:18,520 Speaker 2: the case of Hamiltonian and Lagrangian mechanics. Okay, suppose you 295 00:17:18,720 --> 00:17:23,880 Speaker 2: formulate your theory of classical mechanics. Newton's old theory how 296 00:17:23,960 --> 00:17:28,159 Speaker 2: stuff will move around in space by taking positions and 297 00:17:28,240 --> 00:17:33,440 Speaker 2: velocities is fundamental. Okay, So you think that we should 298 00:17:33,600 --> 00:17:37,840 Speaker 2: specify the energy conditions of a system by laying down 299 00:17:37,880 --> 00:17:42,119 Speaker 2: something that you call a Lagrangian So kind of a 300 00:17:42,160 --> 00:17:46,919 Speaker 2: function on possible configurations of positions and velocities that dictates 301 00:17:47,359 --> 00:17:54,080 Speaker 2: how active or lively these configurations are. Hell me how 302 00:17:54,440 --> 00:17:57,919 Speaker 2: these properties of the system, the positions and velocities of 303 00:17:58,200 --> 00:18:01,679 Speaker 2: particles in your system, will evolve over time by laying 304 00:18:01,720 --> 00:18:04,280 Speaker 2: down a set of equations that you call the Euler 305 00:18:04,320 --> 00:18:09,480 Speaker 2: Legronge equations. Okay, so call your theory Lagrangian mechanics. On 306 00:18:09,520 --> 00:18:15,520 Speaker 2: the other hand, for whatever reason, don't like velocity, Okay, 307 00:18:15,520 --> 00:18:17,919 Speaker 2: I find momentum to be much more elegant. You know, 308 00:18:17,960 --> 00:18:22,639 Speaker 2: it's conserved, and so I formulate my theory by specifying 309 00:18:22,720 --> 00:18:26,719 Speaker 2: energy conditions to the system laying down a Hamiltonian. I 310 00:18:26,800 --> 00:18:32,000 Speaker 2: take positions in momentum as the fundamental properties that a 311 00:18:32,040 --> 00:18:37,159 Speaker 2: system has, and I can tell you how the system 312 00:18:37,200 --> 00:18:40,000 Speaker 2: will evolve over time by laying down a different set 313 00:18:40,040 --> 00:18:43,240 Speaker 2: of equations. So call these Hamilton's equations, and they take 314 00:18:43,240 --> 00:18:47,280 Speaker 2: in the Hamiltonian of the system. So the Hamiltonian describes 315 00:18:47,440 --> 00:18:50,280 Speaker 2: something like the total energy of the system, rather than 316 00:18:50,320 --> 00:18:53,679 Speaker 2: its activity or liveliness, just total energy. I call my 317 00:18:53,760 --> 00:18:57,720 Speaker 2: theory Hamiltonian mechanics. So it turns out that our theories 318 00:18:57,720 --> 00:19:01,199 Speaker 2: are empirically equivalent. So what do we mean by that? 319 00:19:01,760 --> 00:19:06,959 Speaker 2: We mean, there's no possible evidence that is compatible with 320 00:19:07,000 --> 00:19:11,440 Speaker 2: my theory but incompatible with yours, or vice versa. 321 00:19:11,800 --> 00:19:14,520 Speaker 1: So first, like some set of balls or squirrels on 322 00:19:14,640 --> 00:19:17,280 Speaker 1: roller coasters, they always give the same predictions for what's 323 00:19:17,280 --> 00:19:18,440 Speaker 1: going to happen exactly. 324 00:19:18,480 --> 00:19:21,240 Speaker 2: Your theory gives the same prediction as my theory. But 325 00:19:21,560 --> 00:19:25,000 Speaker 2: it seems like we've done things differently, right, You care 326 00:19:25,000 --> 00:19:29,000 Speaker 2: about positions and velocities. I care about positions and momentums. 327 00:19:30,119 --> 00:19:34,359 Speaker 2: The laws of nature, one might say, according to your theory, 328 00:19:34,440 --> 00:19:37,080 Speaker 2: or different than the ones according to my theory, Like 329 00:19:37,200 --> 00:19:40,959 Speaker 2: we laid down different equations when we were saying how 330 00:19:42,080 --> 00:19:45,320 Speaker 2: the stuff was going to behave And so one might 331 00:19:45,400 --> 00:19:48,080 Speaker 2: think that we have a choice to be made here 332 00:19:48,119 --> 00:19:52,439 Speaker 2: between these two theories. But the evidence won't make the 333 00:19:52,560 --> 00:19:59,000 Speaker 2: choice for us. So that's another example of a possible 334 00:19:59,080 --> 00:20:02,800 Speaker 2: case of under termination, where two theories compatible with the 335 00:20:02,840 --> 00:20:05,640 Speaker 2: same body of evidence, but it seems like we might 336 00:20:05,720 --> 00:20:08,960 Speaker 2: have a choice to make between them. In cases like this, 337 00:20:09,520 --> 00:20:16,200 Speaker 2: the standard conclusion to draw is kind of a skeptical thing. 338 00:20:16,640 --> 00:20:20,919 Speaker 2: The things about which these two theories disagree. We now 339 00:20:21,000 --> 00:20:24,400 Speaker 2: don't have answers to these questions unless we can decide 340 00:20:24,400 --> 00:20:27,239 Speaker 2: which one of the two theories is correct, and how 341 00:20:27,280 --> 00:20:29,879 Speaker 2: do we make that decision. The evidence isn't going to 342 00:20:29,920 --> 00:20:33,040 Speaker 2: make the decision for us, so we have to come 343 00:20:33,080 --> 00:20:35,080 Speaker 2: to a decision by some other means. 344 00:20:35,440 --> 00:20:37,960 Speaker 1: So we have two different sets of equations that give 345 00:20:38,000 --> 00:20:41,080 Speaker 1: the same predictions for what happens to squirrels on roller 346 00:20:41,160 --> 00:20:43,720 Speaker 1: coasters or billiar tables and these kinds of things, and 347 00:20:43,760 --> 00:20:46,400 Speaker 1: you're saying that they really are different in some way, 348 00:20:46,600 --> 00:20:49,080 Speaker 1: And because they always give the same predictions, there's no 349 00:20:49,160 --> 00:20:52,159 Speaker 1: way to do this sort of famous scientific test of say, well, 350 00:20:52,240 --> 00:20:55,600 Speaker 1: let's do an experiment and figure out the different hypotheses 351 00:20:55,600 --> 00:20:58,159 Speaker 1: and the different predictions, because they're always the same. But 352 00:20:58,280 --> 00:21:00,720 Speaker 1: if they're always the same, how do we know that 353 00:21:00,760 --> 00:21:03,040 Speaker 1: they really are different theories? I mean, I can take 354 00:21:03,040 --> 00:21:05,119 Speaker 1: any arbitrary theory and say I'm going to multiply everything 355 00:21:05,119 --> 00:21:06,520 Speaker 1: by two, and then at the end I'm going to 356 00:21:06,560 --> 00:21:09,560 Speaker 1: divide by two, and superficially, the equations might look a 357 00:21:09,600 --> 00:21:12,520 Speaker 1: little bit different, but it gives exactly the same predictions. 358 00:21:12,520 --> 00:21:15,320 Speaker 1: But not for an interesting reason, not because I'm really 359 00:21:15,359 --> 00:21:18,440 Speaker 1: saying this different stuff happening behind the scenes of the universe. 360 00:21:18,880 --> 00:21:21,800 Speaker 1: So in the case of Hamiltonian versus Lagrangeen mechanics, or 361 00:21:21,960 --> 00:21:25,080 Speaker 1: really in the case of fields versus Shmields, or any comparison, 362 00:21:25,480 --> 00:21:27,360 Speaker 1: what does it mean to say that they're different? How 363 00:21:27,359 --> 00:21:29,439 Speaker 1: do we know that they're different? Or is there some 364 00:21:29,480 --> 00:21:32,080 Speaker 1: standard we apply to say, like, this theory is telling 365 00:21:32,119 --> 00:21:35,080 Speaker 1: a different story about what's happening in the universe than 366 00:21:35,160 --> 00:21:36,320 Speaker 1: that theory. How do we do that? 367 00:21:36,640 --> 00:21:39,560 Speaker 2: Yeah, good question. So, like the suggestion is something like, 368 00:21:39,840 --> 00:21:44,480 Speaker 2: maybe in some of these worrying cases of underdetermination, you 369 00:21:44,520 --> 00:21:49,320 Speaker 2: don't actually have two genuine rivals. They're the same theory, 370 00:21:49,520 --> 00:21:53,199 Speaker 2: just presented to you in different guises, And so like 371 00:21:53,359 --> 00:21:55,679 Speaker 2: you don't have a real choice to make. It's the 372 00:21:55,840 --> 00:21:59,720 Speaker 2: choice between one theory and itself, just presented to you differently. 373 00:22:00,040 --> 00:22:04,240 Speaker 2: So maybe let me tell a story. The most famous 374 00:22:04,320 --> 00:22:09,399 Speaker 2: case of this happened in the early years of quantum mechanics. Okay, 375 00:22:09,520 --> 00:22:15,760 Speaker 2: so in brief, Heisenberg had his matrix mechanics, Schrodinger had 376 00:22:15,800 --> 00:22:21,320 Speaker 2: his wave mechanics, and these guys like did not vibe 377 00:22:22,840 --> 00:22:27,119 Speaker 2: on the base of it. Their theories seemed incompatible. So 378 00:22:27,160 --> 00:22:30,280 Speaker 2: they made the same predictions, but they used like radically 379 00:22:30,280 --> 00:22:35,200 Speaker 2: different mathematical apparatus. To do so. So Schrodinger at one 380 00:22:35,240 --> 00:22:41,199 Speaker 2: point equipped that Heisenberg's theory lacked visualizability, into which Heisenberg 381 00:22:41,520 --> 00:22:47,159 Speaker 2: shot back, I quote what Schrodinger writes about visualizability as crap. 382 00:22:50,440 --> 00:22:52,840 Speaker 2: We eventually, like, we realized that there's a way to 383 00:22:52,880 --> 00:22:57,760 Speaker 2: translate between the Heisenberg picture and the Schrodinger picture and 384 00:22:57,880 --> 00:23:01,280 Speaker 2: vice versa. And so there's a sense in which there 385 00:23:01,320 --> 00:23:04,760 Speaker 2: are two ways of doing quantum mechanics were not that different. 386 00:23:04,800 --> 00:23:08,760 Speaker 2: After all. The disputes between the two theories, like the 387 00:23:08,800 --> 00:23:13,800 Speaker 2: stuff that they disagreed about is just verbal. It was 388 00:23:13,880 --> 00:23:16,399 Speaker 2: like we were having a verbal dispute. It was the 389 00:23:16,440 --> 00:23:21,399 Speaker 2: same theory presenting in two different ways. And so we 390 00:23:21,480 --> 00:23:23,800 Speaker 2: don't have a trouble in case of underdetermination. There a 391 00:23:23,840 --> 00:23:26,800 Speaker 2: trouble in case of underdetermination was avoided because you didn't 392 00:23:26,800 --> 00:23:30,920 Speaker 2: have a genuine decision to be made between these two 393 00:23:32,160 --> 00:23:34,320 Speaker 2: Between these two theories, the two theories were actually one. 394 00:23:34,600 --> 00:23:36,240 Speaker 1: So it turns out that they were really just the 395 00:23:36,280 --> 00:23:38,640 Speaker 1: same theory dressed in different clothes, right. 396 00:23:38,680 --> 00:23:40,960 Speaker 2: Yeah, yeah, And so this is something that one might 397 00:23:41,000 --> 00:23:44,200 Speaker 2: be tempted to say in the case of Hamiltonian and 398 00:23:44,240 --> 00:23:48,639 Speaker 2: lagrondgy mechanics too, you know, you pick position and velocity 399 00:23:48,680 --> 00:23:52,000 Speaker 2: to do your theory. I pick position and momentum to 400 00:23:52,040 --> 00:23:55,680 Speaker 2: do my theory. But we can translate back and forth 401 00:23:55,840 --> 00:23:58,960 Speaker 2: between these two descriptions. It's not like when you talk 402 00:23:59,000 --> 00:24:02,360 Speaker 2: about position in the law, I can't do that in 403 00:24:02,400 --> 00:24:05,640 Speaker 2: my theory. I would do it, you know, a little differently. 404 00:24:05,680 --> 00:24:08,040 Speaker 2: I'd use a little bit of different language to do so. 405 00:24:08,600 --> 00:24:11,600 Speaker 2: But am I saying a genuinely different thing about the 406 00:24:11,640 --> 00:24:14,879 Speaker 2: world when I decide to say it in position and 407 00:24:14,920 --> 00:24:19,040 Speaker 2: momentum language versus when you say it in position and 408 00:24:19,080 --> 00:24:22,639 Speaker 2: philosophy language. So in general, this is a kind of 409 00:24:22,720 --> 00:24:28,560 Speaker 2: response one can give to underdetermination worries. It's like, look 410 00:24:28,560 --> 00:24:31,879 Speaker 2: in a lot of the problematic cases of underdetermination that 411 00:24:31,960 --> 00:24:34,800 Speaker 2: we see, so cases where you have two theories that 412 00:24:35,080 --> 00:24:38,880 Speaker 2: can't be discriminated between on the basis of the evidence 413 00:24:38,920 --> 00:24:41,880 Speaker 2: we've gathered. In a lot of these cases, you don't 414 00:24:41,880 --> 00:24:45,080 Speaker 2: actually have genuine rivals. The two theories can't be discriminated 415 00:24:45,119 --> 00:24:47,720 Speaker 2: between on the basis of the evidence we've gathered, but 416 00:24:47,720 --> 00:24:48,639 Speaker 2: they're the same theory. 417 00:24:48,800 --> 00:24:52,200 Speaker 1: Yeah, and so what about the case of later sort 418 00:24:52,200 --> 00:24:56,160 Speaker 1: of quantum mechanical interpretations. You know, we have various descriptions 419 00:24:56,200 --> 00:24:59,760 Speaker 1: of what's going on with particles. Is the way function 420 00:24:59,840 --> 00:25:03,080 Speaker 1: call colapsing, or is the universe splitting into multiple universes 421 00:25:03,800 --> 00:25:07,000 Speaker 1: or is the collapse relative? You know, like in relational 422 00:25:07,080 --> 00:25:11,000 Speaker 1: quantum mechanics. Are those examples of true underdetermination where we 423 00:25:11,400 --> 00:25:15,600 Speaker 1: have really different stories, genuinely different accounts of the physical world, 424 00:25:15,800 --> 00:25:18,159 Speaker 1: but that make effectively the same predictions for what we 425 00:25:18,200 --> 00:25:21,479 Speaker 1: could see in experiments, like we can't distinguish between the 426 00:25:21,480 --> 00:25:26,359 Speaker 1: many world hypothesis or the Copenhagen interpretation using experiments. Is 427 00:25:26,359 --> 00:25:27,080 Speaker 1: that an example? 428 00:25:27,320 --> 00:25:30,560 Speaker 2: That is an example where it becomes harder for one 429 00:25:30,600 --> 00:25:34,479 Speaker 2: to say that the theories are genuinely the same, and 430 00:25:34,760 --> 00:25:40,240 Speaker 2: yet they have the same experiments supporting both of them. 431 00:25:40,320 --> 00:25:44,080 Speaker 2: So some folks at this point will say that there's 432 00:25:44,080 --> 00:25:48,000 Speaker 2: another natural way to respond to problems of underdetermination. So 433 00:25:48,160 --> 00:25:51,800 Speaker 2: the empirical evidence doesn't help us decide which theory is correct, 434 00:25:52,560 --> 00:25:54,399 Speaker 2: But we have some stuff that we can use to 435 00:25:54,400 --> 00:25:58,280 Speaker 2: make these decisions not using empirical evidence, and we do 436 00:25:58,320 --> 00:26:01,439 Speaker 2: this all the time. We appear to other virtues that 437 00:26:01,480 --> 00:26:02,919 Speaker 2: a theory might exhibit. 438 00:26:02,840 --> 00:26:05,360 Speaker 1: Like simplicity or exact money. 439 00:26:05,560 --> 00:26:10,159 Speaker 2: Okay, yeah, simplicity, fruitfulness, I don't know something like this, 440 00:26:11,000 --> 00:26:13,080 Speaker 2: And scientists do this all the time. We all do this. 441 00:26:15,800 --> 00:26:18,560 Speaker 1: Well, I was having a conversation with a theoretical physicist 442 00:26:18,800 --> 00:26:21,200 Speaker 1: who's quite well known in particle physics, but I won't 443 00:26:21,280 --> 00:26:23,159 Speaker 1: name him, and I describe this problem to him, and 444 00:26:23,240 --> 00:26:26,200 Speaker 1: he said, well, look, if the theories predict the same 445 00:26:26,240 --> 00:26:30,400 Speaker 1: things but are different, then they're different only in the metaphysics, right, 446 00:26:30,640 --> 00:26:32,760 Speaker 1: only in the irrelevant details, which I think is another 447 00:26:32,760 --> 00:26:35,359 Speaker 1: way to say, like, well, maybe who cares? Right, Like, 448 00:26:35,680 --> 00:26:37,800 Speaker 1: we have two different descriptions of the universe, but they 449 00:26:37,800 --> 00:26:40,439 Speaker 1: give the same predictions. What does it matter? And to 450 00:26:40,480 --> 00:26:42,800 Speaker 1: me this is sort of shocking coming from a theorist 451 00:26:42,880 --> 00:26:45,399 Speaker 1: who you know, I think their job essentially is to 452 00:26:45,920 --> 00:26:49,840 Speaker 1: uncover the mechanisms of the universe, not just to produce 453 00:26:50,040 --> 00:26:52,600 Speaker 1: calculational tools that will get us to the next step, 454 00:26:52,600 --> 00:26:55,960 Speaker 1: but like reveal the nature of reality man. And so 455 00:26:56,000 --> 00:26:57,800 Speaker 1: to hear somebody be like, well, maybe it doesn't matter 456 00:26:57,840 --> 00:27:01,000 Speaker 1: if it's fields or shmields as lung as the numbers 457 00:27:01,040 --> 00:27:01,600 Speaker 1: are right. 458 00:27:01,760 --> 00:27:03,119 Speaker 2: How does that strike you, as sort of. 459 00:27:03,080 --> 00:27:05,600 Speaker 1: A philosopher of science, do you think that that sort 460 00:27:05,640 --> 00:27:08,520 Speaker 1: of instrumental approach is a solution to this problem, or 461 00:27:08,560 --> 00:27:09,920 Speaker 1: are we just avoiding the question. 462 00:27:10,240 --> 00:27:16,280 Speaker 2: It's not an attitude that's uncommon among philosophers. Also, I 463 00:27:16,280 --> 00:27:20,240 Speaker 2: do think it's kind of avoiding sidestepping the question rather 464 00:27:20,320 --> 00:27:23,720 Speaker 2: than taking it on head on. One thing that I 465 00:27:23,720 --> 00:27:28,320 Speaker 2: should say, though, is notice that this kind of attitude. 466 00:27:28,359 --> 00:27:32,320 Speaker 2: So we have two theories, the evidence doesn't distinguish between them, 467 00:27:32,440 --> 00:27:36,520 Speaker 2: so they're the same in all important aspects. There's a 468 00:27:36,560 --> 00:27:41,840 Speaker 2: sense in which that attitude lands oneself in the same 469 00:27:41,960 --> 00:27:46,479 Speaker 2: place as taking the problem of underdetermination seriously ends oneself in. 470 00:27:47,160 --> 00:27:49,480 Speaker 2: The idea is, if you don't think that the theories 471 00:27:49,480 --> 00:27:54,159 Speaker 2: are telling you anything about the non empirical stuff, the 472 00:27:54,240 --> 00:27:57,840 Speaker 2: unobservable stuff, there's a sense in which you're not taking 473 00:27:57,880 --> 00:28:02,760 Speaker 2: your theories all that serious right, which is very close 474 00:28:04,200 --> 00:28:08,280 Speaker 2: to the place that the problem of underdetermination would lead 475 00:28:08,440 --> 00:28:11,159 Speaker 2: us in both cases, So, say you don't take the 476 00:28:11,200 --> 00:28:14,879 Speaker 2: metaphysics of your theory seriously, and there are some unanswered 477 00:28:14,960 --> 00:28:18,879 Speaker 2: questions like is space flat or is it curved? Suppose 478 00:28:18,920 --> 00:28:22,320 Speaker 2: you take the problem of underdetermination seriously, then you end 479 00:28:22,400 --> 00:28:25,520 Speaker 2: up with unanswered questions for a slightly different reason, but 480 00:28:25,560 --> 00:28:28,840 Speaker 2: in both cases you're ending with questions that are not 481 00:28:28,920 --> 00:28:30,520 Speaker 2: being answered by your physics. 482 00:28:31,119 --> 00:28:33,560 Speaker 1: Okay, I have a lot more questions about how this 483 00:28:33,760 --> 00:28:35,680 Speaker 1: all works and how we can make sense of it, 484 00:28:35,720 --> 00:28:51,000 Speaker 1: but first let's take a quick break. All right, we're 485 00:28:51,040 --> 00:28:53,840 Speaker 1: back and we're talking to Professor Thomas Barrett about the 486 00:28:53,920 --> 00:28:58,320 Speaker 1: question of underdeterminism in philosophy of science, whether it's possible 487 00:28:58,320 --> 00:29:01,840 Speaker 1: to have multiple theories that describe the universe and make 488 00:29:01,920 --> 00:29:07,280 Speaker 1: exactly the same predictions but are in themselves fundamentally different. Well, 489 00:29:07,320 --> 00:29:11,480 Speaker 1: in almost every example, we've considered various versions of Newtonon theory. 490 00:29:11,240 --> 00:29:11,680 Speaker 2: Et cetera. 491 00:29:12,320 --> 00:29:14,960 Speaker 1: One can sometimes imagine that maybe in the future or 492 00:29:15,040 --> 00:29:18,000 Speaker 1: somebody will come up with an experiment to help us distinguish, 493 00:29:18,080 --> 00:29:20,520 Speaker 1: or somebody will be the next generation's John Bell will 494 00:29:20,520 --> 00:29:22,800 Speaker 1: come up with a super clever quantum experiment to help 495 00:29:22,880 --> 00:29:25,960 Speaker 1: us reveal multiple universes or something, even in the face 496 00:29:26,000 --> 00:29:30,960 Speaker 1: of like infinite data. Is the argument for underdetermination really 497 00:29:31,000 --> 00:29:33,760 Speaker 1: that it's impossible that, you know, even in a million years, 498 00:29:33,760 --> 00:29:37,880 Speaker 1: a billion years of super Einstein's could never come up 499 00:29:37,880 --> 00:29:41,320 Speaker 1: with a way to distinguish that. It might literally be impossible, 500 00:29:41,440 --> 00:29:43,320 Speaker 1: not just we haven't figured it out yet. 501 00:29:43,480 --> 00:29:46,480 Speaker 2: Yeah, So think back. This is a good question think 502 00:29:46,560 --> 00:29:51,400 Speaker 2: back to the apples and oranges example. The natural thing 503 00:29:51,440 --> 00:29:54,200 Speaker 2: to say in that example is like, look, dude, you've 504 00:29:54,360 --> 00:29:57,200 Speaker 2: just looked at the receed on the table. You want 505 00:29:57,200 --> 00:29:58,840 Speaker 2: to know how many apples and oranges there are? Like, 506 00:29:58,880 --> 00:30:03,560 Speaker 2: go open up the pa entry, right, Like gather more data? 507 00:30:03,640 --> 00:30:08,600 Speaker 2: So problematic, like truly problematic cases of underdetermination, you know, 508 00:30:08,640 --> 00:30:11,080 Speaker 2: the ones that will keep you up at night. Our 509 00:30:11,160 --> 00:30:15,440 Speaker 2: cases where even gathering the more data won't help you 510 00:30:15,560 --> 00:30:20,640 Speaker 2: distinguish between the two theories. Just the two theories are 511 00:30:21,040 --> 00:30:27,280 Speaker 2: provably compatible with precisely the same collection of evidence. So 512 00:30:27,320 --> 00:30:30,920 Speaker 2: maybe one example, one further example will be helpful here. 513 00:30:31,360 --> 00:30:36,720 Speaker 2: So this comes from our recent work my good friend 514 00:30:36,800 --> 00:30:41,720 Speaker 2: and your colleague, get Irvine JB. Mancheck has done in 515 00:30:42,200 --> 00:30:47,400 Speaker 2: general relativity. So what Manchik proves is that in the 516 00:30:47,440 --> 00:30:52,680 Speaker 2: context of Einstein's theory of general relativity, we encounter a 517 00:30:53,000 --> 00:30:58,000 Speaker 2: very pernicious kind of underdetermination. So here's the gist. In 518 00:30:58,040 --> 00:31:02,959 Speaker 2: general relativity. Intuitively, like and signals can't travel faster than 519 00:31:03,040 --> 00:31:08,520 Speaker 2: the speed of light, you can only know at most 520 00:31:08,760 --> 00:31:11,760 Speaker 2: everything that goes on in your past light cone. So 521 00:31:11,880 --> 00:31:14,440 Speaker 2: all the evidence that's available to you at some time 522 00:31:14,560 --> 00:31:18,720 Speaker 2: will have arrived to you via some trajectory that's contained 523 00:31:18,720 --> 00:31:22,040 Speaker 2: in your past, like Cone. Right, like picture the stuff 524 00:31:22,040 --> 00:31:26,800 Speaker 2: that you see, Well, that's arriving to you via photons 525 00:31:26,840 --> 00:31:28,960 Speaker 2: that are reflecting off the surface of the thing. They're 526 00:31:29,000 --> 00:31:32,440 Speaker 2: all contained in your past like Cone. Your colleagues reporting 527 00:31:32,480 --> 00:31:35,760 Speaker 2: to you their evidence, well they came to you in 528 00:31:35,800 --> 00:31:39,560 Speaker 2: your past, like Cone. So Manchik proves now that given 529 00:31:39,600 --> 00:31:44,320 Speaker 2: this information, there's always more than one model of the 530 00:31:44,520 --> 00:31:48,960 Speaker 2: universe according to Einstein's theory that's compatible with the data 531 00:31:49,080 --> 00:31:51,360 Speaker 2: you could have possibly gathered. 532 00:31:51,120 --> 00:31:53,360 Speaker 1: Meaning that there's always part of the universe sort of 533 00:31:53,400 --> 00:31:56,440 Speaker 1: shrouded in darkness because it could be just like so 534 00:31:56,680 --> 00:31:59,040 Speaker 1: far away given the age of the universe, that there 535 00:31:59,040 --> 00:32:01,680 Speaker 1: hasn't been time for light from it to arrive here, 536 00:32:01,720 --> 00:32:04,240 Speaker 1: And so there could be huge purple dragons beyond the 537 00:32:04,280 --> 00:32:06,840 Speaker 1: ende of the universe, or not huge purple dragons beyond 538 00:32:06,880 --> 00:32:07,720 Speaker 1: the edge of the universe. 539 00:32:07,880 --> 00:32:09,720 Speaker 2: Yeah, exactly. I mean, they don't even have to be 540 00:32:09,800 --> 00:32:11,760 Speaker 2: that far from you. They just have to be not 541 00:32:11,920 --> 00:32:14,880 Speaker 2: in your backward like Cone. So the idea is, if 542 00:32:14,920 --> 00:32:19,040 Speaker 2: general relativity is true, if Einstein's theory is true, that 543 00:32:19,320 --> 00:32:25,040 Speaker 2: it itself implies that we can't know the global structure 544 00:32:25,120 --> 00:32:29,040 Speaker 2: of the universe because of the limitations that the theory 545 00:32:29,120 --> 00:32:34,320 Speaker 2: places on how evidence must work. It has to be 546 00:32:34,360 --> 00:32:37,400 Speaker 2: contained in your backward like cone, we have a case 547 00:32:37,440 --> 00:32:41,600 Speaker 2: where no matter how much data you gather, you're going 548 00:32:41,680 --> 00:32:46,040 Speaker 2: to have different possibilities for what the universe is. Like 549 00:32:47,480 --> 00:32:50,040 Speaker 2: that the data doesn't distinguish between well. 550 00:32:49,920 --> 00:32:51,760 Speaker 1: It seems to me in the end to come down 551 00:32:51,800 --> 00:32:54,640 Speaker 1: to a form of skepticism to say, like, look, there 552 00:32:54,680 --> 00:32:58,000 Speaker 1: could always be some other theory out there that makes 553 00:32:58,040 --> 00:33:01,360 Speaker 1: the same predictions but has a different story about the universe, 554 00:33:02,000 --> 00:33:04,680 Speaker 1: and so is the conclusion then, I mean, what does 555 00:33:04,720 --> 00:33:08,200 Speaker 1: that mean about our understanding of the universe? As you say, 556 00:33:08,320 --> 00:33:11,520 Speaker 1: does that mean we shouldn't take too seriously the story 557 00:33:11,800 --> 00:33:14,640 Speaker 1: about what's happening When we write Fineman diagrams there are 558 00:33:14,640 --> 00:33:17,440 Speaker 1: a great little trick for making calculations. But does that 559 00:33:17,520 --> 00:33:20,200 Speaker 1: mean that we can't really believe that the universe is 560 00:33:20,520 --> 00:33:24,080 Speaker 1: doing its own finement calculations that fields are real because 561 00:33:24,120 --> 00:33:26,800 Speaker 1: there could be schmields instead. Does that mean we can 562 00:33:26,880 --> 00:33:30,000 Speaker 1: never really know what's happening out there in the universe. 563 00:33:30,200 --> 00:33:35,160 Speaker 2: Yeah, So it all turns on how seriously you take 564 00:33:35,600 --> 00:33:42,480 Speaker 2: this possibility of alternative theories that have the same empirical 565 00:33:42,520 --> 00:33:47,360 Speaker 2: consequences as are current theories. So notice all we've done 566 00:33:47,440 --> 00:33:51,320 Speaker 2: here is I've given a bunch of examples of pairs 567 00:33:51,360 --> 00:33:55,280 Speaker 2: of theories where the evidence can't tell you which one 568 00:33:55,360 --> 00:34:00,520 Speaker 2: is rund. I haven't given you a general prison siezure 569 00:34:00,640 --> 00:34:04,520 Speaker 2: that you can use to construct from our best physical 570 00:34:04,520 --> 00:34:09,920 Speaker 2: theory arrival that agrees with it in all of its predictions, 571 00:34:10,480 --> 00:34:13,680 Speaker 2: but it's different. So that would be the gold standard, 572 00:34:13,840 --> 00:34:16,160 Speaker 2: right If we could do that, then I would be 573 00:34:17,000 --> 00:34:21,880 Speaker 2: very disturbed. We would have a mechanism for generating pairs 574 00:34:21,880 --> 00:34:25,120 Speaker 2: of theories where the evidence doesn't hell which one is right, 575 00:34:25,160 --> 00:34:28,800 Speaker 2: but they're different, and then we're kind of we're sunk. 576 00:34:28,840 --> 00:34:31,040 Speaker 2: I don't know how to answer our questions about the 577 00:34:31,120 --> 00:34:34,480 Speaker 2: unobservable anymore. We don't have that. All we have is 578 00:34:34,480 --> 00:34:37,960 Speaker 2: a bunch of examples. So what's the right conclusion to draws? 579 00:34:38,200 --> 00:34:40,319 Speaker 2: We do have a lot of examples. I mean, I've 580 00:34:40,320 --> 00:34:42,359 Speaker 2: talked to you as well. I don't know, depends on 581 00:34:42,480 --> 00:34:43,719 Speaker 2: how many you think is a lot. I think I've 582 00:34:43,719 --> 00:34:44,399 Speaker 2: talked about four. 583 00:34:44,760 --> 00:34:46,319 Speaker 1: Let me just make sure I understand what you're saying 584 00:34:46,719 --> 00:34:49,279 Speaker 1: you're trying to be careful not to overstate your conclusions. 585 00:34:49,320 --> 00:34:51,880 Speaker 1: You're saying, we have some examples that suggest that it 586 00:34:51,960 --> 00:34:55,520 Speaker 1: might be possible to have two theories that explain the 587 00:34:55,600 --> 00:34:58,439 Speaker 1: universe equally well but have different stories, But we don't 588 00:34:58,440 --> 00:35:00,920 Speaker 1: have a general proof that that's all we possible. They 589 00:35:00,920 --> 00:35:03,120 Speaker 1: don't have like a procedure that says, if you have 590 00:35:03,160 --> 00:35:05,400 Speaker 1: a great theory, I can always use it to generate 591 00:35:05,440 --> 00:35:08,399 Speaker 1: an alternative theory that works just as well. So you're 592 00:35:08,400 --> 00:35:11,960 Speaker 1: saying there'd be a little bit of skepticism about our skepticism. 593 00:35:12,360 --> 00:35:16,319 Speaker 2: Yeah, that's right, or we should be modest about our skepticism. Right. 594 00:35:16,320 --> 00:35:18,759 Speaker 1: I was reading this article of by Philip Kitchener, and 595 00:35:18,800 --> 00:35:21,760 Speaker 1: he says, give us a rival explanation, and we'll consider 596 00:35:21,880 --> 00:35:25,239 Speaker 1: whether it is sufficiently serious to threaten our confidence, which 597 00:35:25,280 --> 00:35:29,400 Speaker 1: is basically like saying, maybe this is a problem in theory, 598 00:35:29,760 --> 00:35:32,520 Speaker 1: but right now it's not one that's facing us, so 599 00:35:32,600 --> 00:35:33,280 Speaker 1: maybe it won't. 600 00:35:33,480 --> 00:35:37,879 Speaker 2: Yeah. I think that's right. So now philosophers have attempted 601 00:35:38,040 --> 00:35:42,680 Speaker 2: through the years to give kind of algorithmic procedures for 602 00:35:42,880 --> 00:35:48,360 Speaker 2: generating rival theories that are equally compatible with our data. 603 00:35:48,800 --> 00:35:52,440 Speaker 2: The kind of algorithmic procedures they give, though, result in 604 00:35:52,560 --> 00:35:55,680 Speaker 2: theories that most folks would not take seriously. So let 605 00:35:55,719 --> 00:35:58,040 Speaker 2: me give one example. So you have the theory of 606 00:35:58,080 --> 00:36:02,200 Speaker 2: the universe. I have a rival theory, like we'll call 607 00:36:02,239 --> 00:36:05,360 Speaker 2: it the when you turn your back theory. My theory 608 00:36:05,480 --> 00:36:09,120 Speaker 2: says that the universe behaves exactly like your theory says 609 00:36:09,160 --> 00:36:11,839 Speaker 2: it does when it's being observed, but when it's not 610 00:36:11,880 --> 00:36:16,200 Speaker 2: being observed, it behaves in some completely other, specific and 611 00:36:16,239 --> 00:36:20,080 Speaker 2: compatible Why our theories are equally compatible with the evidence. 612 00:36:20,400 --> 00:36:23,120 Speaker 2: My theory says exactly the same thing about how universe 613 00:36:23,120 --> 00:36:25,279 Speaker 2: will behave when it's being observed, as your theory does 614 00:36:25,400 --> 00:36:29,120 Speaker 2: by construction. But my theory is different from your theory. Okay, 615 00:36:29,160 --> 00:36:30,880 Speaker 2: So I mean, like take this over to the physics 616 00:36:30,880 --> 00:36:33,600 Speaker 2: department and tell a physicist. I mean, you can tell 617 00:36:33,640 --> 00:36:36,719 Speaker 2: me no one would take this theory seriously. Right, this 618 00:36:36,800 --> 00:36:40,399 Speaker 2: is ad hoc. It's totally gerrymandered, it's not interesting. It's 619 00:36:40,400 --> 00:36:44,080 Speaker 2: not a scientifically compelling theory. My theory that is. And 620 00:36:44,120 --> 00:36:47,239 Speaker 2: so it's like easy to dismiss this. It's not a 621 00:36:47,360 --> 00:36:50,200 Speaker 2: genuine case of underdetermination. 622 00:36:50,719 --> 00:36:52,680 Speaker 1: Yeah, that's right, that's not something I would take seriously. 623 00:36:52,719 --> 00:36:56,040 Speaker 1: I mean, it's essentially equivalent in all the important bits. Right, 624 00:36:56,080 --> 00:36:59,799 Speaker 1: It's using the same calculational machinery to make predictions for 625 00:37:00,080 --> 00:37:04,640 Speaker 1: actual observations. Is just adding some bells and whistles to 626 00:37:04,760 --> 00:37:08,520 Speaker 1: the non observed side of things. It doesn't really seem 627 00:37:08,520 --> 00:37:11,799 Speaker 1: to me to count as a compellingly different explanation for 628 00:37:11,880 --> 00:37:13,120 Speaker 1: what's happening in the universe. 629 00:37:13,600 --> 00:37:16,279 Speaker 2: Yeah, and going back to something you said earlier, like, 630 00:37:16,800 --> 00:37:20,759 Speaker 2: we have other means by which we can choose what 631 00:37:20,880 --> 00:37:25,520 Speaker 2: theory to believe. So our theories are equally compatible with 632 00:37:25,560 --> 00:37:29,440 Speaker 2: the evidence, but your theory is much simpler than mine, right, 633 00:37:29,480 --> 00:37:32,960 Speaker 2: Yours has a kind of elegance that mine lacks. So 634 00:37:33,000 --> 00:37:34,920 Speaker 2: we might think that that gives us better reason to 635 00:37:34,960 --> 00:37:37,200 Speaker 2: believe your theory than mine. 636 00:37:37,600 --> 00:37:42,680 Speaker 1: And so is that the strongest argument against underdeterminism to say, like, look, 637 00:37:42,680 --> 00:37:46,880 Speaker 1: we don't have a perfect example, and we can't arbitrarily 638 00:37:46,960 --> 00:37:49,480 Speaker 1: generate one, so we don't really know that this is 639 00:37:49,520 --> 00:37:50,160 Speaker 1: a problem. 640 00:37:50,360 --> 00:37:54,560 Speaker 2: Yeah, I would say there are two kinds of arguments 641 00:37:54,600 --> 00:37:58,080 Speaker 2: against the problem of under determination. So one is this 642 00:37:58,160 --> 00:38:01,240 Speaker 2: one that you just mentioned, Like how common are genuine 643 00:38:01,280 --> 00:38:04,480 Speaker 2: cases of underdetermination in order for this to be a 644 00:38:04,560 --> 00:38:08,359 Speaker 2: troubling problem. They had better be really common. The other 645 00:38:08,480 --> 00:38:10,680 Speaker 2: route is the thing that we were just talking about, 646 00:38:10,840 --> 00:38:17,759 Speaker 2: so appealing to what folks will call theoretical virtues that 647 00:38:17,840 --> 00:38:23,600 Speaker 2: are non empirical, so simplicity or fruitfulness or elegance, in 648 00:38:23,719 --> 00:38:28,920 Speaker 2: order to decide between rival theories that are equally compatible 649 00:38:28,960 --> 00:38:32,320 Speaker 2: with the evidence. So just because two theories are equally 650 00:38:32,360 --> 00:38:34,719 Speaker 2: compatible with the evidence, doesn't mean that we don't have 651 00:38:34,840 --> 00:38:38,400 Speaker 2: better reason to believe this one than we have reason 652 00:38:38,440 --> 00:38:41,359 Speaker 2: to believe this one. That opens a whole can of worms. Though, like, 653 00:38:41,400 --> 00:38:45,720 Speaker 2: these are philosophy questions. What are the non empirical reasons 654 00:38:45,760 --> 00:38:49,080 Speaker 2: for believing something? What are the reasons that are not 655 00:38:49,239 --> 00:38:51,680 Speaker 2: exhausted by just looking at the evidence for believing one 656 00:38:51,760 --> 00:38:55,600 Speaker 2: hypothesis over another. That's philosophy, right. 657 00:38:57,840 --> 00:38:59,719 Speaker 1: Right, And you say that in a way that makes 658 00:38:59,719 --> 00:39:02,640 Speaker 1: it to like it's philosophy, it's not science. But I 659 00:39:02,680 --> 00:39:05,879 Speaker 1: wonder sometimes if we're too crisp about, you know, making 660 00:39:05,960 --> 00:39:08,759 Speaker 1: a delineation between those two things, because, as you say, 661 00:39:08,800 --> 00:39:11,600 Speaker 1: often we're using philosophy to make decisions in science, we 662 00:39:11,719 --> 00:39:14,480 Speaker 1: prefer this theory to that theory because it's simpler. Those 663 00:39:14,480 --> 00:39:18,040 Speaker 1: are choices influenced by our philosophy of science. We're doing 664 00:39:18,080 --> 00:39:19,480 Speaker 1: that kind of stuff all the time. The thing I 665 00:39:19,480 --> 00:39:22,560 Speaker 1: find fascinating is that most people in particle physics have 666 00:39:22,760 --> 00:39:27,479 Speaker 1: very strong opinions about philosophical questions, but they also often 667 00:39:27,520 --> 00:39:30,839 Speaker 1: think philosophical questions are a waste of time, you know, 668 00:39:31,520 --> 00:39:33,400 Speaker 1: like if I go around, sir and ask people like, 669 00:39:33,440 --> 00:39:35,360 Speaker 1: do you think the top quark or the Higgs boson 670 00:39:35,600 --> 00:39:38,359 Speaker 1: is real? It's there when we're not looking, or it's 671 00:39:38,400 --> 00:39:41,080 Speaker 1: just a tool in our calculations that are like, dude, 672 00:39:41,080 --> 00:39:43,760 Speaker 1: we discovered the Higgs boson. Here, we know it's real. 673 00:39:43,840 --> 00:39:47,160 Speaker 1: We found it, there's a Nobel prize for it. You're crazy. 674 00:39:48,239 --> 00:39:49,919 Speaker 1: You have to take them on a pretty long walk 675 00:39:49,960 --> 00:39:51,320 Speaker 1: to get them to the place where you're like, Okay, 676 00:39:51,360 --> 00:39:54,000 Speaker 1: that's true. It's not directly observed and therefore we don't 677 00:39:54,040 --> 00:39:56,799 Speaker 1: really know if it's there and there could be another explanation, etcetera, etc. 678 00:39:57,160 --> 00:39:58,920 Speaker 1: All right, I want to hear more about that, but 679 00:39:59,040 --> 00:40:14,399 Speaker 1: first we have to take another quick break. All right, 680 00:40:14,400 --> 00:40:16,719 Speaker 1: this is Daniel and we are doing an episode on 681 00:40:17,120 --> 00:40:21,840 Speaker 1: underdeterminism in science, wondering whether it's possible to explain the 682 00:40:21,960 --> 00:40:26,280 Speaker 1: universe in two different but equivalent ways. Well, my question 683 00:40:26,320 --> 00:40:28,359 Speaker 1: to you is, what do you think are the prospects 684 00:40:28,440 --> 00:40:32,239 Speaker 1: for making progress? Like is this something we can ever 685 00:40:32,280 --> 00:40:34,239 Speaker 1: really resolve? I mean, could it be that in a 686 00:40:34,280 --> 00:40:37,760 Speaker 1: million years we're doing science and we're still worrying about 687 00:40:37,760 --> 00:40:39,960 Speaker 1: this kind of thing, Like maybe somebody's going to come 688 00:40:40,040 --> 00:40:43,000 Speaker 1: up with another theory that explains what's going on. Or 689 00:40:43,120 --> 00:40:45,960 Speaker 1: do you think philosophers can like resolve questions like this, 690 00:40:46,080 --> 00:40:48,839 Speaker 1: that they can come up with a proof that two 691 00:40:48,880 --> 00:40:52,680 Speaker 1: theories that give the same predictions are fundamentally categorically the same, 692 00:40:52,920 --> 00:40:54,400 Speaker 1: or that you could develop the kind of algorithm you're 693 00:40:54,400 --> 00:40:58,840 Speaker 1: talking about earlier to generate an alternative theory that's realistic 694 00:40:59,320 --> 00:41:01,200 Speaker 1: from an existing theory. What do you think are the 695 00:41:01,200 --> 00:41:03,120 Speaker 1: prospects for making progress on this question? 696 00:41:03,320 --> 00:41:05,000 Speaker 2: One thing I think is important to say is like, 697 00:41:06,120 --> 00:41:10,640 Speaker 2: in terms of progress, like setting aside under determination stuff 698 00:41:10,680 --> 00:41:13,680 Speaker 2: like science is always making progress. Right, taking the problem 699 00:41:13,680 --> 00:41:17,400 Speaker 2: of determination seriously doesn't imply that it isn't like progress 700 00:41:17,440 --> 00:41:20,280 Speaker 2: that's made when we moved from Newton's theory of gravity 701 00:41:20,320 --> 00:41:23,719 Speaker 2: to Einstein's, like, our theories get more and more predictively successful, 702 00:41:23,719 --> 00:41:27,200 Speaker 2: and that is definitely progress. So even if we still 703 00:41:27,239 --> 00:41:31,200 Speaker 2: take the problem of underdetermination seriously. Science is making a 704 00:41:31,320 --> 00:41:36,080 Speaker 2: kind of progress, So what about making progress on the 705 00:41:36,120 --> 00:41:40,520 Speaker 2: problem of underdetermination itself? I wish I knew. Note that 706 00:41:40,960 --> 00:41:43,799 Speaker 2: one of the routes that we were talking about in 707 00:41:44,480 --> 00:41:47,399 Speaker 2: responding to the problem just in fact, all of them 708 00:41:47,480 --> 00:41:54,480 Speaker 2: involve one doing like philosophy taking seriously the kinds of 709 00:41:54,600 --> 00:41:58,799 Speaker 2: questions that philosophers of science takes seriously. We have to 710 00:41:58,840 --> 00:42:04,319 Speaker 2: identify what the theoretical virtues are, so like what the 711 00:42:04,400 --> 00:42:08,000 Speaker 2: reasons are we have to believe one theory rather than another, 712 00:42:08,520 --> 00:42:10,920 Speaker 2: and then we have to argue that these help us 713 00:42:11,000 --> 00:42:15,400 Speaker 2: make good decisions, like in terms of which theory we 714 00:42:15,440 --> 00:42:18,000 Speaker 2: should believe. We also have to, as you were mentioning, 715 00:42:18,080 --> 00:42:20,239 Speaker 2: like come to some kind of agreement on win two 716 00:42:20,400 --> 00:42:23,080 Speaker 2: theories or saying the same thing, or when their genuine 717 00:42:23,719 --> 00:42:29,400 Speaker 2: rivals to one another. And these are hard philosophy questions. 718 00:42:30,480 --> 00:42:32,840 Speaker 2: So I mean, going back to something that you said earlier, 719 00:42:33,800 --> 00:42:37,520 Speaker 2: I think there's this famous Fineman quote. So he once 720 00:42:37,680 --> 00:42:42,000 Speaker 2: said that philosophy of sciences is useful to science or 721 00:42:42,040 --> 00:42:45,960 Speaker 2: to scientists, as ornithology is to birds. Oh man, I mean, 722 00:42:46,000 --> 00:42:49,120 Speaker 2: it's a great quote. Makes me chuckle. Every time, but 723 00:42:49,280 --> 00:42:53,600 Speaker 2: man like, look, birds are doing some ornithology here, right, 724 00:42:53,719 --> 00:42:57,160 Speaker 2: or or implicitly at least, or we have to in 725 00:42:57,280 --> 00:42:59,480 Speaker 2: order to make progress on this kind of stuff. 726 00:42:59,640 --> 00:43:01,600 Speaker 1: Yeah, it's true, it's a great zinger, but I think 727 00:43:01,640 --> 00:43:04,520 Speaker 1: it's it's not necessarily very productive. Well, let me make 728 00:43:04,560 --> 00:43:07,160 Speaker 1: the question a little bit more sort of vivid and concrete. 729 00:43:07,200 --> 00:43:10,520 Speaker 1: Let's imagine a hypothetical scenario, say far in the future, 730 00:43:10,640 --> 00:43:13,200 Speaker 1: or maybe not that far in the future. Aliens arrive 731 00:43:13,400 --> 00:43:18,320 Speaker 1: and they are you know, scientific, and they use mathematics, 732 00:43:18,840 --> 00:43:22,040 Speaker 1: and they do physics, and they have also been pursuing 733 00:43:22,080 --> 00:43:25,280 Speaker 1: the project of revealing the fundamental nature of the universe, 734 00:43:25,440 --> 00:43:27,840 Speaker 1: matter and energy and particles in space and time and 735 00:43:27,880 --> 00:43:30,000 Speaker 1: all that stuff. And we get to sit down across 736 00:43:30,000 --> 00:43:32,400 Speaker 1: the table from them and compare notes. So here we 737 00:43:32,440 --> 00:43:35,880 Speaker 1: have like a completely independent scientific tradition, but you know, 738 00:43:36,280 --> 00:43:38,600 Speaker 1: undimently pointing at the same thing. So we can avoid 739 00:43:38,719 --> 00:43:41,200 Speaker 1: questions of like, what aliens do science? And could we 740 00:43:41,280 --> 00:43:43,439 Speaker 1: communicate with them? What do you think the chances are 741 00:43:44,239 --> 00:43:48,040 Speaker 1: that their theory is compatible with ours, that it's the 742 00:43:48,080 --> 00:43:51,000 Speaker 1: same theory, but you know, written with different kind of squiggles, 743 00:43:51,280 --> 00:43:54,759 Speaker 1: dressed in different clothing, or the chances that they really 744 00:43:54,840 --> 00:43:58,480 Speaker 1: have come up with a completely different mechanism to describe 745 00:43:58,520 --> 00:44:00,719 Speaker 1: the universe. What do you think the chances are in 746 00:44:00,719 --> 00:44:04,160 Speaker 1: that scenario that our two theories are compatible or incompatible. 747 00:44:04,360 --> 00:44:06,000 Speaker 2: Yeah, I don't know, man, Your guess is as good 748 00:44:06,000 --> 00:44:11,160 Speaker 2: as mine. If I had to guess, I'd say it's 749 00:44:11,239 --> 00:44:16,520 Speaker 2: pretty unlikely that anyone else does science and exactly the 750 00:44:16,560 --> 00:44:19,440 Speaker 2: way we do it, you know, like so much of 751 00:44:19,480 --> 00:44:22,319 Speaker 2: the way that we do science is grounded in accidental 752 00:44:22,360 --> 00:44:26,360 Speaker 2: things about what humans are, like, you know, we're medium sized, 753 00:44:27,960 --> 00:44:33,880 Speaker 2: we travel pretty slowly. It's grounded and the kinds of 754 00:44:33,920 --> 00:44:35,560 Speaker 2: things that we care about what we want to do 755 00:44:35,600 --> 00:44:39,480 Speaker 2: with our science, how our particular perceptual apparatus works, like 756 00:44:39,560 --> 00:44:43,040 Speaker 2: how you know, our eyes work, stuff like that, and 757 00:44:43,440 --> 00:44:45,960 Speaker 2: the way that we do science is grounded in accidental 758 00:44:46,000 --> 00:44:50,640 Speaker 2: facts about history too. Given all this, it's hard for 759 00:44:50,680 --> 00:44:53,200 Speaker 2: me to imagine that anyone else would do it exactly 760 00:44:53,280 --> 00:44:56,319 Speaker 2: in the way that we do well. 761 00:44:56,360 --> 00:44:57,880 Speaker 1: That's one of the things that makes me excited to 762 00:44:57,920 --> 00:45:01,080 Speaker 1: talk to aliens about science, because you know, if they're 763 00:45:01,120 --> 00:45:03,120 Speaker 1: doing science the same way we are, then hey, we 764 00:45:03,200 --> 00:45:05,840 Speaker 1: might learn some cool science. And if they're not, we 765 00:45:05,960 --> 00:45:08,319 Speaker 1: might learn some cool things about ourselves and the way 766 00:45:08,320 --> 00:45:10,319 Speaker 1: that we explore the universe and the way like being 767 00:45:10,440 --> 00:45:14,200 Speaker 1: human colors how we are seeing the universe, and it's 768 00:45:14,200 --> 00:45:16,360 Speaker 1: so hard to sort of get out of our own heads, 769 00:45:16,360 --> 00:45:18,719 Speaker 1: and that's like maybe one way to do it. 770 00:45:18,840 --> 00:45:21,279 Speaker 2: So, yeah, when you hear from them, let me know. 771 00:45:23,719 --> 00:45:25,160 Speaker 1: I think when they do arrive, we should send the 772 00:45:25,160 --> 00:45:28,120 Speaker 1: philosophers first before we send the physicists, you know, in 773 00:45:28,160 --> 00:45:30,480 Speaker 1: case they're not so friendly. All right, Well, thanks very 774 00:45:30,560 --> 00:45:32,960 Speaker 1: much for chatting with me about this really fascinating question 775 00:45:33,080 --> 00:45:35,920 Speaker 1: in philosophy and in science, and in philosophy and science. 776 00:45:36,280 --> 00:45:38,200 Speaker 1: I really enjoyed it. Thanks very much for your time. 777 00:45:38,320 --> 00:45:40,720 Speaker 2: Yeah, thanks for having me on, Danielle. It was a pleasure. 778 00:45:48,560 --> 00:45:51,400 Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain 779 00:45:51,440 --> 00:45:54,719 Speaker 1: the Universe is a production of iHeart Radio. For more 780 00:45:54,760 --> 00:45:59,360 Speaker 1: podcasts from iHeart Radio, visit the iHeartRadio app, Apple Podcasts, 781 00:45:59,520 --> 00:46:01,880 Speaker 1: or where where you listened to your favorite shows. 782 00:46:07,440 --> 00:46:07,480 Speaker 2: H