WEBVTT - From the Vault: Thought Experiments 0:00:05.720 --> 0:00:07.440 Hey, you welcome to Stuff to Blow Your Mind. My 0:00:07.520 --> 0:00:10.600 name is Robert Lamb and I'm Joe McCormick. And it 0:00:10.680 --> 0:00:13.240 is time to go into the vault because it is Saturday, 0:00:13.240 --> 0:00:15.720 of course, and we're bringing you an episode that originally 0:00:15.720 --> 0:00:19.880 air January third, twenty nineteen. That's right, what's inside the vault? 0:00:19.920 --> 0:00:22.160 I don't know what's not inside the vault. The thing 0:00:22.160 --> 0:00:24.680 inside the vault could be alive, it could be dead. 0:00:24.760 --> 0:00:29.120 It's kind of in a quantum position until we open it. Right, Okay, 0:00:29.160 --> 0:00:33.200 this is our episode about thought experiments. Yeah, I remember 0:00:33.240 --> 0:00:35.280 we were asking the question, what can you really prove 0:00:35.320 --> 0:00:38.200 anything with the thought experiment? Yeah? I think you can. Yeah, 0:00:38.240 --> 0:00:40.680 I think we You know, obviously we're we're pro thought 0:00:40.760 --> 0:00:43.879 experiment on this show. We devote whole episodes to particular 0:00:43.880 --> 0:00:46.720 thought experiments. But I remember this was when we were like, hey, 0:00:46.800 --> 0:00:49.720 let's stop and just actually discuss thought experiments, especially if 0:00:49.720 --> 0:00:53.400 we're going to keep uh invoking them on the show. Uh. Well, 0:00:53.440 --> 0:00:59.160 I say, let's get right into it. Welcome to Stuff 0:00:59.200 --> 0:01:08.120 to Blow your Mind from how Stuffworks dot Com. Hey, 0:01:08.240 --> 0:01:10.000 welcome to Stuff to Blow your Mind. My name is 0:01:10.080 --> 0:01:12.480 Robert Lamb and I'm Joe McCormick, Hey, Robert, what are 0:01:12.520 --> 0:01:15.880 we talking about today? Oh, well, we're talking about thought experiments, 0:01:15.959 --> 0:01:18.399 the things that make some people really mad and make 0:01:18.440 --> 0:01:21.240 other people talk for way too long into time. Well, 0:01:21.240 --> 0:01:23.800 the thought experiments can have both effects on an individual 0:01:23.800 --> 0:01:25.840 at the same time. That's the beauty of a thought experiment. 0:01:25.880 --> 0:01:29.400 I think. So now, we've discussed individual thought experiments on 0:01:29.440 --> 0:01:32.320 the show many times before, but I think today we're 0:01:32.360 --> 0:01:34.440 going to try to look at the idea of a 0:01:34.480 --> 0:01:37.119 thought experiment on the show. In the past, we've talked 0:01:37.120 --> 0:01:41.440 about specific thought experiments. We've talked about Stranger's Cat, We've 0:01:41.440 --> 0:01:45.480 talked about the Infinity Hotel, the ship of Theseus. Other 0:01:45.520 --> 0:01:47.840 times it comes up kind of informally. We might say 0:01:47.840 --> 0:01:50.280 that a particular paper we're talking about is more kin 0:01:50.360 --> 0:01:53.160 to a thought experiment. And I know that I've I've 0:01:53.200 --> 0:01:56.560 talked before about how I think of certain short stories 0:01:56.600 --> 0:01:59.960 as being more thought experiments than you know, true narrative. 0:02:00.120 --> 0:02:03.000 I think of Library of Babbel, Library of Babble, other 0:02:03.040 --> 0:02:05.400 works of a lot of the short stories of jor 0:02:05.480 --> 0:02:07.280 Haluis Borges, as well as a number of the short 0:02:07.320 --> 0:02:09.320 stories of Philip K. Dick they're a number of those 0:02:09.320 --> 0:02:13.560 where you know it's not really important who's doing what exactly. 0:02:13.600 --> 0:02:15.160 You know you're not you're not really invested in a 0:02:15.280 --> 0:02:18.160 story per se, but the story is there to make 0:02:18.200 --> 0:02:20.160 you think, to turn some sort of weird idea on 0:02:20.200 --> 0:02:24.400 its head, the concept driven more than character driven exactly. Now, 0:02:24.440 --> 0:02:26.280 I have to say that one of my favorite comical 0:02:26.280 --> 0:02:29.959 treatments of thought experiments is the humorous essay Shreddnger's Cat 0:02:30.080 --> 0:02:34.600 by Steve Martin, collected in his book Pure Drivel. And 0:02:34.639 --> 0:02:36.600 there's a wonderful audio book of this as well, because 0:02:36.600 --> 0:02:39.919 Steve Martin himself is reading it. Always great when you 0:02:39.919 --> 0:02:42.840 can get one read by the author. Yeah. Now, Martin 0:02:42.960 --> 0:02:47.320 begins this particularly essay by presenting the Streusenger's Cat thought 0:02:47.320 --> 0:02:50.440 experiment just pretty much as it is, and from there 0:02:50.480 --> 0:02:54.120 he proceeds through an increasingly ridiculous mix of thought experiments 0:02:54.120 --> 0:02:58.760 that he's made up himself, such as uh vitkin Stein's banana, 0:02:59.120 --> 0:03:03.800 Elvis's chart ol briquette, chef boy r ds, bungee cord, 0:03:03.919 --> 0:03:08.880 sakagaway is rain, bonnet, apollos, non apple, non strutal, Jim 0:03:08.960 --> 0:03:14.440 Dandy's Bucket of Goo, and the thinman dilemma. Since it's 0:03:14.440 --> 0:03:16.360 one of the shorter ones, I'd like to read Steve 0:03:16.400 --> 0:03:22.280 Martin's description of the thought experiment Elvis's charcoal briquette. A 0:03:22.320 --> 0:03:25.519 barbecue is cooking wieners in an air tight space. As 0:03:25.520 --> 0:03:28.840 the charcoal consumes the oxygen, the integrity of the briquette 0:03:28.880 --> 0:03:32.200 is weakened. An observer riding a roller coaster will become 0:03:32.280 --> 0:03:34.920 hungry for wieners, but will be thrown from the car 0:03:35.040 --> 0:03:38.240 when he stands up and cries, Elvis, get me a 0:03:38.240 --> 0:03:43.080 hot dog. Yeah, that's got the right mouth field. I mean, 0:03:43.120 --> 0:03:47.440 it's it's absurd, it's ridiculous and uh, but it's effective 0:03:47.440 --> 0:03:49.120 as comedy because it does have that feel of a 0:03:49.160 --> 0:03:52.600 thought of experiment, and and many of them are exactly 0:03:52.640 --> 0:03:56.240 this sort of absurd little logic problem or physical scenario, 0:03:56.480 --> 0:03:59.320 but it's utilized not for laughs, but to explore some 0:03:59.400 --> 0:04:02.360 sort of generally a complex topic. I thought this was 0:04:02.400 --> 0:04:04.400 going to be the seventh thought experiments. You can't say 0:04:04.400 --> 0:04:08.680 on TV. It does make me wonder what the most 0:04:08.800 --> 0:04:11.560 risk a thought experiments are. Oh, there are actually quite 0:04:11.560 --> 0:04:14.120 a few. Yeah, all right, well, let's we'll save that 0:04:14.200 --> 0:04:17.800 for the midnight Show. So let's let's talk about thought 0:04:17.839 --> 0:04:21.640 experiments just definition wise, like, what is a thought experiment? Well, yes, first, 0:04:21.680 --> 0:04:25.040 you could consult the idea of an experiment. An experiment 0:04:25.160 --> 0:04:28.400 is basically a test, like you have a condition and 0:04:28.600 --> 0:04:33.960 you you instantiate the condition and you see what happens. Yeah. 0:04:34.000 --> 0:04:36.080 But on the other hand, it's worth pointing out that 0:04:36.120 --> 0:04:39.720 to merely think about an experiment is not a thought experiment. 0:04:40.160 --> 0:04:42.919 So if you if you say, for instance, think about 0:04:42.920 --> 0:04:48.039 the social psychology Stanford prison experiment, that's not a thought experiment. 0:04:48.520 --> 0:04:51.159 Um why not? Well, because you are you were thinking 0:04:51.160 --> 0:04:54.200 about an actual experiment that has been carried out. I 0:04:54.240 --> 0:04:56.200 mean this is kind of obvious, right, but but still 0:04:56.200 --> 0:04:59.160 it it it's worth going through. Now, if you if 0:04:59.200 --> 0:05:02.800 you think about an experiment you might conduct, say to 0:05:02.839 --> 0:05:05.240 see if movie goers who eat twizzlers are more likely 0:05:05.279 --> 0:05:07.280 to joy to enjoy sci fi films and those who 0:05:07.320 --> 0:05:10.000 eat red vines. Well, that's not a thought experiment either. 0:05:10.120 --> 0:05:14.560 That's something you could conceivably do. That's like imagining an 0:05:14.560 --> 0:05:17.880 experiment you could carry out. But thinking about the experiment 0:05:17.880 --> 0:05:22.600 doesn't really reveal anything right now, Very often the experiment 0:05:22.600 --> 0:05:25.240 in a thought experiment is exactly not the sort of 0:05:25.279 --> 0:05:27.680 thing that could be carried out in real life for 0:05:27.720 --> 0:05:32.799 a number of reasons. Maybe it's catastrophically dangerous or or involves, 0:05:33.320 --> 0:05:36.440 you know, in encountering some feature of the universe that 0:05:36.560 --> 0:05:40.320 is not readily accessible. That sort of thing. Very often 0:05:40.360 --> 0:05:44.000 thought experiments, as they apply to science, involved the the 0:05:44.080 --> 0:05:48.680 removal of things that you couldn't actually remove as variables, 0:05:48.720 --> 0:05:52.800 so like imagine a frictionless plane, or involve something that 0:05:52.880 --> 0:05:55.279 just simply does not exist, like a train going near 0:05:55.279 --> 0:05:57.440 the speed of light. We do do not have such 0:05:57.480 --> 0:05:59.479 a thing. We're probably not going to have such a 0:05:59.480 --> 0:06:02.520 thing anytime soon, but it's useful in the thought experiment. 0:06:02.880 --> 0:06:05.400 And then on top of that, they frequently are narrative 0:06:05.400 --> 0:06:08.239 in nature. There's a sequence to things in a way, 0:06:08.279 --> 0:06:11.880 they're they're almost like a joke in many senses. You know, 0:06:11.920 --> 0:06:14.200 it feels like the set up for a joke. It 0:06:14.240 --> 0:06:17.000 feels like there's going to be a punch line. Um. 0:06:17.040 --> 0:06:19.240 And I also I wondered to what extent like really 0:06:19.279 --> 0:06:22.479 successful and quote unquote successful thought experiments, like ones that 0:06:22.560 --> 0:06:26.400 really resonate culturally, if if there is a sense of 0:06:27.520 --> 0:06:30.880 counterintuitive elements to the narrative. I wonder if there's something 0:06:30.960 --> 0:06:34.279 about that as well. Well. Yeah, thought experiments are an 0:06:34.320 --> 0:06:37.760 interesting thing. So like a good thought experiment, what it 0:06:37.800 --> 0:06:43.760 should do is reveal something that is true simply by 0:06:43.960 --> 0:06:46.880 making up a story in your mind and working through 0:06:47.000 --> 0:06:50.720 the conclusions that would result from it. Now, often there 0:06:50.760 --> 0:06:53.600 are a lot of coincidental details of this story that 0:06:53.760 --> 0:06:56.839 do not matter. Uh, they don't have any effect on 0:06:57.040 --> 0:07:00.280 what this thought experiment reveals, if it reveals anything, and 0:07:00.360 --> 0:07:03.160 yet they can be enormously predictive of whether or not 0:07:03.279 --> 0:07:06.680 this is like a popular meme or not how well 0:07:06.720 --> 0:07:09.160 it spreads. Like cat as an example, Like if it 0:07:09.200 --> 0:07:11.960 were a dog, it would probably still resonate, but in 0:07:12.000 --> 0:07:14.320 a slightly different way. But if it were just a 0:07:14.360 --> 0:07:17.440 lizard or a slug, yes, people would be far less 0:07:17.440 --> 0:07:21.480 compelled by the idea of Shreddinger's bug, but they would 0:07:21.480 --> 0:07:25.480 be far more upset by the idea of Shreddinger's child 0:07:25.960 --> 0:07:27.800 or something. So like, if it's a cat, that's the 0:07:27.840 --> 0:07:30.160 bull's eye, that's right in the red zone. It's like 0:07:30.320 --> 0:07:33.560 interesting enough to be killing a cat that people are 0:07:33.600 --> 0:07:36.200 on board to to remember to pay attention, but it's 0:07:36.200 --> 0:07:38.840 not so troubling that you're turned off and you don't 0:07:38.840 --> 0:07:41.320 want to listen, right, And and then also the cat 0:07:41.440 --> 0:07:43.120 kind of makes it more palpable. Like if it was 0:07:43.160 --> 0:07:48.920 Shreddinger's um, let's say, basilisk, that would it would instantly 0:07:48.920 --> 0:07:52.760 sound a little more threatening somehow. How about Shreddinger's apparently 0:07:52.800 --> 0:07:57.200 conscious AI Yes, or that's the that's next level. Yeah, 0:07:57.240 --> 0:08:01.080 that's that's pretty good. Now. Another or an aspect of 0:08:01.200 --> 0:08:04.440 thought experiments is that it's something that should generally be 0:08:04.600 --> 0:08:08.280 visualized in the mind as this, as the thought experiment 0:08:08.280 --> 0:08:11.480 has rolled out, you you're picturing it. Uh. It's in 0:08:11.920 --> 0:08:14.440 doing this it makes a concept more digestible, or it 0:08:14.480 --> 0:08:18.720 explains a you know, fundamental paradox, etcetera. And uh, and 0:08:18.720 --> 0:08:20.200 and and this again. It has a lot in common 0:08:20.200 --> 0:08:22.000 with jokes, It has a lot in common with riddles, 0:08:22.000 --> 0:08:25.000 and they just sort of the basic structure. But it's 0:08:25.000 --> 0:08:28.440 not necessarily bringing you to uh. It's not bringing you 0:08:28.440 --> 0:08:30.520 a punch line. It's not necessarily a correct answer at 0:08:30.520 --> 0:08:33.240 the end. But there is hopefully a deeper understanding of 0:08:33.240 --> 0:08:36.440 a concept via the thought experiment. Now that being said, 0:08:36.559 --> 0:08:39.480 a thought experiment is also not a pristine, blameless thing 0:08:39.600 --> 0:08:42.720 or something set in stone. So others may take issue 0:08:42.720 --> 0:08:45.200 with the thought experiment or just completely knock it down. 0:08:45.200 --> 0:08:48.120 They may roll out their own thought experiment that attempts 0:08:48.160 --> 0:08:51.200 to put your thought experiment to shame. And uh, and 0:08:51.240 --> 0:08:53.640 there may be you know, additional interations off and we've 0:08:53.640 --> 0:08:56.280 certainly explored that on the show before with things such 0:08:56.280 --> 0:09:01.280 as the ship of Theseus. And then finally, one of 0:09:01.320 --> 0:09:05.400 the really cool things about thought experiments is that it's 0:09:06.040 --> 0:09:09.679 ideally this this chance to learn about reality, learn more 0:09:09.679 --> 0:09:13.000 about reality by simply thinking about it. And that would, 0:09:13.160 --> 0:09:15.920 on the surface of things, seem rather odd, right, because 0:09:16.559 --> 0:09:18.960 it would be an exception to the empirical nature of 0:09:18.960 --> 0:09:21.760 how we learn about the world by seeing it, by 0:09:21.800 --> 0:09:25.000 touching it, by feeling it, by poking it, by dissecting 0:09:25.040 --> 0:09:27.880 it and running, um, you know, more or less physical 0:09:27.920 --> 0:09:31.120 experiments upon it. But to simply think about something and 0:09:31.160 --> 0:09:34.199 the idea that that will reveal something that we had 0:09:34.240 --> 0:09:37.440 not seen before it was not clear to us beforehand. Uh. 0:09:37.480 --> 0:09:40.120 That that's rather curious, isn't it. Well, yeah, I mean, 0:09:40.200 --> 0:09:43.839 a thought experiment is a type of logic, which means 0:09:43.880 --> 0:09:48.360 it it lacks the empirical data gathering part of learning 0:09:48.400 --> 0:09:51.280 about the world, so all it can do is draw 0:09:51.400 --> 0:09:55.560 conclusions from what is already known or assumed, though there 0:09:55.600 --> 0:09:58.120 have been plenty of cases where in fact, in the 0:09:58.200 --> 0:10:02.000 history of science interest stuff has come to be known 0:10:02.160 --> 0:10:06.080 without anybody going out and measuring anything new, but just 0:10:06.240 --> 0:10:09.800 by applying what was already known in a logical way 0:10:09.840 --> 0:10:12.320 to arrive at a new conclusion. We'll talk about examples 0:10:12.320 --> 0:10:13.719 of that in a minute, all right, So I want 0:10:13.760 --> 0:10:17.360 to mention one quick example. Uh, it's not so quick 0:10:17.440 --> 0:10:22.439 in the original text, but Lucretius, who lived nine b 0:10:22.600 --> 0:10:27.920 C b C. Wrote on the Nature of Things Sura, yeah, 0:10:28.000 --> 0:10:30.440 and uh, and he has a fun little thought experiment 0:10:30.520 --> 0:10:35.560 he rolls out. So um, Lucretious argues that space is 0:10:35.559 --> 0:10:38.520 is infinite and what you say it isn't? Well, fine, 0:10:38.720 --> 0:10:41.760 then let's march a soldier to the edge of the 0:10:41.800 --> 0:10:45.560 finite universe and have him throw a spear at the edge. Wait, 0:10:45.600 --> 0:10:48.240 what is the soldier's name? This is crucial. Oh I 0:10:48.240 --> 0:10:50.120 see I skipped that part. What is the soldier's name? No, 0:10:50.240 --> 0:10:51.880 I don't know. It's that we don't need to know 0:10:51.920 --> 0:10:54.720 his name. It's just a soldier. We could we could 0:10:54.720 --> 0:10:58.120 call him cat. I guess, but um, his original write 0:10:58.160 --> 0:11:01.320 up of it is a bit longer. This boiled out. So, yeah, 0:11:01.480 --> 0:11:03.360 march the soldier up to the edge of the universe. 0:11:03.400 --> 0:11:06.000 Haven't throw a spear at the edge. Well, one of 0:11:06.040 --> 0:11:08.000 two things is going to happen, he says, Well, if 0:11:08.040 --> 0:11:11.440 it flies through, then there is something beyond and your 0:11:11.480 --> 0:11:14.560 barrier is nonsense. Right, So the universe is not actually 0:11:14.600 --> 0:11:17.600 bounded there, right, because you just threw a spear beyond 0:11:17.880 --> 0:11:21.240 the edge. Now if the spear bounces off the barrier, well, 0:11:21.240 --> 0:11:24.600 then the wall itself is proof of something beyond your 0:11:24.640 --> 0:11:27.040 your your spear just bounced off of something. What is 0:11:27.120 --> 0:11:30.680 that something? The wall is a thing? Yeah, so it 0:11:31.360 --> 0:11:33.680 In looking at this, you can see that it illustrates 0:11:33.720 --> 0:11:37.839 a conceived version of reality and lays out an experiment, 0:11:38.240 --> 0:11:40.079 And of course it also illustrates one of the other 0:11:40.080 --> 0:11:43.280 features of thought experiments you can pick at them. So 0:11:43.400 --> 0:11:45.680 Lucretius may have presented this, as you know, as a 0:11:45.720 --> 0:11:48.280 real sentence stopping comment on the nature of the universe 0:11:48.280 --> 0:11:50.559 at the time, but certainly, if you if you think 0:11:50.600 --> 0:11:52.559 back of even discussions that we've had on the show 0:11:52.640 --> 0:11:57.040 about infinities and different types of infinities, and and some 0:11:57.080 --> 0:11:59.320 of the arguments for you know, for exactly how I 0:11:59.400 --> 0:12:02.960 find ie universe would work. Then you can see that 0:12:03.120 --> 0:12:06.600 his argument doesn't quite hold up to modern cosmology well 0:12:06.640 --> 0:12:08.880 as you've presented it here. This is actually a great 0:12:08.920 --> 0:12:13.040 example of how thought experiments can seem brilliant but actually 0:12:13.040 --> 0:12:19.400 produce flawed conclusions because they contain drum roll hidden assumptions. Here, 0:12:19.559 --> 0:12:24.200 I would say one fatal hidden assumption is that Lucretius 0:12:24.240 --> 0:12:29.720 takes on board without considering the geometry of a finite universe. 0:12:30.040 --> 0:12:32.560 Now again, I'm certainly not going to go and argue 0:12:32.600 --> 0:12:35.000 that space is finite. That's not my goal here. But 0:12:35.120 --> 0:12:38.080 my I would say there are ways in which space 0:12:38.120 --> 0:12:42.400 could be finite that Lucretius is overlooking with this example, 0:12:43.120 --> 0:12:45.920 because there are different ways you could imagine a finite universe. 0:12:46.000 --> 0:12:49.120 One is a sort of closed three D space with 0:12:49.280 --> 0:12:52.360 exterior walls like the inside of a box. And this 0:12:52.440 --> 0:12:55.120 is sort of what Lucretius seems to have in mind here, 0:12:55.559 --> 0:12:57.679 And of course it does seem somewhat absurd. How could 0:12:57.679 --> 0:12:59.640 the universe be like that? It seems like it probably 0:12:59.679 --> 0:13:03.959 couldn't be. But what if the universe is simultaneously finite 0:13:04.120 --> 0:13:09.679 and without boundaries, like the length dimension of a mobius strip. Robert, 0:13:09.920 --> 0:13:12.920 have you ever made a mobius strip, like in geometry 0:13:12.920 --> 0:13:15.960 and school. Yeah. So you just take like one length 0:13:16.040 --> 0:13:18.040 of a piece of paper and then give it a 0:13:18.040 --> 0:13:20.960 half turn and then tape its ends together, and what 0:13:21.040 --> 0:13:24.480 you have created is a piece of paper that has 0:13:24.559 --> 0:13:27.440 one continuous side. You can start drawing a line and 0:13:27.480 --> 0:13:30.160 it goes on the entire thing. So for instance, and 0:13:30.240 --> 0:13:34.720 this this version, the soldier throws the spear and impales 0:13:34.800 --> 0:13:37.319 himself in the back exactly as long as the spear 0:13:37.400 --> 0:13:40.280 goes long enough. Yeah. So the idea, or it could 0:13:40.280 --> 0:13:43.520 be another analogy here, could be that the geometry of 0:13:43.559 --> 0:13:46.000 the three D universe is sort of like the two 0:13:46.120 --> 0:13:50.000 D geometry of the surface of a sphere. It's not infinite. 0:13:50.080 --> 0:13:52.480 The surface area of a sphere is finite. There is 0:13:52.520 --> 0:13:55.240 a limit to it, but it has no boundaries. You 0:13:55.320 --> 0:13:58.520 never reached the edge. So yeah, that soldier, let's let's 0:13:58.520 --> 0:14:01.160 call him Tim. Tim throws the spear and it hits 0:14:01.200 --> 0:14:04.080 him in the butt. Yeah. Yeah. This also reminds, you 0:14:04.080 --> 0:14:06.840 know the idea of saying, well, hey, my soldier throws 0:14:07.000 --> 0:14:08.840 a spear at the edge of the universe and it 0:14:08.920 --> 0:14:11.680 keeps going, then your your argument is nonsense. It also 0:14:11.760 --> 0:14:13.280 kind of sounds like, oh, we had a really cold 0:14:13.360 --> 0:14:16.240 weather today, I guess there's no global warming. I guess 0:14:16.280 --> 0:14:19.720 there's no climate change. Using a far simpler model than 0:14:19.760 --> 0:14:23.200 the than the complexities of reality, try and make your argument. Well, yeah, 0:14:23.200 --> 0:14:25.440 but it does also. I mean, I would say that 0:14:25.520 --> 0:14:28.120 this is a good argument against a certain type of 0:14:28.240 --> 0:14:32.480 idea of the bounded universe, because if if the universe 0:14:32.560 --> 0:14:35.960 were actually finite in that it had walls on the 0:14:36.000 --> 0:14:38.960 outside of it, at any place you approached the wall, 0:14:39.080 --> 0:14:41.800 you could test that condition, right. So I would say 0:14:41.800 --> 0:14:45.200 that highlighting absurdities in a single test case of the 0:14:45.280 --> 0:14:48.200 idea of a universe with walls on the outside of it, 0:14:48.480 --> 0:14:52.080 that I think that's a valid way to criticize the concept. Now, 0:14:52.160 --> 0:14:54.359 I do have to say at the same time, Lucretius 0:14:54.480 --> 0:14:58.800 is a little thought experiment here, even to modern readers 0:14:58.840 --> 0:15:00.880 it it still does something when you think about it, 0:15:00.920 --> 0:15:03.600 like it does force you to think about uh these 0:15:03.640 --> 0:15:07.400 ideas of the finite and the infinite. Uh So, just 0:15:07.440 --> 0:15:09.400 as like a simple thought experiment is kind of a 0:15:09.440 --> 0:15:12.880 logic puzzle, it still carries its own weight. Now, they're 0:15:12.920 --> 0:15:18.760 absolutely have been thought experiments that have been extremely useful 0:15:18.960 --> 0:15:22.160 and powerful in the history of the advancement of science, 0:15:22.240 --> 0:15:25.680 that have not just like made a clever seeming point, 0:15:25.800 --> 0:15:29.640 but have actually pushed science forward. And these happen a 0:15:29.680 --> 0:15:31.880 lot of time in the history of physics because physics 0:15:31.960 --> 0:15:35.800 experiments work best when you can tightly limit the variables. 0:15:35.840 --> 0:15:38.560 But in reality, it is very hard to tightly limit 0:15:38.560 --> 0:15:42.960 the variables on pure physics experiments. Uh there there's often 0:15:43.000 --> 0:15:46.120 just a lot of like more more friction and more resistance, 0:15:46.200 --> 0:15:50.280 more whatever than you actually want. But here's an example. 0:15:50.480 --> 0:15:53.160 Let's say you go up on top of the Washington 0:15:53.280 --> 0:15:56.880 Monument and you drop two objects side by side. They're 0:15:56.920 --> 0:15:59.320 the same shape, but one is heavier than the other. 0:15:59.400 --> 0:16:02.440 Let's say one, say, plastic DVD of Flubber and the 0:16:02.520 --> 0:16:05.720 other is the new Criterion edition of RoboCop two, which 0:16:05.720 --> 0:16:08.680 has a jewel case made out of lead. So which 0:16:08.720 --> 0:16:10.920 one hits the ground first, Well, ideally they're both going 0:16:10.960 --> 0:16:12.920 to hit the ground at the same time, right, And 0:16:12.960 --> 0:16:16.240 you know that because we live in a post Galileo age, 0:16:16.360 --> 0:16:19.840 the post Copernican post Galileo age. But this might have 0:16:19.880 --> 0:16:21.840 been kind of a shock to you if you lived 0:16:21.840 --> 0:16:25.800 in say, ancient Rome or in medieval Europe, where it 0:16:25.880 --> 0:16:28.800 might well have been assumed that the heavier object would 0:16:28.880 --> 0:16:33.600 hit the ground first because heavier objects fall faster. For 0:16:33.840 --> 0:16:38.360 hundreds of years, the conventional wisdom was along these lines. 0:16:38.400 --> 0:16:42.120 It followed our intuitions, like, it makes intuitive sense that 0:16:42.240 --> 0:16:46.000 a heavier object falls faster because let's say it's harder 0:16:46.040 --> 0:16:49.280 to push a heavier object up a hill, right, so 0:16:49.400 --> 0:16:51.600 it would seem that a heavier object should fall to 0:16:51.640 --> 0:16:54.480 the ground through the air faster than a lighter object. 0:16:55.160 --> 0:16:57.720 This was the dominant strain of thinking also in in 0:16:57.880 --> 0:17:01.320 the sphere of scholars who revered the physics of Aristotle. 0:17:01.680 --> 0:17:04.800 Aristotle wrote in in his work on Physics that objects 0:17:04.800 --> 0:17:07.880 have a natural motion, They have a nature, and they 0:17:07.920 --> 0:17:11.240 have motions specific to their nature, and that part of 0:17:11.280 --> 0:17:14.399 that nature is mass, and so heavier objects fall to 0:17:14.440 --> 0:17:18.480 the ground faster than lighter objects. Now, Galileo Galilei was 0:17:18.520 --> 0:17:21.919 reported by some biographers to have actually performed an experiment 0:17:22.000 --> 0:17:25.560 of this kind by like dropping cannonballs of different weights 0:17:25.560 --> 0:17:27.679 from a tower. But whether or not this story is 0:17:27.720 --> 0:17:31.800 true about the physical experiment, Galileo definitely showed that you 0:17:31.880 --> 0:17:34.919 don't even need an experiment to prove that there is 0:17:35.000 --> 0:17:39.080 something wrong with the Aristotelian view of falling bodies. He 0:17:39.080 --> 0:17:41.439 could show it was wrong just by dreaming up a 0:17:41.520 --> 0:17:44.800 scenario in his head. As and as with many of 0:17:44.800 --> 0:17:49.280 the great intellectual smackdowns in history, Galileo didn't just explain 0:17:49.440 --> 0:17:54.400 his position. He wrote a fictional Socratic style dialogue, complete 0:17:54.400 --> 0:17:58.159 with a slack jawed fool to represent the opinion he 0:17:58.240 --> 0:18:03.440 was attacking. And that fool is named Simplicio. That's pretty good. 0:18:03.640 --> 0:18:06.440 Then he's also he's got a smart guy named Salviati 0:18:06.520 --> 0:18:08.960 to represent his own point of view. And this was 0:18:09.000 --> 0:18:14.760 in Dialogues concerning two New Sciences. In so, first Salviati 0:18:14.760 --> 0:18:19.520 and Simplicio argue about experiments concerning cannonballs and bird shot 0:18:19.600 --> 0:18:23.639 and stuff, and Simplicio is not moved from the Aristotelian 0:18:23.720 --> 0:18:26.760 position that objects fall through a medium with a speed 0:18:26.840 --> 0:18:30.800 proportional to their mass. And so I've tried to reconstruct 0:18:30.840 --> 0:18:33.400 the next moment in the dialogue, but sort of rewritten 0:18:33.400 --> 0:18:36.320 in more modern English and simplified to the main points. Robert, 0:18:36.359 --> 0:18:39.240 would you like to do a reading with me? Sure? 0:18:39.280 --> 0:18:41.320 What kind of accents are we going for here, Robert, 0:18:41.320 --> 0:18:43.200 you're gonna be the smart guy. How about you give 0:18:43.240 --> 0:18:49.240 me a combination of like Gandalf wizard Saruman pronouncing from 0:18:49.440 --> 0:18:52.960 from the top of the Tower of Knowledge, combined with 0:18:53.160 --> 0:18:56.920 like Sam Elliott wise old cowboy. All right, I'll give 0:18:56.960 --> 0:19:01.360 that a goiin. Now, look here, we don't even need 0:19:01.359 --> 0:19:04.439 to do any experiments to prove that Aristotle is wrong 0:19:04.480 --> 0:19:07.240 and a heavier body does not fall faster than a 0:19:07.320 --> 0:19:11.240 lighter one. Let's take Aristotle's principles as granted for a minute. 0:19:11.280 --> 0:19:15.359 What are those principles. Well, body falling in a fixed 0:19:15.400 --> 0:19:19.000 medium like air has a fixed velocity, and that's determined 0:19:19.000 --> 0:19:22.280 by its nature. And you can increase this speed unless 0:19:22.320 --> 0:19:25.600 you add momentum, and you can't decrease this speed unless 0:19:25.640 --> 0:19:28.600 you offer some resistance to slow it down. It's all there, 0:19:28.680 --> 0:19:32.800 and its nature. It's a fixed velocity. Great, So imagine 0:19:32.800 --> 0:19:36.600 two objects with different natural speeds, maybe a pebble which 0:19:36.640 --> 0:19:40.200 falls very slowly and a great millstone which falls very fast. 0:19:40.280 --> 0:19:44.600 Now time together. The fallen millstone will be slowed down 0:19:44.600 --> 0:19:46.879 by being tied to the pebble, which is forced by 0:19:46.880 --> 0:19:50.200 its nature to fall slower right right. You are, according 0:19:50.240 --> 0:19:52.760 to Aristotle, that pebble is going to slow down the 0:19:52.760 --> 0:19:55.800 bigger rock because it falls slower. Okay, okay, So by 0:19:55.880 --> 0:19:59.680 by tying the two stones together, the slower falling pebble 0:20:00.040 --> 0:20:03.200 should reduce the speed at which the millstone falls, making 0:20:03.240 --> 0:20:06.439 its speed less than it would have been alone. But 0:20:06.520 --> 0:20:08.840 at the same time, when you tie them together, their 0:20:08.840 --> 0:20:12.560 combined masses greater than the millstone alone. So shouldn't they 0:20:12.560 --> 0:20:17.000 together fall even faster than either one individually? From your 0:20:17.040 --> 0:20:19.960 principles of motion, we are forced to conclude that by 0:20:20.000 --> 0:20:22.560 tying the two stones together, the fallen speed of the 0:20:22.560 --> 0:20:27.119 millstone is both increased and decreased. Well, dang it, I 0:20:27.200 --> 0:20:30.680 am stumped, all right, So that that's this pretty fun 0:20:30.680 --> 0:20:34.280 because it basically illustrates how he's created kind of like 0:20:34.280 --> 0:20:37.359 a little political cartoon right here, right right. And I 0:20:37.400 --> 0:20:41.680 also absolutely love that he makes the representative of Aristotle, 0:20:41.720 --> 0:20:44.840 who was during the seventeenth century widely considered like the 0:20:45.040 --> 0:20:50.280 smartest guy of all time. He names him simplicito, which 0:20:50.400 --> 0:20:53.520 is like if somebody today wrote a dialogue trying to 0:20:53.560 --> 0:20:58.200 refute Einstein's relativity and had the character representing Einstein's point 0:20:58.240 --> 0:21:02.199 of view named like clet Us T. Dip Wad. But anyway, 0:21:02.280 --> 0:21:06.200 Carl Popper apparently wrote of this thought experiment quote one 0:21:06.200 --> 0:21:09.639 of the most important imaginary experiments in the history of 0:21:09.720 --> 0:21:13.400 natural philosophy, and one of the simplest and most ingenious 0:21:13.520 --> 0:21:16.800 arguments in the history of rational thought about our universe. 0:21:17.760 --> 0:21:22.040 And as far as like imagining physical scenarios goes, I 0:21:22.080 --> 0:21:25.520 think this is the equivalent of a reductio ad absurd 0:21:25.600 --> 0:21:28.840 um argument. So reductio ad absurd um is one of 0:21:28.880 --> 0:21:31.600 the most powerful logical tools we have. It's when you 0:21:31.640 --> 0:21:35.040 combine premises that somebody holds to be true and you 0:21:35.119 --> 0:21:38.560 demonstrate that when they're taken together, they force you to 0:21:38.640 --> 0:21:43.080 conclude something absurd that cannot possibly be true, which means 0:21:43.119 --> 0:21:45.920 at least one of the premises, even though you believe them, 0:21:46.080 --> 0:21:49.919 actually cannot be right. And so here Galileo is basically 0:21:50.040 --> 0:21:53.000 using two premises. One is that the the idea that 0:21:53.080 --> 0:21:56.600 objects of different mass have different natural speeds at which 0:21:56.640 --> 0:21:59.480 they fall, and the other is that you can add 0:21:59.520 --> 0:22:02.120 the mass of two objects together to create a greater 0:22:02.280 --> 0:22:05.760 combined mass. And so he constructs a scenario when it's 0:22:05.760 --> 0:22:09.359 actually not implausible at all. To show that, when taken together, 0:22:09.520 --> 0:22:13.800 these two premises implied something absurd and self contradictory. So 0:22:13.960 --> 0:22:16.679 one of the premises has got to be wrong. And 0:22:16.720 --> 0:22:19.480