WEBVTT - Is dark matter a fudge factor? 0:00:07.760 --> 0:00:12.319 Physicists are famously not so great at naming stuff. You've 0:00:12.360 --> 0:00:16.000 got your hadrons, your muons, your fermions, it's a mess. 0:00:16.760 --> 0:00:19.439 Then if you zoom out to the big categories of 0:00:19.480 --> 0:00:23.400 the universe, you have matter, dark matter, and dark energy. 0:00:23.800 --> 0:00:27.360 What's the connection between dark matter and dark energy? What 0:00:27.400 --> 0:00:30.800 does dark really mean? It gives you the impression that 0:00:30.960 --> 0:00:34.960 dark matter is somehow like well dark, but the truth 0:00:35.040 --> 0:00:38.639 is that dark matter is invisible matter. So in the end, 0:00:38.760 --> 0:00:42.720 the name dark matter is probably more misleading than helpful. 0:00:43.320 --> 0:00:46.279 And more broadly, I think physics has not done a 0:00:46.280 --> 0:00:50.000 great job in pr for dark matter. Online you see 0:00:50.080 --> 0:00:52.879 lots of people arguing that dark matter is a scam, 0:00:52.960 --> 0:00:56.680 it's a placeholder, it's a fudge factor, it's not actually science. 0:00:57.440 --> 0:01:00.680 What does that mean and do those criticisms have any merit? 0:01:01.520 --> 0:01:03.800 So on today's episode, we're going to dive into the 0:01:03.880 --> 0:01:07.120 question of fudge factors. What is a fudge factor? Actually? 0:01:07.240 --> 0:01:09.200 Does it have to have peanut butter in it? Is 0:01:09.240 --> 0:01:12.759 it so bad? Does dark matter qualify as a fudge 0:01:12.760 --> 0:01:16.399 factor since we haven't identified what particle it's made out of. 0:01:17.040 --> 0:01:21.560 Is that a fair criticism of modern physics? Welcome to 0:01:21.720 --> 0:01:24.880 Daniel and Kelly's Extraordinarily Fudge Universe. 0:01:38.040 --> 0:01:39.440 Hello, I'm Kelly Windersmith. 0:01:39.440 --> 0:01:42.839 I study parasites and space, and today we're talking about 0:01:42.920 --> 0:01:44.920 fudge factors, but not the kind of. 0:01:44.840 --> 0:01:45.640 Fudge that I like. 0:01:46.920 --> 0:01:50.440 Hi, I'm Daniel. I study particles and aliens, and I 0:01:50.520 --> 0:01:52.320 don't actually even like fudge. 0:01:52.640 --> 0:01:55.360 What who are you? Okay? 0:01:55.360 --> 0:01:57.440 So I understand if you don't like white chocolate fudge, 0:01:57.440 --> 0:01:59.760 none of us would be surprised. But you don't even 0:01:59.840 --> 0:02:03.320 like like chocolate fudge or peanut butter fudge or. 0:02:04.360 --> 0:02:07.240 I mean, I like going to state fairs and I 0:02:07.320 --> 0:02:10.720 like tasting fudge, but it's a little bit like eating butter, 0:02:11.040 --> 0:02:13.200 you know, like the tiniest little bit in your mouth 0:02:13.280 --> 0:02:15.920 is all right, but like nobody wants to like buy 0:02:15.960 --> 0:02:18.440 a big chunk of fudge and walk around snacking on it. 0:02:18.840 --> 0:02:20.040 You know, it just makes me sick. 0:02:20.400 --> 0:02:23.640 Speak for yourself. No, No, you're right, You're right. I 0:02:23.680 --> 0:02:25.679 like fudge in small quantities. But when I was a kid, 0:02:25.720 --> 0:02:28.000 my mom did find me underneath the table snacking on 0:02:28.040 --> 0:02:32.800 a stick of butter. So I'm already a bit of 0:02:32.800 --> 0:02:36.200 a weird, weird kid. But the extraordinary should know that beforehand. 0:02:36.240 --> 0:02:37.880 You and I had a discussion about whether or not 0:02:37.919 --> 0:02:40.560 the jokes were going to be about fudge or about poop, 0:02:40.840 --> 0:02:42.280 and we decided to go with food. 0:02:42.680 --> 0:02:44.880 So everyone should give us a little pet on the 0:02:44.919 --> 0:02:45.360 back for that. 0:02:45.960 --> 0:02:48.160 You're saying we're going to totally avoid poop jokes the 0:02:48.200 --> 0:02:50.000 whole episode, and that's a challenge. 0:02:50.120 --> 0:02:53.680 I doubt it, especially because you have enjoyed making Dark 0:02:53.720 --> 0:02:55.880 Matter poop jokes in the past, and so. 0:02:56.200 --> 0:02:57.480 They're so easy and fun. 0:02:57.680 --> 0:02:59.280 I know it could be either one of us, really, 0:02:59.520 --> 0:03:03.160 but okay, so fudge factor made me think fear factor, 0:03:03.360 --> 0:03:06.880 and so what is one of your irrational fears? 0:03:10.600 --> 0:03:12.200 Let it all out there, Daniel. 0:03:12.040 --> 0:03:14.640 Being trapped in a room and forced to eat fudge? 0:03:18.680 --> 0:03:20.760 Do better? Do better? 0:03:21.600 --> 0:03:23.679 I have a thing where you're standing on a balcony 0:03:23.760 --> 0:03:27.239 like fifty stories up and wonder am I gonna jump? 0:03:28.040 --> 0:03:30.359 Would you like to jump? Maybe I should back away 0:03:30.400 --> 0:03:32.040 from this balcony. What's wrong with me? 0:03:32.560 --> 0:03:32.800 Yeah? 0:03:32.880 --> 0:03:36.480 I don't trust me anymore. I need an adult. 0:03:37.880 --> 0:03:40.480 Because it would just take a second, you know, and 0:03:40.520 --> 0:03:43.040 it's irreversible. And I don't know why my brain goes 0:03:43.080 --> 0:03:45.280 there when I stand at the edge of anything, but 0:03:45.440 --> 0:03:45.960 it's weird. 0:03:46.400 --> 0:03:47.000 That is weird. 0:03:47.280 --> 0:03:49.960 It sounds like you're not afraid, you're more like curious, 0:03:50.400 --> 0:03:52.240 but maybe you should be afraid. 0:03:52.640 --> 0:03:55.240 I'm not that curious. I pretty much know what would happen, 0:03:55.720 --> 0:03:58.520 but somehow I just feel like myself floating out there. 0:03:58.560 --> 0:04:01.400 I don't know. It's weird. So that's an irrational beer 0:04:01.440 --> 0:04:03.360 that I'll just like jump off of alchemy. 0:04:03.560 --> 0:04:07.160 That's yes, Well, please don't do that, and especially don't 0:04:07.240 --> 0:04:09.680 do that before you have explained to all of us 0:04:10.120 --> 0:04:13.120 if dark matter is a fudge factor or not, because 0:04:13.120 --> 0:04:14.480 we're all dying to know. 0:04:15.800 --> 0:04:18.640 This is a topic you see discussed out there, mostly 0:04:18.680 --> 0:04:21.480 folks on the internet dismissing dark matter is an idea, 0:04:21.640 --> 0:04:25.400 calling it a fudge factor or a placeholder. And I 0:04:25.440 --> 0:04:27.919 get a lot of emails about this, and so I thought, 0:04:28.200 --> 0:04:30.720 let's dig into this question. What do we mean by 0:04:30.760 --> 0:04:33.480 a fudge factor? Is it fair to call dark matter 0:04:33.600 --> 0:04:37.200 a fudge factor? Our fudge factors actually so bad even 0:04:37.240 --> 0:04:38.480 if they have chocolate chips. 0:04:38.240 --> 0:04:42.200 In them, that's sorry, or peanut butter. Peanut butter's by thing, really, but. 0:04:42.520 --> 0:04:45.279 Peanut butter fudge is always improved by chocolate chips. 0:04:45.440 --> 0:04:47.919 Yeah, oh yeah, I'll give you that. Okay, So is 0:04:47.920 --> 0:04:50.839 this an episode? There's this like a defensive episode, like 0:04:50.920 --> 0:04:53.160 you guys got to stop picking up dark matter or 0:04:53.640 --> 0:04:55.720 what do you think? Because I was going through presidential 0:04:55.720 --> 0:04:58.240 address for the American Society of Parasitologists and one of 0:04:58.279 --> 0:05:01.839 the address was something like hersitology really is a science, 0:05:01.880 --> 0:05:03.080 and I was like, oh. 0:05:03.400 --> 0:05:05.040 Oh, it's not good to be in the position of 0:05:05.040 --> 0:05:05.880 needing to argue that. 0:05:06.600 --> 0:05:09.279 No, this is not defensive. This is a share the 0:05:09.440 --> 0:05:14.200 joy episode. This is make sure everybody appreciates the incredible 0:05:14.240 --> 0:05:17.520 science behind dark matter, what we do know about the universe, 0:05:17.839 --> 0:05:21.159 and also the open question so we can legitimately discuss 0:05:21.520 --> 0:05:24.839 where we stand as a science, rather than dismissing it 0:05:24.880 --> 0:05:26.040 with silly slogans. 0:05:26.279 --> 0:05:27.120 All right, love it. 0:05:27.200 --> 0:05:29.919 So let's go ahead and see what the extraordinaries know 0:05:30.160 --> 0:05:32.880 about dark matter and how much wonder they feel about 0:05:32.880 --> 0:05:33.320 the topic. 0:05:33.960 --> 0:05:36.960 Dark matter is a fudge factor and that it was 0:05:37.000 --> 0:05:41.599 invented to explain observations. But it seems to be physically real. 0:05:42.279 --> 0:05:45.560 But is this how we can detect it? Stop trying 0:05:45.600 --> 0:05:48.320 to see it, taste it instead. 0:05:48.880 --> 0:05:51.599 Fudge efine chocolate foodge. 0:05:51.880 --> 0:05:55.520 I don't know, but I think it's everywhere, and it's dark, 0:05:56.320 --> 0:05:58.559 and there's dark chocolate, so maybe yes. 0:05:59.040 --> 0:06:03.000 I think dark matter is a fudge factor, because well it. 0:06:03.000 --> 0:06:05.359 Must be, because we don't fully understand dark matter. 0:06:05.400 --> 0:06:10.080 Currently, matter energy lemonade around the corner. Cosmological fudge is. 0:06:10.080 --> 0:06:12.800 Made until we can find out what it is. It 0:06:12.880 --> 0:06:13.839 is a fudge factor. 0:06:14.200 --> 0:06:17.479 I guess dark matter could just be a mathematical artifact, 0:06:17.560 --> 0:06:19.000 but I wouldn't bet money on it. 0:06:19.440 --> 0:06:22.120 I think dark matter is a cosmological fludge factor because 0:06:22.160 --> 0:06:23.560 it shapes our galaxies form. 0:06:24.120 --> 0:06:28.800 The term dark matter is in itself a placeholder because 0:06:28.800 --> 0:06:31.040 we really, we really don't know what it is. 0:06:31.480 --> 0:06:34.800 I don't think that dark matter is a fudge factor. 0:06:35.120 --> 0:06:37.520 Be dark matter is forces that are twisted in a 0:06:37.520 --> 0:06:40.160 different direction. Cosmological fudge factor. 0:06:40.800 --> 0:06:41.680 There's something there. 0:06:42.160 --> 0:06:44.600 I believe that in a way, dark matter is a 0:06:44.680 --> 0:06:48.840 cosmological fudge factor, but it's more of an unknown so 0:06:48.880 --> 0:06:50.800 there could be several contributing factors. 0:06:51.200 --> 0:06:54.040 The matter is more than one thing. 0:06:54.560 --> 0:06:58.640 For now it is, I mean, anything we didn't understand 0:06:59.040 --> 0:07:03.679 first we come a fudge factor, like the ether being 0:07:03.760 --> 0:07:07.200 used to explain things that were not understood. 0:07:07.839 --> 0:07:10.840 The model seems to be working in all kinds of 0:07:10.880 --> 0:07:11.560 good conditions. 0:07:12.000 --> 0:07:14.360 I think it is. But that's quite normal for science, 0:07:14.400 --> 0:07:18.320 isn't it. You find something that you don't understand, give 0:07:18.360 --> 0:07:22.240 it a name, and then hopefully actually provide evidence to 0:07:22.280 --> 0:07:23.520 support its existence. 0:07:23.840 --> 0:07:27.840 There is a hypothesis out there that dark matter doesn't 0:07:27.920 --> 0:07:31.200 exist and we just understand gravity wrong. 0:07:31.680 --> 0:07:34.880 If it's detection requires measurements that can never be performed 0:07:34.960 --> 0:07:38.520 or perceived, then maybe, But it's been proposed to explain 0:07:38.560 --> 0:07:41.080 a real observation, so it's not just a matter of 0:07:41.120 --> 0:07:43.960 being a fudge factor. It just might not be the 0:07:44.040 --> 0:07:44.800 correct deduction. 0:07:45.680 --> 0:07:48.880 Well, I'll notice the extraordinaries went for fudge jokes instead 0:07:48.920 --> 0:07:51.640 of poop jokes. So bonus points for all of you. 0:07:52.120 --> 0:07:53.960 Yeah, I guess, But I feel like that's like they're 0:07:54.000 --> 0:07:56.440 all voting with you, and that's not fair. 0:07:58.920 --> 0:08:01.920 My favorite, as always, the musical answers to these questions. 0:08:02.200 --> 0:08:04.000 Yes, yeah, I love when people are like, you know what, 0:08:04.040 --> 0:08:06.000 I'm gonna put myself out there, I'm gonna make. 0:08:05.920 --> 0:08:08.600 Up poems, I'm gonna sing songs, and you know, let's 0:08:08.640 --> 0:08:09.400 just have some fun. 0:08:10.280 --> 0:08:12.040 I want to what Zach thinks about that, you know, 0:08:12.120 --> 0:08:12.800 since he's. 0:08:12.600 --> 0:08:16.040 So critical, he's you know, what you can't stop Zach 0:08:16.080 --> 0:08:18.600 from judging. It's like you can't stop the sun from shining, 0:08:18.720 --> 0:08:20.000 and so wow. 0:08:20.480 --> 0:08:24.320 Wow, we're spitting fire tonight. 0:08:24.360 --> 0:08:26.200 All right, Zach catching strays. 0:08:28.520 --> 0:08:31.200 Let's maintain Wiener Smith in marital harmony and focus on 0:08:31.240 --> 0:08:31.800 the science. 0:08:32.280 --> 0:08:36.960 Okay, all right, so we were retreating quickly. So, Daniel, 0:08:37.600 --> 0:08:40.000 why is it sometimes called a fudge factor? 0:08:40.600 --> 0:08:42.720 I think dark matter is called a fudge factor because 0:08:42.720 --> 0:08:46.000 most people know only one aspect of the dark matter story. 0:08:46.280 --> 0:08:49.200 It's the historical one and the most famous one. So 0:08:49.320 --> 0:08:53.599 let's dig into that first, and that is galactic rotation curves, 0:08:53.640 --> 0:08:57.400 like how galaxies rotate? How fast are they rotating? And 0:08:57.520 --> 0:09:00.200 can we understand it? This is a fast and any 0:09:00.240 --> 0:09:03.640 bit of astronomical history that goes back almost one hundred years. 0:09:03.920 --> 0:09:04.360 Wow. 0:09:04.400 --> 0:09:07.720 It was the late nineteen thirties when people were looking 0:09:07.720 --> 0:09:10.880 out in the universe. And remember Hubble had only recently 0:09:10.920 --> 0:09:14.040 discovered that there are things beyond the Milky Way, that 0:09:14.080 --> 0:09:17.720 there are more galaxies out there. Until Hubble's work, we 0:09:17.800 --> 0:09:21.360 thought that everything was just one galaxy, and those smudges 0:09:21.400 --> 0:09:24.000 we saw, which we now know are other galaxies were 0:09:24.080 --> 0:09:27.760 just nebula, just blobs in our galaxy, and then people 0:09:27.800 --> 0:09:30.479 started looking out into space and looking at other galaxies 0:09:30.480 --> 0:09:33.400 and looking at galaxy clusters. But it was Babcock in 0:09:33.480 --> 0:09:36.600 nineteen thirty nine who was studying Andromeda, and he was 0:09:36.640 --> 0:09:39.440 looking at how stars rotate in Andromeda and trying to 0:09:39.520 --> 0:09:43.400 understand the connection between the rotation speed and the amount 0:09:43.400 --> 0:09:44.880 of stuff in Andromeda. 0:09:45.480 --> 0:09:47.920 You're one hundred years things makes me wish that I could, like, 0:09:48.200 --> 0:09:50.800 I would like a list of like things that happened 0:09:50.800 --> 0:09:52.800 with one hundred years between them, just to think about 0:09:52.800 --> 0:09:54.240 what it would be like to be a person who 0:09:54.280 --> 0:09:56.600 lived to be one hundred and imagine like I don't 0:09:56.600 --> 0:09:58.600 know the telegraph to the cell phone, and I probably 0:09:58.640 --> 0:09:59.600 have insulted somebody. 0:09:59.640 --> 0:10:01.360 It's anyway, let's move on. 0:10:02.720 --> 0:10:06.520 So the connection here, the basic physics is that if 0:10:06.559 --> 0:10:08.679 you are moving in a circle, you need some force 0:10:08.720 --> 0:10:11.080 to hold you in right, Like if you're on a 0:10:11.080 --> 0:10:13.320 merry go round and somebody spins it, You've got to 0:10:13.320 --> 0:10:15.360 hold on otherwise you're going to get thrown off the 0:10:15.400 --> 0:10:18.280 merry go round. And the faster they spin it, the 0:10:18.360 --> 0:10:20.600 harder you have to hold on right And eventually they 0:10:20.600 --> 0:10:23.079 spin it fast enough you lose your grip. Boom, you're 0:10:23.080 --> 0:10:25.000 flying off the Merry Go Round. We've all seen that 0:10:25.000 --> 0:10:27.600 epic fail video. It's hilarious but dangerous. 0:10:28.040 --> 0:10:30.000 I actually have no idea what video you're talking about, 0:10:30.040 --> 0:10:31.520 but I'll go look it up. 0:10:33.080 --> 0:10:35.120 So the idea is you can also invert that. You 0:10:35.160 --> 0:10:38.720 can measure the velocity that things are rotating around the 0:10:38.720 --> 0:10:41.640 center and use that to infer how strong is the 0:10:41.640 --> 0:10:44.360 force holding them in place? Okay, right, which means that 0:10:44.400 --> 0:10:47.120 you can measure the mass. So just by seeing how 0:10:47.240 --> 0:10:50.560 stars are moving around a galaxy, because they are being 0:10:50.640 --> 0:10:52.640 held in place for the most part, you can tell 0:10:52.679 --> 0:10:54.960 how much mass is they're holding them in. 0:10:55.320 --> 0:10:57.800 Okay, but that's got to be hard to tell from 0:10:57.800 --> 0:11:00.920 the kind of microscope you had in Night teen thirty nine. 0:11:01.480 --> 0:11:03.920 Well, if you're looking at stars through the microscope, you're probably. 0:11:03.720 --> 0:11:05.199 Not going to learn anything telescope. 0:11:05.920 --> 0:11:10.360 You can use a telescope, you got me, Okay, So 0:11:10.640 --> 0:11:14.680 the point stands Webster, But yeah, I mean it's going 0:11:14.720 --> 0:11:17.120 to be hard to get information from a telescope from 0:11:17.160 --> 0:11:17.920 nineteen thirty nine. 0:11:18.040 --> 0:11:20.439 Right, Well, all you need to do is measure the 0:11:20.520 --> 0:11:23.520 velocity of those stars, which means you're measuring the red shift. 0:11:23.880 --> 0:11:26.920 Because we're not watching these galaxies long enough to actually 0:11:26.960 --> 0:11:29.959 see the move and calculate the velocity based on changing distance. 0:11:30.480 --> 0:11:33.000 We're measuring their velocity based on the light that comes 0:11:33.040 --> 0:11:35.640 to us being red shifted or blue shifted. And you 0:11:35.679 --> 0:11:37.760 can definitely do that with these telescopes. I mean that 0:11:37.800 --> 0:11:41.839 was Hubble's discovery a decade before Babcock is measuring the 0:11:41.920 --> 0:11:45.000 red shift of all these galaxies. So that's definitely something 0:11:45.000 --> 0:11:47.280 that we could do back then. So you have now 0:11:47.320 --> 0:11:49.560 the velocity of the stars. You can tell how much 0:11:49.640 --> 0:11:51.360 mass there has to be, and not just like the 0:11:51.400 --> 0:11:54.240 total amount of mass in the galaxy, but because you 0:11:54.280 --> 0:11:56.880 can measure the velocity stars close to the center and 0:11:56.960 --> 0:11:59.040 further from the center, and yet further from the center, 0:11:59.360 --> 0:12:01.000 you can tell how much mass there has to be 0:12:01.040 --> 0:12:04.240 in each of those enclosed shells, which means you can 0:12:04.280 --> 0:12:07.800 tell the mass distribution in the galaxy. It's really amazing. 0:12:08.000 --> 0:12:10.840 Just from the velocity, you can tell not only how 0:12:10.920 --> 0:12:13.120 much mass there is totally in the galaxy, but also 0:12:13.520 --> 0:12:14.880 how it's spread radially. 0:12:14.960 --> 0:12:15.319 Holy g. 0:12:15.760 --> 0:12:18.040 And then you can say, well can I explain that mass? 0:12:18.040 --> 0:12:21.080 Do I know what that mass is? And if you 0:12:21.080 --> 0:12:23.240 look at the distribution of stars you can tell, well, 0:12:23.320 --> 0:12:24.840 there's a big blob of gas here and a big 0:12:24.880 --> 0:12:27.800 blob of gas there. And the problem the galaxy rotation 0:12:27.960 --> 0:12:32.160 puzzle was there wasn't nearly enough stars to explain all 0:12:32.160 --> 0:12:34.800 the mass to give the gravity to hold the galaxy 0:12:34.800 --> 0:12:35.280 in place. 0:12:35.559 --> 0:12:38.760 Yeah, so it's got a here's Kelly being a skeptical 0:12:39.160 --> 0:12:41.720 jerk again, but like, how can you tell from so 0:12:41.800 --> 0:12:43.560 far away how big the stars are? How could you 0:12:43.600 --> 0:12:46.400 be like, ah, no, you couldn't possibly weigh that much, 0:12:46.440 --> 0:12:48.680 Like I'm not good at guessing people's weight. How is 0:12:48.760 --> 0:12:52.360 Babcock guessing the weight of a star from another galaxy 0:12:52.880 --> 0:12:53.960 in nineteen thirty nine? 0:12:54.280 --> 0:12:58.200 Yeah, totally fair. It's hard actually to measure the mass 0:12:58.200 --> 0:13:00.880 of a distant star. We sees the light from it, 0:13:00.880 --> 0:13:02.679 and that's like where the whole other episode of how 0:13:02.760 --> 0:13:05.120 we know the connection between the brightness of a star 0:13:05.679 --> 0:13:08.480 and its mass. There's a lot of complicated science there, 0:13:08.480 --> 0:13:12.440 and you're right, there are uncertainties. But even within those uncertainties, right, 0:13:12.480 --> 0:13:15.360 even if those uncertainties are one hundred percent, that's not 0:13:15.600 --> 0:13:19.160 enough to explain this discrepancy. And it's not just the 0:13:19.200 --> 0:13:21.480 amount but the distribution of the mass if it was 0:13:21.640 --> 0:13:24.160 just stars, then as you got further out towards the 0:13:24.320 --> 0:13:27.160 edge of the galaxy, then you expect the gravity to 0:13:27.200 --> 0:13:29.440 get weaker and weaker because you're getting further from the 0:13:29.480 --> 0:13:32.880 center the cluster of stars. And yet it doesn't. The 0:13:32.960 --> 0:13:35.240 velocity of stars near the edge of the galaxies is 0:13:35.280 --> 0:13:37.840 pretty high. It just stays high. It doesn't fall like 0:13:37.880 --> 0:13:40.280 you would expect. And that suggests that there's a lot 0:13:40.280 --> 0:13:43.120 of mass further out as well. So it's not just 0:13:43.160 --> 0:13:46.520 the amount, but it's the distribution. And so Babcock saw 0:13:46.559 --> 0:13:49.080 this in nineteen thirty nine and he said, well, there 0:13:49.160 --> 0:13:51.480 must be something absorbing the light. Maybe I'm not seeing 0:13:51.520 --> 0:13:54.160 all of it or something. He didn't jump to this 0:13:54.200 --> 0:13:57.600 conclusion of unseen matter. But we saw this already in 0:13:57.640 --> 0:14:00.280 Andromeda in nineteen thirty nine. But it was just like 0:14:00.360 --> 0:14:03.120 a puzzle, like, hmm, that's weird. But you know, there's 0:14:03.160 --> 0:14:05.200 lots of things in the sky that don't quite make sense. 0:14:05.600 --> 0:14:08.480 You don't jump from that to like maybe eighty percent 0:14:08.520 --> 0:14:11.520 of the matter in the universe is invisible, actually, right, right? 0:14:11.720 --> 0:14:13.520 That does seem crazy, Daniel. 0:14:13.280 --> 0:14:16.240 Yes, And it's not like astronomers went straight to that answer, right, 0:14:16.280 --> 0:14:18.640 They were like, let's think about other things and all 0:14:18.679 --> 0:14:19.400 sorts of stuff. 0:14:19.560 --> 0:14:21.040 So wait, he just threw up his arms and he 0:14:21.120 --> 0:14:24.280 was like, oh, that was totally off. Those calculations were 0:14:24.360 --> 0:14:25.480 no wordy or what I thought. 0:14:25.320 --> 0:14:25.960 They were going to be. 0:14:26.120 --> 0:14:28.600 Yeah, and I think people underestimate how often that happens 0:14:28.640 --> 0:14:30.720 in astronomy and how often it used to happen, And 0:14:30.760 --> 0:14:32.760 there's lots of times people were like, well, this is 0:14:32.800 --> 0:14:36.600 weird shrug, and then you know, let's keep studying it. 0:14:36.720 --> 0:14:39.880 This is a puzzle. That's the joy of astronomy actually, 0:14:39.960 --> 0:14:41.440 is that every time you look at into the universe, 0:14:41.440 --> 0:14:43.920 there's something out there that doesn't make sense. And many 0:14:43.920 --> 0:14:47.000 of them have boring explanations like oh, there's dust cloud 0:14:47.040 --> 0:14:50.120 absorbing XYZ. But some of them don't, you know, and 0:14:50.600 --> 0:14:53.360 those are the wonderful ones. So that's where it stood 0:14:53.400 --> 0:14:57.480 for about thirty years until the nineteen seventies. And in 0:14:57.520 --> 0:14:59.760 the seventies it was a revolution and how well be 0:14:59.760 --> 0:15:04.080 could measure these galaxies? So Vera Rubin, who died before 0:15:04.160 --> 0:15:07.320 she could be awarded a Nobel prize, and Kent Ford 0:15:07.720 --> 0:15:11.119 measured this very accurately for a bunch of spiral galaxies 0:15:11.200 --> 0:15:15.400 using new technology. So they use their super fancy astronomical 0:15:15.400 --> 0:15:18.840 microscopes and they pointed them up at the sky and they. 0:15:18.720 --> 0:15:23.160 Measured this speak once, all right, welcome to. 0:15:23.160 --> 0:15:26.360 The podcast, where have you been killing? 0:15:28.040 --> 0:15:29.600 And so they repeat this for lots and lots of 0:15:29.600 --> 0:15:32.200 galaxies and they see the same kind of pattern. And 0:15:32.240 --> 0:15:36.640 then radio astronomers radio astronomy, having been developed basically at 0:15:36.640 --> 0:15:39.440 the advent of World War two, use it to study 0:15:39.440 --> 0:15:43.000 the velocity of hydrogen. So Vera Ruben and folks are 0:15:43.000 --> 0:15:45.960 looking at stars, but they can look at emission from hydrogen, 0:15:45.960 --> 0:15:48.200 and hydrogen is like this huge cloud of gas that 0:15:48.280 --> 0:15:51.880 extends well beyond the visible part of the galaxy. So 0:15:51.920 --> 0:15:53.840 it's like a new kind of tracer that lets you 0:15:53.920 --> 0:15:57.640 measure the velocity past the edge of the stars. So 0:15:57.680 --> 0:15:59.720 now we can measure much further out, which gives you 0:15:59.720 --> 0:16:03.320 a longer lever arm. So by the eighties and nineties 0:16:03.440 --> 0:16:07.440 we had seen similar behavior in like thousands of galaxies. 0:16:07.560 --> 0:16:09.120 This is the kind of thing we saw. 0:16:09.120 --> 0:16:13.320 Everywhere, and was it always off by like the same factor, 0:16:13.520 --> 0:16:16.160 Like it was always fifty percent off of what they expected. 0:16:16.560 --> 0:16:18.920 So that turns out to be a significant variation galaxy 0:16:18.960 --> 0:16:22.200 to galaxy some galaxies have more, some galaxies have less, 0:16:22.440 --> 0:16:25.680 but overall the number is about five to one. To 0:16:25.760 --> 0:16:29.360 explain this using invisible matter, now we call it dark matter, 0:16:29.800 --> 0:16:32.240 you would need invisible matter in the amount of five 0:16:32.400 --> 0:16:35.960 times the matter in stars and gas and dust. So 0:16:36.040 --> 0:16:39.480 like not a small hypothesis, right, And I think this 0:16:39.600 --> 0:16:43.000 is the origin of the fudge factor or the placeholder, 0:16:43.360 --> 0:16:47.080 because dark matter wasn't something directly observed, like, oh, look, 0:16:47.080 --> 0:16:49.800 we found this thing, what is it? There was a 0:16:50.080 --> 0:16:53.880 discrepancy between two measurements, and like, yeah, you could add 0:16:53.920 --> 0:16:57.120 something to your theory to make those measurements fit. And 0:16:57.160 --> 0:17:00.160 so that's why I think it's called a fudge factor 0:17:00.280 --> 0:17:03.200 or a placeholder or this kind of stuff because it 0:17:03.280 --> 0:17:08.159 was introduced to explain a discrepancy between expectations and observations. 0:17:08.440 --> 0:17:09.880 So it's not because we thought it was a load 0:17:09.880 --> 0:17:14.000 of poop, wait, it's a discrepancy. 0:17:13.760 --> 0:17:16.240 Or because Kelly got caught under the table snacking on it. 0:17:16.200 --> 0:17:22.520 All day long, and so there's no there's no way 0:17:22.560 --> 0:17:25.159 that it's like we just didn't realize that suns are 0:17:25.160 --> 0:17:27.479 made out of something like much heavier. It's not that 0:17:27.520 --> 0:17:30.399 we just are totally blowing it on the mass measurements. 0:17:30.920 --> 0:17:33.480 It's got to be something totally different because this fudge 0:17:33.480 --> 0:17:34.560 factor is so big. 0:17:34.920 --> 0:17:37.879 Yeah, the fudge factor is big, and again the distribution 0:17:38.080 --> 0:17:41.359 doesn't match the distribution from stars. And we've done a 0:17:41.400 --> 0:17:44.639 lot of work to understand the masses of stars, and 0:17:44.720 --> 0:17:47.120 we think we do, like, we see binary stars out 0:17:47.119 --> 0:17:49.399 there and we can see them orbiting each other and 0:17:49.440 --> 0:17:52.560 from that you can measure their masses. So it doesn't 0:17:52.640 --> 0:17:55.239 make sense for it to be front stars. Either it's 0:17:55.280 --> 0:17:58.520 a misunderstanding of gravity or something else or in visual matter, 0:17:58.880 --> 0:17:59.720 but it's definitely not. 0:17:59.680 --> 0:18:04.479 From Okay, so you all have gotten away with having 0:18:04.800 --> 0:18:07.080 something like a fudge factor for a long time. What 0:18:07.119 --> 0:18:09.680 are some other fields that are trying to get away 0:18:09.800 --> 0:18:11.080 with having fudge factors? 0:18:12.160 --> 0:18:13.760 Are we okay with this in other domains? 0:18:14.200 --> 0:18:17.040 Yeah? I think the fudge factors, you know, as delicious 0:18:17.040 --> 0:18:20.720 as they sound, often get a bad rap, right because 0:18:20.760 --> 0:18:23.840 often they're very useful to sum up a lot of 0:18:23.880 --> 0:18:27.320 details that you don't yet understand or maybe don't care 0:18:27.400 --> 0:18:30.520 about in a single number. And we do this all 0:18:30.560 --> 0:18:32.680 the time in physics. We say, look, there's a lot 0:18:32.680 --> 0:18:35.280 of complicated stuff going on here. We can't moddel all 0:18:35.320 --> 0:18:37.760 of it. Can we just approximate it with a single 0:18:37.840 --> 0:18:41.480 number and a simplified theory. For example, people who do 0:18:41.520 --> 0:18:45.320 introductory physics learn about the coefficient of friction. Right, Like 0:18:45.720 --> 0:18:48.880 a box is sliding down a plane, right, classic problem, 0:18:49.440 --> 0:18:52.399 and it doesn't slide smoothly. There's friction between them, and 0:18:52.440 --> 0:18:55.400 you can describe that friction with a single number. What's 0:18:55.480 --> 0:18:58.679 really going on in the details is really complicated. You 0:18:58.680 --> 0:19:00.920 have these two surfaces that are grabbing in each other. 0:19:01.520 --> 0:19:04.840 But incredibly you can summarize all of that basically with 0:19:04.920 --> 0:19:07.960 the single number, and different surfaces have a different number, 0:19:08.000 --> 0:19:10.200 and you can measure it for each surface, and that's 0:19:10.240 --> 0:19:13.880 a pretty good model of friction. It ignores or summarizes 0:19:14.000 --> 0:19:18.200 essentially a lot of tiny little details why teflon is slippery, 0:19:18.359 --> 0:19:21.320 why concrete is not, et cetera. But it's useful, so 0:19:21.600 --> 0:19:24.720 fudge factors, you know, let you skip over the details 0:19:24.720 --> 0:19:25.840 that you're not interested in. 0:19:26.280 --> 0:19:28.840 But there you know, like it's you know, one molecule 0:19:28.920 --> 0:19:31.399 hits another molecule and it slows them down or something 0:19:31.480 --> 0:19:33.439 like that. Like you've got like a general sense of 0:19:33.480 --> 0:19:36.720 what it is that you're summarizing, and you're making measurements 0:19:36.800 --> 0:19:38.640 to get that quote unquote fudge factor. 0:19:39.040 --> 0:19:41.080