WEBVTT - Does the Universe need dark matter? 0:00:08.760 --> 0:00:11.080 Hey, Daniel, do you ever wonder if physics might be 0:00:11.200 --> 0:00:13.920 like really wrong? Are you talking about me or like 0:00:13.960 --> 0:00:17.880 the entire community? Well, I know you're never wrong, Daniel, 0:00:18.400 --> 0:00:22.400 that's unthinkable, but you know, like, has physics ever gotten 0:00:22.600 --> 0:00:27.120 something about the very nature of the universe? Kind of? Uh? 0:00:27.280 --> 0:00:30.000 Not right? You mean, like what's the best snack food? 0:00:30.160 --> 0:00:33.040 Or what colored lab coat should we wear? Hey? Yeah, 0:00:33.080 --> 0:00:36.160 you know, like can I eat antimatter or not? Maybe 0:00:36.159 --> 0:00:40.199 it's delicious. Physics could definitely be wrong about snacks for you. Well, 0:00:40.240 --> 0:00:42.400 I mean think bigger, like, is it possible that maybe 0:00:42.680 --> 0:00:44.920 things are not quite what they seem? Well, it wouldn't 0:00:44.920 --> 0:00:47.040 be the first time physics is wrong, and I hope 0:00:47.080 --> 0:01:05.199 it's not the last time. I am organ made cartoonists 0:01:05.200 --> 0:01:08.280 and the creator of PhD comments, Hi, I'm Daniel. I'm 0:01:08.319 --> 0:01:12.039 a particle physicist, and I've never been wrong about snack foods, 0:01:12.040 --> 0:01:15.040 and I've never been wrong about being wrong. So I 0:01:15.080 --> 0:01:18.000 think that means that I'm always wrong. I don't know, 0:01:18.800 --> 0:01:21.520 but welcome to our podcast. I'm definitely right about that. 0:01:21.560 --> 0:01:24.160 This is our podcast, Daniel and Jorge Explain the Universe, 0:01:24.240 --> 0:01:27.440 a production of I Heart Radio. That's right. Our podcast 0:01:27.480 --> 0:01:29.760 in which we take a mental tour of all the 0:01:29.920 --> 0:01:32.400 crazy stuff that's out there in the universe and try 0:01:32.400 --> 0:01:34.880 to bring it into your head. We try to wrap 0:01:34.920 --> 0:01:38.360 up the entire universe, all those trillions and trillions of 0:01:38.440 --> 0:01:42.039 stars and weird blobs of gas and dust and invisible stuff, 0:01:42.360 --> 0:01:45.199 and inserted through a little hole in your ear into 0:01:45.240 --> 0:01:47.840 your brain. Yeah, all of the amazing and incredible stuff 0:01:47.840 --> 0:01:50.200 out there in the universe, and also all of the 0:01:50.240 --> 0:01:53.320 stuff that's normal. You know, And sometimes I think when 0:01:53.360 --> 0:01:56.480 you examine what's spears to be normal in your everyday lives, 0:01:56.600 --> 0:01:58.680 it turns out to have all kinds of wonders and 0:01:58.720 --> 0:02:01.200 all kinds of small miracles in it. Are there small 0:02:01.280 --> 0:02:03.880 miracles in your snack foods? Is that what you're talking about? Like, Oh, 0:02:03.960 --> 0:02:06.320 look this chocolate chips in this trail mix. Every snack 0:02:06.440 --> 0:02:11.760 is a miracle, Daniel, especially banana's net. But in this podcast, 0:02:11.840 --> 0:02:15.040 we go beyond the miracles of banana based snack foods 0:02:15.240 --> 0:02:18.640 and talk about the incredible things that scientists are trying 0:02:18.680 --> 0:02:23.320 to figure out, Because, contrary to popular perception, scientists don't 0:02:23.360 --> 0:02:25.760 have it all figured out. There are lots of really 0:02:25.880 --> 0:02:29.160 big mysteries out there and wondering about the universe is 0:02:29.200 --> 0:02:32.920 something that belongs to everybody, including you. Yeah, so they're 0:02:32.960 --> 0:02:36.120 one of the biggest mysteries out there in the universe, 0:02:36.200 --> 0:02:38.640 and literally sort of like not just like because we 0:02:38.639 --> 0:02:40.839 don't know it, but also because it's a huge part 0:02:40.840 --> 0:02:44.560 of the universe. Is dark matter? Dark matter is a 0:02:44.600 --> 0:02:48.120 little bit crazy, right, It's like twenty of the universe, 0:02:48.160 --> 0:02:50.480 but we have no idea what it is. That's right 0:02:50.560 --> 0:02:53.280 of the energy budget of the universe. It's a pretty 0:02:53.320 --> 0:02:55.640 big slice. It's like a little bit more than a 0:02:55.720 --> 0:02:58.239 quarter of all the energy in the universe. Is this 0:02:58.440 --> 0:03:01.880 weird stuff and we've never seen it directly. We're pretty 0:03:01.919 --> 0:03:04.960 sure it's there, but we don't really know what is it. 0:03:05.000 --> 0:03:07.320 Is it made out of particles? Isn't made out of 0:03:07.320 --> 0:03:10.880 black holes? Isn't made out of lost socks? Two really 0:03:10.960 --> 0:03:14.000 huge mystery in modern physics. In fact, I would say 0:03:14.040 --> 0:03:17.160 it's one of the biggest open questions in science. I 0:03:17.240 --> 0:03:20.000 think it's just dark socks actually, but didn't that makes sense? 0:03:20.520 --> 0:03:23.320 I always lose those. How many dark socks have you 0:03:23.360 --> 0:03:26.400 lost for her? I mean we're talking a lot of songs. Well, 0:03:26.480 --> 0:03:28.200 to be out of time a cartoonists I don't have 0:03:28.240 --> 0:03:31.400 to wear dark socks very often or socks at all, 0:03:32.120 --> 0:03:34.640 because I also lived in California. But yeah, dark matter, 0:03:34.880 --> 0:03:36.880 I mean, it's a big deal. There's five times more 0:03:36.960 --> 0:03:39.920 dark matter than there is regular matter, like planets and 0:03:39.960 --> 0:03:43.280 stars and gas and dust and black holes, there's all 0:03:43.320 --> 0:03:47.120 that stuff. There's actually it's only of the stuff in 0:03:47.160 --> 0:03:50.200 the universe, which means the normal matter, the regular matter, 0:03:50.280 --> 0:03:53.480 the stuff that you're familiar with, is not actually regular 0:03:53.600 --> 0:03:56.600 or normal. It's the unusual stuff. If you just took 0:03:56.640 --> 0:03:59.240 like a survey of stuff in the universe, most of 0:03:59.280 --> 0:04:02.360 the stuff is dark matter. The things that make up 0:04:02.400 --> 0:04:05.560 stars and planets and galaxies and hamsters and me and 0:04:05.600 --> 0:04:08.960 you and bananas and snack foods. That's unusual in the universe. 0:04:09.000 --> 0:04:12.280 It's a minority of what's out there in the universe. 0:04:12.840 --> 0:04:15.920 And yet we still don't know what this dark matter is. 0:04:16.160 --> 0:04:18.680 It's a big mystery and a lot of times, you know, 0:04:18.720 --> 0:04:20.839 whenever people talk about dark matter, I feel like a 0:04:20.880 --> 0:04:23.719 common question we get, at least and in talks and 0:04:23.839 --> 0:04:26.760 appearances is that people ask us like what if dark 0:04:26.800 --> 0:04:29.120 matter doesn't exist? Like what if it's just an error 0:04:29.360 --> 0:04:32.720 in the equations that you have about physics and the universe, 0:04:32.720 --> 0:04:36.320 Like what if we just maybe like misunderstood gravity, or 0:04:36.760 --> 0:04:39.599 haven't counted all the stars in the galaxy, or you 0:04:39.640 --> 0:04:42.599 know what if there's something else that is maybe normal 0:04:42.720 --> 0:04:44.840 but we just haven't thought about. And it's a great 0:04:44.920 --> 0:04:47.320 question because most of the evidence we have for dark 0:04:47.360 --> 0:04:51.359 matter is a little bit indirect, like because dark matter 0:04:51.520 --> 0:04:54.000 is so dark and hard to interact with, we don't 0:04:54.040 --> 0:04:56.760 have clear pictures of it, right, we haven't seen what 0:04:56.839 --> 0:04:59.000 it's made out of. We've only sort of seen its 0:04:59.000 --> 0:05:02.719 effects and sometimes second hand, and so it's tempting to 0:05:02.760 --> 0:05:05.320 wonder if it's really there. You know. It's like if 0:05:05.360 --> 0:05:07.880 you've only seen the footprints of an animal, are you 0:05:07.920 --> 0:05:10.040 really sure it exists? Or could it be something else 0:05:10.120 --> 0:05:13.320 spoofing you Until you really capture one or see one 0:05:13.360 --> 0:05:16.279 in the wild, you don't really believe it exists. And 0:05:16.400 --> 0:05:19.680 dark matter has been eluding our searches for decades and 0:05:19.720 --> 0:05:22.920 makes people wonder like, well, maybe you people have it wrong. Yeah, 0:05:22.960 --> 0:05:24.839 I mean it's kind of a crazy idea, right to 0:05:24.920 --> 0:05:28.680 think that there's that much stuff out there, and conveniently 0:05:28.839 --> 0:05:31.240 it's invisible and you can't see it. You know what, 0:05:31.279 --> 0:05:34.240 I mean like I would be like, maybe you should 0:05:34.279 --> 0:05:36.680 take your math or you know, maybe you should have 0:05:36.720 --> 0:05:39.200 another grad student do the calculation. So, which do you 0:05:39.240 --> 0:05:42.400 think is the conspiracy theory dark matter like there's so 0:05:42.480 --> 0:05:44.920 much of it and you can't see it because it's 0:05:44.920 --> 0:05:47.640 so dark and that proves that it exists, or the 0:05:47.720 --> 0:05:52.080 anti dark matter conspiracy theory. Wait, anti dark matter? That's 0:05:52.080 --> 0:05:56.159 another episode right there? Can you have anti dark matter Danny? Yeah, 0:05:56.200 --> 0:05:59.160 that's another great question. We think probably not because then 0:05:59.160 --> 0:06:01.960 they would annihilate a dark matter and turn into photons, 0:06:01.960 --> 0:06:05.120 which we would see, what if it turns into dark photons? Yeah, 0:06:05.120 --> 0:06:09.920 that's actually a thing, dark photon. Really? Yeah, there goes 0:06:09.960 --> 0:06:11.680 my double price. You don't get credit for that one. 0:06:12.120 --> 0:06:15.120 But you know which idea sounds more bonkers, right, that 0:06:15.160 --> 0:06:18.000 the universe has filled with an incredible amount of invisible 0:06:18.000 --> 0:06:22.839 matter nobody had detected until recently, or that it's not. Yeah. 0:06:22.920 --> 0:06:25.080 So today on the podcast, we'll be asking the question 0:06:30.040 --> 0:06:34.839 does the universe need dark matter? Is it an essential 0:06:34.920 --> 0:06:36.600 part of the unit, Like could you have a universe 0:06:36.640 --> 0:06:39.400 without dark manner? Does that make sense? Or is it 0:06:39.440 --> 0:06:41.800 maybe that the universe doesn't need it? And maybe it 0:06:41.920 --> 0:06:43.520 is kind of an error that we have in our 0:06:43.680 --> 0:06:46.479 calculations and observations about the universe. And this kind of 0:06:46.520 --> 0:06:50.279 skepticism is very healthy. When you have a crazy idea 0:06:50.320 --> 0:06:52.800 you're trying to accommodate when you see results in your 0:06:52.839 --> 0:06:56.080 experiments you don't understand. You need to be flexible about 0:06:56.120 --> 0:06:58.760 this sort of theoretical framework with which you come at 0:06:58.800 --> 0:07:02.120 the problem. You need to be open to crazy new ideas, 0:07:02.120 --> 0:07:03.960 but you also need to be open to the fact 0:07:04.040 --> 0:07:06.800 that maybe you got your measurements wrong. There always can 0:07:06.920 --> 0:07:11.440 be an alternative explanation. So before you go big and say, wow, 0:07:11.560 --> 0:07:14.320 we're going to revolutionize our understanding of the universe, you've 0:07:14.320 --> 0:07:18.520 got to rule out all the more prosaic, basic, simpler explanations. 0:07:18.520 --> 0:07:20.920 And so it's always a good idea to keep those 0:07:20.960 --> 0:07:23.400 ideas in mind. YEA, So how sure are we that 0:07:23.520 --> 0:07:26.280 dark matter exists in the universe? And could it be 0:07:26.320 --> 0:07:28.520 something else? So I went out there into the internet 0:07:28.560 --> 0:07:31.400 and I asked people, can we explain what we see 0:07:31.440 --> 0:07:35.360 in the universe without dark matter? Are there good alternative 0:07:35.400 --> 0:07:38.000 theories that don't require a new particle or a new 0:07:38.040 --> 0:07:40.960 blob of stuff. Before you listen to these answers from 0:07:41.000 --> 0:07:42.920 the internet. Think about it for a second. Do you 0:07:42.960 --> 0:07:46.320 think dark matter is necessary in the universe or do 0:07:46.320 --> 0:07:49.040 you think the universe could ignore it or live without it. 0:07:49.280 --> 0:07:51.360 Here's what people had to say. I would think we 0:07:51.400 --> 0:07:56.640 would be much more baffled if we didn't have dark 0:07:56.680 --> 0:07:59.920 matter to explain the expansion of the universe. Oh man, 0:08:00.000 --> 0:08:02.840 And this is tough because I still don't have a 0:08:02.880 --> 0:08:06.000 good handle on what dark matter really is. But I 0:08:06.040 --> 0:08:09.840 think I think we really don't know what dark matter is, 0:08:09.880 --> 0:08:12.200 So I'm going to say, yeah, we could definitely explain 0:08:12.240 --> 0:08:14.520 what we see without it, because we're kind of just 0:08:14.600 --> 0:08:17.080 making up what it is. Yes, dark matter is just 0:08:17.360 --> 0:08:21.600 a made a term for the stuff that's there that 0:08:21.640 --> 0:08:27.640 we can't explain. So truly, any theory is under the 0:08:27.720 --> 0:08:31.480 umbrella of dark matter. I have a strong suspicion that 0:08:31.720 --> 0:08:36.920 the thing could be explained without dark matter, recalled Daniel, 0:08:37.040 --> 0:08:40.320 saying that dark matter is just the name that we've 0:08:40.360 --> 0:08:43.960 come up with for the phenomenon that we can't explain. 0:08:44.480 --> 0:08:47.079 I don't know what we would see without dark matter. 0:08:47.200 --> 0:08:51.440 My understanding is that we do know that there's dark 0:08:51.480 --> 0:08:55.880 matter because the math doesn't work out. At some point, 0:08:56.000 --> 0:08:58.920 we will have to explain the universe without dark matter, 0:08:59.080 --> 0:09:03.240 because like the dark in the matter sort of implies 0:09:03.280 --> 0:09:05.959 that we don't know what it is. I believe that 0:09:06.040 --> 0:09:09.120 dark matter is a theory that we came up with 0:09:09.320 --> 0:09:12.720 to help explain why we couldn't account for all of 0:09:12.760 --> 0:09:16.440 the gravity that we see in the universe. I think 0:09:16.480 --> 0:09:21.120 it's a fairly recent discovery. I don't believe Einstein knew 0:09:21.160 --> 0:09:25.320 about it, so he must have had some other way 0:09:25.400 --> 0:09:28.680 to account for all of the gravity. All Right, some 0:09:28.720 --> 0:09:31.000 pretty good answers there, Yeah. I like the people who 0:09:31.240 --> 0:09:33.520 treat dark matters just sort of like as an umbrella 0:09:33.640 --> 0:09:36.560 idea for all the things we don't understand. And so 0:09:36.640 --> 0:09:39.120 whatever we find out there, we just call that dark matter. 0:09:39.360 --> 0:09:41.760 And I think that really touches on the sense people 0:09:41.800 --> 0:09:43.920 have that we don't really have a clue what's out there. 0:09:43.920 --> 0:09:46.360 We just sort of labeled it dark matter, and we're 0:09:46.400 --> 0:09:48.400 talking about it as if it's a thing, but it's 0:09:48.400 --> 0:09:51.600 really just a name we applied to our cluelessness. Interesting, 0:09:51.640 --> 0:09:53.080 like if you put an S at d end, it 0:09:53.080 --> 0:09:55.679 becomes dark matters, and then then it's sort of like 0:09:55.760 --> 0:09:59.680 an umbrella term for things that are dark. That's true, 0:10:00.040 --> 0:10:02.800 and you know, that is definitely true of dark energy. 0:10:03.160 --> 0:10:06.200 Dark energy is another piece of the universe pie. Right, 0:10:06.280 --> 0:10:10.920 the universe pie is five percent normal matter, twenty dark matter, 0:10:12.080 --> 0:10:15.360 dark energy. Dark energy definitely in the category of just 0:10:15.600 --> 0:10:18.760 stuff we don't understand. We gave a fancy sounding name 0:10:19.120 --> 0:10:22.160 dark energy, this stuff that's making the universe expand right. 0:10:22.360 --> 0:10:25.679 Dark matter, on the other hand, is much better understood, 0:10:26.160 --> 0:10:30.400 is much more concrete and idea much more detailed observation. 0:10:30.480 --> 0:10:33.679 So they're both called dark both things we don't understand. 0:10:33.840 --> 0:10:37.240 But dark energy definitely a label for our cluelessness, while 0:10:37.440 --> 0:10:40.199 dark matter is a much better founded, well described theory. 0:10:40.640 --> 0:10:44.040 It's less dark. I guess we're less in the dark 0:10:44.080 --> 0:10:46.960 about exactly. We are less in the dark. Our minds 0:10:47.000 --> 0:10:49.200 are not quite so filled with dark shadows. All right. 0:10:49.240 --> 0:10:51.840 Well that's the question for today, And that's the question is, 0:10:51.960 --> 0:10:54.000 you know, do we need dark matter, like is it 0:10:54.080 --> 0:10:57.480 a concept that is totally necessary for the universe to 0:10:57.520 --> 0:11:01.040 make sense or is it just something weird that exists 0:11:01.040 --> 0:11:03.040 out there and that maybe we could have a totally 0:11:03.080 --> 0:11:06.200 wrong idea about, you know, And are there other theories 0:11:06.200 --> 0:11:09.080 that are being worked on in the scientific community that 0:11:09.200 --> 0:11:12.160 might explain it without needing to add some new kind 0:11:12.160 --> 0:11:16.040 of stuff to the universe, darker matter, the darkest matter. 0:11:16.720 --> 0:11:19.640 And you'll find that in science there are always competing voices. 0:11:19.679 --> 0:11:22.320 You know, there's often like a mainstream most people think 0:11:22.360 --> 0:11:24.679 the answer is X, but there's always somebody out there 0:11:24.679 --> 0:11:27.000 who thinks it's why, somebody who thinks it's Z. And 0:11:27.040 --> 0:11:29.760 you've got to give these people room because sometimes they're right, 0:11:30.120 --> 0:11:33.000 and sometimes their ideas of the ones that turn into 0:11:33.040 --> 0:11:36.440 the mainstream. That's how the mainstream became mainstream. It used 0:11:36.480 --> 0:11:41.160 to once be lunatic fringe or their alternative physicists, you know, 0:11:41.240 --> 0:11:44.760 French physicists. There definitely are there are people out there, 0:11:44.960 --> 0:11:48.400 once they get tenure, start working on crazy Bonker's theories 0:11:48.400 --> 0:11:51.920 and sometimes for decades that nobody pays attention, nobody really 0:11:51.920 --> 0:11:54.720 reads their papers, that people even laugh behind their hands. 0:11:54.760 --> 0:11:57.719 But sometimes they're right, you know. Literally, the history of 0:11:57.760 --> 0:12:01.640 physics is filled with revolutions that start as crazy ideas, 0:12:02.160 --> 0:12:04.720 and so we definitely got to pour water on some 0:12:04.760 --> 0:12:07.280 of those seedlings because they could sprout into huge new 0:12:07.320 --> 0:12:12.400 intellectual trees, awesome dark physics trees. I'm picturing all right, Well, 0:12:12.440 --> 0:12:15.680 step us through um like what's the main argument for 0:12:15.960 --> 0:12:19.240 dark matter, Like, what's the main evidence about it, and 0:12:19.480 --> 0:12:22.079 what makes this think that, you know, it's something new 0:12:22.160 --> 0:12:24.679 and different as opposed to maybe it's just more stuff 0:12:24.720 --> 0:12:26.240 out there that we can't see. Yes, So if you're 0:12:26.280 --> 0:12:28.480 going to come up with another theory of the universe, 0:12:28.520 --> 0:12:31.720 another way to explain the way the universe works, you 0:12:31.760 --> 0:12:34.439 have to explain what we do see, right, I mean 0:12:34.440 --> 0:12:37.200 that's the whole idea behind making a theory of physics. 0:12:37.679 --> 0:12:39.400 So if you're gonna come up with your theory, you 0:12:39.400 --> 0:12:41.800 have to understand what are the observations, what are the 0:12:41.880 --> 0:12:45.440 experiments reveal that need to be explained that you know, 0:12:45.520 --> 0:12:48.600 what's the motivation for creating this idea of dark matter? 0:12:48.760 --> 0:12:52.120 And the short version is it's all gravity. Like everything 0:12:52.160 --> 0:12:54.400 we see out there in the universe that we need 0:12:54.520 --> 0:12:58.440 dark matter to explain our weird gravitational effects that we 0:12:58.559 --> 0:13:01.880 can't explain with all the other stuff, just the gas 0:13:01.920 --> 0:13:04.520 and the dust and the stars right with the universe 0:13:04.679 --> 0:13:08.240 feels dark matter in terms of gravity, like it's they're 0:13:08.280 --> 0:13:10.920 affecting the gravity of other things, but you can't see it. 0:13:11.000 --> 0:13:14.560 That's the main evidence for it. Yeah, basically there's unexplained gravity, 0:13:14.640 --> 0:13:16.439 like we thought we knew where all the stuff was 0:13:16.480 --> 0:13:18.719 in the universe from the stars and the gas and 0:13:18.760 --> 0:13:21.079 the dust, and from that you can calculate how much 0:13:21.080 --> 0:13:23.880 gravity there should be, and we can see the effects 0:13:23.880 --> 0:13:25.840 of gravity, and will go through in a list of 0:13:25.840 --> 0:13:28.280 how we see the effects of gravity. But there's more 0:13:28.360 --> 0:13:31.920 gravity than we expected. So either there's more stuff e 0:13:32.080 --> 0:13:35.600 dark matter, or gravity is weird and different, and so 0:13:35.640 --> 0:13:38.439 it's all about the gravity then, right, because that's kind 0:13:38.440 --> 0:13:41.120 of at the basis of the theory about dark matter, 0:13:41.200 --> 0:13:43.720 is that it feels gravity but not anything else exactly, 0:13:43.720 --> 0:13:47.200 and that's why it's dark. Because if it felt electromagnetism, 0:13:47.240 --> 0:13:49.880 it would reflect light, or it would give off light 0:13:49.960 --> 0:13:52.960 like everything else does than the universe, it glows, or 0:13:53.040 --> 0:13:55.200 if it felt the strong force, it would bind with 0:13:55.280 --> 0:13:58.280 corks and form nucleons and interact with us. So it 0:13:58.280 --> 0:14:00.560 doesn't interact with us in any way that we know 0:14:00.640 --> 0:14:03.360 of other than gravitational And that's why we call it 0:14:03.480 --> 0:14:07.040 matter because we think it's something that has new gravity. 0:14:07.080 --> 0:14:08.880 But you know, it could also just be a tweak 0:14:08.920 --> 0:14:11.679 to the way we understand gravity. But at its core, 0:14:11.720 --> 0:14:15.480 it's really an observation that our theory of gravity doesn't 0:14:15.559 --> 0:14:20.240 work either because there's missing mass or the theory is wrong. Right, 0:14:20.280 --> 0:14:22.520 So those are two sides of the coin, right, Like, 0:14:22.640 --> 0:14:25.720 according to what we know about how gravity works, there's 0:14:25.760 --> 0:14:29.760 a lot of gravity missing, or there's too much gravity 0:14:29.760 --> 0:14:32.280 in the universe. Almost. Yeah, there's gravity out there and 0:14:32.280 --> 0:14:35.080 we don't have mass to explain it, and so we 0:14:35.160 --> 0:14:37.440 have to sort of fill in those gaps. And that's 0:14:37.480 --> 0:14:39.680 an uncomfortable feeling, right, You're like, well, you can't just 0:14:39.760 --> 0:14:42.160 like fill in the gaps and assume that your theory 0:14:42.280 --> 0:14:45.440 is right and add extra stuff to make it work out. 0:14:45.920 --> 0:14:49.440 You know, that feels uncomfortable, Like there's snack food missing 0:14:49.440 --> 0:14:52.760 from my fridge. Surely it was my son who cut 0:14:52.800 --> 0:14:54.000 up in the middle of the night to eat it. 0:14:54.080 --> 0:14:56.920 But you can't you can't just assume that. You can't 0:14:56.960 --> 0:14:58.920 just assume that could have been your daughter. Maybe you 0:14:59.000 --> 0:15:01.720 sleepwalked and aided or or And that's when you install 0:15:01.800 --> 0:15:03.440 a camera in front of your fridge and you get 0:15:03.440 --> 0:15:06.280 those weird videos of yourself at four am stuffing cake 0:15:06.320 --> 0:15:13.760 in your face. Experience the hypothetically hypothetically hypathetically right, Alright, 0:15:13.760 --> 0:15:16.200 So we think dark matter is there because of gravity. 0:15:16.240 --> 0:15:19.040 And there are several ways that we have seen this 0:15:19.120 --> 0:15:22.320 kind of missing gravity, right, that's in the galaxy and rotations. 0:15:22.400 --> 0:15:25.600 The way galaxies rotade is kind of one of the 0:15:25.600 --> 0:15:28.000 first one, maybe even Yeah, one of the most dramatic 0:15:28.160 --> 0:15:31.880 and earliest pieces of evidence that there was more gravity 0:15:31.880 --> 0:15:35.040 in the universe than we expected was looking at how 0:15:35.120 --> 0:15:38.640 galaxies rotate. And we can add up all the mass 0:15:38.680 --> 0:15:41.560 of the stars and the stuff in the galaxy and say, okay, 0:15:41.840 --> 0:15:44.320 we know how much gravity there should be, and then 0:15:44.360 --> 0:15:48.080 we can calculate how fast those galaxies are rotating. And 0:15:48.120 --> 0:15:50.720 you know, for a galaxy, when it's rotating, it's trying 0:15:50.760 --> 0:15:52.960 to push stuff off. It's trying to throw stuff off 0:15:53.000 --> 0:15:55.480 the edge. Like if you put ping pong balls on 0:15:55.520 --> 0:15:57.480 a merry go round and spin it, the ping pong 0:15:57.520 --> 0:16:00.680 balls fly out. The thing that keeps the galaxy from 0:16:00.680 --> 0:16:03.760 tearing itself apart from throwing those ping pong balls out 0:16:03.840 --> 0:16:07.440 into inter galactic space, is the gravity. So you can 0:16:07.480 --> 0:16:10.880 ask how fast is the galaxy spinning and is there 0:16:11.000 --> 0:16:14.200 enough gravity to hold it together, because the faster spins, 0:16:14.200 --> 0:16:16.080 the more gravity unied. Right. Yeah, It's kind of like 0:16:16.080 --> 0:16:18.160 our solar system, right, like you know, the mass of 0:16:18.160 --> 0:16:20.000 the Sun is what keeps all the planets kind of 0:16:20.000 --> 0:16:22.600 spinning around it. But what if, like the planets for 0:16:22.680 --> 0:16:25.280 spinning faster than what you could explain by the mass 0:16:25.280 --> 0:16:27.720 of the Sun. You would need some other explanations, that's right, 0:16:27.760 --> 0:16:30.560 You need more force to hold them into their orbits. 0:16:30.840 --> 0:16:32.920 And so you say, well, maybe there's extra gravity or 0:16:32.960 --> 0:16:35.400 some other force or something. And so we know there's 0:16:35.440 --> 0:16:40.200 something else holding the galaxy together. And so the first explanations, 0:16:40.240 --> 0:16:43.040 oh well, what if there's more invisible mass. It's just 0:16:43.080 --> 0:16:46.440 some stuff in the galaxy that's providing gravity and we 0:16:46.560 --> 0:16:50.400 just can't see it. And you can explain these rotation 0:16:50.480 --> 0:16:53.640 curves the way the stars move around centers of galaxies. 0:16:53.960 --> 0:16:56.560 If you distribute a bunch of mass sort of smoothly, 0:16:56.560 --> 0:16:58.440 it's like a big clump in the middle, and then 0:16:58.440 --> 0:17:01.200 sort of smoothly outpass the edge of the galaxy into 0:17:01.280 --> 0:17:04.280 a big halo that's even actually bigger than the galaxy. 0:17:04.480 --> 0:17:06.800 That explains to this as that would give you the 0:17:06.920 --> 0:17:09.239 kind of gravity that we are seeing, right, because if 0:17:09.280 --> 0:17:12.160 you look at a galaxy doesn't have that enough mass, right, 0:17:12.200 --> 0:17:14.639 like there aren't enough stars or planets in it that 0:17:14.680 --> 0:17:16.520 you can see. That's right. We count up all the 0:17:16.600 --> 0:17:19.520 visible stuff and we say how much mass does it have? 0:17:19.640 --> 0:17:22.480 And that just doesn't give us enough gravity to explain 0:17:22.640 --> 0:17:25.800 how those galaxies are holding themselves together. And that was 0:17:25.840 --> 0:17:27.439 the sort of genesis of it. I mean, for a 0:17:27.480 --> 0:17:30.080 long time people were like, well, wow, that's must be 0:17:30.119 --> 0:17:32.639 a mistake, you know, because coming to the idea that 0:17:32.680 --> 0:17:36.240 there's five times as much mass as you can see 0:17:36.359 --> 0:17:38.760 is a really big idea. It's not something people just 0:17:38.800 --> 0:17:41.880 came to an afternoon and then accepted, Yeah, it doesn't 0:17:41.920 --> 0:17:44.240 seem likely. It does not seem likely. It seems more 0:17:44.320 --> 0:17:47.480 likely that you mismeasured something that you got the velocity 0:17:47.560 --> 0:17:50.000 is wrong, or you know your grad student is pranking 0:17:50.040 --> 0:17:52.520 you or something. It's a big idea, right, It's like 0:17:52.760 --> 0:17:55.200 jumping to the conclusion right away that maybe there are 0:17:55.200 --> 0:17:57.560 five ghosts in my house eating my snacks. You know, 0:17:57.680 --> 0:18:00.480 that's like a big that's a big leap from like, hey, 0:18:00.520 --> 0:18:04.280 maybe it's just your u. And so it took other 0:18:04.359 --> 0:18:08.040 pieces of evidence before dark matter became mainstream. Right, all right, 0:18:08.080 --> 0:18:10.400 let's get into those other ways that we know dark 0:18:10.440 --> 0:18:13.520 matter is there, and let's get into whether or not 0:18:14.080 --> 0:18:16.359 it is there, or me we just have gravity wrong. 0:18:16.480 --> 0:18:31.119 But first, let's take a quick break, all right, Daniel, 0:18:31.119 --> 0:18:34.879 we're talking about whether dark matter is necessary in the 0:18:35.000 --> 0:18:37.560 universe or you know, maybe it's just the hanger on 0:18:37.720 --> 0:18:40.639 and the universe could care less about dark matter. But 0:18:40.840 --> 0:18:42.800 we we know it's definitely there because we see it 0:18:42.880 --> 0:18:46.040 from the rotation of galaxies and also we've set off 0:18:46.280 --> 0:18:48.280 kind of can see it, right, We can see it 0:18:48.320 --> 0:18:51.120 in the way that distorts the light from other far 0:18:51.160 --> 0:18:53.679 away stars. That's right. These days, we have a good 0:18:53.720 --> 0:18:58.000 handful of ways to indirectly detect dark matter, and one 0:18:58.000 --> 0:19:01.320 of the coolest is seeing it act like a lens 0:19:01.440 --> 0:19:05.920 in the sky because dark matter only has gravitational forces, 0:19:05.920 --> 0:19:09.359 but gravity can bend space, right, It's a bending of 0:19:09.400 --> 0:19:11.719 space and time. So if you have a big blob 0:19:11.800 --> 0:19:15.520 of invisible stuff in the sky, it will curve the 0:19:15.560 --> 0:19:18.440 space it's in, so that photon is traveling through it 0:19:18.480 --> 0:19:21.560 will get bent as if they're moving through a huge lens. Right, 0:19:21.840 --> 0:19:24.040 So if there's a big blob of dark matter between 0:19:24.080 --> 0:19:27.200 you and some really far away galaxy, it will distort 0:19:27.240 --> 0:19:31.040 that galaxy, creating duplicates of it, stretching it just as 0:19:31.040 --> 0:19:33.040 if there was a huge lens in the sky, right, 0:19:33.119 --> 0:19:35.040 and then we can see that, like if you look 0:19:35.040 --> 0:19:37.800 at pictures as a sky, you see these kind of distortions, 0:19:37.840 --> 0:19:40.600 these ripples, these lensing effects. You can sort of see 0:19:40.680 --> 0:19:42.880 dark matter almost, you can definitely see it. And there's 0:19:42.880 --> 0:19:45.840 sort of two categories. There's strong lensing, like there's a 0:19:45.840 --> 0:19:49.040 big dense blob and it's distorting the galaxies and it's 0:19:49.080 --> 0:19:51.720 pretty hard to explain that kind of lensing in any 0:19:51.760 --> 0:19:54.920 other way. And then there's weak lensing. We just sort 0:19:54.960 --> 0:19:57.919 of like look at all the galaxies out there to see, like, 0:19:58.000 --> 0:19:59.960 are any of them sort of just a little distorted? 0:20:00.000 --> 0:20:02.359 They're just looking a little tweaked. And from that we 0:20:02.400 --> 0:20:04.439 can get sort of like a map of where in 0:20:04.440 --> 0:20:07.360 the sky we think the dark matter is just by 0:20:07.359 --> 0:20:10.520 looking at small distortions. And that's how we've gotten a 0:20:10.560 --> 0:20:13.439 pretty good map for where we think this missing mass is. 0:20:13.440 --> 0:20:15.399 How we know that it's mostly in the center of 0:20:15.400 --> 0:20:18.040 the galaxy and how far out past the edge of 0:20:18.080 --> 0:20:21.040 the visible galaxy the dark matter halo might go. So 0:20:21.080 --> 0:20:23.560 it's a really powerful technique, right, And so that's kind 0:20:23.560 --> 0:20:26.200 of how dark matter entered in kind of our view 0:20:26.240 --> 0:20:30.080 of the universe was these first initial ways. But since 0:20:30.119 --> 0:20:32.600 then and we sort of have put more nails into 0:20:32.680 --> 0:20:35.200 sort of the coffin of whether or not dark matter 0:20:35.320 --> 0:20:38.159 is out there, right, I mean, it's now sort of 0:20:38.240 --> 0:20:41.120 shows up in pictures of the universe, the early universe, 0:20:41.119 --> 0:20:44.280 it kind of shows up in our calculations about all 0:20:44.320 --> 0:20:46.560 of the energy in the universe. Right, It's gotten more 0:20:46.600 --> 0:20:48.960 and more convincing that there's something there that's right, it 0:20:49.000 --> 0:20:52.120 becomes very difficult to explain the universe you see without 0:20:52.240 --> 0:20:55.640 dark matter. For example, we see the influence of dark 0:20:55.680 --> 0:20:59.119 matter on the formation of structures in the universe. Like 0:20:59.200 --> 0:21:02.280 the universe be in as a sort of diffuse cloud, 0:21:02.440 --> 0:21:04.920 you know, just of gas, mostly hydrogen, and then it 0:21:05.000 --> 0:21:08.840 started clumping together, and that clumping comes from gravity. Right, 0:21:08.840 --> 0:21:11.359 So gravity is the thing that draws these things together 0:21:11.400 --> 0:21:14.560 and eventually gives you stars and galaxies and planets and 0:21:14.600 --> 0:21:16.560 all that cool stuff. If you run a stimulation of 0:21:16.600 --> 0:21:19.200 the universe without any dark matter, then you don't get 0:21:19.280 --> 0:21:22.000 galaxies in the first ten billion years. It takes like 0:21:22.040 --> 0:21:25.400 another ten or twenty billion years. So it's dark matter 0:21:25.480 --> 0:21:29.119 that's that's created these like gravitational wells for stuff to 0:21:29.160 --> 0:21:32.480 fall into to make the stars in the galaxies and us. 0:21:33.080 --> 0:21:35.359 So just like the whole structure of the universe would 0:21:35.359 --> 0:21:39.800 look very different without some kind of gravitational stuff out there, 0:21:40.760 --> 0:21:43.119 and we should have just called them dark clumps or 0:21:43.880 --> 0:21:47.520 dark do it. And even earlier in the universe, like 0:21:47.560 --> 0:21:51.120 we've talked on this program about the cosmic microwave background radiation. 0:21:51.600 --> 0:21:54.760 Those are photons from the very very early universe, three 0:21:54.880 --> 0:21:58.359 hundred thousand years after the universe was created, the first 0:21:58.359 --> 0:22:01.879 moment when the universe became Rand's parent to light. Before 0:22:01.920 --> 0:22:04.720 that it was thick and soupy and light got reabsorbed, 0:22:04.920 --> 0:22:06.800 and after that it was cool enough that light could 0:22:06.800 --> 0:22:10.439 travel through the universe without being absorbed. And the shape 0:22:10.440 --> 0:22:13.439 of that plasma that gave off that light was affected 0:22:13.480 --> 0:22:16.000 by dark matter and how much dark matter there was 0:22:16.080 --> 0:22:18.679 and much normal matter there was, and that stuff like 0:22:18.920 --> 0:22:22.040 bounced off each other and oscillated and like squeezed and 0:22:22.080 --> 0:22:25.560 squished that plasma. So the amount of dark matter in 0:22:25.640 --> 0:22:28.880 that moment of the universe affects the shape of that light, 0:22:28.960 --> 0:22:31.320 the currents, the sort of patterns we see in that 0:22:31.400 --> 0:22:34.960 light in a very very precise way that's hard to 0:22:35.000 --> 0:22:38.400 describe in any other way other than there's some other 0:22:38.520 --> 0:22:42.200 kind of stuff out there. So that's giving us this graphic. Yeah, 0:22:42.240 --> 0:22:44.679 you can see like it's imprint in the light from 0:22:44.720 --> 0:22:48.359 the early universe, Like it's visually and like tangibly and like, 0:22:49.040 --> 0:22:51.679 you know, you can calculate it the storts that light. 0:22:51.760 --> 0:22:53.920 That's right. And so if you just take the universe 0:22:53.920 --> 0:22:56.920 and you add to it a new particle, a particle 0:22:56.920 --> 0:22:59.720 that doesn't move really fast, we call it cold and 0:22:59.800 --> 0:23:03.399 doesn't feel anything but gravity, it explains all of this stuff. 0:23:03.440 --> 0:23:06.760 It explains why galaxies rotate the way they do, why 0:23:06.800 --> 0:23:09.880 the cosmic microwave background rediation looks the way it does, 0:23:10.200 --> 0:23:13.880 why the structure of the universe has this structure at 0:23:13.880 --> 0:23:17.600 this time in the universe. And also there are very specific, 0:23:17.880 --> 0:23:20.919 awesome experiments that the universe has done to sort of 0:23:20.960 --> 0:23:24.399 demonstrate dark matter to us. Yeah, I guess, you know, 0:23:24.480 --> 0:23:27.160 I think maybe a question that a lot of people have, 0:23:27.280 --> 0:23:29.520 and I'm sure if physicists had at the beginning, was, 0:23:29.960 --> 0:23:32.800 you know, why does it need to be something special? 0:23:32.920 --> 0:23:35.200 Like why does it need to be a new kind 0:23:35.200 --> 0:23:39.680 of particle or matter? Couldn't it also just be something regular? 0:23:39.760 --> 0:23:41.560 But that you just can't see, Like, you know, what 0:23:41.600 --> 0:23:44.040 if there's a whole bunch of black asteroids out there 0:23:44.119 --> 0:23:46.720 that are hard to see, or you know, a lot 0:23:46.800 --> 0:23:49.359 of small dust that we can see, or maybe even 0:23:49.400 --> 0:23:51.560 like a whole bunch of little black holes kind of 0:23:51.600 --> 0:23:53.919 spread around the universe. Yeah, that's a great question, like 0:23:53.960 --> 0:23:56.040 why do we know it's a new kind of thing. 0:23:56.200 --> 0:23:57.920 Why can't it just be more of the same but 0:23:58.040 --> 0:24:01.080 just kind of dark, right? Yeah, yeah, Well we don't 0:24:01.080 --> 0:24:04.640 really know anything in our current set of particles that 0:24:04.880 --> 0:24:08.440 is that dark. I mean, other than neutrinos. Everything else 0:24:08.520 --> 0:24:11.200 has some kind of interaction, like if it's a black 0:24:11.359 --> 0:24:14.240 rock or something, well that does reflect light, it does 0:24:14.359 --> 0:24:16.639 give off light. So if it's made out of the 0:24:16.680 --> 0:24:18.560 normal kind of matter, it's going to have the kind 0:24:18.560 --> 0:24:22.320 of interactions we have, and therefore we would be able 0:24:22.359 --> 0:24:26.360 to see it, except of course, neutrinos. Neutrinos were candidate 0:24:26.400 --> 0:24:28.239 for dark matter for a long time. The problem is 0:24:28.359 --> 0:24:31.879 neutrinos move away too fast, they zoom around the universe 0:24:31.920 --> 0:24:34.280 because they're so light, so they don't give the same 0:24:34.280 --> 0:24:37.200 sort of structure to the universe that dark matter does. 0:24:37.240 --> 0:24:39.439 You need this thing to be sort of slow moving 0:24:39.480 --> 0:24:42.399 and cold in order to stick around long enough to 0:24:42.480 --> 0:24:46.240 give the structure of galaxies. Could you have cold neutrinos 0:24:46.320 --> 0:24:48.560 like slow moving neutrinos. Then we talk about that the 0:24:48.600 --> 0:24:51.800 other in another episode. Could you have cold neutrinos, Yes, 0:24:52.160 --> 0:24:55.240 but we don't think that neutrinos are that cold. We 0:24:55.320 --> 0:24:58.600 haven't seen cold neutrinos. Neutrinos are so light they have 0:24:58.680 --> 0:25:02.240 almost no mass that they essentially almost always travel near 0:25:02.280 --> 0:25:05.080 the speed of light. They're always in a rush, They're 0:25:05.080 --> 0:25:08.040 always in a hurry. Yes, neutrinos are hot, as we 0:25:08.119 --> 0:25:12.800 call them in particle physics. And it literally and figuratively 0:25:12.920 --> 0:25:15.840 is it's it's a pretty big trend right now, that's right, 0:25:15.880 --> 0:25:18.040 all right? Well, I guess if it's not maybe something 0:25:18.080 --> 0:25:20.119 we know about, could it be that just maybe we 0:25:20.160 --> 0:25:23.280 have our theories wrong about how things work, Like, you know, 0:25:23.320 --> 0:25:25.320 maybe it's not a new particle or a new kind 0:25:25.359 --> 0:25:28.439 of matter, but maybe we just have gravity wrong. Like 0:25:28.520 --> 0:25:31.320 maybe gravity doesn't work the way we think it is. 0:25:31.320 --> 0:25:36.080 And maybe these larger universe size scales could gravity, you know, 0:25:36.160 --> 0:25:38.320 could there be a different theory of gravity that would 0:25:38.320 --> 0:25:40.920 maybe account for what we think is dark matter. It's 0:25:40.960 --> 0:25:44.560 definitely something to consider, right, because all these observations are 0:25:44.640 --> 0:25:48.080 just observations of gravity. And what we're doing is we're saying, 0:25:48.240 --> 0:25:50.440 we assume there's a certain amount of mass out there, 0:25:50.720 --> 0:25:53.560 we assume we know how gravity works. We estimate how 0:25:53.600 --> 0:25:56.440 much gravity there should be based on that mass. Right, 0:25:56.440 --> 0:25:58.679 But there are two steps in there. There's figure out 0:25:58.760 --> 0:26:01.600 where the mass is and in calculate how much gravity 0:26:01.640 --> 0:26:05.080 there is from that mass. If that second step is wrong, right, 0:26:05.240 --> 0:26:07.960 if the theory of gravity works differently from what we expected, 0:26:08.160 --> 0:26:11.800 then yeah, that could possibly explain it. Because remember, gravity 0:26:11.920 --> 0:26:14.840 is very very weak, which makes it very very hard 0:26:14.880 --> 0:26:18.199 to test, Like it's difficult to measure the force of 0:26:18.280 --> 0:26:22.000 gravity at the scale of one centimeter between two pebbles 0:26:22.520 --> 0:26:26.280 because there's force there's almost zero, Like you need to 0:26:26.280 --> 0:26:29.880 build a very sensitive instrument to measure the gravitational force 0:26:29.920 --> 0:26:33.440 between anything that's smaller than you know, planets and moons. Yeah, 0:26:33.480 --> 0:26:36.520 because you know, like our current theory of gravity says that, 0:26:36.640 --> 0:26:40.239 you know, gravity changes by one of our squared, Like 0:26:40.280 --> 0:26:43.080 the force of gravity kind of depends on the distance 0:26:43.119 --> 0:26:45.720 between two things squared. And then you put down in 0:26:45.760 --> 0:26:49.120 the denominator and that always seems kind of almost too 0:26:49.119 --> 0:26:51.520 simple to me, Like, what are the chances at the 0:26:51.600 --> 0:26:55.240 universe would pick such a simple little formula to calculate gravity. 0:26:55.320 --> 0:26:58.480 You know, why isn't it like one over our squared 0:26:58.680 --> 0:27:01.639 times are to the zero point seven five? You know, 0:27:01.960 --> 0:27:04.199 I mean, like it seems so simple. Maybe what if 0:27:04.200 --> 0:27:06.040 it's wrong, Like what if gravity isn't one of our 0:27:06.040 --> 0:27:09.240 our square but maybe changes over distances in a way 0:27:09.359 --> 0:27:11.840 that could maybe explain dark matter. Yeah, that's a totally 0:27:11.840 --> 0:27:14.160 realistic thing to think. Although you know, there's a lot 0:27:14.160 --> 0:27:16.440 of these patterns, these one of our our squared patterns 0:27:16.440 --> 0:27:19.280 in physics and enforces and there is a good reason 0:27:19.320 --> 0:27:21.240 for it and a fairly simple way to understand it. 0:27:21.480 --> 0:27:24.520 If you imagine like the surface of a sphere surrounding 0:27:24.560 --> 0:27:27.320 a point. Think about like all the gravitational energy coming 0:27:27.320 --> 0:27:30.040 out of a point, the surface of a sphere surrounding it, 0:27:30.440 --> 0:27:33.640 all the gravitational energy passes through that sphere, and then 0:27:33.800 --> 0:27:36.600 as the radius of that sphere gets larger, what's the 0:27:36.640 --> 0:27:39.480 surface of that sphere? Will it goes like are squared, 0:27:39.920 --> 0:27:42.560 and so the power at any point should go like 0:27:42.680 --> 0:27:46.480 one over our squared. It sort of makes sense geometrically 0:27:46.840 --> 0:27:50.160 but what if geometry is wrong. What if geometry is wrong? Right? 0:27:50.359 --> 0:27:54.879 What is wrong? What if podcasting is wrong? What if 0:27:54.880 --> 0:27:56.920 one plus one is wrong? Well, it kind of, I mean, 0:27:57.119 --> 0:27:59.920 you know, we talk about sometimes about how space is 0:28:00.080 --> 0:28:02.679 not you know, this nice and neat, orderly thing, and 0:28:02.720 --> 0:28:06.560 that sometimes you can even like measure triangles in real 0:28:06.600 --> 0:28:09.560 space that have angles that are bigger than a hundred 0:28:09.600 --> 0:28:13.199 and eighty degrees, could maybe, like space be weird in 0:28:13.280 --> 0:28:16.520 such a way that it's not really one over our squares? Yeah? Absolutely, 0:28:16.520 --> 0:28:18.560 And there are forces that don't go like one of 0:28:18.560 --> 0:28:20.800 our our squared, Like the strong force doesn't go like 0:28:20.800 --> 0:28:23.520 one of our squared at small distances. It gets even 0:28:23.640 --> 0:28:26.560 stronger as you get further away. So you definitely got 0:28:26.560 --> 0:28:29.400 to be open to weirdness. And so around the time 0:28:29.440 --> 0:28:31.480 when dark matter was sort of coming up in the 0:28:31.520 --> 0:28:34.320 world as an idea, when it was based mostly on 0:28:34.440 --> 0:28:37.800 galaxy rotations, people thought, well, how can I tweak gravity 0:28:38.080 --> 0:28:41.240 to explain what I'm seeing without dark matter? What would 0:28:41.240 --> 0:28:42.960 I need to change? How what would you have to 0:28:42.960 --> 0:28:44.880 be like one over our to the third or one 0:28:44.880 --> 0:28:47.360 of our at one point five or whatever in order 0:28:47.360 --> 0:28:51.200 to explain these galaxy rotations without dark matter, and so 0:28:51.240 --> 0:28:54.600 they came up with a different theory. It's called mond 0:28:54.960 --> 0:29:01.760 m O n D for modified Newtonian dynamics. Know, I 0:29:01.760 --> 0:29:04.000 would have just called the dark bath. I wish you 0:29:04.040 --> 0:29:05.760 could get in a time machine and go back and 0:29:05.800 --> 0:29:08.160 tell them because I hate moms. Would that be a 0:29:08.160 --> 0:29:13.520 lot catch here and fun? Dark bath? Well, mon, I 0:29:13.520 --> 0:29:15.920 guess if you're French, then it's like, oh, yeah, it 0:29:15.960 --> 0:29:19.080 means the world. I suppose it's missing the E and 0:29:19.120 --> 0:29:21.959 it commits the terrible acronym crime of taking two letters 0:29:21.960 --> 0:29:26.120 from one of the words, you know, modified. Yeah, all right, 0:29:26.160 --> 0:29:28.840 so there is a kind of a theory in physics. 0:29:28.920 --> 0:29:31.080 It says like maybe we do have gravity wrong, right, 0:29:31.640 --> 0:29:33.920 is like an idea you guys take seriously, like maybe 0:29:34.040 --> 0:29:36.360 there is no dark matter, it's just dark bath. It's 0:29:36.360 --> 0:29:39.120 definitely an idea that physics should take seriously in the 0:29:39.160 --> 0:29:42.320 sense that we should think about alternatives. This one theory 0:29:42.320 --> 0:29:44.920 in particular doesn't have a lot of supporters, and we'll 0:29:44.920 --> 0:29:47.640 get into exactly why, but you know, it's an interesting 0:29:47.680 --> 0:29:52.000 idea and it says like maybe gravity works differently at 0:29:52.160 --> 0:29:55.640 very very large distances, like you know, we've tested gravity 0:29:55.680 --> 0:29:57.880 here on Earth. We know how it works. We've tested 0:29:57.880 --> 0:30:00.560 gravity in the Solar System pretty well. But you know, 0:30:00.640 --> 0:30:03.800 maybe the first time we're looking at gravity on galaxy scales, 0:30:03.880 --> 0:30:07.320 maybe gravity just works differently over like, you know, fifty 0:30:07.400 --> 0:30:10.840 thou light years, right, we haven't done that experiment before. 0:30:10.920 --> 0:30:13.640 Maybe it gets going, like, maybe it gets stronger in 0:30:13.960 --> 0:30:16.880 galaxy size scales. Yeah, And so the idea is actually 0:30:16.920 --> 0:30:20.560 even weirder than that. It says, maybe gravity works differently 0:30:21.280 --> 0:30:25.840 when you have a very very small acceleration, things are 0:30:25.880 --> 0:30:30.720 not being pulled very hard. Maybe gravity works a little 0:30:30.720 --> 0:30:32.600 bit different. Oh my god, you just blew my mind. 0:30:32.600 --> 0:30:35.560 All right, let's let's get into this crazy idea that 0:30:35.600 --> 0:30:39.040 gravity depends on how you're moving maybe, and whether or 0:30:39.080 --> 0:30:55.040 not that could work. But first let's take another quick break, right, Daniel, 0:30:55.080 --> 0:30:58.600 we're talking about dark math to maybe explain dark matter. 0:30:58.920 --> 0:31:01.880 And so there's an idea that maybe our formulation of 0:31:01.880 --> 0:31:04.400 gravity or how we think gravity works could be wrong. 0:31:04.440 --> 0:31:08.080 Maybe and it could maybe act very differently over larger scales, 0:31:08.120 --> 0:31:11.160 like maybe it gets stronger the galaxy scale or when 0:31:11.360 --> 0:31:14.240 you're telling me it's actually when there's lower accelerations. And 0:31:14.240 --> 0:31:16.200 this is just an idea again, right, this is just 0:31:16.240 --> 0:31:18.640 an idea. But hey, everything is just an idea, right, 0:31:18.680 --> 0:31:21.960 even lunch lunch is just an idea. Remember, Oh no, Daniel, 0:31:22.080 --> 0:31:25.080 lunch is very real to me. Well, the idea is, 0:31:25.240 --> 0:31:27.120 you know, somehow you have to get gravity to be 0:31:27.280 --> 0:31:30.840 stronger without breaking things we already know. So what if 0:31:30.960 --> 0:31:33.480 you know affecting things on the edge of the galaxy, 0:31:33.760 --> 0:31:35.920 you could have gravity instead of going like one over 0:31:36.000 --> 0:31:38.640 our squared, which you make it very very weak as 0:31:38.640 --> 0:31:40.760 our gets large, you can make it go like one 0:31:40.800 --> 0:31:43.760 over R. It doesn't fall off as quickly, doesn't get 0:31:43.800 --> 0:31:47.560 weak as quickly with large distances. Interesting, So like the 0:31:47.640 --> 0:31:50.880 gravity I feel with another planet on the other side 0:31:50.880 --> 0:31:54.400 of the Milky Way, maybe it's stronger than I think. Yeah, 0:31:54.480 --> 0:31:56.560 maybe it's not like one over our squares, more like 0:31:56.600 --> 0:31:59.240 one over R and R is still really really large. 0:31:59.360 --> 0:32:01.880 So you know, those planets don't affect you because the 0:32:01.960 --> 0:32:04.880 gravity from them is still really tiny. But if you're 0:32:04.880 --> 0:32:07.040 adding up lots of planets and you're trying to calculate, 0:32:07.040 --> 0:32:10.040 like how a whole galaxy spins, then it really does 0:32:10.120 --> 0:32:11.960 make a big difference to go like one of our 0:32:11.960 --> 0:32:15.360 are instead of one of are squared. But it seems 0:32:15.400 --> 0:32:18.720 a bit hacky as opposed to dark matter. Dark matter 0:32:18.760 --> 0:32:21.360 doesn't seem hacky. Well, dark matter, you know, you can 0:32:21.440 --> 0:32:24.640 explain a lot of really different things adding just one 0:32:24.760 --> 0:32:27.200 simple idea, like hey, what if there's a new particle 0:32:27.480 --> 0:32:29.800 that's not hacky, Like we don't know why there's a 0:32:29.800 --> 0:32:31.960 certain number of particles in the universe and not more, 0:32:32.120 --> 0:32:34.800 or if there are more, so adding one new particle 0:32:34.800 --> 0:32:37.600 doesn't feel as hacky. Is like let's have gravity have 0:32:37.640 --> 0:32:40.160 a knob on it, or like a distance above which 0:32:40.160 --> 0:32:44.000 it starts behaving different rules, or you know, small accelerations 0:32:44.040 --> 0:32:46.920 below which it starts behaving differently. Really, what why does 0:32:46.920 --> 0:32:49.320 it need to be low accelerations? How does that work? In? 0:32:49.720 --> 0:32:52.000 It doesn't really work as I think I heard you 0:32:52.040 --> 0:32:55.000 react because like the acceleration with respect to what right, 0:32:55.040 --> 0:32:57.600 all of a sudden, that gravity you feel depends on 0:32:57.680 --> 0:33:00.720 your reference frame, and it brings all sorts of symmetries. 0:33:00.960 --> 0:33:04.560 But there is that one idea that accelerations like one 0:33:04.560 --> 0:33:07.280 ten trillions of the gravity on Earth. If you feel 0:33:07.280 --> 0:33:10.080 an acceleration less than that, then the gravity on you 0:33:10.400 --> 0:33:14.160 behaves differently than it does for larger accelerations. Oh, I see. 0:33:14.240 --> 0:33:16.600 It's not you're not saying when you're going at a 0:33:16.680 --> 0:33:19.600 low acceleration, it's just you mean the when the effects 0:33:19.640 --> 0:33:21.760 of gravity are small, maybe it doesn't behave as one 0:33:21.800 --> 0:33:24.000 over our square. Yeah, and the effects of gravity at 0:33:24.120 --> 0:33:27.440 very very far distances are really small. Like what is 0:33:27.520 --> 0:33:30.280 the acceleration on some star at the edge of the 0:33:30.320 --> 0:33:33.560 galaxy due to the black hole the center of the galaxy. Well, 0:33:33.640 --> 0:33:36.600 the distance is fifty thou light years, so the acceleration 0:33:37.160 --> 0:33:40.560 is very small, also because the masses are large, and 0:33:40.600 --> 0:33:42.760 so it's just a way to say, let's have it 0:33:42.800 --> 0:33:46.000 have an effect where we see this weirdness and not 0:33:46.120 --> 0:33:48.400 have an effect anywhere else. Let's try not to break 0:33:48.760 --> 0:33:51.280 what we already know and understand and only have this 0:33:51.400 --> 0:33:54.560 theory turn on in special cases. All right, so that's 0:33:54.560 --> 0:33:56.880 a possibility. But where did this idea come from? Like 0:33:57.000 --> 0:33:59.200 why would we think that maybe gravity is wrong? So 0:33:59.280 --> 0:34:01.080 for a long time there wasn't really a good idea 0:34:01.120 --> 0:34:02.880 that was just like, well, I don't know, but if 0:34:02.920 --> 0:34:05.280 I put in this other formula, I can explain the 0:34:05.280 --> 0:34:09.120 galaxy rotation curves without dark matter. Without dark matter. Yeah, 0:34:09.120 --> 0:34:11.560 So like all right, so either there's missing masks or 0:34:11.600 --> 0:34:15.200 gravity works this other weird way, and then people started thinking, well, 0:34:15.239 --> 0:34:18.080 why would gravity work that way? Is there any reason 0:34:18.200 --> 0:34:20.680 for it? And that's a totally valid line of inquiry, right, 0:34:20.719 --> 0:34:22.760 like what theory do we have to have to explain 0:34:22.800 --> 0:34:25.319 the data? And does that theory make sense? Can we 0:34:25.320 --> 0:34:27.879 come up with a reason why? Maybe that theory is right? 0:34:28.320 --> 0:34:32.279 A theory about a theory underpinnings of the theory, right. 0:34:32.440 --> 0:34:35.240 We always in physics want to have a microscopic understanding. 0:34:35.239 --> 0:34:37.279 We don't want to just say gravity just has this 0:34:37.360 --> 0:34:39.120 number on it. We want to know why does it? 0:34:39.120 --> 0:34:41.399 Where does that come from? Why isn't it something else? 0:34:41.440 --> 0:34:43.239 Just like you were saying earlier, why is it one 0:34:43.280 --> 0:34:45.600 of our square not one over our two point one 0:34:45.719 --> 0:34:50.920 or whatever? That's the next version upgraded gravity. And so 0:34:51.040 --> 0:34:54.040 recently there is an idea from a guy in Holland 0:34:54.080 --> 0:34:57.480 to Eric Verlinda, and he has this crazy idea of 0:34:57.520 --> 0:35:01.440 gravity called entropic gravity that i'd be able to explain 0:35:02.000 --> 0:35:06.480 why gravity works differently at these distance scales. I feel 0:35:06.480 --> 0:35:08.719 like maybe he just grabbed two cool sounding things and 0:35:08.719 --> 0:35:14.000 put them together. Tropic answer like dynamic gravity or something. 0:35:14.040 --> 0:35:15.840 But it comes from a cool place. You know, it 0:35:15.880 --> 0:35:21.520 was Stephen Hawking who first connected sort of thermodynamics and gravity. 0:35:21.680 --> 0:35:25.400 He started thinking about the temperature of black holes and thinking, 0:35:25.760 --> 0:35:28.600 you know, if black holes have temperatures, that means they 0:35:28.600 --> 0:35:32.000 should radiate. Oh wait, and that's Hawking radiation. So in 0:35:32.000 --> 0:35:34.160 the last sort of forty years, people have been thinking 0:35:34.200 --> 0:35:37.359 about gravity and through our dynamics as a connection. They're 0:35:37.360 --> 0:35:40.839 trying to understand like, you know, actually, maybe gravity isn't 0:35:40.880 --> 0:35:44.879 a fundamental force, and maybe, you know Einstein's idea that 0:35:44.960 --> 0:35:48.680 gravity is just a curvature spacetime, maybe that's also wrong. 0:35:49.000 --> 0:35:54.080 Maybe instead, gravity is just like an emergent phenomena of thermodynamics. 0:35:54.600 --> 0:35:58.480 Maybe it's just like comes out of the manipulation and 0:35:58.560 --> 0:36:02.000 interaction of some tiny little bits of space in a 0:36:02.040 --> 0:36:05.560 way that feels like gravity to us. That's a little 0:36:05.560 --> 0:36:08.080 bit mind blowing. Yeah, it's a little bit mind blowing. 0:36:08.160 --> 0:36:11.000 This whole idea of emergent phenomena can be hard to 0:36:11.000 --> 0:36:13.239 get your mind around, but it's actually very familiar. You know, 0:36:13.320 --> 0:36:16.480 Like we can talk about wind, right, Wind is an 0:36:16.520 --> 0:36:19.440 emergent phenomena. It's not a fundamental force in the universe. 0:36:19.760 --> 0:36:23.239 You know, two particles interacting don't feel wind. Wind is 0:36:23.280 --> 0:36:25.960 a combination of lots of other things we do understand 0:36:26.000 --> 0:36:30.279 on a microscopical level that has a macroscopic effect, or 0:36:30.400 --> 0:36:33.680 like economics. You know, there are laws of economics that 0:36:33.760 --> 0:36:35.920 come from you know, supply and demand or whatever. It's 0:36:35.960 --> 0:36:38.440 not a fundamental force in the universe, but still you 0:36:38.440 --> 0:36:41.080 could have an understanding of it. And so they think 0:36:41.120 --> 0:36:45.880 maybe gravity is just like a macroscopic effect of something microscopic, 0:36:45.920 --> 0:36:49.840 maybe the thermodynamics of space time. Like there there is 0:36:49.880 --> 0:36:53.279 no gravity, it's just kind of like how space itself 0:36:53.400 --> 0:36:56.560 kind of arranges itself. Yeah, because we know that space 0:36:56.719 --> 0:37:00.640 likes to increase entropy, likes to increase disorder, and so 0:37:00.719 --> 0:37:03.440 we think entropy always increases in the universe, and so 0:37:03.520 --> 0:37:05.960 maybe gravity is just an effect of that. You know. 0:37:06.000 --> 0:37:08.560 The argument goes something like when things fall into a 0:37:08.600 --> 0:37:12.000 black hole, for example, that increases the entropy of the 0:37:12.040 --> 0:37:14.839 black hole, because otherwise it would violate the second law 0:37:14.880 --> 0:37:18.040 of thermodynamics. Things can't just disappear into the black hole. 0:37:18.520 --> 0:37:21.480 But maybe it's the opposite. Maybe it's not that gravity 0:37:21.520 --> 0:37:24.520 pulls things into the black hole and then increases the entropy. 0:37:24.640 --> 0:37:28.239 Maybe it's entropy that's pushing things into black holes, and 0:37:28.280 --> 0:37:31.239 that's actually what gravity is. That's just like you know, 0:37:31.280 --> 0:37:34.440 the way gas diffuses in a box. You put a 0:37:34.440 --> 0:37:36.480 blob of gas in the corner of a box and 0:37:36.520 --> 0:37:40.439 it spreads out into the box. That's entropy the same way. 0:37:40.480 --> 0:37:44.040 Maybe entropy is stuff falling into itself, like you know, 0:37:44.160 --> 0:37:48.400 having more stuff near itself dense blobs of mass increases 0:37:48.440 --> 0:37:51.839 the temperature, which changes the entropy of the situation. I mean, 0:37:51.920 --> 0:37:55.760 it's a complicated argument involving like quantum entangled space time, 0:37:55.800 --> 0:37:57.799 but I think that's the gist of it, and all 0:37:57.840 --> 0:38:00.680 of that kind of crazy idea is just explain how 0:38:00.800 --> 0:38:03.760 maybe gravity could not be one over our square. Yeah, 0:38:03.800 --> 0:38:06.560 if you have in tropic gravity, so maybe if gravity 0:38:06.719 --> 0:38:09.319 is not a fundamental force in the universe but just 0:38:09.400 --> 0:38:13.000 like an emergent property of quantum space time, and you 0:38:13.040 --> 0:38:17.520 have dark energy, then Virlindis theory predicts that space curs 0:38:17.560 --> 0:38:20.800 in this way, that gravity, the effective force of gravity, 0:38:21.120 --> 0:38:24.480 goes the way mind needs it to explain the galactic 0:38:24.560 --> 0:38:28.279 rotation curves. So that's kind of cool thing. That's an 0:38:28.320 --> 0:38:31.239 alternative to dark matter. Is one alternative to dark matter 0:38:31.320 --> 0:38:35.920 to say we have this weird gravitational thermodynamics idea that 0:38:36.000 --> 0:38:39.239 changes the way gravity works. That explains why we thought 0:38:39.320 --> 0:38:42.200 that was missing stuff. Instead, it's just the gravity works 0:38:42.200 --> 0:38:44.759 differently than we expect it. Interesting alright, So then I 0:38:44.760 --> 0:38:47.719 guess the big question is could that work? Is that 0:38:47.840 --> 0:38:52.560 a valid or plausible theory that maybe explains gravity in 0:38:52.560 --> 0:38:56.040 a different way that then explains dark matter and and 0:38:56.200 --> 0:38:59.080 so that it's not just another particle or kind of stuff. 0:38:59.440 --> 0:39:02.040 Could that war? Well, it's a cool idea, and it 0:39:02.080 --> 0:39:06.320 does explain galaxy rotation curves, and it actually explains galaxy 0:39:06.440 --> 0:39:10.399 rotation curves better than dark matter. There's some galaxies out 0:39:10.400 --> 0:39:12.640 there that we still can't explain using dark matter, Like 0:39:12.760 --> 0:39:15.120 they rotate in weird ways and we don't understand it. 0:39:15.160 --> 0:39:20.719 And you know, but hey, galaxies are weird. They they 0:39:20.719 --> 0:39:26.480 have their own history. No prize, sir. My theory, that's right, 0:39:26.600 --> 0:39:29.240 My theory that the universe is just weird explains everything, 0:39:29.320 --> 0:39:32.880 oh man, the whites and theory of everything, the whites 0:39:32.880 --> 0:39:36.400 and theory of weirdness. But it explains the gaxy rotation 0:39:36.440 --> 0:39:40.120 curves really nicely. But there's a big caveat there, which 0:39:40.120 --> 0:39:43.720 is it was sort of invented to explain those curves, 0:39:43.800 --> 0:39:47.840 like you came up with a theory to fit that data. Really, 0:39:47.960 --> 0:39:50.480 a good test of a theory is does it explain 0:39:50.640 --> 0:39:54.440 other data? Is that a real general principle about the universe, 0:39:54.480 --> 0:39:57.000 something which is really deeply true? Or is it just 0:39:57.080 --> 0:39:59.879 a mathematical tweak to this one plot, this one fig 0:40:00.120 --> 0:40:02.160 or to make. Because if it only works to explain 0:40:02.239 --> 0:40:04.840 one thing, it's it's kind of suspicious, right exactly, And 0:40:04.880 --> 0:40:07.440 if it only works to explain the one thing that 0:40:07.520 --> 0:40:10.160 motivated it, and then probably it's not a deep truth 0:40:10.280 --> 0:40:14.440 of the universe, right a right, So maybe it doesn't work. 0:40:14.680 --> 0:40:16.440 Can it explain some of the other things that we 0:40:16.480 --> 0:40:19.880 know about dark matter, like the lensing and the cosmic 0:40:20.040 --> 0:40:24.200 microwave background and the structure of the universe? A tweak 0:40:24.239 --> 0:40:26.800 to our theory of gravity also explain all of these things? 0:40:26.880 --> 0:40:31.040 In a word, No, it just doesn't work. No, galax 0:40:31.080 --> 0:40:33.360 is are just weird. No galax is just weird. No, 0:40:33.480 --> 0:40:36.160 it does not explain the cosmic microwave background, Like, it's 0:40:36.360 --> 0:40:40.520 very difficult to explain that using anything else other than 0:40:40.840 --> 0:40:43.920 some new kind of particle or promodial black hole or 0:40:43.960 --> 0:40:47.080 something some new kind of stuff. You just can't explain 0:40:47.160 --> 0:40:49.160 it using deviation and gravity because it was on a 0:40:49.200 --> 0:40:51.759 really small scale. This is like, you know, things were 0:40:51.840 --> 0:40:55.799 near by each other. This wasn't galactic distances interesting, And 0:40:55.840 --> 0:40:58.360 it's very difficult to explain the structure of the universe. 0:40:58.520 --> 0:41:01.080 And then there is one really awesome example of dark 0:41:01.120 --> 0:41:03.799 matter that's sort of like a smoking gun that makes 0:41:03.800 --> 0:41:07.319 it almost impossible to explain using anything but some new 0:41:07.400 --> 0:41:10.040 kind of matter stuff, some new kind of stuff. Yeah, 0:41:10.280 --> 0:41:14.200 and that's this Bullet cluster. There was this collision millions 0:41:14.200 --> 0:41:17.399 and millions of years ago, far far away between two 0:41:17.480 --> 0:41:20.560 clusters of galaxy that passed through each other. And we 0:41:20.600 --> 0:41:23.479 thought that those clusters of galaxies they had normal matter 0:41:23.640 --> 0:41:26.480 like stars and planets, etcetera, and then also clumps of 0:41:26.560 --> 0:41:29.799 dark matter. So what happened is they passed through each other, 0:41:30.320 --> 0:41:33.280 and the gas and the dust it all collided amid 0:41:33.320 --> 0:41:36.000 big collisions and slowed down and all that stuff. But 0:41:36.080 --> 0:41:38.479 the dark matter, it doesn't interact with the normal matter, 0:41:38.480 --> 0:41:40.520 and it doesn't interact with itself very much at all 0:41:40.600 --> 0:41:43.479 either because gravity is so weak, so the dark matter 0:41:43.520 --> 0:41:45.920 is sort of passed through. So what we see when 0:41:45.920 --> 0:41:47.560 we look up in the skies, we see like a 0:41:47.600 --> 0:41:50.880 big blob in the center while the gas and dust interacted, 0:41:51.120 --> 0:41:53.799 and then on either side we see the dark matter 0:41:53.840 --> 0:41:56.239 that passed through, and we can see that because of 0:41:56.280 --> 0:41:58.640 the gravitational lensing. Right, But doesn't it all I know, 0:41:58.719 --> 0:42:00.960 we talked about the bullet cluster it before, but doesn't 0:42:01.000 --> 0:42:05.279 it still just come down to gravitational lensing, Like what 0:42:05.400 --> 0:42:09.160 if gravity can explain gravitational lensing, could that also explain 0:42:09.600 --> 0:42:12.200 the bullet cluster that we see. It's very difficult to 0:42:12.239 --> 0:42:14.120 explain the bullet cluster in any other way because you 0:42:14.160 --> 0:42:17.360 need to have gravitational lensing in exactly those right spots 0:42:17.640 --> 0:42:21.920 on opposite sides of this very obvious collision. So it's 0:42:21.920 --> 0:42:24.640 a very nice explanation to think, oh, there's some invisible 0:42:24.640 --> 0:42:27.799 matter that passed through and it's now sitting there distorting 0:42:27.800 --> 0:42:30.720 the background galaxy. See, the bullet cluster is like proved 0:42:30.760 --> 0:42:34.920 that whatever it's causing these gravitational things is mobile, like 0:42:35.120 --> 0:42:37.839 it can move like stuff. But if it was just 0:42:37.880 --> 0:42:41.719 a gravitational theory tweak, that wouldn't like keep going or 0:42:41.800 --> 0:42:44.319 move or change from here to there exactly, and it 0:42:44.360 --> 0:42:46.920 can be separated from the normal matter. It's not just 0:42:47.000 --> 0:42:49.760 a gravitational tweak from the normal matter, right, the normal 0:42:49.760 --> 0:42:52.760 matter was left behind in the middle. It's its own 0:42:52.880 --> 0:42:55.799 kind of stuff. It has its own gravity. And so 0:42:55.880 --> 0:42:58.279 that's sort of like a bullet in the brain of 0:42:58.320 --> 0:43:01.720 the you know, non dark matter theories. The bullet cluster 0:43:01.840 --> 0:43:05.880 is a bullet suspicious. People really took Moms sort of 0:43:05.960 --> 0:43:09.240 seriously until then. And then when the bullet cluster was discovered, 0:43:09.280 --> 0:43:12.200 people are like, oh, well, that's it. Dark matter is real, 0:43:12.640 --> 0:43:16.640 and Mond is dead and never Mond. And at that 0:43:16.680 --> 0:43:20.040 point people really didn't take months seriously. So since then, 0:43:20.480 --> 0:43:23.399 Mond has been much more of a fringe theory. I mean, 0:43:23.680 --> 0:43:26.160 Virlin's idea is more recent, and it's quote of cool, 0:43:26.480 --> 0:43:28.960 but it sort of explains something that nobody really takes 0:43:29.000 --> 0:43:32.239 seriously anymore. So it's very fringe in a way. The 0:43:32.280 --> 0:43:35.359 bullet cluster shows you that dark matter or whatever it's 0:43:35.400 --> 0:43:39.640 causing these gravitational distortions and footprints, is mobile like it's 0:43:39.760 --> 0:43:41.880 it can move like stuff. It moves like a stuff 0:43:41.920 --> 0:43:45.880 can move. Yeah, And so again it's unsatisfying because we 0:43:45.920 --> 0:43:48.360 don't know what it is and and we've been looking 0:43:48.360 --> 0:43:50.480 for for a while it's not like we're just like, oh, 0:43:50.520 --> 0:43:54.320 it's some invisible stuff, let's move on. We've built dedicated 0:43:54.360 --> 0:43:57.239 experiments to look for it. We thought several times that 0:43:57.360 --> 0:43:59.839 we would definitely find it and then haven't seen it. 0:44:00.200 --> 0:44:02.359 So there's definitely some tension there. It's not like dark 0:44:02.400 --> 0:44:04.839 matter is a beautiful theory that's all wrapped up, like 0:44:05.160 --> 0:44:08.120 we don't understand why we haven't been able to find 0:44:08.160 --> 0:44:11.680 the dark matter yet. There's definitely something weird going on there, 0:44:11.840 --> 0:44:14.279 and it's very healthy to think about new ideas, but 0:44:14.480 --> 0:44:18.000 mond doesn't quite work. There is no other idea out 0:44:18.080 --> 0:44:21.440 there that explains what we see nearly as well as 0:44:21.520 --> 0:44:24.480 some new cold particles. I have an idea is it's 0:44:24.480 --> 0:44:27.840 snack based. It's called Hey, maybe dark matter is weird. 0:44:29.880 --> 0:44:32.640 It's weird, yeah, And that's why people are sort of 0:44:32.680 --> 0:44:35.200 digging further and further into the barrel of ideas for 0:44:35.280 --> 0:44:37.520 dark matter. People thought for a long time, Okay, dark 0:44:37.560 --> 0:44:41.319 matter must just be some weakly interacting massive particle, some 0:44:41.400 --> 0:44:44.360 new lava stuff, but we haven't seen it, and so 0:44:44.400 --> 0:44:47.000 then people are well, maybe it's axions, or maybe it's 0:44:47.080 --> 0:44:49.919 primordial black holes, or and there are some other even 0:44:50.080 --> 0:44:55.440 crazier ideas like squirmyons, what like they're uncomfortable and social situations. 0:44:55.520 --> 0:45:00.239 What do you mean introvertons? Yeah, no, squirmy on are 0:45:00.280 --> 0:45:03.279 this crazy idea that you know how particles are like 0:45:03.440 --> 0:45:06.800 excitations of quantum fields are like little bundles of energy 0:45:06.800 --> 0:45:09.960 in a quantum field. People think, well, maybe not all 0:45:10.120 --> 0:45:12.480 energy and quantum fields are particles. Maybe some of them 0:45:12.520 --> 0:45:15.760 are like more distributed or spread out in weird ways. 0:45:15.760 --> 0:45:18.640 And they found that you can like tangle up quantum 0:45:18.680 --> 0:45:21.520 fields in these weird ways, like make nots of them, 0:45:21.800 --> 0:45:24.439 and that's what they call squirmyons. And it's not could 0:45:24.480 --> 0:45:27.880 like it could create gravity. Yeah, because any energy density 0:45:27.920 --> 0:45:32.040 creates gravity. Well, we'll have to dig into that for 0:45:32.120 --> 0:45:36.680 another episode. Sounds pretty for sure. So there's lots of 0:45:36.680 --> 0:45:38.799 ideas the whole spectrum, right, dark matter is not just 0:45:38.960 --> 0:45:42.799 one idea, the sort of spectrum of ideas all satisfied 0:45:42.840 --> 0:45:45.920 the condition that it's some new kind of cold object. 0:45:46.400 --> 0:45:48.680 But what that object is. It could be one particle, 0:45:48.719 --> 0:45:51.880 could be many kinds of particles. It could be black holes, 0:45:51.960 --> 0:45:54.279 it could be squirmyons, it could be something else we 0:45:54.320 --> 0:45:57.240 haven't even thought of yet. Whatever, it is. We're pretty 0:45:57.280 --> 0:46:00.160 sure it's stuff. It's something that has gravity stuff when 0:46:00.160 --> 0:46:02.400 it's there, that's right. But I mean it's really interesting 0:46:02.440 --> 0:46:04.440 because I feel like we've known dark matters is there 0:46:04.480 --> 0:46:06.279 for a while now, and we just can't seem to 0:46:06.280 --> 0:46:08.200 crack it. We can't seem to find it keeps um 0:46:08.200 --> 0:46:11.160 eluding us, you know, like it just keeps on hiding 0:46:11.200 --> 0:46:13.799 there and not letting us know what it is. That's right, 0:46:13.840 --> 0:46:15.440 But we don't know how long the story is. You know, 0:46:15.480 --> 0:46:17.880 we were looking for the Higgs boson for fifty years 0:46:18.000 --> 0:46:20.319 and then we found it. We were looking for the 0:46:20.360 --> 0:46:23.040 top cork for twenty years before we found it. A 0:46:23.040 --> 0:46:25.000 lot of those things. People thought, oh, we'll find this 0:46:25.040 --> 0:46:27.400 in the next year two and then they were confused 0:46:27.400 --> 0:46:29.680 and disappointed to not discover it soon. But you know, 0:46:29.760 --> 0:46:32.239 eventually we got there and we we figured it out. 0:46:32.280 --> 0:46:35.359 So maybe we're just five years away from discovering dark matter, 0:46:35.440 --> 0:46:37.400 or maybe it's going to be another hundred. Maybe we 0:46:37.440 --> 0:46:40.000 need a new crazy idea for what dark matter is. 0:46:40.040 --> 0:46:43.359 But dark matter, I'm pretty sure is so all those 0:46:43.400 --> 0:46:47.800 physicists squirming around relax. Maybe dark matter is in our future. 0:46:47.880 --> 0:46:50.239 That's right. I certainly hope it is. It would be fascinating. 0:46:50.280 --> 0:46:52.879 And remember that it's most of the stuff out there 0:46:52.880 --> 0:46:56.319 in the universe. Like, what a crazy opportunity to learn 0:46:56.360 --> 0:46:59.040 about the way the universe works, you know, to know 0:46:59.120 --> 0:47:01.359 that of the stuff out there in the universe has 0:47:01.400 --> 0:47:03.840 been hidden from us. The day we crack that open 0:47:03.920 --> 0:47:05.759 and get to learn about it, like, it could have 0:47:05.800 --> 0:47:09.719 incredibly complex structure, it could have interactions and biology and 0:47:09.800 --> 0:47:12.600 chemistry and all sorts of crazy stuff. Movest of the 0:47:12.600 --> 0:47:14.960 stuff out there in the universe we haven't yet gotten 0:47:14.960 --> 0:47:17.640 to play with, and so we're eager, we're desperate to 0:47:17.680 --> 0:47:19.600 figure out what this stuff is. Yeah, because if you're 0:47:19.600 --> 0:47:22.200 the scientist that discovers what dark matter is, I mean, 0:47:22.320 --> 0:47:25.399 that's like a lot of three cred you know. It's 0:47:25.440 --> 0:47:29.360 like you could say that you discovered eight eight percent 0:47:29.440 --> 0:47:31.440 of everything in the universe. I think they would have 0:47:31.480 --> 0:47:33.719 to give you five Nobel Prizes, you know, just for 0:47:33.719 --> 0:47:35.840 that one discovery. They have to give you eighty percent 0:47:35.880 --> 0:47:38.600 of all the Nobel prizes. I think, Yeah, yeah, there 0:47:38.600 --> 0:47:40.719 you go. You get all the Nobel Prizes for the 0:47:40.719 --> 0:47:43.560 next four hundred years, just to balance it out. Yeah, 0:47:43.640 --> 0:47:45.560 So it's a big question, and who knows, maybe one 0:47:45.600 --> 0:47:48.279 of our listeners will be the one who discovers it. 0:47:48.360 --> 0:47:49.879 That's right, It could be you out there, it could 0:47:49.880 --> 0:47:51.960 be your kids out there. What we definitely need to 0:47:51.960 --> 0:47:53.759 do or keep our minds open and come up with 0:47:53.800 --> 0:47:57.000 new ideas for what dark matter is really cool? All right, Well, 0:47:57.320 --> 0:48:00.440 we hope you enjoyed that view into this story is 0:48:00.520 --> 0:48:02.520 dark matter and how we know it's there and how 0:48:02.680 --> 0:48:06.640 we know it's not just a weird fluke of gravitational equations. 0:48:06.800 --> 0:48:17.200 Thanks for tuning in, See you next time. Thanks for listening, 0:48:17.280 --> 0:48:20.000 and remember that Daniel and Jorge Explain the Universe is 0:48:20.000 --> 0:48:23.440 a production of I Heart Radio. For more podcast For 0:48:23.520 --> 0:48:27.279 my heart Radio, visit the i heart Radio app, Apple Podcasts, 0:48:27.400 --> 0:48:29.760 or wherever you listen to your favorite shows.