WEBVTT - What is dark radiation? 0:00:08.600 --> 0:00:10.720 Hey, Daniel, how do you like your coffee? Oh? I 0:00:10.800 --> 0:00:15.000 like it very dark, basically black. What about your chocolate? 0:00:15.440 --> 0:00:20.320 Also pretty dark? Maybe? Like? What about your wine? How 0:00:20.360 --> 0:00:22.640 do you drink your wine? Well? I like a pretty 0:00:22.720 --> 0:00:25.959 dark cabernet. Actually, now, are you optimistic about the fate 0:00:26.000 --> 0:00:28.480 of humanity? You know, I'll be honest until we start 0:00:28.520 --> 0:00:31.480 dismantling more nuclear weapons. I have a pretty dark view 0:00:31.520 --> 0:00:36.120 of our future. You kind of a dark physicist. Maybe 0:00:36.120 --> 0:00:38.760 you should lighten up a little, you know, try some dessert, wine, 0:00:38.800 --> 0:00:42.440 some rose, maybe maybe even some white chocolate. No, no, no, man, 0:00:42.520 --> 0:00:45.760 we live in a dark universe where dominated by dark matter, 0:00:45.920 --> 0:00:49.800 dark energy, and dark chocolate. You know what Yoda says, 0:00:50.200 --> 0:00:53.599 once you go into the dark side, forever your destiny 0:00:54.040 --> 0:00:59.160 well dominate. Do you think Yoda like dark chocolate? I 0:00:59.200 --> 0:01:18.120 always knew you were a dark fisicist. Daniel. Hi am 0:01:18.120 --> 0:01:21.120 poor handmade cartoonists and the creator of PhD comics. Hi, 0:01:21.280 --> 0:01:24.840 I'm Daniel. I'm a particle physicist and a professor UC Irvine. 0:01:25.000 --> 0:01:28.160 And white chocolate is not chocolate. It is chocolate. Then 0:01:28.200 --> 0:01:31.320 it's made from chocolate, made from chocolate, not the same 0:01:31.360 --> 0:01:35.800 as chocolate. You just don't like it. You still want 0:01:35.800 --> 0:01:38.680 to categorize this chocolate, But scientifically, I think if you 0:01:38.800 --> 0:01:41.399 asked a you know, chemist, they would say it's a 0:01:41.480 --> 0:01:43.880 it's chocolate. I don't know. I think it doesn't have 0:01:43.920 --> 0:01:47.160 any cocoa in it. It can't be chocolate. Doesn't taste 0:01:47.200 --> 0:01:49.680 like chocolate. You know, white chocolate is chocolate the same 0:01:49.720 --> 0:01:52.200 way deep dish pizza is pizza. But you do know 0:01:52.240 --> 0:01:54.320 it's made from chocolate, right, Like I think it uses 0:01:54.360 --> 0:01:57.560 like the cocoa butter from chocolate beans. Yeah, it's sort 0:01:57.560 --> 0:02:00.280 of like hangs around when chocolate is made, sort calls 0:02:00.320 --> 0:02:05.480 itself chocolate nearby it's chocolate and I'll give it that much. 0:02:05.600 --> 0:02:07.640 Oh man, how can it be a jacent if it 0:02:07.680 --> 0:02:10.040 comes from chocolated Daniel, I think you're stretching things a 0:02:10.080 --> 0:02:13.200 little bit here. My kids are coming from chocolate, but 0:02:13.240 --> 0:02:16.720 they're not chocolate, right. You should be more candy inclusive, Tenny, 0:02:17.960 --> 0:02:20.440 white chocolate is delicious. It's just not chocolate. But welcome 0:02:20.440 --> 0:02:23.239 to our podcast. Daniel and jorhead the Bait Chocolate apparently 0:02:23.360 --> 0:02:26.240 for an hour instead of talking about physics and explain 0:02:26.320 --> 0:02:29.320 the universe, in which we explore all the questions out there, 0:02:29.360 --> 0:02:32.160 the dark ones, the white ones, the milky ones, all 0:02:32.200 --> 0:02:34.840 the questions of the universe that are rattling around in 0:02:34.960 --> 0:02:38.880 your brain and in hours, the questions that make us human, 0:02:38.960 --> 0:02:41.960 the questions that make us wonder why the universe is 0:02:42.040 --> 0:02:44.240 this way and not some other way? Could it have 0:02:44.320 --> 0:02:46.200 been this way? Did it have to turn out in 0:02:46.200 --> 0:02:49.240 this particular manner? What are the rules of this universe? 0:02:49.280 --> 0:02:51.760 And is it possible for them to make sense to us? 0:02:51.840 --> 0:02:54.160 And is it possible for Daniel and Jorge to explain 0:02:54.200 --> 0:02:57.800 them to you in less than an hour while eating chocolates? Apparently, 0:02:57.919 --> 0:03:00.600 but only dark or milk? What about chocolate? Are you 0:03:00.639 --> 0:03:03.160 a fan of milk chocolate? Milk chocolate is chocolate. But 0:03:03.320 --> 0:03:07.359 I'm not a fan, I see, And there are different 0:03:07.360 --> 0:03:09.840 categories here of exclusion for you. Oh yeah, I got 0:03:09.880 --> 0:03:12.160 a whole matrix going here. But it is an amazing 0:03:12.160 --> 0:03:15.480 and beautiful and sometimes even delicious universe, full of amazing 0:03:15.520 --> 0:03:19.359 mysteries and tantalizing questions to answer and discover out there, 0:03:19.480 --> 0:03:21.720 and fortunately humans are here for all of it, to 0:03:21.760 --> 0:03:25.320 answer these questions and to wonder about the amazing things 0:03:25.400 --> 0:03:27.200 that are out there. That's right, and one of the 0:03:27.200 --> 0:03:30.240 most basic questions we ask about the universe is just 0:03:30.600 --> 0:03:33.760 what's in it? What's out there in the universe sharing 0:03:33.840 --> 0:03:36.200 this cosmos with us. There's this sense that if you 0:03:36.200 --> 0:03:38.880 could like make an accounting of all the stuff, all 0:03:38.960 --> 0:03:41.040 the forces in the matter, and all the particles in 0:03:41.040 --> 0:03:44.560 the universe, you'd get a sense for why the universe 0:03:44.760 --> 0:03:47.480 is the way that it is the way. For example, 0:03:47.480 --> 0:03:49.640 if you'd like looked at the ingredients of a pizza, 0:03:49.880 --> 0:03:51.480 you can get a sense for, like what makes a 0:03:51.520 --> 0:03:54.440 pizza a pizza. Yeah, because for thousands of years, we 0:03:54.480 --> 0:03:56.640 thought that, you know, the stuff that we were made 0:03:56.640 --> 0:03:59.360 out of was all there was too stuff, you know, 0:03:59.440 --> 0:04:02.360 the electron and corks and protons and neutrons that we're 0:04:02.400 --> 0:04:04.000 made out of. We thought that was the whole thing 0:04:04.080 --> 0:04:06.400 that was in the universe. But actually it turns out 0:04:06.400 --> 0:04:09.280 that most of the universe is made out of something else, 0:04:09.600 --> 0:04:13.200 something dark and mysterious. Yes, And the history of physics 0:04:13.320 --> 0:04:16.200 is these waves of realization, discovering that we are not 0:04:16.320 --> 0:04:18.320 at the center of the universe, we are not at 0:04:18.360 --> 0:04:20.400 the center of the Solar system, we are not really 0:04:20.400 --> 0:04:22.960 at the center of anything, and then discovering that our 0:04:23.080 --> 0:04:25.599 kind of matter is not even that special that we 0:04:25.680 --> 0:04:29.840 make up a tiny little fraction of this incredible universe pizza. 0:04:29.880 --> 0:04:32.880 Oh boy, Daniel, are you saying we are universe at Jason. 0:04:32.960 --> 0:04:34.680 We're not really part of the universe. We're not really 0:04:34.839 --> 0:04:39.320 universe material. We're sort of dark matter adjacent, right, We're 0:04:39.360 --> 0:04:42.760 around when the dark matter formed all this structure. We 0:04:42.880 --> 0:04:45.680 sort of like we're followers, but we're not dark matter. Yeah. 0:04:46.160 --> 0:04:48.400 Do you think there's some snob courmet I don't know, 0:04:48.640 --> 0:04:52.080 universe eater out there judging us talking down about the 0:04:52.160 --> 0:04:55.680 humanity and all the stars and planets and galaxies in 0:04:55.720 --> 0:04:58.640 the universe, saying that's not really universe. Yeah, I hope. So, 0:04:58.680 --> 0:05:00.440 I hope that there are some dark a adans out 0:05:00.440 --> 0:05:03.599 there made of dark matter, with their incredibly dark dark 0:05:03.680 --> 0:05:05.719 chocolate made of dark matter, and they're looking at our 0:05:05.800 --> 0:05:09.880 dark chocolate. They're like, that's ridiculous. Well, I guess the 0:05:09.880 --> 0:05:12.000 good news is they they're not gonna eat us, because 0:05:12.000 --> 0:05:16.040 if they're there's nobby about it, like you are white chocolate. 0:05:16.160 --> 0:05:18.279 That's good news for the white chocolate. Yeah. Here ago 0:05:18.400 --> 0:05:21.279 you can turn anything into positive news. I appreciate that. Yeah, 0:05:21.279 --> 0:05:23.080 but there is a lot of dark matter in the universe. 0:05:23.120 --> 0:05:25.120 In fact, it's most of the stuff in the universe 0:05:25.360 --> 0:05:27.760 is dark matter. Of the stuff in the universe. I mean, 0:05:27.839 --> 0:05:30.240 that's right. Even though we can't see it directly, we 0:05:30.279 --> 0:05:32.560 can tell that dark matter is there, that it's a 0:05:32.640 --> 0:05:35.480 thing that is affecting the whole shape of the universe. 0:05:35.520 --> 0:05:38.400 It affected their universe early on and its little wiggles 0:05:38.400 --> 0:05:41.600 and jiggles. It affected the formation of structure in the universe. 0:05:41.640 --> 0:05:44.920 It even shapes how galaxies spin today. So we know 0:05:45.040 --> 0:05:46.880 that it's there, we know that it's out there, and 0:05:46.920 --> 0:05:49.360 we know that it dominates the universe in terms of 0:05:49.400 --> 0:05:52.520 like the budget of the universe is mostly dark matter, 0:05:52.839 --> 0:05:56.240 not what we used to call normal matter. I e us. Yeah, 0:05:56.240 --> 0:05:58.920 it's something like, what's the exact budget percentage of dark 0:05:58.920 --> 0:06:00.920 matter in the universe compared to the regular stuff we're 0:06:00.920 --> 0:06:03.640 made out of. It's about five to one dark matter 0:06:03.720 --> 0:06:06.080 to normal matter, all right, So then that's like eight 0:06:06.200 --> 0:06:09.120 percent of the universe is sort of dark matter. Yeah, 0:06:09.160 --> 0:06:12.000 eighty percent of the universe. So you could almost neglect 0:06:12.279 --> 0:06:13.920 our part of the universe and you still got to 0:06:14.040 --> 0:06:20.799 be on your exam Befo, bueno, that's right, bueno. Barry 0:06:20.880 --> 0:06:23.279 on is exactly. Yeah, you could ignore all the atoms 0:06:23.279 --> 0:06:25.880 in the universe and that would only be five percent 0:06:26.000 --> 0:06:28.520 of the energy in the universe or twenty percent of 0:06:28.560 --> 0:06:30.840 the matter in the universe. So in some sense, the 0:06:30.920 --> 0:06:33.800 question what is the universe made out of? What is 0:06:33.839 --> 0:06:36.800 all this crazy stuff? Tells you that what we're made 0:06:36.800 --> 0:06:38.279 out of is not a big part of it is 0:06:38.320 --> 0:06:41.839 not a central element in the structure of the universe. Right, 0:06:41.920 --> 0:06:44.920 And just to clarify, most of this stuff and energy 0:06:44.920 --> 0:06:48.040 in the universe is dark energy, which is something totally different. 0:06:48.240 --> 0:06:50.520 But if we're just talking about stuff like matter, things 0:06:50.520 --> 0:06:53.880 that feel gravity, then most of it is dark matter. 0:06:54.080 --> 0:06:56.840 That's right. The matter portion of the universe is about 0:06:57.640 --> 0:07:02.719 and of that thirty percent, eight percent that is dark matter. 0:07:03.080 --> 0:07:06.039 So if the matter portion of the universe it is 0:07:06.120 --> 0:07:08.560 dark matter, well that's pretty amazing. It's almost like most 0:07:08.600 --> 0:07:10.520 of the stuff in the universe is this other stuff 0:07:10.640 --> 0:07:13.600 called dark matter, but we don't know actually what it is, right, 0:07:13.600 --> 0:07:16.120 It's pretty mysterious. We've only know it's there, we haven't 0:07:16.160 --> 0:07:19.320 actually seen it directly because it's dark. Yeah, but it's 0:07:19.320 --> 0:07:22.280 a great story. You know. I got into physics for 0:07:22.360 --> 0:07:26.160 exactly these kinds of realizations, discovering that the universe out 0:07:26.160 --> 0:07:28.040 there is not the one that you thought it was, 0:07:28.160 --> 0:07:31.160 or that scientists and deep thinkers for thousands of years 0:07:31.360 --> 0:07:34.400 hadn't known the true picture of the universe. You know. 0:07:34.480 --> 0:07:38.080 Physics is this incredible technique to like reveal the truth 0:07:38.200 --> 0:07:42.240 about the universe, to methodically build up knowledge and tell 0:07:42.320 --> 0:07:44.920 us what's actually out there. So for it to discover 0:07:45.080 --> 0:07:48.440 something shocking, like an enormous plot twist, like wow, it 0:07:48.560 --> 0:07:50.560 turns out most of the stuff in the universe out 0:07:50.560 --> 0:07:52.960 there is something you never heard about or thought about 0:07:53.040 --> 0:07:56.320 or felt before. That's fantastic and it's exactly the kind 0:07:56.360 --> 0:07:58.720 of thing that I hope happens, you know, again and again, 0:07:58.880 --> 0:08:01.680 overturning everything we thought we knew about the universe. Yeah, 0:08:01.760 --> 0:08:04.440 we know you went into physics for dark reasons. Daniels 0:08:06.640 --> 0:08:09.160 that it's pretty close to home, given that a group 0:08:09.160 --> 0:08:11.680 in Los Almos where they invented nuclear weapons which are 0:08:11.680 --> 0:08:15.880 now being used to threaten genocide against civilian populations. So yeah, 0:08:15.880 --> 0:08:17.840 that one stings a little bit, but it might say 0:08:17.960 --> 0:08:20.560 humanity even if the media ever comes towards Earth and 0:08:20.680 --> 0:08:23.000 we you know, break it up with nuclear weapons, then 0:08:23.040 --> 0:08:25.880 then your parents would be heroes. There you go. All right, 0:08:25.960 --> 0:08:28.800 So in some scenario we are saving the Earth instead 0:08:28.800 --> 0:08:31.400 of destroying it. You know, you apply the quantum physics principle. 0:08:31.520 --> 0:08:35.079 You know, it's all true. It's just the different probabilities. 0:08:35.160 --> 0:08:38.680 There's a little white chocolate lining to that dark chocolate cloud. 0:08:38.960 --> 0:08:42.720 Oh no, that ruins it for you though. It doesn't 0:08:42.720 --> 0:08:44.960 taste as good, but it goes down easier. Yeah. Yeah, 0:08:44.960 --> 0:08:46.719 So most of the stuff in the universe is made 0:08:46.720 --> 0:08:48.400 out of dark matter, and so it kind of makes 0:08:48.400 --> 0:08:51.680 you wonder if that's all that's dark in the universe. 0:08:51.720 --> 0:08:54.280 Could there be other things in the universe that we're 0:08:54.320 --> 0:08:57.160 not seeing or that we can't see. And it's certainly 0:08:57.200 --> 0:08:59.800 true that most of the universe are things that you 0:09:00.080 --> 0:09:02.680 cannot see directly. If you look out in front of you, 0:09:02.880 --> 0:09:05.359 the information that's coming to you is just from photons, 0:09:05.360 --> 0:09:09.000 and photons can only interact with things that have electric charges. 0:09:09.400 --> 0:09:12.360 For example, there are particles flying right in front of 0:09:12.360 --> 0:09:15.760 you right now that you cannot see. Billions of neutrinos 0:09:15.800 --> 0:09:19.280 coming from the Sun raining down constantly in every square 0:09:19.320 --> 0:09:22.120 centimeter per second, but they are invisible to you. So 0:09:22.160 --> 0:09:25.800 the true universe out there. The actual reality of the 0:09:25.920 --> 0:09:29.400 universe outside your skull is vastly different from the tiny 0:09:29.520 --> 0:09:31.840 slice of it that you can see. Yeah, because if 0:09:31.840 --> 0:09:34.920 we can't see of the stuff in the universe, it 0:09:35.080 --> 0:09:37.280 kind of makes me wonder what else it's doing or 0:09:37.320 --> 0:09:40.640 what else it can do, like is it maybe radiating 0:09:40.880 --> 0:09:44.840 dark forces or dark light? Exactly? Because our kind of 0:09:44.880 --> 0:09:47.560 matter does all sorts of complicated things. It doesn't just 0:09:47.760 --> 0:09:50.360 sit there right. It shoots off photons at each other. 0:09:50.360 --> 0:09:53.440 It has electromagnetic forces and strong forces and weak forces, 0:09:53.440 --> 0:09:56.680 and forms complicated things like ice cream and pizza and chocolate, 0:09:56.720 --> 0:09:58.960 and so a natural question is what's going on with 0:09:59.000 --> 0:10:01.920 the dark matter? What else can it do? Can it 0:10:02.040 --> 0:10:05.160 interact with itself in some way? So today on the podcast, 0:10:05.160 --> 0:10:14.320 we'll be asking the question what is dark radiation? Now, Daniel, 0:10:14.320 --> 0:10:16.440 this sort of sounds like an oxy moron, you know, 0:10:16.440 --> 0:10:19.800 you're almost asking like, what is not light light? Exactly? 0:10:19.840 --> 0:10:21.280 But this is the kind of game we play in 0:10:21.280 --> 0:10:23.560 physics all the time. We don't really know how to 0:10:23.559 --> 0:10:26.319 grapple with the unknown, so we tend to explore it 0:10:26.400 --> 0:10:30.240 in terms of the known. Like when we think about photons, 0:10:30.440 --> 0:10:32.600 we don't really know how to deal with the quantum objects. 0:10:32.600 --> 0:10:34.400 We say, is it a particle? Is it a wave? 0:10:34.440 --> 0:10:36.679 It's kind of both. That's kind of the same. It's 0:10:36.679 --> 0:10:39.320 a contradiction there, right, and so here that's what we're doing. 0:10:39.320 --> 0:10:41.800 We're saying, well, we know about photons, is there like 0:10:41.960 --> 0:10:45.800 another kind of like dark matter version of the photon. 0:10:46.040 --> 0:10:50.280 Were extrapolating from what we know into what we don't know. Interesting, well, 0:10:50.320 --> 0:10:52.960 it sounds like the plot device for a great science 0:10:52.960 --> 0:10:55.800 fic to novel or the next Marvel movie. You know, 0:10:56.000 --> 0:10:59.199 dark radiation. That's how you know Stephen Strange gets his 0:10:59.280 --> 0:11:01.320 powers or something. That's right. And if they are like 0:11:01.360 --> 0:11:05.160 what ten avengers made of normal matter, there should be like, 0:11:05.240 --> 0:11:08.679 you know, forty avengers made of dark matter, the dark avengers, 0:11:09.200 --> 0:11:13.520 Oh many, they can make another gazillion dark billions of dollars. 0:11:13.679 --> 0:11:15.480 That's right, and my one percent cut of that is 0:11:15.480 --> 0:11:19.400 going to be pretty sweet. Hopefully not you don't like 0:11:19.440 --> 0:11:22.959 sweet things exactly, it'll be pretty dark. Pile up those 0:11:23.040 --> 0:11:25.439 dark dollars in my dark bank account. Only pay Daniel 0:11:25.440 --> 0:11:29.400 with bitter dollars. We should start some sort of dark 0:11:29.480 --> 0:11:35.480 matter currency, that's right, dark chocolate coin. But it is 0:11:35.520 --> 0:11:38.360 a real question in physics, what is going on with 0:11:38.400 --> 0:11:41.600 the dark matter? Is it interacting with itself? Are dark 0:11:41.840 --> 0:11:45.960 matter particles shooting dark photons at each other? We just 0:11:46.000 --> 0:11:49.199 don't know. It is a dark question. And so as usual, 0:11:49.240 --> 0:11:51.160 we were wondering how many people out there had thought 0:11:51.200 --> 0:11:55.160 about this question or even know what these two words 0:11:55.200 --> 0:11:57.559 put together could mean. So, as usual, Daniel went out 0:11:57.559 --> 0:12:01.559 there into the Internet to ask people what is dark radiation? 0:12:01.720 --> 0:12:04.040 And I'm very grateful to those of you who volunteered 0:12:04.040 --> 0:12:06.800 to try to answer this question without having the opportunity 0:12:06.840 --> 0:12:09.160 to look it up or Google or get a PhD 0:12:09.200 --> 0:12:11.640 in physics first, And so thank you to all of 0:12:11.640 --> 0:12:13.680 those of you who volunteered. And if you would like 0:12:13.760 --> 0:12:17.360 to hear your voice speculating baselessly on the podcast, please 0:12:17.400 --> 0:12:20.200 don't be shy right to me. Two questions at Daniel 0:12:20.240 --> 0:12:23.400 and Jorge dot com. Has anyone tried that? They're like, oh, 0:12:23.520 --> 0:12:25.640 that's a great question, give me a seven years, I'll 0:12:25.679 --> 0:12:27.360 come back with a PhD and answer. Or is that 0:12:27.400 --> 0:12:29.880 what you do to your grad students every day? Yeah? 0:12:29.920 --> 0:12:31.520 I take the answers people give me. I'm like, oh, 0:12:31.559 --> 0:12:33.200 that's a good idea for a project, and then I 0:12:33.200 --> 0:12:36.360 go write a grand proposal based on it nice, and 0:12:36.360 --> 0:12:39.240 then you get dark bitter money for it, and my 0:12:39.280 --> 0:12:41.920 grad students spend dark bitter years working on it. Yeah. 0:12:41.960 --> 0:12:44.080 So here's what people had to say. When I figure 0:12:44.080 --> 0:12:48.640 of radiation, I think of waves being admitted from something, 0:12:48.679 --> 0:12:50.840 so that could be heat radiation, or it could be 0:12:50.920 --> 0:12:56.000 light radiation. And even when something is invisible light to 0:12:56.160 --> 0:13:01.160 humans radiation, UM, it's still quote unquote light. So dark 0:13:01.280 --> 0:13:05.240 radiation I imagine. I think it has something to do 0:13:05.280 --> 0:13:09.120 with dark energy. Probably I have to give all credit 0:13:09.360 --> 0:13:11.640 to no Degress Tyson for why I know this. But 0:13:12.320 --> 0:13:17.000 dark radiation is the mediator of dark matter particle interaction. 0:13:17.480 --> 0:13:21.760 Say that five times fast. The best analogy for it is, um, 0:13:21.760 --> 0:13:24.320 it's the dark matter equivalent of a photon. I think 0:13:24.520 --> 0:13:28.760 dark radiation is radiation coming from dark matter right away. 0:13:28.800 --> 0:13:31.880 It makes me think of dark matter and dark energy, 0:13:31.960 --> 0:13:34.720 and I know they both interact with regular matter only 0:13:34.720 --> 0:13:39.360 through gravity. So I would guess that it has something 0:13:39.400 --> 0:13:45.520 to do with how dark matter radiates away or evaporates 0:13:45.559 --> 0:13:48.360 in the same manner regular mass does with like a 0:13:48.360 --> 0:13:52.720 black hole. All right, some pretty good answers here, mostly questions. 0:13:53.160 --> 0:13:55.960 I feel like people answered back with some questions too. Yeah, 0:13:55.960 --> 0:13:57.800 and people get the sense that it has something to 0:13:57.880 --> 0:14:00.720 do with dark matter or dark inner g right, because 0:14:00.760 --> 0:14:03.760 people have this concept that radiation energy, and so maybe 0:14:03.760 --> 0:14:06.760 it falls into the like energy category rather than the 0:14:06.840 --> 0:14:10.000 dark matter category. So yeah, some great answers. Yeah, I 0:14:10.040 --> 0:14:13.040 feel like you've really sort of branded that word dark, 0:14:13.200 --> 0:14:15.840 Like people automatically anything you associated with the word dark, 0:14:15.920 --> 0:14:18.560 people know it's oh dark matter or dark energy. Yeah. 0:14:18.559 --> 0:14:20.920 The funny thing is that the word dark and physics 0:14:21.000 --> 0:14:23.800 just means we don't know anything about it. It's like 0:14:24.000 --> 0:14:27.200 hidden from us, something we can't see, and so like 0:14:27.240 --> 0:14:30.680 the only relationship between dark matter and dark energy really 0:14:30.760 --> 0:14:33.000 is that we're pretty clueless about both of them. Well, 0:14:33.040 --> 0:14:34.920 my question is, what's gonna happen when you do discover 0:14:35.000 --> 0:14:36.680 what it is and when you can see it. Do 0:14:36.720 --> 0:14:39.120 you need to change the name. Oh, that's a great question. 0:14:39.280 --> 0:14:42.880 It depends, I suppose, on whether it remains dark or not. 0:14:43.080 --> 0:14:45.280 You know, if we find some way to communicate with 0:14:45.600 --> 0:14:48.840 the dark sector with these dark particles, then they won't 0:14:48.960 --> 0:14:52.200 any longer be totally dark. So yeah, because it depends 0:14:52.320 --> 0:14:54.640 specifically on what we figure out about it. Well, you 0:14:54.720 --> 0:14:56.440 just said that it's you call it dark when you 0:14:56.480 --> 0:14:58.120 don't know anything about it. So if you do know 0:14:58.200 --> 0:15:00.600 something about it and can't see it, maybe think about 0:15:00.640 --> 0:15:03.400 changing the name to like, you know, Horhi matter or 0:15:03.760 --> 0:15:06.480 cam matter, just saying, you know, some suggestions. We'll put 0:15:06.520 --> 0:15:08.680 that on the list, right next to white chocolate matter. Yeah, 0:15:08.960 --> 0:15:10.520 I just realized its kind of running for a guy 0:15:10.600 --> 0:15:13.760 named white sun. It sounds like you have some father issues. Yeah, 0:15:13.840 --> 0:15:18.360 self loathing matter, that's what it is. That's that's pretty dark. 0:15:18.480 --> 0:15:21.440 That's pretty dark. I'm gonna go in some more dark 0:15:21.520 --> 0:15:23.880 chocolate and now feel better. Alright, So Daniel, we're going 0:15:23.920 --> 0:15:26.280 to answer this question. What is dark radiation? Which is 0:15:26.560 --> 0:15:30.239 sounds very tantalizing, it sounds cool. It sounds maybe dangerous 0:15:30.560 --> 0:15:32.880 dark radiation, or maybe dark radiation is good for you 0:15:32.920 --> 0:15:36.040 because it's the opposite of regular radiation. It's not like 0:15:36.400 --> 0:15:39.080 entire radiation like that. What you need is a dose 0:15:39.120 --> 0:15:41.600 of dark radiation that'll cure Peter Parker, right, he'll no 0:15:41.640 --> 0:15:44.880 longer be Spider Man. The you know, damage right out 0:15:44.880 --> 0:15:49.960 of you. No, dark radiation is an analog to radiation, 0:15:50.400 --> 0:15:52.800 but in dark matter. So in our kind of matter, 0:15:52.960 --> 0:15:55.240 we have you know, electrons and quarks, and they can 0:15:55.480 --> 0:15:59.600 radiate things like photons because there are forces between these particles, 0:15:59.720 --> 0:16:03.920 and so dark radiation would imagine that between dark matter 0:16:04.000 --> 0:16:07.840 particles there might be some new dark force, and that 0:16:07.960 --> 0:16:11.280 new dark force would be capable of generating dark radiation. 0:16:12.400 --> 0:16:15.120 But you know, I think technically in physics you use 0:16:15.160 --> 0:16:19.120 the word radiation for basically any particle, any quantum particle 0:16:19.200 --> 0:16:21.360 moving in a quantum field, right, I think that's isn't 0:16:21.400 --> 0:16:24.520 that the technical definition? Unfortunately, we're not totally consistent that 0:16:24.680 --> 0:16:27.640 when we talk about radiation. When we talk about radiation 0:16:27.680 --> 0:16:30.760 sort of chemically like what is producing radiation, that can 0:16:30.800 --> 0:16:33.760 include things like photons, but also, as you say, high 0:16:33.840 --> 0:16:36.800 energy particles. Here, when we talk about radiation and we 0:16:36.840 --> 0:16:39.880 distinguish it from matter, we're talking about the particles that 0:16:39.880 --> 0:16:43.160 are associated with forces rather than the particles that are 0:16:43.160 --> 0:16:46.720 associated with matter. So for example, a photon would be radiation, 0:16:47.000 --> 0:16:49.480 whereas a cork would be matter. Even if a cork 0:16:49.560 --> 0:16:52.440 moving at high speed, a chemist would call it radiation. 0:16:52.600 --> 0:16:55.000 Oh I see, So if we're going with the chemist definition, 0:16:55.040 --> 0:16:58.360 then radiation is just any particle moving kind of what 0:16:58.480 --> 0:17:01.200 if you're going, if you're going with the day annual interpretation. Here, 0:17:01.400 --> 0:17:04.479 radiation just means a force particle or like a particle 0:17:04.520 --> 0:17:07.480 associated with a force moving through space. The idea is 0:17:07.520 --> 0:17:11.760 that maybe dark matter also produces dark radiation. That's the idea, 0:17:11.840 --> 0:17:15.520 and it's a really interesting area to study because you know, 0:17:15.560 --> 0:17:17.960 we don't know what's going on with dark matter. We 0:17:18.040 --> 0:17:20.360 just know that there's a lot of it in the universe. 0:17:20.560 --> 0:17:23.359 But it's tempting to extrapolate from the kind of matter 0:17:23.400 --> 0:17:25.280 that we have, right, the kind of matter we have 0:17:25.400 --> 0:17:28.520 does all sorts of interesting crazy stuff. It feels forces, 0:17:28.800 --> 0:17:32.240 it forms complex objects like ice cream and chocolate and pizza. 0:17:32.680 --> 0:17:34.800 So we don't know what's going on with the dark matter. 0:17:35.000 --> 0:17:37.600 There's various possibilities all the way from like it's totally 0:17:37.600 --> 0:17:39.920 inert it feels no forces. It just sort of sits 0:17:39.960 --> 0:17:43.840 there and feels gravity too. It has like seventy five 0:17:43.960 --> 0:17:47.520 new forces we haven't even imagined. They're capable of forming intricate, 0:17:47.560 --> 0:17:52.040 complex things that would blow our minds. And in that scenario, 0:17:52.280 --> 0:17:55.320 those forces would be mediated by dark particles, and so 0:17:55.359 --> 0:17:58.040 those would be dark radiation, right, Because I think all 0:17:58.080 --> 0:18:00.320 we know about dark matter is that it it sort 0:18:00.359 --> 0:18:03.280 of looks like it's a big giant, fuzzy clump. But 0:18:03.359 --> 0:18:04.879 that's just what we can see of it. You know, 0:18:04.960 --> 0:18:08.359 it could be something really detailed and organized. We just 0:18:08.400 --> 0:18:11.080 have a very unfocused view of it. That's right, And 0:18:11.119 --> 0:18:13.840 that's because so far, our only way to learn things 0:18:13.880 --> 0:18:16.800 about dark matter, to interact with dark matter so as 0:18:16.840 --> 0:18:19.120 to figure out like where it is and what it's doing, 0:18:19.560 --> 0:18:23.159 is through gravity, and gravity is the weakest force in 0:18:23.200 --> 0:18:25.960 the universe we've discovered, and not by a little bit, 0:18:26.000 --> 0:18:28.600 but by like ten to the thirty six. It's like 0:18:28.720 --> 0:18:31.520 super duper crazy week. So it's like trying to look 0:18:31.600 --> 0:18:35.040 at dark matter, but you're looking through very very dark glasses, 0:18:35.080 --> 0:18:37.080 so you can just barely see it. You can only 0:18:37.119 --> 0:18:39.520 see huge clumps of it, and that gives us a 0:18:39.600 --> 0:18:42.199 very fuzzy view of what's going on. The glasses are 0:18:42.240 --> 0:18:44.600 made out of dark matter. I'm a little confused here. 0:18:44.960 --> 0:18:50.760 They filter dark radiation. I think you mean like fuzzy glasses. Yeah, yeah, 0:18:50.880 --> 0:18:52.520 all right, Well maybe for the people who are not 0:18:52.560 --> 0:18:55.080 familiar with dark matter, maybe give us a quick refresher 0:18:55.200 --> 0:18:56.840 of what it is and how we know it's there. 0:18:57.000 --> 0:18:59.040 So we don't know that much about dark matter, but 0:18:59.080 --> 0:19:01.439 we do know that it makes up most of the 0:19:01.480 --> 0:19:04.200 stuff in the universe, and it's some kind of matter 0:19:04.520 --> 0:19:07.560 by which we mean that it provides gravity. And you know, 0:19:07.600 --> 0:19:11.040 we invented the idea of dark matter to explain why 0:19:11.080 --> 0:19:15.119 there was gravity in the universe that we couldn't otherwise explain. So, 0:19:15.160 --> 0:19:18.600 for example, we see that galaxies are rotating really really fast, 0:19:18.920 --> 0:19:21.960 and there's apparently enough gravity to hold them together to 0:19:22.040 --> 0:19:24.920 keep the stars from going out into interstellar space being 0:19:24.960 --> 0:19:27.760 tossed out. But we can't explain where that gravity is 0:19:27.800 --> 0:19:30.840 coming from, so we say probably dark matter. And if 0:19:30.840 --> 0:19:33.520 we want to understand the structure of the universe, how 0:19:33.560 --> 0:19:36.439 it got to have these galaxies and these superclusters and 0:19:36.440 --> 0:19:38.720 all of this stuff. If you run a simulation of 0:19:38.760 --> 0:19:42.080 the universe without dark matter, then it just doesn't form 0:19:42.160 --> 0:19:45.520 galaxies and stars this quickly. You need more gravity to 0:19:45.600 --> 0:19:48.479 pull that stuff together. So we need dark matter not 0:19:48.560 --> 0:19:51.399 just to explain how galaxies are spinning, but also the 0:19:51.440 --> 0:19:54.440 whole structure of the universe. And if we look in 0:19:54.520 --> 0:19:57.240 the very early ever beginnings of the universe and we 0:19:57.280 --> 0:20:00.159 see like how wiggles in the first plasma of the 0:20:00.280 --> 0:20:03.720 universe formed, and how those wiggles propagated, they don't really 0:20:03.760 --> 0:20:07.720 make sense unless you add dark matter to our calculations. 0:20:07.720 --> 0:20:09.560 So we have a lot of evidence that dark matter 0:20:09.600 --> 0:20:11.880 is a thing, that it's out there, that it clumps 0:20:11.960 --> 0:20:15.640 together in these big structures that shaped our whole universe. 0:20:15.840 --> 0:20:18.040 We just don't really know what it's made out of 0:20:18.040 --> 0:20:20.879 other than something that gives gravity. Yeah, we we know 0:20:20.960 --> 0:20:22.880 it's there and it has to be there to explain 0:20:22.960 --> 0:20:25.320 what we see. But I think that's the crazy things 0:20:25.359 --> 0:20:27.840 that we don't know what it is, Like, we really 0:20:27.840 --> 0:20:29.800 have no idea, Like it could be a totally new 0:20:29.880 --> 0:20:32.240 kind of thing that's not even a particle, or even 0:20:32.320 --> 0:20:35.040 something sort of like cohesive. It could be anything, right, Yeah, 0:20:35.040 --> 0:20:37.440 And we've done a lot of podcast episodes diving into 0:20:37.480 --> 0:20:40.560 some of those examples. Sort Of the mainstream idea is 0:20:40.600 --> 0:20:44.439 a whim weakly interacting massive particle that's sort of like, 0:20:44.520 --> 0:20:47.679 you know, a generic idea like what's the simplest possible 0:20:47.680 --> 0:20:50.680 explanation for dark matter? But there's lots of other more 0:20:50.720 --> 0:20:54.800 exotic and fascinating ideas, from things like axions, these weird 0:20:54.920 --> 0:20:59.240 heavy photons, to things like primordial black holes formed very 0:20:59.359 --> 0:21:02.480 very early in the universe to things like super duper 0:21:02.560 --> 0:21:07.199 long wave photons generated by dark stars. So we just 0:21:07.280 --> 0:21:08.880 don't really know what it is. And as you say, 0:21:08.920 --> 0:21:12.200 it might not even be a particle. It might be 0:21:12.280 --> 0:21:15.159 that this whole idea of particles and fields and quantum 0:21:15.240 --> 0:21:18.000 forces only applies to the little bit of the universe 0:21:18.040 --> 0:21:20.160 that we've been studying for the last few hundred years, 0:21:20.200 --> 0:21:22.399 and that you can't extrapolate to the rest of the 0:21:22.480 --> 0:21:24.679 universe the same way you can't, like look at an 0:21:24.720 --> 0:21:27.159 elephant's tail and assume the rest of the elephant is 0:21:27.200 --> 0:21:29.320 like the tail. So it might be that we have 0:21:29.560 --> 0:21:33.160 dramatic mind blowing lessons to be learned about dark matter, 0:21:33.560 --> 0:21:35.400 or it could be super boring and just be one 0:21:35.440 --> 0:21:38.760 particle that doesn't do anything. Some pretty extreme possibilities there. 0:21:39.119 --> 0:21:41.000 But but are you saying that maybe, like maybe even 0:21:41.080 --> 0:21:44.400 quantum mechanics only applies to a small part of the universe. 0:21:44.640 --> 0:21:46.560 I think that's true. Yeah, All of the tests that 0:21:46.600 --> 0:21:49.879 we've done of quantum mechanics use our kind of matter 0:21:50.080 --> 0:21:52.320 and our kind of forces, and so we have a 0:21:52.320 --> 0:21:56.000 pretty good quantum description of quantum particles, but we don't 0:21:56.000 --> 0:21:59.399 really have a quantum description of gravity and gravity is 0:21:59.440 --> 0:22:01.439 our poor to dark matter. The only thing we know 0:22:01.480 --> 0:22:04.359 about dark matter is that it does feel gravity, and 0:22:04.400 --> 0:22:06.800 so it could be some other new, weird kind of 0:22:06.920 --> 0:22:11.119 thing that generates gravity but doesn't otherwise follow the rules 0:22:11.119 --> 0:22:15.520 of quantum mechanics. Well, all right, so that's a dark matter. Now, 0:22:15.560 --> 0:22:18.800 what would you say is a dark force? Besides the 0:22:18.840 --> 0:22:22.600 obvious Star Wars reference, a dark force would be anybody 0:22:22.600 --> 0:22:26.280 who tries to force me to eat white chocolate, the 0:22:26.400 --> 0:22:29.320 dark force in my life. Now, a dark force would 0:22:29.320 --> 0:22:32.159 be in the assumption that dark matter is made of 0:22:32.200 --> 0:22:36.280 particles that follow the rules of quantum mechanics like our particles, 0:22:36.720 --> 0:22:39.240 then you might imagine that they also feel some dark 0:22:39.320 --> 0:22:43.000 forces between them. You know that too. Dark matter particles 0:22:43.000 --> 0:22:47.040 can exchange some like dark photon or dark z boson 0:22:47.240 --> 0:22:50.199 or dark higgs boson that they can like push or 0:22:50.240 --> 0:22:52.159 pull on each other. They can do more than just 0:22:52.280 --> 0:22:55.679 feel each other's gravity. Maybe there's some additional dark forces 0:22:55.760 --> 0:22:58.200 and they're passing particles back and forth as a way 0:22:58.200 --> 0:23:01.040 to mediate those forces. Rights. Even the matter in our 0:23:01.119 --> 0:23:04.280 universe is sort of selective about which forces it feels 0:23:04.359 --> 0:23:07.760 or which forces they give out, right, Like some particles 0:23:07.800 --> 0:23:11.679 in our type of matter only feel like the magnetic forces, 0:23:11.800 --> 0:23:14.159 or they don't feel the strong force and things like that. Right, 0:23:14.280 --> 0:23:17.800 that's exactly right. Neutrinos, for example, only feel the weak force. 0:23:17.960 --> 0:23:22.440 They ignore the strong force, they ignore electromagnetism. Electrons they 0:23:22.560 --> 0:23:25.719 do feel electromagnetism and the weak force, but they ignore 0:23:25.760 --> 0:23:28.680 the strong force. Only the corks feel all of the forces, 0:23:28.800 --> 0:23:32.040 including the strong force. And so for an individual particle, 0:23:32.119 --> 0:23:34.680 you can ask, like whether it has a charge for 0:23:34.760 --> 0:23:38.720 that force. So electromagnetism only interact with particles that have 0:23:38.840 --> 0:23:41.960 electric charges. For example, we know that dark matter doesn't 0:23:41.960 --> 0:23:44.600 have electric charges, and it doesn't have weak charges, or 0:23:44.640 --> 0:23:47.680 it doesn't have strong charges, but it might have charges 0:23:47.760 --> 0:23:51.199 for other forces we haven't yet discovered. Wow, like there 0:23:51.240 --> 0:23:54.000 could be a whole different category of forces that we 0:23:54.119 --> 0:23:56.680 just don't happen to feel in our kind of matter, 0:23:57.040 --> 0:23:59.359 but that maybe dark matter it does feel exactly So 0:23:59.400 --> 0:24:02.359 there could be like one or forty new forces that 0:24:02.400 --> 0:24:05.480 we haven't yet discovered because our particles don't feel those, 0:24:05.800 --> 0:24:09.000 or maybe more, not just forty, maybe four thousand exactly. 0:24:11.119 --> 0:24:13.200 All right, Well, let's dig into what this new kind 0:24:13.200 --> 0:24:16.000 of force might be, this dark force and what it 0:24:16.080 --> 0:24:17.960 could all mean and whether or not we can never 0:24:18.000 --> 0:24:20.760 hope to see it or feel it. But first let's 0:24:20.760 --> 0:24:35.920 take a quick break. All right, we're talking about dark radiation, 0:24:36.080 --> 0:24:37.919 and in this case, the word radiation sort of is 0:24:37.920 --> 0:24:40.920 associated with the word force. So really we're asking does 0:24:41.000 --> 0:24:45.080 dark matter feel dark forces that maybe are out there, 0:24:45.080 --> 0:24:47.399 but that we in our kind of matter can feel 0:24:47.480 --> 0:24:49.960 or touch or detect. But then maybe it is maybe 0:24:50.160 --> 0:24:53.720 organizing dark matter into structures or maybe you know, even 0:24:53.800 --> 0:24:57.400 making dark matter particles and Adams exactly. And it's part 0:24:57.440 --> 0:25:00.439 of this imagination game we play, you know, we wonder 0:25:00.520 --> 0:25:03.320 what's going on out there in the dark universe. Is 0:25:03.320 --> 0:25:06.600 it simple, is it fascinating, is it complex? What is 0:25:06.640 --> 0:25:09.320 going on? What is they're out there to learn? And 0:25:09.560 --> 0:25:11.879 usually when we go out and explore the universe, we 0:25:11.960 --> 0:25:16.120 find that things are crazier and more fascinating and richer 0:25:16.280 --> 0:25:19.120 than we ever imagined. And so we're at this point 0:25:19.160 --> 0:25:21.240 where we really don't know about most of the universe. 0:25:21.280 --> 0:25:22.840 But at some point in the future, I hope a 0:25:22.920 --> 0:25:25.000 hundred years, five hundred years from now, we will know 0:25:25.040 --> 0:25:27.600 what's going on in the dark sector and those people 0:25:27.680 --> 0:25:31.159 will look back at our ideas as ridiculous. Probably you 0:25:31.240 --> 0:25:34.080 might think of us as the Dark Ages physics. They 0:25:34.280 --> 0:25:36.800 like the really dark ages, not that the trial run 0:25:36.840 --> 0:25:40.760 in the Middle Ages, but more serious. Yes, back when 0:25:40.760 --> 0:25:45.359 people ate white chocolate, that's right. Maybe we're looking forward 0:25:45.400 --> 0:25:50.000 to an age of dark enlightenment, in the age of oxymorons. 0:25:50.160 --> 0:25:52.719 But yeah, So in our kind of matter, we feel 0:25:52.880 --> 0:25:56.879 the electromagnetic force, which is what basically holds our atoms together. 0:25:57.040 --> 0:25:58.760 And what you know when you touch something, when you 0:25:58.800 --> 0:26:01.199 touch the table or you hold the banana, that's the 0:26:01.200 --> 0:26:04.479 force you're feeling. And that force is transmitted by a 0:26:04.520 --> 0:26:07.199 particle called the photon. So the photon is not just 0:26:07.320 --> 0:26:10.960 lighted Tosso what transmits the electromagnetic force? And so the 0:26:11.040 --> 0:26:13.919 question daniel I guess is does dark matter have the 0:26:13.960 --> 0:26:17.520 equivalent of a photon or at least an electromagnetic force field. 0:26:17.680 --> 0:26:20.000 We just don't know, and so we're playing this game 0:26:20.040 --> 0:26:22.639 of trying to extrapolate from what we do know. And 0:26:22.640 --> 0:26:25.280 in the same way that we imagine maybe dark matter 0:26:25.560 --> 0:26:28.399 is made of a particle, because we're made of particles, 0:26:28.520 --> 0:26:31.480 we wonder if there are dark forces that look like 0:26:31.600 --> 0:26:34.800 our forces. And so one of the simplest forces to 0:26:34.880 --> 0:26:38.520 understand is electromagnetism because it just has like one particle 0:26:38.600 --> 0:26:41.159 and it interacts with lots of stuff, and so a 0:26:41.280 --> 0:26:44.600 simple proposals to say, well, what if dark matter has 0:26:44.640 --> 0:26:48.840 a dark electromagnetism, meaning a dark photon. This would be 0:26:48.880 --> 0:26:51.399 a particle that has a lot of properties similar to 0:26:51.560 --> 0:26:54.639 our photon, but it would be different. You know, those 0:26:54.720 --> 0:26:58.160 dark matter particles would have like a dark electric charge 0:26:58.480 --> 0:27:01.080 and the dark photon, but only interact with particles with 0:27:01.160 --> 0:27:04.760 a dark electric charge, not ones with our electric charge 0:27:05.040 --> 0:27:09.080 and our normal vanilla photons wouldn't interact with dark matter 0:27:09.160 --> 0:27:12.040 because they don't have an electric charge, only a dark 0:27:12.160 --> 0:27:16.080 electric charge. But it wouldn't necessarily be the same or 0:27:16.119 --> 0:27:19.000 the sort of the analog of light. Right you're just 0:27:19.000 --> 0:27:21.199 saying like, maybe it's a force, and let's why not 0:27:21.359 --> 0:27:23.960 let's qual it the dark electromagnetic force. It doesn't have 0:27:24.040 --> 0:27:26.040 to be, and it could be the dark matter fields 0:27:26.080 --> 0:27:28.439 forces that are more similar to like our weak force, 0:27:28.800 --> 0:27:31.040 or forces that are more similar to our strong force, 0:27:31.400 --> 0:27:34.000 or forces that are totally different from these forces and 0:27:34.080 --> 0:27:37.560 have other new weird capacities. Right before we discovered the 0:27:37.600 --> 0:27:41.399 strong force, who could have imagined this crazy force, you know, 0:27:41.440 --> 0:27:43.960 where it gets stronger as things get further apart, and 0:27:43.960 --> 0:27:46.639 it has like eight different kinds of gluons pulling it together. 0:27:46.920 --> 0:27:49.640 It's bonkers. Nobody would have written that into the script. 0:27:49.880 --> 0:27:52.320 So it's possible that there are other kinds of forces. 0:27:52.440 --> 0:27:54.960 But if there is a dark force that's very similar 0:27:55.040 --> 0:27:58.360 to electromagnetism, then that dark photon would have properties very 0:27:58.359 --> 0:28:01.399 similar to our photon, because those properties come from the 0:28:01.400 --> 0:28:04.800 structure of the force, all right. And also it makes 0:28:04.800 --> 0:28:07.560 for a cool name, dark photon, because it kind of 0:28:07.600 --> 0:28:09.840 it trips up your brain, right, Like, how can a 0:28:09.840 --> 0:28:13.080 photon which transmits light be dark? That's right, because it 0:28:13.119 --> 0:28:18.200 transmits dark light into dark eyeballs. Oh yeah, I feel 0:28:18.200 --> 0:28:20.119 like you should maybe just call it something different. What 0:28:20.160 --> 0:28:23.240 would you call it the dark on the invisible photon? 0:28:23.320 --> 0:28:25.240 I don't know, dark on is good, But then what 0:28:25.280 --> 0:28:27.679 do you find another force? Yeah, we'll have to be 0:28:27.720 --> 0:28:30.320 even more creative with our names. We'll just have, you know, 0:28:30.400 --> 0:28:32.560 a brainstorming session with lots of chocolate, and we'll come 0:28:32.640 --> 0:28:35.080 up with something good and then and then who knows 0:28:35.080 --> 0:28:36.840 what you'll get out of it? Maybe a heart attack, 0:28:37.080 --> 0:28:39.640 all right? So dark matter might feel this new kind 0:28:39.680 --> 0:28:42.360 of or strange new kind of force, a dark force. 0:28:42.600 --> 0:28:44.960 So how would we ever detected Daniel, would we ever 0:28:45.000 --> 0:28:47.480 hope to feel it or you know, know it's there 0:28:47.520 --> 0:28:49.600 if we can't touch it or see it. So in 0:28:49.640 --> 0:28:53.080 the end, this question is really asking what dark matter 0:28:53.200 --> 0:28:56.640 does to itself? You know, can we speculate about what's 0:28:56.640 --> 0:28:59.400 going on in the dark sector beyond these particles existing 0:28:59.680 --> 0:29:02.920 can like touch each other and become sticky and do stuff, 0:29:03.000 --> 0:29:05.160 And so we have sort of two ways to probe this. 0:29:05.360 --> 0:29:07.400 The first category is sort of like indirect ways to 0:29:07.440 --> 0:29:10.120 look at it, and broadly speaking, we can tell that 0:29:10.240 --> 0:29:13.040 dark matter is doing things because of its gravity. And 0:29:13.240 --> 0:29:15.840 even though it's not a great way to study dark matter, 0:29:16.120 --> 0:29:19.040 we can use its gravitational effects to ask questions like 0:29:19.440 --> 0:29:22.680 is it clumping? Is it interacting with itself? Because if 0:29:22.680 --> 0:29:25.400 it interacts with itself, it forms sort of different structures 0:29:25.400 --> 0:29:27.840 that have different gravity. So we can sort of ask 0:29:27.920 --> 0:29:30.800 questions about whether dark matter is feeling itself by trying 0:29:30.840 --> 0:29:33.960 to look to see how it organizes itself in the universe. 0:29:34.240 --> 0:29:36.840 I see, we can't maybe see it directly or touch 0:29:37.000 --> 0:29:40.200 dark matter, but if we can somehow kind of know 0:29:40.280 --> 0:29:42.120 what it's doing, And if we see it doing stuff 0:29:42.120 --> 0:29:44.400 to itself, then we know that it's there must be 0:29:44.440 --> 0:29:47.280 some kind of force that it does interact with exactly. 0:29:47.360 --> 0:29:50.080 For example, if dark matter felt a version of the 0:29:50.120 --> 0:29:53.120 strong force, if it interacted with itself very very strongly 0:29:53.200 --> 0:29:56.400 and could like clump together very very very sticky ways, 0:29:56.600 --> 0:29:59.200 then it would form much denser objects than we see 0:29:59.240 --> 0:30:03.000 currently in the universe. Currently, dark matter looks really big 0:30:03.040 --> 0:30:06.640 and fluffy, like the dark matter in our galaxy isn't 0:30:06.640 --> 0:30:09.400 nearly as compact as the normal matter in our galaxy. 0:30:09.440 --> 0:30:12.320 It spreads out much further out. It's a big, fluffy 0:30:12.360 --> 0:30:16.000 cloud hasn't collapsed nearly as much, and we think that's 0:30:16.040 --> 0:30:19.640 because it's not as sticky as our matter. We think 0:30:19.640 --> 0:30:22.400 that it doesn't feel like a super powerful force that 0:30:22.520 --> 0:30:25.000 sticks it together, because that would help it like form 0:30:25.120 --> 0:30:28.640 denser objects like dark planets and dark stars. So we 0:30:28.680 --> 0:30:32.520 already know very broadly something about how dark matter can't 0:30:32.640 --> 0:30:35.840 feel itself because it stays sort of fluffy and doesn't 0:30:35.880 --> 0:30:38.040 seem to clump as much as normal matter. Right, But 0:30:38.080 --> 0:30:40.160 I wonder you know it sort of looks fluffy to 0:30:40.240 --> 0:30:42.280 us because we don't have a good way of seeing it. 0:30:42.360 --> 0:30:44.560 You know, we talked earlier about having we kind of 0:30:44.600 --> 0:30:47.000 have a fuzzy lens when we look at dark matter 0:30:47.360 --> 0:30:50.040 because we can only see it through gravity. You know, 0:30:50.160 --> 0:30:52.600 is it maybe even possible that there are dark matter 0:30:52.640 --> 0:30:55.760 stars out there, which is don't have the resolution to 0:30:55.840 --> 0:30:58.040 see them. You know, absolutely, there's a very big loophole 0:30:58.040 --> 0:30:59.840 in this argument that you allude to, which is that 0:31:00.040 --> 0:31:02.040 you can see sort of the bulk of dark matter, 0:31:02.080 --> 0:31:04.960 but we can't tell what it's doing in detail. In 0:31:04.960 --> 0:31:08.040 an episode recently about where is the dark matter, and 0:31:08.080 --> 0:31:09.880 we talked about how we can tell sort of the 0:31:10.000 --> 0:31:12.600 dark matters in these big fluffy clouds, but we also 0:31:12.720 --> 0:31:15.280 can't really tell if it is forming clumps. So you 0:31:15.280 --> 0:31:17.920 could imagine that dark matter maybe it's made out of 0:31:17.960 --> 0:31:20.320 a few different kinds of things. So most of it, 0:31:20.360 --> 0:31:22.160 maybe like you know, half of the dark matter or 0:31:22.160 --> 0:31:24.440 three fourths of the dark matter, is some big, fluffy 0:31:24.480 --> 0:31:26.840 stuff that hardly interacts with itself. But there could be 0:31:26.880 --> 0:31:30.160 a component of the dark matter that does do interesting, 0:31:30.280 --> 0:31:34.280 complicated things and has crazy interactions and forms dark stars 0:31:34.280 --> 0:31:36.760 and dark planets and dark life, and that would not 0:31:36.920 --> 0:31:39.920 mess up the distribution of dark matter, because remember, there's 0:31:40.000 --> 0:31:43.360 like so much dark matter out there that even like 0:31:43.640 --> 0:31:46.640 if a quarter of it does more interesting stuff, that's 0:31:46.680 --> 0:31:49.320 still more than all of our kind of matter. So 0:31:49.360 --> 0:31:51.760 there's plenty of room to have like a component that 0:31:51.800 --> 0:31:55.760 has complex interactions without missing up these constraints about the 0:31:55.840 --> 0:31:58.120 big picture of dark matter. So I feel like dark 0:31:58.120 --> 0:31:59.960 matter could be in the shape of I don't know, 0:32:00.120 --> 0:32:03.640 like rubber duckies. It's just that they're sort of distributed 0:32:03.640 --> 0:32:06.440 out in space, these rubber duckies, and to us it 0:32:06.440 --> 0:32:08.920 just seems like a big fluffy cloud. Yeah, most of 0:32:08.960 --> 0:32:10.840 it has to be pretty big and fluffy to form 0:32:10.880 --> 0:32:13.720 that big fluffy cloud. It can't stick to itself. But 0:32:13.800 --> 0:32:16.480 it could be that inside that big fluffy cloud there 0:32:16.520 --> 0:32:19.040 are like rubber duckies made out of like a special 0:32:19.160 --> 0:32:21.080 kind of dark matter, you know, the way they like 0:32:21.160 --> 0:32:23.800 our matter. There's lots of different kinds is electrons, is 0:32:23.840 --> 0:32:27.360 different kinds of quarks. Right, we have twelve different matter particles. 0:32:27.720 --> 0:32:30.240 Dark matter could have like fifty different kinds of particles, 0:32:30.240 --> 0:32:32.520 and maybe most of them don't interact and make a 0:32:32.520 --> 0:32:35.160 big fluffy cloud, but one or two of them form 0:32:35.320 --> 0:32:37.840 dark rubber duckies that are floating out there in the universe, 0:32:37.840 --> 0:32:40.080 and we couldn't tell the difference because the only way 0:32:40.120 --> 0:32:43.640 we can see them is through their overall gravitational interaction. 0:32:43.680 --> 0:32:46.240 I'm pretty sure that's what dark Vader uses in his bathtuff. 0:32:46.560 --> 0:32:48.760 But I guess the question is, you know, isn't the 0:32:48.800 --> 0:32:51.000 fact that dark matter does seem to be sort of 0:32:51.040 --> 0:32:53.720 fluffy and doesn't seem to stick to itself. Is that 0:32:53.760 --> 0:32:57.120 evidence that maybe it doesn't interact with itself other than 0:32:57.160 --> 0:32:59.880 with gravity. It's evidence that it doesn't interact with itself 0:33:00.160 --> 0:33:03.200 very very strongly. But again, the loophole is that some 0:33:03.360 --> 0:33:05.880 component of it might be able to Now. The way 0:33:05.880 --> 0:33:08.080 to probe that a little bit more deeply is to 0:33:08.080 --> 0:33:11.040 do experiments. Is to take like two big clouds of 0:33:11.120 --> 0:33:13.960 dark matter and throw them against each other and see 0:33:14.320 --> 0:33:16.560 if they pass right through each other, or if maybe 0:33:16.560 --> 0:33:19.200 they stick together and make them like dark explosions. That 0:33:19.280 --> 0:33:22.080 kind of experiment is pretty tough to do, but we 0:33:22.080 --> 0:33:24.320 were lucky and the universe did it for us. It 0:33:24.480 --> 0:33:28.760 collided two huge clusters of galaxies, each of which have 0:33:28.880 --> 0:33:32.320 their own dark matter associated with them, smashed them together 0:33:32.400 --> 0:33:34.200 millions of years ago, and we got to see what 0:33:34.280 --> 0:33:36.400 happened and what did happen, and so this is called 0:33:36.400 --> 0:33:38.200 the bullet cluster. You can go ahead and look at 0:33:38.240 --> 0:33:41.480 these pictures online if you're interested. It's really beautiful. What 0:33:41.600 --> 0:33:44.880 happened is that the stars in these galaxy clusters mostly 0:33:44.920 --> 0:33:47.920 passed through themselves because stars are pretty sparse, so it's 0:33:47.920 --> 0:33:50.480 like two clouds of sand passing through each other. The 0:33:50.600 --> 0:33:53.320 gas and the dust that were in these galaxies smashed 0:33:53.360 --> 0:33:55.800 together and admitted a lot of light and radiation. But 0:33:55.840 --> 0:33:59.120 the dark matter looks like it basically passed right through itself. 0:33:59.520 --> 0:34:01.360 You might ask school like, how could we know where 0:34:01.360 --> 0:34:03.240 the dark matter is? We can see the dark matter 0:34:03.280 --> 0:34:06.040 because it distorts the stuff behind it. From the dark 0:34:06.080 --> 0:34:09.240 matter is matter, it feels gravity, so it bends space 0:34:09.280 --> 0:34:12.759 a little bit, which creates like gravitational distortions in the 0:34:12.840 --> 0:34:15.960 light that passes through it. So from this bullet cluster, 0:34:16.040 --> 0:34:18.719 it looks like these two clouds mostly passed right through 0:34:18.760 --> 0:34:21.840 each other. So not it doesn't have any strong interactions 0:34:21.840 --> 0:34:24.200 with itself, but it could still have some interactions with itself, 0:34:24.239 --> 0:34:27.200 which would maybe give rise to something like a dark photon. 0:34:27.360 --> 0:34:30.000 That's right, and so people often cite the bullet cluster 0:34:30.080 --> 0:34:32.760 is evidence that dark matter can't feel anything with itself, 0:34:32.840 --> 0:34:35.600 and that's not exactly true, because, as you say, there's 0:34:35.600 --> 0:34:38.240 still room in there for some kind of interaction. Because 0:34:38.320 --> 0:34:41.640 remember that the stars, which do definitely feel each other, 0:34:41.800 --> 0:34:45.040 also passed right through themselves. Right. The star is hardly collided, 0:34:45.280 --> 0:34:47.960 and that's just because it's pretty sparse, and so could 0:34:48.000 --> 0:34:50.719 be that dark matter forms the structures, but they didn't 0:34:50.719 --> 0:34:53.439 collide with each other because just like the stars, they're 0:34:53.480 --> 0:34:56.160 pretty sparse and space is pretty big. And it could 0:34:56.200 --> 0:34:58.919 also be that some components of the dark matter did 0:34:58.960 --> 0:35:01.600 collide with itself, did get stuck sort of in the 0:35:01.600 --> 0:35:04.080 middle there. But we don't really have the resolution to tell. 0:35:04.160 --> 0:35:07.600 We can't very precisely measure how much dark matter passed 0:35:07.600 --> 0:35:09.640 through and how much stuck. We can just tell that 0:35:09.680 --> 0:35:12.600 a lot of it passed through, but some component could 0:35:12.600 --> 0:35:14.920 have gotten stuck and could be doing like crazy stuff 0:35:14.920 --> 0:35:17.000 there in the middle. I see, like maybe the Rubert 0:35:17.040 --> 0:35:19.279 duckies didn't all crash into each other, but some just 0:35:19.360 --> 0:35:22.040 kept going. I think the key point to understand is 0:35:22.040 --> 0:35:25.080 that there's so much dark matter out there that even 0:35:25.080 --> 0:35:27.680 if a tiny fraction of it is doing interesting things 0:35:28.000 --> 0:35:30.520 we couldn't tell, and that tiny fraction would still be 0:35:30.560 --> 0:35:32.960 more stuff than all of the stars and gas and 0:35:33.040 --> 0:35:34.920 dust in the universe that we know. All right, well, 0:35:35.000 --> 0:35:36.680 let's get into other ways that we might be able 0:35:36.719 --> 0:35:39.839 to detect this dark radiation and maybe even see these 0:35:39.920 --> 0:35:42.319 dark or not see these dark photons. I'm a little 0:35:42.320 --> 0:35:44.960 confused about how he might see are not photon But 0:35:45.000 --> 0:35:59.799 first let's take another quick break. All right, we're talking 0:35:59.800 --> 0:36:03.560 abot dark gradiation and dark photons, which it might be 0:36:03.680 --> 0:36:06.560 what dark matter sees and feels with itself when dark 0:36:06.600 --> 0:36:08.319 matter looks in the mirror. That's what they would see 0:36:08.400 --> 0:36:12.440 dark photons. Yeah, exactly. I hope they haven't eating too 0:36:12.480 --> 0:36:15.000 much dark chocolate. But to us it's pretty elusive because 0:36:15.000 --> 0:36:18.279 we can see or feel the dark matter or maybe 0:36:18.320 --> 0:36:20.719 even these forces. So, Daniel, what are some of the 0:36:20.760 --> 0:36:23.360 other ways that we might hope to detect whether or 0:36:23.360 --> 0:36:26.200 not dark matter has these dark interactions. There are a 0:36:26.320 --> 0:36:30.360 couple other indirect ways, basically again using gravity. One of 0:36:30.360 --> 0:36:34.360 them is looking at neutron stars. Neutron stars are these 0:36:34.440 --> 0:36:37.880 crazy dense objects that are the remnants of stars that 0:36:37.920 --> 0:36:40.640 have blown up and left this very very compact core, 0:36:41.200 --> 0:36:44.399 and sometimes neutron stars come in pairs and then those 0:36:44.440 --> 0:36:47.279 pairs spin around each other in this sort of like 0:36:47.360 --> 0:36:50.400 death spiral before they collide, and when they do that, 0:36:50.440 --> 0:36:53.839 they create gravitational waves that we can see here from Earth. 0:36:53.880 --> 0:36:57.239 This is like the shaking of space itself. If you're 0:36:57.520 --> 0:36:59.200 interested in learning more about that, we have a couple 0:36:59.200 --> 0:37:02.239 of episodes about gravitational waves. It's really cool because the 0:37:02.280 --> 0:37:06.360 gravitational waves reveal in detail how these stars are spiraling 0:37:06.480 --> 0:37:09.560 towards the center, how they're losing energy, and we can 0:37:09.560 --> 0:37:12.520 calculate with great precision how fast they should be going 0:37:12.560 --> 0:37:14.960 and how much energy they're losing. And so this is 0:37:14.960 --> 0:37:17.120 a really nice test of sort of like what's going 0:37:17.200 --> 0:37:19.840 on with this kind of matter, Because if these neutron 0:37:19.960 --> 0:37:24.080 stars were capable, for example, of feeling this dark radiation 0:37:24.200 --> 0:37:27.320 at some level, if the particles in there could feel 0:37:27.320 --> 0:37:29.839 this force at all, then they would radiate a little 0:37:29.840 --> 0:37:32.400 bit of those dark photons and it would change the 0:37:32.440 --> 0:37:34.920 way this inspiral happens, and we would be able to 0:37:34.920 --> 0:37:37.880 see that by looking at the gravitational waves. Wait, so 0:37:38.000 --> 0:37:40.439 these neutron stars would be made out of regular matter, 0:37:40.560 --> 0:37:42.160 the kind we're made out of. But you're saying that 0:37:42.200 --> 0:37:45.240 even though the regular matter it might admit this dark radiation, 0:37:45.560 --> 0:37:48.200 how is that possible. It might be that our matter 0:37:48.480 --> 0:37:50.920 can feel these sort of like new forces, just at 0:37:50.960 --> 0:37:53.440 a very very low level. We don't know, and so 0:37:53.520 --> 0:37:55.480 this is like, you know, one way to look for 0:37:55.560 --> 0:37:57.840 it under the assumption that our kind of matter could 0:37:57.880 --> 0:38:00.239 feel these dark forces, which is not something we know. 0:38:00.280 --> 0:38:02.000 It's just sort of like a guess. We do this 0:38:02.080 --> 0:38:04.279 in physics a lot. We're like, we don't know if 0:38:04.280 --> 0:38:06.479 it's possible to see it this way, but let's check, 0:38:06.600 --> 0:38:09.360 because if it does feel this force, if neutron stars 0:38:09.440 --> 0:38:12.239 can make these dark photons, we would be able to 0:38:12.280 --> 0:38:15.160 see that. I see neutron stars are so it's such 0:38:15.200 --> 0:38:17.320 an extreme event when they crash into each other that 0:38:17.320 --> 0:38:21.120 that's one possible, you know, crazy scenario where it might 0:38:21.200 --> 0:38:23.440 make dark gradiations exactly. And it's a place where we 0:38:23.440 --> 0:38:26.920 can make very very precise calculations about the gravitational waves 0:38:26.920 --> 0:38:29.960 and compare them to very very detailed data. So it's 0:38:29.960 --> 0:38:33.200 an opportunity to look for like very small deviations, you know, 0:38:33.320 --> 0:38:35.320 things that the neutron stars are doing that we can't 0:38:35.360 --> 0:38:40.399 otherwise explain that might be explainable through dark photons. I see, 0:38:40.480 --> 0:38:42.440 all right, what are some other ways we could maybe 0:38:42.520 --> 0:38:45.160 feel this dark force? All the most generic ways you 0:38:45.320 --> 0:38:47.800 just use gravity the kind of tests that we did before, 0:38:47.960 --> 0:38:49.680 But there are some other approaches to look for these 0:38:49.719 --> 0:38:53.160 dark photons, hoping that there's some connection between our kind 0:38:53.160 --> 0:38:56.120 of matter and the dark matter, Like hoping that somehow 0:38:56.200 --> 0:39:00.680 maybe these dark photons can turn into normal photon very 0:39:00.800 --> 0:39:04.120 very rarely, and then we could detect that what how 0:39:04.120 --> 0:39:06.600 can a dark photon turn into a regular photon. It 0:39:06.640 --> 0:39:09.000 turns out that if you have another kind of force 0:39:09.040 --> 0:39:11.319 that's very similar to the photon, has sort of like 0:39:11.480 --> 0:39:15.560 a similar mathematical structure, that these forces like to talk 0:39:15.600 --> 0:39:17.960 to each other, that there's like it's very easy to 0:39:18.000 --> 0:39:20.960 build a physics model in which another kind of photon 0:39:21.120 --> 0:39:25.640 can turn into our photon wha like spontaneously or only 0:39:25.680 --> 0:39:29.040 in like high energy completions or you know, moments where 0:39:29.040 --> 0:39:32.240 you have kind of this a state of pure energy. 0:39:32.320 --> 0:39:34.799 It would be spontaneous, and in order for that to happen, 0:39:34.840 --> 0:39:37.160 they would have to be some kind of particle in 0:39:37.200 --> 0:39:41.280 the universe that has both kinds of charges. So imagine 0:39:41.360 --> 0:39:44.839 some new kind, very very rare dark matter that does 0:39:44.960 --> 0:39:48.160 have electric charges and also has some new kind of 0:39:48.280 --> 0:39:51.839 dark electric charge. That particle could effectively be like a 0:39:51.880 --> 0:39:56.040 portal that connects our photons to these other photons, and 0:39:56.080 --> 0:39:58.759 it might be that these particles never really exist in 0:39:58.800 --> 0:40:01.960 the universe, the way like top corks almost never exist 0:40:02.000 --> 0:40:04.400 in the universe on their own, but they're sort of 0:40:04.440 --> 0:40:07.000 like on the list of possibilities. As long as it's 0:40:07.000 --> 0:40:10.759 on the list of possibilities, then dark photons can use 0:40:10.800 --> 0:40:14.640 that as a portal to become normal photons and vice versa. 0:40:14.760 --> 0:40:18.160 This allows them to spontaneously turn from one into the other. Whoa, 0:40:18.320 --> 0:40:21.680 So that wouldn't make dark matter not dark, right, It 0:40:21.680 --> 0:40:23.680 would mean that you can sort of see them. It would, 0:40:23.680 --> 0:40:25.920 but these particles again wouldn't actually have to exist in 0:40:25.960 --> 0:40:29.279 the universe. So imagine now the dark sector is some 0:40:29.360 --> 0:40:31.840 kind of particle that's actually out there, that most of 0:40:31.840 --> 0:40:33.920 the dark matter is made out of this particle. And 0:40:33.960 --> 0:40:37.040 then there's the possibility for this other particle that has 0:40:37.160 --> 0:40:40.239 electric charges and dark charges, even though it's never really 0:40:40.239 --> 0:40:43.080 out there in the universe, as long as the possibility 0:40:43.200 --> 0:40:46.360 for it to exist is part of sort of nature's menu. 0:40:47.000 --> 0:40:50.879 That possibility allows dark photons to turn into photons. It's 0:40:50.880 --> 0:40:54.759 called kinetic mixing because we see it happening with regular matter, right, 0:40:54.840 --> 0:40:57.520 Like our photons turned into other kinds of stuff all 0:40:57.560 --> 0:41:00.400 the time, yes, exactly, Like photons turned into pairs of 0:41:00.480 --> 0:41:04.239 particles electrons and positrons, and then those can turn into 0:41:04.320 --> 0:41:08.680 z bosons, right because z's also interact with electrons impositron. 0:41:08.800 --> 0:41:11.520 So even if there weren't a single electron or positron 0:41:11.560 --> 0:41:14.239 in the universe, a photon could still turn into a 0:41:14.320 --> 0:41:17.080 z boson. And in the same way, as long as 0:41:17.120 --> 0:41:20.319 there's the possibility for some virtual particle that connects these 0:41:20.320 --> 0:41:23.480 two forces to exist, then photons could turn into dark 0:41:23.480 --> 0:41:26.840 photons and vice versa. And that's kind of our only 0:41:26.880 --> 0:41:29.799 hope of seeing this dark force directly. That's the best 0:41:29.840 --> 0:41:32.960 way to see these dark forces directly, exactly, And so 0:41:33.080 --> 0:41:35.440 people have built really cool experiments to try to like 0:41:35.880 --> 0:41:38.560 make this happen more often, try to like create the 0:41:38.640 --> 0:41:43.319 scenarios that would help induce dark photons to spontaneously turn 0:41:43.400 --> 0:41:47.040 into photons. They have these resonant cavities at Fermilab, for example, 0:41:47.160 --> 0:41:50.000 that should enhance the rate of this happening. If you 0:41:50.120 --> 0:41:52.719 like build something with the right shape and size, it 0:41:52.760 --> 0:41:56.319 creates a situation where this kind of spontaneous transformation is 0:41:56.320 --> 0:41:58.759 more likely to happen. And so they look for this 0:41:58.880 --> 0:42:02.360 kind of signature. Wait, that's being built right now, Like 0:42:02.400 --> 0:42:06.480 there are people building basically dark forest boxes. These things 0:42:06.520 --> 0:42:09.360 exist already and they are being run and they're just 0:42:09.400 --> 0:42:11.080 building them bigger and bigger. It's sort of like the 0:42:11.080 --> 0:42:13.000 way people are looking for a dark matter. They look 0:42:13.040 --> 0:42:15.480 in these containers underground, and they started with small ones, 0:42:15.480 --> 0:42:17.480 and then they're making bigger and bigger and bigger ones. 0:42:17.719 --> 0:42:20.359 Nobody's seeing a dark photon yet, but they're hoping as 0:42:20.360 --> 0:42:23.760 they make these cavities more precise and larger to induce 0:42:23.800 --> 0:42:27.200 a dark photon to turn into a normal photon. Cool, 0:42:27.360 --> 0:42:29.160 and how else can you look for these? Another way 0:42:29.160 --> 0:42:32.000 to look for these is to look for particles appearing 0:42:32.040 --> 0:42:34.480 where they shouldn't be. So one of my favorite kind 0:42:34.480 --> 0:42:37.520 of experiments, it's called a beam dump experiment, where you 0:42:37.560 --> 0:42:39.479 take a particle beam you were using for something else 0:42:39.520 --> 0:42:41.480 and you dump it, meaning you just like shoot it 0:42:41.480 --> 0:42:45.000 into a huge block of concrete or into a mountain side, 0:42:45.280 --> 0:42:47.000 just because you know, it's got to go somewhere. You 0:42:47.000 --> 0:42:50.080 don't want to like sprayed over the neighborhood because it's dangerous, right, 0:42:50.120 --> 0:42:51.840 just shoot it through the earth at people on the 0:42:51.880 --> 0:42:54.120 other side of the earth. Is that what you're saying, Yeah, exactly. 0:42:54.520 --> 0:42:56.319 And so Sho didn't do a mountain. It was on 0:42:56.360 --> 0:42:59.799 the other side of Daniel. It's not California, is I'm 0:43:00.000 --> 0:43:02.480 to have to look that up. But if you shoot 0:43:02.520 --> 0:43:05.239 this particle beam into a mountain, for example, and then 0:43:05.280 --> 0:43:08.200 you put a particle detector on the other side of 0:43:08.280 --> 0:43:10.919 the mountain, none of the particles should make it through 0:43:10.920 --> 0:43:14.319 the mountain, but you might see particles appearing in your 0:43:14.360 --> 0:43:16.920 detector on the other side of the mountain, because dark 0:43:17.000 --> 0:43:19.960 photons might make it through the mountain because they basically 0:43:20.000 --> 0:43:22.600 see the mountain is invisible as transparent. The ideas if 0:43:22.640 --> 0:43:27.600 your beam sometimes occasionally produces dark photons, those dark photons 0:43:27.600 --> 0:43:30.359 would make it through the mountain. And so essentially it's 0:43:30.480 --> 0:43:33.520 like looking for light shining through walls or I see 0:43:33.520 --> 0:43:35.359 so many the ideas that you send this beam out 0:43:35.360 --> 0:43:38.520 into the mountain, some of it turns into dark photons, 0:43:38.760 --> 0:43:42.040 and then somehow it turns back into regular photons before 0:43:42.080 --> 0:43:44.640 it hits your detector. Yeah, that's exactly right. And so 0:43:44.800 --> 0:43:48.399 you're hoping that sometimes those dark photons turned back into 0:43:48.440 --> 0:43:51.040 normal photons. So you're assuming a lot of things here. 0:43:51.080 --> 0:43:54.319 You're assuming that maybe sometimes dark photons are created in 0:43:54.320 --> 0:43:57.640 your beam, and that sometimes they turn back into normal photons. Right, 0:43:57.640 --> 0:43:59.799 But if they turn back into regular photons, how would 0:43:59.840 --> 0:44:02.120 you know they turned into dark photons in the middle. Yeah, 0:44:02.160 --> 0:44:04.160 you wouldn't know for sure. You would just know that 0:44:04.440 --> 0:44:07.680 something passed through the mountain that typically shouldn't be able to. 0:44:07.920 --> 0:44:10.839 So you calculate, like how often should particles be able 0:44:10.840 --> 0:44:14.399 to pass through the mountain and turn into photons? And 0:44:14.520 --> 0:44:17.319 if that happens more often than you expect, then you 0:44:17.320 --> 0:44:20.040 know there's something else and new there, maybe a dark photon, 0:44:20.120 --> 0:44:22.399 maybe something else. But you know, that's often the case 0:44:22.440 --> 0:44:25.680 with particle physics. We find something new, we're not exactly 0:44:25.719 --> 0:44:28.480 sure what it is, and then we study it in detail, 0:44:28.520 --> 0:44:30.839 we try to characterize exactly what it is, just like 0:44:31.040 --> 0:44:33.719 with the Higgs boson. First thing, we saw some new 0:44:33.760 --> 0:44:36.960 particle decaying into two photons, and we weren't sure is 0:44:37.000 --> 0:44:38.759 this the Higgs boson or is it something else? We 0:44:38.760 --> 0:44:41.200 didn't expect, and over decades of study we sort of 0:44:41.239 --> 0:44:43.160 pinned down what it must be because of all of 0:44:43.200 --> 0:44:45.880 its behaviors. I see, it's like, the only way it 0:44:45.880 --> 0:44:48.839 could have made it through the mountain to and out 0:44:48.880 --> 0:44:51.760 into California to hit us it was if it turned 0:44:51.760 --> 0:44:56.520 into something invisible like dark photons somewhere in the middle. 0:44:56.760 --> 0:44:58.719 Otherwise it wouldn't have made it through. Exactly, I have 0:44:58.840 --> 0:45:01.120 to phase through the mountain by turning into something that 0:45:01.160 --> 0:45:04.040 doesn't interact with mountains. All right, cool, Well, what are 0:45:04.120 --> 0:45:05.800 some other ways we might be able to see these 0:45:05.880 --> 0:45:08.400 dark forces? A lot of the other experiments are very similar. 0:45:08.680 --> 0:45:13.279 There's one at CERN called Phaser Forward Search Experiment. It's 0:45:13.320 --> 0:45:16.520 a pretty tortured acronym, but a really cool idea for 0:45:17.480 --> 0:45:19.720 I don't even know what is there an A actually 0:45:19.760 --> 0:45:23.080 in the name, there's an A and forward and an 0:45:23.239 --> 0:45:27.760 R experiment. Oh man, it's a really cool idea because 0:45:27.800 --> 0:45:31.400 they're taking an already existing experiment Atlas where we collide 0:45:31.400 --> 0:45:35.040 protons together and they're wondering like maybe dark photons are 0:45:35.040 --> 0:45:37.680 created and shoot down the beam. So they built a 0:45:37.719 --> 0:45:41.160 detector like really far down along the beam past where 0:45:41.160 --> 0:45:44.000 the collisions happen to see if maybe dark photons are 0:45:44.040 --> 0:45:47.040 created in those collisions and then fly along the beam 0:45:47.160 --> 0:45:49.680 and then turn into something that they can see sort 0:45:49.680 --> 0:45:53.319 of downstream. So they added this little bit to the 0:45:53.360 --> 0:45:55.960 detector that can do something totally novel and new. It's 0:45:55.960 --> 0:45:58.240 actually led by a team here at you see Irvine, 0:45:58.360 --> 0:46:00.480 m M, I see. But we don't actually know if 0:46:00.560 --> 0:46:03.440 dark matter can switch back and forth that easily, right, 0:46:03.640 --> 0:46:05.640 We don't know. And again, it could be that dark 0:46:05.640 --> 0:46:09.160 matter is only some inert particle that feels gravity and 0:46:09.200 --> 0:46:11.319 nothing else and there are no dark forces and no 0:46:11.440 --> 0:46:14.360 way to interact. It could also be that dark matter 0:46:14.480 --> 0:46:17.640 does feel some new dark force, but can only interact 0:46:17.680 --> 0:46:20.359 with itself, and none of those dark forces can ever 0:46:20.520 --> 0:46:24.480 turn into normal matter or normal photons. Here, we're just guessing. 0:46:24.480 --> 0:46:27.640 We're trying to like study the various possibilities in the 0:46:27.719 --> 0:46:32.080 various ways that those possibilities might manifesto well, And so 0:46:32.160 --> 0:46:33.960 what does it all mean? Do you think we will 0:46:34.000 --> 0:46:37.399 find it has interactions with itself or do you think 0:46:37.440 --> 0:46:40.279 it just represents this whole part of the universe that 0:46:40.320 --> 0:46:42.759 we will never be able to see or touch or 0:46:42.800 --> 0:46:45.319 even confirm that it's there. You know, like we could 0:46:45.320 --> 0:46:50.120 be swimming in dark rubber duckies and never ever ever, Yeah, 0:46:50.239 --> 0:46:52.120 part of it comes down to what you think is 0:46:52.160 --> 0:46:54.440 more natural. Does it make sense to you to have 0:46:54.560 --> 0:46:57.920 a huge component of the universe be sort of simple 0:46:58.160 --> 0:47:00.960 and inert and not really doing any being interesting, or 0:47:01.000 --> 0:47:03.680 does this seem more natural for it to be complex 0:47:03.680 --> 0:47:06.680 and interactive the way that our matter is. Now, what 0:47:06.800 --> 0:47:09.239 I know is that the universe doesn't follow what we 0:47:09.360 --> 0:47:12.600 think is natural. Our conceptions of how the universe should 0:47:12.640 --> 0:47:14.680 work don't seem to be very well aligned with how 0:47:14.719 --> 0:47:17.440 it usually does work, and so I suspect there are 0:47:17.480 --> 0:47:19.880 some surprises out there. The other side of that question 0:47:19.960 --> 0:47:22.120 is what you asked, is might we ever be able 0:47:22.160 --> 0:47:24.160 to tell? And it could be that dark matter doesn't 0:47:24.160 --> 0:47:26.240 feel any of our forces, and none of these forces 0:47:26.239 --> 0:47:28.560 can talk to our forces, and we can never find 0:47:28.719 --> 0:47:31.840 these dark rubber duckies. But I have faith in physicists 0:47:31.880 --> 0:47:34.640 and engineers to come up with clever ways to probe 0:47:34.680 --> 0:47:37.799 these things, ways that we can't even today. Imagine kinds 0:47:37.840 --> 0:47:40.439 of experiments that people might think of in ten years 0:47:40.520 --> 0:47:43.200 or twenty years, experiments thought up by you know, clever 0:47:43.320 --> 0:47:46.560 Listeners to this podcast who aren't constrained by the kind 0:47:46.560 --> 0:47:49.359 of thinking that academic physicists have been trained to do. 0:47:49.560 --> 0:47:51.120 I think I know how you can do it, Daniel, 0:47:51.239 --> 0:47:54.960 Dark Chocolate collisions. You just gotta want it enough. You know, 0:47:55.320 --> 0:47:58.360 you have to really want it, because, as Yoda says, 0:47:58.400 --> 0:48:01.960 you know, wanting these to pain and pain needs to suffering, 0:48:02.680 --> 0:48:05.359 and suffering leads to the dark side, and so that's 0:48:05.360 --> 0:48:07.560 that's how you can get there faster. Maybe, Yeah, there 0:48:07.640 --> 0:48:09.640 is no try. I should just do it, that's right, 0:48:09.719 --> 0:48:15.120 Just I mean, do it? You should, yes, all right. 0:48:15.160 --> 0:48:16.439 I don't know why I didn't think of that before. 0:48:16.480 --> 0:48:18.040 I'm just gonna go do it right after we're done 0:48:18.080 --> 0:48:20.239 with this podcast, or not do it. I guess we're 0:48:20.239 --> 0:48:23.040 doing in the dark. Gosh, I'm so confused. But to me, 0:48:23.080 --> 0:48:25.840 it really touches on these deep mysteries of physics that 0:48:25.960 --> 0:48:28.520 we know the universe out there is telling stories that 0:48:28.560 --> 0:48:31.200 we haven't heard yet. We're desperate to hear those stories. 0:48:31.480 --> 0:48:33.760 We have hints that we know the shape of those stories, 0:48:33.760 --> 0:48:35.759 but we don't know any of the details yet, and 0:48:35.840 --> 0:48:37.480 I just hope that one day we'll be able to 0:48:37.520 --> 0:48:39.839 fill those in. Yeah, it's almost like there's a whole 0:48:39.960 --> 0:48:42.440 universe out there, sitting right in front of us that 0:48:42.520 --> 0:48:45.480 we have yet to discover, and that anyone listening to 0:48:45.520 --> 0:48:47.840 this could become part of that search. That's right. So 0:48:47.880 --> 0:48:50.560 there's plenty more of the universe to find out, and 0:48:50.560 --> 0:48:54.120 we desperately need new ideas. And whether the universe counts 0:48:54.120 --> 0:48:56.960 as dark chocolate or not, that's for other people to debate. 0:48:57.719 --> 0:49:00.440 That's right. And if you love white chocolate, take my apologies. 0:49:00.480 --> 0:49:03.440 I love all of them. You love listeners more than 0:49:03.480 --> 0:49:07.239 you love your chocolate, exactly, And if you eat white 0:49:07.280 --> 0:49:11.000 chocolate while listen to this podcast, I forgive you because 0:49:11.120 --> 0:49:13.440 he can't see your or feel you, so it doesn't 0:49:13.440 --> 0:49:17.799 matter to exactly. Please accept my dark apologies. All right, Well, 0:49:17.840 --> 0:49:20.239 we hope you enjoyed that. Thanks for joining us, See 0:49:20.239 --> 0:49:30.680 you next time. Thanks for listening, and remember that Daniel 0:49:30.719 --> 0:49:33.239 and Jorge Explain the Universe is a production of I 0:49:33.480 --> 0:49:36.919 Heart Radio. For more podcast for my heart Radio, visit 0:49:36.920 --> 0:49:40.440 the I heart Radio app, Apple Podcasts, or wherever you 0:49:40.520 --> 0:49:47.799 listen to your favorite shows. Yeah,