1 00:00:08,640 --> 00:00:12,360 Speaker 1: Sometimes my friends and my colleagues asked me, Daniel, why 2 00:00:12,360 --> 00:00:15,040 Speaker 1: do you give out your email address? How can you 3 00:00:15,120 --> 00:00:19,479 Speaker 1: promise to answer every listener email. Don't you worry that 4 00:00:19,560 --> 00:00:22,360 Speaker 1: you're gonna get too many emails or you might get 5 00:00:22,400 --> 00:00:25,360 Speaker 1: some weird questions you don't know how to answer. Well, 6 00:00:25,640 --> 00:00:29,160 Speaker 1: I'm a physicist at a public university. The public pays 7 00:00:29,280 --> 00:00:32,199 Speaker 1: my salary, and I feel like my job is to 8 00:00:32,360 --> 00:00:35,080 Speaker 1: help unravel the nature of the universe. And and this 9 00:00:35,120 --> 00:00:38,600 Speaker 1: is big to teach physics to people. Now, I teach 10 00:00:38,680 --> 00:00:41,320 Speaker 1: classes to students that you see Irvine, But I also 11 00:00:41,360 --> 00:00:43,720 Speaker 1: think that part of the job of being a publicly 12 00:00:43,760 --> 00:00:47,800 Speaker 1: paid physicist is to be available to the public. So 13 00:00:48,040 --> 00:00:51,120 Speaker 1: I want to teach everyone who wants to learn. So 14 00:00:51,200 --> 00:00:54,240 Speaker 1: I answer all these emails not just because it's my job, 15 00:00:54,280 --> 00:00:57,080 Speaker 1: but because I love doing it and I'm not afraid 16 00:00:57,120 --> 00:00:59,000 Speaker 1: that I won't know the answer to a question. Actually, 17 00:00:59,200 --> 00:01:01,280 Speaker 1: I love when I don't know the answer because it 18 00:01:01,320 --> 00:01:19,600 Speaker 1: gives me an excuse to go learn more about it. Hi, 19 00:01:19,920 --> 00:01:23,039 Speaker 1: I'm Daniel. I'm a particle physicist, and I really do 20 00:01:23,360 --> 00:01:27,600 Speaker 1: love answering random physics questions from the Internet. And welcome 21 00:01:27,640 --> 00:01:31,000 Speaker 1: to the podcast. Daniel and Jorge Explain the Universe, a 22 00:01:31,120 --> 00:01:34,040 Speaker 1: production of I Heart Radio. You'll notice that today on 23 00:01:34,080 --> 00:01:37,240 Speaker 1: the podcast just Just Me Daniel, my friend and co 24 00:01:37,440 --> 00:01:40,240 Speaker 1: host Jorge can't be here today, so I'm taking the 25 00:01:40,240 --> 00:01:42,840 Speaker 1: opportunity to fill in and to talk about one of 26 00:01:42,880 --> 00:01:47,240 Speaker 1: my favorite things on the podcast, which is answering listener questions. 27 00:01:47,600 --> 00:01:50,680 Speaker 1: In our podcast, we try to explore all the amazing 28 00:01:50,760 --> 00:01:53,880 Speaker 1: questions about the universe, all the things that science has 29 00:01:53,920 --> 00:01:56,400 Speaker 1: figured out, and all the things that science has yet 30 00:01:56,560 --> 00:01:59,720 Speaker 1: to answer, and all those things that science is working on. 31 00:02:00,120 --> 00:02:03,520 Speaker 1: Those come from questions. Those are the questions asked by 32 00:02:03,600 --> 00:02:06,960 Speaker 1: scientists who are paid to do science, and by scientists 33 00:02:07,240 --> 00:02:09,680 Speaker 1: like you who sit at home or sit in your 34 00:02:09,680 --> 00:02:12,560 Speaker 1: car and just wonder about the nature of the universe. 35 00:02:13,040 --> 00:02:15,720 Speaker 1: All of that is doing science, which makes all of 36 00:02:15,840 --> 00:02:20,280 Speaker 1: us scientists. And that's why I love answering questions from listeners, 37 00:02:20,480 --> 00:02:23,360 Speaker 1: because it means I get to include more people in 38 00:02:23,360 --> 00:02:26,919 Speaker 1: this circle of science. So when Jorge is not around today, 39 00:02:27,040 --> 00:02:29,959 Speaker 1: I'm gonna use this opportunity to dig back into our 40 00:02:30,000 --> 00:02:33,560 Speaker 1: backlog of listener questions. I got a lot of wonderful 41 00:02:33,639 --> 00:02:36,120 Speaker 1: questions I can answer sort of quickly over email, but 42 00:02:36,240 --> 00:02:38,960 Speaker 1: sometimes people send me questions that take a little bit 43 00:02:39,000 --> 00:02:41,960 Speaker 1: more explanation and that I think everybody on the podcast 44 00:02:42,160 --> 00:02:45,079 Speaker 1: might like hearing the answer to. So I saved those 45 00:02:45,160 --> 00:02:48,440 Speaker 1: up for listener Questions episodes, but I'll admit we have 46 00:02:48,480 --> 00:02:50,720 Speaker 1: a bit of a backlog, and so I'm gonna dig 47 00:02:50,800 --> 00:02:54,400 Speaker 1: into some of those today on the program. So today 48 00:02:54,520 --> 00:03:03,359 Speaker 1: on the program, we'll be answering listener questions from the backlog. 49 00:03:03,720 --> 00:03:06,120 Speaker 1: And I love these questions because they really show me 50 00:03:06,280 --> 00:03:09,400 Speaker 1: what people are thinking. I mean, people write me questions, 51 00:03:09,400 --> 00:03:12,080 Speaker 1: but they're not simple questions like hey, tell me about 52 00:03:12,160 --> 00:03:16,200 Speaker 1: black holes or things that are well discussed other places 53 00:03:16,240 --> 00:03:19,080 Speaker 1: on the internet, like the double slit experiment that you 54 00:03:19,080 --> 00:03:22,360 Speaker 1: can just google and find a really wonderful explanation. People 55 00:03:22,400 --> 00:03:25,000 Speaker 1: write to me after they've done some thinking. They have 56 00:03:25,160 --> 00:03:27,760 Speaker 1: some topic they're trying to understand, they're trying to bring 57 00:03:27,800 --> 00:03:30,040 Speaker 1: it together in their minds, and there's something that just 58 00:03:30,160 --> 00:03:34,160 Speaker 1: doesn't quite fit. And that's really what physics is. Physics 59 00:03:34,240 --> 00:03:37,760 Speaker 1: is trying to apply your mental model to the universe 60 00:03:37,800 --> 00:03:40,720 Speaker 1: and seeing doesn't make sense. And often what you try 61 00:03:40,760 --> 00:03:43,200 Speaker 1: to do is sort of climb the same mountain from 62 00:03:43,240 --> 00:03:46,400 Speaker 1: two directions. Start from one side and then later start 63 00:03:46,440 --> 00:03:48,200 Speaker 1: from the other side and see if you can get 64 00:03:48,280 --> 00:03:50,960 Speaker 1: to the same place. And that's wonderful and I love 65 00:03:51,000 --> 00:03:54,320 Speaker 1: helping people sort of navigate the mountain of physics and 66 00:03:54,360 --> 00:03:57,640 Speaker 1: get them to the top. It helps me also because 67 00:03:57,680 --> 00:04:00,120 Speaker 1: I've climbed the mountain from one direction and somebody else 68 00:04:00,240 --> 00:04:02,520 Speaker 1: is trying it from another way, and I wonder, why 69 00:04:02,560 --> 00:04:05,040 Speaker 1: doesn't that work, or is that possible? Or can you 70 00:04:05,080 --> 00:04:08,240 Speaker 1: figure it out using those ideas? And sometimes I have 71 00:04:08,320 --> 00:04:10,480 Speaker 1: to sort of back up and try to understand where 72 00:04:10,520 --> 00:04:13,280 Speaker 1: did somebody go wrong, and then help them navigate around 73 00:04:13,280 --> 00:04:15,440 Speaker 1: that crevass or whatever so they can get to the 74 00:04:15,480 --> 00:04:18,320 Speaker 1: top and they can get that understanding. But for me 75 00:04:18,360 --> 00:04:21,040 Speaker 1: it's a great mental exercise. It lets me go off 76 00:04:21,080 --> 00:04:23,240 Speaker 1: and learn about all sorts of stuff that I don't 77 00:04:23,279 --> 00:04:26,320 Speaker 1: get to think about necessarily on an everyday basis. And 78 00:04:26,360 --> 00:04:29,320 Speaker 1: that's why I'm excited to announce something else new, which 79 00:04:29,360 --> 00:04:32,679 Speaker 1: is my public office hours. If you have a question 80 00:04:32,720 --> 00:04:35,080 Speaker 1: about physics, but you don't really like writing emails or 81 00:04:35,080 --> 00:04:38,240 Speaker 1: sending me tweets, come to my public office hours where 82 00:04:38,279 --> 00:04:40,920 Speaker 1: you can come chat with me and ask me questions 83 00:04:40,960 --> 00:04:45,000 Speaker 1: about physics or just listen while other people ask me questions. 84 00:04:45,160 --> 00:04:49,919 Speaker 1: I'll have my first one December twenty at nine am 85 00:04:50,000 --> 00:04:54,960 Speaker 1: California time. That's noon Eastern time and six pm in Europe. 86 00:04:55,279 --> 00:04:59,680 Speaker 1: So that's December four, twenty at nine a m. California time. 87 00:05:00,120 --> 00:05:03,520 Speaker 1: And you can find the location online for connecting. If 88 00:05:03,520 --> 00:05:06,440 Speaker 1: you go to my website to site dot U c 89 00:05:06,880 --> 00:05:10,200 Speaker 1: I dot E d U slash Daniel, or maybe you 90 00:05:10,240 --> 00:05:12,599 Speaker 1: should just google it, you can find a link to it. 91 00:05:12,839 --> 00:05:15,159 Speaker 1: So come and join me at my public office hours. 92 00:05:15,360 --> 00:05:18,680 Speaker 1: Ask me a question about black holes, or about tiny particles, 93 00:05:18,760 --> 00:05:21,520 Speaker 1: or about whatever is in your head that you can't 94 00:05:21,600 --> 00:05:25,200 Speaker 1: quite figure out about the universe. All right, so I'm 95 00:05:25,200 --> 00:05:28,680 Speaker 1: excited to answer some listener questions. Let's dig in. First, 96 00:05:28,720 --> 00:05:32,400 Speaker 1: we have a question about dark matter. Hi, Daniel and Jorge. 97 00:05:32,440 --> 00:05:35,760 Speaker 1: It's Rocky from California. I have a question about dark matter. 98 00:05:36,240 --> 00:05:38,640 Speaker 1: How can dark matter exist if it cannot feel the 99 00:05:38,680 --> 00:05:42,040 Speaker 1: strong force. I'm assuming dark matter is made up of atoms, 100 00:05:42,080 --> 00:05:44,000 Speaker 1: and if that is the case, then how can it 101 00:05:44,040 --> 00:05:46,279 Speaker 1: not feel the strong force when the strong force is 102 00:05:46,440 --> 00:05:49,359 Speaker 1: necessary to keep the protons and neutrons in the nucleus 103 00:05:49,400 --> 00:05:52,320 Speaker 1: of an atom together. Thanks in advance, all right. So 104 00:05:52,360 --> 00:05:55,599 Speaker 1: that's a great question from Rocky from California. He wants 105 00:05:55,640 --> 00:05:58,279 Speaker 1: to know how can dark matter exist if it can't 106 00:05:58,279 --> 00:06:01,040 Speaker 1: feel a strong force, because he thinks the strong forces 107 00:06:01,120 --> 00:06:04,560 Speaker 1: what's necessary to hold matter together. Now, first of all, 108 00:06:04,600 --> 00:06:07,880 Speaker 1: you're totally right that protons and neutrons are held together 109 00:06:08,000 --> 00:06:10,320 Speaker 1: by the strong force. They're made out of tiny little 110 00:06:10,360 --> 00:06:13,120 Speaker 1: quarks and they're bound together by gluons, and it's a 111 00:06:13,160 --> 00:06:16,960 Speaker 1: strong force to keep these mostly positively charged particles together 112 00:06:17,240 --> 00:06:19,680 Speaker 1: into the protons and neutrons that are familiar for us 113 00:06:19,720 --> 00:06:23,960 Speaker 1: and are also the building blocks of atoms. However, dark 114 00:06:24,040 --> 00:06:27,400 Speaker 1: matter is not made out of atoms. Dark matter is 115 00:06:27,440 --> 00:06:31,120 Speaker 1: made out of something else, something weird, something new, something 116 00:06:31,160 --> 00:06:33,919 Speaker 1: that is not the same kind of stuff that makes 117 00:06:33,920 --> 00:06:36,920 Speaker 1: of our particles. How do we know that? How can 118 00:06:37,000 --> 00:06:40,160 Speaker 1: we possibly know what dark matter is not made out 119 00:06:40,160 --> 00:06:42,920 Speaker 1: of if we don't know what it is made out of. Well, 120 00:06:42,960 --> 00:06:44,920 Speaker 1: we can know that because we can see what dark 121 00:06:44,960 --> 00:06:48,400 Speaker 1: matter can do and what it can't do. For example, 122 00:06:48,920 --> 00:06:52,320 Speaker 1: everything that's made out of atoms has a temperature, and 123 00:06:52,440 --> 00:06:57,279 Speaker 1: it glows. Even really really cold stuff glows in the infrared, 124 00:06:57,360 --> 00:06:59,800 Speaker 1: and really really hot stuff glows in the visible light. 125 00:07:00,120 --> 00:07:02,479 Speaker 1: Like the sun or a rock in front of you. 126 00:07:03,040 --> 00:07:06,719 Speaker 1: Everything that is made out of atoms has electrons and 127 00:07:06,800 --> 00:07:11,040 Speaker 1: has temperatures and eventually will emit light. Also, everything that's 128 00:07:11,080 --> 00:07:14,080 Speaker 1: made out of atoms has electrons in it, which means 129 00:07:14,120 --> 00:07:17,240 Speaker 1: that it reacts to light either emits light on its 130 00:07:17,240 --> 00:07:20,960 Speaker 1: own or reflects light, or it absorbs light. And dark matter, 131 00:07:21,040 --> 00:07:23,800 Speaker 1: we know does not interact with light. That's why we 132 00:07:23,880 --> 00:07:26,480 Speaker 1: call it dark. In fact, we have no way to 133 00:07:26,640 --> 00:07:30,560 Speaker 1: interact with dark matter other than gravity. Remember that we've 134 00:07:30,560 --> 00:07:33,400 Speaker 1: discovered dark matter because we've seen that it's there to 135 00:07:33,520 --> 00:07:36,840 Speaker 1: hold galaxies together as they spin around really really fast, 136 00:07:37,080 --> 00:07:40,720 Speaker 1: where otherwise their stars would be thrown into intergalactic space. 137 00:07:41,040 --> 00:07:43,320 Speaker 1: And we know that dark matter exists because we've seen 138 00:07:43,360 --> 00:07:47,080 Speaker 1: these gravitational effects on the early universe. It's created these 139 00:07:47,120 --> 00:07:50,080 Speaker 1: gravitational wells where normal matter has sort of fallen in, 140 00:07:50,360 --> 00:07:53,120 Speaker 1: and that seated the production of stars and galaxies in 141 00:07:53,120 --> 00:07:56,160 Speaker 1: the early universe. Without the gravitational force of dark matter, 142 00:07:56,440 --> 00:07:59,640 Speaker 1: we wouldn't have the universe that we see today. Galaxies 143 00:07:59,640 --> 00:08:02,400 Speaker 1: would have it can billions of years longer to form, 144 00:08:02,640 --> 00:08:05,480 Speaker 1: and we can also study how dark matter moves around 145 00:08:05,520 --> 00:08:08,560 Speaker 1: the universe. We know that dark matter is fairly cold. 146 00:08:08,640 --> 00:08:12,200 Speaker 1: It doesn't move very very fast. Dark matter moods very fast. 147 00:08:12,200 --> 00:08:14,360 Speaker 1: It would have spread out more smoothly in the early 148 00:08:14,440 --> 00:08:16,760 Speaker 1: universe and we would see a universe with a very 149 00:08:16,880 --> 00:08:20,400 Speaker 1: different structure. So we think that dark matter is fairly cold, 150 00:08:20,480 --> 00:08:23,600 Speaker 1: it's fairly slow moving, and that allows it to clump 151 00:08:23,720 --> 00:08:27,040 Speaker 1: gravitationally and to seed all the structure that we see 152 00:08:27,160 --> 00:08:29,560 Speaker 1: in the universe. So we know a lot about how 153 00:08:29,680 --> 00:08:32,600 Speaker 1: dark matter moves and what it is, but we don't 154 00:08:32,640 --> 00:08:35,720 Speaker 1: really know what it's made out of, right, We don't 155 00:08:35,760 --> 00:08:37,839 Speaker 1: know if it's made out of a particle. We don't 156 00:08:37,880 --> 00:08:40,360 Speaker 1: know if it's made out of several particles. We think 157 00:08:40,400 --> 00:08:43,839 Speaker 1: of it's sort of as like a pressureless fluid because 158 00:08:43,880 --> 00:08:46,400 Speaker 1: we don't think there's anything sort of holding it together 159 00:08:46,600 --> 00:08:50,439 Speaker 1: other than its gravity. Rocky asked about how dark matter 160 00:08:50,520 --> 00:08:52,840 Speaker 1: is held together without the strong force. Well, it's not 161 00:08:52,960 --> 00:08:56,440 Speaker 1: really held together except for the gravity. And that's why 162 00:08:56,520 --> 00:08:59,600 Speaker 1: dark matter, even though there's more of it than normal matter, 163 00:09:00,040 --> 00:09:03,320 Speaker 1: it's much fluffier. It's much more diffused. Like if you 164 00:09:03,360 --> 00:09:06,680 Speaker 1: look at the distribution of stuff in our galaxy, the 165 00:09:06,760 --> 00:09:08,960 Speaker 1: stuff that is normal matter that's made out of me 166 00:09:09,240 --> 00:09:12,440 Speaker 1: and you, and hamsters and stars and everything else that 167 00:09:12,559 --> 00:09:15,280 Speaker 1: we see in the universe. All the visible matter is 168 00:09:15,320 --> 00:09:18,160 Speaker 1: made out of atoms, and it clumps up very very tightly, right, 169 00:09:18,520 --> 00:09:21,439 Speaker 1: stars and rocks and stuff. Well, dark matter, we think, 170 00:09:21,559 --> 00:09:24,800 Speaker 1: is much more diffuse. Even though there's more dark matter 171 00:09:24,840 --> 00:09:27,760 Speaker 1: than everything else, it's really spread out like a volume 172 00:09:27,800 --> 00:09:30,600 Speaker 1: of space. The size of the Earth has only about 173 00:09:30,640 --> 00:09:33,800 Speaker 1: a squirrel's mass of dark matter. That's because the dark 174 00:09:33,800 --> 00:09:36,679 Speaker 1: matter is not clumped together the way planets and stars are. 175 00:09:36,679 --> 00:09:40,360 Speaker 1: It's spread out everywhere, and it extends far beyond where 176 00:09:40,360 --> 00:09:43,720 Speaker 1: the visible galaxy ends. If you could see dark matter, 177 00:09:43,760 --> 00:09:48,199 Speaker 1: you would see a huge halo surrounding the entire galaxy. 178 00:09:48,280 --> 00:09:50,960 Speaker 1: And so that tells you that dark matter isn't tightly 179 00:09:51,040 --> 00:09:54,600 Speaker 1: held together by a strong force the way protons are 180 00:09:54,640 --> 00:09:57,280 Speaker 1: and the way neutrons are. It's really a very different 181 00:09:57,400 --> 00:10:00,600 Speaker 1: kind of stuff. And we know pretty well that it's 182 00:10:00,640 --> 00:10:03,680 Speaker 1: not made out of quarks, not only because we know 183 00:10:03,760 --> 00:10:06,120 Speaker 1: that doesn't build atoms which give off light, and it 184 00:10:06,160 --> 00:10:09,080 Speaker 1: doesn't have that kind of interaction, but because of other 185 00:10:09,160 --> 00:10:12,520 Speaker 1: really fascinating studies. For example, we've looked at the very 186 00:10:12,600 --> 00:10:16,920 Speaker 1: early universe, how atoms were formed, what made helium and 187 00:10:16,960 --> 00:10:19,640 Speaker 1: what made hydrogen, what made any lithium and this kind 188 00:10:19,679 --> 00:10:23,160 Speaker 1: of stuff, And the fraction you get of helium or 189 00:10:23,400 --> 00:10:28,000 Speaker 1: hydrogen or lithium depends really sensitively on the density of 190 00:10:28,120 --> 00:10:30,959 Speaker 1: quarks in the early universe. If you had a lot 191 00:10:31,080 --> 00:10:33,880 Speaker 1: more quarks sort of per cubic meter, then you've got 192 00:10:33,920 --> 00:10:36,680 Speaker 1: more heavy elements, and if you had fewer quarks per 193 00:10:36,720 --> 00:10:39,839 Speaker 1: cubic meter, you've got fewer heavy elements. And we can 194 00:10:39,920 --> 00:10:44,040 Speaker 1: measure the ratio of hydrogen to helium to lithium in 195 00:10:44,080 --> 00:10:47,080 Speaker 1: the early universe, and that tells us essentially what the 196 00:10:47,160 --> 00:10:51,000 Speaker 1: quark density was, how many quarks were around, and then 197 00:10:51,000 --> 00:10:53,200 Speaker 1: we can account for those. We can say, well, if 198 00:10:53,200 --> 00:10:56,160 Speaker 1: there were this many quarks around, then did they turn 199 00:10:56,200 --> 00:10:58,200 Speaker 1: into all the stars and planets and stuff that we 200 00:10:58,280 --> 00:11:01,480 Speaker 1: see and mostly that at up. So that tells us 201 00:11:01,520 --> 00:11:04,640 Speaker 1: basically that there aren't left over quarks from the early 202 00:11:04,720 --> 00:11:07,360 Speaker 1: universe that got turned into dark matter. So we know 203 00:11:07,480 --> 00:11:10,080 Speaker 1: that dark matter is not made out of quarks and 204 00:11:10,080 --> 00:11:13,080 Speaker 1: electrons and all this kind of familiar stuff. It has 205 00:11:13,120 --> 00:11:16,360 Speaker 1: to be made out of something different. And there's also 206 00:11:16,440 --> 00:11:20,360 Speaker 1: confirming evidence from the cosmic microwave background radiation that tells 207 00:11:20,440 --> 00:11:23,840 Speaker 1: us how different kinds of matter sort of slashed around 208 00:11:23,880 --> 00:11:26,400 Speaker 1: in the early universe. There's a kind of matter that 209 00:11:26,480 --> 00:11:29,720 Speaker 1: we're familiar with that we're made out of, interacts with itself, 210 00:11:29,720 --> 00:11:32,920 Speaker 1: it ties itself together very tightly, So it slashed around 211 00:11:32,960 --> 00:11:35,800 Speaker 1: in a different way from dark matter, which seems to 212 00:11:35,840 --> 00:11:39,480 Speaker 1: have no interaction other than gravity. And so it slashed 213 00:11:39,480 --> 00:11:42,560 Speaker 1: around differently and led to sort of different distributions matter 214 00:11:42,559 --> 00:11:44,800 Speaker 1: in the early universe, and we can see those in 215 00:11:44,840 --> 00:11:48,320 Speaker 1: the wiggles of the cosmic microwave background radiation. So the 216 00:11:48,360 --> 00:11:51,160 Speaker 1: picture is pretty clear and from lots of different directions. 217 00:11:51,320 --> 00:11:54,600 Speaker 1: It tells us two things. One that dark matter is 218 00:11:54,679 --> 00:11:56,400 Speaker 1: not made out of the kind of matter that we're 219 00:11:56,400 --> 00:11:58,800 Speaker 1: familiar with, the kind of matter you need to build 220 00:11:58,800 --> 00:12:01,880 Speaker 1: atoms where the strong un force holds itself together, and 221 00:12:01,920 --> 00:12:06,000 Speaker 1: that dark matter only feels gravity. There's no other interaction 222 00:12:06,240 --> 00:12:10,120 Speaker 1: that is participating in. However, there is a limit to 223 00:12:10,120 --> 00:12:13,040 Speaker 1: our knowledge, right We can tell that dark matter doesn't 224 00:12:13,080 --> 00:12:16,079 Speaker 1: have any very powerful interactions the kind that would help 225 00:12:16,120 --> 00:12:19,320 Speaker 1: it clump together and form objects and this kind of stuff, 226 00:12:19,440 --> 00:12:22,120 Speaker 1: But we can never really say that there's no interaction. 227 00:12:22,160 --> 00:12:24,520 Speaker 1: There might be there and just sort of fairly weak. 228 00:12:24,960 --> 00:12:27,760 Speaker 1: And people recently have been studying this in great detail 229 00:12:27,800 --> 00:12:30,680 Speaker 1: and trying to answer the question, is there some other 230 00:12:30,840 --> 00:12:34,000 Speaker 1: kind of force, some new kind of interaction that only 231 00:12:34,120 --> 00:12:38,400 Speaker 1: dark matter feels where dark matter can feel this with itself. Now, 232 00:12:38,440 --> 00:12:41,280 Speaker 1: if it exists, it can't be very very powerful. Otherwise 233 00:12:41,280 --> 00:12:43,800 Speaker 1: it would help dark matter pull together and it wouldn't 234 00:12:43,800 --> 00:12:46,400 Speaker 1: be as diffused. But it still might be there. There 235 00:12:46,480 --> 00:12:48,720 Speaker 1: might be some kind of new force that helps dark 236 00:12:48,760 --> 00:12:52,760 Speaker 1: matter pulled together or interact in some gentle way. So, 237 00:12:53,160 --> 00:12:56,240 Speaker 1: if dark matter is not made out of quarks, then 238 00:12:56,400 --> 00:12:59,120 Speaker 1: what is it made out of? What kind of stuff 239 00:12:59,200 --> 00:13:01,839 Speaker 1: is there out there in the universe that's not made 240 00:13:01,880 --> 00:13:03,880 Speaker 1: out of atoms and the kind of stuff that we 241 00:13:03,960 --> 00:13:07,640 Speaker 1: are familiar with. Well, it might be that dark matter 242 00:13:07,760 --> 00:13:11,040 Speaker 1: is made out of some new weird particle, something like 243 00:13:11,120 --> 00:13:15,480 Speaker 1: a whimp weakly interacting massive particle. It's just like a 244 00:13:15,520 --> 00:13:18,600 Speaker 1: generic idea, sort of like a placeholder idea. We don't 245 00:13:18,640 --> 00:13:21,760 Speaker 1: really have a great reason to believe that whimps exist, 246 00:13:22,160 --> 00:13:24,560 Speaker 1: but it's just sort of like an idea that fits 247 00:13:24,600 --> 00:13:27,000 Speaker 1: all the boxes, and so we go and we look 248 00:13:27,040 --> 00:13:29,440 Speaker 1: for it. And the basic idea is that maybe dark 249 00:13:29,480 --> 00:13:32,080 Speaker 1: matter is just made out of this new kind of particle, 250 00:13:32,440 --> 00:13:35,600 Speaker 1: a heavy, tiny little dot that carries a lot of mass, 251 00:13:35,679 --> 00:13:38,080 Speaker 1: and so it gives us the gravitational effects that we 252 00:13:38,120 --> 00:13:41,120 Speaker 1: see and has no other kinds of interactions except for 253 00:13:41,160 --> 00:13:45,800 Speaker 1: maybe some new weak interaction. When we say weakly interacting 254 00:13:45,840 --> 00:13:49,079 Speaker 1: massive particle, we don't mean weak like the week nuclear 255 00:13:49,120 --> 00:13:51,720 Speaker 1: force we're familiar with. We mean weak with a lower 256 00:13:51,800 --> 00:13:54,320 Speaker 1: case W. We mean sort of a feeble and not 257 00:13:54,600 --> 00:13:57,800 Speaker 1: very strong or not very powerful force. And it could 258 00:13:57,840 --> 00:14:01,240 Speaker 1: have some kind of self interaction. It would have some 259 00:14:01,320 --> 00:14:04,160 Speaker 1: kind of interaction with normal matter, but we don't think 260 00:14:04,200 --> 00:14:06,640 Speaker 1: that it feels the familiar strong force, the one that 261 00:14:06,679 --> 00:14:10,360 Speaker 1: binds atoms together. Then again, dark matter might be something 262 00:14:10,400 --> 00:14:13,160 Speaker 1: different from a whim. It might be several particles, and 263 00:14:13,200 --> 00:14:16,160 Speaker 1: maybe those particles can talk to each other and can 264 00:14:16,200 --> 00:14:20,240 Speaker 1: build interesting structures, but not very powerfully. Then again, there 265 00:14:20,280 --> 00:14:23,240 Speaker 1: are crazy ideas out there, like maybe dark matters made 266 00:14:23,240 --> 00:14:27,040 Speaker 1: out of primordial black holes, dense clumps of matter that 267 00:14:27,120 --> 00:14:30,640 Speaker 1: pulled together even before there were particles, even before there 268 00:14:30,680 --> 00:14:34,400 Speaker 1: were quirks pre corks, right in the very early universe. 269 00:14:34,680 --> 00:14:37,400 Speaker 1: If they were these spots of over density that collapsed 270 00:14:37,400 --> 00:14:41,000 Speaker 1: into little black holes. They might still be around. Nobody's 271 00:14:41,040 --> 00:14:43,440 Speaker 1: ever seen a primordial black hole, and so it's hard 272 00:14:43,480 --> 00:14:45,680 Speaker 1: to say that they explained the dark matter, but we 273 00:14:45,760 --> 00:14:48,560 Speaker 1: haven't been able to rule them out as well. And 274 00:14:48,600 --> 00:14:50,960 Speaker 1: then on the podcast last week, we talked about an 275 00:14:51,000 --> 00:14:55,240 Speaker 1: even crazier idea, which is maybe dark matters not even 276 00:14:55,360 --> 00:14:58,120 Speaker 1: made out of particles. Maybe it's made out of some 277 00:14:58,240 --> 00:15:01,720 Speaker 1: new kind of stuff, some un particle which isn't broken 278 00:15:01,800 --> 00:15:05,120 Speaker 1: up into little bits of definitive mass but acts really differently. 279 00:15:05,520 --> 00:15:08,640 Speaker 1: Remember that dark matter is much more prevalent in the 280 00:15:08,760 --> 00:15:13,000 Speaker 1: universe than normal matter. Our normal matter is actually quite abnormal. 281 00:15:13,400 --> 00:15:16,880 Speaker 1: So everything we've learned about normal matter might be generally 282 00:15:16,920 --> 00:15:19,240 Speaker 1: true about the rest of the universe, but it's a 283 00:15:19,280 --> 00:15:23,120 Speaker 1: bit dangerous to extrapolate from five per cent of the 284 00:15:23,240 --> 00:15:25,640 Speaker 1: energy density of the universe that's what normal matter is 285 00:15:25,640 --> 00:15:28,760 Speaker 1: responsible for to the rest of the universe. It might 286 00:15:28,960 --> 00:15:32,200 Speaker 1: very well be that we're making an error in generalizing 287 00:15:32,520 --> 00:15:34,360 Speaker 1: and the thinking that the rules that apply to this 288 00:15:34,400 --> 00:15:37,400 Speaker 1: five percent also apply to the rest of the universe. 289 00:15:37,440 --> 00:15:40,680 Speaker 1: So it could be something new, something weird, something totally 290 00:15:40,720 --> 00:15:43,760 Speaker 1: crazy and bonders and that's what makes it so exciting 291 00:15:43,800 --> 00:15:47,040 Speaker 1: because we know there's something out there new, something we 292 00:15:47,120 --> 00:15:50,120 Speaker 1: do not yet understand, something when we do figure it out, 293 00:15:50,440 --> 00:15:53,600 Speaker 1: is guaranteed to teach us something new about the universe. 294 00:15:53,720 --> 00:15:57,280 Speaker 1: And that's why physics is exciting. Alright, So thank you 295 00:15:57,360 --> 00:16:00,360 Speaker 1: to Rocky for that wonderful question about what a dark 296 00:16:00,400 --> 00:16:03,280 Speaker 1: matter feels a strong force. No, it cannot feel the 297 00:16:03,360 --> 00:16:06,000 Speaker 1: strong force. It's not made out of atoms. It's made 298 00:16:06,000 --> 00:16:09,160 Speaker 1: out of something new, something weird, which feels gravity, and 299 00:16:09,280 --> 00:16:12,680 Speaker 1: maybe something else, but we're not sure. All right, I 300 00:16:12,720 --> 00:16:15,400 Speaker 1: want to answer some more questions, but first it's time 301 00:16:15,440 --> 00:16:30,120 Speaker 1: to take a quick break. Okay, we're back and it's 302 00:16:30,160 --> 00:16:34,000 Speaker 1: just Nanuel today and I'm answering listener questions from the backlog. 303 00:16:34,400 --> 00:16:36,400 Speaker 1: Thank you to everybody who's sent in these questions, and 304 00:16:36,400 --> 00:16:39,360 Speaker 1: apologies if it's been several months since you sent them 305 00:16:39,360 --> 00:16:41,560 Speaker 1: in and you've been waiting for an answer. I hope 306 00:16:41,680 --> 00:16:44,880 Speaker 1: late is better than never. And this next question is 307 00:16:44,880 --> 00:16:47,240 Speaker 1: one of my favorites because it comes from a seven 308 00:16:47,320 --> 00:16:50,200 Speaker 1: year old listener. So thank you to everybody who listens 309 00:16:50,200 --> 00:16:52,920 Speaker 1: to the podcast, and extra thank you to everybody who 310 00:16:52,920 --> 00:16:56,400 Speaker 1: listens with your kids and answers their questions. And if 311 00:16:56,440 --> 00:16:58,800 Speaker 1: your kids ask you a question about physics and the 312 00:16:58,880 --> 00:17:01,600 Speaker 1: universe that you can't, just send it on to us 313 00:17:01,960 --> 00:17:04,800 Speaker 1: will take care of it for you. So here's a question, 314 00:17:04,800 --> 00:17:08,000 Speaker 1: for example from Bradley who's seven years old. Hi, my 315 00:17:08,119 --> 00:17:12,239 Speaker 1: name is Bradley Stuff. I am seven years old. I 316 00:17:12,280 --> 00:17:16,520 Speaker 1: am from out A Loma, California, and my question is 317 00:17:16,560 --> 00:17:20,399 Speaker 1: why do black holes slow down time? What a wonderful question, 318 00:17:20,440 --> 00:17:22,800 Speaker 1: a deep question about the nature of the universe and 319 00:17:22,920 --> 00:17:25,560 Speaker 1: some of the weirdest things in it. So Bradley is 320 00:17:25,600 --> 00:17:31,320 Speaker 1: wondering why do black holes slow down time? Now? Time 321 00:17:31,400 --> 00:17:34,679 Speaker 1: slowing down? Time dilation is sort of a famous result 322 00:17:34,720 --> 00:17:37,919 Speaker 1: in physics. Most people think of time dilation is what 323 00:17:38,000 --> 00:17:41,560 Speaker 1: happens when you move really, really fast on a spaceship, 324 00:17:41,960 --> 00:17:44,639 Speaker 1: and that's the famous result of one of Einstein's theories, 325 00:17:44,760 --> 00:17:48,639 Speaker 1: special relativity. Special relativity tells us what happens when you 326 00:17:48,720 --> 00:17:51,560 Speaker 1: move near the speed of light, and it shows us 327 00:17:51,560 --> 00:17:54,560 Speaker 1: how time and space are sort of enttangled. And it's 328 00:17:54,600 --> 00:17:57,520 Speaker 1: worth stepping through how it happens in special relativity because 329 00:17:57,520 --> 00:18:00,080 Speaker 1: there's a lesson for us there, and how it happens 330 00:18:00,080 --> 00:18:03,280 Speaker 1: in general relativity, which is what we'll need to talk 331 00:18:03,320 --> 00:18:06,600 Speaker 1: about why time slows down near a black hole. So 332 00:18:06,640 --> 00:18:09,120 Speaker 1: if you get on a spaceship and you travel really 333 00:18:09,160 --> 00:18:12,440 Speaker 1: really really fast compared to the Earth, then your time 334 00:18:12,600 --> 00:18:16,399 Speaker 1: doesn't actually seem to slow down for you. Remember that 335 00:18:16,560 --> 00:18:20,240 Speaker 1: speed is always relative, and time slows down for people 336 00:18:20,640 --> 00:18:24,399 Speaker 1: moving fast relative to an observer. So if you jump 337 00:18:24,440 --> 00:18:27,280 Speaker 1: on a spaceship and you travel really really fast, you 338 00:18:27,359 --> 00:18:30,760 Speaker 1: might expect to see your clocks slow down. Right wrong. 339 00:18:31,240 --> 00:18:34,640 Speaker 1: Clocks only slow down when they are moving. So if 340 00:18:34,680 --> 00:18:37,639 Speaker 1: you see a clock going really really fast, then it 341 00:18:37,720 --> 00:18:41,080 Speaker 1: slows down. If you're on a spaceship and you're holding 342 00:18:41,080 --> 00:18:43,680 Speaker 1: a clock, then it always ticks at the normal rate 343 00:18:44,000 --> 00:18:47,560 Speaker 1: relative to you, because it's not moving relative to you. 344 00:18:48,160 --> 00:18:51,960 Speaker 1: Time only seems to slow down for somebody else watching you, 345 00:18:52,200 --> 00:18:55,000 Speaker 1: for somebody else for whom that clock is moving really 346 00:18:55,000 --> 00:18:58,880 Speaker 1: really fast. So, for example, you jump on a spaceship, 347 00:18:59,160 --> 00:19:02,960 Speaker 1: you travel really really fast relative to the Earth. On 348 00:19:03,000 --> 00:19:05,720 Speaker 1: board the spaceship, you see the clock taking at a 349 00:19:05,760 --> 00:19:09,679 Speaker 1: normal rate. Somebody back on Earth using a telescope to 350 00:19:09,840 --> 00:19:12,880 Speaker 1: look at your clock, they will see your clock ticking slowly. 351 00:19:13,359 --> 00:19:16,840 Speaker 1: So your clock moves slowly only for somebody who sees 352 00:19:16,880 --> 00:19:21,680 Speaker 1: that clock moving quickly. Right, moving clocks run slow. If 353 00:19:21,680 --> 00:19:24,399 Speaker 1: you're holding your clock, you're on the spaceship, that doesn't 354 00:19:24,440 --> 00:19:27,440 Speaker 1: take slow for you. For you, time always moves at 355 00:19:27,480 --> 00:19:29,720 Speaker 1: the normal speed. And the thing that's sort of hard 356 00:19:29,760 --> 00:19:31,600 Speaker 1: to get your mind around there is that time is 357 00:19:31,600 --> 00:19:35,000 Speaker 1: not universal. Time moves differently on the spaceship than it 358 00:19:35,040 --> 00:19:37,320 Speaker 1: does for you. You have a clock, they have a clock, 359 00:19:37,359 --> 00:19:39,880 Speaker 1: and they don't agree. And that's one of the most 360 00:19:39,920 --> 00:19:43,120 Speaker 1: awesome things about relativity is that it unshackles us from 361 00:19:43,119 --> 00:19:46,000 Speaker 1: this sort of universal clock that tells us the whole 362 00:19:46,080 --> 00:19:49,119 Speaker 1: universe ticks forward at the same moment, and tells us 363 00:19:49,119 --> 00:19:52,159 Speaker 1: that how time flows depends on where you are and 364 00:19:52,240 --> 00:19:55,520 Speaker 1: on how fast you are moving. Now, general relativity adds 365 00:19:55,520 --> 00:19:58,359 Speaker 1: something to that. It says that how time ticks forward 366 00:19:58,440 --> 00:20:00,720 Speaker 1: doesn't just depend on where you are are and how 367 00:20:00,800 --> 00:20:04,480 Speaker 1: fast you're moving, but also what you are nearby. And 368 00:20:04,560 --> 00:20:07,240 Speaker 1: so Bradley's question is about a black hole, and he's 369 00:20:07,240 --> 00:20:10,000 Speaker 1: exactly right. If you took a spaceship, and even if 370 00:20:10,000 --> 00:20:12,480 Speaker 1: you never went very very fast, but if you went 371 00:20:12,720 --> 00:20:15,480 Speaker 1: near a black hole, say for example, you went in 372 00:20:15,480 --> 00:20:17,720 Speaker 1: to orbit around a black hole, you stay at a 373 00:20:17,760 --> 00:20:20,119 Speaker 1: safe distance. So you're not going to fall in. You 374 00:20:20,119 --> 00:20:22,159 Speaker 1: can orbit a black hole just the same way you 375 00:20:22,200 --> 00:20:25,280 Speaker 1: can orbit any other object with mass. If you're far 376 00:20:25,400 --> 00:20:27,560 Speaker 1: enough away and you're moving fast enough, and you don't 377 00:20:27,560 --> 00:20:30,200 Speaker 1: get too close to the event horizon, you can orbit 378 00:20:30,240 --> 00:20:32,600 Speaker 1: a black hole. Now, if you orbit a black hole 379 00:20:32,640 --> 00:20:35,000 Speaker 1: for a year and you're pretty close, you might come 380 00:20:35,040 --> 00:20:37,359 Speaker 1: back and discover that the rest of the universe time 381 00:20:37,400 --> 00:20:41,240 Speaker 1: has moved forward much more quickly. So time has slowed down. 382 00:20:41,600 --> 00:20:44,520 Speaker 1: On the spaceship. Time seemed to travel normally for you, 383 00:20:44,760 --> 00:20:47,840 Speaker 1: it was a year according to you. But somebody else 384 00:20:48,000 --> 00:20:50,720 Speaker 1: far away looking at your clock, what is seeing your 385 00:20:50,760 --> 00:20:54,479 Speaker 1: clock running slowly? Which means their clocks are running faster 386 00:20:54,880 --> 00:20:57,880 Speaker 1: than your clocks. And if you come back away from 387 00:20:57,880 --> 00:21:00,000 Speaker 1: the orbit in the black hole, you might have discovered 388 00:21:00,119 --> 00:21:02,560 Speaker 1: that a hundred years have passed on Earth, or a 389 00:21:02,640 --> 00:21:06,320 Speaker 1: thousand years or a million years, depending on how close 390 00:21:06,440 --> 00:21:09,560 Speaker 1: you came to the black hole. So Bradley's question is 391 00:21:09,720 --> 00:21:12,720 Speaker 1: why does that happen? You're not moving very fast. The 392 00:21:12,800 --> 00:21:16,600 Speaker 1: velocity from special relativity is not what's slowing down your clock. 393 00:21:16,960 --> 00:21:21,119 Speaker 1: Why is that time slows down near a black hole? Well, 394 00:21:21,119 --> 00:21:24,000 Speaker 1: the important thing to understand is that time doesn't slow 395 00:21:24,040 --> 00:21:27,240 Speaker 1: down just near black holes. It actually slows down near 396 00:21:27,359 --> 00:21:31,400 Speaker 1: any massive object. That's right. That means that time is slower, 397 00:21:31,440 --> 00:21:34,280 Speaker 1: for example, on the surface of the Earth than it 398 00:21:34,400 --> 00:21:37,240 Speaker 1: is a hundred meters above the Earth or a thousand 399 00:21:37,320 --> 00:21:40,080 Speaker 1: meters above the Earth. And this is precisely why general 400 00:21:40,119 --> 00:21:43,840 Speaker 1: relativity plays an important role in our global positioning system. 401 00:21:43,880 --> 00:21:46,200 Speaker 1: These satellites that over the Earth and tell us where 402 00:21:46,240 --> 00:21:48,240 Speaker 1: we are and what time it is, they have to 403 00:21:48,280 --> 00:21:51,800 Speaker 1: account for the fact that gravity changes time as you 404 00:21:51,840 --> 00:21:55,320 Speaker 1: move closer to the Earth. So any massive object will 405 00:21:55,359 --> 00:21:58,480 Speaker 1: slow down time. Now, black holes, of course slow down 406 00:21:58,480 --> 00:22:01,120 Speaker 1: time much more than anything else because they are much 407 00:22:01,160 --> 00:22:04,560 Speaker 1: more massive. But every massive object will slow down time, 408 00:22:04,600 --> 00:22:07,920 Speaker 1: the Sun, the Earth, even that huge boulder. You get 409 00:22:07,920 --> 00:22:11,040 Speaker 1: closer to that big boulder, time slows down a tiny 410 00:22:11,320 --> 00:22:14,480 Speaker 1: little bit. Now why is it, though, that being near 411 00:22:14,520 --> 00:22:17,560 Speaker 1: a massive object slows down time. The thing you have 412 00:22:17,640 --> 00:22:21,600 Speaker 1: to understand is that gravity here is best understood not 413 00:22:21,760 --> 00:22:24,480 Speaker 1: as a force, not that's something that's pulling on you, 414 00:22:24,720 --> 00:22:28,159 Speaker 1: but as the curving of space. It's changing what it 415 00:22:28,280 --> 00:22:31,520 Speaker 1: means to move in a straight line, for example. And 416 00:22:31,560 --> 00:22:33,960 Speaker 1: I think the best way to understand the relationship between 417 00:22:33,960 --> 00:22:36,960 Speaker 1: gravity is a force and gravity as a curvature of 418 00:22:37,000 --> 00:22:39,280 Speaker 1: the space we're moving through. Is to think about what 419 00:22:39,320 --> 00:22:42,120 Speaker 1: happens to somebody moving on a two D surface. Say, 420 00:22:42,160 --> 00:22:45,040 Speaker 1: for example, you have two people on the Earth, which 421 00:22:45,040 --> 00:22:48,560 Speaker 1: seems flat to them, right, and they're starting in the equator, 422 00:22:48,640 --> 00:22:51,840 Speaker 1: but in different places, and they're walking north. If we 423 00:22:51,960 --> 00:22:54,560 Speaker 1: say to them, all right, everybody walk north, then it 424 00:22:54,600 --> 00:22:57,359 Speaker 1: seems to them like, while we're moving in a parallel line, right, 425 00:22:57,359 --> 00:23:00,239 Speaker 1: we're both moving due north. Now you know that if 426 00:23:00,240 --> 00:23:03,240 Speaker 1: you start the equator and you walk due north, then 427 00:23:03,280 --> 00:23:06,680 Speaker 1: eventually you'll reach the north Pole. Think about how weird 428 00:23:06,760 --> 00:23:09,399 Speaker 1: that is for the people on the surface, right, they're 429 00:23:09,400 --> 00:23:12,800 Speaker 1: moving in parallel, they're separated by a distance. They're moving 430 00:23:12,800 --> 00:23:16,480 Speaker 1: in parallel, and yet their path cross. From their point 431 00:23:16,480 --> 00:23:19,879 Speaker 1: of view, it's like this something pulling them together, something 432 00:23:20,000 --> 00:23:23,479 Speaker 1: bringing them closer and closer together, something like a force. 433 00:23:24,000 --> 00:23:26,439 Speaker 1: From our point of view, we understand that they're on 434 00:23:26,480 --> 00:23:29,760 Speaker 1: a curved surface, then it makes sense for their motion 435 00:23:29,960 --> 00:23:33,040 Speaker 1: to naturally bring them together because their motion is on 436 00:23:33,119 --> 00:23:36,200 Speaker 1: a curved surface. Even if we see no force there 437 00:23:36,480 --> 00:23:38,679 Speaker 1: and that's where gravity is. It takes a bit of 438 00:23:38,680 --> 00:23:41,360 Speaker 1: a mental jiu jitsu. But you have to then extrapolate 439 00:23:41,400 --> 00:23:44,399 Speaker 1: to three dimensions, and remember that gravity is not the 440 00:23:44,480 --> 00:23:48,600 Speaker 1: bending of space relative to some other higher dimensional space 441 00:23:48,640 --> 00:23:52,440 Speaker 1: and four dimensions or in five dimensions. It's an intrinsic bending. 442 00:23:52,760 --> 00:23:56,719 Speaker 1: It changes the relationship between points in space, it changes 443 00:23:56,920 --> 00:24:00,719 Speaker 1: the relative distance between things, but it has the same effect. 444 00:24:01,080 --> 00:24:02,879 Speaker 1: You can think of gravity as a force, but it's 445 00:24:02,960 --> 00:24:05,320 Speaker 1: much more natural to think of it as the curving 446 00:24:05,359 --> 00:24:08,240 Speaker 1: of space, which changes the path that you move on, 447 00:24:08,400 --> 00:24:11,360 Speaker 1: even if there are no forces. And so what happens 448 00:24:11,400 --> 00:24:14,200 Speaker 1: near a massive object, Well, anything with mass, or actually 449 00:24:14,240 --> 00:24:17,560 Speaker 1: anything with energy will bend space a little bit. But 450 00:24:17,640 --> 00:24:22,119 Speaker 1: it doesn't just bend space. It also bends time because 451 00:24:22,119 --> 00:24:26,200 Speaker 1: remember we learn from special relativity that time and space 452 00:24:26,240 --> 00:24:29,880 Speaker 1: are connected. Time ticks differently depending on where you are 453 00:24:30,000 --> 00:24:33,400 Speaker 1: and how fast you are moving, and so the curvature 454 00:24:33,440 --> 00:24:37,600 Speaker 1: of space is also the curvature of space time. And 455 00:24:37,640 --> 00:24:41,439 Speaker 1: where this is more curved, time slows down even more, 456 00:24:41,680 --> 00:24:44,480 Speaker 1: and it gets pretty crazy, like the curvature of space 457 00:24:44,520 --> 00:24:48,040 Speaker 1: gets so intense that if you go inside a black hole, 458 00:24:48,520 --> 00:24:52,280 Speaker 1: then space moves only in one direction. It's so intensely 459 00:24:52,359 --> 00:24:56,400 Speaker 1: curved that every direction of space is now pointing towards 460 00:24:56,600 --> 00:25:00,359 Speaker 1: the singularity. So there's another connection there between space and time. 461 00:25:00,760 --> 00:25:04,600 Speaker 1: Outside the black hole, time only moves forwards, and space 462 00:25:04,640 --> 00:25:08,200 Speaker 1: can go in every direction. Inside the black hole, space 463 00:25:08,320 --> 00:25:11,879 Speaker 1: becomes one directional, the same way time is outside a 464 00:25:11,880 --> 00:25:14,880 Speaker 1: black hole, it only points towards the black hole. There 465 00:25:15,000 --> 00:25:18,240 Speaker 1: is no outwards direction. The reason you can't escape a 466 00:25:18,240 --> 00:25:21,560 Speaker 1: black hole is because literally there is no direction in 467 00:25:21,560 --> 00:25:24,520 Speaker 1: which to escape. It doesn't matter how fast you go. 468 00:25:25,119 --> 00:25:27,760 Speaker 1: And so that curvature of space is very intense, and 469 00:25:27,840 --> 00:25:30,960 Speaker 1: it also curves time. And now, the other lesson we 470 00:25:31,040 --> 00:25:34,040 Speaker 1: learned from special relativity is that it's a different experience 471 00:25:34,240 --> 00:25:38,199 Speaker 1: to go really fast and to watch somebody going really fast. Right, 472 00:25:38,280 --> 00:25:40,639 Speaker 1: the person who's going really fast, they think time has 473 00:25:40,680 --> 00:25:44,439 Speaker 1: flown normally. Person who's watching them move really fast relative 474 00:25:44,520 --> 00:25:47,280 Speaker 1: to the Earth, they see time slowing down. Well, the 475 00:25:47,320 --> 00:25:50,439 Speaker 1: same effect happens for the curvature of space. If you 476 00:25:50,480 --> 00:25:53,000 Speaker 1: and your friend come nearby a black hole, and your 477 00:25:53,080 --> 00:25:56,240 Speaker 1: friend approaches it and orbits the black hole, you will 478 00:25:56,240 --> 00:26:00,480 Speaker 1: see her clock slowing down, but she will experience time normally. 479 00:26:00,680 --> 00:26:03,600 Speaker 1: For her time is taking very normally, but for you, 480 00:26:04,119 --> 00:26:07,320 Speaker 1: her time is moving very very slowly, and in fact, 481 00:26:07,560 --> 00:26:10,080 Speaker 1: if she fell into the black hole, you would never 482 00:26:10,160 --> 00:26:13,439 Speaker 1: actually see her cross the event horizon because time and 483 00:26:13,480 --> 00:26:16,520 Speaker 1: space is so distorted that her time would slow down 484 00:26:16,600 --> 00:26:19,240 Speaker 1: so dramatically as she got closer to the black hole 485 00:26:19,600 --> 00:26:21,880 Speaker 1: that you would never actually see her cross. It takes 486 00:26:21,880 --> 00:26:24,959 Speaker 1: an infinite amount of time for you to see her cross, 487 00:26:25,440 --> 00:26:28,600 Speaker 1: but from her perspective, time is slowing normally, and she 488 00:26:28,640 --> 00:26:31,280 Speaker 1: can pass over the event horizon and into the black 489 00:26:31,280 --> 00:26:36,000 Speaker 1: hole and towards the singularity. So, Bradley, great question. Why 490 00:26:36,040 --> 00:26:38,879 Speaker 1: does time slow down near a black hole? It's because 491 00:26:38,920 --> 00:26:42,960 Speaker 1: time and space are connected, and black holes bend space 492 00:26:43,040 --> 00:26:46,560 Speaker 1: time like every massive object, and so that curvature not 493 00:26:46,680 --> 00:26:49,000 Speaker 1: only makes the weird feature that we call a black hole, 494 00:26:49,200 --> 00:26:52,000 Speaker 1: it also affects the passage of time in the same 495 00:26:52,040 --> 00:26:55,560 Speaker 1: way that moving at high velocities also affects the passage 496 00:26:55,600 --> 00:26:59,479 Speaker 1: of time. All Right, great question from Bradley. Loved it. 497 00:26:59,600 --> 00:27:02,080 Speaker 1: I'll be back in a moment to answer another question, 498 00:27:02,119 --> 00:27:18,040 Speaker 1: but first let's take another break. Okay, I'm back. This 499 00:27:18,160 --> 00:27:22,359 Speaker 1: is Daniel answering listener questions, digging into the backlog and 500 00:27:22,400 --> 00:27:25,600 Speaker 1: trying to find the funnest, most interesting, most exciting questions 501 00:27:25,840 --> 00:27:28,760 Speaker 1: to answer for all of you. So here's another question. 502 00:27:28,800 --> 00:27:31,760 Speaker 1: This one's about particle physics. Hey, guys, I was wondering 503 00:27:32,080 --> 00:27:35,080 Speaker 1: what would it take to make a fundamental particle accelerator 504 00:27:35,240 --> 00:27:38,520 Speaker 1: like an electron collider. What new things would we see 505 00:27:38,560 --> 00:27:42,840 Speaker 1: from colliding fundamental particles like leptons and quarks, and would 506 00:27:42,840 --> 00:27:45,399 Speaker 1: it be different than what we have today? All right, well, 507 00:27:45,440 --> 00:27:48,480 Speaker 1: this is a wonderful question, and I think the motivation 508 00:27:48,560 --> 00:27:51,639 Speaker 1: for this question comes from understanding that the large hadron 509 00:27:51,680 --> 00:27:55,840 Speaker 1: collider is not a collider that shoots fundamental particles. Instead, 510 00:27:55,920 --> 00:27:59,600 Speaker 1: it shoots protons. And remember, protons are not tiny little 511 00:27:59,600 --> 00:28:02,639 Speaker 1: dots in our theory. They are made of smaller particles. 512 00:28:02,640 --> 00:28:05,600 Speaker 1: They are composite particles. They have quirks in them, and 513 00:28:05,600 --> 00:28:08,280 Speaker 1: then a bunch of gluons to hold them together. And 514 00:28:08,320 --> 00:28:10,400 Speaker 1: so I think this is what's motivating his question. He's 515 00:28:10,400 --> 00:28:13,040 Speaker 1: wondering what would it be like to build a collider 516 00:28:13,280 --> 00:28:17,359 Speaker 1: made from actually tiny fundamental particles instead of tossing little 517 00:28:17,440 --> 00:28:20,679 Speaker 1: bags of particles at each other. Well, first, let's think 518 00:28:20,720 --> 00:28:23,840 Speaker 1: about why the large change on collider is a proton collider. 519 00:28:23,880 --> 00:28:26,120 Speaker 1: Where are the pros and cons of that and then 520 00:28:26,119 --> 00:28:30,199 Speaker 1: we'll talk about fundamental particle colliders. So the reason that 521 00:28:30,280 --> 00:28:32,520 Speaker 1: we build a large change on collider out of protons 522 00:28:32,600 --> 00:28:35,119 Speaker 1: is number one, there are protons everywhere, like it's not 523 00:28:35,160 --> 00:28:39,040 Speaker 1: hard to find protons. Everything around us is made of protons. 524 00:28:39,080 --> 00:28:43,840 Speaker 1: But also because heavier particles are easier to accelerate, the 525 00:28:43,880 --> 00:28:47,400 Speaker 1: more massive particle has, the less it will radiate that 526 00:28:47,600 --> 00:28:50,800 Speaker 1: energy when you accelerate it. When you accelerate a particle, 527 00:28:50,800 --> 00:28:53,440 Speaker 1: if it's very low mass, like an electron, it will 528 00:28:53,480 --> 00:28:56,080 Speaker 1: give off a lot of that energy in the form 529 00:28:56,120 --> 00:28:59,920 Speaker 1: of photons. So the heavier particle is the less it radiates. 530 00:29:00,160 --> 00:29:03,440 Speaker 1: So it's actually possible to get protons up to higher 531 00:29:03,520 --> 00:29:06,960 Speaker 1: speeds more easily than it is to get electrons. And 532 00:29:07,040 --> 00:29:09,760 Speaker 1: remember we want these protons to have a lot of energy. 533 00:29:10,040 --> 00:29:12,840 Speaker 1: The more energy you pour into your particle collider, the 534 00:29:12,920 --> 00:29:16,280 Speaker 1: higher energy state you can create, and the more massive 535 00:29:16,360 --> 00:29:19,880 Speaker 1: objects you can create. And the goal of particle colliders 536 00:29:20,040 --> 00:29:23,960 Speaker 1: is to explore the universe by discovering new massive particles, 537 00:29:24,000 --> 00:29:26,600 Speaker 1: by creating energy densities that are so high that it 538 00:29:26,640 --> 00:29:30,560 Speaker 1: becomes possible to make new weird particles that haven't existed 539 00:29:30,560 --> 00:29:34,479 Speaker 1: since the Big Bang and The awesome thing about these colliders, remember, 540 00:29:34,800 --> 00:29:37,280 Speaker 1: is that you don't have to know what you're looking for. 541 00:29:37,560 --> 00:29:39,400 Speaker 1: You don't have to know that those particles are out 542 00:29:39,440 --> 00:29:42,640 Speaker 1: there as long as you pour enough energy into your collider, 543 00:29:42,880 --> 00:29:45,480 Speaker 1: if you're above the threshold, if you have enough energy 544 00:29:45,520 --> 00:29:48,760 Speaker 1: in the collision to make these heavy particles, they will 545 00:29:48,840 --> 00:29:52,240 Speaker 1: eventually appear, which is pretty cool, and that's what motivates 546 00:29:52,360 --> 00:29:55,320 Speaker 1: us to have higher and higher energy. If you double 547 00:29:55,320 --> 00:29:57,920 Speaker 1: the energy and your collider, you can make particles twice 548 00:29:57,960 --> 00:30:00,680 Speaker 1: as massive. It's sort of like getting to explore and 549 00:30:00,720 --> 00:30:03,800 Speaker 1: a whole another Earth life planet. Right. The possibilities for 550 00:30:03,840 --> 00:30:06,640 Speaker 1: a discovery are amazing, and nobody has ever built a 551 00:30:06,640 --> 00:30:10,120 Speaker 1: collider at these energies before. So if you could double 552 00:30:10,200 --> 00:30:12,640 Speaker 1: the energy of your collider, you could see things for 553 00:30:12,680 --> 00:30:15,880 Speaker 1: the first time that nobody has ever seen. Now. The 554 00:30:16,040 --> 00:30:19,480 Speaker 1: disadvantage of using protons or any particle that's not a 555 00:30:19,560 --> 00:30:23,400 Speaker 1: fundamental particle is that it's less precise. Right, you can't 556 00:30:23,480 --> 00:30:27,680 Speaker 1: control the energy of the interaction nearly as tightly as 557 00:30:27,720 --> 00:30:30,920 Speaker 1: if you were shooting tiny, little pin prick particles. I mean, 558 00:30:30,960 --> 00:30:34,240 Speaker 1: what happens when you collide protons together is that the 559 00:30:34,400 --> 00:30:37,600 Speaker 1: energy holding the protons together is kind of negligible compared 560 00:30:37,640 --> 00:30:40,719 Speaker 1: to the energy of the protons moving, so when they 561 00:30:40,760 --> 00:30:43,280 Speaker 1: come near each other, the fact that the corks are 562 00:30:43,280 --> 00:30:46,640 Speaker 1: bound together into a proton becomes kind of irrelevant. You 563 00:30:46,680 --> 00:30:50,040 Speaker 1: have this little sort of flimsy bag holding these corks together, 564 00:30:50,280 --> 00:30:53,040 Speaker 1: but it's really the quarks from one proton that interact 565 00:30:53,080 --> 00:30:55,680 Speaker 1: with the corks from the other proton, or sometimes even 566 00:30:55,720 --> 00:30:59,120 Speaker 1: the gluons, And then you get multiple interactions. You get 567 00:30:59,120 --> 00:31:01,520 Speaker 1: two corks mat shing into each other, or to glue 568 00:31:01,560 --> 00:31:05,080 Speaker 1: on smashing into each other, or multiple things happening at once. 569 00:31:05,520 --> 00:31:07,960 Speaker 1: And it's not just that multiple things happened, but that 570 00:31:08,000 --> 00:31:11,080 Speaker 1: you can't control the energy. You can't say I want 571 00:31:11,120 --> 00:31:14,320 Speaker 1: core collisions at a very specific energy. You can control 572 00:31:14,360 --> 00:31:16,920 Speaker 1: the energy of the protons, but you never know how 573 00:31:17,000 --> 00:31:19,760 Speaker 1: much of the protons energy is going into each cork. 574 00:31:20,160 --> 00:31:22,520 Speaker 1: And in one collision, the quarks you collion could have 575 00:31:22,560 --> 00:31:24,960 Speaker 1: a tiny fraction of the energy of the protons. In 576 00:31:25,040 --> 00:31:27,000 Speaker 1: another one that could have a huge fraction of the 577 00:31:27,080 --> 00:31:29,840 Speaker 1: energy of the protons. So you lose a very precise 578 00:31:29,880 --> 00:31:33,080 Speaker 1: control over the energy that you're putting into your collision, 579 00:31:33,440 --> 00:31:35,600 Speaker 1: but what you're gaining is the ability to have a 580 00:31:35,720 --> 00:31:39,640 Speaker 1: huge amount of energy in that collision. So proton accelerators 581 00:31:39,640 --> 00:31:43,040 Speaker 1: are really good for discovering stuff, for figuring out new 582 00:31:43,080 --> 00:31:45,840 Speaker 1: stuff because they can explore a big range of energy. 583 00:31:46,240 --> 00:31:48,600 Speaker 1: One because the proton can hold a lot of energy 584 00:31:48,600 --> 00:31:51,360 Speaker 1: without radiating it off. And two because the quarks get 585 00:31:51,360 --> 00:31:54,240 Speaker 1: a different fraction the protons energy every time. So you 586 00:31:54,280 --> 00:31:57,480 Speaker 1: can very naturally explore a lot of different energy ranges 587 00:31:57,520 --> 00:32:00,880 Speaker 1: in your collisions. Now, can we make colliders out of 588 00:32:00,920 --> 00:32:05,360 Speaker 1: fundamental particles, Yes, absolutely, and we have when great example 589 00:32:05,560 --> 00:32:08,880 Speaker 1: are electron colliders in the same tunnels that now hold 590 00:32:08,920 --> 00:32:13,040 Speaker 1: the LHC. Twenty years ago we had leapt large electron 591 00:32:13,120 --> 00:32:16,480 Speaker 1: positron collider and it made some great discoveries, and it 592 00:32:16,600 --> 00:32:19,600 Speaker 1: used electrons in one direction and positrons in the other direction, 593 00:32:19,600 --> 00:32:23,400 Speaker 1: and it smashed them together. And the advantage here is 594 00:32:23,480 --> 00:32:26,479 Speaker 1: that it's much more precise. You can control the energy, 595 00:32:26,600 --> 00:32:29,000 Speaker 1: and so if you're looking for a particle that requires 596 00:32:29,040 --> 00:32:31,720 Speaker 1: an exact amount of energy to make it, you can 597 00:32:31,760 --> 00:32:36,200 Speaker 1: tune your collider very precisely to put just that much 598 00:32:36,320 --> 00:32:40,560 Speaker 1: energy into the collisions. Because you're now dealing with fundamental particles, 599 00:32:40,600 --> 00:32:43,760 Speaker 1: not bags of particles, so you know exactly how much 600 00:32:43,880 --> 00:32:46,920 Speaker 1: energy you put into your accelerator and the magnets and 601 00:32:47,040 --> 00:32:50,440 Speaker 1: all that energy is just going into that one fundamental particle, 602 00:32:50,560 --> 00:32:52,920 Speaker 1: and you have the other fundamental particle coming from the 603 00:32:52,960 --> 00:32:56,240 Speaker 1: other direction. So things are very tightly controlled. And there's 604 00:32:56,280 --> 00:32:58,760 Speaker 1: been examples in history when this has been very important, 605 00:32:59,120 --> 00:33:01,440 Speaker 1: when you only makes some new heavy particle when you 606 00:33:01,520 --> 00:33:04,720 Speaker 1: have exactly the right energy to go into the collisions, 607 00:33:04,800 --> 00:33:07,240 Speaker 1: and so you can tune the energy of your collider 608 00:33:07,400 --> 00:33:10,720 Speaker 1: very precisely, sort of scan up and down and see, oh, look, 609 00:33:10,880 --> 00:33:13,880 Speaker 1: we're making a new particle at exactly this energy. An 610 00:33:13,920 --> 00:33:16,720 Speaker 1: example of the discovery of the Jape side and people 611 00:33:16,720 --> 00:33:19,240 Speaker 1: who are interested in the crazy story of the particle 612 00:33:19,280 --> 00:33:22,160 Speaker 1: that has two names go check out our podcast episode 613 00:33:22,440 --> 00:33:25,400 Speaker 1: about that discovery. There's a lot of crazy stuff in 614 00:33:25,440 --> 00:33:28,360 Speaker 1: the history of particle physics. Now, of course, the cons 615 00:33:28,760 --> 00:33:32,040 Speaker 1: the disadvantage of using an electron collider is that you 616 00:33:32,080 --> 00:33:35,280 Speaker 1: can't make electrons go as fast as protons very easily 617 00:33:35,720 --> 00:33:37,840 Speaker 1: because they give off a lot of their energy. They 618 00:33:38,000 --> 00:33:41,880 Speaker 1: radiate away their energy because electrons don't have very much mass, 619 00:33:42,360 --> 00:33:44,040 Speaker 1: and so if you want to go to high energy, 620 00:33:44,080 --> 00:33:46,680 Speaker 1: it's better to use protons, and if you want really 621 00:33:46,680 --> 00:33:50,000 Speaker 1: precise control of the energy, it's better to use electrons. 622 00:33:50,320 --> 00:33:53,400 Speaker 1: The people also have other crazy ideas because the electron 623 00:33:53,520 --> 00:33:57,040 Speaker 1: is not the only fundamental particle we can consider using. Right, 624 00:33:57,400 --> 00:34:00,760 Speaker 1: what about the muan. The muan is just like the 625 00:34:00,840 --> 00:34:03,840 Speaker 1: electron in lots of ways. It's like the electrons cousin, 626 00:34:04,320 --> 00:34:08,040 Speaker 1: but it has more mass. And what that mass means 627 00:34:08,200 --> 00:34:12,200 Speaker 1: that it doesn't radiate energy as quickly as electrons. So 628 00:34:12,440 --> 00:34:16,480 Speaker 1: you could create a muon collider where you create muans, 629 00:34:16,600 --> 00:34:19,840 Speaker 1: accelerate them, smash them into each other. In theory, it 630 00:34:19,840 --> 00:34:21,840 Speaker 1: would be easier to get those muans to go to 631 00:34:21,920 --> 00:34:24,760 Speaker 1: higher energies than it is for electrons because they don't 632 00:34:24,840 --> 00:34:28,080 Speaker 1: radiate as much. Now, the disadvantage is that there aren't 633 00:34:28,080 --> 00:34:31,960 Speaker 1: as many muans around like electrons. They are everywhere. You 634 00:34:32,080 --> 00:34:34,279 Speaker 1: take an atom, you heat it up, boom, you got 635 00:34:34,320 --> 00:34:37,000 Speaker 1: a bunch of electrons. Muans are much harder to produce 636 00:34:37,080 --> 00:34:39,200 Speaker 1: right there, produced in cosmic rays, or you can make 637 00:34:39,200 --> 00:34:41,560 Speaker 1: them in collisions, but you don't have a natural supply 638 00:34:41,640 --> 00:34:44,560 Speaker 1: of muans. The other disadvantage of muans, and this is 639 00:34:44,640 --> 00:34:46,800 Speaker 1: kind of a big one, is that they don't last 640 00:34:46,920 --> 00:34:49,520 Speaker 1: very long. Sure, they don't radiate energy as much as 641 00:34:49,520 --> 00:34:52,439 Speaker 1: electrons when they move fast, but they also don't live 642 00:34:52,480 --> 00:34:56,319 Speaker 1: forever like electrons do. An electrons sitting by itself will 643 00:34:56,320 --> 00:34:58,520 Speaker 1: sit there to the end of the universe. It's a 644 00:34:58,560 --> 00:35:01,560 Speaker 1: stable particle. I you on, on the other hand, last 645 00:35:01,600 --> 00:35:04,480 Speaker 1: two point two micro seconds. So if you have a 646 00:35:04,560 --> 00:35:08,160 Speaker 1: muan sitting by itself in space, it will spontaneously decay 647 00:35:08,200 --> 00:35:10,960 Speaker 1: to an electron and a couple of new trinos. So 648 00:35:11,080 --> 00:35:13,919 Speaker 1: that's pretty tough. Now, you can make the muans live 649 00:35:14,000 --> 00:35:17,320 Speaker 1: longer by getting them to go really fast because time 650 00:35:17,360 --> 00:35:21,720 Speaker 1: dilation happens. The muan lives two point two microseconds by 651 00:35:21,760 --> 00:35:25,200 Speaker 1: its clock right in its frame of reference if it 652 00:35:25,239 --> 00:35:27,319 Speaker 1: had a tiny little clock. If you can get them 653 00:35:27,360 --> 00:35:30,360 Speaker 1: to go really really fast, like moving around an accelerator, 654 00:35:30,680 --> 00:35:33,680 Speaker 1: then their clocks go slower and they last for much 655 00:35:33,760 --> 00:35:37,000 Speaker 1: longer seconds, minutes, as long as you want, depending on 656 00:35:37,080 --> 00:35:40,120 Speaker 1: how fast they are going. So there are some ways, 657 00:35:40,120 --> 00:35:43,840 Speaker 1: and people are talking seriously about building muan colliders for 658 00:35:44,000 --> 00:35:47,319 Speaker 1: future experiments. Now, what you can't do is build a 659 00:35:47,400 --> 00:35:50,359 Speaker 1: cork collider. We'd love to have a cork collider because 660 00:35:50,360 --> 00:35:53,320 Speaker 1: it would let us study all sorts of crazy awesome things. 661 00:35:53,640 --> 00:35:57,319 Speaker 1: But quarks, remember, cannot be by themselves. The strong force 662 00:35:57,360 --> 00:36:00,680 Speaker 1: to hold the proton together. It's very very wrong, and 663 00:36:00,680 --> 00:36:03,879 Speaker 1: it has a really weird feature, the strong force which 664 00:36:03,920 --> 00:36:07,160 Speaker 1: holds the corks together in the proton. As you pull 665 00:36:07,200 --> 00:36:11,280 Speaker 1: those two corks apart, the energy in that bond actually increases, 666 00:36:11,520 --> 00:36:15,000 Speaker 1: the force increases. This is the opposite than all of 667 00:36:15,040 --> 00:36:18,759 Speaker 1: the other forces, like the electromagnetic force between two electrons 668 00:36:19,160 --> 00:36:23,040 Speaker 1: decreases as the electrons get further apart. For quarks, the 669 00:36:23,080 --> 00:36:26,680 Speaker 1: strong force grows stronger as the corks get further apart, 670 00:36:26,880 --> 00:36:30,000 Speaker 1: which means this more and more energy in that bond 671 00:36:30,120 --> 00:36:33,000 Speaker 1: as they get further apart. And that's why quarks can't 672 00:36:33,000 --> 00:36:36,000 Speaker 1: ever be alone, because a cork far away from all 673 00:36:36,040 --> 00:36:39,880 Speaker 1: the other corks would require so much energy that that 674 00:36:40,000 --> 00:36:43,239 Speaker 1: space would be so unstable that that energy would very 675 00:36:43,320 --> 00:36:46,400 Speaker 1: rapidly turn into new particles. And that's exactly what happens 676 00:36:46,400 --> 00:36:49,120 Speaker 1: if you break up a proton into a bunch of 677 00:36:49,160 --> 00:36:51,839 Speaker 1: quarks and send them flying off in different directions than 678 00:36:51,880 --> 00:36:55,000 Speaker 1: they create new matter out of the vacuum using the 679 00:36:55,120 --> 00:36:57,879 Speaker 1: energy held in that strong force, and they bind those 680 00:36:57,920 --> 00:37:00,880 Speaker 1: corks together to these new corks that created out of 681 00:37:00,880 --> 00:37:03,600 Speaker 1: the vacuum, so you can't ever see a cork by itself, 682 00:37:03,719 --> 00:37:06,920 Speaker 1: which means you can't build a collider out of corks, 683 00:37:07,160 --> 00:37:09,720 Speaker 1: which is too bad. But right now in particle physics, 684 00:37:09,719 --> 00:37:11,880 Speaker 1: we happen to be thinking about the future of the 685 00:37:11,920 --> 00:37:14,120 Speaker 1: field and what kind of collider we want to build 686 00:37:14,120 --> 00:37:16,399 Speaker 1: in the next ten or twenty years. So people are 687 00:37:16,400 --> 00:37:19,319 Speaker 1: doing these kind of exercises and wondering like, what kind 688 00:37:19,320 --> 00:37:22,000 Speaker 1: of question can we ask with an electron collider? What 689 00:37:22,120 --> 00:37:24,440 Speaker 1: kind of science can we learned with the mun collider? 690 00:37:24,480 --> 00:37:27,440 Speaker 1: Should we build a photon collider? Or all sorts of 691 00:37:27,440 --> 00:37:29,879 Speaker 1: crazy stuff. So it's a really fun and exciting time 692 00:37:29,920 --> 00:37:32,200 Speaker 1: in the field to be thinking about the five, ten 693 00:37:32,360 --> 00:37:35,160 Speaker 1: fifty year trajectory. Can we come up with new ways 694 00:37:35,200 --> 00:37:38,440 Speaker 1: to accelerate particles so it doesn't cost ten billion dollars 695 00:37:38,520 --> 00:37:42,719 Speaker 1: and require loops underground that are thirty kilometers around. It's 696 00:37:42,719 --> 00:37:44,920 Speaker 1: a fun time and we're all thinking about the crazy 697 00:37:45,040 --> 00:37:50,040 Speaker 1: kind of discoveries that might be coming our way. All right, everybody, 698 00:37:50,080 --> 00:37:52,400 Speaker 1: that's all the time we have for today. Thank you 699 00:37:52,440 --> 00:37:55,040 Speaker 1: to everybody who sends them listener questions, and thank you 700 00:37:55,080 --> 00:37:57,600 Speaker 1: for your patients in getting to them. I plan to 701 00:37:57,719 --> 00:38:00,560 Speaker 1: keep doing these listener question catch up episodes until I've 702 00:38:00,560 --> 00:38:04,200 Speaker 1: answered every single one of your questions. And remember those 703 00:38:04,239 --> 00:38:06,160 Speaker 1: of you who have questions but don't want to write 704 00:38:06,160 --> 00:38:09,880 Speaker 1: in via email. I'll be having public office hours on 705 00:38:10,040 --> 00:38:14,200 Speaker 1: December four, Team twenty twenty. Go to my website sites 706 00:38:14,400 --> 00:38:17,080 Speaker 1: dot U, c I, dot E, d U slash Daniel 707 00:38:17,239 --> 00:38:20,080 Speaker 1: to get all the details. Come ask me questions, or 708 00:38:20,120 --> 00:38:22,919 Speaker 1: just listen to other people ask questions, or come talk 709 00:38:22,960 --> 00:38:26,319 Speaker 1: to me about physics. Thanks everyone, Thanks to everybody who's 710 00:38:26,320 --> 00:38:28,520 Speaker 1: sent in a question. I hope you enjoyed the conversations 711 00:38:28,520 --> 00:38:32,560 Speaker 1: about dark matter and black holes and future particle colliders. 712 00:38:33,280 --> 00:38:43,719 Speaker 1: Tune in next time. Thanks for listening, and remember that 713 00:38:43,840 --> 00:38:46,600 Speaker 1: Daniel and Jorge Explain the Universe is a production of 714 00:38:46,680 --> 00:38:50,040 Speaker 1: I Heart Radio. Or more podcast from my heart Radio, 715 00:38:50,200 --> 00:38:53,760 Speaker 1: visit the I heart Radio app, Apple Podcasts, or wherever 716 00:38:53,880 --> 00:39:01,160 Speaker 1: you listen to your favorite shows. No