1 00:00:08,560 --> 00:00:12,640 Speaker 1: The deepest questions about the nature of the universe have answers. 2 00:00:13,039 --> 00:00:17,040 Speaker 1: Answers that are out there right now, waiting to be discovered. 3 00:00:17,480 --> 00:00:20,880 Speaker 1: The nature of dark matter, the secret to quantum gravity, 4 00:00:21,120 --> 00:00:24,640 Speaker 1: the mystery of dark energy. The answers lie in wait 5 00:00:24,720 --> 00:00:28,720 Speaker 1: for us, but not just the answers, also the clues 6 00:00:28,800 --> 00:00:32,400 Speaker 1: to reveal them. Right now, the clue to unravel these 7 00:00:32,440 --> 00:00:36,720 Speaker 1: mysteries is out there. Probably the information we need to 8 00:00:36,960 --> 00:00:40,000 Speaker 1: crack the code is washing over us in the form 9 00:00:40,080 --> 00:00:44,159 Speaker 1: of messages from space we don't yet know how to decode. 10 00:00:44,479 --> 00:00:47,760 Speaker 1: Think about how much we have learned from listening carefully 11 00:00:47,800 --> 00:00:52,240 Speaker 1: to the sky answers to questions that previous generations didn't 12 00:00:52,320 --> 00:00:55,120 Speaker 1: even know to ask. So that makes us wonder, of course, 13 00:00:55,280 --> 00:00:59,240 Speaker 1: what answers are arriving here on Earth right now, waiting 14 00:00:59,280 --> 00:01:18,160 Speaker 1: for someone clever enough to know how to listen. Hi, 15 00:01:18,360 --> 00:01:21,920 Speaker 1: I'm Daniel. I'm a particle physicist, and I desperately want 16 00:01:22,000 --> 00:01:25,880 Speaker 1: to hear the answers to questions about the universe. I 17 00:01:26,000 --> 00:01:28,520 Speaker 1: know that these answers are out there, and I know 18 00:01:28,640 --> 00:01:31,800 Speaker 1: that humans will figure them out in fifty years and 19 00:01:31,880 --> 00:01:34,679 Speaker 1: a hundred years, in a thousand years, people will know 20 00:01:34,800 --> 00:01:37,720 Speaker 1: the answers to deep questions about the universe that we 21 00:01:37,840 --> 00:01:42,520 Speaker 1: are totally perplexed by. Little children will read books explaining 22 00:01:42,560 --> 00:01:46,200 Speaker 1: to them secrets that it takes Nobel Prize winning discoveries 23 00:01:46,400 --> 00:01:49,560 Speaker 1: to uncover about the universe. They will hear about them. 24 00:01:49,680 --> 00:01:52,120 Speaker 1: They will be bored. They will throw a tantrum. I 25 00:01:52,160 --> 00:01:55,000 Speaker 1: am desperate to read those books. I am desperate to 26 00:01:55,200 --> 00:01:58,120 Speaker 1: know those things about the universe. I know that the 27 00:01:58,160 --> 00:02:00,560 Speaker 1: answers are out there. I know there are are ways 28 00:02:00,640 --> 00:02:04,400 Speaker 1: to figure them out. But science moves slowly and steadily, 29 00:02:04,440 --> 00:02:08,160 Speaker 1: with brief flashes of insight, sometimes revealing the nature of 30 00:02:08,200 --> 00:02:10,360 Speaker 1: the universe, and we just have to wait for it 31 00:02:10,440 --> 00:02:13,160 Speaker 1: to happen. But not just wait, we can also push 32 00:02:13,240 --> 00:02:16,520 Speaker 1: it forward. So welcome to the podcast Daniel and Jorge 33 00:02:16,720 --> 00:02:20,400 Speaker 1: Explain the Universe, a production of I Heart Radio in 34 00:02:20,440 --> 00:02:22,639 Speaker 1: which we do our best to push it forward by 35 00:02:22,760 --> 00:02:28,400 Speaker 1: encouraging your curiosity about science, by encouraging everybody's curiosity about science, 36 00:02:28,480 --> 00:02:32,079 Speaker 1: by asking the big questions about the universe and thinking 37 00:02:32,120 --> 00:02:35,560 Speaker 1: about how we might possibly answer them. On this podcast, 38 00:02:35,639 --> 00:02:39,680 Speaker 1: we talk about everything in the universe, the tiniest little particles, 39 00:02:39,760 --> 00:02:43,399 Speaker 1: the most super massive black holes, and all the signals 40 00:02:43,440 --> 00:02:47,600 Speaker 1: we are receiving from these cosmic and tiny objects that 41 00:02:47,680 --> 00:02:50,840 Speaker 1: are telling us those secrets of the universe. My friend 42 00:02:50,840 --> 00:02:53,240 Speaker 1: and co host Jorge can't be here today to join us, 43 00:02:53,280 --> 00:02:55,320 Speaker 1: so I'm on my own telling you about all the 44 00:02:55,360 --> 00:02:58,040 Speaker 1: things we can learn from the universe. If we just 45 00:02:58,240 --> 00:03:01,600 Speaker 1: knew how to listen, and is no shortage of questions 46 00:03:01,639 --> 00:03:04,720 Speaker 1: about the universe, we'd like answers too. Of course, there 47 00:03:04,720 --> 00:03:08,200 Speaker 1: are the known unknowns, the things that we know we 48 00:03:08,280 --> 00:03:11,919 Speaker 1: don't know, and we also know how to figure them out. 49 00:03:12,280 --> 00:03:14,760 Speaker 1: There are so many things in science where we know 50 00:03:14,880 --> 00:03:17,040 Speaker 1: exactly what it is we need to do. We know 51 00:03:17,160 --> 00:03:19,920 Speaker 1: exactly what question we want to answer, and we just 52 00:03:20,200 --> 00:03:24,240 Speaker 1: haven't done it yet, either because of time or expertise, 53 00:03:24,560 --> 00:03:27,960 Speaker 1: or frankly, just money. Think about all we could accomplish 54 00:03:28,000 --> 00:03:31,640 Speaker 1: if we poured more money into science. We know how 55 00:03:31,760 --> 00:03:34,800 Speaker 1: to send rovers to other planets. We know how to 56 00:03:34,920 --> 00:03:37,960 Speaker 1: send satellites to land on the moons of Jupiter. We 57 00:03:38,040 --> 00:03:40,960 Speaker 1: know how to build big space telescopes. We can do 58 00:03:41,040 --> 00:03:43,520 Speaker 1: these things, and we know that if we did them, 59 00:03:43,800 --> 00:03:47,240 Speaker 1: we would essentially just be buying scientific knowledge. We know 60 00:03:47,760 --> 00:03:49,840 Speaker 1: that the answers to some of the questions we have 61 00:03:49,960 --> 00:03:53,000 Speaker 1: about whether there are life in the oceans, on those moons, 62 00:03:53,080 --> 00:03:56,320 Speaker 1: and what is going on in the deepest, darkest reaches 63 00:03:56,400 --> 00:03:59,160 Speaker 1: of the universe. Those a answers are out there waiting 64 00:03:59,160 --> 00:04:02,200 Speaker 1: for us if we just buy them. We are like 65 00:04:02,400 --> 00:04:05,920 Speaker 1: children walking around in a scientific candy shop, keeping all 66 00:04:05,960 --> 00:04:10,080 Speaker 1: of our money in our pockets and not purchasing those tasty, tasty, 67 00:04:10,120 --> 00:04:13,360 Speaker 1: delicious scientific treats. So that's why on this program and 68 00:04:13,360 --> 00:04:16,279 Speaker 1: everywhere in my life, I'm always advocating for increasing the 69 00:04:16,360 --> 00:04:20,160 Speaker 1: spending to government agencies. We could buy so much knowledge 70 00:04:20,160 --> 00:04:22,960 Speaker 1: about the universe. We could crack open some of these 71 00:04:23,000 --> 00:04:26,200 Speaker 1: mysteries if we just spent a few more pennies. All right, 72 00:04:26,400 --> 00:04:29,600 Speaker 1: maybe not pennies, maybe a few more millions of dollars, 73 00:04:29,600 --> 00:04:32,479 Speaker 1: but on the scale of government spending, it really is pennies. 74 00:04:32,720 --> 00:04:35,280 Speaker 1: But in the face of those budget realities, we have 75 00:04:35,400 --> 00:04:38,120 Speaker 1: to get clever. And one of my favorite things that 76 00:04:38,240 --> 00:04:43,440 Speaker 1: astrophysicists do is that they don't try to build experiments themselves. 77 00:04:43,480 --> 00:04:46,039 Speaker 1: They just go out and look for them. Like in 78 00:04:46,200 --> 00:04:49,160 Speaker 1: particle physics, if I want to know what happens when 79 00:04:49,200 --> 00:04:51,760 Speaker 1: I smash two protons together, then I say, let's go 80 00:04:51,880 --> 00:04:55,000 Speaker 1: build an accelerator that does just that, that smashes the 81 00:04:55,000 --> 00:04:57,919 Speaker 1: particles together and see what comes out. We are creating 82 00:04:58,120 --> 00:05:01,880 Speaker 1: the conditions that we want to The astrophysicists don't usually 83 00:05:01,880 --> 00:05:05,240 Speaker 1: have that luxury. For example, if you're curious about what 84 00:05:05,400 --> 00:05:08,599 Speaker 1: happened to be a smash two galaxies together, well you 85 00:05:08,640 --> 00:05:13,400 Speaker 1: can't go out and build a galaxy sized collider. Fortunately, however, 86 00:05:13,680 --> 00:05:17,080 Speaker 1: the universe is vast, and it is crazy, and it 87 00:05:17,200 --> 00:05:20,200 Speaker 1: is filled with all sorts of amazing stuff, including, if 88 00:05:20,240 --> 00:05:23,800 Speaker 1: you look hard enough, almost every experiment you would want 89 00:05:23,839 --> 00:05:27,320 Speaker 1: to do, including colliding galaxies. The same thing goes for 90 00:05:27,400 --> 00:05:30,680 Speaker 1: colliding things like black holes. Who doesn't want to shoot 91 00:05:30,680 --> 00:05:33,159 Speaker 1: one black hole at another one to see what happens? 92 00:05:33,320 --> 00:05:35,480 Speaker 1: Does one black hole eat the other one? Do they 93 00:05:35,520 --> 00:05:38,640 Speaker 1: eat each other somehow? Is it some crazy cosmic dance? 94 00:05:38,760 --> 00:05:40,520 Speaker 1: We now know, of course, that when you do that, 95 00:05:40,600 --> 00:05:45,520 Speaker 1: you emit enormous quantities of energy in gravitational waves. We've 96 00:05:45,520 --> 00:05:49,360 Speaker 1: actually seen these things using gravitational wave detectors. So while 97 00:05:49,440 --> 00:05:51,880 Speaker 1: we didn't have to build the experiment to shoot black 98 00:05:51,880 --> 00:05:54,800 Speaker 1: holes at each other, we did have to build the 99 00:05:54,839 --> 00:05:58,599 Speaker 1: experiments to see the gravitational waves. But what if we 100 00:05:58,640 --> 00:06:01,240 Speaker 1: didn't have to build the experiment and we didn't have 101 00:06:01,320 --> 00:06:04,120 Speaker 1: to build the detector. What if nature said it all 102 00:06:04,279 --> 00:06:07,119 Speaker 1: up for us. What if all we had to do 103 00:06:07,480 --> 00:06:10,039 Speaker 1: was listen? And so today on the podcast we'll be 104 00:06:10,080 --> 00:06:14,159 Speaker 1: talking about just that, a crazy new idea that might 105 00:06:14,240 --> 00:06:16,800 Speaker 1: just work. So on today's program will be answering the 106 00:06:16,880 --> 00:06:26,120 Speaker 1: question can we use the entire galaxy as a gravitational 107 00:06:26,320 --> 00:06:30,159 Speaker 1: wave detector? I know that sounds preposterous, but astrophysicists like 108 00:06:30,279 --> 00:06:33,279 Speaker 1: to think big, and when they do, sometimes they make 109 00:06:33,320 --> 00:06:35,560 Speaker 1: it work. So I was wondering how much people have 110 00:06:35,680 --> 00:06:38,479 Speaker 1: heard about this topic already, if this was something everybody 111 00:06:38,560 --> 00:06:41,720 Speaker 1: was talking about or only people in the physics community. So, 112 00:06:41,880 --> 00:06:44,560 Speaker 1: as usual, I asked for volunteers out there on the 113 00:06:44,600 --> 00:06:48,520 Speaker 1: Internet to answer random physics questions with no preparation. It 114 00:06:48,600 --> 00:06:50,880 Speaker 1: gives me an idea for what people out there already 115 00:06:50,880 --> 00:06:53,760 Speaker 1: know and what they think about when they hear this question. 116 00:06:53,920 --> 00:06:57,240 Speaker 1: If you'd like to participate for future episodes of the podcast, 117 00:06:57,320 --> 00:07:00,320 Speaker 1: please don't be shy. It's easy, it's fun, and we 118 00:07:00,400 --> 00:07:02,880 Speaker 1: love hearing from you. Please just write to me two 119 00:07:02,960 --> 00:07:06,800 Speaker 1: questions at Daniel and Jorge dot com. So think for 120 00:07:06,800 --> 00:07:08,880 Speaker 1: a moment, Do you have an idea for how you 121 00:07:08,880 --> 00:07:13,960 Speaker 1: could use the entire galaxy to detect gravitational waves. Here's 122 00:07:14,000 --> 00:07:19,480 Speaker 1: what our volunteers had to say. I don't know. I 123 00:07:19,560 --> 00:07:23,960 Speaker 1: had no idea. I don't know how detectors like Ligo 124 00:07:24,200 --> 00:07:27,360 Speaker 1: measure gravitational waves. I don't know the mechanism. But objects 125 00:07:27,360 --> 00:07:31,480 Speaker 1: in our galaxy are quite spread out and comparted to 126 00:07:31,560 --> 00:07:34,040 Speaker 1: the size of the galaxy, each of them is quite small. 127 00:07:34,560 --> 00:07:37,600 Speaker 1: So I don't think our galaxy could be an effective 128 00:07:37,600 --> 00:07:42,640 Speaker 1: gravitational wave detector. I don't know. The ones on Earth 129 00:07:43,120 --> 00:07:46,400 Speaker 1: I believe use lasers and obviously their own distance apart. 130 00:07:46,720 --> 00:07:50,040 Speaker 1: I sort of seen lectures one time about using dust 131 00:07:50,160 --> 00:07:52,280 Speaker 1: or hydrogen gas or something in the universe. Whether that's 132 00:07:52,360 --> 00:07:54,840 Speaker 1: gravitational waves or something else, I don't know. I'm not 133 00:07:54,920 --> 00:07:56,800 Speaker 1: quite sure how you do that one. Yeah, if you 134 00:07:57,240 --> 00:08:01,560 Speaker 1: think about how they measure gravity waves, uh, you're essentially 135 00:08:01,600 --> 00:08:05,760 Speaker 1: like measuring the separation between two mirrors in one direction 136 00:08:05,880 --> 00:08:09,280 Speaker 1: versus another direction. That's what the Liego observatory does, so 137 00:08:09,360 --> 00:08:12,400 Speaker 1: you get the disoscillation signal. So I imagine you can 138 00:08:12,440 --> 00:08:15,760 Speaker 1: do something similar with the entire galaxy. Um, you can 139 00:08:15,760 --> 00:08:17,840 Speaker 1: just look at the Milky Way galaxy and see if 140 00:08:18,400 --> 00:08:21,760 Speaker 1: if things get squished in one direction relative to another, 141 00:08:21,840 --> 00:08:25,200 Speaker 1: for like supermassive gravitational waves, Like maybe you can look 142 00:08:25,240 --> 00:08:27,560 Speaker 1: at the red shift at one end versus the blue 143 00:08:27,560 --> 00:08:30,240 Speaker 1: shift at the other and see if there's a difference 144 00:08:30,320 --> 00:08:34,080 Speaker 1: that sort of correlates as you move around. Yes, yes 145 00:08:34,120 --> 00:08:39,559 Speaker 1: we can. We just have to observe how gravitational waves 146 00:08:39,559 --> 00:08:43,720 Speaker 1: are affecting all the bodies in the galaxy. I don't 147 00:08:43,920 --> 00:08:46,920 Speaker 1: see why you couldn't. In fact, that would be probably 148 00:08:46,960 --> 00:08:51,600 Speaker 1: a good way to measure antitecht gravitational waves. So if 149 00:08:51,600 --> 00:08:55,120 Speaker 1: you used an entire galaxy, and let's say you're one 150 00:08:55,240 --> 00:08:58,360 Speaker 1: edge of the galaxy versus the opposite edge of the galaxy, 151 00:08:58,400 --> 00:09:02,080 Speaker 1: and you were using the same principle, you should be 152 00:09:02,120 --> 00:09:06,400 Speaker 1: able to pick up the movement of a gravitational wave 153 00:09:06,640 --> 00:09:10,880 Speaker 1: through that galaxy. Since you're asking that question, I would say, yes, 154 00:09:10,920 --> 00:09:14,480 Speaker 1: you can use the whole galaxies of gravitational wave detector. 155 00:09:15,360 --> 00:09:22,319 Speaker 1: If you have a large gravitational waves traveling through the galaxy, 156 00:09:22,440 --> 00:09:28,000 Speaker 1: you will impact some stars before others, and will increase 157 00:09:28,040 --> 00:09:33,000 Speaker 1: and decrease the length the distance between two far apart 158 00:09:33,080 --> 00:09:37,880 Speaker 1: stars quite significantly. So it's probably a very good gravitational 159 00:09:37,880 --> 00:09:41,720 Speaker 1: wave detective. All right. So our listeners are smart, they 160 00:09:41,720 --> 00:09:44,480 Speaker 1: know something about gravitational waves, and they have the idea 161 00:09:44,760 --> 00:09:48,240 Speaker 1: that the gravitational waves must be somehow affecting things in 162 00:09:48,280 --> 00:09:51,520 Speaker 1: the galaxy, and then we could see that effect somehow. 163 00:09:52,080 --> 00:09:56,040 Speaker 1: But nobody quite figured out exactly how we see those effects. 164 00:09:56,200 --> 00:09:58,839 Speaker 1: These ideas there about red shift and blue shift and 165 00:09:58,960 --> 00:10:03,560 Speaker 1: optical lensing and ripples against things. But it's a tricky topic, 166 00:10:03,600 --> 00:10:05,720 Speaker 1: and we're gonna dig to it and explain to you 167 00:10:05,800 --> 00:10:10,559 Speaker 1: exactly how to use the entire galaxy as your physics experiment. 168 00:10:10,800 --> 00:10:13,920 Speaker 1: But first, let's just remind ourselves what we're talking about observing, 169 00:10:14,280 --> 00:10:16,880 Speaker 1: what we want to see out there, what we're trying 170 00:10:16,920 --> 00:10:20,520 Speaker 1: to study, what we're using the entire galaxy as a 171 00:10:20,559 --> 00:10:25,640 Speaker 1: detector of. Are these crazy things called gravitational waves? What 172 00:10:25,800 --> 00:10:28,760 Speaker 1: is a gravitational wave anyway? Well, you know what a 173 00:10:28,840 --> 00:10:31,679 Speaker 1: wave is. A wave is when something moves up and down, 174 00:10:31,840 --> 00:10:33,480 Speaker 1: Like you put your hand in your bathtub and you 175 00:10:33,520 --> 00:10:36,559 Speaker 1: slap the water and you get a wave of the water. Right, 176 00:10:36,600 --> 00:10:38,200 Speaker 1: The water goes down and then goes up, and then 177 00:10:38,200 --> 00:10:39,960 Speaker 1: it goes down and then goes up. Or you see 178 00:10:40,000 --> 00:10:42,640 Speaker 1: waves in the ocean here in southern California and you 179 00:10:42,679 --> 00:10:44,800 Speaker 1: can serve them, and you might wonder like, well, why 180 00:10:45,040 --> 00:10:47,480 Speaker 1: are there waves? Right? Why does the water in the 181 00:10:47,480 --> 00:10:50,600 Speaker 1: bathtub go down in waves rather than all going down 182 00:10:50,679 --> 00:10:53,400 Speaker 1: at once? And that's because of a really important property 183 00:10:53,440 --> 00:10:56,559 Speaker 1: in physics called locality. When your hand hits the water, 184 00:10:56,960 --> 00:10:59,760 Speaker 1: it only affects the water that it touches, doesn't affect 185 00:10:59,760 --> 00:11:01,559 Speaker 1: the water water on the other side of the bathtub 186 00:11:01,720 --> 00:11:05,120 Speaker 1: or in bathtubs all over the universe. Right, Physics is 187 00:11:05,160 --> 00:11:08,920 Speaker 1: local and information takes time to propagate, So the water 188 00:11:09,000 --> 00:11:11,600 Speaker 1: on the other side of the bathtub doesn't know that 189 00:11:11,640 --> 00:11:14,439 Speaker 1: you've hit the water on this side until it gets 190 00:11:14,480 --> 00:11:18,400 Speaker 1: that information, until the wave arrives there. It's the same story. 191 00:11:18,559 --> 00:11:21,320 Speaker 1: For example, you pluck a guitar string, right, which part 192 00:11:21,320 --> 00:11:23,760 Speaker 1: of the string starts to vibrate at first? Well, the 193 00:11:23,800 --> 00:11:26,760 Speaker 1: part that you plucked, and the rest then moves as 194 00:11:26,800 --> 00:11:30,080 Speaker 1: that information moves down the string. So then why do 195 00:11:30,080 --> 00:11:32,400 Speaker 1: you get a wave because the part that you pluck 196 00:11:32,520 --> 00:11:34,880 Speaker 1: moves down and then it comes back up, and then 197 00:11:34,880 --> 00:11:36,840 Speaker 1: it goes back down and then it comes back up 198 00:11:36,920 --> 00:11:40,720 Speaker 1: and the wave are those ripples moving down the string. 199 00:11:40,960 --> 00:11:45,000 Speaker 1: If information propagated instantaneously, the whole string would move at once. 200 00:11:45,120 --> 00:11:46,960 Speaker 1: But the reason it doesn't, the reason you get a 201 00:11:47,000 --> 00:11:51,280 Speaker 1: wave is because information doesn't propagate instantaneously. So let's get 202 00:11:51,280 --> 00:11:57,120 Speaker 1: back to gravity. Gravitational waves are the waves in space itself, right, 203 00:11:57,160 --> 00:11:59,480 Speaker 1: How do you make waves in space? Why does that 204 00:11:59,600 --> 00:12:03,319 Speaker 1: even mean? Well, remember that we know now that space 205 00:12:03,400 --> 00:12:05,679 Speaker 1: is not just like the backdrop. It's not just like 206 00:12:05,800 --> 00:12:09,080 Speaker 1: where things happen in the universe. It's a thing in 207 00:12:09,120 --> 00:12:12,719 Speaker 1: and of itself. It has properties. It can do things 208 00:12:12,760 --> 00:12:17,800 Speaker 1: that emptiness or nothingness can do. For example, it can bend. 209 00:12:18,200 --> 00:12:21,760 Speaker 1: If you put a big mass in space, what happens, Well, 210 00:12:22,120 --> 00:12:27,000 Speaker 1: space bends around that mass. It changes the curvature of space. 211 00:12:27,480 --> 00:12:29,240 Speaker 1: And a lot of you are probably thinking like a 212 00:12:29,280 --> 00:12:32,120 Speaker 1: bowling ball on a rubber sheet, right, And that's a 213 00:12:32,200 --> 00:12:35,040 Speaker 1: helpful analogy to sort of shape your mind out of 214 00:12:35,040 --> 00:12:38,199 Speaker 1: the idea that space is nothingness, that it can have curvature. 215 00:12:38,520 --> 00:12:42,400 Speaker 1: But it's also confusing because it's suggesting that space is 216 00:12:42,440 --> 00:12:45,520 Speaker 1: curving in some other dimension. In that example, space is 217 00:12:45,559 --> 00:12:48,080 Speaker 1: a two dimensional rubber sheet, and it's curving in some 218 00:12:48,320 --> 00:12:52,120 Speaker 1: third dimension because the bowling ball is pulling it down right, Well, 219 00:12:52,120 --> 00:12:54,599 Speaker 1: that's not what happens in our universe. Our space is 220 00:12:54,640 --> 00:12:58,040 Speaker 1: already three dimensional, and when it curves, what we mean 221 00:12:58,120 --> 00:13:01,880 Speaker 1: is that it changes the relative of distance between two points. 222 00:13:02,160 --> 00:13:04,559 Speaker 1: Means that things that might have seemed further away are 223 00:13:04,559 --> 00:13:08,040 Speaker 1: now closer because space is sort of scrunched. And that's why, 224 00:13:08,080 --> 00:13:12,640 Speaker 1: for example, photons bend around massive objects, because photons always 225 00:13:12,679 --> 00:13:15,840 Speaker 1: take the shortest path available to them, and that shortest 226 00:13:15,880 --> 00:13:19,400 Speaker 1: path looks like a curve. If you aren't aware of 227 00:13:19,440 --> 00:13:21,640 Speaker 1: the bending of space, and we have no way to 228 00:13:21,720 --> 00:13:24,040 Speaker 1: detect the bending of space, we can't see it, we 229 00:13:24,080 --> 00:13:27,640 Speaker 1: can't feel it other than watching things trace it out. 230 00:13:27,880 --> 00:13:30,360 Speaker 1: So that's why the Earth moves in a circle around 231 00:13:30,360 --> 00:13:32,320 Speaker 1: the Sun, because the space is bent in a way 232 00:13:32,320 --> 00:13:35,800 Speaker 1: that makes that its most natural motion. Alright, so space 233 00:13:35,840 --> 00:13:38,040 Speaker 1: can bend, But how does it ripple. How do you 234 00:13:38,080 --> 00:13:40,880 Speaker 1: get a wave in space? Well, the same way you 235 00:13:40,880 --> 00:13:44,120 Speaker 1: get a wave in your bathtub. Say, for example, you 236 00:13:44,400 --> 00:13:47,800 Speaker 1: deleted the Sun from our solar system. What would happen. Well, 237 00:13:47,880 --> 00:13:50,920 Speaker 1: you guys know that gravity doesn't move instantaneously, so we 238 00:13:50,960 --> 00:13:55,320 Speaker 1: wouldn't notice for eight minutes. That's a gravitational wave. That's 239 00:13:55,440 --> 00:13:59,800 Speaker 1: information about the shape of space propagating through space. It's 240 00:14:00,480 --> 00:14:03,520 Speaker 1: just like when you plug a guitar string, the information 241 00:14:03,559 --> 00:14:06,400 Speaker 1: that the string was plucked moves down the string. If 242 00:14:06,400 --> 00:14:09,439 Speaker 1: you delete the Sun, the information that space is no 243 00:14:09,559 --> 00:14:14,400 Speaker 1: longer bent moves through space, making it flat rather than curved. 244 00:14:14,880 --> 00:14:17,800 Speaker 1: And if you have two black holes, for example, orbiting 245 00:14:17,880 --> 00:14:21,320 Speaker 1: each other, then they are making huge gravitational waves. Because 246 00:14:21,320 --> 00:14:25,440 Speaker 1: anything that has mass and accelerates makes a gravitational wave. 247 00:14:25,520 --> 00:14:28,920 Speaker 1: It's changing the curvature of space through time, and that's 248 00:14:28,960 --> 00:14:32,840 Speaker 1: what creates gravitational waves. And so black holes, for example, 249 00:14:32,960 --> 00:14:36,040 Speaker 1: orbiting each other and eventually collapsing into a single mega 250 00:14:36,080 --> 00:14:39,280 Speaker 1: black hole, they send out these ripples as they orbit 251 00:14:39,320 --> 00:14:41,880 Speaker 1: each other. They're changing the shape of space around them 252 00:14:41,920 --> 00:14:44,960 Speaker 1: because they're very massive, and they're bending space, and the 253 00:14:45,040 --> 00:14:48,000 Speaker 1: way they're doing is changing because they are orbiting each other. 254 00:14:48,320 --> 00:14:51,000 Speaker 1: So that's where those gravitational waves come from. That's where 255 00:14:51,000 --> 00:14:53,920 Speaker 1: the ripples in space come from. And so how do 256 00:14:53,960 --> 00:14:56,920 Speaker 1: you detect the ripples in space and time? I said earlier, 257 00:14:57,000 --> 00:14:59,720 Speaker 1: And we can't see or feel the bending of space. 258 00:15:00,120 --> 00:15:04,400 Speaker 1: All we can do is detect the change in relative distances. 259 00:15:04,440 --> 00:15:07,040 Speaker 1: If the space between me and you contracts, then the 260 00:15:07,080 --> 00:15:10,280 Speaker 1: distance between us contracts. You might think, well, whold lot 261 00:15:10,320 --> 00:15:12,760 Speaker 1: of second. If we have a ruler between us and 262 00:15:12,960 --> 00:15:16,680 Speaker 1: space between us contracts, won't the ruler also contract. There's 263 00:15:16,680 --> 00:15:19,120 Speaker 1: a chance of that. So to avoid that, we build 264 00:15:19,200 --> 00:15:22,440 Speaker 1: rulers out of light. We send light pulses back and forth, 265 00:15:22,720 --> 00:15:25,560 Speaker 1: because if the space between me and you get smaller, 266 00:15:25,720 --> 00:15:28,520 Speaker 1: then light will cover that distance more quickly. And if 267 00:15:28,520 --> 00:15:30,560 Speaker 1: you have a mirror, I can shoot my laser at 268 00:15:30,600 --> 00:15:33,040 Speaker 1: your mirror and measure how long it takes for that 269 00:15:33,120 --> 00:15:35,200 Speaker 1: light to come back. And so if a gravitational wave 270 00:15:35,240 --> 00:15:37,640 Speaker 1: passes between you and me, and I'm doing that all 271 00:15:37,640 --> 00:15:40,560 Speaker 1: the time, I'll notice because all of a sudden, the 272 00:15:40,600 --> 00:15:43,880 Speaker 1: space between us will be shorter and then longer as 273 00:15:43,920 --> 00:15:47,800 Speaker 1: the gravitational wave passes. And this is not a theoretical idea, 274 00:15:47,960 --> 00:15:51,280 Speaker 1: This is real. This is something we have actually seen. 275 00:15:51,520 --> 00:15:55,400 Speaker 1: People have built these detectors they're called Ligo and Vitigo, 276 00:15:55,480 --> 00:15:58,400 Speaker 1: and they have these mirrors underground and the mirrors are 277 00:15:58,520 --> 00:16:00,760 Speaker 1: very very stable. They try not to shake them at 278 00:16:00,760 --> 00:16:03,480 Speaker 1: all because any shaking those mirrors makes it impossible to 279 00:16:03,520 --> 00:16:06,760 Speaker 1: see gravitational waves, which after all look a lot like 280 00:16:06,840 --> 00:16:09,480 Speaker 1: the shaking of the mirrors. So they have these mirrors 281 00:16:09,560 --> 00:16:12,920 Speaker 1: hyper stabilized. They're hanging from cords, and those cords are 282 00:16:12,920 --> 00:16:15,080 Speaker 1: attached to something else, which is buffered, which is attached 283 00:16:15,120 --> 00:16:17,720 Speaker 1: to something else, which is protected from shaking. It's like 284 00:16:17,920 --> 00:16:21,440 Speaker 1: nine layers of protection against any sort of activity trucks 285 00:16:21,520 --> 00:16:24,360 Speaker 1: driving by, or people slamming screen doors, or any kind 286 00:16:24,400 --> 00:16:26,320 Speaker 1: of thing that would make a signal that looks like 287 00:16:26,360 --> 00:16:28,560 Speaker 1: a gravitational wave. The first one we saw was in 288 00:16:28,600 --> 00:16:31,320 Speaker 1: ten It won a Nobel Prize. And now we've seen 289 00:16:31,360 --> 00:16:33,840 Speaker 1: more than a dozen of these things from black holes 290 00:16:33,880 --> 00:16:37,120 Speaker 1: nearby that have collided and sent these pulses, and we 291 00:16:37,120 --> 00:16:39,760 Speaker 1: were kind of surprised by how common these things were. 292 00:16:40,280 --> 00:16:42,480 Speaker 1: So now you might be thinking, great, we have a 293 00:16:42,520 --> 00:16:45,840 Speaker 1: gravitational wave detector. We've seen these things. Why would we 294 00:16:45,880 --> 00:16:48,960 Speaker 1: need to build a gravitational wave detector at the size 295 00:16:49,040 --> 00:16:52,080 Speaker 1: of the galaxy. Well, gravitational waves come in lots of 296 00:16:52,120 --> 00:16:55,600 Speaker 1: different colors, basically, just the same way light has lots 297 00:16:55,640 --> 00:17:00,160 Speaker 1: of different frequencies. Light is electromagnetic radiation, and it can 298 00:17:00,200 --> 00:17:02,160 Speaker 1: have a frequency that puts it in the visible so 299 00:17:02,200 --> 00:17:04,680 Speaker 1: it has different colors, or it can have very long 300 00:17:04,800 --> 00:17:07,159 Speaker 1: frequencies like down in the radio, or it can have 301 00:17:07,240 --> 00:17:09,480 Speaker 1: very short frequencies and be an X ray or a 302 00:17:09,520 --> 00:17:12,000 Speaker 1: gamma ray. So all of these are different kinds of 303 00:17:12,040 --> 00:17:15,800 Speaker 1: electromagnetic radiation and we need different kind of instruments to 304 00:17:16,000 --> 00:17:18,320 Speaker 1: see them. You can't see the same thing with an 305 00:17:18,320 --> 00:17:21,760 Speaker 1: optical telescope that you can see whether radio antenna or 306 00:17:21,800 --> 00:17:24,800 Speaker 1: an X ray telescope. Well, the same thing is true 307 00:17:24,840 --> 00:17:29,879 Speaker 1: for gravitational waves. Gravitational waves come in all different frequencies. 308 00:17:30,040 --> 00:17:33,200 Speaker 1: Space can ripple it lots of different frequencies, and very 309 00:17:33,320 --> 00:17:37,000 Speaker 1: high frequency ripples are different from very low frequency ripples, 310 00:17:37,040 --> 00:17:38,720 Speaker 1: and the kind of things that we can see with 311 00:17:38,880 --> 00:17:42,959 Speaker 1: LIGO are in a sort of narrow range of gravitational waves. 312 00:17:43,160 --> 00:17:47,280 Speaker 1: It was designed to see gravitational waves from solar mass 313 00:17:47,320 --> 00:17:50,040 Speaker 1: black holes that were colliding with each other, and so 314 00:17:50,080 --> 00:17:53,200 Speaker 1: it's sort of only sensitive to that little spectrum. Imagine 315 00:17:53,240 --> 00:17:55,840 Speaker 1: if we had only ever built optical telescopes and we 316 00:17:55,840 --> 00:17:58,399 Speaker 1: couldn't look at the sky in the UV or in 317 00:17:58,440 --> 00:18:01,040 Speaker 1: the X ray or in the IDEO, we would be 318 00:18:01,119 --> 00:18:04,159 Speaker 1: missing a huge slice of the picture. So what we 319 00:18:04,200 --> 00:18:07,679 Speaker 1: need to do our build gravitational wave detectors that can 320 00:18:07,720 --> 00:18:12,080 Speaker 1: detect various different frequencies of gravitational waves so we can 321 00:18:12,160 --> 00:18:15,199 Speaker 1: listen to the messages from the universe and learn all 322 00:18:15,240 --> 00:18:17,439 Speaker 1: of its crazy secrets. So we'll talk about how to 323 00:18:17,480 --> 00:18:21,000 Speaker 1: build gravitational wave detectors that can detect very very low 324 00:18:21,160 --> 00:18:24,680 Speaker 1: frequency gravitational waves and tell us all about what's going 325 00:18:24,760 --> 00:18:28,280 Speaker 1: on in the early universe and the collisions of supermassive 326 00:18:28,359 --> 00:18:44,920 Speaker 1: black holes. But first, let's take a quick break. All right, 327 00:18:44,960 --> 00:18:48,720 Speaker 1: we're back and we are talking about building a gravitational 328 00:18:48,760 --> 00:18:52,879 Speaker 1: wave detector the size of the galaxy actually made out 329 00:18:52,920 --> 00:18:56,840 Speaker 1: of the galaxy, and we reminded ourselves what gravitational waves 330 00:18:56,880 --> 00:18:59,440 Speaker 1: are and how they have been seen so far by 331 00:18:59,520 --> 00:19:04,080 Speaker 1: gravity aational wave observatories on Earth that use delicate mirrors 332 00:19:04,119 --> 00:19:09,480 Speaker 1: balanced underground miles apart to detect very very small deviations 333 00:19:09,520 --> 00:19:13,000 Speaker 1: in the distances between those mirrors. These deviations are like 334 00:19:13,160 --> 00:19:16,800 Speaker 1: one part in ten to the twenty into the extraordinary 335 00:19:16,840 --> 00:19:19,680 Speaker 1: experimental accomplishment that they can do these things. It took 336 00:19:19,680 --> 00:19:23,399 Speaker 1: a huge amount of work to make those mirrors insensitive 337 00:19:23,640 --> 00:19:25,639 Speaker 1: to all sorts of things that would shake them, that 338 00:19:25,640 --> 00:19:28,879 Speaker 1: would look like the gravitational waves, and when they finally 339 00:19:28,920 --> 00:19:31,480 Speaker 1: did see them, it was a really nice, very clear 340 00:19:31,480 --> 00:19:34,080 Speaker 1: signature because they knew exactly what they were looking for. 341 00:19:34,359 --> 00:19:37,600 Speaker 1: They knew what kind of gravitational waves black holes should 342 00:19:37,680 --> 00:19:40,520 Speaker 1: make as they fall into each other. What happens is 343 00:19:40,560 --> 00:19:44,160 Speaker 1: that the black holes start slowly moving towards each other 344 00:19:44,520 --> 00:19:47,080 Speaker 1: as they get closer and closer, and they start spiraling 345 00:19:47,160 --> 00:19:50,800 Speaker 1: faster and faster. So the frequency of the gravitational wave 346 00:19:50,960 --> 00:19:54,479 Speaker 1: increases as the black holes get closer together. And so 347 00:19:54,560 --> 00:19:57,520 Speaker 1: they call this like a chirp because it goes faster, faster, faster, faster, 348 00:19:57,600 --> 00:19:59,200 Speaker 1: faster and higher entire and hire and higher and high, 349 00:19:59,480 --> 00:20:01,719 Speaker 1: and that's a hi, as my voice will go. So 350 00:20:01,760 --> 00:20:03,600 Speaker 1: they knew sort of what they were looking for. They 351 00:20:03,640 --> 00:20:07,359 Speaker 1: did all these numerical relativity calculations to figure out just 352 00:20:07,440 --> 00:20:09,720 Speaker 1: what it looks for. But you know, those black holes 353 00:20:09,720 --> 00:20:13,680 Speaker 1: were generating gravitational waves long before we saw them. It 354 00:20:13,760 --> 00:20:16,639 Speaker 1: took years for these black holes to actually merge. What 355 00:20:16,760 --> 00:20:20,080 Speaker 1: we saw was just the last little bit as the 356 00:20:20,160 --> 00:20:23,440 Speaker 1: frequency moved into a range that Ligo could see it. 357 00:20:23,680 --> 00:20:27,160 Speaker 1: Ligo was designed to see gravitational waves from black hole mergers, 358 00:20:27,200 --> 00:20:30,120 Speaker 1: but only the last few seconds of them. Right there 359 00:20:30,119 --> 00:20:33,240 Speaker 1: were years, probably a gravitational waves that we couldn't see. 360 00:20:33,600 --> 00:20:37,560 Speaker 1: So why can LIGO not see gravitational waves that are longer? 361 00:20:37,680 --> 00:20:41,880 Speaker 1: The problem is seismic noise. The Earth itself is shaking. 362 00:20:42,040 --> 00:20:43,760 Speaker 1: We live on the surface of the Earth, which is 363 00:20:43,760 --> 00:20:46,480 Speaker 1: part of the crust, and the crust is always sliding, 364 00:20:46,640 --> 00:20:50,040 Speaker 1: and that makes it very difficult to see little ripples 365 00:20:50,080 --> 00:20:52,399 Speaker 1: in space and time. We can see them if the 366 00:20:52,480 --> 00:20:55,080 Speaker 1: ripples are fast enough, sort of faster than the Earth 367 00:20:55,160 --> 00:21:00,320 Speaker 1: typically shakes, but anything at a lower frequency, the sizemic vways, 368 00:21:00,400 --> 00:21:04,040 Speaker 1: the shaking of the Earth itself makes basically impossible to 369 00:21:04,119 --> 00:21:07,600 Speaker 1: see those things. The Earth is shaking more loudly than 370 00:21:07,720 --> 00:21:10,879 Speaker 1: those gravitational waves, and it's not just the frequency, it's 371 00:21:10,920 --> 00:21:14,199 Speaker 1: because of the amplitude. Also, the intensity of the gravitational 372 00:21:14,240 --> 00:21:17,520 Speaker 1: wave signal gets stronger as you get near the end 373 00:21:17,560 --> 00:21:19,520 Speaker 1: of the black hole merger. As the black holes are 374 00:21:19,520 --> 00:21:22,720 Speaker 1: getting close and closer together, the gravitational waves get stronger. 375 00:21:22,800 --> 00:21:24,919 Speaker 1: So the gravitational waves from the early part of the 376 00:21:24,960 --> 00:21:29,919 Speaker 1: story we're missing because they're longer frequencies that our detectors 377 00:21:29,960 --> 00:21:32,280 Speaker 1: can't see over the seis mc noise of the Earth, 378 00:21:32,480 --> 00:21:35,399 Speaker 1: and they're much quieter, which makes it harder for us 379 00:21:35,440 --> 00:21:38,240 Speaker 1: to see them. So how do you see these longer 380 00:21:38,359 --> 00:21:42,000 Speaker 1: frequency gravitational waves. Then, well, the problem is that you're 381 00:21:42,160 --> 00:21:45,800 Speaker 1: buried in the Earth. One idea is, don't be buried 382 00:21:45,800 --> 00:21:49,120 Speaker 1: in the Earth. Take it to space. Right. So one 383 00:21:49,280 --> 00:21:53,399 Speaker 1: science fiction sounding project that's actually very real is a 384 00:21:53,440 --> 00:21:58,239 Speaker 1: project called LISA, which is a laser interferometer in space. Right. 385 00:21:58,320 --> 00:22:01,160 Speaker 1: It takes the same concept of having mirrors where you're 386 00:22:01,160 --> 00:22:04,040 Speaker 1: bouncing lasers back and forth, and it puts it out 387 00:22:04,119 --> 00:22:07,800 Speaker 1: there in space. That's much more technologically difficult and expensive, 388 00:22:07,840 --> 00:22:10,800 Speaker 1: of course, but it does solve this problem of the 389 00:22:10,880 --> 00:22:14,520 Speaker 1: Earth background noise. There is no seismic noise out there 390 00:22:14,600 --> 00:22:17,760 Speaker 1: in space. So LISA would be much more powerful, much 391 00:22:17,800 --> 00:22:22,800 Speaker 1: more sensitive, and able to hear gravitational waves at longer frequencies. 392 00:22:23,119 --> 00:22:26,159 Speaker 1: But again that's expensive and that's far off in the future, 393 00:22:26,320 --> 00:22:28,920 Speaker 1: and so until then people are thinking, do we need 394 00:22:28,960 --> 00:22:32,639 Speaker 1: to build our own gravitational wave detectors or can we 395 00:22:32,720 --> 00:22:36,680 Speaker 1: find one already existing in the galaxy? Can we use 396 00:22:36,720 --> 00:22:40,520 Speaker 1: the galaxy itself as a gravitational wave detector? And the answer, 397 00:22:40,600 --> 00:22:43,239 Speaker 1: of course, obviously is yes, because if we're doing an 398 00:22:43,240 --> 00:22:45,360 Speaker 1: whole episode about it, I wouldn't get to this point 399 00:22:45,359 --> 00:22:48,000 Speaker 1: of the episode and then just say no goodbye, see 400 00:22:48,000 --> 00:22:49,960 Speaker 1: you later. The way we do it is us an 401 00:22:49,960 --> 00:22:54,560 Speaker 1: ocean of very precise clocks that naturally exist in the galaxy. 402 00:22:54,800 --> 00:22:58,960 Speaker 1: Of course, I'm talking about pulsars. Pulsars are the end 403 00:22:59,040 --> 00:23:01,640 Speaker 1: point of a stall are you know. The star forms 404 00:23:01,640 --> 00:23:05,320 Speaker 1: when gas and dust swirl together and compactify and eventually 405 00:23:05,359 --> 00:23:08,280 Speaker 1: get dense enough that fusion happens. Then hangs out for 406 00:23:08,320 --> 00:23:11,479 Speaker 1: a few billion years, burning all of that fuel, pushing 407 00:23:11,520 --> 00:23:15,440 Speaker 1: back against gravity, preventing it from a collapse. But eventually 408 00:23:15,560 --> 00:23:18,200 Speaker 1: that fuel gives out and it can no longer provide 409 00:23:18,200 --> 00:23:21,879 Speaker 1: the heat and the radiation to prevent gravity from compacting 410 00:23:21,920 --> 00:23:25,040 Speaker 1: it even further. And depending on the mass of the star, 411 00:23:25,280 --> 00:23:27,280 Speaker 1: it can end up in various scenarios. It might turn 412 00:23:27,320 --> 00:23:29,680 Speaker 1: into a black hole if it's very massive, might turn 413 00:23:29,720 --> 00:23:33,200 Speaker 1: into a white dwarf basically a hot lump of stuff 414 00:23:33,680 --> 00:23:36,119 Speaker 1: if it's not that massive. In the middle is a 415 00:23:36,200 --> 00:23:40,400 Speaker 1: category of object called neutron stars. Here there's enough gravity 416 00:23:40,440 --> 00:23:44,000 Speaker 1: to compact ify it to squeeze it down really really dense. 417 00:23:44,080 --> 00:23:46,520 Speaker 1: We're talking about a significant fraction of the mass of 418 00:23:46,560 --> 00:23:50,080 Speaker 1: the Sun in an area like the size of Los Angeles. 419 00:23:50,080 --> 00:23:53,920 Speaker 1: It's incredibly dense, it's incredibly weird matter. Also, it's called 420 00:23:53,920 --> 00:23:57,120 Speaker 1: a neutron star because it's been taken and squeezed so 421 00:23:57,200 --> 00:23:59,920 Speaker 1: much that the electrons and the protons and he had 422 00:24:00,080 --> 00:24:04,280 Speaker 1: ms are squeezed together and turn into neutrons. Usually it 423 00:24:04,320 --> 00:24:06,400 Speaker 1: goes the other way. You have a neutron hanging out, 424 00:24:06,440 --> 00:24:09,840 Speaker 1: it turns into a proton and an electron. But here 425 00:24:09,880 --> 00:24:12,520 Speaker 1: because the pressure that's basically been reversed, and you've got 426 00:24:12,520 --> 00:24:15,120 Speaker 1: an object which is mostly neutrons and in some really 427 00:24:15,160 --> 00:24:18,960 Speaker 1: weird intense state. In addition, these things are spinning really 428 00:24:19,000 --> 00:24:21,920 Speaker 1: really fast because they have all the angular momentum of 429 00:24:21,960 --> 00:24:24,200 Speaker 1: the original stuff that made them. But now they're a 430 00:24:24,280 --> 00:24:27,879 Speaker 1: really small space. And because angular momentum is conserved, you 431 00:24:27,880 --> 00:24:30,400 Speaker 1: can't just get rid of it. It doesn't just disappear. 432 00:24:30,640 --> 00:24:33,600 Speaker 1: Then it has to spin faster as it gets smaller, 433 00:24:33,960 --> 00:24:36,560 Speaker 1: just like a figure skater pulling in her arms and 434 00:24:36,680 --> 00:24:39,800 Speaker 1: you get more compact, you need to higher velocity to 435 00:24:39,840 --> 00:24:43,960 Speaker 1: match the smaller radius to have exactly the same angular momentum. 436 00:24:44,000 --> 00:24:46,600 Speaker 1: All right, So we have a spinning object, the neutron star, 437 00:24:47,119 --> 00:24:51,359 Speaker 1: some fraction of these have also really powerful magnetic fields, 438 00:24:51,440 --> 00:24:54,159 Speaker 1: and those magnetic fields operate on the particles on the 439 00:24:54,200 --> 00:24:57,840 Speaker 1: surface of the neutron star and can generate beams of energy. 440 00:24:57,960 --> 00:25:00,560 Speaker 1: They push the protons and the neutrons and they generate 441 00:25:00,600 --> 00:25:04,200 Speaker 1: these massive beams of energy which follow the magnetic fields. 442 00:25:04,240 --> 00:25:07,000 Speaker 1: So you have this spinning object with a very powerful 443 00:25:07,000 --> 00:25:09,879 Speaker 1: magnetic field, with a beam of energy coming out the 444 00:25:09,880 --> 00:25:13,160 Speaker 1: top and the bottom, the magnetic north and the magnetic south. 445 00:25:13,400 --> 00:25:16,000 Speaker 1: What happens to the spin of this object is not 446 00:25:16,119 --> 00:25:19,440 Speaker 1: aligned with the magnetic axis. What if the beam is 447 00:25:19,480 --> 00:25:21,480 Speaker 1: not shooting straight up, so it's always going in the 448 00:25:21,480 --> 00:25:23,800 Speaker 1: same direction, but sort of off to the side a 449 00:25:23,840 --> 00:25:26,520 Speaker 1: little bit, then what happens is that that beam sweeps 450 00:25:26,560 --> 00:25:29,639 Speaker 1: around it points in a different direction. Right. Imagine holding 451 00:25:29,640 --> 00:25:32,680 Speaker 1: a flashlight and spinning around. If you're holding it straight up, 452 00:25:32,840 --> 00:25:35,680 Speaker 1: the flashlight doesn't change as you spin, But if you're 453 00:25:35,680 --> 00:25:38,080 Speaker 1: holding it to the side, then you're gonna be blinding 454 00:25:38,119 --> 00:25:40,960 Speaker 1: different people as you spin around. Right. That's what a 455 00:25:41,000 --> 00:25:44,800 Speaker 1: pulsar is a very intense beam of light pointing outside ways, 456 00:25:44,880 --> 00:25:47,960 Speaker 1: so that as it sweeps around, that beam passes over 457 00:25:48,040 --> 00:25:50,760 Speaker 1: different things. And from Earth we see these things when 458 00:25:50,840 --> 00:25:53,560 Speaker 1: that beam passes us. So there's a lot of pulsars 459 00:25:53,600 --> 00:25:55,720 Speaker 1: out there in the galaxy that we can't see because 460 00:25:55,720 --> 00:25:58,080 Speaker 1: their beam never passes us. But the ones where the 461 00:25:58,119 --> 00:26:02,200 Speaker 1: beam does sweep over the Earth, we see that as pulses. 462 00:26:02,520 --> 00:26:04,760 Speaker 1: We got a pulse every time it sweeps by. The 463 00:26:04,760 --> 00:26:07,879 Speaker 1: incredible thing is that they're very very regular. Here you 464 00:26:07,920 --> 00:26:11,399 Speaker 1: have an object of incredible mass, trillions of tons of 465 00:26:11,400 --> 00:26:15,280 Speaker 1: stuff spinning at very high speeds up to like hundreds 466 00:26:15,280 --> 00:26:18,280 Speaker 1: of hurts, right like an incredible amount of stuff, spending 467 00:26:18,400 --> 00:26:22,360 Speaker 1: many times per second, and doing it very regularly. It's 468 00:26:22,359 --> 00:26:24,680 Speaker 1: not like every point two seconds and then every point 469 00:26:24,760 --> 00:26:27,720 Speaker 1: three seconds and every point four seconds. These things are 470 00:26:27,800 --> 00:26:31,040 Speaker 1: more precise than some atomic clocks. They're like the most 471 00:26:31,119 --> 00:26:33,879 Speaker 1: precise natural clocks out there we have found, and the 472 00:26:33,960 --> 00:26:37,040 Speaker 1: universe is filled with them. They are all over the galaxy. 473 00:26:37,200 --> 00:26:39,560 Speaker 1: So you might imagine then how we might be able 474 00:26:39,600 --> 00:26:43,400 Speaker 1: to use them to measure the distortion of space. If 475 00:26:43,440 --> 00:26:45,640 Speaker 1: you are on Earth and you're surrounded by a bunch 476 00:26:45,640 --> 00:26:48,679 Speaker 1: of pulsars, and even watching these pulsars for a while 477 00:26:48,720 --> 00:26:51,160 Speaker 1: so you know them. You know how long it takes 478 00:26:51,200 --> 00:26:54,119 Speaker 1: between pulses for a given pulsar then what you can 479 00:26:54,160 --> 00:26:57,040 Speaker 1: do is see if that changes. Think about what happens 480 00:26:57,080 --> 00:27:01,000 Speaker 1: as a gravitational wave passes over the Earth. It changes 481 00:27:01,600 --> 00:27:05,399 Speaker 1: the distance between us and those pulsars. What that means 482 00:27:05,600 --> 00:27:09,120 Speaker 1: is that the pulses would take longer or shorter amounts 483 00:27:09,119 --> 00:27:12,000 Speaker 1: of time to arrive here on Earth. So if you 484 00:27:12,160 --> 00:27:14,679 Speaker 1: know how often the pulses should be arriving and you 485 00:27:14,720 --> 00:27:18,400 Speaker 1: see a deviation, you see your residual from what you expect, 486 00:27:18,560 --> 00:27:21,639 Speaker 1: then that means something happened. The distance between you and 487 00:27:21,640 --> 00:27:25,160 Speaker 1: that pulsar has changed. And so a while ago people 488 00:27:25,200 --> 00:27:28,080 Speaker 1: figured out how to use all of these pulsars, these 489 00:27:28,119 --> 00:27:32,720 Speaker 1: precise clocks to calculate what would happen if a gravitational 490 00:27:32,760 --> 00:27:35,639 Speaker 1: wave past us, and it wouldn't affect all pulsars the 491 00:27:35,680 --> 00:27:38,720 Speaker 1: same way, right, because gravitational waves have this sort of 492 00:27:38,800 --> 00:27:42,879 Speaker 1: quadruple effect. They squeeze in one direction at the same 493 00:27:42,920 --> 00:27:45,720 Speaker 1: time they're pulling in another direction. So we can't look 494 00:27:45,760 --> 00:27:48,600 Speaker 1: at an individual pulsar and say, oh, there was a 495 00:27:48,640 --> 00:27:51,000 Speaker 1: gravitation wave. What we need to do is have a 496 00:27:51,040 --> 00:27:54,040 Speaker 1: whole network of pulsars, have them all around us in 497 00:27:54,080 --> 00:27:57,160 Speaker 1: every direction, so that a gravitational wave has a very 498 00:27:57,160 --> 00:28:01,480 Speaker 1: distinct signature, so it looks different from other random weird 499 00:28:01,560 --> 00:28:04,359 Speaker 1: blips we might see, or changes in our instrument or 500 00:28:04,400 --> 00:28:08,000 Speaker 1: anything else that might affect the timing but isn't due 501 00:28:08,000 --> 00:28:11,879 Speaker 1: to gravitational waves. Is a classic trick and experimental physics 502 00:28:12,000 --> 00:28:14,360 Speaker 1: is to make the thing you're looking for look unique, 503 00:28:14,480 --> 00:28:16,919 Speaker 1: so that when you see it, you know you saw it. 504 00:28:17,200 --> 00:28:19,320 Speaker 1: And so there were a couple of folks named Hellings 505 00:28:19,320 --> 00:28:22,240 Speaker 1: and Downs, and they did this analysis and they showed 506 00:28:22,480 --> 00:28:25,720 Speaker 1: what would happen if a gravitational wave passed over the 507 00:28:25,720 --> 00:28:30,160 Speaker 1: Earth and between us and a whole network of pulsars, 508 00:28:30,200 --> 00:28:33,879 Speaker 1: And what would happen is a predictable pattern in the 509 00:28:33,920 --> 00:28:36,919 Speaker 1: way that the pulses arrive on Earth. You can google 510 00:28:37,000 --> 00:28:39,240 Speaker 1: this and check it out if you're interested in learning 511 00:28:39,240 --> 00:28:42,520 Speaker 1: more details. But there's a particular signature we would expect 512 00:28:42,560 --> 00:28:46,400 Speaker 1: to see in the pulses from pulsars and the timing 513 00:28:46,480 --> 00:28:50,440 Speaker 1: of those pulsars arriving here on Earth if a gravitational 514 00:28:50,480 --> 00:28:54,360 Speaker 1: wave passed. And remember that we're not targeting fast gravitational 515 00:28:54,400 --> 00:28:57,160 Speaker 1: waves the ones that liego can see. Those are things 516 00:28:57,160 --> 00:28:59,880 Speaker 1: where it's like a hundred hurts in the frequency. There 517 00:29:00,240 --> 00:29:03,320 Speaker 1: is fast ripples in space and time. We're interested in 518 00:29:03,480 --> 00:29:06,480 Speaker 1: slow ripples in space and time. We're interested in very 519 00:29:06,520 --> 00:29:10,000 Speaker 1: long gravitational waves. Were interested in like the beginnings of 520 00:29:10,080 --> 00:29:13,480 Speaker 1: black holes coming together, and not just little itty bitty 521 00:29:13,520 --> 00:29:16,480 Speaker 1: black holes like the ones that Lego has seen. We're 522 00:29:16,520 --> 00:29:21,120 Speaker 1: interested in super massive black holes right because we think 523 00:29:21,240 --> 00:29:24,560 Speaker 1: that those black holes also combined. We talked earlier about 524 00:29:24,800 --> 00:29:28,880 Speaker 1: galaxy colliders shooting one galaxy at another. Well, that actually 525 00:29:28,920 --> 00:29:31,680 Speaker 1: happens in the universe. I don't know who's controlling it, 526 00:29:31,760 --> 00:29:35,040 Speaker 1: or if anybody ever is, but galaxies do merge. We 527 00:29:35,080 --> 00:29:37,920 Speaker 1: see evidence for this in lots of galaxies. We can 528 00:29:37,920 --> 00:29:40,880 Speaker 1: tell that some galaxies have recently undergone a merger because 529 00:29:40,880 --> 00:29:43,400 Speaker 1: they're sort of chaotic, and we can see other galaxies 530 00:29:43,400 --> 00:29:45,960 Speaker 1: that have had mergers billions of years ago. We think 531 00:29:46,000 --> 00:29:48,720 Speaker 1: that the Milky Way, for example, has remnants of other 532 00:29:48,760 --> 00:29:53,000 Speaker 1: galaxies that it's eaten. So if galaxies have supermassive black 533 00:29:53,040 --> 00:29:57,280 Speaker 1: holes at their center, then what happens when two galaxies merge? 534 00:29:57,320 --> 00:30:00,320 Speaker 1: What happens when one eats another one, which you get 535 00:30:00,400 --> 00:30:04,040 Speaker 1: is the merger of super massive black holes. These things 536 00:30:04,120 --> 00:30:06,640 Speaker 1: are black holes, not like just a little bit bigger 537 00:30:06,640 --> 00:30:09,840 Speaker 1: than our Sun. These things have masses like ten million 538 00:30:09,960 --> 00:30:13,440 Speaker 1: or sometimes billions of times the mass of our Sun. 539 00:30:13,520 --> 00:30:16,560 Speaker 1: It's staggering. It's hard to even get your mind around. Now, 540 00:30:16,600 --> 00:30:19,720 Speaker 1: imagine two of them and they're coming together, and they're 541 00:30:19,800 --> 00:30:24,960 Speaker 1: eating each other. They're forming one huge Grandma black hole right. Well, 542 00:30:25,000 --> 00:30:27,680 Speaker 1: that is going to admit a lot of gravitational waves, 543 00:30:27,760 --> 00:30:30,720 Speaker 1: and in the very beginning, very early part of that, 544 00:30:31,120 --> 00:30:34,680 Speaker 1: while the galaxies are still merging, while those black holes 545 00:30:34,720 --> 00:30:38,080 Speaker 1: are just beginning their dance, there's going to be very 546 00:30:38,120 --> 00:30:42,760 Speaker 1: low frequency, long gravitational waves that take a long time 547 00:30:42,800 --> 00:30:46,080 Speaker 1: to propagate, in a long time to measure as they 548 00:30:46,160 --> 00:30:49,080 Speaker 1: move through the universe. And so that's what a pulsar 549 00:30:49,400 --> 00:30:53,960 Speaker 1: array could be sensitive to. It could see gravitational waves 550 00:30:54,240 --> 00:30:57,960 Speaker 1: from the collisions of super massive black holes from the 551 00:30:58,000 --> 00:31:01,400 Speaker 1: beginning stages of those collisions while the two galaxies are 552 00:31:01,400 --> 00:31:04,840 Speaker 1: still beginning to form together. And we also don't understand 553 00:31:04,920 --> 00:31:08,000 Speaker 1: that the size of supermassive black holes. We know that 554 00:31:08,040 --> 00:31:12,240 Speaker 1: there's a relationship between galaxies and supermassive black holes that 555 00:31:12,280 --> 00:31:16,000 Speaker 1: typically the larger the black hole, the larger the galaxy, 556 00:31:16,040 --> 00:31:19,000 Speaker 1: But we don't understand how these supermassive black holes got 557 00:31:19,080 --> 00:31:22,000 Speaker 1: so big. We look back in the very early universe 558 00:31:22,240 --> 00:31:25,160 Speaker 1: and we see that there are already black holes like 559 00:31:25,240 --> 00:31:28,280 Speaker 1: a billion times the mass of the Sun, only a 560 00:31:28,360 --> 00:31:31,360 Speaker 1: billion years into the history of the universe, and in 561 00:31:31,400 --> 00:31:35,160 Speaker 1: our calculations, that's just not enough time to make that 562 00:31:35,240 --> 00:31:38,680 Speaker 1: bigger black holes. The deep mystery how these supermassive black 563 00:31:38,680 --> 00:31:42,160 Speaker 1: holes got so supermassive, and so one way to figure 564 00:31:42,160 --> 00:31:44,840 Speaker 1: this out is to see them merging. Is to understand 565 00:31:44,960 --> 00:31:47,520 Speaker 1: what happens when these two things combine. Is to look 566 00:31:47,520 --> 00:31:50,200 Speaker 1: at the early parts and say, oh, okay, this came 567 00:31:50,280 --> 00:31:53,120 Speaker 1: from too slightly smaller black holes, or maybe three, or 568 00:31:53,160 --> 00:31:56,400 Speaker 1: maybe something else entirely is going on. That's why we 569 00:31:56,440 --> 00:31:59,920 Speaker 1: are desperate to listen to these messages and to understand 570 00:32:00,040 --> 00:32:03,960 Speaker 1: what's going on with these very low frequency black holes. 571 00:32:04,000 --> 00:32:06,800 Speaker 1: So we talked about how to listen through low frequency 572 00:32:06,800 --> 00:32:10,240 Speaker 1: black holes by building a system of pulsars all across 573 00:32:10,280 --> 00:32:14,160 Speaker 1: the galaxy and watching as the signals from those pulsars 574 00:32:14,240 --> 00:32:17,560 Speaker 1: shift in frequency as a gravitational wave passes, and we 575 00:32:17,560 --> 00:32:20,600 Speaker 1: talked about what might be generating those gravitational waves. I 576 00:32:20,600 --> 00:32:22,760 Speaker 1: want to tell you all about an experiment that claims 577 00:32:22,760 --> 00:32:26,560 Speaker 1: to maybe have seen some of these low frequency gravitational 578 00:32:26,600 --> 00:32:30,040 Speaker 1: waves by using a pulsar array. But first, let's take 579 00:32:30,200 --> 00:32:45,440 Speaker 1: another break. All right, we're back and we are talking 580 00:32:45,480 --> 00:32:49,600 Speaker 1: about using the entire galaxy as a gravitational wave detector. 581 00:32:50,000 --> 00:32:53,800 Speaker 1: We reminded ourselves that gravitational waves are these ripples in 582 00:32:54,000 --> 00:32:57,520 Speaker 1: space and time. Sometimes they are generated when two small 583 00:32:57,600 --> 00:33:00,600 Speaker 1: black holes merged become a larger black hole, but they 584 00:33:00,600 --> 00:33:04,560 Speaker 1: can also be generated by super massive black holes as 585 00:33:04,600 --> 00:33:08,160 Speaker 1: galaxies merge and their central masses do a dance to 586 00:33:08,200 --> 00:33:10,440 Speaker 1: find out who's going to be in charge of the 587 00:33:10,480 --> 00:33:13,680 Speaker 1: new galaxy, and you can use pulsars to watch these 588 00:33:13,680 --> 00:33:17,200 Speaker 1: things happen. Pulsars are very regular clocks that send us 589 00:33:17,240 --> 00:33:20,560 Speaker 1: pulses at a very precise intervals, and as a gravitational 590 00:33:20,600 --> 00:33:24,240 Speaker 1: wave passes between us and them, shortening or extending the 591 00:33:24,280 --> 00:33:27,160 Speaker 1: distance between us and them, it can change the frequency 592 00:33:27,240 --> 00:33:29,840 Speaker 1: which those pulses arrive and give us a clue that 593 00:33:29,960 --> 00:33:32,920 Speaker 1: gravitational wave may have passed us. And this is not 594 00:33:32,960 --> 00:33:35,400 Speaker 1: a brand new idea, which means people have been doing 595 00:33:35,400 --> 00:33:38,240 Speaker 1: this for a while now. There's a group called Nano 596 00:33:38,320 --> 00:33:41,520 Speaker 1: grab that's been doing it for the last fifteen years. 597 00:33:41,720 --> 00:33:44,520 Speaker 1: They have a set of about forty five pulsars that 598 00:33:44,560 --> 00:33:47,520 Speaker 1: they've been listening to very regularly. They picked them and 599 00:33:47,520 --> 00:33:50,160 Speaker 1: they watch them with radio telescopes, and they observe the 600 00:33:50,280 --> 00:33:53,680 Speaker 1: frequency at which these pulses arrive here on Earth. And 601 00:33:53,720 --> 00:33:56,840 Speaker 1: after twelve and a half years they think they see 602 00:33:56,960 --> 00:34:00,719 Speaker 1: something interesting. They see something which they can't explain. They 603 00:34:00,760 --> 00:34:05,120 Speaker 1: see deviations in the patterns of these pulsars, right, And 604 00:34:05,120 --> 00:34:07,840 Speaker 1: that's exactly what you would expect to see if there 605 00:34:07,960 --> 00:34:11,040 Speaker 1: was a gravitational wave. You would expect that the pulsars 606 00:34:11,200 --> 00:34:14,040 Speaker 1: wouldn't be sending you their pulses at the very precise 607 00:34:14,080 --> 00:34:17,719 Speaker 1: atomic clock level, calibrated pulses that we're used to, but 608 00:34:17,800 --> 00:34:20,840 Speaker 1: that there would be these deviations. Now, nanogravi is not 609 00:34:20,920 --> 00:34:24,080 Speaker 1: his own experiment. It's of course using pulsars that are 610 00:34:24,120 --> 00:34:26,640 Speaker 1: already out there in the universe, and it uses telescopes 611 00:34:26,680 --> 00:34:29,759 Speaker 1: that already exist on Earth. For example, the Green Bank 612 00:34:29,760 --> 00:34:32,719 Speaker 1: Observatory that we always talked about in the center of 613 00:34:32,760 --> 00:34:35,359 Speaker 1: the radio quiet zone in the United States where you're 614 00:34:35,400 --> 00:34:38,000 Speaker 1: not allowed to own a telephone or turn on your microwave, 615 00:34:38,080 --> 00:34:42,080 Speaker 1: they used the Aristobo radio telescope before it's unfortunate collapse, 616 00:34:42,480 --> 00:34:44,480 Speaker 1: and they use all of these things together to try 617 00:34:44,520 --> 00:34:47,520 Speaker 1: to monitor all of these pulsars. Now, in January of 618 00:34:48,440 --> 00:34:51,120 Speaker 1: one they release their preliminary results, and what they see 619 00:34:51,640 --> 00:34:55,000 Speaker 1: is not consistent with no gravitational waves. Right, it's not 620 00:34:55,520 --> 00:34:59,480 Speaker 1: what you would expect if everything was normal. Unfortunately, it's 621 00:34:59,480 --> 00:35:03,400 Speaker 1: also not it's consistent with gravitational waves. We talked about 622 00:35:03,400 --> 00:35:05,920 Speaker 1: how if there were gravitational waves, you would expect to 623 00:35:05,920 --> 00:35:08,640 Speaker 1: see sort of a regular pattern. You would see pulsars 624 00:35:08,680 --> 00:35:11,719 Speaker 1: in one direction from Earth looking closer to you, and 625 00:35:11,760 --> 00:35:16,400 Speaker 1: pulsars in another direction, looking further because gravitational waves squeeze 626 00:35:16,400 --> 00:35:19,600 Speaker 1: space in one direction and lengthen it in another direction. 627 00:35:19,800 --> 00:35:22,680 Speaker 1: So that's not what they see. What they see can't 628 00:35:22,719 --> 00:35:25,799 Speaker 1: be explained by gravitational waves, but it also can't be 629 00:35:25,840 --> 00:35:29,760 Speaker 1: explained by anything we know. And that's exciting, right, because 630 00:35:29,800 --> 00:35:32,360 Speaker 1: every time you open up a new kind of eyeball 631 00:35:32,480 --> 00:35:34,560 Speaker 1: or build a new kind of ear to listen to 632 00:35:34,600 --> 00:35:38,400 Speaker 1: the universe's messages, we hear a surprise. Because sometimes we 633 00:35:38,440 --> 00:35:41,279 Speaker 1: go out there trying to answer one question and we 634 00:35:41,320 --> 00:35:44,400 Speaker 1: get evidence to answer another one, one we didn't even 635 00:35:44,440 --> 00:35:48,279 Speaker 1: know existed. We all remember stories of accidental discoveries. In fact, 636 00:35:48,360 --> 00:35:52,160 Speaker 1: pulsars themselves were an accidental discovery. Somebody was out there 637 00:35:52,239 --> 00:35:55,600 Speaker 1: looking to study quasars in the distant universe and hear 638 00:35:55,640 --> 00:35:59,359 Speaker 1: their radio messages and accidentally discovered pulsars. So it would 639 00:35:59,360 --> 00:36:01,960 Speaker 1: be pretty funny if pulsars then in turn gave us 640 00:36:01,960 --> 00:36:04,560 Speaker 1: clues about something else in the universe and we didn't 641 00:36:04,560 --> 00:36:07,719 Speaker 1: even know to look for. There are several of these 642 00:36:07,719 --> 00:36:10,840 Speaker 1: groups doing these studies watching pulsars. It takes a while 643 00:36:11,000 --> 00:36:14,080 Speaker 1: because we're talking about very low frequency events. We're talking 644 00:36:14,120 --> 00:36:19,200 Speaker 1: about gravitational waves. They could take years, decades, centuries to 645 00:36:19,440 --> 00:36:22,960 Speaker 1: propagate across the universe. Not that they're moving slowly, but 646 00:36:23,000 --> 00:36:26,520 Speaker 1: that their frequency is very very long, So the information 647 00:36:26,560 --> 00:36:30,200 Speaker 1: moves quickly, but the ripples in space themselves are moving 648 00:36:30,239 --> 00:36:32,480 Speaker 1: at a very slow speed, just like you can have 649 00:36:32,840 --> 00:36:35,399 Speaker 1: light traveling at the speed of light. Having very low 650 00:36:35,480 --> 00:36:38,359 Speaker 1: frequency waves like radio, and the kind of things they 651 00:36:38,360 --> 00:36:42,160 Speaker 1: can look for are not just super massive black hole collisions, 652 00:36:42,200 --> 00:36:46,080 Speaker 1: although that is super fascinating. We're also interested in general, 653 00:36:46,200 --> 00:36:50,120 Speaker 1: in what is the gravitational signal out there. We recently 654 00:36:50,120 --> 00:36:54,319 Speaker 1: did an episode about the cosmic gravitational background because we 655 00:36:54,400 --> 00:36:57,880 Speaker 1: suspect that the universe is filled with these low frequency 656 00:36:57,920 --> 00:37:00,880 Speaker 1: gravitational waves. We know that every thing that has mass 657 00:37:00,920 --> 00:37:04,880 Speaker 1: and accelerates creates gravitational waves. That means that as the 658 00:37:04,880 --> 00:37:07,799 Speaker 1: Earth goes around the Sun, it generates gravitational waves. It 659 00:37:07,840 --> 00:37:10,000 Speaker 1: means that every time you run to the store to 660 00:37:10,000 --> 00:37:13,120 Speaker 1: get a pint of ice cream, you generate gravitational waves. 661 00:37:13,239 --> 00:37:15,919 Speaker 1: And so there should be gravitational waves everywhere. There should 662 00:37:15,920 --> 00:37:17,719 Speaker 1: be sort of hard to make out. It's not like 663 00:37:17,760 --> 00:37:20,480 Speaker 1: we can pick out individual things unless they are very 664 00:37:20,560 --> 00:37:24,800 Speaker 1: dramatic events, like to nearby black holes colliding. But in general, 665 00:37:24,840 --> 00:37:26,880 Speaker 1: there should be sort of like a low level hum 666 00:37:27,160 --> 00:37:30,440 Speaker 1: of gravitational waves in the universe, some of them from 667 00:37:30,480 --> 00:37:34,520 Speaker 1: inspiring supermassive black holes and some of them from neutron 668 00:37:34,600 --> 00:37:37,719 Speaker 1: stars being formed or other black holes being created, or 669 00:37:37,840 --> 00:37:41,840 Speaker 1: supernovas should be generating gravitational waves. It should be everywhere. 670 00:37:41,960 --> 00:37:43,600 Speaker 1: So we should be able to sort of pick up 671 00:37:43,719 --> 00:37:47,680 Speaker 1: this low frequency gravitational waves as it sort of slashes 672 00:37:47,760 --> 00:37:50,680 Speaker 1: through the universe. And if we see something in those 673 00:37:50,800 --> 00:37:54,640 Speaker 1: low frequency gravitational waves that we don't expect, we might 674 00:37:54,800 --> 00:37:58,479 Speaker 1: learn something new about the universe. For example, we said 675 00:37:58,520 --> 00:38:02,239 Speaker 1: that one way to generate frequency gravitational waves that you 676 00:38:02,280 --> 00:38:06,759 Speaker 1: could detect with a galaxy size pulsar array come from 677 00:38:06,920 --> 00:38:09,920 Speaker 1: inspiraling black holes. Well, that might be true. What it 678 00:38:10,000 --> 00:38:13,120 Speaker 1: might be that the way these black holes merge, these 679 00:38:13,160 --> 00:38:16,720 Speaker 1: supermassive black holes merge, is different from what we expect. 680 00:38:16,719 --> 00:38:19,640 Speaker 1: There might be something else going on, and that might 681 00:38:19,640 --> 00:38:22,040 Speaker 1: help us understand how they get so big and how 682 00:38:22,120 --> 00:38:25,480 Speaker 1: galaxies form. Because when black holes pull each other together, 683 00:38:25,640 --> 00:38:28,440 Speaker 1: mostly what's going on is the force of gravity that 684 00:38:28,480 --> 00:38:32,200 Speaker 1: dominates everything. But black holes have other properties as well. Right, 685 00:38:32,239 --> 00:38:35,319 Speaker 1: black holes can spin because when something falls into a 686 00:38:35,320 --> 00:38:38,359 Speaker 1: black hole doesn't lose its angular momentum. So if something 687 00:38:38,400 --> 00:38:40,640 Speaker 1: falls into a black hole with angular momentum, then the 688 00:38:40,640 --> 00:38:44,280 Speaker 1: black hole itself has to spin. Anglo momentum doesn't go away, 689 00:38:44,520 --> 00:38:47,920 Speaker 1: same way electric charge doesn't go away. If you have 690 00:38:48,000 --> 00:38:50,719 Speaker 1: a black hole which is electrically neutral and you throw 691 00:38:50,760 --> 00:38:53,360 Speaker 1: an electron into it, what happens, Well, now you have 692 00:38:53,400 --> 00:38:55,880 Speaker 1: a black hole with a charge. So there's a famous 693 00:38:55,920 --> 00:38:59,080 Speaker 1: theorem called me no hair theorem that tells us that 694 00:38:59,120 --> 00:39:04,240 Speaker 1: black holes can have only those properties mass, spin, and charge, 695 00:39:04,560 --> 00:39:06,840 Speaker 1: and any other information about what's going on inside the 696 00:39:06,840 --> 00:39:09,360 Speaker 1: black hole is hidden from you, and that's not because 697 00:39:09,440 --> 00:39:11,359 Speaker 1: you can't give it a charge. It's because it's sort 698 00:39:11,360 --> 00:39:14,239 Speaker 1: of unstable that the process is going on there will 699 00:39:14,360 --> 00:39:17,040 Speaker 1: seek to balance it out. If, for example, you throw 700 00:39:17,040 --> 00:39:19,800 Speaker 1: a cork into a black hole, well, a cork feels 701 00:39:19,840 --> 00:39:23,200 Speaker 1: the strong nuclear force. It's a colored object, where color 702 00:39:23,320 --> 00:39:26,640 Speaker 1: is the equivalent of electric charge for the strong nuclear force. 703 00:39:26,960 --> 00:39:29,160 Speaker 1: What happens if you throw that into a black hole, 704 00:39:29,160 --> 00:39:31,239 Speaker 1: but there's so much energy there that it will pull 705 00:39:31,360 --> 00:39:34,799 Speaker 1: other corks out of the vacuum and eventually balance itself out. 706 00:39:35,200 --> 00:39:37,400 Speaker 1: That's why most things around us don't have a strong 707 00:39:37,480 --> 00:39:41,279 Speaker 1: nuclear charge, because those charges are inherently unstable. So that's 708 00:39:41,280 --> 00:39:44,000 Speaker 1: something that's going on with black holes, and black holes 709 00:39:44,000 --> 00:39:47,400 Speaker 1: are able to neutralize all those forces except for spin, 710 00:39:47,960 --> 00:39:51,160 Speaker 1: charge and mass. But what if there are other forces 711 00:39:51,200 --> 00:39:53,719 Speaker 1: out there? We know that there's a lot we don't 712 00:39:53,719 --> 00:39:56,120 Speaker 1: know yet about the universe. We know that there are 713 00:39:56,239 --> 00:39:59,879 Speaker 1: huge questions that are unanswered. There might be entirely new 714 00:40:00,040 --> 00:40:03,800 Speaker 1: forces out there. What if, for example, dark matter feels 715 00:40:03,800 --> 00:40:06,080 Speaker 1: a force, not a force that we're familiar with, but 716 00:40:06,120 --> 00:40:08,800 Speaker 1: a force that only dark matter can feel with itself. 717 00:40:09,000 --> 00:40:11,640 Speaker 1: Imagine if there was like a dark photon out there 718 00:40:11,880 --> 00:40:15,240 Speaker 1: that interacted with dark matter particles that had a dark charge. 719 00:40:15,719 --> 00:40:19,360 Speaker 1: In that case, it might be that supermassive black holes 720 00:40:19,600 --> 00:40:22,880 Speaker 1: have more than just spin and mass and electric charge. 721 00:40:22,920 --> 00:40:26,680 Speaker 1: They might also have a dark charge, in which case 722 00:40:26,920 --> 00:40:29,640 Speaker 1: that could affect the way that these supermassive black holes 723 00:40:29,680 --> 00:40:32,000 Speaker 1: fall into each other. It could have a powerful force 724 00:40:32,280 --> 00:40:36,000 Speaker 1: that changes the way they're interacting and how fast they're 725 00:40:36,040 --> 00:40:38,120 Speaker 1: falling into each other, and that could change the way 726 00:40:38,160 --> 00:40:42,680 Speaker 1: these gravitational waves look. These very low frequency gravitational waves 727 00:40:42,719 --> 00:40:45,520 Speaker 1: as they're beginning their dance would look different if there 728 00:40:45,520 --> 00:40:48,640 Speaker 1: are different forces in play, because it would change the frequency. 729 00:40:49,040 --> 00:40:52,080 Speaker 1: Remember that the frequency of the gravitational wave is determined 730 00:40:52,120 --> 00:40:55,000 Speaker 1: by how fast the black holes are moving around each other, 731 00:40:55,239 --> 00:40:58,680 Speaker 1: which depends entirely on the forces between them. So we 732 00:40:58,719 --> 00:41:01,640 Speaker 1: could use these gravitational waves as a probe to look 733 00:41:01,680 --> 00:41:05,319 Speaker 1: for new physics, new beyond the standard model, things that 734 00:41:05,360 --> 00:41:07,759 Speaker 1: we do not yet understand. So, while it would be 735 00:41:07,800 --> 00:41:11,200 Speaker 1: exciting to see gravitational waves and have them be exactly 736 00:41:11,239 --> 00:41:13,759 Speaker 1: what we expect, have them be just the kind of 737 00:41:13,800 --> 00:41:17,840 Speaker 1: gravitational waves we expect from neutron stars and supernovas and 738 00:41:18,000 --> 00:41:21,520 Speaker 1: inspiring supermassive black holes. It might be even more exciting 739 00:41:21,760 --> 00:41:24,640 Speaker 1: if these pulse are arraysed detect gravitational waves that we 740 00:41:24,760 --> 00:41:29,400 Speaker 1: don't understand that need new explanations, they need new ideas, 741 00:41:29,680 --> 00:41:32,279 Speaker 1: because they are clues that there are things going on 742 00:41:32,440 --> 00:41:34,840 Speaker 1: out there in the universe that we don't know about. 743 00:41:34,920 --> 00:41:37,640 Speaker 1: And in the end, that's the biggest goal. That's the 744 00:41:37,719 --> 00:41:40,040 Speaker 1: reason we listen to the nights guy, That's the reason 745 00:41:40,080 --> 00:41:43,000 Speaker 1: we do science because we want to find something new. 746 00:41:43,320 --> 00:41:46,680 Speaker 1: We want to gain a broader understanding of what's out 747 00:41:46,719 --> 00:41:48,880 Speaker 1: there in the universe. We want to break the cognitive 748 00:41:48,880 --> 00:41:52,200 Speaker 1: shackles of being here on Earth and be creatures of 749 00:41:52,239 --> 00:41:54,879 Speaker 1: the universe. We want to understand everything that's out there, 750 00:41:55,160 --> 00:41:56,920 Speaker 1: and we want to use all of our tools to 751 00:41:57,040 --> 00:41:59,560 Speaker 1: find it. Unfortunately, we are trapped here on the Earth 752 00:41:59,600 --> 00:42:01,680 Speaker 1: and we can only use the signals that get here. 753 00:42:02,000 --> 00:42:04,560 Speaker 1: But at the very least we should pay careful attention 754 00:42:04,600 --> 00:42:07,240 Speaker 1: to those signals. So even if they are little hints 755 00:42:07,280 --> 00:42:10,200 Speaker 1: from pulsear timings, that's something weird is going on in 756 00:42:10,239 --> 00:42:13,400 Speaker 1: the space between us and the pulsears, revealing that something 757 00:42:13,400 --> 00:42:16,440 Speaker 1: else weird is going on between super massive black holes 758 00:42:16,520 --> 00:42:19,040 Speaker 1: as they dance. These are the kind of clues that 759 00:42:19,080 --> 00:42:22,120 Speaker 1: we need to unravel, these subtle little stories that tell 760 00:42:22,200 --> 00:42:25,719 Speaker 1: us the deepest secrets of the universe. So write to 761 00:42:25,760 --> 00:42:28,240 Speaker 1: your politicians and tell them we should fund more science 762 00:42:28,280 --> 00:42:30,840 Speaker 1: because we want to learn more about the universe. But 763 00:42:30,960 --> 00:42:33,840 Speaker 1: until then, we will come up with clever and cheaper 764 00:42:33,880 --> 00:42:36,960 Speaker 1: ways to listen to those signals from the universe and 765 00:42:37,000 --> 00:42:40,640 Speaker 1: hope to unravel those mysteries. Thanks for listening to this 766 00:42:40,840 --> 00:42:45,839 Speaker 1: crazy story of ingenuity and creativity in astrophysics. Stay tuned, 767 00:42:45,880 --> 00:42:47,719 Speaker 1: and if you have a topic you would like to 768 00:42:47,719 --> 00:42:49,799 Speaker 1: hear us talk about, please don't be shy. Or if 769 00:42:49,800 --> 00:42:52,479 Speaker 1: you have any question at all about physics or something 770 00:42:52,520 --> 00:42:55,160 Speaker 1: you read, I answer all my emails, so right to 771 00:42:55,239 --> 00:42:58,000 Speaker 1: us two questions at Daniel and Jorge dot com. Can't 772 00:42:58,000 --> 00:43:08,440 Speaker 1: wait to hear from you. Thanks everybody, Yeah, thanks for listening, 773 00:43:08,440 --> 00:43:11,160 Speaker 1: and remember that Daniel and Jorge explained. The Universe is 774 00:43:11,200 --> 00:43:14,600 Speaker 1: a production of I Heart Radio or more podcast For 775 00:43:14,719 --> 00:43:18,480 Speaker 1: my Heart Radio, visit the I Heart Radio app, Apple Podcasts, 776 00:43:18,600 --> 00:43:20,920 Speaker 1: or wherever you listen to your favorite shows.