1 00:00:08,960 --> 00:00:12,200 Speaker 1: What's the biggest number that you can really hold in 2 00:00:12,240 --> 00:00:15,079 Speaker 1: your mind. Let's do a little mental exercise. Start with 3 00:00:15,120 --> 00:00:18,800 Speaker 1: a number like five. Surely you can imagine like five, 4 00:00:18,880 --> 00:00:22,000 Speaker 1: I don't know, bananas floating in your mind, right, each 5 00:00:22,040 --> 00:00:24,880 Speaker 1: one crisp and the unique and different. It's a simple, 6 00:00:25,000 --> 00:00:28,760 Speaker 1: small number that's easy to visualize, all right, But can 7 00:00:28,800 --> 00:00:31,920 Speaker 1: you do ten? Can you keep ten individual bananas in 8 00:00:31,960 --> 00:00:34,720 Speaker 1: your head? Can you do a hundred? Now it starts 9 00:00:34,720 --> 00:00:38,600 Speaker 1: to get challenging, right, So imagine a thousand, a hundred thousand. 10 00:00:38,600 --> 00:00:42,519 Speaker 1: Can you imagine a billion individual bananas, all unique, floating 11 00:00:42,560 --> 00:00:45,800 Speaker 1: in your mind? Unless you're some sort of crazy genius, 12 00:00:45,840 --> 00:00:49,519 Speaker 1: probably not. But the universe throws these numbers at us 13 00:00:49,560 --> 00:00:53,159 Speaker 1: all the time, right, you hear millions, billions, trillions, numbers 14 00:00:53,159 --> 00:00:55,959 Speaker 1: that frankly sound made up. What do these numbers mean? 15 00:00:56,160 --> 00:01:15,440 Speaker 1: Can we really grasp them? Hi? I'm Daniel. I'm a 16 00:01:15,480 --> 00:01:18,120 Speaker 1: particle physicist and the co author of the book We 17 00:01:18,200 --> 00:01:21,480 Speaker 1: Have No Idea, A Guide to the Unknown Universe. My 18 00:01:21,800 --> 00:01:25,039 Speaker 1: co author in that book, Jorge cham, a cartoonist, is 19 00:01:25,080 --> 00:01:29,080 Speaker 1: not here today on the podcast, so welcome to the podcast. 20 00:01:29,280 --> 00:01:33,160 Speaker 1: Daniel and Jorge explain the universe, but without Jorge, who 21 00:01:33,240 --> 00:01:35,480 Speaker 1: has to be away. This week there's a production of 22 00:01:35,560 --> 00:01:38,720 Speaker 1: I Heart Media, a podcast in which we zoom all 23 00:01:38,800 --> 00:01:42,160 Speaker 1: around the universe trying to understand all the crazy, mind 24 00:01:42,200 --> 00:01:44,959 Speaker 1: blowing things that the universe has to offer. And the 25 00:01:45,040 --> 00:01:48,480 Speaker 1: universe is filled with things that are difficult to understand 26 00:01:48,680 --> 00:01:51,640 Speaker 1: but fun to struggle with. And one of those things 27 00:01:51,960 --> 00:01:55,920 Speaker 1: is numbers. Because the universe is vast, there are so 28 00:01:56,000 --> 00:01:59,720 Speaker 1: many things out there. They're huge numbers of stuff to 29 00:01:59,760 --> 00:02:03,000 Speaker 1: think about, to look at, to try to understand. I mean, 30 00:02:03,000 --> 00:02:05,720 Speaker 1: if you talk about just our galaxy, the Milky Way, 31 00:02:05,960 --> 00:02:09,400 Speaker 1: there are a hundred billion stars in the universe, how 32 00:02:09,440 --> 00:02:11,760 Speaker 1: do you comprehend that number? How do you know what 33 00:02:11,840 --> 00:02:15,880 Speaker 1: that number really means? Frankly, anything bigger than a thousand 34 00:02:16,040 --> 00:02:18,359 Speaker 1: is to meet infinity? Right, you talk about a million 35 00:02:18,400 --> 00:02:21,399 Speaker 1: dollars versus ten million dollars, What difference does that really 36 00:02:21,440 --> 00:02:24,200 Speaker 1: make to me? A billion dollars a trillion dollars. I 37 00:02:24,280 --> 00:02:26,600 Speaker 1: can never be an economist because to me, all these 38 00:02:26,680 --> 00:02:31,400 Speaker 1: numbers are ungraspable. They're hard to really put my head around, 39 00:02:31,400 --> 00:02:34,120 Speaker 1: to really wrap my fingers around and manipulating my mind. 40 00:02:34,120 --> 00:02:35,760 Speaker 1: I mean, sure, I can do the math with them 41 00:02:35,840 --> 00:02:38,800 Speaker 1: on paper, but I can't visualize them, and as a 42 00:02:38,880 --> 00:02:41,200 Speaker 1: visual thinker, it's difficult for me to understand what these 43 00:02:41,200 --> 00:02:45,520 Speaker 1: things mean. But yet the universe throws these numbers at us, right, 44 00:02:45,520 --> 00:02:48,720 Speaker 1: And you try to do science at this scale particle physics. 45 00:02:49,000 --> 00:02:52,280 Speaker 1: Every baseball is filled with ten to the twenty three 46 00:02:52,280 --> 00:02:55,000 Speaker 1: times some number of atoms. Right, It's hard to imagine. 47 00:02:55,240 --> 00:02:57,840 Speaker 1: Every time you're holding a banana or a baseball in 48 00:02:57,880 --> 00:03:02,080 Speaker 1: your hand, you're interacting with a ridiculously huge number of particles. 49 00:03:02,680 --> 00:03:04,639 Speaker 1: And so that's what we want to focus on today. 50 00:03:05,000 --> 00:03:08,200 Speaker 1: That's the topic of today's podcast, and most specifically today, 51 00:03:08,240 --> 00:03:16,880 Speaker 1: we're asking the question how many stars are there in 52 00:03:16,919 --> 00:03:19,120 Speaker 1: this sky? And of course there are a huge number 53 00:03:19,120 --> 00:03:20,880 Speaker 1: of stars out there in the Milky Way, right. A 54 00:03:20,960 --> 00:03:24,480 Speaker 1: hundred billion stars in the Milky Way times two trillion 55 00:03:24,600 --> 00:03:28,360 Speaker 1: galaxies makes a number that's like, really hard to even understand. 56 00:03:28,480 --> 00:03:31,680 Speaker 1: Two times ten to the twenty three stars in the 57 00:03:31,680 --> 00:03:35,160 Speaker 1: observable universe. I don't even know the name or that number, right, 58 00:03:35,160 --> 00:03:38,120 Speaker 1: somebody's have to make up the new prefix, the new 59 00:03:38,200 --> 00:03:41,600 Speaker 1: scientific phrase for that number, because it's so big that 60 00:03:41,680 --> 00:03:44,040 Speaker 1: all you can do is write it in scientific notation, right, 61 00:03:44,040 --> 00:03:46,880 Speaker 1: it's not even a number anybody ever actually sits down 62 00:03:46,920 --> 00:03:49,240 Speaker 1: and writes out with all those zeros, you know, we 63 00:03:49,280 --> 00:03:51,640 Speaker 1: need like a new way to write numbers, just to 64 00:03:51,720 --> 00:03:55,920 Speaker 1: talk about this kind of number, a number in this category. 65 00:03:56,280 --> 00:03:58,360 Speaker 1: And so that's a huge number, right, two times ten 66 00:03:58,440 --> 00:04:00,880 Speaker 1: of the twenty three. But there are lots of big 67 00:04:00,960 --> 00:04:04,200 Speaker 1: numbers in science, not just in physics. I mean, if 68 00:04:04,240 --> 00:04:07,680 Speaker 1: somebody asked you, what are there more of stars in 69 00:04:07,720 --> 00:04:10,880 Speaker 1: the Milky Way or trees on Earth? You might think, well, 70 00:04:10,920 --> 00:04:12,880 Speaker 1: of course there are more stars in the Milky Way. 71 00:04:12,920 --> 00:04:15,960 Speaker 1: That's a huge, ridiculous number compared to this tiny little 72 00:04:16,000 --> 00:04:19,640 Speaker 1: planet we find ourselves on, right, But not true. It 73 00:04:19,680 --> 00:04:23,679 Speaker 1: turns out that there are three trillion trees on Earth, 74 00:04:24,040 --> 00:04:28,200 Speaker 1: three trillion, which is more than the hundred billion stars 75 00:04:28,240 --> 00:04:31,200 Speaker 1: in the Milky Way. Right, So there are numbers all 76 00:04:31,200 --> 00:04:34,280 Speaker 1: over the place, not just in physics, but also in biology. Here, 77 00:04:34,320 --> 00:04:36,560 Speaker 1: just on this one planet, there are more of those 78 00:04:36,600 --> 00:04:40,000 Speaker 1: trees than all the stars in our galaxy. And if 79 00:04:40,040 --> 00:04:44,200 Speaker 1: you look inside our body, there are forty trillion cells 80 00:04:44,279 --> 00:04:46,600 Speaker 1: that make up a human body. Every single one of 81 00:04:46,680 --> 00:04:50,120 Speaker 1: you walking around, squishing and breathing and living, has a 82 00:04:50,200 --> 00:04:53,120 Speaker 1: huge number of these things all cooperating to make you 83 00:04:53,440 --> 00:04:55,880 Speaker 1: who you are. So there are more cells in the 84 00:04:55,920 --> 00:04:59,480 Speaker 1: body than trees on Earth, and more trees on Earth 85 00:04:59,560 --> 00:05:02,520 Speaker 1: than ours in the galaxy. And you can keep going. 86 00:05:02,680 --> 00:05:06,000 Speaker 1: The number of grains of sand on all the beaches 87 00:05:06,040 --> 00:05:07,880 Speaker 1: and all the deserts on the Earth is an even 88 00:05:07,880 --> 00:05:12,200 Speaker 1: bigger number. That's four times ten to the nineteen. So 89 00:05:12,320 --> 00:05:15,800 Speaker 1: for every tree on Earth, for every cell in the body, 90 00:05:16,200 --> 00:05:19,760 Speaker 1: there are millions of grains of sand. And this is 91 00:05:19,800 --> 00:05:22,240 Speaker 1: what I talk about not being able to grasp a number. 92 00:05:22,360 --> 00:05:25,160 Speaker 1: Like you walk on a beach. You see all that sand, 93 00:05:25,400 --> 00:05:28,039 Speaker 1: but you can't count it. If somebody drops a handful 94 00:05:28,080 --> 00:05:29,840 Speaker 1: of objects on the sand, you can say, oh, look, 95 00:05:29,880 --> 00:05:31,960 Speaker 1: there's your car, keys and your wallet and your phone. 96 00:05:32,160 --> 00:05:34,320 Speaker 1: There are three things there, right, that makes sense. You 97 00:05:34,320 --> 00:05:36,640 Speaker 1: can look at three things and count them instantly. You 98 00:05:36,640 --> 00:05:39,279 Speaker 1: don't actually have to count. You just sort of recognize 99 00:05:39,640 --> 00:05:42,679 Speaker 1: the numeracy there. You don't have to actually individually count. 100 00:05:43,040 --> 00:05:45,160 Speaker 1: But if you wanted to count the number of grains 101 00:05:45,200 --> 00:05:47,400 Speaker 1: of sand on the beach under your feet, you'd have 102 00:05:47,480 --> 00:05:50,240 Speaker 1: to actually count them. I mean, the information is there, 103 00:05:50,560 --> 00:05:53,400 Speaker 1: it's coming into your eyes. Even just the number of 104 00:05:53,400 --> 00:05:55,600 Speaker 1: grains that you see the number of grains that are 105 00:05:55,680 --> 00:05:58,400 Speaker 1: visible to your eyes when you're looking at the beach. 106 00:05:59,040 --> 00:06:02,520 Speaker 1: That imprinciple, you have that information coming into your eyeballs. 107 00:06:02,520 --> 00:06:05,279 Speaker 1: But of course nobody can count. That it's too big 108 00:06:05,320 --> 00:06:08,040 Speaker 1: a number to grasp. And so that's what fascinates me, 109 00:06:08,160 --> 00:06:11,160 Speaker 1: that that there are these numbers out there, that they're everywhere, 110 00:06:11,160 --> 00:06:13,280 Speaker 1: that they're all around us, and so you might think, well, 111 00:06:13,320 --> 00:06:15,680 Speaker 1: that's certainly a big number. Two times ten of the 112 00:06:15,760 --> 00:06:18,400 Speaker 1: nineteen is a huge number of grains of sand. It's 113 00:06:18,440 --> 00:06:20,640 Speaker 1: hard to imagine. It also means that there are more 114 00:06:20,760 --> 00:06:24,240 Speaker 1: grains of sand than stars in the galaxy, which means 115 00:06:24,240 --> 00:06:27,440 Speaker 1: that for every star out there, all those individual balls 116 00:06:27,440 --> 00:06:30,000 Speaker 1: of plasma, there are more than a million grains of 117 00:06:30,040 --> 00:06:33,159 Speaker 1: sand on Earth. It's hard to really grasp these ratios. 118 00:06:33,600 --> 00:06:36,200 Speaker 1: But of course I'm married to a biologist, and the 119 00:06:36,320 --> 00:06:39,280 Speaker 1: king of big numbers turns out to not be physics. 120 00:06:39,400 --> 00:06:44,320 Speaker 1: The king of big numbers is biology, and specifically microbes. 121 00:06:44,400 --> 00:06:46,640 Speaker 1: And of course I'm married to a microbiologist. So she 122 00:06:46,760 --> 00:06:49,840 Speaker 1: reminded me that there are ten to the thirty one 123 00:06:49,960 --> 00:06:53,240 Speaker 1: pages in the biome. That means there are ten to 124 00:06:53,320 --> 00:06:56,800 Speaker 1: the thirty one little viruses out there attacking bacteria. And 125 00:06:56,880 --> 00:07:00,200 Speaker 1: that's a ridiculous number. That's bigger than all the stars 126 00:07:00,279 --> 00:07:03,560 Speaker 1: in the observable universe. That was ten to the twenty three. 127 00:07:03,640 --> 00:07:07,280 Speaker 1: So for every star in every single one of those galaxies, 128 00:07:07,720 --> 00:07:11,320 Speaker 1: there are like a billion viruses here on Earth. To 129 00:07:11,400 --> 00:07:13,480 Speaker 1: count all the stars in our galaxy and all the 130 00:07:13,480 --> 00:07:17,520 Speaker 1: stars and other galaxies is just a ridiculous number. And 131 00:07:17,600 --> 00:07:20,800 Speaker 1: for each of those there's a billion, which already is 132 00:07:20,840 --> 00:07:24,520 Speaker 1: hard to grasp. A billion viruses here on Earth. So 133 00:07:24,720 --> 00:07:27,160 Speaker 1: science is filled with these big numbers. But I was 134 00:07:27,200 --> 00:07:30,320 Speaker 1: interested in something more specific. You take a drive out 135 00:07:30,440 --> 00:07:32,880 Speaker 1: to the desert, you look up at the night sky, 136 00:07:32,960 --> 00:07:35,480 Speaker 1: and you're confronted with enormity. You look up at the 137 00:07:35,560 --> 00:07:38,200 Speaker 1: night sky, you see all these twinkling lights, You see 138 00:07:38,240 --> 00:07:41,760 Speaker 1: all these stars, and you wonder, wow, how many are there? 139 00:07:42,160 --> 00:07:45,480 Speaker 1: Certainly seems like a lot, right. We're used to science 140 00:07:45,520 --> 00:07:48,080 Speaker 1: and physics having big numbers in it. We know the 141 00:07:48,160 --> 00:07:51,080 Speaker 1: universe has vast and so we imagine we can see 142 00:07:51,080 --> 00:07:54,240 Speaker 1: a lot of stars. Turns out we might not be 143 00:07:54,280 --> 00:07:56,920 Speaker 1: able to see that many. So I was curious what 144 00:07:56,960 --> 00:07:59,760 Speaker 1: people knew about this, what people thought about the number 145 00:07:59,760 --> 00:08:02,320 Speaker 1: of stars in the night sky. So I walked around 146 00:08:02,320 --> 00:08:04,360 Speaker 1: the campus if you see Irvine, and I asked, folks, 147 00:08:04,720 --> 00:08:06,960 Speaker 1: how many stars can you see in the night sky 148 00:08:07,160 --> 00:08:12,200 Speaker 1: on a beautiful, crystal clear night, right, no pollution, no clouds, um, 149 00:08:12,360 --> 00:08:15,800 Speaker 1: no moon, no light from Los Angeles? How many stars 150 00:08:15,840 --> 00:08:19,000 Speaker 1: can you see in the sky? But first think for yourself, 151 00:08:19,040 --> 00:08:21,560 Speaker 1: if you've been out on a nice clear night, how 152 00:08:21,560 --> 00:08:23,480 Speaker 1: many stars do you think you can see in the 153 00:08:23,600 --> 00:08:28,600 Speaker 1: night sky. Here's what people had to say. Millions. Okay, 154 00:08:28,680 --> 00:08:30,720 Speaker 1: I know there is many more in the universe. I 155 00:08:30,760 --> 00:08:34,560 Speaker 1: even know how many there are in the universe. Tend 156 00:08:34,640 --> 00:08:39,240 Speaker 1: to the five between a billion and a trillion roughly, 157 00:08:39,480 --> 00:08:43,400 Speaker 1: Let's see. I would say at least Avocata's number, like 158 00:08:43,400 --> 00:08:46,680 Speaker 1: tend toy three. I don't know I would I would 159 00:08:46,679 --> 00:08:50,480 Speaker 1: guess less than that, maybe like time stend of the 160 00:08:50,520 --> 00:08:53,000 Speaker 1: ten power, but I don't know. I'm gonna say tend 161 00:08:53,000 --> 00:08:56,800 Speaker 1: to the twenty like a million guests somewhere in the billions. 162 00:08:56,840 --> 00:08:59,040 Speaker 1: But I have no idea. All right, So you hear 163 00:08:59,080 --> 00:09:01,640 Speaker 1: a lot of big number is people definitely feel like 164 00:09:02,120 --> 00:09:04,200 Speaker 1: it's got to be a big number because they know 165 00:09:04,400 --> 00:09:06,560 Speaker 1: there are a lot of stars out there and they're right, 166 00:09:06,640 --> 00:09:08,640 Speaker 1: there are a lot of stars out there in the sky. 167 00:09:08,800 --> 00:09:12,040 Speaker 1: That doesn't necessarily mean that you can see all of those, right, 168 00:09:12,120 --> 00:09:15,079 Speaker 1: or even that you can see very many, but people 169 00:09:15,160 --> 00:09:17,440 Speaker 1: wanted to say a big number. You hear millions and 170 00:09:17,600 --> 00:09:20,560 Speaker 1: billions and ten to the ten, and so people want 171 00:09:20,600 --> 00:09:23,440 Speaker 1: we're prepared to be saying a big number. And maybe 172 00:09:23,440 --> 00:09:25,199 Speaker 1: it's a bit of a gotcha question because a lot 173 00:09:25,240 --> 00:09:27,800 Speaker 1: of times you'll be asked a question about science and 174 00:09:27,840 --> 00:09:29,960 Speaker 1: the answer is supposed to impress you, right, the answer 175 00:09:30,040 --> 00:09:32,679 Speaker 1: is supposed to be so much bigger than you even imagined. 176 00:09:33,200 --> 00:09:35,400 Speaker 1: So I don't know, maybe people were rounding up a 177 00:09:35,440 --> 00:09:38,480 Speaker 1: little bit, trying to make sure they hit an impressive number. 178 00:09:38,800 --> 00:09:41,240 Speaker 1: We'll break it down and talk about how many stars 179 00:09:41,360 --> 00:09:44,000 Speaker 1: you can actually see in the night sky, but first 180 00:09:44,240 --> 00:09:59,640 Speaker 1: let's take a quick break. Alright, So we're talking about 181 00:09:59,679 --> 00:10:03,120 Speaker 1: how any stars you can see in the night sky. Now, 182 00:10:03,160 --> 00:10:05,560 Speaker 1: first let's start out with how many stars there are. Right, 183 00:10:05,600 --> 00:10:09,160 Speaker 1: we talked about this quickly already, But in the observable universe, 184 00:10:09,480 --> 00:10:12,319 Speaker 1: there are ten to the twenty three stars out there, 185 00:10:12,360 --> 00:10:15,880 Speaker 1: basically a trillion times a hundred billion. It's a huge 186 00:10:15,960 --> 00:10:19,280 Speaker 1: number of stars. However, most of the stars are really 187 00:10:19,280 --> 00:10:21,440 Speaker 1: really far away. So let's talk about the light from 188 00:10:21,480 --> 00:10:24,520 Speaker 1: the star. The stars this huge burning ball of plasma 189 00:10:24,720 --> 00:10:26,880 Speaker 1: and it's shooting out a lot of light. Our Sun, 190 00:10:26,960 --> 00:10:30,200 Speaker 1: for example, is not a particularly bright star, but already 191 00:10:30,280 --> 00:10:32,680 Speaker 1: it's pretty bright. You know, it's shooting out a huge 192 00:10:32,800 --> 00:10:35,280 Speaker 1: number of photons. If you look up at the Sun, 193 00:10:35,480 --> 00:10:38,240 Speaker 1: please don't, then you'll burn your eyeballs. Right, and we're 194 00:10:38,240 --> 00:10:40,439 Speaker 1: not even that close to it. So the Sun is 195 00:10:40,440 --> 00:10:42,800 Speaker 1: pretty bright, which means the stars out there must be 196 00:10:42,840 --> 00:10:45,880 Speaker 1: pretty bright. The problem is, in order to see something, 197 00:10:46,160 --> 00:10:50,040 Speaker 1: it has to be either pretty close or super duper bright, 198 00:10:50,640 --> 00:10:55,120 Speaker 1: because the brightness of an object falls really quickly with distance. 199 00:10:56,200 --> 00:10:59,360 Speaker 1: Imagine all the photons leaving the Sun, right, there's a 200 00:10:59,440 --> 00:11:03,120 Speaker 1: huge number of them. They're screaming out into space, ready 201 00:11:03,160 --> 00:11:05,240 Speaker 1: to go on some cosmic journey and land on some 202 00:11:05,320 --> 00:11:08,400 Speaker 1: alien eyeballs. Right, So all these photons are leaving the Sun. 203 00:11:09,000 --> 00:11:10,839 Speaker 1: But they're leaving the Sun and there's a fixed number 204 00:11:11,000 --> 00:11:13,679 Speaker 1: seven gajillion, I don't know, some certain number of photons 205 00:11:13,679 --> 00:11:16,000 Speaker 1: are leaving the Sun. So if you're really close to 206 00:11:16,040 --> 00:11:18,400 Speaker 1: the Sun, then your eyeball is going to get hit 207 00:11:18,400 --> 00:11:20,280 Speaker 1: with a lot of those photons. But now take a 208 00:11:20,280 --> 00:11:23,680 Speaker 1: step away, take go a thousand kilometers further, you have 209 00:11:23,760 --> 00:11:26,440 Speaker 1: the same number of photons. Right, it's not adding any 210 00:11:26,440 --> 00:11:29,280 Speaker 1: more photons. I mean there's another wave of photons coming 211 00:11:29,320 --> 00:11:32,679 Speaker 1: along behind it, but in that one blast of light 212 00:11:32,720 --> 00:11:35,679 Speaker 1: that we're talking about, you don't get any fresh photons. 213 00:11:36,080 --> 00:11:39,000 Speaker 1: These same photons continue out, but now they cover a 214 00:11:39,120 --> 00:11:43,320 Speaker 1: larger area. That cover a sphere that has a larger radius. 215 00:11:43,360 --> 00:11:46,960 Speaker 1: And the area of a sphere grows with the radius squared, 216 00:11:47,559 --> 00:11:49,880 Speaker 1: and so as the radius of that sphere that the 217 00:11:49,880 --> 00:11:54,239 Speaker 1: photons are trying to illuminate grows, the number of photons 218 00:11:54,400 --> 00:11:58,760 Speaker 1: per area drops like one over distance squared one over 219 00:11:58,880 --> 00:12:02,400 Speaker 1: radius squared. So if you're twice as far from the star, 220 00:12:02,640 --> 00:12:05,760 Speaker 1: the brightness is one fourth. If you're four times the 221 00:12:05,800 --> 00:12:09,280 Speaker 1: distance from the star, then the brightness is one And 222 00:12:09,280 --> 00:12:11,840 Speaker 1: that doesn't seem like a big effect for small numbers, 223 00:12:11,880 --> 00:12:14,319 Speaker 1: but it adds to pretty quickly. If you're a thousand 224 00:12:14,320 --> 00:12:17,400 Speaker 1: times further away, then the brightness goes down by a million, 225 00:12:17,840 --> 00:12:20,079 Speaker 1: And those are pretty big numbers, and so they can 226 00:12:20,080 --> 00:12:23,400 Speaker 1: impact even really bright stuff like stars. So what that 227 00:12:23,440 --> 00:12:26,240 Speaker 1: means is that for us to see a star. Right, 228 00:12:26,240 --> 00:12:27,960 Speaker 1: we have to be able to see a certain number 229 00:12:28,000 --> 00:12:30,440 Speaker 1: of photons. When you look up at the night sky, 230 00:12:30,880 --> 00:12:33,520 Speaker 1: you turn your eyes to the sky. You have to 231 00:12:33,559 --> 00:12:37,280 Speaker 1: get photons from that star. And already that's a fascinating journey. 232 00:12:37,360 --> 00:12:40,079 Speaker 1: You know, those photons were created in the heat of 233 00:12:40,160 --> 00:12:44,120 Speaker 1: that cosmic fusion billions of miles away and have flown 234 00:12:44,240 --> 00:12:47,480 Speaker 1: through space for thousands or millions or billions of years 235 00:12:47,480 --> 00:12:50,079 Speaker 1: before they hit your eyeball. They've lived all that time, 236 00:12:50,120 --> 00:12:53,280 Speaker 1: and then they're just sucked up by your eyeball and 237 00:12:53,360 --> 00:12:55,360 Speaker 1: are no more. Right, you just take that little bit 238 00:12:55,400 --> 00:12:58,160 Speaker 1: of energy. Anyway, for you to see a star in 239 00:12:58,200 --> 00:13:00,800 Speaker 1: the sky means that a photon is left that star 240 00:13:01,000 --> 00:13:04,360 Speaker 1: and arrived at your eyeball. And your eyeballs are pretty good, right, 241 00:13:04,400 --> 00:13:06,920 Speaker 1: they're pretty good detectors. But you need to see a 242 00:13:06,960 --> 00:13:10,160 Speaker 1: few photons in order to register a star. So there's 243 00:13:10,160 --> 00:13:12,920 Speaker 1: a threshold. All the stars are out there, but in 244 00:13:13,000 --> 00:13:14,719 Speaker 1: order for you to see them with your eye, in 245 00:13:14,800 --> 00:13:16,560 Speaker 1: order for you to say, hey, I see a star, 246 00:13:16,920 --> 00:13:19,480 Speaker 1: you have to get a certain number of photons, and 247 00:13:19,520 --> 00:13:22,000 Speaker 1: so that cuts down on the number of stars that 248 00:13:22,040 --> 00:13:25,160 Speaker 1: are visible to the naked eye by a huge fraction. 249 00:13:25,400 --> 00:13:27,480 Speaker 1: If they're really far away, then that have to be 250 00:13:27,640 --> 00:13:31,040 Speaker 1: super duper bright for you to still get enough photons, right, 251 00:13:31,120 --> 00:13:34,160 Speaker 1: because remember the density of photons that are hitting your 252 00:13:34,160 --> 00:13:37,800 Speaker 1: eye from that star falls with a distance squared, So 253 00:13:37,800 --> 00:13:40,559 Speaker 1: if it's super far away, then has to be ridiculously bright, 254 00:13:40,800 --> 00:13:43,120 Speaker 1: which is why it's so amazing sometimes when we see 255 00:13:43,120 --> 00:13:46,080 Speaker 1: things like quasars, which we know are really far away 256 00:13:46,120 --> 00:13:49,160 Speaker 1: and yet still seem bright, which means at their source 257 00:13:49,400 --> 00:13:52,360 Speaker 1: they're riduculously bright, or if they're closer they don't have 258 00:13:52,400 --> 00:13:54,800 Speaker 1: to be quite as bright. But being closer is a 259 00:13:54,840 --> 00:13:58,400 Speaker 1: really small fraction of the universe. So that's cut to 260 00:13:58,400 --> 00:14:00,400 Speaker 1: the chase. In the end, you can see the only 261 00:14:00,440 --> 00:14:04,880 Speaker 1: between five to ten thousand stars in the night sky 262 00:14:04,960 --> 00:14:07,720 Speaker 1: with the human eye, and of course you can't see 263 00:14:07,720 --> 00:14:10,600 Speaker 1: the entire night sky from earth right, you can at 264 00:14:10,679 --> 00:14:13,400 Speaker 1: best see half of it, So cut that number in half. 265 00:14:13,760 --> 00:14:17,240 Speaker 1: We're talking just a few thousand stars in the night 266 00:14:17,360 --> 00:14:19,960 Speaker 1: sky that you can see with the naked eye. And 267 00:14:20,000 --> 00:14:22,280 Speaker 1: you might imagine, no, I'm sure I could see many, 268 00:14:22,280 --> 00:14:24,440 Speaker 1: many more, right, Well, it might be that you've just 269 00:14:24,520 --> 00:14:27,480 Speaker 1: seen these pictures either from Hubble, which we'll talk about 270 00:14:27,520 --> 00:14:30,800 Speaker 1: in a minute, or from long exposure cameras which accumulate 271 00:14:30,840 --> 00:14:33,560 Speaker 1: a lot of photons over time, so you can see 272 00:14:33,560 --> 00:14:36,840 Speaker 1: things that are dimmer um. People have the impression, I think, 273 00:14:36,920 --> 00:14:40,600 Speaker 1: from those photographs or from astronomical pictures from space telescopes, 274 00:14:41,040 --> 00:14:43,160 Speaker 1: that there's a huge number of stars you can see 275 00:14:43,200 --> 00:14:46,040 Speaker 1: in the sky, but those are not, of course, using 276 00:14:46,080 --> 00:14:48,680 Speaker 1: the naked eye. The naked eye, you have to get 277 00:14:48,720 --> 00:14:51,680 Speaker 1: a certain number of photons per second in order to 278 00:14:51,720 --> 00:14:55,760 Speaker 1: register the star, and so very few stars a tiny 279 00:14:55,800 --> 00:14:58,720 Speaker 1: fraction of stars in the universe satisfy the criterion of 280 00:14:58,760 --> 00:15:02,120 Speaker 1: either being close enough or being bright enough that you 281 00:15:02,160 --> 00:15:06,520 Speaker 1: get enough individual photons and your personal eyeball to see 282 00:15:06,560 --> 00:15:10,080 Speaker 1: those stars, and people often use as a sort of metric. 283 00:15:10,320 --> 00:15:13,080 Speaker 1: There's one particularly bright star in the sky. It's called Vega, 284 00:15:13,760 --> 00:15:16,400 Speaker 1: and the threshold for being able to see a star 285 00:15:16,600 --> 00:15:19,600 Speaker 1: using the naked eye for most humans is brightness of 286 00:15:19,600 --> 00:15:23,400 Speaker 1: about zero point to five per cent the brightness of Vega. 287 00:15:23,640 --> 00:15:26,400 Speaker 1: So anything brighter than that you can see. Anything dimmer 288 00:15:26,400 --> 00:15:28,440 Speaker 1: than that you just can't see with the naked eye. 289 00:15:28,480 --> 00:15:31,440 Speaker 1: You just don't get enough photons to even know it's there. 290 00:15:31,760 --> 00:15:34,960 Speaker 1: I mean, it's there, and it's sending photons into space, 291 00:15:35,240 --> 00:15:37,680 Speaker 1: but those photons are just not dense enough by the 292 00:15:37,720 --> 00:15:39,840 Speaker 1: time they get here for you to spot one. Right, 293 00:15:39,840 --> 00:15:41,840 Speaker 1: maybe you're standing between is like a photon over there 294 00:15:41,840 --> 00:15:43,440 Speaker 1: and a photon over there, and none of them hit 295 00:15:43,480 --> 00:15:46,120 Speaker 1: your eye, right, or maybe one of them hits your eye. 296 00:15:46,280 --> 00:15:48,560 Speaker 1: But you need a certain number of photons. You need 297 00:15:48,760 --> 00:15:52,440 Speaker 1: several photons for to really register something. Okay, but then 298 00:15:52,520 --> 00:15:54,480 Speaker 1: you can soup it up. Right, you can say, well, 299 00:15:54,640 --> 00:15:57,720 Speaker 1: I don't necessarily just need to use the naked eye. 300 00:15:58,160 --> 00:16:00,840 Speaker 1: Certainly you can see more. We have tell lescopes, and 301 00:16:00,920 --> 00:16:04,920 Speaker 1: that's exactly what telescopes are for. And even binoculars. Binoculars 302 00:16:04,920 --> 00:16:08,440 Speaker 1: and telescopes, they don't actually do much zooming. Mostly the 303 00:16:08,520 --> 00:16:12,480 Speaker 1: power of a telescope or binoculars is in gathering light. 304 00:16:13,040 --> 00:16:15,880 Speaker 1: In the front of a telescope, you have a large lens, 305 00:16:15,920 --> 00:16:18,760 Speaker 1: and that lens gathers more light than your eye, right, 306 00:16:18,760 --> 00:16:22,040 Speaker 1: it's bigger than your eye. And this is why bigger 307 00:16:22,080 --> 00:16:24,880 Speaker 1: telescopes are more powerful, because they gather more light and 308 00:16:24,920 --> 00:16:28,320 Speaker 1: they focus it so you have a larger area to 309 00:16:28,480 --> 00:16:31,920 Speaker 1: receive those photons, which means you're gonna get more photons, 310 00:16:31,960 --> 00:16:34,840 Speaker 1: which means you're more likely to see something. Imagine you 311 00:16:34,880 --> 00:16:37,200 Speaker 1: had a telescope the size of the Earth, right, you 312 00:16:37,200 --> 00:16:40,600 Speaker 1: would gather a huge number of photons per second from 313 00:16:40,640 --> 00:16:44,000 Speaker 1: some distant star compared to only the photons that fall 314 00:16:44,080 --> 00:16:46,800 Speaker 1: on the tiny little spot on Earth that is your eyeball. 315 00:16:47,560 --> 00:16:51,160 Speaker 1: So the power of a telescope or binoculars is frankly 316 00:16:51,200 --> 00:16:54,960 Speaker 1: just to gather more light so you can see dimmer things, right, 317 00:16:54,960 --> 00:16:57,600 Speaker 1: because it takes the light from a large area and 318 00:16:57,600 --> 00:17:00,320 Speaker 1: it puts it onto a small area. So it's like 319 00:17:00,520 --> 00:17:03,400 Speaker 1: multiplying the number of photons you're seeing from every source 320 00:17:03,760 --> 00:17:07,480 Speaker 1: by some factor, and that makes a really big difference 321 00:17:08,000 --> 00:17:09,520 Speaker 1: because it means that you can see sort of a 322 00:17:09,600 --> 00:17:13,199 Speaker 1: larger sphere away from the Earth and that spear right. 323 00:17:13,240 --> 00:17:16,320 Speaker 1: The radius of that sphere, the number of stars net 324 00:17:16,359 --> 00:17:19,439 Speaker 1: fear grows very quickly with the radius, and so if 325 00:17:19,440 --> 00:17:23,240 Speaker 1: you're multiplying the power of your eyeballs using a telescope, 326 00:17:23,400 --> 00:17:26,560 Speaker 1: you can actually see up to about three hundred thousand 327 00:17:26,680 --> 00:17:29,320 Speaker 1: stars in the sky. Right. You can go down to 328 00:17:29,480 --> 00:17:32,080 Speaker 1: compare to Vega again, you can you can go down 329 00:17:32,119 --> 00:17:34,880 Speaker 1: to a number of about zero point zero one percent 330 00:17:35,240 --> 00:17:38,720 Speaker 1: of Vega. Vega is a particularly bright star in the sky, 331 00:17:38,840 --> 00:17:41,399 Speaker 1: and you can see a lot more stars if you 332 00:17:41,480 --> 00:17:45,880 Speaker 1: just use a telescope or binoculars. It's a huge multiplication factor. Now, 333 00:17:45,880 --> 00:17:47,720 Speaker 1: another thing you can do, of course, is you can 334 00:17:47,760 --> 00:17:50,240 Speaker 1: just put your camera on right, and you can turn 335 00:17:50,240 --> 00:17:51,800 Speaker 1: it on, and you can leave it open for a while. 336 00:17:52,480 --> 00:17:55,640 Speaker 1: And if you just leave a camera fixed and looking 337 00:17:55,640 --> 00:17:58,240 Speaker 1: at the night sky, then you'll see these traces because 338 00:17:58,280 --> 00:18:00,800 Speaker 1: stars move right there with its hours don't move, but 339 00:18:00,880 --> 00:18:03,800 Speaker 1: the earth moves right the earth rotates relative to the 340 00:18:03,840 --> 00:18:06,840 Speaker 1: star field. And so you take a picture and you 341 00:18:06,920 --> 00:18:09,600 Speaker 1: just leave your camera fixed, and you'll notice the stars 342 00:18:09,680 --> 00:18:13,159 Speaker 1: making this circular trail across the film. And so you 343 00:18:13,200 --> 00:18:15,840 Speaker 1: see like this photon hit and then that photon hit, 344 00:18:15,920 --> 00:18:18,200 Speaker 1: and then that photon hit. Each of those is a photon. 345 00:18:18,480 --> 00:18:22,240 Speaker 1: It's taken its journey across the cosmos from the star 346 00:18:22,560 --> 00:18:25,919 Speaker 1: to your film, from the star to your eyeballs. And 347 00:18:26,000 --> 00:18:28,880 Speaker 1: so the power of the photography there is to again 348 00:18:28,920 --> 00:18:32,120 Speaker 1: accumulate photons over time. And if you'd like to see 349 00:18:32,160 --> 00:18:34,760 Speaker 1: a really crisp picture of the night sky, what you 350 00:18:34,800 --> 00:18:37,280 Speaker 1: need to do is get a camera that moves with 351 00:18:37,359 --> 00:18:40,240 Speaker 1: the stars right, that tracks the stars. Usually finds one 352 00:18:40,320 --> 00:18:42,840 Speaker 1: guide star. It's got a little motor on it which 353 00:18:42,880 --> 00:18:46,239 Speaker 1: will turn the camera so that it captures photons from 354 00:18:46,280 --> 00:18:48,199 Speaker 1: the same star in the same place and sort of 355 00:18:48,240 --> 00:18:50,320 Speaker 1: adds them up. And that's how you can do this 356 00:18:50,400 --> 00:18:53,679 Speaker 1: long exposure photography that gives you the sense of seeing 357 00:18:53,720 --> 00:18:56,840 Speaker 1: something really deep in space, because that's exactly what you're doing. 358 00:18:57,160 --> 00:18:59,040 Speaker 1: The longer you look at the night sky, the more 359 00:18:59,119 --> 00:19:02,119 Speaker 1: you accumulate the those photons, the more you're seeing stuff 360 00:19:02,160 --> 00:19:05,160 Speaker 1: that's far away right where the photons are spread out 361 00:19:05,200 --> 00:19:07,240 Speaker 1: more by the time they get here, so it takes 362 00:19:07,320 --> 00:19:10,480 Speaker 1: longer to gather enough photons from them in order to 363 00:19:10,480 --> 00:19:12,560 Speaker 1: see them in your eye or to see them in 364 00:19:12,600 --> 00:19:15,760 Speaker 1: the camera. All right, but let's talk about what we 365 00:19:15,880 --> 00:19:18,520 Speaker 1: can do with crazy telescopes and how deep we can 366 00:19:18,560 --> 00:19:22,000 Speaker 1: see into the night sky using technology. But first let's 367 00:19:22,040 --> 00:19:36,960 Speaker 1: take another break. All right, So we're talking about how 368 00:19:37,000 --> 00:19:39,320 Speaker 1: many stars there are are in the sky and how 369 00:19:39,359 --> 00:19:42,000 Speaker 1: many of them we can see. Now, of course, we're 370 00:19:42,040 --> 00:19:44,960 Speaker 1: not limited to looking at the night sky with our eyeballs, 371 00:19:45,080 --> 00:19:47,000 Speaker 1: and we're not limited to looking at the night sky 372 00:19:47,080 --> 00:19:50,840 Speaker 1: with binoculars or dinky telescopes that we have in our backyard. 373 00:19:51,480 --> 00:19:55,280 Speaker 1: As a species. We have invested incredible technology which floats 374 00:19:55,320 --> 00:19:57,919 Speaker 1: out in space, so it's not even limited by the 375 00:19:57,920 --> 00:20:00,679 Speaker 1: resolution of the atmosphere. It floats in space and it 376 00:20:00,680 --> 00:20:03,679 Speaker 1: looks deep out into the universe to give us pictures. 377 00:20:03,680 --> 00:20:05,959 Speaker 1: And of course I'm talking about the Hubble space telescope 378 00:20:06,200 --> 00:20:09,119 Speaker 1: and a whole battery of other space telescopes which have 379 00:20:09,200 --> 00:20:12,160 Speaker 1: given us amazing insights into what's going on in the universe. 380 00:20:12,440 --> 00:20:14,960 Speaker 1: So how does that work, Well, it's the same story. 381 00:20:15,480 --> 00:20:17,480 Speaker 1: All you need to do to see deeper into the 382 00:20:17,560 --> 00:20:20,760 Speaker 1: universe is gather more light, and your options there are 383 00:20:20,920 --> 00:20:23,600 Speaker 1: make your telescope bigger, and so Hubble is huge, right 384 00:20:23,640 --> 00:20:26,440 Speaker 1: compared to your back backyard telescope. It's got a really 385 00:20:26,560 --> 00:20:30,960 Speaker 1: big light gathering lens that gives it a multiplication. But 386 00:20:31,040 --> 00:20:33,439 Speaker 1: Hubble also can point it stuff and you can just 387 00:20:33,560 --> 00:20:36,399 Speaker 1: stay pointed at it for a while, and so we 388 00:20:36,480 --> 00:20:41,080 Speaker 1: can gather enough light to see really distant objects. Imagine 389 00:20:41,119 --> 00:20:44,280 Speaker 1: some galaxy from very early in the universe. It's super 390 00:20:44,280 --> 00:20:46,840 Speaker 1: far away, right, it's billions and billions of light years, 391 00:20:46,840 --> 00:20:50,600 Speaker 1: say ten billion light years away. Then the intensity of 392 00:20:50,600 --> 00:20:53,800 Speaker 1: the light from that star here ten billion light years 393 00:20:53,800 --> 00:20:58,160 Speaker 1: away is a tiny factor compared to the intensity. If 394 00:20:58,200 --> 00:21:01,160 Speaker 1: you were like you know, one a like earth distance 395 00:21:01,200 --> 00:21:06,120 Speaker 1: from that star, something like one over ten billion squared. 396 00:21:06,359 --> 00:21:09,080 Speaker 1: In order to see that star, then you need to 397 00:21:09,119 --> 00:21:12,080 Speaker 1: gather photons from it, and there just aren't very many. 398 00:21:12,240 --> 00:21:14,919 Speaker 1: If you imagine a sphere centered at that star, and 399 00:21:14,960 --> 00:21:17,719 Speaker 1: the radius of that sphere is our distance from it, 400 00:21:17,720 --> 00:21:20,560 Speaker 1: we're sort of sitting out on a sphere that's that 401 00:21:20,680 --> 00:21:22,960 Speaker 1: distance from the star. Then all the light from that 402 00:21:23,000 --> 00:21:26,000 Speaker 1: star is spread out across this enormous sphere right that 403 00:21:26,600 --> 00:21:30,520 Speaker 1: radius is ten billion light years. Then the photons are 404 00:21:30,600 --> 00:21:33,280 Speaker 1: really dispersed, right, Not very many of them land in 405 00:21:33,359 --> 00:21:36,040 Speaker 1: any particular area. So what you have to do is 406 00:21:36,080 --> 00:21:37,800 Speaker 1: you have to wait a long time. You have to 407 00:21:37,840 --> 00:21:40,960 Speaker 1: point Hubble at it for a while and just gather light. 408 00:21:41,480 --> 00:21:43,600 Speaker 1: And this is why Hubble time is so valuable, because 409 00:21:43,600 --> 00:21:46,159 Speaker 1: if you point Hubble at any random speck of space, 410 00:21:46,280 --> 00:21:49,040 Speaker 1: the Hubble deep field, for example, is a tiny little 411 00:21:49,080 --> 00:21:51,639 Speaker 1: patch of space that they pointed the camera at for 412 00:21:51,680 --> 00:21:54,840 Speaker 1: a long time, long enough to gather light from super 413 00:21:54,880 --> 00:21:58,240 Speaker 1: distant galaxies. And of course the longer they look, the 414 00:21:58,320 --> 00:22:01,080 Speaker 1: more they see. Because the longer they look, the deeper 415 00:22:01,160 --> 00:22:04,640 Speaker 1: into space they can see, and there's really no limit, right, 416 00:22:04,840 --> 00:22:07,679 Speaker 1: Hubble can just point at something basically as long as 417 00:22:07,720 --> 00:22:10,800 Speaker 1: we want. And since the universe has a finite age, 418 00:22:10,920 --> 00:22:13,960 Speaker 1: is a maximum distance that anything can be that we 419 00:22:14,000 --> 00:22:17,280 Speaker 1: could see. And there's really no limit on the brightness 420 00:22:17,320 --> 00:22:19,840 Speaker 1: of something that we can see with Hubble, right, because 421 00:22:20,200 --> 00:22:23,200 Speaker 1: we could just keep gathering light and wait until eventually 422 00:22:23,200 --> 00:22:25,920 Speaker 1: photons hit us. But there is a limit. There is 423 00:22:25,960 --> 00:22:28,920 Speaker 1: a limit to what Hubble can see. And that's because 424 00:22:29,040 --> 00:22:32,080 Speaker 1: the universe is expanding. Things that are far away in 425 00:22:32,080 --> 00:22:35,040 Speaker 1: the universe are moving away from us, and that expansion 426 00:22:35,119 --> 00:22:38,320 Speaker 1: is accelerating. And all this means that that the light 427 00:22:38,359 --> 00:22:41,679 Speaker 1: from those objects, because it's moving away from us, the 428 00:22:41,720 --> 00:22:45,000 Speaker 1: wavelength of the light from those objects is shifted in color, 429 00:22:45,280 --> 00:22:48,199 Speaker 1: called this red shifting, and things that are further away 430 00:22:48,520 --> 00:22:51,879 Speaker 1: are moving away more quickly. So you can think about 431 00:22:51,880 --> 00:22:54,320 Speaker 1: the red shift as a sort of measure of distance. 432 00:22:54,359 --> 00:22:57,400 Speaker 1: And this is how astronomers talk about the distance to something. 433 00:22:57,440 --> 00:23:00,240 Speaker 1: They say red shift four, red shift five, or ever. 434 00:23:00,600 --> 00:23:03,840 Speaker 1: And this talks about how much the light is changed 435 00:23:03,920 --> 00:23:06,560 Speaker 1: in color from where when it was admitted to by 436 00:23:06,560 --> 00:23:08,879 Speaker 1: the time it gets here on Earth, and along the 437 00:23:08,960 --> 00:23:11,840 Speaker 1: way it gets shifted down into the red end of 438 00:23:11,840 --> 00:23:14,439 Speaker 1: the spectrum because things that are moving away from us 439 00:23:14,560 --> 00:23:17,840 Speaker 1: have their wavelength stretched. And Hubble of course has a 440 00:23:17,840 --> 00:23:20,760 Speaker 1: certain frequency of light that it can see. It can't 441 00:23:20,760 --> 00:23:24,720 Speaker 1: just see photons throughout the entire electromagnetic spectrum. It's got 442 00:23:24,720 --> 00:23:27,240 Speaker 1: a certain range of photons that can see because of 443 00:23:27,600 --> 00:23:29,760 Speaker 1: the you know, the material that the lens is made 444 00:23:29,760 --> 00:23:32,360 Speaker 1: out of, and the camera is sensitive. Right, There's no 445 00:23:32,480 --> 00:23:36,439 Speaker 1: device that is sensitive across the entire electromagnetic spectrum. So 446 00:23:36,480 --> 00:23:39,280 Speaker 1: there are some things that are so red shifted that 447 00:23:39,400 --> 00:23:42,399 Speaker 1: Hubble can't see them. They're basically invisible to Hubble. No 448 00:23:42,440 --> 00:23:45,800 Speaker 1: matter how long you point Hubble at these things, you 449 00:23:45,880 --> 00:23:48,560 Speaker 1: just will never see them because the light that's getting 450 00:23:48,600 --> 00:23:52,119 Speaker 1: here is at the wrong frequency. And that's why we 451 00:23:52,200 --> 00:23:56,600 Speaker 1: have other space telescopes, right. We have the Spitzer Infrared Telescope, 452 00:23:56,640 --> 00:23:59,800 Speaker 1: for example. It works in the infrared and specifically to 453 00:23:59,800 --> 00:24:03,240 Speaker 1: see things that are super duper red shifted, right, because 454 00:24:03,240 --> 00:24:06,680 Speaker 1: those are the things that are super duper far away. Now, 455 00:24:06,720 --> 00:24:10,920 Speaker 1: the furthest thing ever seen by Hubble is a galaxy 456 00:24:10,960 --> 00:24:14,200 Speaker 1: at red shift called seven point seven, which means twenty 457 00:24:14,320 --> 00:24:17,840 Speaker 1: nine billion light years away. This is something that's so 458 00:24:17,880 --> 00:24:21,359 Speaker 1: old that when it was made, this galaxy was made, 459 00:24:21,640 --> 00:24:24,800 Speaker 1: the whole universe was just about six hundred million years old. 460 00:24:24,840 --> 00:24:27,520 Speaker 1: I mean the universe basically a baby when this thing 461 00:24:27,600 --> 00:24:29,960 Speaker 1: was born. This thing has been around for a super 462 00:24:30,080 --> 00:24:33,320 Speaker 1: long time, and now it's really far away. That's the 463 00:24:33,440 --> 00:24:36,720 Speaker 1: furthest thing the Hubble has ever seen. But remember Hubble 464 00:24:36,800 --> 00:24:39,680 Speaker 1: can't see things that are super red shifted because it's 465 00:24:39,680 --> 00:24:42,439 Speaker 1: out of the range of frequency that Hubble is sensitive to. 466 00:24:43,200 --> 00:24:45,640 Speaker 1: So we use other cameras and we can see things 467 00:24:45,680 --> 00:24:48,639 Speaker 1: that are out to redshift eleven point nine, which means 468 00:24:48,840 --> 00:24:52,960 Speaker 1: more than thirty two billion light years away. The universe 469 00:24:53,040 --> 00:24:56,159 Speaker 1: was a mere four hundred million years old when this 470 00:24:56,200 --> 00:24:59,600 Speaker 1: thing was formed, So that's the record, a red shift 471 00:24:59,640 --> 00:25:03,920 Speaker 1: eleven point nine, thirty two billion light years away. That's 472 00:25:03,960 --> 00:25:07,960 Speaker 1: the furthest thing we've seen. And with our telescopes and 473 00:25:08,000 --> 00:25:10,200 Speaker 1: with our cameras, and we can look really deep into 474 00:25:10,200 --> 00:25:13,440 Speaker 1: the universe and we can see a huge number of objects. 475 00:25:13,440 --> 00:25:15,440 Speaker 1: But even if we see these things that, first of all, 476 00:25:15,520 --> 00:25:18,240 Speaker 1: we can't see the entire sky this way because looking 477 00:25:18,320 --> 00:25:21,640 Speaker 1: this far into space seeing things that are this dim 478 00:25:21,640 --> 00:25:25,439 Speaker 1: takes time, and Hubble just hasn't existed long enough to 479 00:25:25,560 --> 00:25:29,880 Speaker 1: scan the entire sky at this resolution to spend enough 480 00:25:29,960 --> 00:25:32,679 Speaker 1: time looking at every little patch of the sky in 481 00:25:32,760 --> 00:25:35,560 Speaker 1: order to see this, So most of the night sky 482 00:25:36,080 --> 00:25:39,320 Speaker 1: is unexamined. What we think of as the Hubble deep field, 483 00:25:39,480 --> 00:25:41,639 Speaker 1: if you look it up, is actually a tiny little 484 00:25:41,680 --> 00:25:44,560 Speaker 1: patch of the sky. Most of the night sky has 485 00:25:44,600 --> 00:25:48,920 Speaker 1: photons coming to us from distant, old, ancient objects which 486 00:25:49,000 --> 00:25:52,200 Speaker 1: might not even exist anymore, and nobody's looking at them 487 00:25:52,400 --> 00:25:54,840 Speaker 1: right because we don't have enough Hubbles and it would 488 00:25:54,840 --> 00:25:58,560 Speaker 1: take forever for Hubble to scan the entire sky. So 489 00:25:58,760 --> 00:26:01,399 Speaker 1: most of the things that are out there, uncountably huge 490 00:26:01,520 --> 00:26:04,800 Speaker 1: numbers of stars out there, nobody can see them, and 491 00:26:04,840 --> 00:26:08,680 Speaker 1: nobody's even looking. But maybe one day we'll build enough telescopes, 492 00:26:09,080 --> 00:26:11,400 Speaker 1: or we'll spend enough time to look all the way 493 00:26:11,400 --> 00:26:13,919 Speaker 1: through the entire sky, we will be able to see 494 00:26:14,080 --> 00:26:18,040 Speaker 1: all of those uncountably many objects. But even if you've 495 00:26:18,080 --> 00:26:21,320 Speaker 1: made a pile of bananas, one banana per per star 496 00:26:21,400 --> 00:26:23,480 Speaker 1: in the sky, I would still not be able to 497 00:26:23,520 --> 00:26:26,800 Speaker 1: get my mind around the huge number of objects out there. 498 00:26:27,040 --> 00:26:29,520 Speaker 1: So next time you're out there camping, look up at 499 00:26:29,520 --> 00:26:32,080 Speaker 1: the night sky and try to count how many stars 500 00:26:32,119 --> 00:26:34,800 Speaker 1: can you see? I think you'll be surprised to discover 501 00:26:35,040 --> 00:26:37,679 Speaker 1: it's not actually that many. It's hard to count up 502 00:26:37,720 --> 00:26:40,240 Speaker 1: to thousands and thousands of stars, and maybe you get 503 00:26:40,240 --> 00:26:43,280 Speaker 1: bored before you get there. But remember it's a tiny 504 00:26:43,400 --> 00:26:45,840 Speaker 1: fraction of the stars that are out there, and we're 505 00:26:45,920 --> 00:26:48,280 Speaker 1: lucky that as humans we can build devices that let 506 00:26:48,320 --> 00:26:50,920 Speaker 1: us peer deeper and deeper into the universe and unravel 507 00:26:51,200 --> 00:26:55,160 Speaker 1: the secrets that those distant objects hold. Thanks for listening 508 00:26:55,280 --> 00:26:58,920 Speaker 1: and tune in next time for more crazy facts about 509 00:26:58,960 --> 00:27:09,399 Speaker 1: the universe. If you still have a question after listening 510 00:27:09,400 --> 00:27:12,480 Speaker 1: to all these explanations, please drop us a line. We'd 511 00:27:12,520 --> 00:27:15,359 Speaker 1: love to hear from you. You can find us at Facebook, Twitter, 512 00:27:15,440 --> 00:27:19,119 Speaker 1: and Instagram at Daniel and Jorge That's one word, or 513 00:27:19,240 --> 00:27:23,160 Speaker 1: email us at Feedback at Daniel and Jorge dot com. 514 00:27:23,200 --> 00:27:26,000 Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain 515 00:27:26,080 --> 00:27:28,920 Speaker 1: the Universe is a production of I Heart Radio. For 516 00:27:29,080 --> 00:27:32,000 Speaker 1: more podcast from my Heart Radio, visit the I Heart 517 00:27:32,080 --> 00:27:35,680 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 518 00:27:35,760 --> 00:27:36,479 Speaker 1: favorite shows.