1 00:00:08,440 --> 00:00:10,520 Speaker 1: Hey, Daniel, what's your favorite kind of pie? 2 00:00:10,680 --> 00:00:13,240 Speaker 2: Oh? Boy, what's not my favorite? I mean, they're all 3 00:00:13,320 --> 00:00:13,800 Speaker 2: so good. 4 00:00:14,040 --> 00:00:15,239 Speaker 1: Are you a fan of chocolate pie? 5 00:00:15,520 --> 00:00:15,800 Speaker 3: You know? 6 00:00:15,920 --> 00:00:17,279 Speaker 2: I am? I mean who isn't? 7 00:00:17,480 --> 00:00:18,880 Speaker 1: What about white chocolate pie? 8 00:00:19,600 --> 00:00:22,160 Speaker 2: Hold on? Is that a thing? I mean, who would 9 00:00:22,239 --> 00:00:23,280 Speaker 2: do that to a pie? 10 00:00:23,480 --> 00:00:25,720 Speaker 1: I'm sure there's a whole universe of pie out there. 11 00:00:26,000 --> 00:00:28,200 Speaker 1: I imagine there's a you know, someone in this infinite 12 00:00:28,280 --> 00:00:30,560 Speaker 1: universe that thinks white chocolate pie is the best. 13 00:00:30,640 --> 00:00:33,400 Speaker 2: If so, then that's definitely proof that aliens exist. 14 00:00:33,760 --> 00:00:36,000 Speaker 1: But I thought your favorite might be the number pie 15 00:00:36,159 --> 00:00:39,160 Speaker 1: pie are squared? Give you the area of the pie, 16 00:00:39,320 --> 00:00:40,440 Speaker 1: the actual pie you want to eat. 17 00:00:43,200 --> 00:01:00,200 Speaker 3: I guess pie are around pie for everyone. 18 00:01:01,080 --> 00:01:03,560 Speaker 1: Hi am Jorge Made, cartoonist and the author of Oliver's 19 00:01:03,600 --> 00:01:04,640 Speaker 1: Great Big Universe. 20 00:01:05,080 --> 00:01:07,840 Speaker 2: Hi. I'm Daniel. I'm a particle physicist and a professor 21 00:01:07,920 --> 00:01:10,920 Speaker 2: at UC Irvine, and I'll try almost any kind. 22 00:01:10,720 --> 00:01:14,200 Speaker 1: Of pie, really, any kind of pie. What about Durian pie? 23 00:01:14,760 --> 00:01:15,679 Speaker 1: Have you tried that one? 24 00:01:15,760 --> 00:01:17,520 Speaker 2: I might have to hold my nose, but I hear 25 00:01:17,640 --> 00:01:18,679 Speaker 2: Durian's delicious. 26 00:01:18,840 --> 00:01:22,360 Speaker 1: Yeah, I've come across Durian pie, and you kind of 27 00:01:22,400 --> 00:01:24,600 Speaker 1: do have to hold your nose. If it's not something 28 00:01:24,640 --> 00:01:26,600 Speaker 1: you're used to, it's pretty powerful stuff. 29 00:01:26,640 --> 00:01:28,280 Speaker 2: Sounds like an exotic adventure. 30 00:01:27,920 --> 00:01:30,279 Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain 31 00:01:30,360 --> 00:01:32,960 Speaker 1: the Universe, a production of iHeartRadio. 32 00:01:32,480 --> 00:01:35,040 Speaker 2: In which we take you on an exotic tour through 33 00:01:35,040 --> 00:01:38,520 Speaker 2: the craziness and mysteries of our universe. We hope to 34 00:01:38,600 --> 00:01:41,080 Speaker 2: explain to you everything that makes sense to us and 35 00:01:41,160 --> 00:01:43,640 Speaker 2: everything that doesn't make sense to us, about the way 36 00:01:43,720 --> 00:01:48,160 Speaker 2: this amazing, beautiful, sometimes tasty, and sometimes stinky universe works. 37 00:01:48,400 --> 00:01:51,680 Speaker 1: That's right. It is a delicious universe and fragrant as well, 38 00:01:51,760 --> 00:01:54,680 Speaker 1: full of amazing facts and incredible processes going on, all 39 00:01:54,720 --> 00:01:57,160 Speaker 1: of which we take together, mix it up, put it 40 00:01:57,160 --> 00:01:59,360 Speaker 1: inside of a crust, and bake it for you here 41 00:01:59,360 --> 00:01:59,960 Speaker 1: on the podcast. 42 00:02:00,120 --> 00:02:02,680 Speaker 2: One of the deepest but most concrete mysteries of the 43 00:02:02,760 --> 00:02:06,480 Speaker 2: universe is what's it all made out of? Anyway? What's 44 00:02:06,560 --> 00:02:08,880 Speaker 2: out there in the universe? How much of it is 45 00:02:08,919 --> 00:02:11,040 Speaker 2: this stuff? How much of it is that stuff? And 46 00:02:11,160 --> 00:02:13,720 Speaker 2: why Daniel, would you eat mystery pie? 47 00:02:13,720 --> 00:02:16,600 Speaker 1: Like, if somebody gave you mystery pie, would you still 48 00:02:16,639 --> 00:02:17,320 Speaker 1: eat it? 49 00:02:17,360 --> 00:02:18,520 Speaker 2: Depends on the somebody. 50 00:02:18,560 --> 00:02:21,440 Speaker 1: I gotta say, Yeah, I guess if it's like a 51 00:02:21,480 --> 00:02:23,880 Speaker 1: ten year old, you don't want to try a mystery pie. 52 00:02:24,160 --> 00:02:26,000 Speaker 1: But if it's like a famous chef, maybe. 53 00:02:25,880 --> 00:02:28,679 Speaker 2: Yeahah, sure, absolutely, yeah, I'll eat a mystery pie and 54 00:02:28,800 --> 00:02:29,280 Speaker 2: no problem. 55 00:02:29,440 --> 00:02:31,640 Speaker 1: What if it's like a world famous ten year old chef. 56 00:02:32,880 --> 00:02:35,360 Speaker 2: Is this some reality prank show? Then probably no. 57 00:02:38,120 --> 00:02:41,880 Speaker 1: That sounds like a great idea for the next YouTube 58 00:02:41,919 --> 00:02:43,800 Speaker 1: pit mystery pie. 59 00:02:43,840 --> 00:02:45,920 Speaker 2: But one reason you might take a bite of mystery 60 00:02:45,960 --> 00:02:48,480 Speaker 2: pie is just your curiosity. You want to know what 61 00:02:48,560 --> 00:02:50,800 Speaker 2: kind of pies are out there in the universe, what's 62 00:02:50,919 --> 00:02:53,680 Speaker 2: possible to make out of the basic building blocks? What 63 00:02:53,800 --> 00:02:56,280 Speaker 2: kinds of stuff are there in the universe? In the end, 64 00:02:56,360 --> 00:02:59,800 Speaker 2: that provides some crucial context to the nature of our existence. 65 00:03:00,240 --> 00:03:02,160 Speaker 2: Are we made out of the most common stuff? What 66 00:03:02,240 --> 00:03:04,480 Speaker 2: other kinds of stuff is out there? How does it 67 00:03:04,520 --> 00:03:07,040 Speaker 2: all come together to make this glorious cosmos? 68 00:03:07,280 --> 00:03:08,960 Speaker 1: I guess the universe is kind of like a deep 69 00:03:09,000 --> 00:03:12,679 Speaker 1: dish pie of mystery, isn't it, Because there's so much 70 00:03:12,720 --> 00:03:14,919 Speaker 1: we don't know about it. Ninety five percent of the 71 00:03:15,000 --> 00:03:16,639 Speaker 1: universe is a total mystery. 72 00:03:16,280 --> 00:03:18,440 Speaker 2: To us exactly. And we can take this pie metaphor 73 00:03:18,680 --> 00:03:21,639 Speaker 2: one step further and describe what the universe is made 74 00:03:21,680 --> 00:03:24,600 Speaker 2: out of In terms of a pie chart, Basically, some 75 00:03:24,800 --> 00:03:26,799 Speaker 2: fraction of the universe is made out of our kind 76 00:03:26,840 --> 00:03:29,360 Speaker 2: of matter, another fraction is made out of dark matter, 77 00:03:29,560 --> 00:03:33,120 Speaker 2: A much bigger fraction is dark energy, mysterious stuff we 78 00:03:33,160 --> 00:03:36,720 Speaker 2: don't even know. So understanding the universe pie is a 79 00:03:36,760 --> 00:03:38,000 Speaker 2: basic goal of physics. 80 00:03:38,320 --> 00:03:40,760 Speaker 1: Yeah, that's a very basic and deep question about the 81 00:03:40,840 --> 00:03:43,440 Speaker 1: universe that you can ask, what is the universe made 82 00:03:43,440 --> 00:03:46,080 Speaker 1: out of? What is it all about? And so we've 83 00:03:46,080 --> 00:03:49,040 Speaker 1: discovered some pretty eye opening facts about the universe, and 84 00:03:49,040 --> 00:03:51,480 Speaker 1: one of those facts is the idea that the kind 85 00:03:51,480 --> 00:03:54,320 Speaker 1: of stuff we're made out of, You and I, apples 86 00:03:54,320 --> 00:03:57,520 Speaker 1: and chocolate and white chocolate. Also, they're all made out 87 00:03:57,520 --> 00:04:00,160 Speaker 1: of kind of stuff that only represents five percent of 88 00:04:00,200 --> 00:04:01,360 Speaker 1: the entire universe. 89 00:04:01,440 --> 00:04:04,280 Speaker 2: Some of the most delicious moments in physics are those 90 00:04:04,320 --> 00:04:07,640 Speaker 2: times when you realize that everything you've understood is just 91 00:04:07,680 --> 00:04:10,600 Speaker 2: a tiny fraction of reality, that you've been looking at 92 00:04:10,640 --> 00:04:14,080 Speaker 2: it like an unrepresentative sample of everything, and that the 93 00:04:14,120 --> 00:04:17,640 Speaker 2: wider context is very different from what you imagined. It's 94 00:04:17,680 --> 00:04:20,200 Speaker 2: like you're opening a third eye to understanding what the 95 00:04:20,279 --> 00:04:22,920 Speaker 2: universe is really like. And in the last few decades. 96 00:04:23,040 --> 00:04:26,200 Speaker 2: That's been our experience discovering that most of the universe 97 00:04:26,320 --> 00:04:27,880 Speaker 2: is not the kind of stuff that makes up me 98 00:04:28,160 --> 00:04:31,480 Speaker 2: and you and hamsters and lamas and pies. 99 00:04:31,440 --> 00:04:34,240 Speaker 1: And stars and galaxies. It must have been pretty incredible 100 00:04:34,360 --> 00:04:36,960 Speaker 1: to think that all of these thousands of years of 101 00:04:37,040 --> 00:04:40,520 Speaker 1: science and knowledge seeking as humans have all been just 102 00:04:40,560 --> 00:04:42,960 Speaker 1: for the five percent of the universe that we now 103 00:04:43,160 --> 00:04:43,919 Speaker 1: know we represent. 104 00:04:44,040 --> 00:04:46,200 Speaker 2: Yeah, and it's sort of a special moment in science 105 00:04:46,520 --> 00:04:49,680 Speaker 2: when we know very well how little we know. We're 106 00:04:49,680 --> 00:04:51,800 Speaker 2: always prepared for the fact that there's stuff we don't 107 00:04:51,800 --> 00:04:54,720 Speaker 2: know out there. But now we can measure very precisely 108 00:04:54,920 --> 00:04:57,120 Speaker 2: what fraction of the universe is the stuff we know 109 00:04:57,200 --> 00:05:01,039 Speaker 2: anything about, which tells us very accurately how little we 110 00:05:01,120 --> 00:05:02,080 Speaker 2: know about the universe. 111 00:05:02,360 --> 00:05:04,360 Speaker 1: Yeah, And so today on the podcast, we'll be asking 112 00:05:04,400 --> 00:05:12,760 Speaker 1: the question, what's the matter with the matter in the universe? 113 00:05:13,680 --> 00:05:15,839 Speaker 1: Something wrong with the universe? Or is it more like, 114 00:05:15,880 --> 00:05:18,480 Speaker 1: what's the matter with you? Like it's doing something it 115 00:05:18,520 --> 00:05:19,200 Speaker 1: shouldn't be doing. 116 00:05:19,279 --> 00:05:21,680 Speaker 2: Well, there's lots of really interesting questions you can ask 117 00:05:21,760 --> 00:05:24,560 Speaker 2: about this universe. Pie the fractions of the universe that 118 00:05:24,600 --> 00:05:26,800 Speaker 2: are made up of the various components. One of them 119 00:05:26,880 --> 00:05:28,840 Speaker 2: is like why is it this way? Another another way? 120 00:05:28,920 --> 00:05:31,200 Speaker 2: But you can also ask questions like has it always 121 00:05:31,240 --> 00:05:34,359 Speaker 2: been this way? Has the universe had different distributions of 122 00:05:34,440 --> 00:05:37,560 Speaker 2: matter and dark matter and dark energy at other points 123 00:05:37,600 --> 00:05:40,320 Speaker 2: in its history? And what does the future hold? 124 00:05:41,200 --> 00:05:43,080 Speaker 1: Like how long has this pie been sitting out there? 125 00:05:43,240 --> 00:05:48,719 Speaker 1: And has it changed or decayed or rotted or changed 126 00:05:48,800 --> 00:05:50,680 Speaker 1: to another kind of pie In the meantime? 127 00:05:50,839 --> 00:05:52,640 Speaker 2: Does it matter when you get a slice of the 128 00:05:52,720 --> 00:05:55,120 Speaker 2: universe pie, You might get a very different serving. It 129 00:05:55,200 --> 00:05:58,600 Speaker 2: might be more chocolatey or less chocolity, depending on when 130 00:05:58,640 --> 00:05:59,680 Speaker 2: you got your slice. 131 00:06:00,000 --> 00:06:02,320 Speaker 1: Oh, like not just a mystery pie, but like an 132 00:06:02,400 --> 00:06:04,200 Speaker 1: ever changing mystery pie. 133 00:06:04,600 --> 00:06:08,479 Speaker 2: Exactly because the universe is a dynamic place. It's not static. 134 00:06:08,560 --> 00:06:12,000 Speaker 2: It's expanding and it's cooling, and it's flashing around and frothing, 135 00:06:12,240 --> 00:06:15,080 Speaker 2: it's making galaxies and black holes. All sorts of stuff 136 00:06:15,160 --> 00:06:17,320 Speaker 2: is happening, and so we have no reason to believe 137 00:06:17,360 --> 00:06:20,240 Speaker 2: that the Universe pie today is the Universe pie that's 138 00:06:20,279 --> 00:06:20,880 Speaker 2: always been. 139 00:06:21,440 --> 00:06:23,720 Speaker 1: Do you think the universe pie is getting more delicious 140 00:06:23,839 --> 00:06:24,960 Speaker 1: or less delicious? 141 00:06:25,920 --> 00:06:27,640 Speaker 2: I'm an optimist, so I like to think that the 142 00:06:27,720 --> 00:06:30,080 Speaker 2: Universe pies most delicious days are ahead of us. 143 00:06:30,240 --> 00:06:32,360 Speaker 1: Oh wait, so that means you're never going to eat 144 00:06:32,400 --> 00:06:36,040 Speaker 1: some are you until the day before you die or something? 145 00:06:36,279 --> 00:06:38,840 Speaker 2: No, it means I'll continuously eat it and every bite 146 00:06:38,880 --> 00:06:40,360 Speaker 2: will be more tasty than the last. 147 00:06:40,520 --> 00:06:43,560 Speaker 1: Oh but what if it's not infinite? What if it's finite? 148 00:06:43,640 --> 00:06:45,320 Speaker 1: Then you got to play some sort of like you know, 149 00:06:45,400 --> 00:06:48,320 Speaker 1: optimization game here? How much of the pie should you 150 00:06:48,360 --> 00:06:48,920 Speaker 1: eat every day? 151 00:06:49,279 --> 00:06:51,599 Speaker 2: You think there's some scenario where I eat the last 152 00:06:51,640 --> 00:06:53,840 Speaker 2: bite of the universe and use it up. 153 00:06:55,600 --> 00:06:58,120 Speaker 1: I don't know how hungry are you for knowledge about 154 00:06:58,120 --> 00:06:58,719 Speaker 1: the universe? 155 00:06:59,400 --> 00:07:01,599 Speaker 2: Famished, But you know what they say that last bite 156 00:07:01,720 --> 00:07:04,080 Speaker 2: is always the most delicious, like the last cookie in 157 00:07:04,080 --> 00:07:04,479 Speaker 2: the bag. 158 00:07:04,800 --> 00:07:06,680 Speaker 1: Yeah yeah, but although if you eat it right before 159 00:07:06,680 --> 00:07:09,120 Speaker 1: you talk, you're not going to have a very long 160 00:07:09,200 --> 00:07:10,120 Speaker 1: lasting memory of it. 161 00:07:10,240 --> 00:07:12,280 Speaker 2: But I guess if I eat the entire universe, then 162 00:07:12,360 --> 00:07:14,120 Speaker 2: I'm the last bite of the universe. I'd have to 163 00:07:14,160 --> 00:07:14,960 Speaker 2: like eat myself. 164 00:07:15,040 --> 00:07:17,200 Speaker 1: Wait, are you saying you're the most delicious thing in 165 00:07:17,240 --> 00:07:17,800 Speaker 1: the universe? 166 00:07:20,000 --> 00:07:22,160 Speaker 2: If I eat everything else, then I'm the only thing 167 00:07:22,240 --> 00:07:24,280 Speaker 2: left in the universe, and I'm both the most and 168 00:07:24,440 --> 00:07:29,120 Speaker 2: least delicious thing in this very realistic example. 169 00:07:29,320 --> 00:07:32,120 Speaker 1: Right right, Yeah, yeah, I don't know that. I think 170 00:07:32,160 --> 00:07:33,960 Speaker 1: our whole analogy just just broke down. 171 00:07:34,520 --> 00:07:37,160 Speaker 2: Yeah, Daniel contains super massive black holes. 172 00:07:37,400 --> 00:07:39,360 Speaker 1: But anyways, we have found out that the pie of 173 00:07:39,400 --> 00:07:42,480 Speaker 1: the universe is made out of only five percent of 174 00:07:42,520 --> 00:07:44,320 Speaker 1: the stuff that we're familiar with. The rest of the 175 00:07:44,360 --> 00:07:47,080 Speaker 1: stuff is a big mystery. And as you said, Daniel, 176 00:07:47,160 --> 00:07:49,679 Speaker 1: these percentages have been changing exactly. 177 00:07:49,720 --> 00:07:52,640 Speaker 2: You might think that five percent is a minuscule fraction 178 00:07:52,800 --> 00:07:55,120 Speaker 2: of the universe, but wait till you hear about the 179 00:07:55,120 --> 00:07:56,960 Speaker 2: fraction that it's been in the past. 180 00:07:57,240 --> 00:07:59,320 Speaker 1: Well, it's usually what we were wondering how many people 181 00:07:59,360 --> 00:08:02,160 Speaker 1: out there had thought about the pighness of the universe 182 00:08:02,200 --> 00:08:04,280 Speaker 1: and its composition, And so Daniel went out there and 183 00:08:04,360 --> 00:08:08,320 Speaker 1: asked folks, has normal matter always been five percent of 184 00:08:08,360 --> 00:08:09,040 Speaker 1: the universe? 185 00:08:09,320 --> 00:08:12,480 Speaker 2: Thanks very much to everybody who answers these questions. I 186 00:08:12,520 --> 00:08:15,280 Speaker 2: really appreciate it, and we love hearing your voices on 187 00:08:15,360 --> 00:08:17,640 Speaker 2: the podcast. Gives us the sense that the podcast is 188 00:08:17,640 --> 00:08:21,400 Speaker 2: not one directional. It's an interactive learning experience. So if 189 00:08:21,480 --> 00:08:23,800 Speaker 2: you'd like to participate in the future, please write to 190 00:08:23,840 --> 00:08:26,760 Speaker 2: me two questions at Danielandjorge dot com. 191 00:08:26,800 --> 00:08:29,720 Speaker 1: So think about it for a second. Do you think 192 00:08:29,960 --> 00:08:33,680 Speaker 1: normal matter has always been five percent of the universe. 193 00:08:34,440 --> 00:08:35,600 Speaker 1: Here's what people had to say. 194 00:08:36,000 --> 00:08:39,640 Speaker 4: Well, I guess you've got normal matter, and you've got 195 00:08:39,720 --> 00:08:42,840 Speaker 4: dark matter, and you've got dark energy. I know that 196 00:08:42,960 --> 00:08:47,800 Speaker 4: dark energy is getting bigger as the universe expands, so 197 00:08:47,880 --> 00:08:50,680 Speaker 4: I would guess that when the universe was really small, 198 00:08:50,800 --> 00:08:53,440 Speaker 4: just after the Big Bang, there wasn't any dark energy, 199 00:08:53,880 --> 00:08:59,240 Speaker 4: so therefore normal matter would have been a much greater proportion. 200 00:09:00,240 --> 00:09:02,800 Speaker 5: I don't think that there is any reason for that 201 00:09:03,440 --> 00:09:06,880 Speaker 5: percentage to be constant, but to assume that is also 202 00:09:07,000 --> 00:09:10,520 Speaker 5: to assume that regular matter, dark matter, or dark energy 203 00:09:10,800 --> 00:09:13,359 Speaker 5: to be created spontaneously. 204 00:09:13,920 --> 00:09:15,960 Speaker 6: No, norm matter has not always been five percent of 205 00:09:16,000 --> 00:09:18,520 Speaker 6: the universe dark or the Big Bang. As far as 206 00:09:18,559 --> 00:09:20,240 Speaker 6: I know, normal matter an inche matter almost out of 207 00:09:20,240 --> 00:09:23,200 Speaker 6: one ratio, but no matter one out is there for 208 00:09:23,200 --> 00:09:25,040 Speaker 6: a part of our own universe. As for dark round 209 00:09:25,080 --> 00:09:26,560 Speaker 6: and dark energy, I don't know about that part. 210 00:09:26,760 --> 00:09:30,120 Speaker 1: All right, awesome answers here. Most people just assume that 211 00:09:30,240 --> 00:09:31,800 Speaker 1: it hasn't always been five percent. 212 00:09:31,960 --> 00:09:34,200 Speaker 2: Yeah, I think people are ready to be surprised. 213 00:09:34,320 --> 00:09:36,520 Speaker 1: I guess maybe people are used to having a universe 214 00:09:36,559 --> 00:09:39,040 Speaker 1: be always changing, so like, why would it be the same. 215 00:09:39,160 --> 00:09:42,280 Speaker 2: Yeah, that's true, although the universe is fourteen billion years old, 216 00:09:42,320 --> 00:09:45,080 Speaker 2: so you might speculate that it's kind of grown up 217 00:09:45,160 --> 00:09:47,400 Speaker 2: already and not going to change that much anymore. 218 00:09:47,880 --> 00:09:50,400 Speaker 1: M all right, well let's dig into it, Daniel. Let's 219 00:09:50,440 --> 00:09:52,160 Speaker 1: first of all talk about this pie and where it 220 00:09:52,200 --> 00:09:53,960 Speaker 1: came from, and what we know about the pie of 221 00:09:53,960 --> 00:09:56,920 Speaker 1: the universe, how much normal matter is there now, and 222 00:09:57,040 --> 00:09:59,400 Speaker 1: is it really that normal? 223 00:10:00,160 --> 00:10:03,080 Speaker 2: Normal is really a very inappropriate label for our kind 224 00:10:03,080 --> 00:10:05,400 Speaker 2: of matter, because we're not the biggest chunk of the 225 00:10:05,440 --> 00:10:08,839 Speaker 2: pie at all. Really, we should call that like familiar matter, 226 00:10:09,000 --> 00:10:10,480 Speaker 2: or just our kind of matter, or. 227 00:10:10,400 --> 00:10:13,680 Speaker 1: Something delicious matter. Apparently we are the most delicious things 228 00:10:13,679 --> 00:10:14,679 Speaker 1: in the universe. 229 00:10:14,400 --> 00:10:16,640 Speaker 2: And so on the podcast, we often talk about the 230 00:10:16,720 --> 00:10:21,480 Speaker 2: universe pie in three different categories normal matter, dark matter, 231 00:10:21,520 --> 00:10:25,280 Speaker 2: and dark energy. Physicists usually break this down into four 232 00:10:25,360 --> 00:10:30,560 Speaker 2: different categories, where they distinguish normal matter and radiation into 233 00:10:30,600 --> 00:10:34,160 Speaker 2: two different categories. So let's break that down. Normal matter 234 00:10:34,600 --> 00:10:36,080 Speaker 2: is the kind of stuff that you and I are 235 00:10:36,120 --> 00:10:38,960 Speaker 2: made out of, things built out of quarks and electrons, 236 00:10:39,040 --> 00:10:41,679 Speaker 2: which usually go to making protons and neutrons, and then 237 00:10:41,880 --> 00:10:45,680 Speaker 2: electrons make atoms, etc. So all the atomic matter, but 238 00:10:45,720 --> 00:10:48,520 Speaker 2: it also includes things made out of exotic quarks, top 239 00:10:48,640 --> 00:10:51,920 Speaker 2: quarks and down corks and bottom quarks, stuff that doesn't 240 00:10:52,040 --> 00:10:54,280 Speaker 2: make up the proton and the neutron but can be 241 00:10:54,360 --> 00:10:56,760 Speaker 2: created in the universe. All this kind of stuff we 242 00:10:56,840 --> 00:10:59,120 Speaker 2: call baryonic matter or normal matter. 243 00:11:00,080 --> 00:11:03,120 Speaker 1: Guys, all that stuff is stuff that has mass. Like, 244 00:11:03,280 --> 00:11:04,840 Speaker 1: those are all particles with mass. 245 00:11:05,120 --> 00:11:08,079 Speaker 2: Those are all particles with mass, but not all particles 246 00:11:08,080 --> 00:11:10,760 Speaker 2: with mass are in that category. Dark matter, for example, 247 00:11:11,160 --> 00:11:13,120 Speaker 2: we think has mass, but is not in that. 248 00:11:13,080 --> 00:11:15,320 Speaker 1: Category assuming it's a particle though. 249 00:11:15,280 --> 00:11:18,240 Speaker 2: Assuming it's a particle or some kind of matter with mass. 250 00:11:18,280 --> 00:11:20,640 Speaker 2: So yeah, all the normal matter has mass. That's one 251 00:11:20,679 --> 00:11:23,760 Speaker 2: of the distinctions, is this draw between matter and radiation. 252 00:11:24,040 --> 00:11:27,840 Speaker 2: Radiation is things that are effectively massless, things moving at 253 00:11:27,960 --> 00:11:31,200 Speaker 2: or very near the speed of light. So photons, for example, 254 00:11:31,320 --> 00:11:34,560 Speaker 2: are radiation. That's obvious. They have always been radiation, they 255 00:11:34,559 --> 00:11:38,079 Speaker 2: always will be radiation. Neutrinos are very very low mass 256 00:11:38,120 --> 00:11:40,600 Speaker 2: particles that move at almost to the speed of light, 257 00:11:40,679 --> 00:11:44,000 Speaker 2: so we count them as radiation even though technically they're 258 00:11:44,040 --> 00:11:46,440 Speaker 2: made out of stuff. They have mass to them. 259 00:11:46,600 --> 00:11:49,160 Speaker 1: Wait, neutrinas we don't count as normal matter. Why not. 260 00:11:49,280 --> 00:11:51,720 Speaker 2: We count them in the sort of normal slice, but 261 00:11:51,800 --> 00:11:54,640 Speaker 2: we don't call them matter. We call them radiation if 262 00:11:54,679 --> 00:11:56,600 Speaker 2: they're moving near the speed of light. And you'll see 263 00:11:56,600 --> 00:11:58,800 Speaker 2: why this distinction is important when we talk about how 264 00:11:58,800 --> 00:12:02,200 Speaker 2: the universe expand, because the expansion of the universe affects 265 00:12:02,280 --> 00:12:03,960 Speaker 2: radiation and matter differently. 266 00:12:04,640 --> 00:12:07,280 Speaker 1: All right, then what are the other slices of the pie. 267 00:12:07,440 --> 00:12:10,880 Speaker 2: One more caveat on the matter radiation distinction is that 268 00:12:10,960 --> 00:12:13,840 Speaker 2: the same particle can be in a different category depending 269 00:12:13,840 --> 00:12:16,560 Speaker 2: on its speed. If you take an electron, for example, 270 00:12:16,600 --> 00:12:19,760 Speaker 2: and it's just sitting there, it's not moving, it has mass, 271 00:12:19,840 --> 00:12:21,520 Speaker 2: it's not moving near the speed of light, you call 272 00:12:21,600 --> 00:12:24,840 Speaker 2: it matter. Speed up that electron to nearly the speed 273 00:12:24,880 --> 00:12:29,240 Speaker 2: of light, physicists now call that radiation because it's effectively massless, 274 00:12:29,240 --> 00:12:32,040 Speaker 2: its energy is so much bigger than its mass. It's 275 00:12:32,040 --> 00:12:34,920 Speaker 2: going near the speed of light, now you'd call that radiation. 276 00:12:35,400 --> 00:12:37,880 Speaker 2: So the same kind of particles can move from one 277 00:12:37,920 --> 00:12:41,480 Speaker 2: category to the other as the universe cools or heats, So, 278 00:12:41,559 --> 00:12:44,520 Speaker 2: as usual, physicists have given things kind of confusing. 279 00:12:44,200 --> 00:12:48,360 Speaker 1: Names, also kind of arbitrary. Is it's like when it 280 00:12:48,440 --> 00:12:53,120 Speaker 1: goes kind of fast, it's totally categorized it as one thing, 281 00:12:53,440 --> 00:12:56,600 Speaker 1: and when it goes kind of slow, it's totally something 282 00:12:56,600 --> 00:12:59,760 Speaker 1: totally different. Doesn't seem very scientific, Daniel. 283 00:12:59,480 --> 00:13:02,200 Speaker 2: Yeah, well, there are differences in the way the universe 284 00:13:02,280 --> 00:13:04,520 Speaker 2: treats things moving near the speed of light or at 285 00:13:04,559 --> 00:13:07,480 Speaker 2: the speed of light, and things moving slower. It's not 286 00:13:07,559 --> 00:13:10,600 Speaker 2: a bright line between them. There's a transition there. But 287 00:13:10,640 --> 00:13:13,160 Speaker 2: that's true for basically all of science. You know, it 288 00:13:13,320 --> 00:13:16,040 Speaker 2: was it different between water vapor and water liquid. There 289 00:13:16,120 --> 00:13:18,640 Speaker 2: is a difference, right, It's not a bright line, there's 290 00:13:18,640 --> 00:13:21,640 Speaker 2: a transition there between them. But we notice these trends 291 00:13:21,679 --> 00:13:23,520 Speaker 2: and we draw a dotted line and we treat them 292 00:13:23,559 --> 00:13:26,360 Speaker 2: as different stuff. So here physicists notice that as the 293 00:13:26,400 --> 00:13:30,400 Speaker 2: universe expands, matter and radiation get treated differently, so they've 294 00:13:30,440 --> 00:13:33,000 Speaker 2: drawn this line between them. Though you're right, it's really 295 00:13:33,120 --> 00:13:36,119 Speaker 2: part of a continuum. 296 00:13:34,880 --> 00:13:36,600 Speaker 1: All right. So then what are some of the other 297 00:13:36,640 --> 00:13:37,320 Speaker 1: pieces of the pie? 298 00:13:37,480 --> 00:13:40,280 Speaker 2: So the really big pieces of the pie are dark matter? 299 00:13:40,520 --> 00:13:40,679 Speaker 3: Right. 300 00:13:40,760 --> 00:13:42,720 Speaker 2: Dark matter is something that's out there in the universe. 301 00:13:42,760 --> 00:13:45,559 Speaker 2: We know. It's not made out of quarks and electrons 302 00:13:45,600 --> 00:13:48,520 Speaker 2: or photons or neutrinos or any kind of particle that 303 00:13:48,559 --> 00:13:51,440 Speaker 2: we know about. It's some kind of matter that's out there. 304 00:13:51,880 --> 00:13:54,720 Speaker 2: We see its effect gravitationally, so we know that it 305 00:13:54,800 --> 00:13:57,880 Speaker 2: has some kind of mass because it bends space in 306 00:13:57,920 --> 00:14:00,400 Speaker 2: the universe. It causes things to move, it hold together, 307 00:14:00,480 --> 00:14:03,959 Speaker 2: galaxies that spind changes the structure of the universe, all 308 00:14:04,000 --> 00:14:06,000 Speaker 2: this kind of stuff. So we know that it's out there, 309 00:14:06,120 --> 00:14:07,320 Speaker 2: but we don't know what it. 310 00:14:07,320 --> 00:14:09,679 Speaker 1: Is, right, And so far we only categorize it as 311 00:14:09,679 --> 00:14:11,760 Speaker 1: something different because we don't know what it is. It 312 00:14:11,800 --> 00:14:13,840 Speaker 1: could be like, if we know what it is, we 313 00:14:13,880 --> 00:14:16,960 Speaker 1: would maybe categorize it as normal matter too, right, Or 314 00:14:17,000 --> 00:14:19,000 Speaker 1: if a physicist looks at it and squints, maybe it'll 315 00:14:19,000 --> 00:14:21,560 Speaker 1: say it's radiation too well. 316 00:14:21,600 --> 00:14:24,360 Speaker 2: There could be dark matter and dark radiation, right. If 317 00:14:24,360 --> 00:14:26,760 Speaker 2: you have dark matter particles moving near the speed of light, 318 00:14:26,800 --> 00:14:29,680 Speaker 2: there would be dark radiation. We are very confident, though 319 00:14:29,760 --> 00:14:32,440 Speaker 2: nobody can ever be certain, that dark matter is not 320 00:14:32,560 --> 00:14:35,040 Speaker 2: made out of normal matter. It's not like a novel 321 00:14:35,120 --> 00:14:38,800 Speaker 2: rearrangement of quarks that hides in dark blobs, or some 322 00:14:38,880 --> 00:14:43,160 Speaker 2: weird combination of neutrinos, or just zillions and zillions of neutrinos. 323 00:14:43,400 --> 00:14:45,480 Speaker 2: And if you're curious about more details about that, check 324 00:14:45,480 --> 00:14:48,240 Speaker 2: out all of our episodes on dark matter. Briefly, we 325 00:14:48,280 --> 00:14:51,080 Speaker 2: are pretty sure that dark matter is not made of quarks, 326 00:14:51,080 --> 00:14:53,640 Speaker 2: because we know a lot about the number of quarks 327 00:14:53,640 --> 00:14:56,320 Speaker 2: in their universe that controls the amount of helium and 328 00:14:56,400 --> 00:14:59,720 Speaker 2: hygien made very early in the universe. So we're pretty 329 00:14:59,760 --> 00:15:01,920 Speaker 2: sure we can account for the number of quarks and 330 00:15:01,920 --> 00:15:04,640 Speaker 2: there's not enough to explain the dark matter. We know 331 00:15:04,680 --> 00:15:07,480 Speaker 2: that dark matter is not neutrinos because neutrinos move at 332 00:15:07,480 --> 00:15:09,600 Speaker 2: nearly the speed of light, and for dark matter to 333 00:15:09,640 --> 00:15:12,040 Speaker 2: have affected the shape and the structure of the universe 334 00:15:12,080 --> 00:15:14,960 Speaker 2: that we see today, the galaxies and their distributions, it 335 00:15:15,040 --> 00:15:18,160 Speaker 2: can't be moving very fast. It's low speed, and so 336 00:15:18,200 --> 00:15:20,480 Speaker 2: we're pretty sure dark matter is not made of neutrinos. 337 00:15:20,560 --> 00:15:22,200 Speaker 2: All of which to say, we're pretty sure that dark 338 00:15:22,240 --> 00:15:25,000 Speaker 2: matter is a different kind of stuff. It's not made 339 00:15:25,040 --> 00:15:27,160 Speaker 2: out of normal matter. It really is a different slice 340 00:15:27,200 --> 00:15:27,680 Speaker 2: of the pie. 341 00:15:27,960 --> 00:15:30,760 Speaker 1: All right. Well, let's get into maybe the deeper parts 342 00:15:30,760 --> 00:15:34,080 Speaker 1: of our mystery pie, which is dark energy. So let's 343 00:15:34,160 --> 00:15:36,240 Speaker 1: dig into that. But first let's take a quick break. 344 00:15:48,720 --> 00:15:50,840 Speaker 1: All right, we're eating up the pie of the universe 345 00:15:50,880 --> 00:15:53,760 Speaker 1: here today. We're serving folks a big slice or a 346 00:15:53,800 --> 00:15:54,360 Speaker 1: little slide. 347 00:15:54,600 --> 00:15:57,880 Speaker 2: We are serving up a big fat slice of universe pie, 348 00:15:57,920 --> 00:16:00,640 Speaker 2: and it's mostly a dark pie. I'm hoping it's chocolate. 349 00:16:01,760 --> 00:16:05,440 Speaker 1: You're hoping. What else could something dark in a pie case? 350 00:16:06,880 --> 00:16:10,440 Speaker 2: Yeah, mud pie is the most innocent example. 351 00:16:10,640 --> 00:16:11,440 Speaker 1: You go, boison berry. 352 00:16:12,480 --> 00:16:12,680 Speaker 5: Go. 353 00:16:13,080 --> 00:16:15,640 Speaker 1: Well, the pie of the universe, as we talked about, 354 00:16:15,880 --> 00:16:18,080 Speaker 1: is about five percent the normal stuff that you and 355 00:16:18,200 --> 00:16:20,400 Speaker 1: I are made out of, that hamsters and stars and 356 00:16:20,440 --> 00:16:23,040 Speaker 1: planets are made out of. About twenty seven percent is 357 00:16:23,120 --> 00:16:25,640 Speaker 1: dark matter, at least matter. We so far that we 358 00:16:25,680 --> 00:16:28,600 Speaker 1: don't know whether where to categorize it or we don't 359 00:16:28,640 --> 00:16:30,800 Speaker 1: know much about it. But there is the big piece 360 00:16:30,840 --> 00:16:32,920 Speaker 1: of the pie. Basically, the filling of the pie is 361 00:16:32,920 --> 00:16:33,960 Speaker 1: something totally different. 362 00:16:34,240 --> 00:16:37,760 Speaker 2: All the stuff we talked about today, dark matter, normal matter, 363 00:16:38,080 --> 00:16:41,760 Speaker 2: radiation only adds up to be like thirty two percent 364 00:16:42,280 --> 00:16:45,320 Speaker 2: of the stuff in the universe. Normal matter is five percent, 365 00:16:45,520 --> 00:16:48,760 Speaker 2: dark matter is twenty seven percent. Radiation is almost zero. 366 00:16:49,040 --> 00:16:52,840 Speaker 2: It's like ten to the minus four fraction. Dark energy 367 00:16:53,000 --> 00:16:56,080 Speaker 2: is sixty eight percent of the energy of the universe, 368 00:16:56,640 --> 00:16:58,520 Speaker 2: and we don't know what it is. All we know 369 00:16:58,640 --> 00:17:01,840 Speaker 2: is that dark energy is the mysterious stuff that's making 370 00:17:01,880 --> 00:17:04,160 Speaker 2: the universe expand faster and faster. 371 00:17:04,720 --> 00:17:06,480 Speaker 1: Yeah, I guess. One day we notice that the universe 372 00:17:06,520 --> 00:17:10,199 Speaker 1: is expanding, it's accelerating in its expansion, and so we 373 00:17:10,359 --> 00:17:12,800 Speaker 1: gave that acceleration or whatever it might be causing that 374 00:17:12,880 --> 00:17:15,160 Speaker 1: acceleration a name. That's the name dark energy. 375 00:17:15,359 --> 00:17:18,240 Speaker 2: Yeah, exactly. And we measure that expansion and we think 376 00:17:18,240 --> 00:17:20,560 Speaker 2: how much energy does it take to make that accelerating 377 00:17:20,560 --> 00:17:23,359 Speaker 2: and expansion happen. And that's what we call dark energy. 378 00:17:23,400 --> 00:17:25,760 Speaker 2: And we have a couple different ways to measure dark energy. 379 00:17:25,840 --> 00:17:28,120 Speaker 2: One is just by measuring the expansion of the universe, 380 00:17:28,160 --> 00:17:31,240 Speaker 2: and the other is by looking at the overall curvature 381 00:17:31,359 --> 00:17:35,159 Speaker 2: of the universe. All these pieces of the pie have energy, 382 00:17:35,240 --> 00:17:38,359 Speaker 2: so they all contribute energy density to the universe. And 383 00:17:38,480 --> 00:17:41,960 Speaker 2: Einstein tells us that energy density, not just mass, is 384 00:17:41,960 --> 00:17:45,600 Speaker 2: what curves space and causes the effect we call gravity. 385 00:17:46,000 --> 00:17:48,840 Speaker 2: So all of these things contribute to the overall energy 386 00:17:48,840 --> 00:17:51,960 Speaker 2: density of the universe, which affects its curvature. As we 387 00:17:52,040 --> 00:17:54,639 Speaker 2: recently talked about on the podcast, they all add up 388 00:17:54,680 --> 00:17:57,920 Speaker 2: to make space nice and flat. So they all add 389 00:17:57,960 --> 00:18:00,239 Speaker 2: up to what we call the critical density. We can 390 00:18:00,240 --> 00:18:02,640 Speaker 2: measure the sum of all of these components by measuring 391 00:18:02,680 --> 00:18:04,800 Speaker 2: the overall curvature of the universe. 392 00:18:05,640 --> 00:18:08,040 Speaker 1: It's a flat pie universe. It's more like a pizza pie. 393 00:18:08,080 --> 00:18:11,560 Speaker 2: You're saying, it's a thin and crispy pie, not a 394 00:18:11,600 --> 00:18:12,160 Speaker 2: deep dish. 395 00:18:12,240 --> 00:18:13,720 Speaker 1: Well, I guess I have a question, which is, like, 396 00:18:13,840 --> 00:18:18,040 Speaker 1: what form is dark energy present in the universe? Like 397 00:18:18,160 --> 00:18:20,720 Speaker 1: is it actually there or is it kind of like 398 00:18:20,880 --> 00:18:23,080 Speaker 1: hidden behind the scenes that it only comes out when 399 00:18:23,200 --> 00:18:24,280 Speaker 1: to expand the universe. 400 00:18:24,359 --> 00:18:26,800 Speaker 2: We don't know what dark energy is like. We don't 401 00:18:26,800 --> 00:18:30,679 Speaker 2: have a microscopic picture of what it looks like, or 402 00:18:30,720 --> 00:18:33,080 Speaker 2: what it's doing, or how it works. We know really 403 00:18:33,560 --> 00:18:36,280 Speaker 2: very little about it. It fits into our model of 404 00:18:36,320 --> 00:18:38,879 Speaker 2: the expansion of the universe and the accelerating expansion of 405 00:18:38,920 --> 00:18:41,600 Speaker 2: the universe if it does a couple of things. If 406 00:18:41,640 --> 00:18:44,080 Speaker 2: it's some kind of field the way that light is 407 00:18:44,119 --> 00:18:46,960 Speaker 2: a wiggle in the electromagnetic field, we imagine some other 408 00:18:47,119 --> 00:18:49,560 Speaker 2: new kind of field, some kind of field that has 409 00:18:49,680 --> 00:18:52,920 Speaker 2: high potential energy the way, for example, the Higgs field 410 00:18:53,000 --> 00:18:56,560 Speaker 2: has high potential energy. It's stuck in its little local minimum, 411 00:18:56,600 --> 00:18:58,600 Speaker 2: which is why it has so much energy stored in it. 412 00:18:58,640 --> 00:18:59,919 Speaker 2: So if you have some field with a bunch of 413 00:19:00,000 --> 00:19:04,240 Speaker 2: potential energy stored. It has this accelerating expansion effect according 414 00:19:04,280 --> 00:19:07,240 Speaker 2: to general relativity. So that's basically all we know about it. 415 00:19:07,280 --> 00:19:09,280 Speaker 2: We don't know what field it is. We don't know 416 00:19:09,359 --> 00:19:12,080 Speaker 2: why it exists. It's a big mystery. If you try 417 00:19:12,119 --> 00:19:14,399 Speaker 2: to ask, like, well, do the fields we know about 418 00:19:14,600 --> 00:19:17,800 Speaker 2: can they provide that potential energy? Do to calculation, that 419 00:19:17,920 --> 00:19:19,919 Speaker 2: turns out the answer is know and the fields we 420 00:19:19,960 --> 00:19:21,960 Speaker 2: know about are off by about a factor of ten 421 00:19:22,000 --> 00:19:25,639 Speaker 2: to the one hundred. So we really very clueless about 422 00:19:25,720 --> 00:19:29,200 Speaker 2: what it is that's creating this accelerating expansion. And when 423 00:19:29,200 --> 00:19:31,240 Speaker 2: you hear dark energy, you should really just think about 424 00:19:31,280 --> 00:19:35,159 Speaker 2: it as a description of our observation of the expansion, 425 00:19:35,520 --> 00:19:38,040 Speaker 2: not any sort of understanding of what's causing it. 426 00:19:38,200 --> 00:19:39,919 Speaker 1: I wonder if it's like if you take two bowling 427 00:19:39,920 --> 00:19:43,080 Speaker 1: balls and you connect them with an invisible spring, and 428 00:19:43,080 --> 00:19:45,720 Speaker 1: then you bring the bowling balls together, you're creating like 429 00:19:46,040 --> 00:19:49,040 Speaker 1: some stored potential energy between the two boiling balls. It's 430 00:19:49,080 --> 00:19:51,240 Speaker 1: like you can't see it, but it's there. There's that 431 00:19:51,280 --> 00:19:54,119 Speaker 1: potential energy hitting there is and dark energy sort of 432 00:19:54,160 --> 00:19:56,600 Speaker 1: like that, like there's something about space that has this 433 00:19:56,680 --> 00:20:00,159 Speaker 1: potential energy stored in it. That's making everything accelerate then 434 00:20:00,200 --> 00:20:00,720 Speaker 1: get bigger. 435 00:20:00,840 --> 00:20:03,680 Speaker 2: Yeah, that's a great description. Potential energy can be sort 436 00:20:03,720 --> 00:20:06,919 Speaker 2: of invisible, right, it's just the configuration of that field. 437 00:20:06,920 --> 00:20:09,280 Speaker 2: That's what potential energy is. Like you put that bowling 438 00:20:09,280 --> 00:20:11,960 Speaker 2: ball up on a shelf, It's got energy stored in 439 00:20:12,000 --> 00:20:14,119 Speaker 2: its configuration, the fact that it's up on the shelf 440 00:20:14,160 --> 00:20:16,119 Speaker 2: and not on the floor. Now you take a field 441 00:20:16,240 --> 00:20:18,080 Speaker 2: and you displace it from zero, you say, okay, the 442 00:20:18,119 --> 00:20:20,880 Speaker 2: field has some value. And fields can have all sorts 443 00:20:20,920 --> 00:20:23,359 Speaker 2: of different potential energies depending on their values. And so 444 00:20:23,720 --> 00:20:26,639 Speaker 2: this particular field, whatever it is, seems to have a 445 00:20:26,640 --> 00:20:29,640 Speaker 2: lot of potential energy stored in it, in whatever configuration 446 00:20:29,800 --> 00:20:32,119 Speaker 2: it happens to be in. It's like an infinite number 447 00:20:32,119 --> 00:20:36,200 Speaker 2: of invisible bowling balls stored on the shelves everywhere. 448 00:20:35,720 --> 00:20:38,200 Speaker 1: In space, or like in an infinite number of invisible 449 00:20:38,240 --> 00:20:41,720 Speaker 1: springs tied between different everything together. Right. 450 00:20:41,800 --> 00:20:45,600 Speaker 2: Yeah, that are precompressed exactly. And there's a seeming contradiction 451 00:20:45,720 --> 00:20:47,879 Speaker 2: here in dark energy. Like on one hand, we say 452 00:20:48,080 --> 00:20:50,359 Speaker 2: dark energy is sixty eight percent of the energy in 453 00:20:50,359 --> 00:20:53,000 Speaker 2: the universe. You might think, wow, it's overwhelming, it's dominant, 454 00:20:53,080 --> 00:20:56,359 Speaker 2: it controls everything, But in our lives and in our 455 00:20:56,400 --> 00:21:00,000 Speaker 2: experience and in our Solar system. Dark energy is basically negligible, 456 00:21:00,440 --> 00:21:02,280 Speaker 2: like we didn't discover it until we looked at the 457 00:21:02,320 --> 00:21:05,080 Speaker 2: expansion of the universe on large scales. You can't see 458 00:21:05,119 --> 00:21:07,239 Speaker 2: it in the Solar System. You can't feel it with 459 00:21:07,240 --> 00:21:11,040 Speaker 2: gravitational experiences here on Earth. Because dark energy gets stronger 460 00:21:11,200 --> 00:21:15,040 Speaker 2: over greater distances. It's the opposite of gravity. Gravity gets 461 00:21:15,040 --> 00:21:18,399 Speaker 2: weaker over greater distances. Like we have two bowling balls 462 00:21:18,400 --> 00:21:20,399 Speaker 2: next to each other, they feel each other's gravity. You 463 00:21:20,480 --> 00:21:23,320 Speaker 2: put one on Jupiter, you can basically ignore the gravity 464 00:21:23,400 --> 00:21:26,159 Speaker 2: the other bowling ball. But dark energy because it's a 465 00:21:26,200 --> 00:21:29,520 Speaker 2: feature of space itself. As you get more space between stuff, 466 00:21:29,520 --> 00:21:31,960 Speaker 2: it gets stronger and stronger. So you don't see dark 467 00:21:32,080 --> 00:21:35,640 Speaker 2: energy unless you're looking over really really large distance scales, 468 00:21:35,800 --> 00:21:37,840 Speaker 2: And so it has no effect on my life, or 469 00:21:37,920 --> 00:21:40,040 Speaker 2: door life, or our life in the Solar System or 470 00:21:40,280 --> 00:21:43,600 Speaker 2: super high precision measurements of the orbit of Jupiter can't 471 00:21:43,720 --> 00:21:47,040 Speaker 2: detect any dark energy. But it is the dominant fraction 472 00:21:47,119 --> 00:21:48,360 Speaker 2: of energy in the universe. 473 00:21:48,480 --> 00:21:50,959 Speaker 1: I guess it's the reminder of how big the universe is. 474 00:21:51,080 --> 00:21:53,280 Speaker 1: Right like places like Earth where you have a lot 475 00:21:53,320 --> 00:21:57,240 Speaker 1: of normal matter clumped together, or even our Solar System, 476 00:21:57,280 --> 00:22:00,280 Speaker 1: they're pretty rare in the universe, right Like, outside the Earth, 477 00:22:00,280 --> 00:22:03,159 Speaker 1: it's mostly empty space. Outside of the Solar System, it's 478 00:22:03,480 --> 00:22:04,440 Speaker 1: even more empty space. 479 00:22:04,520 --> 00:22:07,000 Speaker 2: In the same way that dark matter overwhelms the kind 480 00:22:07,040 --> 00:22:10,600 Speaker 2: of matter in the universe that's also not in our experience, right, Like, 481 00:22:10,680 --> 00:22:13,240 Speaker 2: you can't detect dark matter in our Solar System by 482 00:22:13,240 --> 00:22:16,080 Speaker 2: looking at like how the voyager probe moves in its gravity, 483 00:22:16,320 --> 00:22:19,080 Speaker 2: and that's because it's spread out through all that empty space. 484 00:22:19,400 --> 00:22:22,200 Speaker 2: Dark matter is just not nearly as clumped as normal matter. 485 00:22:22,359 --> 00:22:24,480 Speaker 2: So all the space between us and other stars, where 486 00:22:24,480 --> 00:22:27,800 Speaker 2: there's almost no normal matter, is smoothly filled with dark matter. So, 487 00:22:27,840 --> 00:22:30,560 Speaker 2: as you say, the bigness of the universe means that 488 00:22:30,560 --> 00:22:32,480 Speaker 2: that adds up to a big chunk of the pie. 489 00:22:32,680 --> 00:22:34,840 Speaker 1: All right, Well, let's summarize the pie. Then we know 490 00:22:34,880 --> 00:22:36,680 Speaker 1: that the pie of the universe is about five percent 491 00:22:36,720 --> 00:22:42,040 Speaker 1: normal matter, twenty seven percent dark matter, almost zero radiation, 492 00:22:42,400 --> 00:22:45,560 Speaker 1: and about sixty eight percent dark energy. That's the pie 493 00:22:45,560 --> 00:22:47,399 Speaker 1: of the universe as we know it today. And so 494 00:22:47,480 --> 00:22:50,199 Speaker 1: the big question of the episode today is has that 495 00:22:50,280 --> 00:22:53,520 Speaker 1: always been the case? Has it always been those percentages 496 00:22:53,720 --> 00:22:55,840 Speaker 1: and will it change in the future. So what do 497 00:22:55,880 --> 00:22:56,560 Speaker 1: we know of that new. 498 00:22:56,600 --> 00:22:59,880 Speaker 2: So we know that these fractions can change and have changed, 499 00:23:00,080 --> 00:23:02,639 Speaker 2: and we're radically different earlier in the history of the 500 00:23:02,720 --> 00:23:06,280 Speaker 2: universe and very likely will be radically different in the 501 00:23:06,320 --> 00:23:09,400 Speaker 2: future of the universe. And it turns out we live 502 00:23:09,400 --> 00:23:11,720 Speaker 2: in a very peculiar time in the history of the 503 00:23:11,840 --> 00:23:15,000 Speaker 2: universe when these fractions are at all similar to each other. 504 00:23:15,520 --> 00:23:19,320 Speaker 2: Most times in the universe, one of these fractions totally dominated, 505 00:23:19,480 --> 00:23:21,560 Speaker 2: and in the deep future of the universe, we expect 506 00:23:21,560 --> 00:23:24,520 Speaker 2: one of these fractions to totally dominate. Sort of weird 507 00:23:24,600 --> 00:23:27,680 Speaker 2: that things are kind of at all in balance right now. 508 00:23:28,600 --> 00:23:31,040 Speaker 1: Well, I guess there are different ways that the universe 509 00:23:31,280 --> 00:23:36,119 Speaker 1: can change its composition, right, Like maybe a normal matter 510 00:23:36,320 --> 00:23:39,280 Speaker 1: turns into dark matter, or dark matter turns into dark energy, 511 00:23:39,359 --> 00:23:42,199 Speaker 1: or something like pies is there, but the ingredients change 512 00:23:43,040 --> 00:23:44,879 Speaker 1: from one to the other. Or you could have like 513 00:23:45,040 --> 00:23:47,600 Speaker 1: the pies growing and just like every day there's more 514 00:23:47,680 --> 00:23:50,439 Speaker 1: dark energy, there's more dark matter, and so the percentages 515 00:23:50,560 --> 00:23:53,359 Speaker 1: change in that way, right, So in which way is 516 00:23:53,359 --> 00:23:54,200 Speaker 1: the universe changing? 517 00:23:54,400 --> 00:23:57,119 Speaker 2: So in all of those ways? Number one, a certain 518 00:23:57,160 --> 00:23:59,080 Speaker 2: kind of stuff can turn into other kinds of stuff. 519 00:23:59,480 --> 00:24:03,040 Speaker 2: For example, matter can emit radiation. An electron hanging out 520 00:24:03,040 --> 00:24:05,480 Speaker 2: in the universe can give off a photon that increases 521 00:24:05,800 --> 00:24:09,320 Speaker 2: the radiation fraction of the universe. Photons can turn into matter, 522 00:24:09,440 --> 00:24:12,439 Speaker 2: a photon can convert into an electron, and a positron 523 00:24:12,600 --> 00:24:15,840 Speaker 2: that's converting radiation into matter. Very straightforward, and these kind 524 00:24:15,840 --> 00:24:18,800 Speaker 2: of processes happen. Also, we think between normal matter and 525 00:24:18,880 --> 00:24:22,200 Speaker 2: dark matter that we can dig into that in a minute. Also, 526 00:24:22,400 --> 00:24:26,080 Speaker 2: the universe is expanding, and as it expands, the various 527 00:24:26,080 --> 00:24:30,680 Speaker 2: fractions get treated differently. They dilute differently as the universe 528 00:24:30,760 --> 00:24:35,400 Speaker 2: gets bigger. Finally, the universe is cooling. It's lowering in temperature, 529 00:24:35,600 --> 00:24:38,280 Speaker 2: and as the temperature gets colder, some of these processes 530 00:24:38,320 --> 00:24:41,040 Speaker 2: that convert one thing to another turn on or off 531 00:24:41,080 --> 00:24:44,359 Speaker 2: at various times. So all of these things change through 532 00:24:44,400 --> 00:24:47,040 Speaker 2: the history of the universe because of all of those reasons. 533 00:24:47,800 --> 00:24:50,040 Speaker 1: Interesting. So there are many ways in which the universe 534 00:24:50,080 --> 00:24:52,040 Speaker 1: is changing. Although I feel like you forgot the third 535 00:24:52,080 --> 00:24:53,520 Speaker 1: way in which the universe can change. 536 00:24:53,680 --> 00:24:54,560 Speaker 2: What's that puberty? 537 00:24:56,600 --> 00:24:58,720 Speaker 1: No, when a physicist you know, looks at it differently 538 00:24:58,800 --> 00:25:02,399 Speaker 1: or wakes up differently, I think that's radiation. No, you 539 00:25:02,400 --> 00:25:04,639 Speaker 1: know today that looks like normal matter to it. 540 00:25:06,359 --> 00:25:09,119 Speaker 2: There's always an arbitrariness to how we call these things, 541 00:25:09,400 --> 00:25:11,680 Speaker 2: and you know, I look forward to arguing with alien 542 00:25:11,720 --> 00:25:13,840 Speaker 2: physicists about the meaning of radiation. 543 00:25:14,040 --> 00:25:15,639 Speaker 1: But as you said, the universe has gone through a 544 00:25:15,640 --> 00:25:20,160 Speaker 1: lot of changes in its body. I guess it's gone 545 00:25:20,200 --> 00:25:22,919 Speaker 1: through puberty, or is going through puberty. And so Daniel 546 00:25:22,960 --> 00:25:25,199 Speaker 1: maybe steps through what some of these changes have been 547 00:25:25,280 --> 00:25:26,640 Speaker 1: and what are they like, what happened in them. 548 00:25:26,720 --> 00:25:29,080 Speaker 2: So let's start at the very beginning and zoom back 549 00:25:29,119 --> 00:25:31,639 Speaker 2: to the earliest point we know, which is when the 550 00:25:31,720 --> 00:25:35,159 Speaker 2: universe was very dense and very hot, right, filled with 551 00:25:35,200 --> 00:25:37,800 Speaker 2: some kind of plasma. We don't know what happened before this. 552 00:25:37,880 --> 00:25:40,360 Speaker 2: We don't know what came before this to create this hot, 553 00:25:40,400 --> 00:25:44,960 Speaker 2: dense plasma. Their theories about inflation and infulton particles and 554 00:25:45,000 --> 00:25:47,440 Speaker 2: all that is very very speculative. What we are very 555 00:25:47,480 --> 00:25:50,840 Speaker 2: certain about is that about thirteen point eight billion years ago, 556 00:25:50,880 --> 00:25:54,240 Speaker 2: the universe was very hot and very dense and everything 557 00:25:54,359 --> 00:25:57,040 Speaker 2: was sloshing around. And from that point on we can 558 00:25:57,080 --> 00:25:59,960 Speaker 2: model very precisely how that expands and how it cools, 559 00:26:00,040 --> 00:26:02,480 Speaker 2: and everything changes and that's about as far back as 560 00:26:02,480 --> 00:26:05,040 Speaker 2: we can go and be confident. We can speculate deeper 561 00:26:05,080 --> 00:26:07,600 Speaker 2: and talk about like crazy theories about before that. But 562 00:26:07,680 --> 00:26:10,440 Speaker 2: what we know very well precision cosmology takes us back 563 00:26:10,440 --> 00:26:12,800 Speaker 2: to that moment when the universe was very hot and 564 00:26:12,960 --> 00:26:15,800 Speaker 2: very dense, and at that moment we think the universe 565 00:26:15,960 --> 00:26:19,760 Speaker 2: was ninety nine point ninety nine a bunch more nine 566 00:26:19,800 --> 00:26:23,639 Speaker 2: percent radiation, that it was essentially all radiation and everything 567 00:26:23,640 --> 00:26:25,280 Speaker 2: else was a tiny fraction. 568 00:26:25,160 --> 00:26:27,840 Speaker 1: Like it was all basically light in the Trino's right, 569 00:26:27,880 --> 00:26:30,200 Speaker 1: because that's the only thing you count as radiation is 570 00:26:30,280 --> 00:26:31,280 Speaker 1: light in theatrinas. 571 00:26:31,400 --> 00:26:34,080 Speaker 2: Oh, I'm going to disappoint you. Actually, if you had 572 00:26:34,200 --> 00:26:37,800 Speaker 2: electrons back then, they counted as radiation because the universe 573 00:26:37,960 --> 00:26:40,960 Speaker 2: was so hot, electrons were moving at the speed of light, 574 00:26:41,240 --> 00:26:44,520 Speaker 2: and basically everything was moving it nearly the speed of light. 575 00:26:44,840 --> 00:26:47,480 Speaker 2: Because the universe was so hot, everything was so fast 576 00:26:47,520 --> 00:26:49,560 Speaker 2: that it didn't really matter how much mass it had, 577 00:26:50,000 --> 00:26:52,320 Speaker 2: even like a top cork if it existed back then. 578 00:26:52,880 --> 00:26:55,359 Speaker 2: The top cork is the most massive fundamental particle we 579 00:26:55,400 --> 00:26:57,920 Speaker 2: know about. But back then, in the very early universe, 580 00:26:58,119 --> 00:27:00,000 Speaker 2: it was moving it basically the speed of light because 581 00:27:00,119 --> 00:27:03,680 Speaker 2: the universe was that hot, and so everything gets counted 582 00:27:03,760 --> 00:27:04,560 Speaker 2: as radiation. 583 00:27:08,320 --> 00:27:10,800 Speaker 1: I feel like you're basically just making stuff up that. 584 00:27:13,040 --> 00:27:14,000 Speaker 2: I tried to warn you. 585 00:27:15,280 --> 00:27:16,959 Speaker 1: It's been taken to it for a second here, like, 586 00:27:17,040 --> 00:27:19,040 Speaker 1: why is it important that if it's moving it closest 587 00:27:19,040 --> 00:27:22,200 Speaker 1: to the speed of flight you call electron radiation. Isn't 588 00:27:22,200 --> 00:27:23,240 Speaker 1: it still an electron? 589 00:27:23,480 --> 00:27:26,240 Speaker 2: It's still an electron. Absolutely, but it's going to be 590 00:27:26,240 --> 00:27:29,640 Speaker 2: important as soon as the universe starts expanding and cooling. 591 00:27:29,760 --> 00:27:31,200 Speaker 2: I just want to add that there are other reasons 592 00:27:31,240 --> 00:27:34,120 Speaker 2: to think that the very early universe was filled with radiation, 593 00:27:34,440 --> 00:27:37,879 Speaker 2: not just because we call it radiation, but also because frankly, 594 00:27:37,920 --> 00:27:40,439 Speaker 2: it was very hot and filled with charge particles. And 595 00:27:40,520 --> 00:27:43,680 Speaker 2: what do hot charge particles do? They give off photons. 596 00:27:43,680 --> 00:27:46,159 Speaker 2: So there really were a lot of photons in the 597 00:27:46,200 --> 00:27:48,920 Speaker 2: early universe, many more than we have today. It's not 598 00:27:49,000 --> 00:27:50,360 Speaker 2: just a slippery naming. 599 00:27:50,040 --> 00:27:54,000 Speaker 1: Scheme, but it's partly a slippery naming scheme. 600 00:27:54,119 --> 00:27:58,840 Speaker 2: Yes, absolutely, it's partly a slippery naming scheme, but not entirely. Also, 601 00:27:59,000 --> 00:28:01,560 Speaker 2: in the early universe there was matter and antimatter, and 602 00:28:01,560 --> 00:28:05,040 Speaker 2: that annihilates and forms photons, So there really was a 603 00:28:05,080 --> 00:28:07,920 Speaker 2: lot of photons in the early universe. So it's partially 604 00:28:07,920 --> 00:28:11,400 Speaker 2: a slippery naming scheme calling stuff radiation that today we wouldn't. 605 00:28:11,480 --> 00:28:14,359 Speaker 2: But also there really was a lot of radiation stuff 606 00:28:14,359 --> 00:28:16,160 Speaker 2: that we would call radiation today. 607 00:28:16,320 --> 00:28:19,760 Speaker 1: Well, then let's maybe be helpful to people and break 608 00:28:19,800 --> 00:28:22,479 Speaker 1: it down out of this is what you call radiation, 609 00:28:22,560 --> 00:28:24,760 Speaker 1: how much of it was actually light and how much 610 00:28:24,840 --> 00:28:28,760 Speaker 1: of it was electrons or quarks or you know things 611 00:28:28,760 --> 00:28:30,960 Speaker 1: with that today we would call normal matter. 612 00:28:31,280 --> 00:28:34,720 Speaker 2: Thanks to the CMB and bearing on acoustic oscillation, we 613 00:28:34,760 --> 00:28:38,840 Speaker 2: can actually make measurements of like the photon to quark ratios. 614 00:28:39,240 --> 00:28:42,080 Speaker 2: So we do have those numbers. They change sort of 615 00:28:42,240 --> 00:28:44,240 Speaker 2: rapidly as the universe is cooling. 616 00:28:44,440 --> 00:28:47,840 Speaker 1: Okay, So then so then what was causing these changes 617 00:28:47,880 --> 00:28:50,240 Speaker 1: between like electrons and photons. 618 00:28:50,440 --> 00:28:53,040 Speaker 2: So what happens very early on is the universe starts 619 00:28:53,040 --> 00:28:56,760 Speaker 2: to expand, Right. What's happening is more space is being created, 620 00:28:56,960 --> 00:28:59,720 Speaker 2: but you're not creating more stuff, right, and so what 621 00:28:59,720 --> 00:29:02,640 Speaker 2: how if you have like ten particles in a tiny 622 00:29:02,680 --> 00:29:05,240 Speaker 2: box and then you make the box bigger, all now 623 00:29:05,240 --> 00:29:09,520 Speaker 2: the density decreases, right, and it gets more dilute, And 624 00:29:09,560 --> 00:29:12,680 Speaker 2: that makes sense. So the energy density is dropping, dropping, dropping, 625 00:29:12,760 --> 00:29:15,280 Speaker 2: So that's how it works for matter. Right, you increase 626 00:29:15,320 --> 00:29:18,600 Speaker 2: the box, you get a drop in energy density. For radiation, 627 00:29:18,760 --> 00:29:21,840 Speaker 2: the rules are a little bit different. For radiation. The 628 00:29:21,960 --> 00:29:25,760 Speaker 2: energy density actually drops faster as you increase the size 629 00:29:25,760 --> 00:29:28,760 Speaker 2: of the box because the particles get red shifted. The 630 00:29:28,800 --> 00:29:33,000 Speaker 2: expansion of space stretches the wavelengths of these particles. 631 00:29:32,600 --> 00:29:36,680 Speaker 1: Of the photons, but doesn't it stretch also the electron. 632 00:29:36,360 --> 00:29:39,800 Speaker 2: If they're moving very fast, if they're treated as radiation, 633 00:29:39,920 --> 00:29:42,880 Speaker 2: And that's the distinction. If you're considered radiation, it's because 634 00:29:42,920 --> 00:29:46,760 Speaker 2: effectively you have no mass, which makes your wavelength expand. 635 00:29:47,040 --> 00:29:50,200 Speaker 2: As space gets expanded, that means that your energy density 636 00:29:50,280 --> 00:29:52,960 Speaker 2: is dropping more quickly, because not only are you getting 637 00:29:52,960 --> 00:29:56,400 Speaker 2: more dilute, you're also getting red shifted. So as time 638 00:29:56,480 --> 00:30:00,320 Speaker 2: goes on, the energy density of radiation drops fast faster 639 00:30:00,480 --> 00:30:03,760 Speaker 2: than the energy density of matter, which does two things. One, 640 00:30:04,080 --> 00:30:07,440 Speaker 2: now some of that radiation slides over into the matter category, 641 00:30:07,640 --> 00:30:10,520 Speaker 2: and also the radiation slice of the pie starts to 642 00:30:10,560 --> 00:30:12,880 Speaker 2: decrease relative to the matter slice of the pie. 643 00:30:13,600 --> 00:30:16,040 Speaker 1: Okay, I think what you're maybe saying is that as 644 00:30:16,080 --> 00:30:19,640 Speaker 1: the universe expands, the amount of energy that's stored in 645 00:30:19,760 --> 00:30:24,000 Speaker 1: momentum is changing. That's really kind of what's happening, right, 646 00:30:24,400 --> 00:30:27,280 Speaker 1: And so at some point, for example, the electrons were 647 00:30:27,280 --> 00:30:29,680 Speaker 1: mostly momentum because we're going so fast, but at some 648 00:30:29,720 --> 00:30:32,800 Speaker 1: point they slowed down so much that they were mostly 649 00:30:33,000 --> 00:30:34,120 Speaker 1: just the mass of the electron. 650 00:30:34,320 --> 00:30:37,040 Speaker 2: Yeah, that's exactly right. But remember that there's something else 651 00:30:37,120 --> 00:30:40,640 Speaker 2: also happening for photons, right. Photons do get red shifted, 652 00:30:41,280 --> 00:30:43,240 Speaker 2: and people write and ask about this all the time, 653 00:30:43,360 --> 00:30:46,280 Speaker 2: like what happens to the energy of a red shifted photon? 654 00:30:46,360 --> 00:30:48,680 Speaker 2: Where did it go? Because we've had the concept of 655 00:30:48,720 --> 00:30:52,040 Speaker 2: conservation of energy banged into our head for so many years. Well, 656 00:30:52,080 --> 00:30:55,280 Speaker 2: expanding space does not respect the conservation of energy. If 657 00:30:55,320 --> 00:30:56,960 Speaker 2: you have a photon in a chunk of space and 658 00:30:56,960 --> 00:30:59,960 Speaker 2: then you expand that space, the wavelength of that phot 659 00:31:00,040 --> 00:31:03,560 Speaker 2: quoton also gets expanded because space itself is expanding, and 660 00:31:03,600 --> 00:31:06,160 Speaker 2: so now it has less energy. And that energy didn't 661 00:31:06,200 --> 00:31:09,160 Speaker 2: go anywhere. There's just is less of it, because the 662 00:31:09,240 --> 00:31:13,400 Speaker 2: universe doesn't respect conservation of energy unless space is fixed. 663 00:31:13,480 --> 00:31:15,280 Speaker 1: But I guess the question is, like, it sounds like 664 00:31:15,360 --> 00:31:18,360 Speaker 1: our classification of what you call radiation and matter was 665 00:31:18,440 --> 00:31:21,760 Speaker 1: changing very rapidly during those times. But were the actual 666 00:31:21,920 --> 00:31:24,880 Speaker 1: like number of electrons changing, Were there more electrons being 667 00:31:24,880 --> 00:31:28,440 Speaker 1: created or destroyed? Was there more light being created or destroyed? 668 00:31:28,640 --> 00:31:30,800 Speaker 1: Or did that mostly stay the same. 669 00:31:30,640 --> 00:31:32,720 Speaker 2: In the very beginning that mostly stayed the same, like 670 00:31:32,760 --> 00:31:34,800 Speaker 2: you had a bunch of processes. These things are sloshing 671 00:31:34,840 --> 00:31:38,040 Speaker 2: back and forth. Photons can turn into electron positron pairs. 672 00:31:38,280 --> 00:31:41,320 Speaker 2: Electron positron pairs can annihilate back into photons. The very 673 00:31:41,360 --> 00:31:44,480 Speaker 2: early universe, we think was in thermal equilibrium. They have 674 00:31:44,560 --> 00:31:47,360 Speaker 2: all these things going in both directions and they basically equalized. 675 00:31:47,400 --> 00:31:49,239 Speaker 2: That's what happens at a hot plasma if you give 676 00:31:49,240 --> 00:31:52,680 Speaker 2: it enough time. Then the universe is expanding and some 677 00:31:52,680 --> 00:31:54,800 Speaker 2: stuff gets slowed down, so it falls out of the 678 00:31:54,920 --> 00:31:57,880 Speaker 2: radiation category into matter, and stuff that got left in 679 00:31:57,920 --> 00:32:01,400 Speaker 2: the radiation category is losing energy density compared to the 680 00:32:01,440 --> 00:32:04,200 Speaker 2: matter category. So now the matter category is growing and 681 00:32:04,240 --> 00:32:07,840 Speaker 2: the radiation category is dropping, and so eventually we get 682 00:32:07,880 --> 00:32:11,560 Speaker 2: to a matter dominated universe. The universe started out dominated 683 00:32:11,600 --> 00:32:14,520 Speaker 2: by radiation, but as it expands and cools, it becomes 684 00:32:14,520 --> 00:32:16,240 Speaker 2: a matter dominated universe. 685 00:32:17,160 --> 00:32:18,920 Speaker 1: And so in that way, you would say that the 686 00:32:18,960 --> 00:32:21,920 Speaker 1: percentages of matter and radiation in the universe were changing. 687 00:32:22,160 --> 00:32:26,000 Speaker 2: That's exactly right, and that happened about fifty thousand years 688 00:32:26,040 --> 00:32:28,240 Speaker 2: after the Big Bang. At that point, the matter and 689 00:32:28,320 --> 00:32:31,240 Speaker 2: radiation sort of hit a crossover point. Radiation is dropping 690 00:32:31,240 --> 00:32:34,160 Speaker 2: more quickly, but it started out higher, and that's the 691 00:32:34,160 --> 00:32:37,360 Speaker 2: point where they cross each other. Meanwhile, dark energy is 692 00:32:37,440 --> 00:32:40,160 Speaker 2: humming along like a tiny fraction of the universe like 693 00:32:40,440 --> 00:32:43,320 Speaker 2: zeros or zerz are one this whole time, playing the 694 00:32:43,400 --> 00:32:46,080 Speaker 2: long game, waiting for its turn to dominate. But at 695 00:32:46,120 --> 00:32:50,160 Speaker 2: around fifty thousand years the universe became matter dominated. It 696 00:32:50,240 --> 00:32:52,480 Speaker 2: was cooled enough that a lot of stuff slowed down 697 00:32:52,800 --> 00:32:56,680 Speaker 2: and became essentially called matter, and the photon energies got 698 00:32:56,720 --> 00:32:59,240 Speaker 2: decreased because of this radiation stretching. 699 00:33:00,000 --> 00:33:02,120 Speaker 1: And let's get into then the long game of dark 700 00:33:02,160 --> 00:33:05,240 Speaker 1: matter and the newcomer dark energy and how it took 701 00:33:05,280 --> 00:33:08,680 Speaker 1: over the entire pie of the universe. Let's dig into that, 702 00:33:08,720 --> 00:33:23,640 Speaker 1: but first let's take another quick break. All right, we're 703 00:33:23,680 --> 00:33:27,520 Speaker 1: talking about the universe pie, the chocolate pie, the white 704 00:33:27,560 --> 00:33:30,200 Speaker 1: chocolate pies, all the pies in the universe and what 705 00:33:30,200 --> 00:33:32,680 Speaker 1: they're made out of, and how that's been changing since 706 00:33:32,720 --> 00:33:34,880 Speaker 1: the birth of the universe and throughout all of its 707 00:33:34,920 --> 00:33:37,160 Speaker 1: history and maybe into the future. And so if we've 708 00:33:37,240 --> 00:33:39,880 Speaker 1: learned that at the beginning of the universe, physicists would 709 00:33:39,920 --> 00:33:42,200 Speaker 1: qualify most of the stuff in the universe as radiation 710 00:33:42,240 --> 00:33:44,160 Speaker 1: because it was going so fast. But as it cooled 711 00:33:44,200 --> 00:33:46,680 Speaker 1: down and expanded, things sort of slowed down enough that 712 00:33:46,720 --> 00:33:49,320 Speaker 1: they started to be called more a regular matter, which 713 00:33:49,320 --> 00:33:51,120 Speaker 1: is the kind of matter that we're made out of. 714 00:33:51,160 --> 00:33:52,960 Speaker 1: And so you were saying that dark matter was sort 715 00:33:52,960 --> 00:33:55,320 Speaker 1: of waiting in the wings to make an appearance here 716 00:33:55,320 --> 00:33:56,720 Speaker 1: in the history of the universe. 717 00:33:56,440 --> 00:33:58,760 Speaker 2: Well, it was more thinking about dark energy as waiting 718 00:33:58,760 --> 00:34:00,600 Speaker 2: in the wings. Playing the very very very long the 719 00:34:00,640 --> 00:34:03,960 Speaker 2: billion year game, the first few tens of thousands of 720 00:34:04,040 --> 00:34:08,000 Speaker 2: years were a battle between radiation and matter, including normal 721 00:34:08,040 --> 00:34:11,319 Speaker 2: matter and dark matter. Both of those contributions combined were 722 00:34:11,360 --> 00:34:14,440 Speaker 2: still smaller than radiation in the very early times. Than 723 00:34:14,480 --> 00:34:19,920 Speaker 2: after about fifty thousand years, matter together overwhelmed the radiation category, 724 00:34:19,920 --> 00:34:22,799 Speaker 2: and that includes dark matter and normal matter. But there's 725 00:34:22,800 --> 00:34:25,040 Speaker 2: an interesting mix there between the matter and the dark 726 00:34:25,080 --> 00:34:27,680 Speaker 2: matter fractions, Like there were a bunch of electrons and 727 00:34:27,680 --> 00:34:29,359 Speaker 2: there were a bunch of protons, but we also think 728 00:34:29,440 --> 00:34:32,200 Speaker 2: there was a lot of dark matter in the early universe, 729 00:34:32,320 --> 00:34:35,440 Speaker 2: and we suspect very strongly that in the early universe, 730 00:34:35,480 --> 00:34:37,640 Speaker 2: matter and dark matter were turning into each other, that 731 00:34:37,680 --> 00:34:40,360 Speaker 2: there was some kind of force that allowed one to 732 00:34:40,400 --> 00:34:42,000 Speaker 2: turn into the other or back. 733 00:34:42,200 --> 00:34:44,160 Speaker 1: Wait. And so in the point zero zero zero zero 734 00:34:44,239 --> 00:34:46,720 Speaker 1: zero zero one percent of stuff in the early universe 735 00:34:46,760 --> 00:34:49,600 Speaker 1: that you call matter, you're also including dark matter in there. 736 00:34:49,480 --> 00:34:52,560 Speaker 2: Also including dark matter in there exactly. And we think 737 00:34:52,600 --> 00:34:55,120 Speaker 2: that there was a higher percentage of that that was 738 00:34:55,239 --> 00:34:57,880 Speaker 2: dark matter than there is today. That at the matter 739 00:34:57,920 --> 00:35:00,680 Speaker 2: section of the pie, dark matter plus normal matter, that 740 00:35:00,760 --> 00:35:03,520 Speaker 2: there was more dark matter as a fraction than there 741 00:35:03,640 --> 00:35:04,160 Speaker 2: is today. 742 00:35:04,280 --> 00:35:06,800 Speaker 1: And you're saying that dark matter can turn and was 743 00:35:06,920 --> 00:35:09,960 Speaker 1: turning into regular matter and vice versa because it was 744 00:35:10,000 --> 00:35:10,359 Speaker 1: so hot. 745 00:35:10,480 --> 00:35:12,440 Speaker 2: Yes, And we don't understand how this works, because we 746 00:35:12,480 --> 00:35:14,279 Speaker 2: don't know what dark matter is and whether it's a 747 00:35:14,280 --> 00:35:17,040 Speaker 2: particle and what forces it feels. But in order to 748 00:35:17,080 --> 00:35:19,759 Speaker 2: tell the story and be consistent with everything we understand, 749 00:35:19,960 --> 00:35:22,160 Speaker 2: there needs to be some mechanism for dark matter and 750 00:35:22,200 --> 00:35:24,640 Speaker 2: normal matter to slosh into each other to explain how 751 00:35:24,640 --> 00:35:26,600 Speaker 2: we got from having more dark matter in the early 752 00:35:26,680 --> 00:35:29,879 Speaker 2: universe to having less of it. Today. The story goes 753 00:35:29,920 --> 00:35:33,360 Speaker 2: something like this dark matter we think is some massive particle, 754 00:35:33,680 --> 00:35:36,520 Speaker 2: some very heavy particle, And as the universe is cooling, 755 00:35:36,920 --> 00:35:39,160 Speaker 2: matter and dark matter are turning back and forth into 756 00:35:39,200 --> 00:35:42,320 Speaker 2: each other. But as things get colder and colder, matter 757 00:35:42,400 --> 00:35:45,399 Speaker 2: can no longer turn into dark matter because dark matter 758 00:35:45,480 --> 00:35:47,960 Speaker 2: is too heavy. No longer is there enough energy around 759 00:35:48,480 --> 00:35:51,479 Speaker 2: to smash together normal matter particles and turn it into 760 00:35:51,560 --> 00:35:54,839 Speaker 2: dark matter. So dark matter creation stops, but dark matter 761 00:35:54,880 --> 00:35:57,919 Speaker 2: annihilation doesn't. Dark matter is still turning into normal matter 762 00:35:58,040 --> 00:36:00,520 Speaker 2: right in that one direction, but the reverse this process 763 00:36:00,600 --> 00:36:03,600 Speaker 2: is no longer happening. So instead of being in balance, 764 00:36:03,719 --> 00:36:06,359 Speaker 2: now dark matter is turning into normal matter, but it's 765 00:36:06,400 --> 00:36:10,080 Speaker 2: not happening the reverse, and so the dark matter fraction shrinks. 766 00:36:10,560 --> 00:36:13,800 Speaker 1: Whoa. So like the regular matter was growing. 767 00:36:13,600 --> 00:36:16,040 Speaker 2: In the early universe, some dark matter got turned into 768 00:36:16,080 --> 00:36:18,680 Speaker 2: normal matter and then it got frozen out. It didn't 769 00:36:18,680 --> 00:36:20,680 Speaker 2: get turned back into dark matter like it did when 770 00:36:20,719 --> 00:36:22,880 Speaker 2: things were hot and slashing around freely. 771 00:36:23,760 --> 00:36:25,759 Speaker 1: Then to pie bake exactly. 772 00:36:26,160 --> 00:36:29,480 Speaker 2: Somebody baked the pie. And then as the universe expands, 773 00:36:29,520 --> 00:36:32,560 Speaker 2: it cools further and there's less and less dark matter. 774 00:36:32,640 --> 00:36:35,200 Speaker 2: Then there's not enough dark matter around for there to 775 00:36:35,239 --> 00:36:38,840 Speaker 2: be much annihilation, So dark matter stops turning into normal 776 00:36:38,880 --> 00:36:41,520 Speaker 2: matter and it gets freezes in or baked in. I 777 00:36:41,560 --> 00:36:43,480 Speaker 2: guess you could call it in our analogy, but in 778 00:36:43,480 --> 00:36:45,920 Speaker 2: physics terms they call it dark matter freeze out. 779 00:36:46,040 --> 00:36:48,560 Speaker 1: So then when when did this freeze out or baking happen? 780 00:36:48,800 --> 00:36:51,880 Speaker 2: It happened about ten to the miners eight seconds after 781 00:36:51,920 --> 00:36:52,560 Speaker 2: the Big Bang? 782 00:36:52,880 --> 00:36:56,400 Speaker 1: WHOA what? And since then it's been the same proportion 783 00:36:56,480 --> 00:36:57,960 Speaker 1: of regular matter and dark matter. 784 00:36:58,160 --> 00:37:01,640 Speaker 2: Yeah, the dark matter normal matter fraction got frozen in 785 00:37:01,880 --> 00:37:05,160 Speaker 2: very early on as the universe expanded and cooled, and 786 00:37:05,160 --> 00:37:09,160 Speaker 2: then the radiation normal matter fraction changes as things expand further. 787 00:37:09,280 --> 00:37:12,480 Speaker 2: And that turnover point was like ten thousand years. So 788 00:37:12,520 --> 00:37:14,759 Speaker 2: there's lots of really fascinating time scales here. 789 00:37:14,880 --> 00:37:17,520 Speaker 1: Okay, So then since ten to the minus second, since 790 00:37:17,520 --> 00:37:19,719 Speaker 1: the Big Bang, and we've had the same amount of 791 00:37:19,800 --> 00:37:22,720 Speaker 1: regular matter and dark matter. It sounds like what you're saying, 792 00:37:22,800 --> 00:37:25,240 Speaker 1: and so those proportions stayed the same, right, it would 793 00:37:25,239 --> 00:37:28,200 Speaker 1: be about five to one, right, m M. But then 794 00:37:28,560 --> 00:37:31,040 Speaker 1: waiting in the wings, you're saying there was dark energy. 795 00:37:31,080 --> 00:37:32,800 Speaker 1: So back then there was no dark energy. 796 00:37:32,920 --> 00:37:35,160 Speaker 2: There was not no dark energy, but there was less 797 00:37:35,280 --> 00:37:38,120 Speaker 2: universe than there is today, and dark energy is built 798 00:37:38,160 --> 00:37:41,000 Speaker 2: into space. Every chunk of space comes with dark energy. 799 00:37:41,280 --> 00:37:43,720 Speaker 2: So you have less universe, you have less dark energy, 800 00:37:43,880 --> 00:37:47,320 Speaker 2: but it's constant in density, right, more universe, less universe, 801 00:37:47,440 --> 00:37:50,480 Speaker 2: You don't change the density of dark energy. But as 802 00:37:50,520 --> 00:37:52,840 Speaker 2: you expand the universe, you do change the density of 803 00:37:52,880 --> 00:37:55,600 Speaker 2: matter and radiation. As we talked about, you expand the box, 804 00:37:55,640 --> 00:37:58,560 Speaker 2: you have a smaller density of matter, and radiation drops 805 00:37:58,600 --> 00:38:02,400 Speaker 2: even faster. As the universe is expanding, both matter and 806 00:38:02,560 --> 00:38:05,880 Speaker 2: radiation are having their energy density drop very very quickly. 807 00:38:06,160 --> 00:38:09,680 Speaker 2: But dark energy isn't. It's a constant density. You make 808 00:38:09,760 --> 00:38:12,360 Speaker 2: more space, you get more dark energy. That doesn't happen 809 00:38:12,400 --> 00:38:15,960 Speaker 2: for electrons. So as the universe expands, dark energy starts 810 00:38:15,960 --> 00:38:17,200 Speaker 2: to creep up in its fraction. 811 00:38:17,320 --> 00:38:19,120 Speaker 1: Although I wonder if you can make the case that 812 00:38:19,239 --> 00:38:22,000 Speaker 1: dark energy was always there, like if we don't know 813 00:38:22,000 --> 00:38:24,400 Speaker 1: what it is, and it's just like a hidden, invisible 814 00:38:24,440 --> 00:38:28,319 Speaker 1: potential energy that could may move things, wouldn't you say 815 00:38:28,320 --> 00:38:31,280 Speaker 1: it was already built into the universe from the beginning. 816 00:38:31,360 --> 00:38:33,480 Speaker 2: Yeah, that's exactly the model, right. We think it's an 817 00:38:33,480 --> 00:38:36,240 Speaker 2: inherent part of space. As long as you had space, 818 00:38:36,280 --> 00:38:38,799 Speaker 2: you had dark energy, and it was there during this 819 00:38:38,840 --> 00:38:41,000 Speaker 2: first ten to the minus eight seconds, but the other 820 00:38:41,040 --> 00:38:44,040 Speaker 2: stuff had such a high energy density that it swamped 821 00:38:44,080 --> 00:38:46,600 Speaker 2: the whole pie. The dark energy was always there with 822 00:38:46,719 --> 00:38:49,560 Speaker 2: its same energy density, it was just small compared to 823 00:38:49,600 --> 00:38:52,720 Speaker 2: the energy density of the other components, which then faded 824 00:38:52,760 --> 00:38:54,200 Speaker 2: as the universe expanded. 825 00:38:54,680 --> 00:38:56,520 Speaker 1: I guess what I mean is like, if you're closing 826 00:38:56,560 --> 00:38:58,799 Speaker 1: the universe off at a certain point, and you're saying 827 00:38:58,840 --> 00:39:01,560 Speaker 1: that the energy of the universe is not conserve, there's 828 00:39:01,560 --> 00:39:04,080 Speaker 1: more energy being pumped into it. But what if you 829 00:39:04,160 --> 00:39:06,879 Speaker 1: count the pump and where this energy is coming from. 830 00:39:06,960 --> 00:39:09,759 Speaker 1: Then maybe I wonder if you could say that dark 831 00:39:09,840 --> 00:39:11,759 Speaker 1: energy was always there at the same percentage. 832 00:39:11,960 --> 00:39:13,960 Speaker 2: Yeah, perhaps when there's lots of the theories of dark 833 00:39:14,080 --> 00:39:15,799 Speaker 2: energy and what it might be is it's some kind 834 00:39:15,840 --> 00:39:18,400 Speaker 2: of weird field, is it some kind of other stuff? 835 00:39:18,520 --> 00:39:21,680 Speaker 2: And so those various theories would upset these fractions if 836 00:39:21,680 --> 00:39:22,440 Speaker 2: you included them. 837 00:39:22,600 --> 00:39:25,280 Speaker 1: Yeah, And so that's how the universe pie has been changing. 838 00:39:25,360 --> 00:39:27,960 Speaker 1: But it seems like it hasn't really changed much since 839 00:39:28,120 --> 00:39:30,200 Speaker 1: ten to the minus eight seconds, since the Big Bang, 840 00:39:30,560 --> 00:39:32,800 Speaker 1: except just that dark energy has been growing. 841 00:39:32,880 --> 00:39:35,120 Speaker 2: Yeah, dark energy has been growing, which makes for a 842 00:39:35,160 --> 00:39:38,719 Speaker 2: fascinating tug of war because dark energy is growing. But 843 00:39:38,840 --> 00:39:41,120 Speaker 2: in the early universe, like a billion years in, we're 844 00:39:41,160 --> 00:39:44,360 Speaker 2: still matter dominated, right, Radiation is faded away. We're in 845 00:39:44,360 --> 00:39:47,719 Speaker 2: a matter dominated universe. The universe is expanding, but that 846 00:39:47,840 --> 00:39:51,840 Speaker 2: expansion is now decelerating. It's slowing down because the universe 847 00:39:51,920 --> 00:39:54,520 Speaker 2: is dominated by matter, and what does matter tend to do? 848 00:39:54,680 --> 00:39:57,960 Speaker 2: Pulls things together, right, It slows down the expansion of 849 00:39:57,960 --> 00:40:01,720 Speaker 2: the universe. But because it was expanding still even though decelerating, 850 00:40:02,320 --> 00:40:04,360 Speaker 2: dark energy is creeping up and up and up, and 851 00:40:04,480 --> 00:40:07,880 Speaker 2: dark energy makes the universe expand faster, and eventually the 852 00:40:07,960 --> 00:40:11,080 Speaker 2: universe expanded enough so that dark energy just took over. 853 00:40:11,520 --> 00:40:14,720 Speaker 2: And around eight billion years after the beginning of the universe, 854 00:40:14,840 --> 00:40:17,520 Speaker 2: dark energy was the dominant fraction. And you'll see that 855 00:40:17,560 --> 00:40:20,920 Speaker 2: the universe start to accelerate its expansion because dark energy 856 00:40:20,960 --> 00:40:24,239 Speaker 2: takes over. And that's basically the future. Dark energy is 857 00:40:24,280 --> 00:40:27,239 Speaker 2: a runaway process. If nothing else changes, dark energy will 858 00:40:27,239 --> 00:40:29,880 Speaker 2: continue to grow as a fraction of the energy density 859 00:40:29,920 --> 00:40:32,960 Speaker 2: of the universe, making the universe accelerate faster and faster, 860 00:40:33,320 --> 00:40:35,960 Speaker 2: increasing the dark energy fraction faster and faster. 861 00:40:36,120 --> 00:40:38,479 Speaker 1: All right, So then in like a billion years from now, 862 00:40:38,600 --> 00:40:40,960 Speaker 1: what's going to be the percentage or a pie breakdown 863 00:40:40,960 --> 00:40:43,680 Speaker 1: of the universe if you had to get well. 864 00:40:43,560 --> 00:40:46,600 Speaker 2: It's like sixty eight percent dark energy. Now it's just 865 00:40:47,000 --> 00:40:49,080 Speaker 2: going to increase. It's going to go to ninety percent, 866 00:40:49,160 --> 00:40:51,799 Speaker 2: ninety five percent, ninety nine percent. But this is over 867 00:40:51,920 --> 00:40:55,040 Speaker 2: billions and billions and trillions of years into the future. 868 00:40:55,080 --> 00:40:56,480 Speaker 2: But it's only going to crank up. But you know, 869 00:40:56,520 --> 00:40:58,480 Speaker 2: we don't know that, right. Remember, we don't know what 870 00:40:58,600 --> 00:41:01,279 Speaker 2: dark energy is. We don't know for sure what its 871 00:41:01,280 --> 00:41:03,120 Speaker 2: behavior is going to be in the future. This model 872 00:41:03,120 --> 00:41:06,280 Speaker 2: describes very very well the history of these energy fractions 873 00:41:06,280 --> 00:41:08,680 Speaker 2: and how the universe pie has changed, with a couple 874 00:41:08,760 --> 00:41:11,560 Speaker 2: of caveats, like the measurements of the dark energy in 875 00:41:11,560 --> 00:41:14,400 Speaker 2: the early universe don't one hundred percent agree with our 876 00:41:14,440 --> 00:41:16,920 Speaker 2: measurements in the late universe. There is this hubble tension. 877 00:41:17,560 --> 00:41:20,120 Speaker 2: But mostly this picture of the sloshing pieces of the 878 00:41:20,160 --> 00:41:23,080 Speaker 2: pie holds together very well and matches all of our data. 879 00:41:23,120 --> 00:41:26,080 Speaker 1: All right. So then in the future, normal matter, dark matter, 880 00:41:26,120 --> 00:41:28,840 Speaker 1: and radiation, they're all going to stay the same amount, 881 00:41:29,280 --> 00:41:31,879 Speaker 1: but the percentage is going to go down because dark 882 00:41:31,960 --> 00:41:34,839 Speaker 1: energy is growing, and so in the far future it's 883 00:41:34,840 --> 00:41:36,880 Speaker 1: going to be like ninety nine nine nine nine percent 884 00:41:37,000 --> 00:41:38,200 Speaker 1: dark energy then the universe. 885 00:41:38,280 --> 00:41:41,040 Speaker 2: Yeah, exactly. And the universe started out dominated by one 886 00:41:41,080 --> 00:41:43,080 Speaker 2: fraction of the pie, it's going to end up dominated 887 00:41:43,080 --> 00:41:45,760 Speaker 2: by another fraction of the pie. And there's this little 888 00:41:45,760 --> 00:41:49,120 Speaker 2: window in the middle where multiple fractions are not zero. 889 00:41:49,480 --> 00:41:52,280 Speaker 2: It's a very unusual time to be in the universe 890 00:41:52,320 --> 00:41:54,360 Speaker 2: when you have a bunch of different kinds of stuff around. 891 00:41:54,400 --> 00:41:56,239 Speaker 2: You got dark matter, you've got normal matter, you've got 892 00:41:56,280 --> 00:41:58,120 Speaker 2: dark energy, all at the same time. 893 00:41:58,400 --> 00:42:00,960 Speaker 1: But according to you, we're still in the undelicious part 894 00:42:01,120 --> 00:42:07,640 Speaker 1: of the universe. Apparently, apparently, thanks, things can't get worse, 895 00:42:07,640 --> 00:42:08,799 Speaker 1: but they can only get better. 896 00:42:09,040 --> 00:42:12,160 Speaker 2: I wouldn't say undelicious, I'd say less delicious than the future. 897 00:42:12,400 --> 00:42:14,120 Speaker 2: That's the optimistic way to think about it. 898 00:42:14,440 --> 00:42:16,600 Speaker 1: Oh, there you go. And let's hope that dark energy 899 00:42:16,960 --> 00:42:18,880 Speaker 1: is the most delicious thing in the universe, because that 900 00:42:19,560 --> 00:42:21,160 Speaker 1: seems to be the only thing that's going to be 901 00:42:21,160 --> 00:42:22,799 Speaker 1: around in the future percentage wise. 902 00:42:22,840 --> 00:42:24,400 Speaker 2: And caveats for those of you who they like to 903 00:42:24,400 --> 00:42:26,960 Speaker 2: think a lot about dark matter. This assumes a fairly 904 00:42:27,040 --> 00:42:29,560 Speaker 2: simple model of dark matter. That it was in thermal 905 00:42:29,640 --> 00:42:32,400 Speaker 2: equilibrium with everything else early in the universe. That doesn't 906 00:42:32,440 --> 00:42:34,480 Speaker 2: have to be the case. You can have other theories 907 00:42:34,480 --> 00:42:37,880 Speaker 2: of dark matter axions, et cetera that are so weakly 908 00:42:37,920 --> 00:42:40,640 Speaker 2: coupled that hardly interacts, so they're not thermally mixed with 909 00:42:40,680 --> 00:42:42,680 Speaker 2: the stuff in the universe. There's lots of other ways 910 00:42:42,719 --> 00:42:44,920 Speaker 2: you could change this picture. This is like the simplest 911 00:42:44,920 --> 00:42:47,319 Speaker 2: model we can make that describes everything we see, and 912 00:42:47,400 --> 00:42:48,840 Speaker 2: it works really pretty well. 913 00:42:49,000 --> 00:42:52,560 Speaker 1: All right, Well, it's another big reminder that the universe 914 00:42:52,719 --> 00:42:55,680 Speaker 1: is a big, mysterious piece of pastry out there. There's 915 00:42:55,680 --> 00:42:57,640 Speaker 1: still a lot to learn, a lot to explore, a 916 00:42:57,640 --> 00:43:00,000 Speaker 1: lot to taste, and a lot to bake as well. 917 00:43:00,320 --> 00:43:02,440 Speaker 2: And as you take a big bite of the universe, 918 00:43:02,520 --> 00:43:05,560 Speaker 2: remember that not only is our kind of stuff unusual 919 00:43:05,600 --> 00:43:08,680 Speaker 2: in the universe, it's getting more and more unusual. And 920 00:43:08,719 --> 00:43:11,879 Speaker 2: we live in an unusual time in the universe when 921 00:43:11,920 --> 00:43:14,200 Speaker 2: our kind of stuff and dark matter is a really 922 00:43:14,239 --> 00:43:16,920 Speaker 2: significant fraction of the stuff out there in the universe, 923 00:43:17,280 --> 00:43:19,759 Speaker 2: alien civilizations in the year three trillion, that we'll have 924 00:43:19,800 --> 00:43:21,640 Speaker 2: a very different kind of physics to deal with. 925 00:43:21,960 --> 00:43:24,040 Speaker 1: All right, Well, we hope you go out there and 926 00:43:24,040 --> 00:43:26,480 Speaker 1: grab your piece of the pie of the curiosity and 927 00:43:26,560 --> 00:43:30,000 Speaker 1: mystery of the universe. You hope you enjoyed that. Thanks 928 00:43:30,040 --> 00:43:32,160 Speaker 1: for joining us, See you next time. 929 00:43:40,000 --> 00:43:42,800 Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain 930 00:43:42,840 --> 00:43:46,839 Speaker 2: the Universe is a production of iHeartRadio. For more podcasts 931 00:43:46,840 --> 00:43:51,520 Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever 932 00:43:51,600 --> 00:43:53,320 Speaker 2: you listen to your favorite shows.