WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.839 slumber under the night sky. 7 00:00:26.960 --> 00:00:29.679 Imagine you have spent your entire life living in a 8 00:00:29.719 --> 00:00:35.000 house like you know every single creaky floorboard in the hallway. 9 00:00:34.719 --> 00:00:36.840 Right, You've memorized the whole layout exactly. 10 00:00:37.640 --> 00:00:39.960 You know the precise angle the sunlight hits the kitchen 11 00:00:40.000 --> 00:00:43.520 window in the morning, and you feel completely, perfectly secure 12 00:00:44.159 --> 00:00:47.600 in your understanding of this building. You have mapped its dimensions, 13 00:00:47.600 --> 00:00:51.600 you've calculated its structural integrity. But then you wake up 14 00:00:51.640 --> 00:00:54.479 one morning and realize something genuinely terrifying. 15 00:00:54.759 --> 00:00:55.520 Okay, what's that? 16 00:00:55.840 --> 00:00:59.119 You'll suddenly realize that eighty five percent of the building, 17 00:01:00.159 --> 00:01:02.799 like the vast majority of the load bearing walls, the 18 00:01:02.840 --> 00:01:06.680 steel beams, the roof, is completely invisible to you. 19 00:01:06.959 --> 00:01:07.480 Wow. 20 00:01:07.640 --> 00:01:10.439 Yeah, you can't see it, you can't touch it. And worse, 21 00:01:10.840 --> 00:01:13.120 you look down and realize the foundation of this house 22 00:01:13.239 --> 00:01:16.920 is constantly, unpredictably shifting its shape underneath your feet. 23 00:01:17.000 --> 00:01:20.120 I mean, that is the deeply unsettling image. It forces 24 00:01:20.159 --> 00:01:23.439 a complete reevaluation of literally everything you thought you understood 25 00:01:23.439 --> 00:01:26.239 about your environment. Right, and yet that is precisely the 26 00:01:26.280 --> 00:01:28.159 reality we're waking up to right now. When we look 27 00:01:28.159 --> 00:01:29.359 at the universe, it's. 28 00:01:29.319 --> 00:01:34.120 Wild, and that is exactly the crisis currently facing modern astrophysics. 29 00:01:34.640 --> 00:01:39.319 So today we are exploring a really groundbreaking mathematical framework 30 00:01:39.560 --> 00:01:41.359 from the Chinese Academy of Sciences. 31 00:01:41.599 --> 00:01:46.760 Yeah, specifically the work of Yunchen, Tengpengzu and Zumingzong exactly. 32 00:01:46.560 --> 00:01:49.439 And they're attempting to solve two of the most stubborn, 33 00:01:49.840 --> 00:01:52.200 entrenched mysteries in the cosmos. 34 00:01:51.680 --> 00:01:54.840 The true nature of dark energy and this massive discrepancy 35 00:01:54.879 --> 00:01:57.359 in how fast the universe is actually expanding. 36 00:01:57.599 --> 00:02:00.239 Right, So we are going to break down the actual 37 00:02:00.319 --> 00:02:03.799 mechanics of the cosmos today, looking at the very edge 38 00:02:03.799 --> 00:02:06.239 of human understanding, because I feel like this stuff can 39 00:02:06.280 --> 00:02:07.680 get so abstract, right. 40 00:02:07.560 --> 00:02:11.560 It absolutely can, But we will connect these incredibly complex, 41 00:02:11.680 --> 00:02:14.639 high level mathematical theories back to the fundamental question of 42 00:02:14.919 --> 00:02:18.560 how reality actually operates. Because as abstract as the math 43 00:02:18.560 --> 00:02:21.360 of cosmology can get It is ultimately describing the physical 44 00:02:21.400 --> 00:02:23.319 space you and I occupy right now. 45 00:02:23.159 --> 00:02:24.879 The space the listener's sitting in right. 46 00:02:24.719 --> 00:02:27.759 Now, exactly. We are talking about the mechanics of the universe, 47 00:02:28.199 --> 00:02:30.840 and while to understand how the rules of the universe 48 00:02:30.919 --> 00:02:33.199 might be breaking right now, we first have to understand 49 00:02:33.199 --> 00:02:34.400 what those rules were supposed to be. 50 00:02:34.599 --> 00:02:37.039 Okay, let's unpack this. Let's start with the bedrock, like 51 00:02:37.560 --> 00:02:41.560 the standard model of cosmology that scientists have basically relied 52 00:02:41.599 --> 00:02:42.599 on for decades. 53 00:02:42.879 --> 00:02:45.759 Right, So, the standard model is known in physics as 54 00:02:45.800 --> 00:02:47.719 the Lambda CDM. 55 00:02:47.199 --> 00:02:49.360 Framework glambda CDM. Yeah. 56 00:02:49.759 --> 00:02:51.879 You can think of it as a structure built on 57 00:02:52.039 --> 00:02:56.280 three massive pillars. So the first pillar is represented by 58 00:02:56.280 --> 00:02:59.400 that Greek letter Lambda. Okay, that stands for the cosmological 59 00:02:59.439 --> 00:03:03.319 constant constant, right, and this is the mathematical value we 60 00:03:03.360 --> 00:03:07.199 associate with dark energy, which we understand to be the 61 00:03:07.240 --> 00:03:11.800 mechanism that is actively driving the accelerating expansion of the universe. 62 00:03:11.919 --> 00:03:14.159 I want to pause on that word constant, because that 63 00:03:14.199 --> 00:03:16.879 seems to be the lynchpin of this entire discussion. The 64 00:03:16.919 --> 00:03:19.879 assumption has always been the dark energy just does not change. 65 00:03:20.080 --> 00:03:23.240 Yeah, that has been the prevailing consensus for a long time. 66 00:03:23.599 --> 00:03:26.120 The idea is that the density of the dark energy 67 00:03:26.199 --> 00:03:30.680 remains perfectly fixed, so as the universe expands and creates 68 00:03:30.719 --> 00:03:35.199 more empty space, more dark energy simply exists to fill 69 00:03:35.240 --> 00:03:36.680 that new void. 70 00:03:36.560 --> 00:03:39.960 Keeping the overall density identical to what it was, say, 71 00:03:40.479 --> 00:03:42.080 a billion years ago exactly. 72 00:03:42.639 --> 00:03:45.080 And the history of this idea actually goes all the 73 00:03:45.080 --> 00:03:46.560 way back to Albert Einstein. 74 00:03:46.599 --> 00:03:47.520 Oh really, yeah. 75 00:03:47.599 --> 00:03:51.639 When Einstein formulated his theory of general relativity, the equations 76 00:03:51.680 --> 00:03:54.560 actually suggested the universe should be collapsing. 77 00:03:54.159 --> 00:03:56.280 In on itself because of gravity, right, yes. 78 00:03:56.319 --> 00:03:59.080 Due to the gravitational pull of all the matter inside it. 79 00:03:59.360 --> 00:04:02.240 But to fix this and to keep the universe static, 80 00:04:02.360 --> 00:04:06.039 which was the philosophical preference of the time, he introduced 81 00:04:06.120 --> 00:04:10.800 a quote unquote cosmological constant into his equations just. 82 00:04:10.759 --> 00:04:13.639 To push back against gravity. Basically, yeah, so he essentially 83 00:04:13.680 --> 00:04:16.959 invented a repulsive force just to balance his mathematical ledger. 84 00:04:17.079 --> 00:04:19.120 He did. He literally just put it in there to 85 00:04:19.160 --> 00:04:22.160 make the math work. And when Edwin Hubble later proved 86 00:04:22.160 --> 00:04:24.759 the universe was actually expanding, it wasn't static at all. 87 00:04:25.000 --> 00:04:29.160 Einstein famously called the cosmological constant his biggest blunder. Yeah, 88 00:04:29.160 --> 00:04:31.759 he completely threw it out. But then in the late 89 00:04:31.839 --> 00:04:36.120 nineteen nineties, a stromer studying distant supernovae discovered that the 90 00:04:36.199 --> 00:04:39.920 universe wasn't just expanding, it was accelerating exactly. The expansion 91 00:04:40.040 --> 00:04:42.800 was accelerating. Something was pushing it apart faster and faster. 92 00:04:43.360 --> 00:04:47.680 So theoretical physicists actually dusted off Einstein's blunder. 93 00:04:48.000 --> 00:04:49.519 They brought the constant back. 94 00:04:49.360 --> 00:04:52.879 They reintroduced lambda to the equations, and they called it 95 00:04:53.120 --> 00:04:57.399 dark energy. And honestly, it worked perfectly to explain the acceleration. 96 00:04:57.639 --> 00:05:01.959 Okay, so that is pillar one and unchanging constant energy 97 00:05:02.040 --> 00:05:05.600 pushing everything apart. Yeah, so what is the second pillar 98 00:05:05.720 --> 00:05:06.399 of this model. 99 00:05:06.680 --> 00:05:10.519 The second pillar is the CDM, part of the acronym cold. 100 00:05:10.480 --> 00:05:13.199 Dark matter, Cold dark matter, right. 101 00:05:13.000 --> 00:05:15.399 And this is the invisible bulk of the cosmos. It 102 00:05:15.439 --> 00:05:18.319 makes up roughly eighty five percent of all the matter 103 00:05:18.360 --> 00:05:19.040 in the universe. 104 00:05:19.120 --> 00:05:21.120 Eighty five percent. That's the invisible house. 105 00:05:21.199 --> 00:05:23.680 That's the invisible house exactly. And we call it cold 106 00:05:23.720 --> 00:05:26.240 because it moves slowly compared to the speed of light. 107 00:05:26.360 --> 00:05:27.600 Why does the speed matter? 108 00:05:28.160 --> 00:05:31.480 That slow movement is crucial because it allows the dark 109 00:05:31.519 --> 00:05:36.160 matter to actually clump together under its own gravity. It 110 00:05:36.240 --> 00:05:40.639 forms this invisible scaffolding, these massive halos that our visible 111 00:05:40.680 --> 00:05:42.279 galaxies are actually built within. 112 00:05:43.000 --> 00:05:45.439 But the catch here, and I mean the thing that 113 00:05:45.480 --> 00:05:48.879 always invites skepticism when you bring this up, is that 114 00:05:50.040 --> 00:05:53.079 despite making up the vast majority of the matter out there, 115 00:05:53.639 --> 00:05:55.240 it has never been directly observed. 116 00:05:55.319 --> 00:05:57.759 We have never caught a particle of dark matter in a. 117 00:05:57.680 --> 00:05:59.360 Detective which is crazy to think about it. 118 00:05:59.480 --> 00:06:01.480 It is does an interact with light at all. It 119 00:06:01.480 --> 00:06:03.879 doesn't absorb it, reflect it, or emit it. 120 00:06:03.879 --> 00:06:06.920 Which brings up a very natural question, Like, if you're 121 00:06:07.000 --> 00:06:09.680 listening to this, you might be thinking, if we have 122 00:06:09.800 --> 00:06:13.000 never directly observed eighty five percent of the matter in 123 00:06:13.000 --> 00:06:16.560 the universe, how can we be so confident it actually exists? 124 00:06:16.680 --> 00:06:16.879 Right? 125 00:06:17.319 --> 00:06:20.800 Like? Are astrophysicists just making up invisible stuff to make 126 00:06:20.839 --> 00:06:24.240 their broken math work? Again? Isn't just a mathematical house 127 00:06:24.279 --> 00:06:24.759 of cards? 128 00:06:24.959 --> 00:06:28.800 I completely understand that skepticism. It's a totally necessary part 129 00:06:28.800 --> 00:06:31.279 of the scientific process to ask those exact questions. But 130 00:06:31.439 --> 00:06:34.800 in astrophysics we often have to measure the invisible by 131 00:06:34.800 --> 00:06:37.759 the shadows it casts. We may not be able to 132 00:06:37.759 --> 00:06:40.040 put dark matter in a jar in a laboratory desk, 133 00:06:40.439 --> 00:06:43.720 but we can measure its gravitational pull with extreme precision. 134 00:06:43.959 --> 00:06:45.120 Okay, so how do we do that? 135 00:06:45.439 --> 00:06:48.439 Well? The history of this goes back to the astronomer VERA. 136 00:06:48.519 --> 00:06:51.839 Rubin in the nineteen seventies. She was studying the rotation 137 00:06:52.040 --> 00:06:55.800 curves of galaxies, specifically the Andromeda galaxy. 138 00:06:55.959 --> 00:06:57.800 Right, So she was looking at how fast the stars 139 00:06:57.800 --> 00:06:59.560 were spinning around the galactic center. 140 00:06:59.720 --> 00:07:04.560 Yes, and based on standard Newtonian physics and the visible 141 00:07:04.600 --> 00:07:07.199 mass of the galaxy, the stuff we can actually see, 142 00:07:07.680 --> 00:07:10.439 the stars on the outer edges should have been moving 143 00:07:10.560 --> 00:07:13.560 much slower than the stars near the dense heavy. 144 00:07:13.279 --> 00:07:15.759 Core, like how our solar system works exactly. 145 00:07:15.839 --> 00:07:18.480 Think of our solar system. Mercury zips around the Sun 146 00:07:18.680 --> 00:07:22.600 very quickly while Neptune plods along very very slowly on 147 00:07:22.680 --> 00:07:25.639 the outer edge. Makes sense, But Reuben found that the 148 00:07:25.680 --> 00:07:29.160 stars on the outer edges of Andromeda were moving incredibly fast, 149 00:07:29.759 --> 00:07:32.439 so fast in fact, that the visible mass of the 150 00:07:32.480 --> 00:07:35.800 galaxy didn't have anywhere near enough gravitational pull to hold 151 00:07:35.800 --> 00:07:36.079 them in. 152 00:07:36.199 --> 00:07:37.439 They should have just flown off. 153 00:07:37.839 --> 00:07:40.399 They should have been flung out into deep space entirely. 154 00:07:41.000 --> 00:07:43.240 The only way to explain the physics of what we 155 00:07:43.240 --> 00:07:47.439 were seeing was the presence of a massive, invisible halo of. 156 00:07:47.519 --> 00:07:50.519 Matter providing the necessary gravitational glue. 157 00:07:50.639 --> 00:07:53.680 Exactly, providing the glue. We know the dark matter is 158 00:07:53.720 --> 00:07:55.639 there because of what it does to the things we 159 00:07:55.680 --> 00:07:56.120 can see. 160 00:07:56.279 --> 00:07:59.600 Okay, so it's the mathematical necessity of dark matter to 161 00:07:59.639 --> 00:08:02.839 exp plain gravity's behavior on a galactic scale. 162 00:08:03.160 --> 00:08:06.720 That and how light bends around massive objects, a phenomenon 163 00:08:06.759 --> 00:08:10.759 known as gravitational lensing. The framework is held together by 164 00:08:10.759 --> 00:08:13.519 the very real, observable effects of gravity. 165 00:08:13.680 --> 00:08:16.360 Got it. So that leaves the third pillar of the 166 00:08:16.439 --> 00:08:20.079 LAMB to CDM model. We have dark energy, dark. 167 00:08:19.839 --> 00:08:23.160 Matter, and the third pillar is ordinary matter. This is 168 00:08:23.199 --> 00:08:26.360 the baryonic matter, the stuff we know, the stars, the planets, 169 00:08:26.399 --> 00:08:28.600 the dust, the microphone you are speaking into right now, 170 00:08:28.639 --> 00:08:33.000 everything we can actually see, touch, and detect through the electromagnetic. 171 00:08:32.159 --> 00:08:33.960 Spectrum, which is how much of the universe. 172 00:08:34.159 --> 00:08:37.240 It accounts for a tiny, almost negligible fraction of the 173 00:08:37.360 --> 00:08:40.759 universe's total composition, roughly five percent five percent. 174 00:08:41.360 --> 00:08:45.720 So those three pillars a constant dark energy pushing outward, 175 00:08:45.919 --> 00:08:49.679 invisible dark matter pulling inward, and a tiny sprinkle of 176 00:08:49.799 --> 00:08:53.360 ordinary matter make up the standard model. Yes, and this 177 00:08:53.399 --> 00:08:56.919 has been the gold standard because mathematically it predicts the 178 00:08:57.000 --> 00:09:00.000 observable universe with astonishing accuracy. 179 00:09:00.120 --> 00:09:02.799 It is incredibly robust. When we look at the distribution 180 00:09:02.840 --> 00:09:06.240 of galaxies across billions of late years, the model predicts 181 00:09:06.240 --> 00:09:12.000 that clustering perfectly. It is withstood intense scientific scrutiny for decades. 182 00:09:12.559 --> 00:09:16.639 It's elegant, it is relatively simple, and it has successfully 183 00:09:16.720 --> 00:09:20.679 explained almost every major astronomical observation we have thrown at. 184 00:09:20.600 --> 00:09:22.919 It until right now. Until right now, because we are 185 00:09:22.960 --> 00:09:25.799 looking at this new analysis of observations from the Dark 186 00:09:25.879 --> 00:09:30.399 Energy Spectroscopic Instrument or DAAI, and this data is fundamentally 187 00:09:30.480 --> 00:09:33.879 undermining that first pillar, the cosmological constant. Yes, it is. 188 00:09:33.960 --> 00:09:36.840 It's suggesting that dark energy might not be a fixed, 189 00:09:37.000 --> 00:09:38.639 unchanging value at all. 190 00:09:38.679 --> 00:09:42.799 Right. So DSi is this incredibly powerful instrument mounted on 191 00:09:42.840 --> 00:09:46.600 a telescope in Arizona. It is designed to map millions 192 00:09:46.600 --> 00:09:49.720 of galaxies and quasars to trace the expansion history of 193 00:09:49.759 --> 00:09:54.879 the universe with unprecedented three dimensional precision, like the highest 194 00:09:54.919 --> 00:09:59.080 resolution map we've got exactly, and the data coming back 195 00:09:59.120 --> 00:10:03.440 is whispering something revolutionary. It is hinting that the density 196 00:10:03.480 --> 00:10:06.080 of dark energy might be changing over time. It might 197 00:10:06.120 --> 00:10:06.840 be evolving. 198 00:10:07.200 --> 00:10:10.440 Okay, to put this in perspective, this sounds like relying 199 00:10:10.480 --> 00:10:14.360 on a trusted generation's old family recipe, but suddenly the 200 00:10:14.399 --> 00:10:15.759 cake keeps exploding in the oven. 201 00:10:15.840 --> 00:10:16.799 That's a great way to put it. 202 00:10:16.960 --> 00:10:19.200 Or to use a driving analogy, we thought we're driving 203 00:10:19.240 --> 00:10:21.559 a car on an endless, perfectly flat highway with the 204 00:10:21.559 --> 00:10:25.440 cruise control set. The cruise control represents the cosmological constant, 205 00:10:26.080 --> 00:10:29.960 a steady, unchanging acceleration, but the DSi data is showing 206 00:10:30.039 --> 00:10:32.320 us that maybe a ghost is actually in the passenger seat, 207 00:10:32.480 --> 00:10:34.840 pressing its foot down harder and harder on the gas pedal, 208 00:10:35.000 --> 00:10:38.120 and then maybe letting off slightly. The acceleration is dynamic, 209 00:10:38.440 --> 00:10:39.240 it is changing. 210 00:10:39.519 --> 00:10:43.840 That captures the mechanical implication perfectly. If dark energy is 211 00:10:43.879 --> 00:10:47.440 not a constant, it is a genuine structural tremor. In 212 00:10:47.519 --> 00:10:48.919 this foundational. 213 00:10:48.320 --> 00:10:50.000 Framework, the house is shaking. 214 00:10:50.039 --> 00:10:54.360 The house is shaking violently. It means a core assumption 215 00:10:54.399 --> 00:10:57.480 we've held since the late nineties and essentially since Einstein 216 00:10:57.840 --> 00:11:01.879 might be fundamentally flawed. I'm not just tweaking the margins 217 00:11:01.919 --> 00:11:02.960 of the model here. 218 00:11:02.759 --> 00:11:06.879 We are questioning the core engine of cosmic expansion itself exactly. 219 00:11:07.399 --> 00:11:10.639 But the thing is this d side data challenging dark 220 00:11:10.799 --> 00:11:14.480 energy isn't an isolated problem, is it. It connects directly 221 00:11:14.720 --> 00:11:18.240 to an even older, more deeply rooted headache in astrophysics 222 00:11:18.559 --> 00:11:20.960 regarding the speed limit of the universe itself. 223 00:11:21.200 --> 00:11:23.559 Yes, it walks us right into the Hubble tension. 224 00:11:23.639 --> 00:11:25.679 Hubble tension. I love talking about this because it's such 225 00:11:25.679 --> 00:11:28.960 a stubborn mystery. Let's set the stage with Hubble's law. Okay, 226 00:11:29.000 --> 00:11:32.799 back in the nineteen twenties, Edwin Hubble realizes the universe 227 00:11:32.879 --> 00:11:37.679 is expanding, and he establishes this beautifully simple linear relationship. 228 00:11:38.120 --> 00:11:40.559 The farther away a galaxy is from the Milky Way, 229 00:11:40.759 --> 00:11:42.879 the faster it is flying away from us. If you 230 00:11:42.960 --> 00:11:46.360 imagine a balloon covered in dots. As you inflate the balloon, 231 00:11:46.879 --> 00:11:50.360 the rubber stretches. Every dot moves away from every other dot, 232 00:11:50.720 --> 00:11:53.159 and the docks that are farthest apart have more stretching 233 00:11:53.200 --> 00:11:55.600 rubber between them, so they appear to move away from 234 00:11:55.639 --> 00:11:56.600 each other the fastest. 235 00:11:56.960 --> 00:12:00.200 That's the classic analogy, and it works perfectly. There's a 236 00:12:00.279 --> 00:12:03.000 rate of that expansion. The speed at which that balloon 237 00:12:03.080 --> 00:12:06.440 is inflating today is known as the hubble constant. Okay, 238 00:12:06.519 --> 00:12:10.200 But the problem the tension is that we have two 239 00:12:10.240 --> 00:12:15.240 completely different, highly precise ways of measuring that exact present 240 00:12:15.320 --> 00:12:16.639 day expansion rate. 241 00:12:16.639 --> 00:12:19.159 And they give us two conflicting answers may not match. 242 00:12:19.159 --> 00:12:22.240 So we have measurement A and measurement B. Let's break 243 00:12:22.279 --> 00:12:25.039 down the mechanics of measurement A first, which relies on 244 00:12:25.080 --> 00:12:26.759 looking at the very early universe. 245 00:12:27.080 --> 00:12:30.759 Right, So, measurement A utilizes the cosmic microwave background or 246 00:12:30.799 --> 00:12:34.399 the CMB. This is the relic radiation, basically the afterglow 247 00:12:34.639 --> 00:12:36.720 from just three hundred and eighty thousand years after the 248 00:12:36.759 --> 00:12:37.559 Big Bang. 249 00:12:37.320 --> 00:12:39.799 Which in cosmic terms is like right after the universe 250 00:12:39.879 --> 00:12:40.159 was born. 251 00:12:40.200 --> 00:12:44.200 Yeah, it's a baby picture. Before that moment, the universe 252 00:12:44.320 --> 00:12:49.000 was a hot, dense soup of plasma, just protons, electrons, 253 00:12:49.039 --> 00:12:52.240 and photons all smashing into each other constantly, so. 254 00:12:52.240 --> 00:12:53.519 Light couldn't travel freely. 255 00:12:53.759 --> 00:12:57.279 No, it was constantly scattering off the electrons. But as 256 00:12:57.320 --> 00:13:00.919 the universe expanded, it cooled and eventually cooled enough for 257 00:13:00.960 --> 00:13:04.039 the electrons to bind to the protons, forming the very 258 00:13:04.159 --> 00:13:06.200 first neutral hydrogen atoms. 259 00:13:06.279 --> 00:13:07.759 Okay, and this event has a name. 260 00:13:07.679 --> 00:13:11.159 Right, Yes, it's called recombination. And suddenly, once that happened, 261 00:13:11.200 --> 00:13:14.919 the photons were free to travel across the universe completely unimpeded. 262 00:13:15.279 --> 00:13:17.879 And we can actually still see those exact photons. 263 00:13:17.480 --> 00:13:20.919 Today, we can. Over billions of years, the expansion of 264 00:13:20.960 --> 00:13:24.759 the universe has stretched those original high energy photons down 265 00:13:24.799 --> 00:13:26.440 into the microwave spectrum. 266 00:13:26.480 --> 00:13:28.759 So when we map this radiation today. 267 00:13:28.480 --> 00:13:32.919 We see tiny microscopic fluctuations in temperature across the sky. 268 00:13:33.559 --> 00:13:37.080 These temperature differences correspond to regions of slightly higher or 269 00:13:37.080 --> 00:13:40.279 lower density in that original primordial plasma. 270 00:13:40.399 --> 00:13:42.679 Okay, so how does that give us the expansion rate today? 271 00:13:43.120 --> 00:13:46.840 By looking at these fluctuations and running them through the 272 00:13:46.840 --> 00:13:50.320 equations of our standard LAMB to CDM model, we can 273 00:13:50.399 --> 00:13:53.840 predict exactly what the expansion rate of the universe should 274 00:13:53.840 --> 00:13:54.759 be right now. 275 00:13:55.240 --> 00:13:58.559 So measurement A is like looking at the biological markers 276 00:13:58.559 --> 00:14:02.279 in a baby picture f'plying our understanding of human growth 277 00:14:02.639 --> 00:14:06.240 and calculating a prediction of exactly how tall that person 278 00:14:06.279 --> 00:14:08.120 will be when they're thirty years old. 279 00:14:08.200 --> 00:14:11.679 That is precisely the methodology. Now, contrast that with measurement 280 00:14:11.759 --> 00:14:13.519 B which we call the distance. 281 00:14:13.200 --> 00:14:14.960 Ladder measurements a distance ladder. 282 00:14:15.039 --> 00:14:17.559 Instead of looking at the beginning of time and extrapolating 283 00:14:17.600 --> 00:14:20.720 forward like a prediction, this method looks at the local, 284 00:14:20.879 --> 00:14:24.159 relatively recent universe and measures the expansion directly. 285 00:14:24.440 --> 00:14:26.720 But how do we actually do that. You can't just 286 00:14:26.759 --> 00:14:28.600 stretch a tape measure to another galaxy. 287 00:14:28.799 --> 00:14:31.200 No, we use what a ghenre is called standard candles. 288 00:14:31.480 --> 00:14:35.799 A standard candle is an astronomical object whose intrinsic brightness 289 00:14:35.960 --> 00:14:38.080 is a known absolute value. 290 00:14:38.320 --> 00:14:41.480 Okay, so we know exactly how bright it truly is. Yes. 291 00:14:42.200 --> 00:14:45.000 The foundational work for this was actually done by Henrietta 292 00:14:45.039 --> 00:14:48.320 swan Ligott in the early twentieth century. She was studying 293 00:14:48.360 --> 00:14:51.559 a specific type of star called a cephed variable. A 294 00:14:51.600 --> 00:14:56.159 cephed variable, right, These stars physically pulse. They grow brighter 295 00:14:56.200 --> 00:14:58.919 and dimmer over a regular period of days or weeks, 296 00:14:59.360 --> 00:15:02.840 and leave it to discovered this direct mathematical relationship between 297 00:15:02.840 --> 00:15:07.159 the length of a cephade's pulse and its true intrinsic luminosity. 298 00:15:07.559 --> 00:15:10.559 So if you measure the pulse, you know exactly how 299 00:15:10.600 --> 00:15:13.720 bright the star actually is at its source exactly. And 300 00:15:13.759 --> 00:15:16.039 if you know exactly how bright a star actually is, 301 00:15:16.279 --> 00:15:18.559 and you measure how dim it appears to be from Earth, 302 00:15:19.159 --> 00:15:21.720 you can calculate precisely how far away it is. 303 00:15:21.919 --> 00:15:25.960 Because light phage at a perfectly predictable mathematical rate over distance, 304 00:15:26.159 --> 00:15:27.720 the inverse square law of light. 305 00:15:27.840 --> 00:15:29.799 Okay, so that works for stars today. 306 00:15:29.879 --> 00:15:34.039 We use Sepheid variables for nearby galaxies, yes, But for 307 00:15:34.159 --> 00:15:38.440 much more distant galaxies we use type IA supernovae, exploding stars, 308 00:15:38.519 --> 00:15:42.159 exploding white dwarf stars. Specifically, they detonate with a very 309 00:15:42.200 --> 00:15:46.799 consistent known luminosity. They are the ultimate standard candles. So 310 00:15:46.960 --> 00:15:50.879 by measuring the distance to these objects and simultaneously measuring 311 00:15:50.919 --> 00:15:53.159 how much their light has been stretched into the red 312 00:15:53.279 --> 00:15:55.759 end of the spectrum by the expansion of space, which 313 00:15:55.799 --> 00:15:59.240 we call their red shift, we directly calculate how fast 314 00:15:59.240 --> 00:16:01.200 the local universe versus expanding right now. 315 00:16:01.240 --> 00:16:03.399 The measurement B is basically just taking out a tape 316 00:16:03.399 --> 00:16:06.519 measure and physically measuring the thirty year old adult. 317 00:16:06.159 --> 00:16:11.320 Today exactly and the tension is this the prediction from 318 00:16:11.399 --> 00:16:15.600 the early universe. The baby picture gives us a significantly 319 00:16:15.759 --> 00:16:19.919 slower expansion rate than the direct measurements of the local universe. 320 00:16:19.960 --> 00:16:20.639 The tape measure. 321 00:16:20.759 --> 00:16:21.759 How big is the difference. 322 00:16:21.879 --> 00:16:26.120 We are talking about roughly sixty seven kilometers per second 323 00:16:26.159 --> 00:16:29.799 per megaparsec from the early universe versus about seventy three 324 00:16:30.000 --> 00:16:30.960 from the local universe. 325 00:16:31.000 --> 00:16:34.399 That's a massive gap. It's like having two incredibly expensive, 326 00:16:34.519 --> 00:16:36.639 hyper accurate spedometers in your car. 327 00:16:36.559 --> 00:16:36.679 Right. 328 00:16:37.039 --> 00:16:39.360 One is hooked up to the engine analyzing the fuel 329 00:16:39.360 --> 00:16:41.799 injection at the start of your road trip to calculate 330 00:16:41.840 --> 00:16:44.279 your average speed. The other is hooked up to the tires, 331 00:16:44.559 --> 00:16:46.919 physically measuring the rotation at the end of the trip. 332 00:16:47.600 --> 00:16:50.080 But they are giving you entirely different average speeds for 333 00:16:50.120 --> 00:16:51.240 the exact same journey. 334 00:16:51.399 --> 00:16:53.799 This raises an important question, right yeah, I mean. 335 00:16:53.759 --> 00:16:57.200 Is it possible one of these spedometers is just fundamentally broken, 336 00:16:58.120 --> 00:17:01.759 or is the road itself stretching while we drive? Could 337 00:17:01.799 --> 00:17:04.000 we just be misinterpreting the data. 338 00:17:04.039 --> 00:17:08.440 Cosmologists have absolutely agonized over that possibility for years. The 339 00:17:08.480 --> 00:17:11.759 assumption was that there had to be some hidden systematic. 340 00:17:11.319 --> 00:17:14.799 Error, like someone carried a one in the math, or perhaps. 341 00:17:14.559 --> 00:17:19.039 We were miscalibrating our standard candles somehow, or our instruments 342 00:17:19.079 --> 00:17:23.119 reading the CMB had a flaw. But observational technology has 343 00:17:23.160 --> 00:17:28.480 advanced so dramatically. The instruments are incredibly precise. 344 00:17:28.160 --> 00:17:30.720 Now, so it's not a mistake the error. 345 00:17:30.480 --> 00:17:33.359 Bars on both measurements. The margins of error have shrunk 346 00:17:33.440 --> 00:17:36.799 so significantly that they no longer overlap at all. The 347 00:17:36.880 --> 00:17:39.279 numbers are too precise to be a mistake. We simply 348 00:17:39.359 --> 00:17:41.160 can't blame the tools anymore. 349 00:17:40.759 --> 00:17:42.519 The tools working perfectly they. 350 00:17:42.319 --> 00:17:45.559 Are, which leaves us with a much more profound alternative. 351 00:17:46.640 --> 00:17:49.680 The universe itself is behaving in a way our standard 352 00:17:49.680 --> 00:17:51.160 model simply does not account for. 353 00:17:51.279 --> 00:17:53.599 The road itself is stretching while we drive, and the 354 00:17:53.680 --> 00:17:56.160 rules of that stretching are changing exactly. 355 00:17:56.200 --> 00:17:59.240 The hubble tension is a screaming alarm bell that our 356 00:17:59.319 --> 00:18:04.519 fundamental understanding of physics, specifically regarding dark energy and cosmic expansion, is. 357 00:18:04.559 --> 00:18:07.279 Flawed, which brings us back to the core of this 358 00:18:07.359 --> 00:18:10.480 new research from Young Chen and his team. With a 359 00:18:10.519 --> 00:18:14.319 standard model shaking and this hubble tension refusing to budge, 360 00:18:14.759 --> 00:18:17.720 they realized that looking at all the data at once 361 00:18:18.240 --> 00:18:20.480 was actually creating a tangled mess. 362 00:18:20.559 --> 00:18:22.599 It was creating a mathematical traffic jam. 363 00:18:22.799 --> 00:18:25.720 Right. They needed a new way to untangle the history 364 00:18:25.720 --> 00:18:26.480 of the cosmos. 365 00:18:26.960 --> 00:18:30.359 So When researchers are confronted with conflicting data sets, the 366 00:18:30.440 --> 00:18:33.599 instinct is often to just combine everything, hoping the sheer 367 00:18:33.680 --> 00:18:36.680 volume of data will smooth out the anomalies and reveal 368 00:18:36.759 --> 00:18:37.839 some average truth. 369 00:18:38.000 --> 00:18:39.000 Just throw it all on a blunder. 370 00:18:39.400 --> 00:18:43.279 But Chen, along with Teng Peng Shoe and Swumingzeng, built 371 00:18:43.279 --> 00:18:47.039 a unified mathematical framework to investigate both the dark energy 372 00:18:47.079 --> 00:18:51.359 mystery and the Hubble tension simultaneously, and their key innovation 373 00:18:51.599 --> 00:18:52.680 was methodological. 374 00:18:52.720 --> 00:18:53.599 They didn't use the blender. 375 00:18:53.720 --> 00:18:57.920 They decided to stop mashing all the observational data together. Instead, 376 00:18:58.039 --> 00:19:02.279 they separated out different probes of the universe's expansion based 377 00:19:02.480 --> 00:19:05.599 entirely on the specific periods of cosmic history they are 378 00:19:05.680 --> 00:19:06.519 most sensitive to. 379 00:19:06.839 --> 00:19:10.680 Okay, let's define probes in this context. We're talking about 380 00:19:10.720 --> 00:19:15.000 the different astronomical phenomena we use to measure distance in time. 381 00:19:15.559 --> 00:19:20.640 Yes, different probes act as highly specialized windows into distinct eras. 382 00:19:20.960 --> 00:19:25.119 So in their framework, they strictly isolated the cosmic microwave background. 383 00:19:25.359 --> 00:19:28.200 They use the CMB solely to probe the high redshift 384 00:19:28.519 --> 00:19:29.359 early universe. 385 00:19:29.480 --> 00:19:32.160 They kept the baby picture strictly as a baby picture. 386 00:19:32.200 --> 00:19:34.759 They did not allow the early universe math to bleed 387 00:19:34.799 --> 00:19:36.880 into the late universe measurements. 388 00:19:36.440 --> 00:19:38.519 And for the late universe they use different tools. 389 00:19:38.559 --> 00:19:41.599 They relied on type Ia supernovae, which we discuss as 390 00:19:41.599 --> 00:19:46.240 our standard candles, and another incredibly fascinating phenomenon called baryon 391 00:19:46.319 --> 00:19:48.200 acoustic oscillations or. 392 00:19:48.279 --> 00:19:52.240 Bao okay, baryon acoustic oscillations. That sounds a concept pulled 393 00:19:52.240 --> 00:19:55.319 straight from science fiction. What physically is an acoustic ostellation 394 00:19:55.440 --> 00:19:55.880 in space? 395 00:19:56.319 --> 00:19:58.960 It goes back to that hot, dense plasma of the 396 00:19:59.079 --> 00:19:59.960 early universe. 397 00:20:00.079 --> 00:20:01.839 Talking about before recombination. 398 00:20:02.079 --> 00:20:05.559 Yes, before recombination, gravity was trying to pull the dark 399 00:20:05.640 --> 00:20:09.599 matter and the ordinary baryonic matter together into clumps. But 400 00:20:09.839 --> 00:20:14.480 the intense radiation the photons were exerting this immense. 401 00:20:14.039 --> 00:20:15.960