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 --> 00:00:26.879 slumber under the night sky. 7 00:00:26.960 --> 00:00:29.640 If you look up at the Little Dipper tonight, you 8 00:00:29.679 --> 00:00:32.840 aren't just seeing a familiar pattern of stars, right. 9 00:00:32.840 --> 00:00:35.640 It's so easy to just see it as this static, 10 00:00:36.520 --> 00:00:37.600 you know, beautiful canopy. 11 00:00:37.759 --> 00:00:41.000 Yeah exactly, But you are actually looking at the very 12 00:00:41.159 --> 00:00:44.359 edge of the largest and honestly the most impossible map 13 00:00:44.479 --> 00:00:46.320 ever constructed by human beings. 14 00:00:46.399 --> 00:00:48.799 It really does shatter your entire sense of scale. 15 00:00:48.880 --> 00:00:51.960 It does, because we're talking about a three dimensional model 16 00:00:52.000 --> 00:00:55.799 of the universe that is so vast and like so 17 00:00:56.079 --> 00:00:59.000 detailed that the data pouring out of it right now 18 00:00:59.079 --> 00:01:01.520 might actually prove that the fundamental laws of physics are 19 00:01:01.600 --> 00:01:03.560 actively changing right over our heads. 20 00:01:03.679 --> 00:01:07.159 And that specific patch of the cosmos near the Little 21 00:01:07.159 --> 00:01:11.439 Dipper that actually served as the final observation target for 22 00:01:11.560 --> 00:01:13.040 this monumental. 23 00:01:12.480 --> 00:01:15.359 Project, which is just wild. We are talking about mapping 24 00:01:15.400 --> 00:01:19.159 structures that stretch across eleven billion years of history. 25 00:01:19.239 --> 00:01:22.480 Eleven billion. Yes, it's a number that is almost impossible 26 00:01:22.959 --> 00:01:25.920 for the human brain to truly internalize. 27 00:01:25.280 --> 00:01:27.079 And to put that into context for you listening. We 28 00:01:27.120 --> 00:01:29.319 aren't talking about a map that helps us, you know, 29 00:01:29.439 --> 00:01:32.040 find nearby planets or plot a Corset alfasentory. 30 00:01:32.560 --> 00:01:34.439 No, the scale is entirely different, right. 31 00:01:34.920 --> 00:01:39.480 The Dark Energy Spectroscopic Instrument, or DAI as it's called, 32 00:01:40.000 --> 00:01:43.480 has just wrapped up its primary run and it delivered 33 00:01:43.480 --> 00:01:46.760 the highest resolution, most comprehensive three D map of the 34 00:01:46.840 --> 00:01:47.920 universe in existence. 35 00:01:48.000 --> 00:01:51.439 So the map itself, interestingly enough, is almost a byproduct. 36 00:01:51.959 --> 00:01:54.359 Yeah, the map wasn't the actual goal. 37 00:01:54.280 --> 00:01:56.920 Was it not at all. It's a tool built for 38 00:01:56.959 --> 00:02:02.159 a very specific, incredibly high stakes. The goal was never 39 00:02:02.359 --> 00:02:05.159 just cartography for the sake of having a nice atlas 40 00:02:05.159 --> 00:02:06.040 of the cosmos. 41 00:02:06.200 --> 00:02:08.400 So they didn't just want to hang a shiny map. 42 00:02:08.159 --> 00:02:11.960 On the wall exactly. The purpose of mapping millions upon 43 00:02:12.080 --> 00:02:15.840 millions of distant galaxies is to track down and understand 44 00:02:15.879 --> 00:02:16.439 a phantom. 45 00:02:16.599 --> 00:02:18.159 A phantom I love that description. 46 00:02:18.479 --> 00:02:22.199 Well, we're dealing with dark energy, the invisible repulsive force 47 00:02:22.240 --> 00:02:24.599 that currently makes up roughly seventy percent of everything in 48 00:02:24.639 --> 00:02:25.120 the universe. 49 00:02:25.199 --> 00:02:28.599 Seventy percent that is, I mean everything we can see, touch, 50 00:02:28.719 --> 00:02:31.439 or interact with is basically a rounding error compared to 51 00:02:31.479 --> 00:02:31.960 this force. 52 00:02:32.080 --> 00:02:33.439 It's all just a tiny fraction of. 53 00:02:33.400 --> 00:02:37.280 Reality, which sets the stakes at an existential level. If 54 00:02:37.400 --> 00:02:40.680 seventy percent of reality is driven by something we can't see, 55 00:02:40.840 --> 00:02:43.719 and this new map is suddenly suggesting that our basic 56 00:02:43.719 --> 00:02:46.800 assumptions about how that force operates are wrong. 57 00:02:46.919 --> 00:02:48.800 Then we're looking at a paradigm. 58 00:02:48.439 --> 00:02:51.800 Shift, a total paradigm shift that rewrites the fate of 59 00:02:51.840 --> 00:02:55.479 the universe. Okay, let's unpack this because before we get 60 00:02:55.520 --> 00:02:58.680 to the physics breaking anomaly they found, I want to 61 00:02:58.719 --> 00:03:01.639 ground this in the far physical reality of how you 62 00:03:01.719 --> 00:03:02.439 even build a. 63 00:03:02.400 --> 00:03:06.039 Map like this. The sheer engineering is staggering, it really is. 64 00:03:06.080 --> 00:03:08.719 This entire operation is based in Arizona, right, Yeah. 65 00:03:08.520 --> 00:03:11.479 At the kit Peak National Observatory, which is managed by 66 00:03:11.479 --> 00:03:14.759 the US Department of Energies Lawrence Berkeley National Laboratory. Okay, 67 00:03:15.159 --> 00:03:17.919 And it is vital to understand that DSi is not 68 00:03:18.120 --> 00:03:19.560 a space telescope. 69 00:03:19.159 --> 00:03:22.400 Oh right, because we always hear about James Web or 70 00:03:22.479 --> 00:03:23.479 Hubble exactly. 71 00:03:23.639 --> 00:03:26.560 It is not floating out in the vacuum, free from interference. 72 00:03:26.960 --> 00:03:30.639 It is a ground based instrument retrofitted onto an existing 73 00:03:30.680 --> 00:03:32.479 telescope structure on a mountain. 74 00:03:32.240 --> 00:03:35.919 Peak, which makes it sound almost I don't know, quoint, 75 00:03:36.360 --> 00:03:38.159 but the instrumentation is anything but quaint. 76 00:03:38.280 --> 00:03:40.000 It's a marvel of modern engineering. 77 00:03:40.319 --> 00:03:42.400 Because when I think of a telescope, I think of 78 00:03:43.120 --> 00:03:46.520 like a giant mirror or a massive glass lens pointed 79 00:03:46.560 --> 00:03:47.639 at a patch of sky. 80 00:03:47.879 --> 00:03:49.879 Right, the traditional galileo setup. 81 00:03:50.000 --> 00:03:53.840 Yeah, but the DSi instrument operates on a completely different 82 00:03:53.840 --> 00:03:57.960 mechanical level. The focal plane is packed with five thousand 83 00:03:58.039 --> 00:03:59.960 individual fiber optic sensors. 84 00:04:00.199 --> 00:04:02.319 Let's examine the mechanics of that, because it is an 85 00:04:02.360 --> 00:04:05.360 astonishing feat of miniaturization and robotics. 86 00:04:05.400 --> 00:04:07.199 Please, because I can barely visualize it. 87 00:04:07.319 --> 00:04:10.680 So you have a circular plane, and embedded into it 88 00:04:10.759 --> 00:04:14.599 are these five thousand robotic positioners, Okay, and each one 89 00:04:14.639 --> 00:04:17.839 holds a tiny fiber optic cable. In the space of 90 00:04:17.920 --> 00:04:21.680 just a few seconds, all five thousand robots can simultaneously 91 00:04:21.720 --> 00:04:23.680 pivot and adjust their positions. 92 00:04:23.319 --> 00:04:24.519 Wait all at the same time. 93 00:04:24.600 --> 00:04:27.240 All at the same time, they align perfectly with the 94 00:04:27.279 --> 00:04:32.160 incoming light from five thousand completely different, highly specific distant galaxies. 95 00:04:32.199 --> 00:04:35.120 That's insant. Wait, how do they move that fast without colliding? 96 00:04:35.279 --> 00:04:37.399 That is a big question, because if you have five 97 00:04:37.399 --> 00:04:40.920 thousand robotic arms packed onto a single plate, all swarming 98 00:04:41.000 --> 00:04:43.560 to find new targets for the next exposure, I mean 99 00:04:43.560 --> 00:04:45.600 the collision algorithms alone must be a nightmare. 100 00:04:45.720 --> 00:04:50.040 The choreography is entirely automated and highly highly complex. They 101 00:04:50.079 --> 00:04:52.560 operate in this tightly packed honeycomb structure. 102 00:04:52.680 --> 00:04:54.240 Oh, a honeycomb, that makes sense. 103 00:04:54.360 --> 00:04:58.279 Yeah, And the targeting software calculates the optimal orientation for 104 00:04:58.439 --> 00:05:02.240 every single positioner. It maximizes the number of galaxies captured 105 00:05:02.279 --> 00:05:06.319 in a single exposure without any fibers, crossing paths or jamming. 106 00:05:06.319 --> 00:05:06.480 Oh. 107 00:05:07.079 --> 00:05:09.560 Once they lock into place, they captured the light, feed 108 00:05:09.600 --> 00:05:12.920 it down into the spectrographs, and then instantly realign for 109 00:05:12.959 --> 00:05:13.920 the next patch of sky. 110 00:05:14.120 --> 00:05:17.399 So it is just an absolute observing machine, completely relentless, 111 00:05:17.480 --> 00:05:20.160 and the numbers back that up. When the projects spun 112 00:05:20.279 --> 00:05:22.959 up in May of twenty twenty one, I read that 113 00:05:23.000 --> 00:05:25.920 the stated goal was to capture light from about thirty 114 00:05:25.920 --> 00:05:29.120 four million galaxies and quasars. 115 00:05:28.680 --> 00:05:30.160 Which alone would have been historic. 116 00:05:30.360 --> 00:05:32.639 Right, thirty four million is a massive number. 117 00:05:32.720 --> 00:05:35.800 It would have completely redefined the field of cosmology, but. 118 00:05:35.759 --> 00:05:38.759 The efficiency of the instrument and the clarity of those 119 00:05:38.800 --> 00:05:42.720 targeting protocols allowed them to vastly outpace their own projection 120 00:05:42.879 --> 00:05:44.920 by a huge market. Yeah, by the time they took 121 00:05:45.000 --> 00:05:48.120 that final scheduled shot near the Little Dipper, they hadn't 122 00:05:48.160 --> 00:05:49.839 just hit thirty four million. 123 00:05:49.800 --> 00:05:50.480 Not even close. 124 00:05:50.600 --> 00:05:55.279 They captured over forty seven million galaxies and quasars. 125 00:05:54.879 --> 00:05:58.800 Plus another twenty million stars just for the sake of completeness, just. 126 00:05:58.800 --> 00:06:01.560 Threw them in there. That is data set containing information 127 00:06:01.680 --> 00:06:05.120 from six times as many galaxies and quasars as every 128 00:06:05.240 --> 00:06:08.759 single previous cosmic survey ever conducted combined. 129 00:06:09.000 --> 00:06:12.600 The jumpin scale is it's honestly difficult to process. 130 00:06:12.759 --> 00:06:15.279 It's like we spent decades trying to map a continent 131 00:06:15.360 --> 00:06:18.879 by looking through a foggy keyhole, and suddenly someone handed 132 00:06:18.959 --> 00:06:21.160 us a four k drone flying overhead. 133 00:06:21.519 --> 00:06:23.759 That's a great way to put it. It's the difference 134 00:06:23.800 --> 00:06:27.079 between mapping a coastline by walking along it with a 135 00:06:27.160 --> 00:06:30.720 yardstick versus deploying a fleet of light our equipped satellites. 136 00:06:30.839 --> 00:06:33.079 Yeah, the density of the data is just unprecedented. 137 00:06:33.199 --> 00:06:36.399 Exactly we are no longer looking at broad, blurry estimates 138 00:06:36.399 --> 00:06:39.480 of where galaxies tend to gather. We're seeing the intricate, 139 00:06:39.839 --> 00:06:42.759 thread like structures of the costic web in high definition. 140 00:06:42.959 --> 00:06:45.319 So let's talk about the visual reality of that three 141 00:06:45.399 --> 00:06:47.399 D map, because if you sit down and look at 142 00:06:47.439 --> 00:06:49.600 the rendering of this data, it doesn't look like a 143 00:06:49.639 --> 00:06:50.879 solid sphere of stars. 144 00:06:50.959 --> 00:06:52.920 No, it has a very specific geometry. 145 00:06:53.040 --> 00:06:55.680 Right. It looks like a massive series of wedges, or 146 00:06:56.000 --> 00:06:59.720 like slices of a pie, radiating out from a central point, 147 00:07:00.240 --> 00:07:02.839 and Earth is sitting right at the very tip of 148 00:07:02.879 --> 00:07:03.519 those wedges. 149 00:07:03.839 --> 00:07:07.399 The wedge shape is an artifact of our vantage point. 150 00:07:07.639 --> 00:07:11.560 We are observing from a fixed location inside a spiral galaxy, 151 00:07:11.800 --> 00:07:15.399 the Milky Way. Exactly. We cannot just peel away our 152 00:07:15.439 --> 00:07:19.160 own galactic environment to get a perfect, unobstructed three hundred 153 00:07:19.160 --> 00:07:21.879 and sixty degree view of the deeper universe. 154 00:07:21.639 --> 00:07:24.639 Which explains the most glaring feature of the visual map. 155 00:07:24.639 --> 00:07:27.560 When you look at it, there is this massive, empty 156 00:07:27.639 --> 00:07:30.759 black gap cutting right through the middle of the wedges. 157 00:07:30.879 --> 00:07:31.920 It looks like a blind spot. 158 00:07:32.000 --> 00:07:34.240 Yeah, it is exactly a blind spot. Why is that there? 159 00:07:34.360 --> 00:07:37.199 We refer to it as the zone of avoidance because 160 00:07:37.199 --> 00:07:39.399 our solar system is embedded within the disc of the 161 00:07:39.399 --> 00:07:42.319 Milky Way. When we aim our telescopes along the plane 162 00:07:42.360 --> 00:07:44.800 of that disk, we are attempting to look through tens 163 00:07:44.839 --> 00:07:47.600 of thousands of light years of our own galactic material. 164 00:07:47.879 --> 00:07:52.240 Oh so it's just blocked gas dust nearby stars. All 165 00:07:52.279 --> 00:07:54.279 of it is in the way. It's like trying to 166 00:07:54.319 --> 00:07:56.879 spot a firefly a mile away while someone is shining 167 00:07:56.879 --> 00:07:59.839 a high beam flashlight directly into your eyes through a 168 00:07:59.839 --> 00:08:00.680 cloud of smoke. 169 00:08:00.879 --> 00:08:04.040 That's exactly it. The extinction of light is severe in 170 00:08:04.040 --> 00:08:08.360 that direction. The interstellar dust absorbs and scatters the faint 171 00:08:08.399 --> 00:08:12.319 optical light from ancient galaxies, rendering them virtually invisible to 172 00:08:12.399 --> 00:08:13.480 dii's sensors. 173 00:08:13.639 --> 00:08:14.240 Wow. 174 00:08:14.279 --> 00:08:18.079 So the mapping naturally carves out these sweeping wedges above 175 00:08:18.120 --> 00:08:21.079 and below the galactic plane, where the view out into 176 00:08:21.120 --> 00:08:23.079 the deep cosmos is relatively clear. 177 00:08:23.199 --> 00:08:26.480 Okay, so that covers horizontal and vertical spread of the map. 178 00:08:26.519 --> 00:08:29.959 But a map of the universe is useless if it's flat. True, 179 00:08:30.040 --> 00:08:33.320 The true triumph here is the third dimension depth. How 180 00:08:33.360 --> 00:08:36.720 do five thousand robotic fibers in Arizona actually plot the 181 00:08:36.759 --> 00:08:39.600 depth of a galaxy that is billions of light years away. 182 00:08:39.639 --> 00:08:41.840 I mean they aren't bouncing radar off these things. 183 00:08:41.879 --> 00:08:45.639 No, no radar. The third dimension is derived through spectroscopy, 184 00:08:45.960 --> 00:08:48.639 which is where the true power of the instrument lies. 185 00:08:48.720 --> 00:08:49.879 Okay, break that down for me. 186 00:08:50.120 --> 00:08:52.879 So the instrument isn't just taking a picture of a galaxy. 187 00:08:53.399 --> 00:08:56.600 It is taking the light from that galaxy and breaking 188 00:08:56.639 --> 00:09:01.200 it apart into its constituent colors, its spectrums, exactly like 189 00:09:01.200 --> 00:09:02.559 a prism. And this is where we have to talk 190 00:09:02.600 --> 00:09:06.639 about redshift. Because the universe is expanding, everything is moving 191 00:09:06.639 --> 00:09:07.759 away from us, right. 192 00:09:08.120 --> 00:09:10.360 I always hear this compared to the Doppler effect with 193 00:09:10.840 --> 00:09:13.600 sound like a police siren dropping in pitch as its 194 00:09:13.639 --> 00:09:14.600 speeds past you. 195 00:09:15.039 --> 00:09:17.679 It is the optical equivalent of that exact effect. As 196 00:09:17.720 --> 00:09:19.879 a distant galaxy is carried away from us by the 197 00:09:19.879 --> 00:09:23.600 expansion of space, the light waves it emitted are physically 198 00:09:23.639 --> 00:09:24.399 stretched out. 199 00:09:24.240 --> 00:09:26.559 Over their journey, and longer waves mean red light. 200 00:09:26.960 --> 00:09:29.840 Correct. Longer light waves shift toward the red end of 201 00:09:29.879 --> 00:09:31.320 the electromagnetic spectrum. 202 00:09:31.360 --> 00:09:34.000 So the faster it's moving away from us, the redder 203 00:09:34.039 --> 00:09:36.279 the light appears by the time it hits the sensor at. 204 00:09:36.279 --> 00:09:39.759 Kitpeak precisely mm hm. And because we know the expansion 205 00:09:39.799 --> 00:09:42.919 rate of the universe. That red shift acts as a 206 00:09:43.000 --> 00:09:46.799 direct proxy for distance. The more the light is shifted 207 00:09:46.799 --> 00:09:49.200 to the red, the further way the galaxy is. 208 00:09:49.240 --> 00:09:50.399 That is so elegant. 209 00:09:50.600 --> 00:09:54.559 What's fascinating here is the crucial realization about time. The 210 00:09:54.600 --> 00:09:57.080 thing that elevates this from just a map of space 211 00:09:57.159 --> 00:10:00.000 to a map of time is the finite speed of light. 212 00:10:00.279 --> 00:10:03.080 Right. I want to clarify how this translates to time 213 00:10:03.120 --> 00:10:07.159 travel for our listeners, because if DSi locks onto a 214 00:10:07.200 --> 00:10:10.039 galaxy and measures a red shift that tells us it 215 00:10:10.080 --> 00:10:13.000 is five billion light years away. 216 00:10:12.840 --> 00:10:14.840 We aren't seeing where that galaxy. 217 00:10:14.399 --> 00:10:17.039 Is right now exactly. We are seeing the light that 218 00:10:17.200 --> 00:10:20.000 left that galaxy five billion years ago. 219 00:10:20.320 --> 00:10:24.240 You are observing the universe exactly as it existed at 220 00:10:24.240 --> 00:10:26.399 that precise moment in cosmic history. 221 00:10:26.120 --> 00:10:28.360 Which just blows my mind every time I think about it. 222 00:10:28.360 --> 00:10:31.840 It's incredible. When DISI pushes its sensors to the absolute limit, 223 00:10:32.159 --> 00:10:35.039 capturing the faintest targets, it is looking at light that 224 00:10:35.080 --> 00:10:37.480 has been traveling for eleven billion years. 225 00:10:37.200 --> 00:10:41.000 Which means those wedges radiating out from Earth are literal timelines, 226 00:10:41.039 --> 00:10:43.480 little timelines. Yes, the tip of the wedge is us 227 00:10:43.559 --> 00:10:45.759 right now, and as you travel outward along the wedge, 228 00:10:45.759 --> 00:10:48.240 you are moving backward through the epochs of the universe, 229 00:10:48.279 --> 00:10:52.039 slice by slice, tracing the history of reality back eleven 230 00:10:52.240 --> 00:10:53.440 billion years. 231 00:10:53.480 --> 00:10:56.639 A point underscored by d side director doctor Michael Levi, 232 00:10:57.200 --> 00:11:00.159 who noted how the instrument performed beyond the wildest to 233 00:11:00.200 --> 00:11:02.879 expectations of the team that built it. I can imagine 234 00:11:03.000 --> 00:11:06.960 pushing the boundaries of spectroscopy to capture these incredibly faint 235 00:11:07.080 --> 00:11:11.399 ancient signals requires a level of precision that is honestly 236 00:11:11.440 --> 00:11:12.600 difficult to overstate. 237 00:11:12.799 --> 00:11:16.000 And they needed that precision because, as we established earlier, 238 00:11:16.080 --> 00:11:17.080 they were hunting. 239 00:11:16.840 --> 00:11:18.720 A ghost, the biggest ghost of all. 240 00:11:18.879 --> 00:11:22.240 Yeah. They didn't build a time traveling three D map 241 00:11:22.399 --> 00:11:25.559 just to account galaxies. They built it to watch how seventy 242 00:11:25.600 --> 00:11:28.799 percent of the universe behaves over time. Let's pivot to 243 00:11:28.879 --> 00:11:29.440 dark energy. 244 00:11:29.559 --> 00:11:30.039 Let's do it. 245 00:11:30.240 --> 00:11:33.360 What exactly was the prevailing assumption about this force before 246 00:11:33.639 --> 00:11:35.399 DSi started churning out data. 247 00:11:35.679 --> 00:11:38.080 Well, to frame dark energy correctly, you have to look 248 00:11:38.120 --> 00:11:41.039 at the fundamental conflict governing the universe. It is a 249 00:11:41.159 --> 00:11:44.519 cosmic tug of war. Okay, on one side, you have matter, 250 00:11:44.759 --> 00:11:49.039 This includes stars, planets, gas clouds, and dark matter. All 251 00:11:49.080 --> 00:11:53.279 of this matter possesses mass, and therefore it exerts gravity. 252 00:11:52.919 --> 00:11:54.519 And gravity pulls things together. 253 00:11:54.840 --> 00:11:59.159 Right, Gravity is an attractive force. Its inherent tendency is 254 00:11:59.200 --> 00:12:02.240 to pull things together, to cause the universe to contract 255 00:12:02.320 --> 00:12:02.919 and clump. 256 00:12:03.039 --> 00:12:06.240 So logically, if gravity is the only player on the field, 257 00:12:06.720 --> 00:12:09.639 the universe should be pulling itself back inward after the 258 00:12:09.679 --> 00:12:12.519 initial explosion of the Big Bang, like the expansion should 259 00:12:12.559 --> 00:12:13.360 be slowing down. 260 00:12:13.639 --> 00:12:18.120 That was the widely held cosmological consensus for decades. Really, yes, 261 00:12:18.679 --> 00:12:22.559 everyone assumed the expansion must be decelerating due to the 262 00:12:22.600 --> 00:12:25.799 collective gravitational drag of all the matter in existence. 263 00:12:25.919 --> 00:12:27.200 But then something changed. 264 00:12:27.519 --> 00:12:31.480 Observations in the late nineteen nineties absolutely shattered that model. 265 00:12:31.639 --> 00:12:35.519 Oh wow, instead of slowing down, astronomers realize the expansion 266 00:12:35.559 --> 00:12:39.440 of the universe is accelerating. Distant galaxies are flying apart 267 00:12:39.559 --> 00:12:41.720 at an ever increasing velocity. 268 00:12:41.360 --> 00:12:43.679 Which just defies common sense. I mean, if you throw 269 00:12:43.679 --> 00:12:46.320 a ball straight up into the air, gravity slows it down, 270 00:12:46.360 --> 00:12:49.200 it doesn't suddenly accelerate upward into the stratosphere. 271 00:12:49.240 --> 00:12:52.399 Exactly. For the universe to accelerate its expansion, there must 272 00:12:52.480 --> 00:12:56.000 be a repulsive force overpowering the attractive force of gravity 273 00:12:56.279 --> 00:12:58.039 on a macroscopic. 274 00:12:57.360 --> 00:12:58.600 Scale, and that's the ghost. 275 00:12:58.879 --> 00:13:02.559 That's the ghost. This invisible pressure driving the fabric of 276 00:13:02.600 --> 00:13:05.799 space apart is what we term dark energy. 277 00:13:05.720 --> 00:13:08.919 And because it is responsible for the accelerating expansion of 278 00:13:08.960 --> 00:13:12.759 the entirety of space, mathematical models dictate that it must 279 00:13:12.799 --> 00:13:16.159 account for roughly seventy percent of the total energy density 280 00:13:16.200 --> 00:13:19.480 of the universe. That's right, Okay, so we knew dark 281 00:13:19.559 --> 00:13:22.080 energy existed, or at least we knew something was pushing 282 00:13:22.080 --> 00:13:25.720 the universe apart. But how did physicists define it mathematically? 283 00:13:25.799 --> 00:13:28.000 Because this is where the D sign map throws a 284 00:13:28.120 --> 00:13:29.879 massive wrench into the machine. 285 00:13:30.000 --> 00:13:33.799 Right, So the most elegant and widely accepted mathematical explanation 286 00:13:34.600 --> 00:13:38.279 was to treat dark energy as a cosmological. 287 00:13:37.519 --> 00:13:40.559 Constant, the operative word being constant. 288 00:13:40.080 --> 00:13:43.919 Exactly constant. The assumption was that this repulsive energy is 289 00:13:43.919 --> 00:13:47.080 an intrinsic property of the vacuum of space itself. It's 290 00:13:47.240 --> 00:13:50.919 uniform everywhere, okay, and crucially, its density never changes. 291 00:13:50.639 --> 00:13:52.159 Over time, so it's always the same. 292 00:13:52.320 --> 00:13:55.519 Yes. As the universe expands, it creates more empty space 293 00:13:55.559 --> 00:13:58.840 and therefore more total dark energy. But the inherent strength 294 00:13:58.879 --> 00:14:02.720 of that repulsive push per cubic meter remains absolutely rigid 295 00:14:02.759 --> 00:14:04.879 and unchanging across eternity. 296 00:14:05.159 --> 00:14:07.519 It's a static rule of the game, a fixed value 297 00:14:07.519 --> 00:14:10.320 that you just plug into your equations exactly. But the 298 00:14:10.360 --> 00:14:13.440 bombshell from DSI's early data, and this is just the 299 00:14:13.480 --> 00:14:17.120 initial three year data set, is that this foundational assumption 300 00:14:17.639 --> 00:14:19.000 might be entirely wrong. 301 00:14:19.120 --> 00:14:21.679 It's a massive shock to the community because. 302 00:14:21.360 --> 00:14:24.519 The data is heavily implying that dark energy is not 303 00:14:24.639 --> 00:14:28.600 a constant. It suggests that this repulsive force is actually evolving. 304 00:14:28.759 --> 00:14:32.080 The implications of that word evolving are monumental in the 305 00:14:32.120 --> 00:14:33.200 field of cosmology. 306 00:14:33.240 --> 00:14:34.879 I mean, it sounds like it breaks everything. 307 00:14:35.080 --> 00:14:38.519 It really does. If dark energy is dynamic, if its 308 00:14:38.559 --> 00:14:42.240 strength fluctuates or changes character as the universe ages, then 309 00:14:42.240 --> 00:14:44.960 the cosmological constant is a flawed model. 310 00:14:45.039 --> 00:14:46.639 So what does that mean? It actually is? 311 00:14:47.080 --> 00:14:49.799 It suggests dark energy might not be a simple property 312 00:14:49.840 --> 00:14:53.720 of empty space, but rather some kind of dynamic shifting field, 313 00:14:54.679 --> 00:14:58.240 or even more radically, perhaps an indication that our underlying 314 00:14:58.279 --> 00:15:02.919 theory of gravity is fundamentally incomplete on cosmic scales. 315 00:15:03.039 --> 00:15:04.799 Let me stop you there, because here's where it gets 316 00:15:04.840 --> 00:15:08.200 really interesting. If we throw out the constant part of 317 00:15:08.240 --> 00:15:10.679 the cosmological constant, what does that. 318 00:15:10.639 --> 00:15:12.879 Actually leave us with a lot of uncertainty? 319 00:15:13.000 --> 00:15:17.799 Doesn't a dynamic shifting dark energy completely obliterate our ability 320 00:15:17.840 --> 00:15:21.200 to predict how the universe ends? Because the ultimate fate 321 00:15:21.240 --> 00:15:24.639 of reality relies entirely on who wins that cosmic tug 322 00:15:24.679 --> 00:15:27.279 of war between gravity and dark energy. 323 00:15:27.440 --> 00:15:29.919 You hit the nail on the head. It entirely rewrites 324 00:15:30.000 --> 00:15:34.039 the predictive models. Wow. Under the assumption of a cosmological constant, 325 00:15:34.240 --> 00:15:37.799 the fate of the universe is a slow, relentless expansion. 326 00:15:38.519 --> 00:15:41.440 It is a scenario often called the Big Freeze or 327 00:15:41.440 --> 00:15:42.000 heat death. 328 00:15:42.120 --> 00:15:44.799 The Big Freeze sounds cozy. 329 00:15:44.559 --> 00:15:48.600 Not quite. The acceleration continues steadily forever, pushing galaxies so 330 00:15:48.720 --> 00:15:52.080 far apart that they become isolated islands, Stars burn out, 331 00:15:52.080 --> 00:15:55.480 matter decays, and the universe drifts into a cold, dark, 332 00:15:55.600 --> 00:15:56.639 infinite emptiness. 333 00:15:56.799 --> 00:15:57.159 Bleak. 334 00:15:57.320 --> 00:16:00.879 But you know, predictable, very predictable. But if the strength 335 00:16:00.879 --> 00:16:04.120 of dark energy is actively changing, then what if the 336 00:16:04.159 --> 00:16:07.840 force is dynamic? The future becomes wildly uncertain. If dark 337 00:16:07.960 --> 00:16:12.200 energy is gradually weakening over time, gravity could eventually reclaim dominance. 338 00:16:12.320 --> 00:16:15.039 Oh, so it could pull everything back together exactly. 339 00:16:15.200 --> 00:16:19.279 The expansion could halt, reverse and pull all matter back 340 00:16:19.320 --> 00:16:22.480 together in a catastrophic collapse, A big crunch, A big crunch. 341 00:16:23.000 --> 00:16:24.679 Okay, And what if it goes the other way? What 342 00:16:24.799 --> 00:16:26.159 if the push gets stronger? 343 00:16:26.480 --> 00:16:30.519 Conversely, if the repulsive strength of dark energy is increasing, 344 00:16:30.840 --> 00:16:34.919 the acceleration could become so violently intense that it eventually 345 00:16:34.960 --> 00:16:39.639 overpowers the gravitational forces holding galaxy clusters together. Oh no, 346 00:16:40.320 --> 00:16:44.639 then stellar systems, then planets, and ultimately the atomic bonds 347 00:16:44.639 --> 00:16:45.320 of matter. 348 00:16:45.080 --> 00:16:48.840 Itself, literally tearing the actual fabric of reality to shreds. 349 00:16:49.000 --> 00:16:51.440 Yes, that scenario is known as the big rip. 350 00:16:51.639 --> 00:16:53.879 The big rip. Okay, I need a minute. That's terrifying. 351 00:16:54.120 --> 00:16:57.919 It's traumatic, certainly. Doctor Suhadri Natzer, who is an associate 352 00:16:57.919 --> 00:17:00.399 professor at the University of Portsmouth and co chair of 353 00:17:00.440 --> 00:17:03.720 the Clustering Working Group for DE and I frame this perfectly. 354 00:17:03.799 --> 00:17:04.400 What did he say? 355 00:17:04.559 --> 00:17:06.960 He pointed out that the mere possibility of dark energy 356 00:17:07.000 --> 00:17:10.440 evolving with time is revolutionary on its own. It demands 357 00:17:10.440 --> 00:17:13.039 a foundational reassessment of the math we use to describe 358 00:17:13.079 --> 00:17:13.839 the cosmos. 359 00:17:14.079 --> 00:17:16.839 But that creates a massive logical problem. In my head. 360 00:17:17.119 --> 00:17:20.599 We've established that dark energy is totally invisible. We can't 361 00:17:20.599 --> 00:17:23.119 put it in a jar, we can't directly measure its 362 00:17:23.119 --> 00:17:26.480 temperature or its mass. So how on earth are these 363 00:17:26.559 --> 00:17:30.799 researchers using a map of visible tangible galaxies to prove 364 00:17:30.880 --> 00:17:34.880 that an invisible phantom force is changing its behavior over 365 00:17:34.920 --> 00:17:35.960 billions of years. 366 00:17:36.160 --> 00:17:38.319 It's a great question. They do it by tracking the 367 00:17:38.359 --> 00:17:42.279 physical consequences of that cosmic tug of war over eleven 368 00:17:42.359 --> 00:17:43.079 billion years. 369 00:17:43.200 --> 00:17:43.799 Okay, go on. 370 00:17:44.119 --> 00:17:47.759 Dark energy is invisible, but gravity is not, and the 371 00:17:47.759 --> 00:17:51.960 way gravity pulls visible matter together leads a structural footprint 372 00:17:51.960 --> 00:17:52.920 that we can actually measure. 373 00:17:53.000 --> 00:17:56.359 You're talking about cosmic clustering, specifically. 374 00:17:55.759 --> 00:17:59.480 Buryon acoustic oscillations, but the broader concept is clustering. 375 00:17:59.640 --> 00:17:59.880 Right. 376 00:18:00.160 --> 00:18:04.000 To trace dark energy DSi isn't just looking at individual galaxies. 377 00:18:04.319 --> 00:18:07.559 It is analyzing the spatial relationships between them. It is 378 00:18:07.599 --> 00:18:11.559 measuring exactly how galaxies group together at different points in 379 00:18:11.599 --> 00:18:12.359 cosmic history. 380 00:18:12.400 --> 00:18:14.839 I need a physical analogy for this, because measuring the 381 00:18:14.880 --> 00:18:18.200 distance between dots on a map to track an invisible 382 00:18:18.200 --> 00:18:19.440 force is a leap for me. 383 00:18:19.559 --> 00:18:20.039 Let's hear it. 384 00:18:20.240 --> 00:18:23.359 Okay, imagine looking at a crowd of people dispersing after 385 00:18:23.400 --> 00:18:26.880 a concert from a helicopter. By tracking how the clusters 386 00:18:26.880 --> 00:18:29.640 of people spread out over an hour, you could deduce 387 00:18:29.720 --> 00:18:32.240 if there was like a sudden rainstorm pushing them to 388 00:18:32.319 --> 00:18:32.880 run faster. 389 00:18:33.279 --> 00:18:35.279 That's a good start. Let's make it a bit more 390 00:18:35.359 --> 00:18:39.160 physical though. Imagine a giant rubber band stretched across a table. 391 00:18:39.359 --> 00:18:40.759 Okay, a rubber band. 392 00:18:40.960 --> 00:18:44.039 You have two heavy iron weights resting on it, pulling 393 00:18:44.079 --> 00:18:47.599 the rubber band slightly toward each other. The tension of 394 00:18:47.640 --> 00:18:50.160 the weights pulling together represents gravity. 395 00:18:50.279 --> 00:18:50.680 Got it. 396 00:18:51.359 --> 00:18:54.720 Now, the rubber band itself being slowly pulled from the 397 00:18:54.839 --> 00:18:57.640 edges of the table. That is dark energy. 398 00:18:57.720 --> 00:19:00.880 Oh, that is a highly functional analogy. So the weights 399 00:19:00.960 --> 00:19:03.599 naturally want to slide toward each other and clump together, 400 00:19:03.960 --> 00:19:06.599 but the surface they are resting on is actively being 401 00:19:06.640 --> 00:19:07.960