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 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.960 --> 00:00:30.160 Imagine looking up at the night sky, I mean really 8 00:00:30.199 --> 00:00:34.159 looking and asking that huge question, what's the ultimate fate 9 00:00:34.240 --> 00:00:35.759 of well. 10 00:00:35.560 --> 00:00:37.840 Everything, It's the biggest question really. 11 00:00:37.679 --> 00:00:41.320 For decades, the answer seemed pretty set, if a bit 12 00:00:41.600 --> 00:00:45.719 uh chilling. The universe is expanding faster and faster. 13 00:00:45.679 --> 00:00:48.799 Right heading towards this sort of cold, dark, lonely end, 14 00:00:49.280 --> 00:00:52.759 driven by this mysterious anti gravity. 15 00:00:52.280 --> 00:00:55.920 Stuff dark energy. Yeah, but what if what if the 16 00:00:56.079 --> 00:00:58.840 very measurements that led us there had a kind of 17 00:00:58.920 --> 00:01:03.039 hidden flaw, a systematic bias. What if everything we thought 18 00:01:03.079 --> 00:01:06.400 we knew about the future of the cosmos is suddenly well, 19 00:01:06.480 --> 00:01:07.079 maybe wrong. 20 00:01:07.280 --> 00:01:09.079 That's exactly what we're digging into today. 21 00:01:09.280 --> 00:01:12.480 We are diving into a challenge to a cosmological idea 22 00:01:12.760 --> 00:01:14.319 that's been around for what thirty years? 23 00:01:14.400 --> 00:01:14.799 About that? 24 00:01:14.959 --> 00:01:18.079 Yeah, and it's a challenge so deep it basically pulls 25 00:01:18.120 --> 00:01:20.760 the rugout from under the discovery that won the twenty 26 00:01:20.799 --> 00:01:22.560 eleven Nobel Prize in physics. 27 00:01:22.599 --> 00:01:24.280 It really does question that foundation. 28 00:01:24.599 --> 00:01:29.159 There's this new, really meticulously researched study suggesting the universe 29 00:01:29.200 --> 00:01:32.560 isn't speeding up anymore. Might have actually switched gears and 30 00:01:32.599 --> 00:01:34.879 started slowing down right now today. 31 00:01:34.599 --> 00:01:35.920 Which is a huge turnaround. 32 00:01:36.120 --> 00:01:41.400 So our mission today is to unpack these frankly remarkable findings. 33 00:01:42.079 --> 00:01:46.640 It all seems to hinge on correcting a subtle, maybe 34 00:01:46.680 --> 00:01:51.000 but absolutely critical, systematic bias in one of astronomy's most 35 00:01:51.040 --> 00:01:52.239 trusted tools. 36 00:01:51.959 --> 00:01:55.719 The type IA supernova, the standard candle exactly. 37 00:01:55.959 --> 00:01:58.760 And this isn't just tweaking a number here or there. 38 00:01:58.959 --> 00:02:02.159 This could fundamentally you write the cosmic timeline and maybe 39 00:02:02.280 --> 00:02:05.000 change our whole understanding of the dominant force in the universe. 40 00:02:05.239 --> 00:02:08.120 It's fascinating because of the sheer scale of what might 41 00:02:08.199 --> 00:02:11.199 need reorienting. We're talking about dark energy, yeah, Mysteryes, this 42 00:02:11.360 --> 00:02:14.479 unseen influence that makes up what roughly seventy percent of 43 00:02:14.520 --> 00:02:18.840 everything in the universe. Our standard picture, the Lambda cold 44 00:02:18.919 --> 00:02:22.159 dark matter model or SCDM for short. It's built on 45 00:02:22.159 --> 00:02:26.639 one massive assumption that dark energy is a cosmological constant. 46 00:02:26.719 --> 00:02:31.000 Its strength never changes, it's just there, uniformly dense through 47 00:02:31.000 --> 00:02:31.520 space and. 48 00:02:31.479 --> 00:02:33.759 Time like a background hum kind of. 49 00:02:33.960 --> 00:02:37.439 But now we've got evidence, pretty robust evidence, actually suggesting 50 00:02:37.439 --> 00:02:41.000 that this foundational pillar might be seriously flawed. Well, the 51 00:02:41.080 --> 00:02:45.599 analysis shows that what we interpreted purely as a cosmological effect, 52 00:02:46.360 --> 00:02:51.520 this accelerated expansion, might actually be tangled up with stellar astrophysics, 53 00:02:52.199 --> 00:02:55.280 specifically how stars age. 54 00:02:55.000 --> 00:02:58.840 So not just space stretching, but the stars themselves exactly. 55 00:02:59.280 --> 00:03:03.479 It means our note isn't just evolving, it's being fundamentally reoriented. 56 00:03:03.479 --> 00:03:06.000 By looking really carefully at the data we already have, 57 00:03:06.719 --> 00:03:09.919 you really can't overstate the implications if you start questioning 58 00:03:10.000 --> 00:03:12.159 the gold standard of cosmic measurement like this. 59 00:03:12.360 --> 00:03:15.879 Okay, let's definitely unpack that ranting cosmology first, because to 60 00:03:15.919 --> 00:03:18.759 grasp how big this challenge is, we need to understand 61 00:03:18.759 --> 00:03:21.520 the foundation it's questioning. Let's go back to the mid 62 00:03:21.639 --> 00:03:24.560 nineties and that incredible discovery announced in ninety eight. 63 00:03:24.840 --> 00:03:27.879 Right before then, the expectation was pretty straightforward. You have 64 00:03:27.919 --> 00:03:30.800 the Big Bang, this initial huge expansion. 65 00:03:30.360 --> 00:03:32.759 Seventeen pointy eight billion years ago roughly right. 66 00:03:32.680 --> 00:03:35.120 And then gravity, you know, the poll of all the matter, 67 00:03:35.199 --> 00:03:37.759 should have been putting the brakes on, slowing the expansion down. 68 00:03:37.879 --> 00:03:39.960 And for billions of years that seemed to be the case. 69 00:03:40.080 --> 00:03:42.680 It was gravity was in charge. The universe was sort 70 00:03:42.719 --> 00:03:44.599 of coasting, decelerating gradually. 71 00:03:44.960 --> 00:03:47.719 But then something changed exactly. 72 00:03:47.960 --> 00:03:52.439 Two independent teams of astronomers, the Supernova Cosmology Project and 73 00:03:52.439 --> 00:03:56.280 the Heisy Supernova Search Team. They were using distance measurements 74 00:03:56.360 --> 00:04:00.159 looking way back in time, billions of light years away. 75 00:04:00.159 --> 00:04:01.680 Seeing the universe as it was long. 76 00:04:01.560 --> 00:04:05.360 Ago, precisely, and their results were shocking. Around nine billion 77 00:04:05.439 --> 00:04:09.159 years after the Big Bang, something flipped. The slowdown stopped, 78 00:04:09.439 --> 00:04:11.719 and the expansion actually started to speed up again. 79 00:04:11.919 --> 00:04:14.080 Whoa Okay, yeah, whoa. 80 00:04:14.000 --> 00:04:17.920 Was about right. That accelerating push needed an explanation, you know. 81 00:04:18.000 --> 00:04:21.639 To overcome gravity's constant pull, you needed something pushing back, 82 00:04:21.680 --> 00:04:25.600 a repulsive force, some kind of inherent energy of space itself. 83 00:04:25.680 --> 00:04:27.240 And that's what God called dark energy. 84 00:04:27.439 --> 00:04:30.279 That's it. It acts like this anti gravity, pushing distant 85 00:04:30.319 --> 00:04:33.959 galaxies away faster and faster. And this discovery, based on 86 00:04:34.079 --> 00:04:39.279 using these distant supernovae as cosmic mile markers, was so revolutionary. Well, 87 00:04:39.319 --> 00:04:42.079 it deservedly won the twenty eleven Nobel Prize. 88 00:04:41.639 --> 00:04:44.439 And really cement to the idea that the universe was 89 00:04:44.480 --> 00:04:47.519 accelerating and would just keep doing so forever. 90 00:04:47.639 --> 00:04:50.000 Maybe that became the standard picture and the. 91 00:04:50.040 --> 00:04:52.959 Key measuring tool for all of this was the Type 92 00:04:53.000 --> 00:04:56.800 EA supernova. Why were they considered so reliable? Why the 93 00:04:56.959 --> 00:04:58.079 standard cand well. 94 00:04:58.000 --> 00:05:00.560 They were thought to be Anyway, there, your idea is 95 00:05:00.600 --> 00:05:04.360 pretty neat. Type A supernovae happen in binary star systems. 96 00:05:04.720 --> 00:05:07.040 You have a white dwarf, which is a dense remnant 97 00:05:07.079 --> 00:05:10.000 of a star like our Sun, and it's pulling material 98 00:05:10.079 --> 00:05:13.360 off its companion star. It accretes mass bit by bit 99 00:05:14.079 --> 00:05:17.399 until it hits a very specific limit, the Chanda Sakar limit. 100 00:05:17.519 --> 00:05:20.800 It's called about one point four times the mass of 101 00:05:20.839 --> 00:05:24.439 our Sun. When the white dwarf reaches that exact mass, 102 00:05:24.680 --> 00:05:29.000 it becomes unstable and just boom, catastrophically detonates. 103 00:05:29.160 --> 00:05:31.439 Uh Okay, So the trigger is always the same mass. 104 00:05:31.519 --> 00:05:34.920 That was the crucial assumption. Because the explosion mechanism was 105 00:05:34.920 --> 00:05:38.240 thought to be identical every time hitting that specific critical mass, 106 00:05:38.480 --> 00:05:42.639 astronomers assume these explosions would have a highly uniform intrinsic brightness, 107 00:05:43.120 --> 00:05:46.079 their absolute magnitude would always be the same, right. 108 00:05:46.079 --> 00:05:47.920 Like, no, you have a perfect one hundred white light. 109 00:05:47.800 --> 00:05:51.279 Bulb exactly if you know it's true wattage, it's intrinsic brightness. 110 00:05:51.279 --> 00:05:52.920 You can figure out how far away it is just 111 00:05:52.959 --> 00:05:54.519 by seeing how dim it looks from Earth. 112 00:05:54.800 --> 00:05:57.680 The dimmer it appears the farther away. It must be 113 00:05:58.279 --> 00:05:59.879 simple physics, That was the prince. 114 00:06:00.519 --> 00:06:03.959 So when astronomers looked at these really distant type Ia supernovae, 115 00:06:04.000 --> 00:06:06.879 the ones with high redshift that exploded billions of years ago, 116 00:06:07.519 --> 00:06:10.959 they found they were significantly dimmer than you'd expect if 117 00:06:10.959 --> 00:06:13.560 the universe was just decelerating or even. 118 00:06:13.399 --> 00:06:15.839 Coasting, dimmer than they should have been, right. 119 00:06:16.040 --> 00:06:20.600 And the interpretation of that unexpected dimness was purely cosmological, 120 00:06:20.759 --> 00:06:24.720 meaning The thinking went like this, They looked dimmer mostly 121 00:06:24.759 --> 00:06:29.000 because space itself is expanding faster, carrying these distant galaxies 122 00:06:29.040 --> 00:06:30.160 away from us more quickly. 123 00:06:30.360 --> 00:06:32.920 So the light gets stretched out more diluted by the 124 00:06:32.959 --> 00:06:35.040 accelerating expansion between us and them. 125 00:06:35.079 --> 00:06:39.800 Precisely, more distance, more acceleration meant more dimness, and that 126 00:06:39.920 --> 00:06:45.199 required some kind of constant, pervasive repulsive force pushing everything apart. 127 00:06:45.439 --> 00:06:48.319 Dark energy the cosmological. 128 00:06:47.560 --> 00:06:50.519 Constant exactly, and that's how we landed on the consensus 129 00:06:50.600 --> 00:06:54.399 view the MLCDM model. The universe is still accelerating today 130 00:06:54.639 --> 00:06:57.560 and dark energy is constant. Its strength doesn't change. 131 00:06:57.600 --> 00:06:59.000 If we get technical for a second. 132 00:06:59.199 --> 00:07:01.839 In technical term, yeah, the equation of state parameter for 133 00:07:01.920 --> 00:07:05.040 dark energy, often written as W is a seam to 134 00:07:05.040 --> 00:07:06.480 be exactly minus one. 135 00:07:06.560 --> 00:07:08.360 W eagles minus one, right. 136 00:07:08.319 --> 00:07:11.920 And W reals one means the dark energy density is constant. 137 00:07:12.399 --> 00:07:16.720 It behaves exactly like Einstein's cosmological constant Lambda. And that 138 00:07:16.839 --> 00:07:20.040 constancy that W egles one is the core pillar that's 139 00:07:20.079 --> 00:07:21.600 now being seriously challenged. 140 00:07:21.879 --> 00:07:24.519 Okay, that brings us right to the new evidence, and 141 00:07:24.839 --> 00:07:27.079 this is where the science seems to be finding cracks 142 00:07:27.120 --> 00:07:30.920 in that seemingly perfect standard candle. This work comes from 143 00:07:31.120 --> 00:07:35.600 Professor Young Wook Lee and his team at yonse University, published. 144 00:07:35.240 --> 00:07:39.759 Recently yes in Monthly Notices of the Royal Astronomical Society, and. 145 00:07:39.680 --> 00:07:42.399 Their core idea is well, it sounds simple, but the 146 00:07:42.439 --> 00:07:47.319 implications are huge. Type IA supernovae are not perfect standard candles. 147 00:07:47.720 --> 00:07:51.839 Their brightness is strongly systematically affected by the age and crucially, 148 00:07:52.040 --> 00:07:54.639 the chemical makeup the metallicity of the stars that blew up, 149 00:07:55.519 --> 00:07:57.160 and that has nothing to do with how far away 150 00:07:57.199 --> 00:07:57.480 they are. 151 00:07:57.879 --> 00:08:00.920 This is the subtle point that potential changes the whole 152 00:08:00.959 --> 00:08:05.399 cosmic calculation. See Astronomers already knew supernova weren't perfectly identical. 153 00:08:05.759 --> 00:08:10.480 They applied corrections luminosity standardizations based on how quickly the 154 00:08:10.560 --> 00:08:13.560 light curve faded, the stretch and its color. 155 00:08:13.519 --> 00:08:16.240 Right, trying to iron out the small differences exactly. 156 00:08:16.800 --> 00:08:19.399 But the Yonce team showed that even after you apply 157 00:08:19.480 --> 00:08:23.160 those standard corrections, something else still matters a lot, the 158 00:08:23.240 --> 00:08:28.639 underlying stellar population, the age and the metallicity, the amount 159 00:08:28.639 --> 00:08:31.160 of heavy elements in the stars that eventually became that 160 00:08:31.240 --> 00:08:32.000 white dwarf. 161 00:08:32.200 --> 00:08:35.679 Okay, so explain the systematic bias. How does age or 162 00:08:35.679 --> 00:08:37.559 metallicity mess with the brightness. 163 00:08:37.720 --> 00:08:40.120 Well, let's break it down. Think about the early universe. 164 00:08:40.480 --> 00:08:43.519 Stars formed back then, and stars in younger star forming 165 00:08:43.559 --> 00:08:46.679 regions today tend to be metal poor. They have fewer 166 00:08:46.720 --> 00:08:50.240 elements heavier than hydrogen and helium. Okay, The finding is this, 167 00:08:50.679 --> 00:08:53.000 When a type EA supernova comes from one of these 168 00:08:53.000 --> 00:08:58.200 younger metal poor stellar populations, that supernova appears systematically fainter, 169 00:08:58.679 --> 00:09:03.279 intrinsically dimmer than its cousins from older populations. And conversely, conversely, 170 00:09:03.440 --> 00:09:07.240 supernovae that come from older, more metal rich populations like 171 00:09:07.279 --> 00:09:11.200 you'd find in more evolve galaxies appear systematically brighter. 172 00:09:11.279 --> 00:09:14.080 Hang on, why why would the amount of metal or 173 00:09:14.120 --> 00:09:16.759 the age of the system change the brightness of an 174 00:09:16.799 --> 00:09:20.080 explosion that's supposed to be triggered at exactly the same 175 00:09:20.159 --> 00:09:22.399 mass that one point four solar mass limit. 176 00:09:22.840 --> 00:09:26.200 That's the key stellar astrophysics question they seem to have answered. 177 00:09:26.799 --> 00:09:30.399 The leading theory relates to how metallicity affects the progenitor system. 178 00:09:30.960 --> 00:09:34.519 In environments with fewer heavy elements, the winds from the 179 00:09:34.519 --> 00:09:36.960 companion star might be different. Maybe the structure of the 180 00:09:36.960 --> 00:09:40.039 white dwarf itself just before it explodes is subtly altered. 181 00:09:40.120 --> 00:09:41.200 How does that change the boom? 182 00:09:41.399 --> 00:09:46.480 It seems to affect the thermonuclear runaway, the explosion physics itself. Basically, 183 00:09:46.559 --> 00:09:49.320 a lower metallicity environment seems to lead to a lower 184 00:09:49.440 --> 00:09:52.759 yield of radioactive nickel fifty six during the explosion. 185 00:09:52.840 --> 00:09:54.080 Nickel fifty six that's. 186 00:09:53.960 --> 00:09:58.080 Important, critically important. Nickel fifty six decays into cobalt fifty six, 187 00:09:58.279 --> 00:10:01.159 and that radioactive decay chain is what primarily powers the 188 00:10:01.159 --> 00:10:04.840 peak brightness of the supernova's visible light. So less nickel 189 00:10:04.879 --> 00:10:06.320 means less fuel for the light. 190 00:10:06.159 --> 00:10:08.200 Show, meaning less intrinsic brightness. 191 00:10:08.440 --> 00:10:13.440 Exactly, a metal poor younger system produces a less bright explosion, 192 00:10:13.759 --> 00:10:15.679 even if it started from the same mass trigger. 193 00:10:16.120 --> 00:10:19.840 Wow. Okay, So the implication for cosmology is if you're 194 00:10:19.879 --> 00:10:23.840 looking way back in time at the most distant supernovae. 195 00:10:23.159 --> 00:10:25.519 The ones used to prove acceleration, right. 196 00:10:25.799 --> 00:10:29.639 You were inherently looking at younger stellar populations from a 197 00:10:29.679 --> 00:10:31.799 time when the universe was less chemically. 198 00:10:31.480 --> 00:10:34.080 Enriched, correct, less metal rich overall. 199 00:10:34.240 --> 00:10:38.279 So those distant supernovae were already intrinsically functor to begin with, 200 00:10:38.639 --> 00:10:40.279 just because of when and where they were born. 201 00:10:40.600 --> 00:10:44.679 That's the core argument. They look dimmer for two reasons. Yes, 202 00:10:44.759 --> 00:10:48.600 they're far away and subject to cosmological redshift and expansion effects, 203 00:10:49.000 --> 00:10:51.720 but also they were just less bright from the get 204 00:10:51.759 --> 00:10:55.159 go due to this stellar age metallicity. 205 00:10:54.559 --> 00:10:57.960 Bias, which means the amount of dimness we blamed entirely 206 00:10:58.000 --> 00:10:59.320 on acceleration might. 207 00:10:59.200 --> 00:11:03.000 Be significantly overestimated. Part of that dimness is just astrophysics, 208 00:11:03.000 --> 00:11:06.639 not cosmology. It weakens the case that acceleration alone caused 209 00:11:06.679 --> 00:11:07.759 all the dimming we observed. 210 00:11:07.919 --> 00:11:09.879 That makes a lot of sense. But hang on, if 211 00:11:09.879 --> 00:11:12.639 this effect is real, how did the original Nobel winning 212 00:11:12.679 --> 00:11:14.919 studies miss it? Was there data not good. 213 00:11:14.879 --> 00:11:17.919 Enough for That's a fair question. It wasn't necessarily a 214 00:11:17.960 --> 00:11:20.399 flaw in their methods at the time, but more a 215 00:11:20.480 --> 00:11:23.360 limitation of the data samples they had and the instruments 216 00:11:23.360 --> 00:11:24.200 available back then. 217 00:11:24.360 --> 00:11:25.080 Ah okay. 218 00:11:25.240 --> 00:11:27.960 To really nail down this bias, you need to accurately 219 00:11:27.960 --> 00:11:31.080 measure the age and metallicity of the host galaxies. For 220 00:11:31.279 --> 00:11:34.919 hundreds of supernovae covering a huge range of cosmic time. 221 00:11:34.840 --> 00:11:36.799 Or red shift, you need to know the neighborhood the 222 00:11:36.840 --> 00:11:38.080 star lived in precisely. 223 00:11:38.720 --> 00:11:42.399 The Yonse team used a much larger, more modern sample 224 00:11:42.600 --> 00:11:47.360 three hundred host galaxies, and crucially, they used detailed spectroscopy 225 00:11:47.440 --> 00:11:51.200 and color magnitude diagrams. They looked at the precise colors 226 00:11:51.240 --> 00:11:53.720 and spectral fingerprints of the other stars in the host 227 00:11:53.720 --> 00:11:56.639 galaxy to really pin down the age of the stellar 228 00:11:56.679 --> 00:11:58.919 population that likely spawned the supernova. 229 00:11:59.080 --> 00:12:01.960 So they did detailed demographic studies of three hundred different 230 00:12:01.960 --> 00:12:04.279 galactic homes for these explosions. 231 00:12:03.799 --> 00:12:06.559 That's a good way to put it. And this much larger, 232 00:12:06.679 --> 00:12:10.000 more detailed analysis gave them the statistical muscle they needed 233 00:12:10.000 --> 00:12:13.480 to isolate this subtle effect, this systematic. 234 00:12:12.879 --> 00:12:15.240 Trend, and the confidence level that's the kicker. 235 00:12:15.320 --> 00:12:18.600 They confirm this age bias exists at an extremely high 236 00:12:18.600 --> 00:12:23.000 significance level ninety nine point nine nine nine percent confidence. 237 00:12:23.360 --> 00:12:28.519 Wow, ninety nine point nine nine nine percent. That's basically certain. 238 00:12:28.320 --> 00:12:31.080 In statistical terms. Yeah, it means the chance of this 239 00:12:31.120 --> 00:12:34.360 correlation being just a random flup in the data is 240 00:12:34.399 --> 00:12:38.840 incredibly tiny, vanishingly small. It strongly suggests this bias is 241 00:12:38.919 --> 00:12:42.000 real and must be accounted for when using supernovae to 242 00:12:42.080 --> 00:12:43.600 measure cosmic distances. 243 00:12:43.879 --> 00:12:47.799 Okay, here's where it gets really interesting. Then this finding 244 00:12:47.919 --> 00:12:50.919 means that the dimming of those distant supernovae, which we 245 00:12:51.039 --> 00:12:55.159 previously chalked up entirely to faster and faster cosmic expansion huh, 246 00:12:55.600 --> 00:13:00.879 actually arises in a significant way from stellar astrophysics from 247 00:13:00.919 --> 00:13:02.960 a flaw in our standard candle. 248 00:13:02.679 --> 00:13:04.960 Itself, and that connects the dots directly back to the 249 00:13:04.960 --> 00:13:08.600 acceleration problem. If those distant supernovae looked dimmer partly because 250 00:13:08.600 --> 00:13:11.840 they're intrinsically fainter due to their age and metallicity, not 251 00:13:11.879 --> 00:13:13.440 just because space stretched faster. 252 00:13:13.320 --> 00:13:15.840 Than our calculation of how much faster space was stretching 253 00:13:15.919 --> 00:13:18.360 must be wrong. It must be inflated exactly. 254 00:13:18.399 --> 00:13:20.960 We had changed all the extra dimness to acceleration, but 255 00:13:21.000 --> 00:13:22.879 if a chunk of that dimness was just the star 256 00:13:23.000 --> 00:13:26.840 being young and metal poor, then the actual cosmological acceleration 257 00:13:26.879 --> 00:13:29.279 effect must have been smaller than we calculated. 258 00:13:29.519 --> 00:13:32.440 Okay, so when you apply this correction, this ninety nine 259 00:13:32.480 --> 00:13:35.440 point nine nine nine percent certain correction, you have to 260 00:13:35.440 --> 00:13:37.720 go back to the drawing board with the data, right, 261 00:13:37.879 --> 00:13:40.080 see what the universe actually looks like according to these 262 00:13:40.120 --> 00:13:41.039 refined measurements. 263 00:13:41.080 --> 00:13:43.879 Absolutely, you have to revisit the historical data and see 264 00:13:43.879 --> 00:13:45.039 what the new numbers tell you. 265 00:13:45.360 --> 00:13:47.279 And what do they tell them. Did the corrected data 266 00:13:47.320 --> 00:13:48.799 still fit the standard model? 267 00:13:48.919 --> 00:13:52.480 No, that's the crucial point. The researchers took the raw 268 00:13:52.519 --> 00:13:55.559 supernova data, specifically using large data sets like the Dark 269 00:13:55.639 --> 00:13:59.759 Energy Survey, they applied their systematic age bias correction, and 270 00:13:59.799 --> 00:14:03.720 then and they tested it against the standard CDM. 271 00:14:03.320 --> 00:14:06.279 Model, the one with constant dark energy W equals one. 272 00:14:06.480 --> 00:14:11.279 Right, and unsurprisingly, the corrected supernova data no longer matched 273 00:14:11.279 --> 00:14:13.399 that model. There is a clear discrepancy. 274 00:14:13.480 --> 00:14:16.039 How did they show that visually? Yeah? 275 00:14:16.080 --> 00:14:18.600 They use something called the Hubble residual diagram. It's a 276 00:14:18.639 --> 00:14:22.679 really important tool. It basically plots how much the observed 277 00:14:22.720 --> 00:14:26.799 brightness of the supernovae deviates from what a specific cosmological 278 00:14:26.840 --> 00:14:30.240 model predicts at different distances or red shifts. If the 279 00:14:30.320 --> 00:14:34.759 universe behaved exactly like the standard constant dark energy model says, 280 00:14:35.399 --> 00:14:38.200 then the data points on this plot after the standard 281 00:14:38.240 --> 00:14:42.399 corrections should basically follow along a flat horizontal line, meaning 282 00:14:42.759 --> 00:14:44.120 no systematic deviation. 283 00:14:44.399 --> 00:14:46.399 And did they before this new correction? 284 00:14:46.919 --> 00:14:51.039 Loosely yes, The uncorrected data after standard stretch and color 285 00:14:51.080 --> 00:14:54.279 fixes kind of scattered around that flat line, which supported 286 00:14:54.279 --> 00:14:56.200 the ACDM model more or less. 287 00:14:56.279 --> 00:14:58.919 But after the Yon say Age bias correction. 288 00:14:58.759 --> 00:15:03.480 Big difference. Corrected data points showed a clear significant systematic 289 00:15:03.559 --> 00:15:07.559 shift away from that flat line. Instead of staying flat. 290 00:15:07.600 --> 00:15:11.039 The corrected data traces a curve that deviates significantly from 291 00:15:11.039 --> 00:15:12.840 the constant dark energy prediction. 292 00:15:13.000 --> 00:15:16.960 A curve meaning that deviation isn't random, It changes with distance. 293 00:15:16.720 --> 00:15:20.279 Or time exactly, and that deviation immediately tells you that 294 00:15:20.320 --> 00:15:24.120 the cosmological constant model Lambda is probably wrong. It doesn't 295 00:15:24.159 --> 00:15:25.320 fit the refined data. 296 00:15:25.440 --> 00:15:27.679 So if the standard model is out, what does fit 297 00:15:27.720 --> 00:15:28.720 the corrected data better? 298 00:15:29.000 --> 00:15:32.080 The corrected data aligns much much better with models where 299 00:15:32.240 --> 00:15:35.960 dark energy is not constant. Instead, the data supports models 300 00:15:36.000 --> 00:15:39.840 where the density and therefore the repulsive force of dark 301 00:15:39.960 --> 00:15:43.759 energy actually weakens and evolves significantly over cosmic time. 302 00:15:43.960 --> 00:15:46.320 So WOM isn't stuck at minus one exactly. 303 00:15:46.399 --> 00:15:49.080 It suggests w is dynamic. Maybe it was more negative 304 00:15:49.080 --> 00:15:52.399 in the past, driving acceleration, but perhaps today it's slightly 305 00:15:52.440 --> 00:15:56.120 greater than minus one, indicating a force that's decaying, losing 306 00:15:56.159 --> 00:15:56.639 its punch. 307 00:15:56.919 --> 00:16:00.399 You know this sounds familiar, haven't There been other hints 308 00:16:00.559 --> 00:16:03.879 recently that dark energy might not be constant. 309 00:16:03.919 --> 00:16:06.320 You're absolutely right. This fits with growing evidence from other 310 00:16:06.360 --> 00:16:08.159 corners of cosmology. 311 00:16:07.600 --> 00:16:08.879 Like the DCESI project. 312 00:16:08.960 --> 00:16:13.120 Exactly. Just last year, results from the Dark Energy Spectroscopic 313 00:16:13.159 --> 00:16:17.200 Instrument DSi, based in Arizona, which looks at how galaxies 314 00:16:17.240 --> 00:16:20.240 cluster together, already hinted that the strength of dark energy 315 00:16:20.320 --> 00:16:21.440 might have changed over time. 316 00:16:21.639 --> 00:16:24.480 So DCII was seen potential evolution in W two. 317 00:16:25.000 --> 00:16:28.919 Yes, their data derived from these large scale structure patterns 318 00:16:29.320 --> 00:16:33.440 pointed towards a dynamic w So the idea of evolving 319 00:16:33.480 --> 00:16:36.559 dark energy wasn't completely out of the blue. But this 320 00:16:36.720 --> 00:16:42.440 corrected supernova data provides really strong independent confirmation. It brings 321 00:16:42.480 --> 00:16:45.679 the supernova measurements into alignment with those other hints. 322 00:16:45.759 --> 00:16:49.600 Okay, so bringing it all together, the correct and supernova 323 00:16:49.679 --> 00:16:52.080 may be combined with other data. What's the bottom line 324 00:16:52.080 --> 00:16:53.720 on the standard CDM model. 325 00:16:53.799 --> 00:16:56.080 The bottom line, according to this analysis is that the 326 00:16:56.080 --> 00:17:01.080 combined data rules out the standard CDM model with overwhelming significance. 327 00:17:01.120 --> 00:17:03.320 Overwhelming significance, not just a maybe. 328 00:17:03.440 --> 00:17:06.759 No, this isn't a small statistical wabble they're reporting. It's 329 00:17:06.799 --> 00:17:10.240 presented as a definitive rejection of the current consensus model 330 00:17:10.319 --> 00:17:11.720 based on this corrected evidence. 331 00:17:11.759 --> 00:17:15.319 And if you reject the constant dark energy model, you 332 00:17:15.400 --> 00:17:18.240 have to accept the alternative scenario that does fit the 333 00:17:18.279 --> 00:17:21.440 corrected data. What does that imply for the expansion of 334 00:17:21.440 --> 00:17:23.400 the universe right now today? 335 00:17:23.799 --> 00:17:26.720 It implies something truly profound. It means the universe is 336 00:17:26.759 --> 00:17:29.240 not accelerating today as we've thought for the last twenty 337 00:17:29.240 --> 00:17:29.640 five years. 338 00:17:29.680 --> 00:17:30.559 Wait say that again. 339 00:17:30.680 --> 00:17:34.400 The analysis suggests that universe has already passed peak acceleration. 340 00:17:35.200 --> 00:17:39.200 It has transitioned into a state of decelerated expansion. It's 341 00:17:39.240 --> 00:17:41.920 still expanding, but the rate of expansion is now decreasing. 342 00:17:42.119 --> 00:17:46.640 So we are currently living in a slowing universe. 343 00:17:46.319 --> 00:17:49.400 According to these findings. Yes, Professor Lee stated it very clearly. 344 00:17:49.440 --> 00:17:52.279 He said the universe has already entered a phase of 345 00:17:52.359 --> 00:17:57.039 decelerated expansion at the present epic, and that dark energy 346 00:17:57.079 --> 00:17:59.240 evolves much faster than previously thought. 347 00:17:59.440 --> 00:18:01.640 That is a spleet reversal of the picture that won 348 00:18:01.680 --> 00:18:02.480 the Nobel Prize. 349 00:18:02.519 --> 00:18:05.799 It's a massive shift in perspective. The expansion is ongoing, 350 00:18:06.079 --> 00:18:08.519 but gravity seems to be slowly winning the tug of 351 00:18:08.559 --> 00:18:11.759 war again, causing the rate of expansion to slow down. 352 00:18:12.559 --> 00:18:15.640 It's incredible to think about these cosmic transition points. You 353 00:18:15.680 --> 00:18:18.519 had the first nine billion years or so, gravity slowing 354 00:18:18.519 --> 00:18:21.079 things down the iteration right then dark energy kicks in, 355 00:18:21.160 --> 00:18:23.799 It becomes dominant and speeds things up for a few 356 00:18:23.839 --> 00:18:24.759 billion years. 357 00:18:24.559 --> 00:18:26.920 Acceleration the arrow we thought we were still in. 358 00:18:27.240 --> 00:18:30.640 And now if this is right, because dark energy appears 359 00:18:30.720 --> 00:18:34.319 to be weakening, gravity is starting to reassert its influence 360 00:18:34.319 --> 00:18:37.440 on the largest scales, causing the expansion rate to slow 361 00:18:37.480 --> 00:18:37.960 down again. 362 00:18:38.240 --> 00:18:41.039 The dominance of forces seems to have flipped once more. 363 00:18:41.240 --> 00:18:44.000 It's a much more dynamic cosmic history than the standard 364 00:18:44.000 --> 00:18:44.839 model suggested. 365 00:18:45.039 --> 00:18:47.359 What really gives this study punch, though, isn't just the 366 00:18:47.400 --> 00:18:50.880 statistics on the age bias, right. It's how it clicks 367 00:18:51.039 --> 00:18:52.039 with other measurements. 368 00:18:52.359 --> 00:18:56.519 Absolutely, that's perhaps the most compelling part. It's not just 369 00:18:56.720 --> 00:19:00.160 the ninety nine point nine nine nine percent confidence the 370 00:19:00.160 --> 00:19:03.440 correction itself, but the fact that when you apply this correction, 371 00:19:03.799 --> 00:19:07.680 the supernova data suddenly aligns beautifully with independent ways of 372 00:19:07.720 --> 00:19:09.160 measuring the universe. 373 00:19:09.039 --> 00:19:12.559 Methods that previously didn't quite line up with the supernova. 374 00:19:12.039 --> 00:19:15.400 Result exactly, measurements that had been kind of quietly problematic 375 00:19:15.440 --> 00:19:18.440 because they just didn't agree with the gold standard results 376 00:19:18.480 --> 00:19:21.000 from the potentially flawed supernova method. 377 00:19:21.240 --> 00:19:23.960 Okay, let's talk about those independent data sets. Yeah, you 378 00:19:24.000 --> 00:19:28.680 mentioned DSi before. The corrected supernova data now aligns with 379 00:19:28.799 --> 00:19:33.200 models favored by projects like DSi, which used buryonic acoustic 380 00:19:33.240 --> 00:19:38.480 oscillations BAO and the cosmic microwave background CMB, right. 381 00:19:38.799 --> 00:19:43.119 Two pillars of modern cosmology completely independent of supernova. 382 00:19:44.079 --> 00:19:47.440 We hear BAO and CMB mentioned a lot. Maybe, let's 383 00:19:47.480 --> 00:19:50.240 quickly recap what they actually are, why they're reliable cosmic 384 00:19:50.279 --> 00:19:51.119 rulers in their own right. 385 00:19:51.200 --> 00:19:54.880 Good idea. So the CMB the cosmic microwave background. That's 386 00:19:54.960 --> 00:19:56.880 literally the oldest light in the universe. 387 00:19:56.920 --> 00:19:59.240 We can see the afterglow of the Big Bang pretty much. 388 00:19:59.240 --> 00:20:01.759 It's the residual heat and light left over from about 389 00:20:01.759 --> 00:20:04.200 three hundred and eighty thousand years after the Big Bang. 390 00:20:04.440 --> 00:20:07.279 That was when the universe cooled down enough for electrons 391 00:20:07.279 --> 00:20:09.519 and protons to finally combine and form. 392 00:20:09.400 --> 00:20:11.839 Neutral atoms called recombination, right. 393 00:20:11.880 --> 00:20:15.079 And that event essentially made the universe transparent to light 394 00:20:15.119 --> 00:20:17.440 for the first time. So the CME gives us this 395 00:20:17.480 --> 00:20:20.440 incredible snapshot of the universe when it was extremely young 396 00:20:20.480 --> 00:20:24.839 and incredibly smooth, but with tiny temperature fluctuations. These fluctuations 397 00:20:24.839 --> 00:20:26.400 were the seeds of all future structure. 398 00:20:26.519 --> 00:20:29.599 Okay, that's the CNB a picture of the early universe. 399 00:20:29.839 --> 00:20:36.160 What about BAO baryonic acoustic oscillations. Sounds complicated. 400 00:20:36.240 --> 00:20:38.759 It sounds complicated, but the concept is actually based on 401 00:20:38.839 --> 00:20:41.920