WEBVTT 1 00:00:01.480 --> 00:00:05.599 Welcome to the quart Side Quantum Physics Podcast, an exploration 2 00:00:05.679 --> 00:00:10.880 of the fundamental structure of reality, where quantum laws govern matter, energy, 3 00:00:11.199 --> 00:00:16.239 and information. Here, uncertainty is a feature, not a flaw, 4 00:00:16.719 --> 00:00:19.239 and understanding begins with the smallest scales. 5 00:00:27.600 --> 00:00:31.199 So I want you to just, uh imagine the entire 6 00:00:31.320 --> 00:00:33.799 history of the universe for a second, like that simple 7 00:00:33.840 --> 00:00:36.399 story you probably learned back in grade school, right. 8 00:00:36.280 --> 00:00:38.799 The whole big bang expanding outward kind of thing. 9 00:00:38.960 --> 00:00:43.359 Exactly, There's big bang and then gravity slowly starts pulling 10 00:00:43.399 --> 00:00:46.000 everything back together. It's you know, it's like throwing a 11 00:00:46.000 --> 00:00:47.399 baseball straight up into the air. 12 00:00:47.560 --> 00:00:49.920 It shoots up, but eventually it has to slow down. 13 00:00:50.039 --> 00:00:54.320 Right, But here is the massive twist that changes literally everything. 14 00:00:54.880 --> 00:00:56.479 The baseball isn't slowing down. 15 00:00:56.359 --> 00:00:58.520 Yeah, it's actually shooting upward faster and. 16 00:00:58.479 --> 00:01:02.799 Faster, faster and faster. And the invisible force that's driving 17 00:01:02.799 --> 00:01:06.439 this crazy acceleration is what we call dark energy. And 18 00:01:06.480 --> 00:01:09.000 the scale of this is just mind bending because it 19 00:01:09.040 --> 00:01:12.680 makes up what nearly seventy percent of the entire cosmos, Yeah. 20 00:01:12.560 --> 00:01:14.640 Right around sixty eight to seventy percent. I mean, it 21 00:01:14.719 --> 00:01:17.680 is the dominant feature of reality. 22 00:01:17.120 --> 00:01:19.760 Which is wild and For the longest time, science just 23 00:01:19.799 --> 00:01:25.000 thought this mysterious energy was a fixed, unchanging background feature 24 00:01:25.000 --> 00:01:25.640 of the universe. 25 00:01:25.680 --> 00:01:29.719 It's constant cosmological constant. Yeah, that was the absolute bedrock 26 00:01:29.760 --> 00:01:31.239 assumption for decades. 27 00:01:31.480 --> 00:01:33.719 But and this is why we're talking about this today. 28 00:01:34.079 --> 00:01:36.920 Recent discoveries are suggesting that it might not be constant 29 00:01:36.959 --> 00:01:41.920 at all, might actually be alive in a sense dynamic evolving, which. 30 00:01:41.760 --> 00:01:46.079 Is a terrifying and thrilling prospect for astrophysics honestly, totally. 31 00:01:46.120 --> 00:01:48.680 So our mission right now is to figure out what 32 00:01:48.879 --> 00:01:51.599 happens when the foundation of reality turns out to be 33 00:01:51.640 --> 00:01:55.400 shifting beneath our feet. And you know how this evolving 34 00:01:55.480 --> 00:01:59.560 mystery might actually determine the ultimate destiny of existence itself. 35 00:01:59.680 --> 00:02:02.200 Yeah, it literally rewrites how the world ends. 36 00:02:02.400 --> 00:02:06.480 Right, But before we get into how dark energy is changing, 37 00:02:06.840 --> 00:02:08.879 we probably need to talk about what we actually thought 38 00:02:08.879 --> 00:02:09.759 it was doing in the first. 39 00:02:09.639 --> 00:02:12.039 Place, the whole illusion of the constant exactly. 40 00:02:12.080 --> 00:02:14.240 So walk me through this. What is the establishment view here? 41 00:02:14.360 --> 00:02:17.000 Well, it's all anchored in what we call the standard 42 00:02:17.000 --> 00:02:19.919 cosmological model. And understand it, you really have to go 43 00:02:20.080 --> 00:02:20.479 back to. 44 00:02:20.560 --> 00:02:22.960 Albert Einstein always, back to Einstein. 45 00:02:22.560 --> 00:02:26.360 Always, so he had this concept called the cosmological constant, 46 00:02:26.759 --> 00:02:30.120 and the idea was that empty space itself possesses a 47 00:02:30.199 --> 00:02:31.479 fixed energy density. 48 00:02:31.800 --> 00:02:34.759 Okay, so empty space isn't just nothing, it has an 49 00:02:34.879 --> 00:02:35.560 energy to it. 50 00:02:35.919 --> 00:02:39.520 Right. When Einstein was working on his field equations for 51 00:02:39.639 --> 00:02:43.400 general relativity, the math basically showed that a universe filled 52 00:02:43.400 --> 00:02:47.039 with matter should be dynamically unstable, like it should either 53 00:02:47.080 --> 00:02:49.919 be collapsing in on itself or blowing apart. 54 00:02:49.719 --> 00:02:51.439 Because gravity's pulling all the matter together. 55 00:02:51.520 --> 00:02:56.240 Yeah, exactly. But back in the nineteen tens, everyone including Einstein, 56 00:02:56.479 --> 00:03:00.960 just assumed the universe was static, eternal, and unmoving. So 57 00:03:01.199 --> 00:03:04.319 to make his equations work with the static universe, he 58 00:03:04.599 --> 00:03:09.319 threw in this cosmological constant, a mathematical fix. Essentially, it 59 00:03:09.360 --> 00:03:13.560 acted as the steady, uniform outward push to perfectly balance 60 00:03:13.599 --> 00:03:15.479 out the inward pull of gravity. 61 00:03:15.599 --> 00:03:17.439 Oh wow, So he just added it to make the 62 00:03:17.479 --> 00:03:20.159 math match what people believed at the time pretty much. 63 00:03:20.479 --> 00:03:23.240 And of course, a few years later Edwin Hubble realizes 64 00:03:23.280 --> 00:03:27.120 the universe is actually expanding, and Einstein calls the constant 65 00:03:27.240 --> 00:03:29.400 his biggest blunder. He just drops it. 66 00:03:29.560 --> 00:03:31.680 That's so funny. But then we brought it back didn't. 67 00:03:31.719 --> 00:03:34.080 We We had to because in the late nineteen nineties 68 00:03:34.120 --> 00:03:37.240 we realized the expansion of the universe was accelerating. So 69 00:03:37.280 --> 00:03:41.120 physicists resurrected Einstein's constant. But this time it wasn't just 70 00:03:41.199 --> 00:03:44.240 balancing gravity, it was completely overpowering it. 71 00:03:44.599 --> 00:03:47.280 So in this model, does the energy ever change? 72 00:03:47.919 --> 00:03:51.479 No, that's the key. In this constant model, dark energy 73 00:03:51.520 --> 00:03:56.080 remains perfectly identical across all of time. As the universe expands, 74 00:03:56.159 --> 00:03:59.240 you get more empty space, which just means you get 75 00:03:59.240 --> 00:04:00.879 proportionally or dark energy. 76 00:04:01.080 --> 00:04:04.719 Huh. So it's a steady, uniform push that just causes 77 00:04:04.800 --> 00:04:08.080 galaxies to drift apart faster and faster forever exactly. 78 00:04:08.319 --> 00:04:13.439 It offered this incredible mathematical elegance for decades. The equations 79 00:04:13.479 --> 00:04:18.560 aligned perfectly with everything we observed distant supernovae, how galaxies 80 00:04:18.600 --> 00:04:21.879 are distributed, even the cosmic microwave background. 81 00:04:22.040 --> 00:04:24.199 I mean, I get why scientists love that. It makes 82 00:04:24.240 --> 00:04:27.920 the universe predictable. It's like setting your cruise control on 83 00:04:27.959 --> 00:04:28.399 the highway. 84 00:04:28.439 --> 00:04:29.519 You know, it's a great way to put it. 85 00:04:29.519 --> 00:04:31.199 You said it to sixty five. You expect the car 86 00:04:31.279 --> 00:04:34.399 to maintain the exact same steady push forward. We basically 87 00:04:34.439 --> 00:04:36.399 thought the universe was on cosmic cruise control. 88 00:04:36.439 --> 00:04:38.600 We really did, and they're psychological comfort in that. 89 00:04:39.000 --> 00:04:42.360 But if the equations work so remarkably well for so long, 90 00:04:42.720 --> 00:04:46.160 what made us start questioning the dashboard like why did 91 00:04:46.160 --> 00:04:48.240 the cruise control start flashing warning lights? 92 00:04:48.360 --> 00:04:51.160 Well, it really comes down to our instruments getting better. 93 00:04:51.839 --> 00:04:55.839 The universe wasn't on cruise control, and the transition happened 94 00:04:56.000 --> 00:04:58.560 when the math just literally stopped adding up. 95 00:04:58.639 --> 00:05:00.000 And this is what we call the Hubble tension. 96 00:05:00.279 --> 00:05:03.839 Yes, the Hubble tension. It is arguably the most famous 97 00:05:03.879 --> 00:05:07.839 and frankly most frustrating inconsistency in modern astronomy today. 98 00:05:08.040 --> 00:05:10.600 Break that down for me, what exactly is the tension? 99 00:05:10.879 --> 00:05:13.879 So we're trying to measure the expansion rate of the universe, 100 00:05:14.279 --> 00:05:18.240 and to do that we have two completely different, highly 101 00:05:18.319 --> 00:05:21.560 precise methods. Okay, the first method looks at the really 102 00:05:21.600 --> 00:05:24.839 early universe. We look at the cosmic microwave background, which 103 00:05:24.879 --> 00:05:27.959 is basically the afterglow of the Big Bang. 104 00:05:27.879 --> 00:05:29.959 Right from when the universe was super young. 105 00:05:29.920 --> 00:05:32.439 Exactly just a few hundred thousand years old. We take 106 00:05:32.439 --> 00:05:35.920 that data, apply our standard model of a constant dark energy, 107 00:05:36.079 --> 00:05:38.759 and fast forward to predict how fast the universe should 108 00:05:38.800 --> 00:05:39.800 be expanding. 109 00:05:39.360 --> 00:05:41.040 Today, and we get a specific number. 110 00:05:41.160 --> 00:05:44.319 We do around sixty seven kilometers per second per megaparsec. 111 00:05:44.439 --> 00:05:46.240 Okay, sixty seven, got it. 112 00:05:46.279 --> 00:05:49.519 And the second method, the second method ignores the early 113 00:05:49.600 --> 00:05:52.800 universe completely. It just looks at nearby galaxies. Right now, 114 00:05:53.000 --> 00:05:56.639 we use a cosmic distance ladder looking at specific stars 115 00:05:56.720 --> 00:06:00.560 and supernovae to directly measure how fast the look universe 116 00:06:00.639 --> 00:06:01.959 is stretching out today. 117 00:06:01.720 --> 00:06:03.319 And that gives us a different number, a. 118 00:06:03.240 --> 00:06:08.240 Completely different number, around seventy three kilometers per second per megaparsec. 119 00:06:08.360 --> 00:06:10.279 Wait, really, it's a huge gap. 120 00:06:10.319 --> 00:06:14.160 It's about a nine percent difference. And initially everyone just 121 00:06:14.240 --> 00:06:17.199 assumed it was human error, right, like a calibration glitch 122 00:06:17.279 --> 00:06:20.839 or something exactly, a smudge on a telescope lens, some 123 00:06:21.000 --> 00:06:24.439 dust obscuring the stars, just some kind of experimental mistake. 124 00:06:25.079 --> 00:06:29.879 It's imagine you're measuring your living room to buy a rug, right, yeah, 125 00:06:30.120 --> 00:06:34.480 and you use two different highly precise tape measures. One 126 00:06:34.480 --> 00:06:36.680 says the room is ten feet wide and the other says. 127 00:06:36.480 --> 00:06:38.600 It's twelve feet and you check it again and again. 128 00:06:38.720 --> 00:06:40.879 Right, no matter how many times you check, they give 129 00:06:40.920 --> 00:06:43.439 different answers. So at some point you have to admit 130 00:06:43.480 --> 00:06:46.319 the tape measures are fine, the room itself is changing. 131 00:06:46.560 --> 00:06:50.600 That's exactly the disturbing implication of the Hubble tension. The 132 00:06:50.639 --> 00:06:54.399 measurements have become insanely precise over the last decade, the 133 00:06:54.439 --> 00:06:59.680 Hubble space telescope, the Plank satellite. They've practically eliminated the 134 00:06:59.759 --> 00:07:01.800 chance of this being a statistical fluke. 135 00:07:01.959 --> 00:07:03.639 So the error is not in the tools. 136 00:07:03.959 --> 00:07:06.759 No, the tools are fine, which means the universe has 137 00:07:06.800 --> 00:07:09.240 evolved differently than our foundational theory is assumed. 138 00:07:09.399 --> 00:07:11.759 Okay, So if the early universe in the modern universe 139 00:07:11.800 --> 00:07:16.000 are playing by different speed limits, the underlying engine, dark 140 00:07:16.120 --> 00:07:18.480 energy must be shifting gears. 141 00:07:18.639 --> 00:07:20.279 It has to be. It can't be a constant. 142 00:07:20.399 --> 00:07:22.720 So what kind of shifting room are we actually dealing 143 00:07:22.759 --> 00:07:25.639 with here? If the walls are stretching at varying speeds, 144 00:07:25.800 --> 00:07:26.759 what is causing that? 145 00:07:26.920 --> 00:07:28.839 Well, this is where we get into some really radical 146 00:07:28.879 --> 00:07:32.199 new theories. Recent large scale surveys are hinting that dark 147 00:07:32.279 --> 00:07:35.399 energy was actually weaker or stronger at different periods in 148 00:07:35.399 --> 00:07:36.639 cosmic history. 149 00:07:36.360 --> 00:07:38.519 Which totally breaks the Einstein. 150 00:07:38.079 --> 00:07:42.480 Model, completely shatters it, and the leading concept to replace 151 00:07:42.519 --> 00:07:44.199 it is something called quintessence. 152 00:07:44.360 --> 00:07:46.519 Quintessence, it sounds like a sci fi movie. 153 00:07:46.600 --> 00:07:48.600 I know, it sounds a bit mystical, but it's grounded 154 00:07:48.639 --> 00:07:52.399 in quantum physics. The theory of quintessence is that dark 155 00:07:52.519 --> 00:07:56.759 energy is not a property of empty space itself. Instead, 156 00:07:57.160 --> 00:08:01.839 it's a dynamic quantum field that permeates the entire universe. 157 00:08:01.519 --> 00:08:03.839 A field like magnetic field kind of. 158 00:08:03.879 --> 00:08:06.560 It's a scaler field. And the important thing is that 159 00:08:06.600 --> 00:08:10.319 it can slowly fluctuate and evolve over billions of years. 160 00:08:10.480 --> 00:08:12.639 Okay, so it's not a rigid law. It's more like 161 00:08:12.720 --> 00:08:13.839 a physical substance. 162 00:08:14.000 --> 00:08:17.680 Yes, exactly. It treats dark energy like a fluid that 163 00:08:17.720 --> 00:08:22.399 can have shifting properties like variations in pressure density over time. 164 00:08:22.879 --> 00:08:25.560 But wait, how does empty space have a fluctuating field 165 00:08:25.639 --> 00:08:27.319 in it? Isn't it you know? Empty? 166 00:08:27.680 --> 00:08:30.920 Ah? Well, from a quantum physics perspective, empty space is 167 00:08:30.959 --> 00:08:31.920 never truly. 168 00:08:31.639 --> 00:08:33.759 Empty, right, because of quantum mechanics. 169 00:08:34.000 --> 00:08:37.279 Yeah, the vacuum of space is actually filled with fluctuating energies. 170 00:08:37.279 --> 00:08:39.639 You have these virtual particles just constantly bubbling in and 171 00:08:39.639 --> 00:08:40.360 out of existence. 172 00:08:40.519 --> 00:08:43.559 It's it's almost like a boiling pot of water. Yes, 173 00:08:43.639 --> 00:08:47.039 empty space is less like a blank canvas and more 174 00:08:47.080 --> 00:08:49.879 like this boiling pot, just constantly bubbling with energy. 175 00:08:50.000 --> 00:08:53.720 That's a perfect analogy, and so physicists thought, hey, maybe 176 00:08:53.720 --> 00:08:57.759 the energy from all this bubbling quantum vacuum is the 177 00:08:57.879 --> 00:08:58.720 dark energy. 178 00:08:58.840 --> 00:09:01.720 That makes logical sense. Yeah, it provides the mechanism for 179 00:09:01.759 --> 00:09:02.559 the push it. 180 00:09:02.480 --> 00:09:05.200 Does until you actually try to calculate it. And this 181 00:09:05.279 --> 00:09:07.919 leads to what physicists call the quantum catastrophe. 182 00:09:08.000 --> 00:09:09.879 The catastrophe that sounds bad. 183 00:09:10.000 --> 00:09:13.320 It's widely considered the most embarrassing mismatch in the entire 184 00:09:13.480 --> 00:09:14.360 history of science. 185 00:09:14.440 --> 00:09:15.759 Oh wow, how bad is it? 186 00:09:16.000 --> 00:09:19.159 Well, when physicists theoretically calculate how much energy should be 187 00:09:19.240 --> 00:09:21.840 in this bubbling quantum vacuum, the answer they get is 188 00:09:22.039 --> 00:09:24.759 larger than the observed dark energy by a factor of 189 00:09:24.840 --> 00:09:26.559 ten to the one hundred and twentieth power. 190 00:09:26.840 --> 00:09:29.080 Wait, ten to the one hundred and twentieth that's not 191 00:09:29.159 --> 00:09:30.399 just a rounding error. 192 00:09:30.279 --> 00:09:33.639 No, it's a one followed by one hundred and twenty zeros. 193 00:09:34.200 --> 00:09:37.279 If the quantum vacuum actually had that much energy, the 194 00:09:37.360 --> 00:09:40.480 repulsive force would be so violent that the entire universe 195 00:09:40.480 --> 00:09:42.879 would have ripped itself apart before a single atom could 196 00:09:42.879 --> 00:09:43.399 even form. 197 00:09:43.559 --> 00:09:47.120 That's insane. So our calculations are just catastrophically. 198 00:09:46.519 --> 00:09:50.240 Wrong, fundamentally broken. We are missing something profoundly important about 199 00:09:50.240 --> 00:09:51.840 the fundamental nature of reality. 200 00:09:52.200 --> 00:09:55.840 But if our calculations are that wrong, why do we 201 00:09:55.840 --> 00:09:58.679 trust our understanding of quantum fields at all when it 202 00:09:58.679 --> 00:10:01.679 comes to the cosmos, Like, maybe we're barking up the 203 00:10:01.720 --> 00:10:02.919 completely wrong tree. 204 00:10:03.039 --> 00:10:06.039 And that is exactly what some physicists are saying. Because 205 00:10:06.039 --> 00:10:09.840 the calculations are so badly misaligned, some people are abandoning 206 00:10:09.840 --> 00:10:12.120 the idea of an energy field altogether. 207 00:10:12.720 --> 00:10:15.080 Really, so if it's not an energy field, what else 208 00:10:15.080 --> 00:10:15.519 could it be. 209 00:10:15.759 --> 00:10:19.200 Well, they're looking for even stranger explanations, like what if 210 00:10:19.200 --> 00:10:22.279 cosmic acceleration isn't a new energy at all, but a 211 00:10:22.320 --> 00:10:24.720 sign that we need to modify the laws of gravity. 212 00:10:24.799 --> 00:10:27.679 Modify gravity? You mean Einstein was wrong about that too. 213 00:10:27.799 --> 00:10:31.480 Potentially, the idea is that gravity might behave fundamentally differently 214 00:10:31.519 --> 00:10:36.200 across enormous intergalactic distances than general relativity predicts. 215 00:10:36.440 --> 00:10:39.360 So on a small scale like our solar system, gravity 216 00:10:39.399 --> 00:10:42.600 works normally, but when you zoom out to billions of 217 00:10:42.720 --> 00:10:44.399 light years, it starts acting weird. 218 00:10:44.600 --> 00:10:47.879 Exactly the attractive force might weaken faster than we thought, 219 00:10:48.000 --> 00:10:50.960 or maybe it even becomes repulsive at those massive scales. 220 00:10:51.120 --> 00:10:54.080 But modifying gravity feels, i don't know, almost like. 221 00:10:54.120 --> 00:10:56.039 Cheating, like a mathematical cop out. 222 00:10:56.279 --> 00:10:58.799 Yeah, it's like looking at a mirage on a highway. Right. 223 00:10:58.960 --> 00:11:00.799 You see this wavy stuff in the distance, and you 224 00:11:00.799 --> 00:11:02.600 think you're seeing a puddle of water, like a brand 225 00:11:02.600 --> 00:11:06.480 new physical thing. But actually it's just the laws of 226 00:11:06.600 --> 00:11:08.919 light bending in a way you didn't expect over a 227 00:11:08.919 --> 00:11:13.919 long distance. So are we just seeing a gravitational mirage. 228 00:11:14.320 --> 00:11:18.919 That's a huge area of debate, differentiating between adding a 229 00:11:18.960 --> 00:11:22.960 new ingredient like dark energy, versus changing the rules of 230 00:11:23.000 --> 00:11:27.120 the game itself, like modified gravity is really difficult. 231 00:11:27.320 --> 00:11:29.759 Are there other options besides just changing gravity? 232 00:11:29.840 --> 00:11:32.679 Oh, it gets weirder. We get into extra dimensions beyond 233 00:11:32.759 --> 00:11:33.759 ordinary space time. 234 00:11:33.840 --> 00:11:35.519 Oh man, like string theory. 235 00:11:35.559 --> 00:11:38.919 Stuff exactly like string theory. There are models suggesting our 236 00:11:39.000 --> 00:11:42.399 universe is just interacting with a much larger multiversal structure, 237 00:11:42.519 --> 00:11:45.440 like we are a three dimensional membrane floating in a 238 00:11:45.519 --> 00:11:46.720 higher dimensional space. 239 00:11:46.759 --> 00:11:48.919 Okay, you caa have to slow down a membrane. 240 00:11:49.000 --> 00:11:52.000 Yeah, they call them brains. And the idea is that 241 00:11:52.080 --> 00:11:55.559 while forces like light and electromagnetism are stuck on our brain, 242 00:11:56.039 --> 00:11:59.960 Gravity isn't Gravity might be leaking out into these extra dimensions. 243 00:12:00.200 --> 00:12:02.639 Wait, gravity's leaking out of our universe. 244 00:12:02.440 --> 00:12:07.200 That's the theory, and over huge cosmological distances, that leakage 245 00:12:07.320 --> 00:12:10.159 dilutes the strength of gravity, which makes it look like 246 00:12:10.200 --> 00:12:12.919 the universe is accelerating its expansion. 247 00:12:12.600 --> 00:12:15.679 Because the rubber band pulling it together is losing its snap. 248 00:12:15.960 --> 00:12:19.879 Exactly, it mimics dark energy perfectly without actually needing a 249 00:12:19.919 --> 00:12:23.559 new energy field. Or the universe might be transitioning through 250 00:12:23.679 --> 00:12:27.279 vast landscapes of possible energy states over cosmic time. 251 00:12:27.759 --> 00:12:30.840 So what does it actually mean for our understanding of 252 00:12:30.879 --> 00:12:34.639 reality if gravity itself is just like a shape shifter, 253 00:12:35.480 --> 00:12:37.360 or if we're bleeding into extra dimensions. 254 00:12:37.480 --> 00:12:41.120 Well, whether it's an evolving quantum field like quintessence or 255 00:12:41.200 --> 00:12:46.279 changing gravity or multiverse interactions, a fluctuating dark energy doesn't 256 00:12:46.320 --> 00:12:49.399 just change our past, it completely rewrites the end of. 257 00:12:49.399 --> 00:12:52.120 The world, ah the ultimate fate of the universe. 258 00:12:52.240 --> 00:12:55.240 Right, because if this energy isn't constant, the ending isn't fixed. 259 00:12:55.279 --> 00:12:57.879 Okay, So let's walk through these doomsday scenarios. Because if 260 00:12:57.919 --> 00:13:00.840 the standard model was right, and dark energy is constant, 261 00:13:01.000 --> 00:13:03.279 we get what's called the heat death, right, correct. 262 00:13:03.440 --> 00:13:07.120 The heat death is basically a slow freezing fade to black. 263 00:13:07.440 --> 00:13:10.519 Right. Constant dark energy just keeps pushing things apart forever. 264 00:13:11.279 --> 00:13:14.320 Galaxies drift away from each other until they vanish from 265 00:13:14.320 --> 00:13:14.919 the night sky. 266 00:13:15.120 --> 00:13:19.600 Yeah, the stars eventually burnout. Gas for new stars gets exhausted. 267 00:13:20.399 --> 00:13:27.159 Matter decays into this cold, dark, near eternal emptiness, absolute zero. 268 00:13:27.519 --> 00:13:29.559 It's like stretching a giant rubber band and it just 269 00:13:29.600 --> 00:13:31.440 freezes in that stretched position forever. 270 00:13:31.600 --> 00:13:33.840 Exactly. It's bleak, but it's stable. 271 00:13:34.159 --> 00:13:37.480 But if dark energy is evolving, we get some different options. Yeah, 272 00:13:37.519 --> 00:13:39.320 like the big rip. Tell me about the big rip. 273 00:13:39.559 --> 00:13:42.919 The big rip happens if this evolving dark energy actually 274 00:13:42.919 --> 00:13:46.879 gets stronger over time? Oh no, Yeah, the expansion doesn't 275 00:13:46.879 --> 00:13:49.600 just push galaxies apart. It becomes so violent that it 276 00:13:49.639 --> 00:13:54.240 eventually overcomes gravity entirely. First it tears apart galaxy clusters, 277 00:13:54.559 --> 00:13:56.840 Then it strips stars away from their galaxies. 278 00:13:56.840 --> 00:13:58.240 And it doesn't stop there, does it. 279 00:13:58.320 --> 00:14:02.759 No. Months before the end, planetary orbits destabilize, planets are 280 00:14:02.799 --> 00:14:05.519 ripped away from their suns. Minutes before the end, the 281 00:14:05.559 --> 00:14:07.399 planets themselves are torn apart. 282 00:14:07.480 --> 00:14:09.639 The rubber band gets buled so hard that the rubber 283 00:14:09.679 --> 00:14:11.120 itself dissolves into nothing. 284 00:14:11.279 --> 00:14:17.399 Literally. Eventually, the expansion outpaces the electromagnetic forces holding molecules together, 285 00:14:17.840 --> 00:14:22.000 and then the strong nuclear force holding atoms together. Individual 286 00:14:22.080 --> 00:14:23.679 atoms are shredded. 287 00:14:23.399 --> 00:14:27.080 So total sub atomic dissolution. That's horrifying. But there's a 288 00:14:27.120 --> 00:14:29.279 third option, right, the big crunch. 289 00:14:29.440 --> 00:14:32.480 Right, This is the opposite. This happens if dark energy 290 00:14:32.519 --> 00:14:36.200 weakens over time or actually reverses its polarity. 291 00:14:35.759 --> 00:14:37.879 So the rubber band snaps back exactly. 292 00:14:38.159 --> 00:14:41.679 The expansion slows down, stops, and the universe starts collapsing 293 00:14:41.759 --> 00:14:42.799 inward on itself. 294 00:14:42.960 --> 00:14:44.559 It hits you in the hand and hits hard. 295 00:14:45.000 --> 00:14:48.559 Galaxies collide, the background radiation of the universe heats up, 296 00:14:48.559 --> 00:14:52.320 basically roasting everything until all matter and energy are crushed 297 00:14:52.360 --> 00:14:55.279 into a single, infinitely dense singularity. 298 00:14:55.799 --> 00:14:58.399 But a lot of physicists think a big crunch wouldn't 299 00:14:58.440 --> 00:15:01.679 just be the end, right, like it could a cyclic rebirth. 300 00:15:01.840 --> 00:15:04.559 Yeah, cyclic models. The idea is that the big crunch 301 00:15:04.600 --> 00:15:07.399 bounces back and triggers a new big bang. The universe 302 00:15:07.480 --> 00:15:09.440 dies and is reborn over and. 303 00:15:09.360 --> 00:15:12.559 Over, which is fascinating. We're gonna have to ask if 304 00:15:12.559 --> 00:15:16.559 the universe is this evolving dynamic system. Does a cyclic 305 00:15:16.639 --> 00:15:20.159 rebirth actually make more physic sense or is that just 306 00:15:20.279 --> 00:15:23.559 human bias? Like we like seasons, we like the idea 307 00:15:23.759 --> 00:15:27.080 of life and death and rebirth. Does a cyclic model 308 00:15:27.559 --> 00:15:29.879 just feel better than a one way trip to oblivion? 309 00:15:30.360 --> 00:15:33.879 That is a phenomenal question. There is definitely a philosophical 310 00:15:33.919 --> 00:15:37.919 comfort in cyclic models. It avoids the messy problem of 311 00:15:37.960 --> 00:15:41.399 an absolute beginning or an absolute end. It's poetic, it 312 00:15:41.440 --> 00:15:45.279 is poetic, but theoretical physics isn't built on poetry. Models 313 00:15:45.320 --> 00:15:48.240 like the ex pyrotic universe, which uses those colliding brains 314 00:15:48.240 --> 00:15:52.200 we talked about to explain the bounce. They are mathematically rigorous, so. 315 00:15:52.200 --> 00:15:53.320 They aren't just wishful thinking. 316 00:15:53.600 --> 00:15:56.080 No, not at all. But ultimately, the only way to 317 00:15:56.120 --> 00:15:58.320 strip away the human bias and figure out which of 318 00:15:58.320 --> 00:16:01.279 these three apocalypses is our actual destiny is through observation. 319 00:16:01.639 --> 00:16:05.000 We have to map the exact evolutionary curve of dark energy. 320 00:16:04.759 --> 00:16:07.519 Which brings us to the ultimate problem. We're hunting ghosts 321 00:16:07.879 --> 00:16:10.639 pretty much because to figure out which doom awaits us, 322 00:16:10.919 --> 00:16:13.759 we need proof. Ah, but how do you measure something 323 00:16:13.799 --> 00:16:17.240 you literally can't see, touch, or isolate in a lab. 324 00:16:18.000 --> 00:16:20.360 Dark energy is entirely invisible. 325 00:16:20.440 --> 00:16:23.679 It's the ultimate forensic astronomy. We are looking for the 326 00:16:23.679 --> 00:16:26.759 invisible shadows and wakes left behind by this force. 327 00:16:27.360 --> 00:16:29.200 So how do we actually do that well? 328 00:16:29.240 --> 00:16:33.120 Cosmologists and for its existence by looking for tiny, tiny 329 00:16:33.159 --> 00:16:37.399 deviations in large scale cosmic behavior, like what like looking 330 00:16:37.480 --> 00:16:41.519 at distant supernovae, how galaxies cluster together over billions of years, 331 00:16:41.879 --> 00:16:43.840 and something called gravitational lensing. 332 00:16:44.000 --> 00:16:48.279 Gravitational lensing, that's when the gravity of huge objects bends light. 333 00:16:48.159 --> 00:16:52.559 Around them, right, exactly, Massive structures like filaments of dark 334 00:16:52.600 --> 00:16:55.799 matter distort the space time around them. As light from 335 00:16:55.879 --> 00:16:59.399 background galaxies travels to us, it passes through these distortions, 336 00:16:59.440 --> 00:17:02.600 and the shape of those distant galaxies look slightly stretched 337 00:17:02.720 --> 00:17:03.360 or smeared. 338 00:17:03.639 --> 00:17:05.640 But the distortion has to be microscopic. 339 00:17:05.839 --> 00:17:07.160 It's incredibly subtle. 340 00:17:08.279 --> 00:17:10.680 It's like trying to prove the wind exists, right, but 341 00:17:10.720 --> 00:17:12.440 you're not allowed to feel it on your skin. You 342 00:17:12.440 --> 00:17:14.920 can only look at photographs of trees bending in the distance. 343 00:17:15.240 --> 00:17:17.599 That is exactly what it's like. We look at the 344 00:17:17.640 --> 00:17:19.839 bending of light to map out where the dark matter 345 00:17:19.920 --> 00:17:24.359 is because dark matter pulls things together while dark energy pushes. 346 00:17:23.960 --> 00:17:25.720 Them apart, a cosmic tug of war. 347 00:17:25.880 --> 00:17:29.559 Yes, and by mapping this tug of war across billions 348 00:17:29.599 --> 00:17:33.240 of years of cosmic history, we can reconstruct exactly how 349 00:17:33.279 --> 00:17:35.880 strong dark energy was at different epochs. 350 00:17:36.200 --> 00:17:39.400 Okay, so why does mapping the history of the universe's 351 00:17:39.440 --> 00:17:42.079 structure help us predict its future shape? 352 00:17:42.160 --> 00:17:43.920 Because if we can see that the push of dark 353 00:17:44.000 --> 00:17:47.200 energy was weaker five billion years ago than it is today, 354 00:17:47.680 --> 00:17:50.559 we have proven it's an evolving field. We can plot 355 00:17:50.599 --> 00:17:52.799 that curve and project it forward to see if we're 356 00:17:52.839 --> 00:17:55.880 headed for a rip, a crunch, or a freeze. 357 00:17:56.200 --> 00:17:59.000 Wow. And we have new instruments coming online to do this. 358 00:17:59.000 --> 00:18:01.519 Right, Yes, and they are completely transforming the science. We 359 00:18:01.559 --> 00:18:04.640 have the James Web Space Telescope, obviously, but there's also 360 00:18:04.720 --> 00:18:07.000 the European Space Agency's EUCLID mission. 361 00:18:07.119 --> 00:18:10.279 EUCLID is up there now mapping the dark universe exactly. 362 00:18:10.359 --> 00:18:12.559 Its entire goal is to map the cosmic web out 363 00:18:12.599 --> 00:18:15.119 to ten billion light years. And then on the ground 364 00:18:15.160 --> 00:18:17.200 we have the Vera Reuben Observatory in Chile. 365 00:18:17.480 --> 00:18:20.000 I've heard about this one. It's taking a massive time 366 00:18:20.079 --> 00:18:20.839 lapse of the sky. 367 00:18:21.039 --> 00:18:24.720 It's unprecedented. It will capture the entire southern sky every 368 00:18:24.759 --> 00:18:28.759 few nights, generating petabytes of data. It will catalog millions 369 00:18:28.759 --> 00:18:33.000 of supernovae. By combining data from Euclid and Reuben, we 370 00:18:33.039 --> 00:18:34.960 are finally going to get the precision we need. 371 00:18:35.680 --> 00:18:38.319 It's so much data. We're talking about measuring the shapes 372 00:18:38.359 --> 00:18:39.880 of billions of galaxies. 373 00:18:39.960 --> 00:18:44.200 Billions. It requires supercomputers just to process the images, but 374 00:18:44.240 --> 00:18:46.519 it's the only way to pin down exactly what dark 375 00:18:46.599 --> 00:18:47.440 energy is doing. 376 00:18:47.839 --> 00:18:50.920 It really forces a philosophical paradigm shift, doesn't it. The 377 00:18:50.960 --> 00:18:54.279 pursuit of these invisible forces leads to this really profound 378 00:18:54.319 --> 00:18:57.079 realization about our own limitations as a species. 379 00:18:57.160 --> 00:18:58.799 It's incredibly humbling. 380 00:18:58.440 --> 00:19:01.920 Because, I mean, you think about evolutionary biology. Human brains 381 00:19:01.920 --> 00:19:05.640 evolve to survive on Earth. We evolve to dodge predators, 382 00:19:05.720 --> 00:19:07.559 fine food, build shelters, right. 383 00:19:07.599 --> 00:19:11.359 We didn't evolve to instinctively understand the quantum architecture of 384 00:19:11.400 --> 00:19:14.680 space time across billions of light years exactly. 385 00:19:15.079 --> 00:19:18.519 And the humbling truth is that all the visible stuff, 386 00:19:18.559 --> 00:19:21.000 the stars, the planets, the galaxies, everything we can see 387 00:19:21.039 --> 00:19:24.599 with our eyes is just a tiny surface layer. It's 388 00:19:24.720 --> 00:19:26.400 less than five percent of the universe. 389 00:19:26.839 --> 00:19:30.200 The real mechanics of reality are governed by invisible structures 390 00:19:30.559 --> 00:19:34.359 dark matter and dark energy that are currently beyond our comprehension. 391 00:19:34.960 --> 00:19:38.960 It's historically parallel to every major scientific revolution, right No, Oh, absolutely, 392 00:19:39.039 --> 00:19:42.039 like discovering the Earth isn't the center of the universe, 393 00:19:42.559 --> 00:19:45.720 or that space and time aren't absolute, or that solid 394 00:19:45.759 --> 00:19:50.359 matter is mostly empty space. Every single time our basic 395 00:19:50.359 --> 00:19:52.200 assumptions get shattered. 396 00:19:51.880 --> 00:19:55.680 And dark energy is forcing the next great conceptual transformation. 397 00:19:56.079 --> 00:19:58.559 It's introducing the idea of a living universe. 398 00:19:58.759 --> 00:20:00.839 I love that phrase living universe. 399 00:20:01.079 --> 00:20:04.240 If dark energy evolves, the cosmos isn't just a passive 400 00:20:04.279 --> 00:20:07.799 mechanical backdrop where galaxies drift around like dust motes. It's 401 00:20:07.799 --> 00:20:13.440