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 --> 00:00:26.679 slumber under the night sky. 7 00:00:26.960 --> 00:00:30.879 Imagine for a second you're driving down this long, flat 8 00:00:31.000 --> 00:00:33.960 stretch of highway, you know, the kind where you can 9 00:00:34.000 --> 00:00:37.880 just see for miles totally clear day. You're cruising along 10 00:00:38.240 --> 00:00:40.600 and you pass a police car parked on the shoulder. 11 00:00:41.159 --> 00:00:45.640 The officer points a radar gun at you clocks your speed. 12 00:00:45.719 --> 00:00:48.000 I think most of us have felt that specific spike 13 00:00:48.039 --> 00:00:48.600 of adrenalist. 14 00:00:48.640 --> 00:00:51.359 Absolutely. But then a mile down the road there's another 15 00:00:51.399 --> 00:00:55.320 police officer, also an expert, also holding a state of 16 00:00:55.359 --> 00:00:59.759 the art, perfectly calibrated radar gun, and he clocks you too. Okay, Now, 17 00:01:00.560 --> 00:01:03.880 imagine both of these officers are the best in the business. 18 00:01:04.239 --> 00:01:08.319 Their equipment is flawless, They technically never make mistakes. But 19 00:01:08.400 --> 00:01:10.640 a week later you get the ticket. The first officer 20 00:01:10.680 --> 00:01:13.159 says you were going seventy three miles per hour. Right, 21 00:01:13.239 --> 00:01:15.879 the second officer says you were going sixty seven miles 22 00:01:15.879 --> 00:01:16.239 per hour. 23 00:01:16.359 --> 00:01:18.040 That is a very confusing court date. 24 00:01:18.200 --> 00:01:21.439 Right, who do you believe? They're both experts. They're using 25 00:01:21.439 --> 00:01:24.560 top gear technology to measure the exact same event, your 26 00:01:24.599 --> 00:01:26.879 car moving, but the numbers don't match. 27 00:01:26.879 --> 00:01:30.879 In our world, you'd probably blame it on a faulty battery. 28 00:01:30.599 --> 00:01:33.799 Or something exactly. But in astrophysics, this isn't about a 29 00:01:33.840 --> 00:01:36.599 speeding ticket. It's about the speed of the universe itself, 30 00:01:37.079 --> 00:01:40.480 and this discrepancy it is, and this is not an exaggeration, 31 00:01:41.040 --> 00:01:43.599 the single biggest headache in modern cosmology. 32 00:01:44.120 --> 00:01:46.680 You were referring to the hubble tension. Yeah, and you're 33 00:01:46.719 --> 00:01:49.359 right to frame it as a headache. It's it's really 34 00:01:49.359 --> 00:01:51.599 more of a crisis. We aren't talking about a car. 35 00:01:51.920 --> 00:01:54.359 We're talking about the fabric of space. 36 00:01:54.200 --> 00:01:56.319 Expanding, the universe getting bigger, and. 37 00:01:56.280 --> 00:01:59.599 We have two very different, very precise ways of measuring 38 00:01:59.599 --> 00:02:02.519 that exp ancient and for the last decade they have 39 00:02:02.680 --> 00:02:04.319 just refused to agree. 40 00:02:04.359 --> 00:02:06.799 It's the cosmic speed trap. And usually when we talk 41 00:02:06.799 --> 00:02:09.759 about this, the solutions people propose are I mean, they're 42 00:02:09.759 --> 00:02:10.800 incredibly wild. 43 00:02:10.879 --> 00:02:13.240 Oh yeah, you get into some really high concept stuff. 44 00:02:13.240 --> 00:02:16.439 People start talking about dark energy changing over time or 45 00:02:16.520 --> 00:02:20.199 gravity leaking into other dimensions. But today we're looking at 46 00:02:20.199 --> 00:02:23.879 a new contender. A new paper just dropped literally today 47 00:02:24.039 --> 00:02:27.680 February fifteenth, twenty twenty six, that suggests the answer isn't 48 00:02:27.719 --> 00:02:31.360 some new phantom force. It might be something, well, something 49 00:02:31.360 --> 00:02:32.520 surprisingly domestic. 50 00:02:32.800 --> 00:02:35.400 Domestic is an interesting word for it, considering the scale. 51 00:02:35.479 --> 00:02:38.159 But yes, the fundamental force is certainly something you encounter 52 00:02:38.199 --> 00:02:39.120 in your kitchen every day. 53 00:02:39.280 --> 00:02:42.840 We were talking about magnetism. The same force that holds your 54 00:02:42.879 --> 00:02:45.319 grocery list to the fridge might just be the key 55 00:02:45.400 --> 00:02:47.879 to fixing the biggest broken number in physics. 56 00:02:47.960 --> 00:02:50.759 Although to be fair, the magnets we're discussing today are 57 00:02:52.400 --> 00:02:54.400 a little different than a fridge magnet. We're talking about 58 00:02:54.400 --> 00:02:56.000 primordial magnetic fields. 59 00:02:56.080 --> 00:02:58.319 Primordial, so ancient. 60 00:02:58.199 --> 00:03:02.360 Incredibly ancient. These are invisible fields that were generated mere 61 00:03:02.879 --> 00:03:06.840 milliseconds after the Big Bang, and we think stretch across 62 00:03:06.840 --> 00:03:07.840 the entire cosmos. 63 00:03:08.520 --> 00:03:10.439 So on today's deep dive, we are going to look 64 00:03:10.479 --> 00:03:14.080 at why the universe's speedometers seems broken. We're going to 65 00:03:14.159 --> 00:03:18.400 unpack this new paper by researchers Pagosian, Jadamziic and Abel 66 00:03:19.039 --> 00:03:21.280 we'll find out what a peicogus. 67 00:03:20.719 --> 00:03:23.240 Is, and why clumping is the technical. 68 00:03:22.879 --> 00:03:25.479 Term you need to know, and how these invisible magnetic 69 00:03:25.520 --> 00:03:28.080 webs might be the bridge between two numbers that just 70 00:03:28.159 --> 00:03:29.199 won't play nice. 71 00:03:29.479 --> 00:03:31.680 And I think this is the most exciting part. We're 72 00:03:31.719 --> 00:03:35.719 going to explore how this research doesn't just fix a 73 00:03:35.719 --> 00:03:40.639 math problem. It potentially opens a window into high energy 74 00:03:40.639 --> 00:03:44.520 physics that we could never ever hope to replicate in 75 00:03:44.599 --> 00:03:45.199 a lab on. 76 00:03:45.159 --> 00:03:49.520 Earth, using the universe as its own particle collider precisely. Okay, 77 00:03:49.599 --> 00:03:51.919 let's unpack this. We have to start with the problem itself, 78 00:03:52.120 --> 00:03:54.719 the Hubble tension. I feel like we hear this term 79 00:03:54.759 --> 00:03:57.479 a lot, but let's really drill down. It all starts 80 00:03:57.479 --> 00:03:58.719 with Edwin Hubble, doesn't. 81 00:03:58.520 --> 00:04:00.759 It does. You have to go back to thenineteen twenties, 82 00:04:01.240 --> 00:04:05.080 before Hubble, the scientific consensus was that the universe was static. 83 00:04:05.319 --> 00:04:08.039 It was just there, eternal, unchanging. 84 00:04:08.159 --> 00:04:09.759 The way it is now is the way it's always 85 00:04:09.800 --> 00:04:10.639 been exactly. 86 00:04:11.280 --> 00:04:14.560 But Hubble pointed his telescope at the night sky and 87 00:04:14.680 --> 00:04:17.600 just fundamentally shattered that view of reality. He showed that 88 00:04:17.600 --> 00:04:20.600 the universe is actually getting bigger. Galaxies are moving away 89 00:04:20.639 --> 00:04:21.120 from us. 90 00:04:21.079 --> 00:04:23.000 And it wasn't just random movement, right. There was a 91 00:04:23.040 --> 00:04:24.399 distinct pattern to it. 92 00:04:24.519 --> 00:04:26.920 Very clear pattern. He found that the farther away a 93 00:04:26.959 --> 00:04:30.560 galaxy is the faster it's receding from us. It's the 94 00:04:30.600 --> 00:04:32.160 classic analogy of dots on. 95 00:04:32.120 --> 00:04:33.800 A balloon, right as you inflate it. 96 00:04:34.079 --> 00:04:37.600 As you inflate the balloon, every dot moves away from 97 00:04:37.639 --> 00:04:40.639 every other dot. But the dots that start further apart 98 00:04:40.680 --> 00:04:43.079 seem to move away from each other much faster because 99 00:04:43.120 --> 00:04:45.079 there's just more balloon expanding between them. 100 00:04:45.399 --> 00:04:48.519 And that rate of recession, that specific relationship between speed 101 00:04:48.519 --> 00:04:50.439 and distance, that's the Hubble constant. 102 00:04:50.480 --> 00:04:53.319 Correct, it's the fundamental expansion rate of the cosmos. Now, 103 00:04:53.360 --> 00:04:55.360 the units we used to measure it are a bit 104 00:04:55.399 --> 00:04:58.240 of a mouthful kilometers per second per megaparsec. 105 00:04:58.319 --> 00:05:01.040 Okay, hold on, let's break that down per second. That's easy, 106 00:05:01.079 --> 00:05:05.600 that's just speed. But per megaparsec. What on Earth is 107 00:05:05.639 --> 00:05:06.560 a megaparsec? 108 00:05:06.680 --> 00:05:09.240 Right, Let's build up to it. So, a parsek is 109 00:05:09.319 --> 00:05:12.160 a unit of distance we use in astronomy. One parsek 110 00:05:12.240 --> 00:05:14.279 is about three point twenty six light years. 111 00:05:14.240 --> 00:05:17.399 Which is already an incomprehensibly huge distance. 112 00:05:17.600 --> 00:05:21.199 Massive, but a megaparsek is one million parsecs. 113 00:05:20.839 --> 00:05:23.040 So we are talking about a distance of roughly three 114 00:05:23.040 --> 00:05:24.720 point twenty six million light years. 115 00:05:24.720 --> 00:05:26.800 That's the one. So we say the Hubble constant is, 116 00:05:26.839 --> 00:05:30.560 for example, seventy kilometers mpc. It means that for every 117 00:05:30.560 --> 00:05:32.720 megaparsek you go further out into space. 118 00:05:32.560 --> 00:05:34.680 A galaxy appears to be moving away from US seventy 119 00:05:34.759 --> 00:05:36.160 kilometers per second faster. 120 00:05:36.519 --> 00:05:39.480 Precisely, it's a rate of stretching. If a galaxy is 121 00:05:39.519 --> 00:05:43.480 one megaparsec away, it's moving its seventy kilometers. If it's 122 00:05:43.480 --> 00:05:45.680 two away, it's one hundred and forty kilometers. It just 123 00:05:45.720 --> 00:05:46.279 scales up. 124 00:05:46.399 --> 00:05:48.240 Okay, got it. So we have the speed limit we're 125 00:05:48.240 --> 00:05:50.600 trying to measure now. As we said in the intro, 126 00:05:51.000 --> 00:05:54.079 there are two police officers, two ways to measure this number. 127 00:05:54.839 --> 00:05:57.040 And this is where the fight starts. Let's call the 128 00:05:57.120 --> 00:06:00.720 METHODA and method B. Method A is the approach, the 129 00:06:00.839 --> 00:06:02.040 look out the window method. 130 00:06:02.240 --> 00:06:04.399 That's a good way to put it. Method A looks 131 00:06:04.439 --> 00:06:07.399 at the late universe, the universe as it exists now 132 00:06:07.800 --> 00:06:11.160 or in the relatively recent cosmic past. This is the 133 00:06:11.199 --> 00:06:14.720 method that follows directly in Edwin Hubble's footsteps. We look 134 00:06:14.720 --> 00:06:17.240 at galaxies and we measure how fast they're moving away. 135 00:06:17.319 --> 00:06:19.639 Okay, speed seems easy enough to measure, right, You just 136 00:06:19.720 --> 00:06:20.319 use red shift. 137 00:06:20.360 --> 00:06:23.160 Speed is very straightforward. Yeah, we look at the light spectrum. 138 00:06:23.199 --> 00:06:25.279 If it's shifted toward the red that's moving away, we 139 00:06:25.279 --> 00:06:29.319 can measure that to an incredibly high precision. The tricky part, 140 00:06:29.720 --> 00:06:34.240 the absolute nightmare of observational astronomy, is knowing exactly how 141 00:06:34.279 --> 00:06:37.040 far away the object is. You can't just use a 142 00:06:37.079 --> 00:06:37.959 tape measure. 143 00:06:37.839 --> 00:06:42.000 Because in space you completely lose depth perception. A really 144 00:06:42.040 --> 00:06:45.319 bright thing far away can look exactly the same as 145 00:06:45.360 --> 00:06:47.680 a dim thing that's close up exactly. 146 00:06:48.319 --> 00:06:51.600 To solve this, astronomers use something called standard candles. 147 00:06:52.120 --> 00:06:54.199 I love this analogy. Break it down for us. 148 00:06:54.240 --> 00:06:58.079 Okay, so imagine you are standing in a long dark 149 00:06:58.120 --> 00:07:00.800 field at night. You see a light in the distance. 150 00:07:01.560 --> 00:07:04.199 Is it a dim, little flashlight ten feet away or 151 00:07:04.240 --> 00:07:06.319 is it a massive search light ten miles away? You 152 00:07:06.360 --> 00:07:10.040 can't really tell just by looking. But what if you 153 00:07:10.160 --> 00:07:13.560 knew for a fact that the light was a specific 154 00:07:13.639 --> 00:07:15.199 brand of sixty watt light. 155 00:07:15.079 --> 00:07:17.439 Bulb, then you'd know exactly how bright it should be at. 156 00:07:17.399 --> 00:07:21.000 The source, exactly if you know, it's intrinsic brightness. The wattage, 157 00:07:21.279 --> 00:07:23.120 you can measure how dim it appears to your eye, 158 00:07:23.439 --> 00:07:25.959 and then some simple physics tells you exactly how far 159 00:07:26.000 --> 00:07:27.839 away it must be to look that dimp. 160 00:07:27.879 --> 00:07:30.920 So we need to find the universe's sixty watt light bulbs. 161 00:07:30.519 --> 00:07:33.079 And we have them. Our primary standard candles are what 162 00:07:33.079 --> 00:07:36.439 we call Type EA supernovae exploding stars. 163 00:07:36.600 --> 00:07:39.560 But why are they all the same brightness? Explosions seem 164 00:07:39.639 --> 00:07:41.839 like they'd be messy and you know, kind of random. 165 00:07:42.160 --> 00:07:45.800 They're incredibly messy, but the physics that triggers them is 166 00:07:45.879 --> 00:07:49.959 remarkably consistent. A type as supernova happens in a binary 167 00:07:50.000 --> 00:07:53.480 star system. You have a white dwarf, which is a dead, 168 00:07:53.639 --> 00:07:57.480 super dense star core orbiting a companion star. Okay, the 169 00:07:57.480 --> 00:07:59.959 white dwarf's gravity is so strong it starts to steal 170 00:08:00.160 --> 00:08:02.800 matter from its companion. It just siphons it off, getting 171 00:08:02.800 --> 00:08:06.519 heavier and heavier. But there is a strict fundamental limit 172 00:08:06.639 --> 00:08:07.759 to how heavy a white. 173 00:08:07.600 --> 00:08:09.600 Dwarf can get, the Chundra Sicar limit. 174 00:08:09.720 --> 00:08:12.000 That's the one. It's about one point four times the 175 00:08:12.040 --> 00:08:14.240 mass of our Sun. Once the white dwarf hits that 176 00:08:14.360 --> 00:08:16.439 exact limit, it can no longer support its own weight 177 00:08:16.480 --> 00:08:20.160 against gravity. It collapses and detonates in a thermonuclear explosion. 178 00:08:20.360 --> 00:08:23.399 And because the mass at the moment of detonation is always. 179 00:08:23.079 --> 00:08:25.480 The same, the brightness of the explosion is always the same. 180 00:08:25.759 --> 00:08:27.000 It's nature's standard bomb. 181 00:08:27.040 --> 00:08:27.399 Wow. 182 00:08:28.160 --> 00:08:31.120 We also use another kind of star, cephade variables, which 183 00:08:31.160 --> 00:08:34.399 pulse and the speed of their pulse is directly related 184 00:08:34.440 --> 00:08:38.639 to their intrinsic brightness. So by combining these measurements using 185 00:08:38.639 --> 00:08:41.440 the Whole Space telescope, and now that James webistronomers have 186 00:08:41.559 --> 00:08:44.320 built this very precise cosmic distance ladder. 187 00:08:44.399 --> 00:08:46.399 They climb that ladder, they check the speedometer, and what 188 00:08:46.519 --> 00:08:47.320 number do they get? 189 00:08:47.919 --> 00:08:51.440 Consistently, when looking at the late universe with supernovae and cephades, 190 00:08:51.879 --> 00:08:55.480 we get a hubble constant of roughly seventy three kilometers 191 00:08:55.519 --> 00:08:57.399 per second per mega parsek. 192 00:08:57.080 --> 00:09:00.320 Okay, seventy three. Lock that number in. That's officer number one. 193 00:09:00.600 --> 00:09:03.440 Now let's look at method B, the indirect approach. This 194 00:09:03.519 --> 00:09:06.000 is the look at the baby pictures method. 195 00:09:06.120 --> 00:09:08.879 Yes, this method is completely different. It has nothing to 196 00:09:08.919 --> 00:09:11.159 do with stars or galaxies. It looks at the cosmic 197 00:09:11.200 --> 00:09:12.759 microwave background the CMB. 198 00:09:12.759 --> 00:09:14.720 The after glow of the Big Bang. 199 00:09:14.519 --> 00:09:17.559 Itself the oldest light in the universe. It was released 200 00:09:17.559 --> 00:09:19.879 when the cosmos was only about three hundred and eighty 201 00:09:19.919 --> 00:09:25.120 thousand years old. Before that moment, the universe was this hot, dense, 202 00:09:25.200 --> 00:09:28.919 opaque fog like a plasma exactly. And when it cooled 203 00:09:29.000 --> 00:09:32.639 enough that fog cleared and light could finally travel freely. 204 00:09:33.000 --> 00:09:35.480 That light has been streaming through space for thirteen point 205 00:09:35.559 --> 00:09:39.480 eight billion years, stretching as the universe expands, until today 206 00:09:39.600 --> 00:09:41.759 it falls into the microwave part of the spectrum. 207 00:09:41.879 --> 00:09:45.080 So we have this picture, the snapshot of the baby universe, 208 00:09:45.200 --> 00:09:48.600 and when we look at it, it's not perfectly smooth, 209 00:09:48.679 --> 00:09:48.960 is it. 210 00:09:49.279 --> 00:09:52.720 No, not at all. It has tiny fluctuations, hot spots 211 00:09:52.720 --> 00:09:56.720 and cold spots that correspond to tiny, tiny ripples in density. 212 00:09:56.799 --> 00:09:59.320 So we have a map, a map of the infant cosmos. 213 00:10:00.000 --> 00:10:01.399 What on Earth do you get a speed limit out 214 00:10:01.440 --> 00:10:02.320 of a static map? 215 00:10:02.720 --> 00:10:06.000 Ah? Well, we use our best understanding of physics. It's 216 00:10:06.000 --> 00:10:09.960 called the Standard Model of cosmology. It's this incredible mathematical 217 00:10:10.000 --> 00:10:14.320 framework for gravity, matter, dark energy, everything. We take the 218 00:10:14.399 --> 00:10:17.519 data from that baby picture, which was measured with incredible 219 00:10:17.519 --> 00:10:20.039 precision by the Plank Space telescope and we plug it 220 00:10:20.080 --> 00:10:23.200 into the model. We basically hit fast forward on a 221 00:10:23.200 --> 00:10:24.480 giant cosmic simulation. 222 00:10:24.720 --> 00:10:28.440 You're simulating the entire thirteen point eight billion year history 223 00:10:28.440 --> 00:10:29.120 of the universe. 224 00:10:29.240 --> 00:10:31.799 In a sense, yes, we say, okay, if the universe 225 00:10:31.799 --> 00:10:35.360 started with these specific ingredients and these specific density patterns, 226 00:10:35.559 --> 00:10:37.399 and if the laws of physics are what we think 227 00:10:37.440 --> 00:10:40.799 they are, how fast should the universe be expanding today? 228 00:10:41.159 --> 00:10:43.519 So it's a prediction. It's like looking at a Toddler's 229 00:10:43.519 --> 00:10:45.519 growth chart and predicting how tall I'll be when they 230 00:10:45.559 --> 00:10:46.120 turn twenty. 231 00:10:46.200 --> 00:10:48.840 It's a very very precise prediction based on what we 232 00:10:48.960 --> 00:10:52.200 believe to be fundamental physics. And when we do that calculation, 233 00:10:52.759 --> 00:10:54.519 the number we get is not seventy three. 234 00:10:54.759 --> 00:10:55.399 What is it? 235 00:10:55.120 --> 00:10:59.759 It is roughly sixty seven kilometers per second per megaparsec. 236 00:10:59.399 --> 00:11:01.679 Sixty seven versus seventy three. Now I have to play 237 00:11:01.720 --> 00:11:04.240 Devil's advocate here for a second. To someone on the street, 238 00:11:04.320 --> 00:11:07.159 that sounds I mean, that sounds pretty close. If I 239 00:11:07.200 --> 00:11:09.840 guessed a jar had sixty seven jelly beans and it 240 00:11:09.840 --> 00:11:12.399 turned out to have seventy three, I'd be thrilled with myself. 241 00:11:12.919 --> 00:11:14.039 Are we sure this matters. 242 00:11:14.440 --> 00:11:17.600 In many many fields, that would be a celebratory agreement, 243 00:11:18.320 --> 00:11:22.480 but in precision cosmology it is a disaster. Or a disaster, yes, 244 00:11:23.000 --> 00:11:27.080 because over the last decade both sides have refined their 245 00:11:27.120 --> 00:11:30.799 measurements again and again. The air bars, you know, the 246 00:11:30.840 --> 00:11:34.519 margins of uncertainty, have shrunk to be incredibly small, and 247 00:11:34.559 --> 00:11:36.080 they do not overlap anymore. 248 00:11:36.159 --> 00:11:38.080 So it's definitely not just a rounding error. 249 00:11:38.120 --> 00:11:41.720 The statistical significance is over what we call five sigma 250 00:11:41.840 --> 00:11:44.039 in science. That means the odds of this being a 251 00:11:44.120 --> 00:11:46.799 random fluke are less than one in three point five million. 252 00:11:47.159 --> 00:11:49.279 It is a genuine, undeniable conflict. 253 00:11:49.440 --> 00:11:52.360 So either the police officer looking at the supernovae is wrong, 254 00:11:52.759 --> 00:11:55.399 maybe our understanding of cosmic dust is off, or our 255 00:11:55.480 --> 00:11:57.080 light bulbs aren't as standard as we. 256 00:11:57.080 --> 00:11:59.720 Think, or the officer looking at the baby picture is. 257 00:11:59.720 --> 00:12:02.559 Wrong, or the law of the road itself is wrong. 258 00:12:02.759 --> 00:12:05.519 The physics we're using to connect to the two is broken. 259 00:12:05.679 --> 00:12:08.279 Exactly. If the measurements are as good as we think 260 00:12:08.320 --> 00:12:13.080 they are, then our standard model, our entire understanding of 261 00:12:13.080 --> 00:12:15.960 how the universe evolved, is missing a piece. We get 262 00:12:15.960 --> 00:12:18.679 a tiebreaker, or a whole new rule of physics. 263 00:12:18.799 --> 00:12:21.679 And this brings us to the new research this paper 264 00:12:21.799 --> 00:12:25.840 published today, authored by Pagosian, Jadamziic and Abel. They are 265 00:12:25.879 --> 00:12:29.120 suggesting the missing piece is magnetism. 266 00:12:28.720 --> 00:12:32.440 Yes, primordial magnetic fields. And to understand why this is 267 00:12:32.480 --> 00:12:34.919 such a compelling idea, we actually have to talk about 268 00:12:34.960 --> 00:12:38.759 another mystery, a totally different problem in astrophysics that seems 269 00:12:38.879 --> 00:12:41.320 unrelated but might just be the key to the whole thing. 270 00:12:41.559 --> 00:12:43.600 I love a good subplot. What's the second mystery. 271 00:12:43.679 --> 00:12:46.279 It's the mystery of where cosmic magnetic fields come from. 272 00:12:46.279 --> 00:12:48.399 In the first place, I feel like we take magnetism 273 00:12:48.440 --> 00:12:50.600 for granted. I mean, Earth has a magnetic field. It 274 00:12:50.639 --> 00:12:53.519 protects us from solar radiation. The Sun has one, We 275 00:12:53.559 --> 00:12:56.559 have magnets on our fridge. It just seems like it's everywhere. 276 00:12:56.799 --> 00:13:00.279 It is everywhere, And we understand planetary instellar fee fields 277 00:13:00.279 --> 00:13:05.279 pretty well. They're generated by dynamos basically churning conducting fluids 278 00:13:05.399 --> 00:13:08.960 inside the planet or star. The spinning molten iron in 279 00:13:09.039 --> 00:13:11.440 Earth's core is what creates our field. 280 00:13:11.600 --> 00:13:13.639 It's like a generator, a natural. 281 00:13:13.279 --> 00:13:16.600 Generator, yes, But when we look out at the cosmos 282 00:13:16.639 --> 00:13:20.879 on a grander scale, we see something puzzling. We see 283 00:13:21.120 --> 00:13:25.039 massive magnetic fields threading through entire galaxies. 284 00:13:25.200 --> 00:13:28.720 You mean the Milky Way itself is magnetic, very much so, and. 285 00:13:28.639 --> 00:13:31.320 Not just galaxies. We see magnetic fields in the gas 286 00:13:31.399 --> 00:13:34.240 between galaxies and clusters, and we think they might even 287 00:13:34.320 --> 00:13:37.879 exist in the great cosmic voids, the emptiest parts of space. 288 00:13:38.240 --> 00:13:40.000 The question is where did those come from? 289 00:13:40.200 --> 00:13:42.200 It's the classic chicken and egg problem, isn't it. Did 290 00:13:42.240 --> 00:13:45.120 the galaxy form first and then spin up a magnetic field, 291 00:13:45.399 --> 00:13:47.679 or was a magnetic field there first, maybe helping the 292 00:13:47.679 --> 00:13:48.600 galaxy to form. 293 00:13:48.639 --> 00:13:51.399 And here's the problem with the galaxy first idea. It 294 00:13:51.480 --> 00:13:54.240 is very, very difficult to explain the strength of the 295 00:13:54.240 --> 00:13:57.240 galactic fields we see today just by spinning them up 296 00:13:57.240 --> 00:14:00.000 from nothing. You need a seed You need some tiny 297 00:14:00.279 --> 00:14:03.320 initial bit of magnetism to get the dynamo process started. 298 00:14:03.600 --> 00:14:05.960 A starter used for the sourdough, if you will. 299 00:14:06.279 --> 00:14:09.679 That's a perfect analogy. Without a seed field, the math 300 00:14:09.840 --> 00:14:12.639 just doesn't work to grow the strong fields we observe. 301 00:14:13.519 --> 00:14:16.279 And this is what leads to the theory of primordial 302 00:14:16.320 --> 00:14:20.000 magnetic fields. The idea is that magnetism wasn't made by 303 00:14:20.039 --> 00:14:22.559 stars and galaxies. It arose in the chaos of the 304 00:14:22.559 --> 00:14:23.480 Big Bang itself. 305 00:14:23.720 --> 00:14:27.039 So the universe was born with magnetism warven right into 306 00:14:27.080 --> 00:14:28.440 the fabric of space time. 307 00:14:28.559 --> 00:14:31.399 That's the theory. It could have been generated during cosmic 308 00:14:31.399 --> 00:14:34.159 inflation or during one of the big phase transitions in 309 00:14:34.200 --> 00:14:36.600 the first fraction of a second. But for a long 310 00:14:36.639 --> 00:14:39.399 time this was just a hypothesis to solve that one problem, 311 00:14:39.440 --> 00:14:40.519 the seed problem. 312 00:14:40.879 --> 00:14:45.519 But now these authors Pagosian, Jadamziic, and Abel are asking 313 00:14:45.559 --> 00:14:49.639 a much bigger question. They're asking, if these primordial fields exist, 314 00:14:49.799 --> 00:14:52.679 could they do more than just seed galaxies? Could they 315 00:14:52.720 --> 00:14:55.200 actually fix the Hubble tension exactly? 316 00:14:55.519 --> 00:14:58.200 They wondered if this one invisible force could solve two 317 00:14:58.200 --> 00:15:00.960 of the biggest problems in cosmology at the same time, 318 00:15:01.440 --> 00:15:04.279 the seed problem and the broken speedometer problem. 319 00:15:04.440 --> 00:15:07.320 Okay, so let's get into the mechanics of this. How 320 00:15:07.360 --> 00:15:11.000 does a magnetic field, primordial or not, actually change the 321 00:15:11.080 --> 00:15:14.440 expansion rate of the universe. It feels like those two 322 00:15:14.480 --> 00:15:15.960 things shouldn't be related at all. 323 00:15:16.360 --> 00:15:19.000 To understand the mechanism, we have to go back to 324 00:15:19.039 --> 00:15:22.000 that moment I mentioned earlier, the formation of the cosmic 325 00:15:22.039 --> 00:15:25.919 microwave background. It's an era of the universe called recombination. 326 00:15:26.240 --> 00:15:28.559 Right, let's set the scene. The universe is about three 327 00:15:28.639 --> 00:15:32.879 hundred thousand years old. It's hot, it's dense, it's a soup. 328 00:15:32.840 --> 00:15:35.759 It's a plasma, and that means it's just too hot 329 00:15:35.759 --> 00:15:39.279 for atoms to hold together. The electrons, which have a 330 00:15:39.320 --> 00:15:42.639 negative charge have been ripped away from the protons, which 331 00:15:42.639 --> 00:15:45.600 have a positive charge. They're just flying around independently. 332 00:15:45.679 --> 00:15:49.279 And because those electrons are free, they scatter light like crazy, 333 00:15:49.440 --> 00:15:49.720 like a. 334 00:15:49.679 --> 00:15:54.159 Thick, impenetrable fog. A photon, a particle of light, can't 335 00:15:54.200 --> 00:15:56.840 travel more than a tiny distance before it smacks into 336 00:15:56.879 --> 00:15:59.120 a free electron and gets bounced in a random direction, 337 00:16:00.000 --> 00:16:01.200 and the universe is opaque. 338 00:16:01.240 --> 00:16:04.639 But all this time, the universe is expanding, and it's cooling. 339 00:16:04.320 --> 00:16:07.240 Down right, And eventually it gets cool enough down to 340 00:16:07.240 --> 00:16:11.240 about three thousand kelvin that the protons can finally capture 341 00:16:11.240 --> 00:16:14.080 the electrons, they can finally bond. They form the first 342 00:16:14.320 --> 00:16:15.759 neutral hydrogen atoms. 343 00:16:15.840 --> 00:16:16.799 They hold hands. 344 00:16:16.960 --> 00:16:19.840 And this is the crucial part. Neutral hydrogen does not 345 00:16:19.919 --> 00:16:23.600 scatter light the same way the fog lifts. The universe 346 00:16:23.679 --> 00:16:27.519 in an instant goes from opaque to transparent. That moment 347 00:16:27.639 --> 00:16:28.639 is called recombination. 348 00:16:29.240 --> 00:16:32.840 Okay, so that's the standard story. Now let's throw a 349 00:16:32.879 --> 00:16:37.159 primordial magnetic field into that hot, foggy soup. What changes. 350 00:16:37.360 --> 00:16:40.600 Well, magnetic fields interact with charged particles. They push and 351 00:16:40.600 --> 00:16:42.960 pall on them. It's called the Lorentz force. So now 352 00:16:43.080 --> 00:16:45.600 imagine you have this plasma. Gravity is trying to pull 353 00:16:45.639 --> 00:16:48.720 the matter together into little clumps, but the intense pressure 354 00:16:48.759 --> 00:16:50.679 of all that radiation is trying to push it apart. 355 00:16:50.759 --> 00:16:51.919 It's a constant tug of war. 356 00:16:52.080 --> 00:16:54.360 And the magnetic field jumps in as a third player. 357 00:16:54.519 --> 00:16:56.960 Yes, And what it does is it creates what we 358 00:16:57.039 --> 00:17:00.799 call baryon clumping. The magnetic fields create these lowize spots 359 00:17:00.799 --> 00:17:03.559 of pressure and tension in the plasma. They force the 360 00:17:03.679 --> 00:17:06.960 charged particles, the protons and electrons, to clump together just 361 00:17:07.039 --> 00:17:09.400 a little bit more than gravity would do on its own. 362 00:17:09.720 --> 00:17:12.400 So the soup gets lumpy, a little bit lumpier than 363 00:17:12.400 --> 00:17:12.960 it would have been. 364 00:17:13.119 --> 00:17:15.880 The soup gets lumpy. And here is the key bit 365 00:17:15.920 --> 00:17:22.000 of chemistry. Recombination. The process of protons and electrons forming 366 00:17:22.079 --> 00:17:25.440 those hydrogen atoms happens faster in denser regions. 367 00:17:25.680 --> 00:17:26.200 Why is that? 368 00:17:26.640 --> 00:17:29.119 Think of it like a crowded party or a singles mixer. 369 00:17:29.759 --> 00:17:32.000 If you have one hundred people spread out across a 370 00:17:32.079 --> 00:17:35.119 huge football field, it might take a long time for 371 00:17:35.119 --> 00:17:36.359 people to find each other and. 372 00:17:36.319 --> 00:17:37.880 Pair up right the too far apart. 373 00:17:38.039 --> 00:17:40.319 But if you crowd all one hundred people into one 374 00:17:40.319 --> 00:17:43.519 corner of the room, they're constantly bumping into each other, 375 00:17:43.519 --> 00:17:45.200 They're going to pair up much much faster. 376 00:17:45.640 --> 00:17:49.920 That is a surprisingly perfect analogy. So by clumping the 377 00:17:49.960 --> 00:17:53.400 matter together, the magnetic fields make it easier for protons 378 00:17:53.440 --> 00:17:55.839 to find their electron dance partners exactly. 379 00:17:56.160 --> 00:17:58.880 And the consequence of that is that recombination as a 380 00:17:58.880 --> 00:18:00.519 whole finishes sooner, sooner. 381 00:18:00.720 --> 00:18:03.680 That's the key word, isn't it. The fog lifts earlier 382 00:18:03.720 --> 00:18:05.519 than our standard model assumes it does. 383 00:18:05.839 --> 00:18:09.799 The universe becomes transparent earlier. The baby picture is taken 384 00:18:09.839 --> 00:18:11.319 earlier in cosmic history. 385 00:18:11.519 --> 00:18:13.960 Okay, I'm following the physics, I think, but I'm still 386 00:18:13.960 --> 00:18:16.960 missing the final connection to the sixty seven versus seventy 387 00:18:17.000 --> 00:18:20.440 three number. Why does the fog lifting a bit early 388 00:18:20.599 --> 00:18:22.240 change the speed reading we get today? 389 00:18:22.400 --> 00:18:24.200 This is the most technical part, but it's also the 390 00:18:24.200 --> 00:18:27.720 most elegant. Nora method B the indirect method, the one 391 00:18:27.799 --> 00:18:28.920 using the baby picture. 392 00:18:28.720 --> 00:18:29.839 The one that gives us sixty seven. 393 00:18:29.920 --> 00:18:33.039 Yes, it relies on measuring the size of the patterns 394 00:18:33.039 --> 00:18:36.279 in the CMB. Those patterns, those hot and cold spots, 395 00:18:36.519 --> 00:18:39.519 are essentially sound waves that were traveling through the plasma. 396 00:18:39.640 --> 00:18:42.839 Sound waves in the early universe. That's just wild to 397 00:18:42.880 --> 00:18:43.319 think about. 398 00:18:43.440 --> 00:18:47.079 We call them veryan acoustic oscillations. Imagine dropping a stone 399 00:18:47.079 --> 00:18:50.640 in a pond. Ripples spread out. In the early universe. 400 00:18:50.680 --> 00:18:53.839 These ripples of pressure traveled through the plasma until the 401 00:18:53.880 --> 00:18:57.319