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 --> 00:00:30.079 Look at the clock on your wall right now, or 8 00:00:30.320 --> 00:00:32.200 you know, check the time on your phone, or just 9 00:00:32.280 --> 00:00:33.679 glance at the watch on your wrist. 10 00:00:33.759 --> 00:00:35.840 Yeah, take us up and to really look at it. 11 00:00:35.719 --> 00:00:40.960 Because every single time that secondhand ticks forward or that 12 00:00:41.039 --> 00:00:45.799 digital number rolls over, well, it's lying. 13 00:00:45.560 --> 00:00:48.759 To you, completely lying, and it's it's funny because we 14 00:00:48.840 --> 00:00:53.359 all share this incredibly deep, almost unquestionable intuition about what 15 00:00:53.399 --> 00:00:54.280 those numbers mean. 16 00:00:54.560 --> 00:00:57.119 Right. We go through our entire lives operating on this 17 00:00:57.159 --> 00:01:00.759 assumption that time is a universal river, and you, me, 18 00:01:01.039 --> 00:01:03.240 the listener, we are all just floating in that exact 19 00:01:03.280 --> 00:01:07.480 same river, being carried downstream with the exact same speed exactly. 20 00:01:07.560 --> 00:01:09.840 I mean, the fundamental assumption of human existence is that 21 00:01:09.920 --> 00:01:12.280 a minute for you sitting right there, right now, is 22 00:01:12.319 --> 00:01:14.719 exactly the same as a minute for someone making coffee 23 00:01:14.719 --> 00:01:17.560 on the other side of the planet, or a minute 24 00:01:17.560 --> 00:01:19.079 for an astronaut orbiting the Earth. 25 00:01:19.319 --> 00:01:20.159 It's just a given. 26 00:01:20.920 --> 00:01:25.200 But that intuition is it's mathematically and observably wrong. The 27 00:01:25.280 --> 00:01:28.159 universal river of time is just a localized illusion. 28 00:01:28.400 --> 00:01:31.799 Wow. Okay, so this isn't some abstract, you know, philosophical wordplay. 29 00:01:32.159 --> 00:01:35.959 You are saying that our literal physical understanding of time, 30 00:01:36.079 --> 00:01:38.480 this masterclock we think is ticking away in the background 31 00:01:38.480 --> 00:01:39.719 of the universe, is just. 32 00:01:39.719 --> 00:01:43.359 Broken, completely shattered. Yeah. I mean the concept of a 33 00:01:43.400 --> 00:01:48.439 single steady master clock governing everything everywhere. It simply does 34 00:01:48.599 --> 00:01:53.159 not exist. Time is local, local, Yeah, it's malleable. It 35 00:01:53.200 --> 00:01:55.640 does not flow at the same rate for all observers. 36 00:01:55.840 --> 00:01:59.840 The actual fabric of time stretches and compresses, depending entirely 37 00:02:00.239 --> 00:02:00.959 on two things. 38 00:02:01.079 --> 00:02:01.959 Okay, what are they? 39 00:02:02.159 --> 00:02:06.040 How fast you're moving through space and how deep you're 40 00:02:06.120 --> 00:02:08.080 resting within a gravitational field. 41 00:02:08.159 --> 00:02:10.680 Okay, let's unpack this, because this means we are talking 42 00:02:10.719 --> 00:02:14.759 about the literal, structural source code of reality. 43 00:02:14.280 --> 00:02:15.159 Here, we really are. 44 00:02:15.280 --> 00:02:18.199 We're exploring how Albert Einstein realized the universe was playing 45 00:02:18.199 --> 00:02:21.919 this massive trick on us, and how this totally counterintuitive. 46 00:02:21.919 --> 00:02:25.280 Physics is secretly the engine running our modern world right now? 47 00:02:25.400 --> 00:02:27.960 Yeah, and why the whole concept of now, like this 48 00:02:28.039 --> 00:02:31.039 specific moment you and I are experiencing, might actually just 49 00:02:31.080 --> 00:02:33.120 be a psychological hallucination. 50 00:02:32.879 --> 00:02:38.719 Which is terrifying and fascinating because we are talking about cold, hard, 51 00:02:39.240 --> 00:02:40.520 miserable facts today. 52 00:02:40.719 --> 00:02:44.680 Absolutely, if you take two identical clocks, right, synchronize them 53 00:02:44.680 --> 00:02:47.560 perfectly so they tick in absolute unison, and then you 54 00:02:47.599 --> 00:02:50.280 just put them on different paths through space time, they 55 00:02:50.319 --> 00:02:51.680 will diverge, like they. 56 00:02:51.520 --> 00:02:54.680 Will physically show different times when you bring them back together. 57 00:02:54.840 --> 00:02:59.199 Yes, and neither clock is broken, neither has a mechanical flaw. 58 00:02:59.280 --> 00:03:02.120 They just traveled through different densities. 59 00:03:01.439 --> 00:03:05.319 Of time, different densities of time. That's such a wild phrase, eh, 60 00:03:05.479 --> 00:03:06.960 And this has been tested. 61 00:03:06.639 --> 00:03:09.879 Right, oh, tested and confirmed by experiment after experiment for 62 00:03:09.960 --> 00:03:13.560 over a century. And honestly, if we didn't mathematically correct 63 00:03:13.599 --> 00:03:16.159 for this warping of time every single second of the day, 64 00:03:16.599 --> 00:03:20.479 our twenty first century infrastructure would literally tear itself apart 65 00:03:20.479 --> 00:03:21.280 before lunchtime. 66 00:03:21.560 --> 00:03:24.199 Okay, So to really grasp why that clock on the 67 00:03:24.199 --> 00:03:27.199 wall is feeding us a localized fiction, we actually have 68 00:03:27.280 --> 00:03:29.240 to stop looking at time. Right, we have to look 69 00:03:29.280 --> 00:03:29.639 at light. 70 00:03:29.919 --> 00:03:32.520 Yeah, because to understand how time bends, you have to 71 00:03:32.639 --> 00:03:35.280 establish the one thing in the entire universe that refuses 72 00:03:35.319 --> 00:03:38.439 to bend, the speed of light exactly. So to trace 73 00:03:38.479 --> 00:03:41.039 that realization, we really need to go back to nineteen 74 00:03:41.080 --> 00:03:44.879 oh five, to the first of Albert Einstein's two big breakthroughs. 75 00:03:44.400 --> 00:03:46.240 Write his paper on special relativity. 76 00:03:46.360 --> 00:03:49.400 Yeah, at the time, physics was still living in the 77 00:03:49.400 --> 00:03:53.639 house Isaac Newton built. Newtonian physics assumes space is just 78 00:03:53.680 --> 00:03:57.879 an empty static stage and time is the unchangeable clock 79 00:03:57.960 --> 00:03:59.599 on the wall of that stage. 80 00:04:00.000 --> 00:04:02.120 Einstein basically took a sledgehammer to that. 81 00:04:02.400 --> 00:04:06.039 He really did. He looked at objects moving at constant velocities, 82 00:04:06.080 --> 00:04:09.719 and he built his entire theory on a single, uncompromising rule. 83 00:04:10.479 --> 00:04:12.639 The speed of light in a vacuum is exactly the 84 00:04:12.719 --> 00:04:15.280 same for all observers, no matter how fast the light 85 00:04:15.319 --> 00:04:16.839 source or the observer is moving. 86 00:04:16.959 --> 00:04:19.079 Okay, on the surface, if you don't know the physics, 87 00:04:19.120 --> 00:04:22.160 that sounds kind of mundane. Light goes fast, and it 88 00:04:22.279 --> 00:04:23.639 always goes the same amount of fast. 89 00:04:23.720 --> 00:04:25.439 Right, it doesn't sound revolutionary, But. 90 00:04:25.480 --> 00:04:29.120 Let's map that onto how everyday objects work, because that's 91 00:04:29.160 --> 00:04:32.959 where the absolute absurdity of Einstein's rule kicks him. Think 92 00:04:32.959 --> 00:04:35.759 about a highway. If I'm driving down the highway at 93 00:04:35.759 --> 00:04:38.680 sixteen miles an hour and another car passes me doing 94 00:04:38.759 --> 00:04:42.240 seventy my perspective from the driver's seat is that the 95 00:04:42.240 --> 00:04:44.240 passing car is only creeping ahead of me at ten 96 00:04:44.279 --> 00:04:44.759 miles an. 97 00:04:44.639 --> 00:04:48.079 Hour, exactly because velocities are additive and subtractive. 98 00:04:48.199 --> 00:04:50.360 Right. If I throw a baseball at one hundred miles 99 00:04:50.360 --> 00:04:51.879 an hour out the front of a train that's moving 100 00:04:51.920 --> 00:04:54.240 at one hundred miles an hour, someone standing on the 101 00:04:54.279 --> 00:04:57.839 platform sees that baseball traveling at two hundred miles an hour. 102 00:04:58.079 --> 00:04:59.519 That makes logical sense. 103 00:04:59.319 --> 00:05:03.199 To us, because the human brain relies on Galilean relativity, 104 00:05:03.319 --> 00:05:07.399 that simple addition of speeds. But light completely refuses to 105 00:05:07.439 --> 00:05:08.319 play by that rule. 106 00:05:08.560 --> 00:05:10.600 So how does light behave in that scenario. 107 00:05:11.079 --> 00:05:15.480 Well, imagine you're flying in a hyperadvanced spaceship at ninety 108 00:05:15.519 --> 00:05:16.720 nine percent of the speed of light. 109 00:05:16.839 --> 00:05:19.040 Okay, moving incredibly fast. 110 00:05:18.839 --> 00:05:21.560 Right, and you shine a flashlight at the front window. 111 00:05:21.879 --> 00:05:24.480 That beam of light does not travel at one hundred 112 00:05:24.480 --> 00:05:26.480 and ninety nine percent of the speed of light relative 113 00:05:26.519 --> 00:05:27.600 to someone watching. 114 00:05:27.319 --> 00:05:29.959 You, because there's a speed limit exactly. 115 00:05:30.319 --> 00:05:32.879 But it also doesn't just pull away from your ship 116 00:05:32.879 --> 00:05:35.120 at a mere one percent of the speed of light, 117 00:05:35.160 --> 00:05:37.399 which is what the highway logic would suggest, right. 118 00:05:37.480 --> 00:05:41.000 Seventy minus sixty is ten, so light speed minus ninety 119 00:05:41.079 --> 00:05:42.439 nine percent should be one percent. 120 00:05:42.519 --> 00:05:45.839 But it isn't. From your perspective inside the ship, that 121 00:05:45.879 --> 00:05:48.680 beam pulls away from you at exactly the full speed 122 00:05:48.680 --> 00:05:51.399 of light. Wait, and from the perspective of someone standing 123 00:05:51.439 --> 00:05:54.560 still on a planet watching you fly by, that exact 124 00:05:54.560 --> 00:05:57.600 same beam of light is also moving at exactly the 125 00:05:57.639 --> 00:05:58.279 speed of light. 126 00:05:58.480 --> 00:06:01.160 Okay, so this is the exact moment the universe backs 127 00:06:01.240 --> 00:06:05.120 us into a mathematical corner. You have two people moving 128 00:06:05.120 --> 00:06:09.160 at vastly different speeds, observing the exact same beam of light, 129 00:06:09.279 --> 00:06:11.639 and they both measure it moving at the exact same 130 00:06:11.680 --> 00:06:13.360 speed relatives to themselves. 131 00:06:13.439 --> 00:06:14.959 Yeah, which should be impossible. 132 00:06:15.279 --> 00:06:19.399 Right. To make that true, the universe has to cheat. 133 00:06:19.839 --> 00:06:21.879 It has to alter something else to keep the speed 134 00:06:21.879 --> 00:06:25.279 of light constant. Let's walk through the light clock thought experiment, 135 00:06:25.279 --> 00:06:28.639 because visualizing the geometry here is really what finally made 136 00:06:28.639 --> 00:06:29.319 this click for me. 137 00:06:29.560 --> 00:06:32.160 The light clock is perfect for this. It strips away 138 00:06:32.160 --> 00:06:35.839 all the mechanical complications, you know, gears and springs. Just 139 00:06:35.959 --> 00:06:39.000 imagine the simplest possible timekeeping device. 140 00:06:39.120 --> 00:06:40.120 Okay, I'm fixturing it. 141 00:06:40.240 --> 00:06:44.360 You have two highly polished mirrors facing each other, one 142 00:06:44.399 --> 00:06:46.519 mounted on the floor and one mounted on the ceiling 143 00:06:46.519 --> 00:06:49.240 directly above it, and a single pulse of light is 144 00:06:49.360 --> 00:06:52.439 trapped between them, just bouncing endlessly up and down. 145 00:06:52.600 --> 00:06:55.079 Got it. And we define one tick of this clock 146 00:06:55.560 --> 00:06:57.879 as the time it takes for the light pulse to 147 00:06:58.000 --> 00:07:00.800 leave the bottom mirror, hit the top mirror, and bounce. 148 00:07:00.560 --> 00:07:02.879 Back down exactly, up and down, tick, up and down. 149 00:07:02.959 --> 00:07:05.639 Tick. Okay. Now, let's take this light clock and mount 150 00:07:05.720 --> 00:07:08.759 it inside a transparent spaceship, and that spaceship is going 151 00:07:08.800 --> 00:07:11.759 to fly past me at a massive velocid, let's say, 152 00:07:11.759 --> 00:07:14.639 half the speed of light. I'm standing perfectly still on 153 00:07:14.720 --> 00:07:17.800 an asteroid watching the ship zoom by from left to right. 154 00:07:18.000 --> 00:07:21.680 So let's isolate the perspectives here, starting with the astronaut 155 00:07:21.720 --> 00:07:25.279 inside the spaceship. From their point of view, they're perfectly 156 00:07:25.319 --> 00:07:29.120 stationary inside their cabin. The floor is below them, the 157 00:07:29.199 --> 00:07:32.399 ceiling is above them. They watch the light clock, and 158 00:07:32.439 --> 00:07:35.240 they see the pulse of light traveling perfectly straight up 159 00:07:35.319 --> 00:07:37.000 and perfectly straight down, So. 160 00:07:37.040 --> 00:07:39.680 The distance the light travels for one tick is just 161 00:07:39.759 --> 00:07:41.279 twice the height of the cabin, right. 162 00:07:41.680 --> 00:07:45.879 Simple. But your perspective standing outside watching the ship fly 163 00:07:46.040 --> 00:07:47.920 past is entirely. 164 00:07:47.519 --> 00:07:49.279 Different because the ship is moving. 165 00:07:49.560 --> 00:07:52.920 Yes, when the light pulse leaves the bottom mirror, the 166 00:07:53.000 --> 00:07:55.800 ship is at let's say position A, But by the 167 00:07:55.839 --> 00:07:58.000 time the light travels up to hit the ceiling mirror, 168 00:07:58.319 --> 00:08:01.079 the entire ship has moved forward to position. 169 00:08:00.800 --> 00:08:03.720 B oh right. So from my vantage point outside, the 170 00:08:03.800 --> 00:08:06.399 light pulse didn't go straight up. It had to travel 171 00:08:06.480 --> 00:08:09.560 diagonally forward and upward to catch the moving ceiling. 172 00:08:09.279 --> 00:08:12.600 Mirror exactly, and the geometry continues on the return trip. 173 00:08:13.000 --> 00:08:15.000 By the time the light bounces off the ceiling and 174 00:08:15.040 --> 00:08:17.639 returns to the floor mirror, the ship has moved even 175 00:08:17.800 --> 00:08:21.240 further forward to position C, so the light has. 176 00:08:21.120 --> 00:08:23.199 To travel diagonally forward and downward. 177 00:08:23.560 --> 00:08:27.560 You got it. From your stationary perspective outside the ship, 178 00:08:28.000 --> 00:08:30.720 the light pulse isn't moving in a vertical line at all. 179 00:08:31.040 --> 00:08:34.519 It's tracing a zigzag pattern, a series of long diagonomal 180 00:08:34.600 --> 00:08:35.519 lines through space. 181 00:08:35.720 --> 00:08:39.159 And here's where the trap closes on us. Because basic 182 00:08:39.200 --> 00:08:42.960 pythagore and geometry tells us that a diagonal line connecting 183 00:08:42.960 --> 00:08:46.840 two horizontal points is always physically longer than a straight 184 00:08:46.919 --> 00:08:48.039 vertical line between them. 185 00:08:48.120 --> 00:08:49.600 It has to be so. 186 00:08:49.679 --> 00:08:52.159 The path the light took from my perspective outside the 187 00:08:52.200 --> 00:08:55.720 ship is a definitively longer distance than the path it 188 00:08:55.720 --> 00:08:58.200 took from the astronaut's perspective inside the ship. 189 00:08:58.360 --> 00:09:01.759 And this is where we apply einstein unbreakable rule. And 190 00:09:01.840 --> 00:09:05.840 the equation for speed is universally simple. Right. Speed equals 191 00:09:05.879 --> 00:09:09.159 distance divided by time. Right, we've established that the distance 192 00:09:09.200 --> 00:09:11.840 the light traveled from your perspective is greater than the 193 00:09:11.840 --> 00:09:15.000 distance it traveled from the astronaut's perspective, but the speed 194 00:09:15.039 --> 00:09:17.879 of the light cannot change. It must be identical for 195 00:09:17.960 --> 00:09:18.399 both of you. 196 00:09:18.799 --> 00:09:21.240 Right, So the distance is a larger number for me, 197 00:09:21.480 --> 00:09:24.240 and the speed is locked as a constant. The math 198 00:09:24.480 --> 00:09:27.039 physically forces the time to be a larger number. Two. 199 00:09:27.279 --> 00:09:29.799 The only way to balance the equation is if the 200 00:09:29.840 --> 00:09:32.759 time it took for the clock to tick was literally 201 00:09:32.840 --> 00:09:34.840 longer for me than it was for the astronaut. 202 00:09:34.879 --> 00:09:38.840 The inescapable mathematical reality is that the moving clock ticks 203 00:09:38.960 --> 00:09:43.120 more slowly than the stationary one from your perspective. Looking 204 00:09:43.159 --> 00:09:47.000 into that moving ship. Time itself is dragging. The physical 205 00:09:47.039 --> 00:09:50.279 progression of reality has slowed down to compensate for the 206 00:09:50.399 --> 00:09:52.919 longer distance the light had to travel just. 207 00:09:52.879 --> 00:09:55.679 To ensure the speed of light remains perfectly constant. 208 00:09:55.840 --> 00:09:58.600 Yes, this is special relativistic time dilation. 209 00:09:58.919 --> 00:10:00.919 You know. I always try to find the trick here 210 00:10:01.480 --> 00:10:04.039 to say, well, it's just an optical illusion. The light 211 00:10:04.159 --> 00:10:06.200 is just taking longer to reach my eyeballs because the 212 00:10:06.240 --> 00:10:09.600 ship is moving away. But that's not what's happening, is it. 213 00:10:09.799 --> 00:10:13.600 No, not at all. The actual biological aging of the astronaut, 214 00:10:13.799 --> 00:10:16.320 the decay of atoms in the ship's hull, the thoughts 215 00:10:16.360 --> 00:10:20.480 firing in the astronaut's brain, every single localized physical process 216 00:10:20.600 --> 00:10:23.039 is happening in slow motion relative to the rest of 217 00:10:23.080 --> 00:10:23.639 the universe. 218 00:10:23.799 --> 00:10:27.320 It's a genuine asymmetry in the fundamental rate at which 219 00:10:27.360 --> 00:10:31.039 reality unfolds. It's not an artifact of observation, right. 220 00:10:31.240 --> 00:10:34.720 Observers in different states of uniformation experience different intervals of 221 00:10:34.759 --> 00:10:36.360 time between the exact sam events. 222 00:10:36.519 --> 00:10:39.840 But the immediate counter argument anyone would have is, Okay, 223 00:10:40.039 --> 00:10:43.080 if motion slows down time, why don't I experience a 224 00:10:43.120 --> 00:10:46.200 time warp when I merge onto the interstate. Why don't 225 00:10:46.200 --> 00:10:49.960 my watch in my car's dashboard clock stay perfectly syncd Well. 226 00:10:50.000 --> 00:10:52.559 The physics is governed by a mathematical term called the 227 00:10:52.639 --> 00:10:56.320 Lorentz factor, and this factor dictates exactly how much time dilates, 228 00:10:56.360 --> 00:10:59.399 how much length contracts, and how much mass increases as 229 00:10:59.440 --> 00:11:01.519 an object's velocity approaches the speed of light. 230 00:11:02.039 --> 00:11:03.279 Okay, and the key. 231 00:11:03.159 --> 00:11:06.480 To understanding why our daily lives feel strictly Newtonian is 232 00:11:06.519 --> 00:11:09.639 the shape of that Lorentz curve. At the relatively sluggish 233 00:11:09.679 --> 00:11:13.399 speeds humans travel at, walking, driving a car, even launching 234 00:11:13.399 --> 00:11:16.320 a rocket into orbit, the velocity is such a tiny 235 00:11:16.360 --> 00:11:18.919 fraction of the speed of light that the Lorentz factor 236 00:11:18.919 --> 00:11:20.879 remains incredibly close to one. 237 00:11:20.759 --> 00:11:24.240 Meaning the time dilation multiplier is basically like one point 238 00:11:24.360 --> 00:11:27.799 zero zero zero zero zero zero zero one. It's so 239 00:11:27.919 --> 00:11:30.960 infinitesimally small that it completely falls beneath the threshold of 240 00:11:31.000 --> 00:11:31.720 human perception. 241 00:11:32.159 --> 00:11:34.679 Exactly to put a number on it, If you board 242 00:11:34.679 --> 00:11:37.360 a commercial jetliner and fly at a cruising speed of 243 00:11:37.440 --> 00:11:41.559 roughly one thousand kilometers per hour, you are absolutely experiencing 244 00:11:41.639 --> 00:11:46.000 special relativistic time dilation. I am yes, but the amount 245 00:11:46.039 --> 00:11:48.679 your local time slows down compared to someone on the 246 00:11:48.679 --> 00:11:52.039 ground is measured in a few nanoseconds per hour. 247 00:11:52.159 --> 00:11:54.759 A nanosecond being one billionth of a second. 248 00:11:54.840 --> 00:11:58.039 Right, So the biological difference is practically non existent to 249 00:11:58.080 --> 00:11:58.720 our senses. 250 00:11:58.799 --> 00:12:01.759 But the Lorenz factor isn't linear, is it. It's an asymptote. 251 00:12:02.799 --> 00:12:06.080 When we start pushing the velocity higher, the math stops 252 00:12:06.120 --> 00:12:10.000 being a rounding air and becomes violently dramatic. Let's say 253 00:12:10.039 --> 00:12:13.120 we finally invent a propulsion drive. They can push a 254 00:12:13.159 --> 00:12:15.320 spacecraft to ninety percent of the speed of light. 255 00:12:15.519 --> 00:12:17.559 At ninety percent of the speed of light, the Lorentz 256 00:12:17.600 --> 00:12:20.639 curve spikes sharply. Time for the crew on that ship 257 00:12:20.679 --> 00:12:22.519 would run at less than half the rate of a 258 00:12:22.519 --> 00:12:23.960 stationary observer on Earth. 259 00:12:24.039 --> 00:12:26.559 So for every hour that ticks by on the ship's. 260 00:12:26.240 --> 00:12:29.200 Clock, more than two hours pass for mission control back home. 261 00:12:29.639 --> 00:12:32.399 Wow, Let's push the engines to ninety nine percent of 262 00:12:32.399 --> 00:12:33.039 the speed of light. 263 00:12:33.279 --> 00:12:37.240 At ninety nine percent, the dilation becomes severe. Time on 264 00:12:37.279 --> 00:12:40.080 the ship runs at roughly one seventh the normal rate. 265 00:12:40.600 --> 00:12:43.759 If the crew spends a single year traveling at that speed, 266 00:12:43.919 --> 00:12:45.799 seven years will have evaporated on Earth. 267 00:12:45.960 --> 00:12:47.840 What about ninety nine point nine percent. 268 00:12:47.960 --> 00:12:51.000 The closer you shave the margin to the absolute speed limit, 269 00:12:51.399 --> 00:12:55.240 the more extreme the temporal distortion gets. At ninety nine 270 00:12:55.279 --> 00:12:58.200 point nine percent of the speed of light, time slows 271 00:12:58.240 --> 00:13:01.200 to about one twenty second of the stationary rate. The 272 00:13:01.240 --> 00:13:04.879 denominator in the Lorenz equation shrinks towards zero, which means 273 00:13:04.919 --> 00:13:07.519 the time dilation factor explodes toward infinity. 274 00:13:07.720 --> 00:13:10.039 And if we somehow breach the limit, if we hit 275 00:13:10.080 --> 00:13:12.320 exactly one hundred percent of the speed of light, if. 276 00:13:12.200 --> 00:13:15.000 An object with mass could somehow reach the exact speed 277 00:13:15.039 --> 00:13:18.159 of light, the mathematics dictate that time would stop entirely, 278 00:13:18.480 --> 00:13:21.759 just freeze. The internal clock of that object would freeze. 279 00:13:21.799 --> 00:13:23.720 I mean, think about a photon. A photon is a 280 00:13:23.759 --> 00:13:26.639 particle of light, so it naturally travels at the speed 281 00:13:26.639 --> 00:13:29.080 of light. It essentially experiences no time. 282 00:13:29.159 --> 00:13:32.399 Wait, really no time at all none. 283 00:13:32.440 --> 00:13:35.720 From a photon's perspective, the moment it is emitted from 284 00:13:35.720 --> 00:13:38.840 a star and the moment it strikes your retina millions 285 00:13:38.840 --> 00:13:40.960 of years later happens simultaneously. 286 00:13:41.120 --> 00:13:42.159 That is mind blowing. 287 00:13:42.360 --> 00:13:46.799 But for anything with mass, a human, a spaceship, even 288 00:13:46.840 --> 00:13:50.519 a single proton, reaching the speed of light is physically impossible. 289 00:13:51.240 --> 00:13:55.080 As the Lorentz factor approaches infinity, the energy required to 290 00:13:55.120 --> 00:13:59.679 accelerate the object also approaches infinity. The universe forbids mass 291 00:13:59.720 --> 00:14:01.039 from reaching the speed limit. 292 00:14:01.240 --> 00:14:04.279 This all sounds like a brilliant piece of chalkpord theoretical physics. 293 00:14:05.120 --> 00:14:07.399 But what blows my mind is that physicists didn't just 294 00:14:07.480 --> 00:14:11.200 lead this as a mathematical curiosity. They actually found ways 295 00:14:11.240 --> 00:14:13.480 to physically prove it. I mean, I know there was 296 00:14:13.480 --> 00:14:16.960 an experiment in the early nineteen seventies, the halfle keating experiment, Yes, 297 00:14:17.080 --> 00:14:20.600 a classic, where they supposedly put atomic clocks on commercial airplanes. 298 00:14:20.919 --> 00:14:22.879 But my first thought when I read about that was, 299 00:14:23.000 --> 00:14:25.840 how could a normal passenger plane flying at maybe six 300 00:14:25.919 --> 00:14:28.639 hundred miles an hour possibly go fast enough to measure 301 00:14:28.639 --> 00:14:30.960 in effect that requires the speed of light to become obvious. 302 00:14:31.039 --> 00:14:33.200 Weren't they just flying around the world on standard pan 303 00:14:33.279 --> 00:14:33.840 Am flights. 304 00:14:34.200 --> 00:14:37.759 Your right to be skeptical, because, as we established, passenger 305 00:14:37.840 --> 00:14:41.279 jets are crawling compared to the speed of light. The 306 00:14:41.360 --> 00:14:45.600 time dilation at those speeds is incredibly minuscule. But the 307 00:14:45.720 --> 00:14:48.840 brilliance of the hefel keating experiment wasn't in the speed 308 00:14:48.879 --> 00:14:49.399 of the planes. 309 00:14:49.559 --> 00:14:50.279 What was it? 310 00:14:50.279 --> 00:14:53.799 It was in the sheer, unfathomable precision of the instruments. 311 00:14:54.559 --> 00:14:58.399 In nineteen seventy one, Joseph Heffel and Richard Keating took 312 00:14:58.600 --> 00:15:02.879 four caesium beam atomic clocks. These are devices that measure 313 00:15:02.919 --> 00:15:07.159 time by counting the exact microwave resonances of caesium atoms. 314 00:15:07.600 --> 00:15:10.360 They're so precise they might lose or gain a single 315 00:15:10.399 --> 00:15:12.600 second over tens of millions of years. 316 00:15:12.679 --> 00:15:15.559 So they took these ultra sensitive instruments literally, bought them 317 00:15:15.600 --> 00:15:18.799 passenger tickets and strapped them into the seats of commercial airliners. 318 00:15:19.000 --> 00:15:21.960 Literally, they flew one set of clocks eastward around the 319 00:15:21.960 --> 00:15:25.240 world and another set westward around the world. And meanwhile 320 00:15:25.279 --> 00:15:28.919 they kept a reference set of identical atomic clocks, completely 321 00:15:28.960 --> 00:15:31.720 stationary at the United States Naval Observatory. 322 00:15:31.960 --> 00:15:34.360 Okay, so the goal was to see if the flying clocks, 323 00:15:34.399 --> 00:15:38.080 heavy experienced the velocity of the airplanes, would physically disagree 324 00:15:38.080 --> 00:15:40.639 with the stationary clocks when they got back. But why 325 00:15:40.679 --> 00:15:44.440 eastward and westward? Does the direction matter when you're just 326 00:15:44.480 --> 00:15:45.240 measuring speed? 327 00:15:45.360 --> 00:15:48.480 Oh, it matters immensely because the Earth itself is spinning 328 00:15:48.799 --> 00:15:52.120 the stationary clocks. The observatory are already moving because the 329 00:15:52.159 --> 00:15:55.320 surface of the Earth is rotating. Right when the plane 330 00:15:55.320 --> 00:15:59.039 flew eastward in the same direction as the Earth's rotation, 331 00:15:59.679 --> 00:16:02.559 it's velocity added to the rotational speed of the Earth. 332 00:16:03.120 --> 00:16:05.639 It was moving faster relative to the center of the 333 00:16:05.679 --> 00:16:10.080 Earth than the stationary clocks. Therefore, special relativity predicted the 334 00:16:10.120 --> 00:16:14.360 eastward clocks should run significantly slower and lose time. 335 00:16:14.360 --> 00:16:17.039 And the westward flight was flying against the rotation of 336 00:16:17.080 --> 00:16:21.440 the Earth, essentially subtracting from that rotational speed, so relative 337 00:16:21.480 --> 00:16:23.600 to the center of the Earth, the westward plane was 338 00:16:23.600 --> 00:16:26.320 actually moving slower than the stationary observatory on. 339 00:16:26.320 --> 00:16:31.000 The ground exactly. The mathematics predicted a very specific Chiny 340 00:16:31.039 --> 00:16:35.080 discrepancy for both journeys, and when Hafili and Keating brought 341 00:16:35.080 --> 00:16:37.519 the flying clocks back into the lab and compared the 342 00:16:37.559 --> 00:16:41.039 readouts to the reference clocks, the numbers did not match. 343 00:16:41.519 --> 00:16:44.919 The eastward clocks had lost time, the westward clocks had 344 00:16:44.919 --> 00:16:47.720 gained time. The physical time displayed on the instruments was 345 00:16:47.759 --> 00:16:52.360 fundamentally different, and the discrepancy perfectly matched the nanosecond calculations 346 00:16:52.639 --> 00:16:55.440 derived from Einstein's equations fifty years prior. 347 00:16:55.399 --> 00:16:58.600 They physically carried a slice of reality into a different 348 00:16:58.639 --> 00:17:02.600 temporal flow it'st deep there, and brought it back. That 349 00:17:02.720 --> 00:17:06.440 is profound, It's incredible. But there's another real world proof 350 00:17:06.440 --> 00:17:09.640 of special relativity that is even more dramatic because it 351 00:17:09.640 --> 00:17:13.119 doesn't require man made atomic clocks. Right. It happens naturally 352 00:17:13.599 --> 00:17:16.559 millions of times every single second right above our heads 353 00:17:16.599 --> 00:17:19.359 in the atmosphere. Uh the muons survival test. 354 00:17:19.559 --> 00:17:24.000 Ah. Yes, the behavior of muons is a continuous, naturally 355 00:17:24.039 --> 00:17:28.559 occurring demonstration of time dilation. Particle physicists rely on it daily. 356 00:17:28.960 --> 00:17:30.880 To understand it, we have to look at the upper 357 00:17:30.880 --> 00:17:33.920 limits of the Earth's atmosphere. Deep space is filled with 358 00:17:34.039 --> 00:17:38.160 high energy cosmic rays, mostly protons, traveling at immense speeds. 359 00:17:38.480 --> 00:17:42.160 When these cosmic rays slam into the molecules of oxygen 360 00:17:42.200 --> 00:17:46.400 and nitrogen in our upper atmosphere, the violent collision creates 361 00:17:46.400 --> 00:17:50.279 a shower of secondary sub atomic particles, and among these 362 00:17:50.319 --> 00:17:51.759 are particles called muons. 363 00:17:52.079 --> 00:17:54.799 So these muons are born high up in the atmosphere, 364 00:17:54.839 --> 00:17:57.920 maybe ten miles above the surface, and the momentum from 365 00:17:57.960 --> 00:18:01.880 the collision sends them hurtling downward toward the ground at 366 00:18:01.960 --> 00:18:04.319 velocities incredibly close to the speed of light. 367 00:18:04.440 --> 00:18:08.000 Correct, But the muon has a fatal flaw. It's a 368 00:18:08.079 --> 00:18:11.720 highly unstable particle. Once a muon is created, it has 369 00:18:11.759 --> 00:18:15.839 an incredibly short half life of roughly two point two microseconds. 370 00:18:15.880 --> 00:18:17.759 That's two point two millions of a second. 371 00:18:17.839 --> 00:18:21.400 Right after that microscypic flicker of time, it decays into 372 00:18:21.480 --> 00:18:24.759 an electron and a couple of neutrinos. It ceases to 373 00:18:24.799 --> 00:18:25.839 exist as a muon. 374 00:18:26.160 --> 00:18:28.279 Wait, let's look at the mat there. If a muon 375 00:18:28.359 --> 00:18:30.799 only lives for two millions of a second, it shouldn't 376 00:18:30.799 --> 00:18:32.799 be able to survive the trip to the ground, even 377 00:18:32.799 --> 00:18:34.880 if it's traveling at ninety nine point nine percent of 378 00:18:34.880 --> 00:18:37.720 the speed of light. The atmosphere is miles thick. Light 379 00:18:37.759 --> 00:18:41.359 itself takes significantly longer than two microseconds to travel ten 380 00:18:41.440 --> 00:18:44.680 miles it does. If time is a universal constant ticking 381 00:18:44.680 --> 00:18:48.200 away at the same rate for everything, every single muon 382 00:18:48.279 --> 00:18:51.559 ever created should die miles up in the sky. Yet 383 00:18:51.599 --> 00:18:53.839 we have detectors on the surface of the Earth and 384 00:18:53.920 --> 00:18:57.599 even deep underground in mines that are constantly being pinged 385 00:18:57.640 --> 00:19:00.480 by intact muons. How is that part possible? 386 00:19:00.720 --> 00:19:03.640 This is the exact paradox that makes time dilation an 387 00:19:03.799 --> 00:19:08.559 undeniable physical reality. If the universe operated on Newtonian time, 388 00:19:08.720 --> 00:19:11.359 the probability of a muon reaching the surface would be 389 00:19:11.440 --> 00:19:14.680 functionally zero. But we detect massive. 390 00:19:14.319 --> 00:19:16.440 Swarms of them, So how do they make it. 391 00:19:16.839 --> 00:19:18.640 To resolve the contradiction, you have to look at the 392 00:19:18.680 --> 00:19:22.359 journey from two completely different reference frames. Let's start from 393 00:19:22.400 --> 00:19:25.720 our perspective standing on the Earth next to our muon detector. 394 00:19:26.160 --> 00:19:29.599 Okay, from my perspective, I'm stationary, and the subatomic particle 395 00:19:29.640 --> 00:19:32.599 is rocketing toward me at ninety nine point nine percent 396 00:19:32.599 --> 00:19:35.400 of the speed of light. Because it's moving so incredibly 397 00:19:35.440 --> 00:19:38.359 fast relative to my frame of reference, the Lorenz factor 398 00:19:38.440 --> 00:19:42.319 is huge. Special relativity dictates that the muon's internal clock, 399 00:19:42.640 --> 00:19:45.200 the rate at which it experiences its own decay process, 400 00:19:45.640 --> 00:19:47.240 must be running exceptionally slowly. 401 00:19:47.480 --> 00:19:50.480