1 00:00:04,400 --> 00:00:07,800 Speaker 1: Welcome to tech Stuff, a production from I Heart Radio. 2 00:00:12,440 --> 00:00:15,440 Speaker 1: Hey there, and welcome to tech Stuff. I'm your host, 3 00:00:15,600 --> 00:00:18,720 Speaker 1: Jonathan Strickland. I'm an executive producer with I Heart Radio. 4 00:00:18,920 --> 00:00:22,720 Speaker 1: And how the tech are you. Well, I'm still on vacation, y'all. 5 00:00:23,040 --> 00:00:25,560 Speaker 1: I'll be back soon. But in the meantime, we have 6 00:00:25,640 --> 00:00:29,640 Speaker 1: an episode that originally published on July one, twenty. It's 7 00:00:29,680 --> 00:00:32,960 Speaker 1: called It's All Relative. And when I was a kid, 8 00:00:33,000 --> 00:00:37,120 Speaker 1: I was convinced that Einstein's theories were the these super 9 00:00:37,240 --> 00:00:41,800 Speaker 1: complicated explanations of the universe that really had no real 10 00:00:42,000 --> 00:00:44,840 Speaker 1: intersection with my daily life. But as it turns out, 11 00:00:44,880 --> 00:00:48,920 Speaker 1: without an understanding of relativity, a lot of the technology 12 00:00:49,000 --> 00:00:53,400 Speaker 1: we rely upon wouldn't work properly. It's fascinating stuff. I 13 00:00:53,479 --> 00:01:00,000 Speaker 1: hope you enjoy. The hurts unit refers to the numb 14 00:01:00,120 --> 00:01:03,640 Speaker 1: or of repeated phenomena over the course of a second. 15 00:01:04,080 --> 00:01:07,959 Speaker 1: So imagine that you're dribbling a basketball, so that the 16 00:01:08,000 --> 00:01:11,040 Speaker 1: ball goes from your hand to the ground back up 17 00:01:11,080 --> 00:01:14,560 Speaker 1: to your hand once per second. Well, you could describe 18 00:01:14,640 --> 00:01:19,119 Speaker 1: your dribbling as being one hurts in frequency, one full 19 00:01:19,200 --> 00:01:23,119 Speaker 1: cycle per second. Up down, up, Now, if you dribbled 20 00:01:23,160 --> 00:01:26,119 Speaker 1: twice as fast, so that the ball went up down 21 00:01:26,280 --> 00:01:29,520 Speaker 1: up two full times per second, then there would be 22 00:01:29,680 --> 00:01:33,640 Speaker 1: two hurts. Well, we can describe lots of stuff with 23 00:01:33,760 --> 00:01:36,480 Speaker 1: the unit hurts. We use it to describe sounds, in 24 00:01:36,480 --> 00:01:40,720 Speaker 1: which case we're talking about the frequency at which stuff vibrates. 25 00:01:41,360 --> 00:01:45,200 Speaker 1: Typical human hearing spans a range of frequencies that at 26 00:01:45,240 --> 00:01:48,160 Speaker 1: the low end is that twenty hurts. That represents the 27 00:01:48,240 --> 00:01:50,680 Speaker 1: lowest pitches of sounds. So you can think of those 28 00:01:50,680 --> 00:01:54,760 Speaker 1: deep bass notes. That's around the twenty hurts of area uh, 29 00:01:54,800 --> 00:01:57,000 Speaker 1: and then it goes all the way up to twenty 30 00:01:57,120 --> 00:02:01,360 Speaker 1: killer hurts or twenty thousand hurts. That represents the very 31 00:02:01,440 --> 00:02:05,480 Speaker 1: highest pitches that people can typically here, And those frequencies 32 00:02:05,760 --> 00:02:10,000 Speaker 1: correlate to how quickly stuff is vibrating back and forth. Now, 33 00:02:10,000 --> 00:02:12,440 Speaker 1: when it comes to us hearing things, we usually mean 34 00:02:12,600 --> 00:02:16,520 Speaker 1: that we're talking about the vibrations and fluctuation and air pressure, 35 00:02:16,760 --> 00:02:20,160 Speaker 1: and those fluctuations and air pressure interact with our ear drums. 36 00:02:20,840 --> 00:02:23,240 Speaker 1: But we can use hurts to talk about all sorts 37 00:02:23,280 --> 00:02:27,160 Speaker 1: of stuff, including the processor speed of a CPU. In 38 00:02:27,200 --> 00:02:29,799 Speaker 1: that case, we're really talking about the number of clock 39 00:02:30,040 --> 00:02:33,560 Speaker 1: cycles per second, so you get it. This is a 40 00:02:33,639 --> 00:02:37,040 Speaker 1: description of the frequency of the number of times a 41 00:02:37,120 --> 00:02:40,320 Speaker 1: certain thing happens, like within a second. And I also 42 00:02:40,400 --> 00:02:43,720 Speaker 1: explained that we measure the rate at which we can 43 00:02:43,760 --> 00:02:47,600 Speaker 1: send data using the term bits. A bit is a 44 00:02:47,600 --> 00:02:51,000 Speaker 1: basic unit of digital information, and when we talk about computers, 45 00:02:51,200 --> 00:02:53,920 Speaker 1: we're talking about bits in the form of a zero 46 00:02:54,200 --> 00:02:58,400 Speaker 1: or a one binary information, just like your basic two 47 00:02:58,400 --> 00:03:02,480 Speaker 1: way physical switch has two positions off or on. So 48 00:03:02,520 --> 00:03:04,840 Speaker 1: if you hear a term like kill a bit, that 49 00:03:04,880 --> 00:03:08,519 Speaker 1: means one thousand bits, and a megabit is one million bits, 50 00:03:08,560 --> 00:03:13,519 Speaker 1: and a gigabit would be one billion bits. Likewise, megabits 51 00:03:13,560 --> 00:03:17,280 Speaker 1: per second tells us how many million bits can move 52 00:03:17,400 --> 00:03:20,720 Speaker 1: from one point to another per second over that connection. 53 00:03:21,120 --> 00:03:24,239 Speaker 1: So if you've got a one hundred megabit per second connection, 54 00:03:24,840 --> 00:03:28,400 Speaker 1: theoretically it would mean that up to one hundred million 55 00:03:28,480 --> 00:03:33,360 Speaker 1: bits can transfer across that communication channel per second, though 56 00:03:33,520 --> 00:03:36,400 Speaker 1: that's not how it works out most of the time, 57 00:03:36,440 --> 00:03:39,360 Speaker 1: but that's a matter for a different episode. I didn't 58 00:03:39,400 --> 00:03:43,640 Speaker 1: mention that this is different from something like megabytes. So 59 00:03:43,760 --> 00:03:47,000 Speaker 1: a bite is a unit that consists of eight bits, 60 00:03:47,840 --> 00:03:50,760 Speaker 1: and this gets confusing because we often describe stuff like 61 00:03:50,840 --> 00:03:55,000 Speaker 1: file sizes in terms of bites, but transfer speeds in 62 00:03:55,120 --> 00:03:58,280 Speaker 1: terms of bits. So let's say that you do have 63 00:03:58,400 --> 00:04:01,840 Speaker 1: that one hundred megabits person, I can download speed, and 64 00:04:02,000 --> 00:04:05,600 Speaker 1: you want to download a one hundred megabyte file, Well, 65 00:04:05,600 --> 00:04:09,440 Speaker 1: that means it's not going to take one second. It's 66 00:04:09,440 --> 00:04:12,520 Speaker 1: gonna take eight seconds to download the file, because a 67 00:04:12,520 --> 00:04:16,640 Speaker 1: megabyte is eight times larger than a megabit. And actually 68 00:04:17,160 --> 00:04:19,919 Speaker 1: even that is a little bit misleading because in computer 69 00:04:20,040 --> 00:04:23,320 Speaker 1: memory terms, we typically look at units of memory based 70 00:04:23,360 --> 00:04:27,440 Speaker 1: on powers of two rather than powers of ten. So 71 00:04:27,480 --> 00:04:31,040 Speaker 1: instead of a killer byte being one thousand bytes, it's 72 00:04:31,080 --> 00:04:35,400 Speaker 1: actually one thousand twenty four bytes. And there's no standardization 73 00:04:35,520 --> 00:04:38,760 Speaker 1: in the tech industry, so sometimes people will say a 74 00:04:38,839 --> 00:04:41,920 Speaker 1: kill a byte and they mean one thousand bytes. Sometimes 75 00:04:41,920 --> 00:04:43,960 Speaker 1: they'll say kill a byte and they mean one thousand 76 00:04:44,040 --> 00:04:47,160 Speaker 1: twenty four bytes, and you will want to tear your 77 00:04:47,200 --> 00:04:50,280 Speaker 1: hair out, and then you'll look like I do, I'm 78 00:04:50,320 --> 00:04:52,880 Speaker 1: bald if you didn't know. But this episode isn't about 79 00:04:52,880 --> 00:04:57,880 Speaker 1: the peculiarities of our naming conventions and the computer information age. Instead, 80 00:04:58,200 --> 00:05:02,080 Speaker 1: I wanted to tackle something else. It affects everything, really, 81 00:05:02,160 --> 00:05:04,680 Speaker 1: but in particular we really had to suss it out 82 00:05:04,760 --> 00:05:08,000 Speaker 1: in order to make certain types of satellites work properly. 83 00:05:08,279 --> 00:05:11,320 Speaker 1: And this is the concept of relativity. So in this 84 00:05:11,360 --> 00:05:14,599 Speaker 1: episode we're really going to learn why an understanding of 85 00:05:14,600 --> 00:05:19,320 Speaker 1: relativity is important if we want our certain satellite technologies 86 00:05:19,360 --> 00:05:22,159 Speaker 1: to work, and it serves as a great reminder that 87 00:05:22,240 --> 00:05:26,400 Speaker 1: technology is only really possible through an understanding of science. 88 00:05:26,760 --> 00:05:30,200 Speaker 1: You can think of tech as the physical manifestation of 89 00:05:30,240 --> 00:05:34,080 Speaker 1: our understanding of scientific principles, and that means if we 90 00:05:34,080 --> 00:05:37,760 Speaker 1: were wrong in our understanding of science, the technology shouldn't 91 00:05:37,800 --> 00:05:40,680 Speaker 1: really work. So in a way, you can think of 92 00:05:40,800 --> 00:05:44,720 Speaker 1: technology that works as evidence that the scientific method is 93 00:05:44,760 --> 00:05:48,800 Speaker 1: a darned good formula. Since we're talking about relativity, it 94 00:05:48,839 --> 00:05:52,160 Speaker 1: means we're gonna be talking about a real Einstein today. 95 00:05:52,320 --> 00:05:57,159 Speaker 1: His name was Einstein, which is convenient. But before we 96 00:05:57,200 --> 00:06:03,680 Speaker 1: get to Einstein, we have Galileo Galileo, Galileo Figaro. Wait no, 97 00:06:03,760 --> 00:06:08,320 Speaker 1: I'm sorry, Wait that's Bohemian Rhapsody. I meant Galileo galile This. 98 00:06:08,440 --> 00:06:12,680 Speaker 1: Galileo made an observation that if you've got two observers 99 00:06:13,000 --> 00:06:16,480 Speaker 1: moving at a constant speed and direction, so they're moving 100 00:06:16,520 --> 00:06:19,320 Speaker 1: at the same velocity, they will get the same results 101 00:06:19,400 --> 00:06:23,800 Speaker 1: for any experiment that involves moving stuff around a mechanical experiment. 102 00:06:24,520 --> 00:06:28,280 Speaker 1: This is easier to understand if we use an example, 103 00:06:28,640 --> 00:06:31,839 Speaker 1: and I like one that my colleague Robert Lamb used 104 00:06:31,880 --> 00:06:34,800 Speaker 1: when he wrote about relativity for how Stuff Works dot 105 00:06:34,800 --> 00:06:37,800 Speaker 1: Com back in the day. He used an example of 106 00:06:37,839 --> 00:06:41,760 Speaker 1: a train and a scientific ping pong ball. Alright, so 107 00:06:42,120 --> 00:06:45,000 Speaker 1: imagine you've got a scientist who's standing in the middle 108 00:06:45,040 --> 00:06:48,360 Speaker 1: of an aisle on a moving train, and the train 109 00:06:48,560 --> 00:06:51,320 Speaker 1: is moving at a steady speed in a straight line, 110 00:06:51,440 --> 00:06:56,160 Speaker 1: so there are no active forces of acceleration going on here. Remember, 111 00:06:56,400 --> 00:07:00,880 Speaker 1: acceleration describes a force that involves a chain and velocities. 112 00:07:01,000 --> 00:07:04,120 Speaker 1: That other means a change in direction or a change 113 00:07:04,160 --> 00:07:08,440 Speaker 1: in speed or both, but in this case constant speed 114 00:07:08,880 --> 00:07:13,520 Speaker 1: constant direction. Robert used nice round numbers in his examples, 115 00:07:13,560 --> 00:07:15,920 Speaker 1: so he suggested that the train is moving at one 116 00:07:16,320 --> 00:07:19,280 Speaker 1: miles per hour. Well it's not round. If we go 117 00:07:19,360 --> 00:07:22,840 Speaker 1: to the metric system, that would be one kilometers per hour. 118 00:07:23,360 --> 00:07:26,800 Speaker 1: If the train stays steady to the scientist, it will 119 00:07:26,840 --> 00:07:29,560 Speaker 1: feel as if that scientist is actually just standing still, 120 00:07:29,800 --> 00:07:33,720 Speaker 1: just anywhere, and we're conveniently ignoring an emotion that would 121 00:07:33,720 --> 00:07:36,960 Speaker 1: happen due to irregularities with the trains wheels or the 122 00:07:36,960 --> 00:07:39,680 Speaker 1: train tracks or anything like that. And if this is 123 00:07:39,720 --> 00:07:42,360 Speaker 1: hard for you to imagine, just think about how you 124 00:07:42,440 --> 00:07:46,040 Speaker 1: feel when you're standing still or sitting still or laying down. 125 00:07:46,240 --> 00:07:50,160 Speaker 1: Here on Earth. We know the Earth is moving through space. 126 00:07:50,800 --> 00:07:53,680 Speaker 1: It is a body in motion, but when we are 127 00:07:54,040 --> 00:07:58,640 Speaker 1: still relative to the Earth itself, we don't feel that motion. 128 00:07:58,960 --> 00:08:02,320 Speaker 1: Assuming there's not mother weird event going on like an earthquake, 129 00:08:02,360 --> 00:08:06,120 Speaker 1: which is something separate. But back to our hypothetical train, 130 00:08:06,640 --> 00:08:11,000 Speaker 1: the scientist tosses the ping pong ball down the aisle. Now, 131 00:08:11,080 --> 00:08:15,080 Speaker 1: from the scientist's perspective, this ping pong ball will travel 132 00:08:15,120 --> 00:08:18,840 Speaker 1: at whatever speed they threw it at. Robert actually suggests 133 00:08:18,880 --> 00:08:22,320 Speaker 1: a relatively gentle toss of five miles per hour or 134 00:08:22,320 --> 00:08:26,040 Speaker 1: eight kilometers per hour. The ping pong ball would bounce 135 00:08:26,200 --> 00:08:28,680 Speaker 1: down the aisle, just as it would if the scientists 136 00:08:28,680 --> 00:08:30,800 Speaker 1: were to toss the ball on a train that isn't 137 00:08:30,800 --> 00:08:35,079 Speaker 1: moving at all, or on just flat ground. However, let's 138 00:08:35,080 --> 00:08:38,640 Speaker 1: say we have a second observer who's not on the train. 139 00:08:38,679 --> 00:08:41,040 Speaker 1: They're standing off to the side, and they can see 140 00:08:41,080 --> 00:08:44,280 Speaker 1: through the train. To this person, it will appear as 141 00:08:44,320 --> 00:08:47,880 Speaker 1: if the ping pong ball is moving very fast. Indeed, 142 00:08:48,200 --> 00:08:52,120 Speaker 1: relative to this stationary observer, the ping pong ball will 143 00:08:52,160 --> 00:08:54,120 Speaker 1: appear to move at the speed at which it was 144 00:08:54,160 --> 00:08:57,960 Speaker 1: thrown in addition to the speed of the train itself. 145 00:08:58,320 --> 00:09:00,800 Speaker 1: So if we take the two figures, we get one 146 00:09:00,920 --> 00:09:03,960 Speaker 1: hundred five miles per hour or a hundred sixty nine 147 00:09:04,000 --> 00:09:09,920 Speaker 1: kilometers per hour. This is called a Galilean transformation. Alternatively, 148 00:09:10,240 --> 00:09:12,400 Speaker 1: if the scientists were throwing the ping pong ball in 149 00:09:12,440 --> 00:09:15,440 Speaker 1: the opposite direction of the trains travel, so they're facing 150 00:09:15,600 --> 00:09:17,920 Speaker 1: towards the back of the train, it would appear to 151 00:09:18,000 --> 00:09:21,040 Speaker 1: this second observer that the ping pong ball was moving 152 00:09:21,120 --> 00:09:24,040 Speaker 1: at a slightly slower speed than the overall train was, 153 00:09:24,200 --> 00:09:27,080 Speaker 1: whereas to the scientist on board, the ping pong ball 154 00:09:27,160 --> 00:09:30,280 Speaker 1: would still be traveling at that five mile per hour speed. 155 00:09:30,960 --> 00:09:35,400 Speaker 1: So this is where the term relativity comes into play. 156 00:09:35,480 --> 00:09:40,480 Speaker 1: The effects observed are relative to the perspective of the observer. 157 00:09:41,000 --> 00:09:44,680 Speaker 1: It's all based on the reference frame of that observer. 158 00:09:45,280 --> 00:09:47,640 Speaker 1: If you're on the train, then you're just looking at 159 00:09:47,640 --> 00:09:50,680 Speaker 1: a ping pong ball bouncing at a relatively slow speed 160 00:09:50,720 --> 00:09:53,280 Speaker 1: down the aisle. If you're not on the train, the 161 00:09:53,320 --> 00:09:56,840 Speaker 1: ping pong ball is moving quite fast, so it's all relative. 162 00:09:57,480 --> 00:10:00,800 Speaker 1: Isaac Newton would follow along and say, yeah, mate, this 163 00:10:00,840 --> 00:10:03,320 Speaker 1: old tracks. I don't know why I talked like that. 164 00:10:04,040 --> 00:10:07,280 Speaker 1: In his Laws of Motion, Newton stated that these laws 165 00:10:07,320 --> 00:10:10,800 Speaker 1: emotions should hold in an inertial frame as well as 166 00:10:10,880 --> 00:10:13,680 Speaker 1: a reference frame that was moving at a constant velocity 167 00:10:13,720 --> 00:10:16,800 Speaker 1: relative to the inertial frame. And inertial frame, by the way, 168 00:10:17,120 --> 00:10:19,160 Speaker 1: is just a frame of reference in which there are 169 00:10:19,280 --> 00:10:22,480 Speaker 1: zero net forces acting upon it, so that there are 170 00:10:22,520 --> 00:10:25,280 Speaker 1: no forces of acceleration in play. So in our example, 171 00:10:25,480 --> 00:10:28,040 Speaker 1: the train that we talked about, that would be our 172 00:10:28,080 --> 00:10:32,640 Speaker 1: inertial frame. All of this is fairly intuitive, but then 173 00:10:32,679 --> 00:10:36,560 Speaker 1: we get to something really tricky. Einstein would establish that 174 00:10:36,640 --> 00:10:39,240 Speaker 1: the speed of light in a vacuum is the fastest 175 00:10:39,240 --> 00:10:43,160 Speaker 1: speed in our universe. Nothing can go faster than that. Hey, 176 00:10:43,160 --> 00:10:45,760 Speaker 1: what if you're on the train that's traveling one per 177 00:10:45,840 --> 00:10:48,959 Speaker 1: hour and you're facing forward, you're facing the direction of travel, 178 00:10:49,440 --> 00:10:52,280 Speaker 1: and then you have a flashlight and you turn on 179 00:10:52,440 --> 00:10:55,560 Speaker 1: the flashlight. Well, doesn't that mean you should perform a 180 00:10:55,600 --> 00:10:59,360 Speaker 1: Galilean transformation on this and say the light from that 181 00:10:59,400 --> 00:11:02,600 Speaker 1: flashlight in your hands is actually traveling at the normal 182 00:11:02,640 --> 00:11:06,000 Speaker 1: speed of light on board the train, but also get 183 00:11:06,040 --> 00:11:08,400 Speaker 1: that boost of the trains travel, So it should be 184 00:11:08,400 --> 00:11:11,320 Speaker 1: the speed of light plus one miles per hour. Doesn't 185 00:11:11,320 --> 00:11:15,040 Speaker 1: that make sense? Well, according to actual experiments performed before 186 00:11:15,080 --> 00:11:19,640 Speaker 1: Einstein would come around to explain things, the answer was Nope, 187 00:11:19,640 --> 00:11:23,400 Speaker 1: doesn't look like it works that way. Scientists Edward Morley 188 00:11:23,440 --> 00:11:27,840 Speaker 1: and Albert A. Michelson created an experiment to measure the 189 00:11:27,840 --> 00:11:31,400 Speaker 1: speed of light back in seven and actually they were 190 00:11:31,400 --> 00:11:34,800 Speaker 1: looking for something else. They were looking for evidence of 191 00:11:34,800 --> 00:11:41,400 Speaker 1: a hypothetical substance called luminiferous ether. Say what, all right, 192 00:11:41,440 --> 00:11:44,680 Speaker 1: We'll stick with me, because in a way this does 193 00:11:44,760 --> 00:11:48,760 Speaker 1: make sense. Okay, So on Earth we see waves traveling 194 00:11:48,800 --> 00:11:52,200 Speaker 1: through a medium, right, Like if you look out in 195 00:11:52,240 --> 00:11:55,959 Speaker 1: the ocean, you can see actual waves in the water, 196 00:11:56,360 --> 00:11:59,200 Speaker 1: and the water is a physical medium through which these 197 00:11:59,200 --> 00:12:04,000 Speaker 1: waves travel. Sound can't travel in space because space is 198 00:12:04,080 --> 00:12:08,040 Speaker 1: effectively a vacuum. The particles that are in space are 199 00:12:08,080 --> 00:12:10,800 Speaker 1: so far apart from one another there's no way for 200 00:12:10,840 --> 00:12:14,240 Speaker 1: the vibration of one particle to come into contact and 201 00:12:14,280 --> 00:12:18,079 Speaker 1: affect another particle, so sound can't travel. Sound travels through 202 00:12:18,080 --> 00:12:22,160 Speaker 1: the propagation of vibrational waves, and if your stuff isn't 203 00:12:22,200 --> 00:12:24,520 Speaker 1: in contact with each other, there's no way for them 204 00:12:24,559 --> 00:12:27,640 Speaker 1: to have that wave propagate. So there has to be 205 00:12:27,720 --> 00:12:32,200 Speaker 1: some sort of medium like air or solid surfaces or 206 00:12:32,320 --> 00:12:37,120 Speaker 1: something in order for sound travel. Well, if that's the case, 207 00:12:37,480 --> 00:12:40,679 Speaker 1: said the folks of the time, then stuff like light 208 00:12:41,040 --> 00:12:43,760 Speaker 1: must need some sort of medium to travel through, right. 209 00:12:43,880 --> 00:12:45,960 Speaker 1: I mean sound has to have something. Light must have 210 00:12:46,040 --> 00:12:50,040 Speaker 1: something too. Light can definitely travel through space. I mean 211 00:12:50,040 --> 00:12:52,520 Speaker 1: that's how we can see anything, because light from the 212 00:12:52,559 --> 00:12:56,160 Speaker 1: Sun travels through space to hit the Earth. So the 213 00:12:56,240 --> 00:12:58,920 Speaker 1: light has to be moving through some sort of medium 214 00:12:58,960 --> 00:13:04,040 Speaker 1: we cannot observe directly. This hypothetical medium was the aforementioned 215 00:13:04,200 --> 00:13:09,600 Speaker 1: luminiferous ether. But assuming this ether existed at all, it 216 00:13:09,640 --> 00:13:12,839 Speaker 1: had to be pretty darn special because we can't feel it, 217 00:13:13,200 --> 00:13:17,440 Speaker 1: we can't detect it, it creates no observable effects, So 218 00:13:17,600 --> 00:13:20,520 Speaker 1: if it were real, it had to be unlike pretty 219 00:13:20,600 --> 00:13:24,520 Speaker 1: much anything else we had discovered up to that point. Now, 220 00:13:24,800 --> 00:13:29,040 Speaker 1: let's assume that the universe is filled with this ether stuff. 221 00:13:29,360 --> 00:13:33,000 Speaker 1: The question rises, how the heck does the ether interact 222 00:13:33,040 --> 00:13:35,440 Speaker 1: with all the physical stuff that's in the universe, the 223 00:13:35,440 --> 00:13:40,760 Speaker 1: actual matter and also energy. After all, the bodies in 224 00:13:40,880 --> 00:13:44,720 Speaker 1: space like stars, planets, moons, and all that other stuff. 225 00:13:44,960 --> 00:13:48,559 Speaker 1: All of that is moving, none of it is standing still, 226 00:13:48,800 --> 00:13:52,400 Speaker 1: and if it is moving, it would presumably disturb this 227 00:13:52,679 --> 00:13:56,520 Speaker 1: ether medium, right. I mean, if you move your hand 228 00:13:56,559 --> 00:13:59,360 Speaker 1: through a pool of water, you are disturbing that water. 229 00:13:59,440 --> 00:14:02,560 Speaker 1: You're making currents and eddies. So it was thought that 230 00:14:02,640 --> 00:14:06,000 Speaker 1: the motion of all these elements in space would disturb 231 00:14:06,080 --> 00:14:09,600 Speaker 1: the ether in some way, and hypothetically there would be 232 00:14:09,679 --> 00:14:13,760 Speaker 1: some sort of ether wind. But if there were a wind, 233 00:14:14,240 --> 00:14:17,920 Speaker 1: then presumably the speed of light would be affected depending 234 00:14:18,000 --> 00:14:22,080 Speaker 1: upon the wind's direction in relation to the lights direction. 235 00:14:22,400 --> 00:14:25,360 Speaker 1: So think of a really windy day in the real world. 236 00:14:25,720 --> 00:14:29,320 Speaker 1: If you're walking against a very very tough wind, like 237 00:14:29,360 --> 00:14:32,240 Speaker 1: a gale force wind, you have to power through it 238 00:14:32,280 --> 00:14:35,800 Speaker 1: to keep moving forward. Now, if you're walking with the wind, 239 00:14:36,160 --> 00:14:38,040 Speaker 1: like the wind is to your back and pushing you, 240 00:14:38,360 --> 00:14:41,120 Speaker 1: then you get a big boost. Well, the same thing 241 00:14:41,200 --> 00:14:45,160 Speaker 1: should be happening with light if ether wind were real, 242 00:14:45,800 --> 00:14:49,280 Speaker 1: and so Mickelson and Morley devised a gadget that would 243 00:14:49,280 --> 00:14:53,520 Speaker 1: split light into two beams, directing those beams down different 244 00:14:53,560 --> 00:14:57,520 Speaker 1: paths using mirrors in different directions, and seeing if those 245 00:14:57,560 --> 00:15:01,000 Speaker 1: two beams of light would hit an eyepiece at different times, 246 00:15:01,040 --> 00:15:05,120 Speaker 1: the thought being well, one of these directions would theoretically 247 00:15:05,160 --> 00:15:08,000 Speaker 1: be in the same direction as the ether wind, and 248 00:15:08,120 --> 00:15:10,880 Speaker 1: one would be at a cross direction of ether wind. 249 00:15:11,160 --> 00:15:13,120 Speaker 1: So we should see a difference in the amount of 250 00:15:13,120 --> 00:15:16,400 Speaker 1: time it takes for the light from this one source 251 00:15:16,600 --> 00:15:19,720 Speaker 1: that's been split into two to arrive at an eyepiece. 252 00:15:20,680 --> 00:15:25,440 Speaker 1: But that's not what they found. They observed no such effect. 253 00:15:25,560 --> 00:15:27,960 Speaker 1: So if there were such a thing as ether, the 254 00:15:28,000 --> 00:15:31,440 Speaker 1: stuff wasn't giving either a boost or a drag on 255 00:15:31,640 --> 00:15:34,720 Speaker 1: light itself. No matter what. The light was traveling at 256 00:15:34,760 --> 00:15:37,760 Speaker 1: a constant speed, which turned out to be approximately one 257 00:15:38,520 --> 00:15:41,640 Speaker 1: six thousand miles per second or around three hundred thousand 258 00:15:41,680 --> 00:15:45,320 Speaker 1: kilometers per second. Now that flew in the face of 259 00:15:45,440 --> 00:15:49,400 Speaker 1: classic Newtonian physics clearly. With the example of the ping 260 00:15:49,440 --> 00:15:52,000 Speaker 1: pong ball and the train, the ping pong ball has 261 00:15:52,080 --> 00:15:54,960 Speaker 1: to be traveling faster than the train it's on. I mean, 262 00:15:55,000 --> 00:15:57,200 Speaker 1: that just makes sense. If you were standing on the 263 00:15:57,240 --> 00:15:59,920 Speaker 1: top of the very front of the train, and then 264 00:16:00,040 --> 00:16:03,160 Speaker 1: you through the ping pong ball, and we ignore stuff 265 00:16:03,200 --> 00:16:06,680 Speaker 1: like wind resistance, the ping pong ball would land ahead 266 00:16:06,720 --> 00:16:09,120 Speaker 1: of the train, so it has to be going faster. 267 00:16:09,600 --> 00:16:12,280 Speaker 1: So what the heck was so special about light and 268 00:16:12,320 --> 00:16:14,680 Speaker 1: what was going on? Well, this was one of the 269 00:16:14,720 --> 00:16:18,480 Speaker 1: great mysteries that Albert Einstein's that is mine to unraveling, 270 00:16:18,760 --> 00:16:21,120 Speaker 1: and it formed the basis of one of his great 271 00:16:21,200 --> 00:16:24,280 Speaker 1: theories of relativity. And this would be the theory of 272 00:16:24,400 --> 00:16:28,000 Speaker 1: special relativity, which poses that the laws of physics are 273 00:16:28,000 --> 00:16:31,760 Speaker 1: in the same in all inertial frames of references. And 274 00:16:31,800 --> 00:16:33,560 Speaker 1: that means the speed of light will be the same 275 00:16:33,600 --> 00:16:38,160 Speaker 1: for all observers, regardless of their relative perspectives. It doesn't 276 00:16:38,200 --> 00:16:41,440 Speaker 1: matter the context. The speed of light is the speed 277 00:16:41,440 --> 00:16:44,840 Speaker 1: of light. Now, there's an implication to this theory that 278 00:16:44,960 --> 00:16:47,920 Speaker 1: really got people scratching their heads. If the speed of 279 00:16:48,000 --> 00:16:51,760 Speaker 1: light is absolutely constant, that would mean that stuff like 280 00:16:51,920 --> 00:16:55,920 Speaker 1: distance and time are not. And as a heck of 281 00:16:55,920 --> 00:16:59,280 Speaker 1: a brain teaser, when we come back, we'll explore this more. 282 00:17:07,920 --> 00:17:11,360 Speaker 1: Let's imagine that you live half a mile away from 283 00:17:11,359 --> 00:17:14,520 Speaker 1: a lovely park, and it's a half mile away in 284 00:17:14,560 --> 00:17:17,760 Speaker 1: the morning, it's a half mile away. At night, it's 285 00:17:17,800 --> 00:17:20,359 Speaker 1: a half mile away. On a Tuesday, it's a half 286 00:17:20,400 --> 00:17:24,320 Speaker 1: mile away. On a Saturday. Half a mile is half 287 00:17:24,359 --> 00:17:28,360 Speaker 1: a mile, right, it's a reliable constant in our lives. 288 00:17:28,440 --> 00:17:31,600 Speaker 1: If it weren't, we could never give directions to anywhere 289 00:17:31,680 --> 00:17:34,960 Speaker 1: because all the measurements and landmarks would change all the time, 290 00:17:35,240 --> 00:17:38,440 Speaker 1: and our world wouldn't make sense the way it does 291 00:17:38,480 --> 00:17:42,520 Speaker 1: to us now. So in our individual experiences, in our 292 00:17:42,600 --> 00:17:46,800 Speaker 1: day to day lives, stuff like distance seems pretty darn 293 00:17:46,880 --> 00:17:51,919 Speaker 1: reliable and fixed. So how dare Einstein come along with 294 00:17:51,960 --> 00:17:55,760 Speaker 1: this theory of special relativity in nineteen o five and say, well, yeah, 295 00:17:55,760 --> 00:17:59,879 Speaker 1: but see, the speed of light is really the true constant, 296 00:18:00,280 --> 00:18:03,920 Speaker 1: and for that to work, time and distance or space 297 00:18:04,000 --> 00:18:09,600 Speaker 1: in other words, must be somewhat mutable. Einstein positive that 298 00:18:09,680 --> 00:18:13,760 Speaker 1: there is no absolute frame of reference in our universe, 299 00:18:13,960 --> 00:18:17,040 Speaker 1: which means there is no place in the universe that 300 00:18:17,200 --> 00:18:21,919 Speaker 1: is totally stationary. Everything is moving, which means all motion 301 00:18:22,119 --> 00:18:25,280 Speaker 1: is relative. You can't really talk about moving except in 302 00:18:25,320 --> 00:18:29,280 Speaker 1: reference to some other moving thing. So even as we 303 00:18:29,520 --> 00:18:33,199 Speaker 1: sit still and try to meditate, we do so on 304 00:18:33,280 --> 00:18:37,320 Speaker 1: a planet that is hurtling through space. We are in motion. 305 00:18:37,520 --> 00:18:40,680 Speaker 1: We're all moving through space and time, and we all 306 00:18:40,760 --> 00:18:44,920 Speaker 1: have a frame of reference, and each frame of reference 307 00:18:45,280 --> 00:18:48,720 Speaker 1: is just as legitimate as every other frame of reference 308 00:18:49,400 --> 00:18:51,960 Speaker 1: or I guess you could say, if everybody is super, 309 00:18:52,160 --> 00:18:56,880 Speaker 1: nobody is. I guess I've watched The Incredibles too many times. Well, anyway, 310 00:18:56,920 --> 00:19:00,720 Speaker 1: this particular nineteen o five theory is called special relativity 311 00:19:00,920 --> 00:19:06,240 Speaker 1: because Einstein's explanation only covered special cases, that being when 312 00:19:06,359 --> 00:19:09,959 Speaker 1: two inertial frames are in constant motion with regard to 313 00:19:10,000 --> 00:19:13,080 Speaker 1: one another, and there can be no acceleration, so the 314 00:19:13,119 --> 00:19:15,280 Speaker 1: motion had to be in a straight line at a 315 00:19:15,320 --> 00:19:19,080 Speaker 1: constant speed. A change in direction or speed would be 316 00:19:19,119 --> 00:19:22,399 Speaker 1: an acceleration, and to cover those instances we would have 317 00:19:22,440 --> 00:19:25,000 Speaker 1: to wait a decade for Einstein to work out his 318 00:19:25,080 --> 00:19:28,680 Speaker 1: theory of general relativity. We'll get to that, but we've 319 00:19:28,680 --> 00:19:31,679 Speaker 1: got a lot more to say about special relativity. So 320 00:19:31,760 --> 00:19:34,760 Speaker 1: Einstein was taking a different approach to the results of 321 00:19:34,800 --> 00:19:38,199 Speaker 1: the experiments done by people like Michelson and Morley. The 322 00:19:38,280 --> 00:19:42,440 Speaker 1: scientific world at large was essentially saying, well, this can't 323 00:19:42,440 --> 00:19:45,080 Speaker 1: be right. These results can't be right. There must be 324 00:19:45,119 --> 00:19:48,680 Speaker 1: something wrong with the experiment or the equipment, because we're 325 00:19:48,760 --> 00:19:52,359 Speaker 1: sure this theory is correct and that ether is there. 326 00:19:52,920 --> 00:19:55,800 Speaker 1: Einstein was taking a totally different perspective. He was saying, 327 00:19:56,440 --> 00:20:00,720 Speaker 1: if we assume the experiments are producing accurate result, then 328 00:20:00,760 --> 00:20:04,080 Speaker 1: it stands to reason that the prevailing theory is flawed 329 00:20:04,400 --> 00:20:07,000 Speaker 1: and we have to figure out what the real explanation is. 330 00:20:07,359 --> 00:20:09,720 Speaker 1: And this is one of those important points in science. 331 00:20:10,240 --> 00:20:13,840 Speaker 1: It's that if your results in your experiment don't meet 332 00:20:13,880 --> 00:20:19,080 Speaker 1: your hypothesis, it's very possible that your hypothesis is wrong. 333 00:20:19,280 --> 00:20:22,399 Speaker 1: Now you need to do multiple experiments to find out 334 00:20:22,840 --> 00:20:25,480 Speaker 1: and to test your equipment make sure there's not any 335 00:20:25,600 --> 00:20:28,879 Speaker 1: errors there that could be causing the issues. But it 336 00:20:28,920 --> 00:20:31,760 Speaker 1: does mean that you need to re examine that hypothesis, 337 00:20:32,320 --> 00:20:36,440 Speaker 1: and at this time the scientific community wasn't really doing that, 338 00:20:37,080 --> 00:20:41,560 Speaker 1: so Einstein did away with the ether. His explanation suggested 339 00:20:41,600 --> 00:20:45,880 Speaker 1: that our observable universe has four dimensions, not that there 340 00:20:45,880 --> 00:20:49,080 Speaker 1: can only be four dimensions, but rather there are four 341 00:20:49,119 --> 00:20:56,720 Speaker 1: dimensions we can detect and observe, and these would be up, down, left, right, forward, backward, 342 00:20:57,119 --> 00:21:01,920 Speaker 1: and then the fourth dimension, which is time. Collectively, those 343 00:21:01,920 --> 00:21:05,640 Speaker 1: three dimensions are space. The fourth dimension is time, and 344 00:21:05,680 --> 00:21:10,639 Speaker 1: we get the space time continuum, this intrinsic relationship between 345 00:21:10,680 --> 00:21:14,600 Speaker 1: space and time or spacetime continuum, which also gives us 346 00:21:15,480 --> 00:21:17,800 Speaker 1: dozens of Star Trek episodes that would use it as 347 00:21:17,800 --> 00:21:21,520 Speaker 1: shorthand for things are about to get really weird. Einstein 348 00:21:21,600 --> 00:21:25,119 Speaker 1: positive that the speed of light is measured as constant 349 00:21:25,160 --> 00:21:28,320 Speaker 1: in all frames of reference. And let's think for a second. 350 00:21:28,600 --> 00:21:32,280 Speaker 1: What we mean by speed. Speed is a description of 351 00:21:32,320 --> 00:21:36,000 Speaker 1: how much distance can be covered per unit of time. 352 00:21:36,520 --> 00:21:39,479 Speaker 1: So a speed of one miles per hour means that 353 00:21:39,560 --> 00:21:42,199 Speaker 1: in one hour's time we will cover a distance of 354 00:21:42,240 --> 00:21:46,000 Speaker 1: one hundred miles. That's very obvious. But if the speed 355 00:21:46,000 --> 00:21:50,080 Speaker 1: of light is constant for all frames of reference, regardless 356 00:21:50,200 --> 00:21:53,000 Speaker 1: of how those frames are moving relative to each other, 357 00:21:53,640 --> 00:21:57,399 Speaker 1: that must mean something about space and or time is 358 00:21:57,440 --> 00:22:01,399 Speaker 1: a little wonky. And let's think about our train experiment again. 359 00:22:01,960 --> 00:22:04,600 Speaker 1: If you are aboard a train moving at a smooth 360 00:22:04,640 --> 00:22:07,679 Speaker 1: one hour in a straight line, and you toss a 361 00:22:07,720 --> 00:22:10,440 Speaker 1: ping pong ball straight up in the air, well, it's 362 00:22:10,440 --> 00:22:12,840 Speaker 1: gonna go straight up and come right back down to 363 00:22:12,880 --> 00:22:16,120 Speaker 1: your hand in a nice vertical line. From an outside 364 00:22:16,119 --> 00:22:18,720 Speaker 1: observer who isn't on the train, it would look a 365 00:22:18,760 --> 00:22:21,240 Speaker 1: little differently. You would throw the ball up at one 366 00:22:21,280 --> 00:22:24,480 Speaker 1: point relative to this outside observer, and the ball would 367 00:22:24,480 --> 00:22:27,560 Speaker 1: appear to move not just vertically, but horizontally before coming 368 00:22:27,560 --> 00:22:30,639 Speaker 1: back down. Now, if we repeat this experiment, but we 369 00:22:30,760 --> 00:22:34,200 Speaker 1: use light, we really see how it gets confusing. Okay, 370 00:22:34,240 --> 00:22:37,840 Speaker 1: so now you're on a train, but it's going really fast, 371 00:22:38,119 --> 00:22:41,320 Speaker 1: like let's say, half the speed of light, but the 372 00:22:41,400 --> 00:22:44,640 Speaker 1: speed and direction are constant. So you're on this train. 373 00:22:44,680 --> 00:22:48,480 Speaker 1: You don't feel any acceleration forces because you're moving at 374 00:22:48,480 --> 00:22:52,320 Speaker 1: a constant speed and a constant direction, so your velocity 375 00:22:52,359 --> 00:22:55,320 Speaker 1: remains the same. In fact, if there were no windows 376 00:22:55,359 --> 00:22:57,240 Speaker 1: on the train, you wouldn't even be able to tell 377 00:22:57,240 --> 00:22:59,760 Speaker 1: that the train was moving at all. So let's say 378 00:22:59,760 --> 00:23:02,520 Speaker 1: you've a laser pointer and you've got a mirror on 379 00:23:02,600 --> 00:23:05,600 Speaker 1: the ceiling of the train and a photon detector on 380 00:23:05,640 --> 00:23:08,200 Speaker 1: the floor of the train. You shoot the laser up 381 00:23:08,200 --> 00:23:11,320 Speaker 1: at the mirror, it reflects off the mirror, and then 382 00:23:11,359 --> 00:23:14,360 Speaker 1: it comes back down and hits the detector on the floor, 383 00:23:14,600 --> 00:23:17,080 Speaker 1: and it registers how long it took the light to 384 00:23:17,119 --> 00:23:20,280 Speaker 1: travel from your laser pointer to hit the detector. And 385 00:23:20,359 --> 00:23:23,159 Speaker 1: to you, the laser makes a vertical line. All that 386 00:23:23,200 --> 00:23:25,960 Speaker 1: makes sense, right, you can imagine that, But for our 387 00:23:26,080 --> 00:23:29,080 Speaker 1: outside observer who's not on the train, it would appear 388 00:23:29,160 --> 00:23:32,040 Speaker 1: as though the laser were actually traveling at a diagonal 389 00:23:32,359 --> 00:23:35,240 Speaker 1: up to that mirror and then a diagonal back down 390 00:23:35,359 --> 00:23:39,080 Speaker 1: towards the detector. So for one observer, the one on 391 00:23:39,119 --> 00:23:42,080 Speaker 1: the train, we have a straight line. It's vertical up down. 392 00:23:42,600 --> 00:23:45,520 Speaker 1: For the second observer off the train, we have an 393 00:23:45,560 --> 00:23:48,040 Speaker 1: angled path, sort of like how a billiard ball can 394 00:23:48,119 --> 00:23:50,000 Speaker 1: hit the side of a pool table and bounce off 395 00:23:50,000 --> 00:23:53,719 Speaker 1: at an angle. But this creates an apparent paradox. The 396 00:23:53,760 --> 00:23:57,000 Speaker 1: path viewed by you on the train is a straight line, 397 00:23:57,040 --> 00:24:00,359 Speaker 1: and by definition that is the shortest distance between two points. 398 00:24:00,840 --> 00:24:03,320 Speaker 1: The path observed by the person who is not on 399 00:24:03,359 --> 00:24:06,359 Speaker 1: the train is an angled line, and by definition that 400 00:24:06,440 --> 00:24:09,639 Speaker 1: has to be longer. The speed of light is constant 401 00:24:09,720 --> 00:24:13,200 Speaker 1: in both cases, but the distance is different between the 402 00:24:13,240 --> 00:24:16,879 Speaker 1: two points of reference. And because speed is distance divided 403 00:24:16,920 --> 00:24:19,960 Speaker 1: by time, if the distance is different, the time must 404 00:24:20,040 --> 00:24:25,880 Speaker 1: also be different between those two points of reference. Crazy 405 00:24:26,119 --> 00:24:29,560 Speaker 1: This brings us to the concept of time dilation. It also, 406 00:24:29,640 --> 00:24:34,080 Speaker 1: by the way, can affect distance. The faster and object gets, 407 00:24:34,640 --> 00:24:39,040 Speaker 1: the more squished it gets. So if you had this 408 00:24:39,160 --> 00:24:41,800 Speaker 1: train and you were to get up to near the 409 00:24:41,840 --> 00:24:45,160 Speaker 1: speed of light, the train to an outside observer would 410 00:24:45,160 --> 00:24:49,119 Speaker 1: appear to be shorter than it normally would be to 411 00:24:49,280 --> 00:24:53,080 Speaker 1: anyone inside the train, the dimensions would remain exactly the same. 412 00:24:53,320 --> 00:24:56,399 Speaker 1: You would not suddenly see a shorter train. It wouldn't 413 00:24:56,440 --> 00:24:58,960 Speaker 1: be like you were in that compressor scene in Star Wars. 414 00:24:59,280 --> 00:25:01,600 Speaker 1: The train would a to be normal. Only from an 415 00:25:01,600 --> 00:25:04,760 Speaker 1: outside observer who is not traveling at that speed would 416 00:25:04,760 --> 00:25:10,159 Speaker 1: it appear that the train itself was getting squished shorter. Likewise, 417 00:25:10,560 --> 00:25:14,320 Speaker 1: the faster something goes with respect to some other point 418 00:25:14,320 --> 00:25:18,080 Speaker 1: of reference that's important, the more quickly time appears to 419 00:25:18,119 --> 00:25:22,240 Speaker 1: pass for those at the other point of reference. Or alternatively, 420 00:25:22,600 --> 00:25:26,520 Speaker 1: the more slowly time seems to pass for the fast 421 00:25:26,640 --> 00:25:29,640 Speaker 1: moving thing from the frame of reference of the person 422 00:25:29,680 --> 00:25:33,080 Speaker 1: who's not moving fast. This gets really clunky. I know, 423 00:25:33,160 --> 00:25:35,480 Speaker 1: it gets confusing. So let's talk about space travel some more, 424 00:25:35,520 --> 00:25:39,000 Speaker 1: because examples actually make this way easier to explain. All right, 425 00:25:39,080 --> 00:25:42,040 Speaker 1: So let's say you've built a spaceship and this spaceship 426 00:25:42,080 --> 00:25:45,880 Speaker 1: can go wicked fast, like eight of the speed of light, 427 00:25:46,480 --> 00:25:49,560 Speaker 1: and you're gonna go on a year long jaunt out 428 00:25:49,600 --> 00:25:53,320 Speaker 1: in space, and your best friend is hanging back on Earth. 429 00:25:53,720 --> 00:25:57,080 Speaker 1: Now we now have our two frames of reference. We 430 00:25:57,160 --> 00:25:59,960 Speaker 1: have the spaceship and then we have the person on Earth. 431 00:26:00,280 --> 00:26:04,720 Speaker 1: So let's ignore accelerative forces for the moment, because we're 432 00:26:05,119 --> 00:26:07,600 Speaker 1: going to have to just focus on special relativity. We'll 433 00:26:07,640 --> 00:26:10,439 Speaker 1: get to general relativity in a moment. So you're in 434 00:26:10,480 --> 00:26:14,320 Speaker 1: your spaceship. You're zooming around at the speed of light, 435 00:26:14,720 --> 00:26:17,760 Speaker 1: and for you, time is passing normally. The seconds feel 436 00:26:17,760 --> 00:26:21,240 Speaker 1: like seconds, minutes feel like minutes, hours feel like hours, etcetera. 437 00:26:21,320 --> 00:26:24,439 Speaker 1: And you're on there for a full year. Back on Earth, 438 00:26:24,800 --> 00:26:27,720 Speaker 1: time is passing normally. For your best friend who's just 439 00:26:27,760 --> 00:26:31,000 Speaker 1: hanging out on Earth, they feel their seconds passed like seconds, 440 00:26:31,040 --> 00:26:34,679 Speaker 1: their minutes passing minutes, and so on. However, when we 441 00:26:34,720 --> 00:26:37,560 Speaker 1: look at the two of you in reference to one another, 442 00:26:37,840 --> 00:26:40,960 Speaker 1: something unusual happens. So to your best friend on Earth, 443 00:26:41,119 --> 00:26:44,359 Speaker 1: it looks like time is passing very slowly for you 444 00:26:44,560 --> 00:26:48,600 Speaker 1: aboard your spaceship. To you on your spaceship, it looks 445 00:26:48,640 --> 00:26:51,760 Speaker 1: like time is passing super fast for your friend back 446 00:26:51,800 --> 00:26:54,440 Speaker 1: on Earth. So when you do get back to Earth 447 00:26:54,480 --> 00:26:56,720 Speaker 1: a year later than the two of you enter the 448 00:26:56,800 --> 00:27:01,520 Speaker 1: same point of reference, things are weird. Your perspective, you've 449 00:27:01,560 --> 00:27:03,879 Speaker 1: only aged a year because you spend a year aboard 450 00:27:03,920 --> 00:27:06,199 Speaker 1: your spaceship, but a little more than a year and 451 00:27:06,240 --> 00:27:08,920 Speaker 1: a half has passed on Earth while you were gone. 452 00:27:09,359 --> 00:27:12,679 Speaker 1: Your calendars wouldn't line up anymore. The faster you go 453 00:27:12,800 --> 00:27:16,119 Speaker 1: relative to your frame of reference, the more pronounced the 454 00:27:16,160 --> 00:27:18,920 Speaker 1: time dilation. Now, I do want to be clear about this, 455 00:27:19,040 --> 00:27:22,399 Speaker 1: it's not really correct to say that as speed increases 456 00:27:22,480 --> 00:27:26,040 Speaker 1: time slows down. You have to always relay this in 457 00:27:26,160 --> 00:27:29,639 Speaker 1: terms of having another frame of reference, because within a 458 00:27:29,680 --> 00:27:34,160 Speaker 1: single frame of reference, time just passes normally. There's no difference. 459 00:27:34,400 --> 00:27:37,960 Speaker 1: By the way. This is also why star dates in 460 00:27:38,000 --> 00:27:40,919 Speaker 1: the Star Trek universe don't make a whole lot of sense. 461 00:27:41,359 --> 00:27:46,359 Speaker 1: They try to retroactively make it makes sense. But keeping 462 00:27:46,400 --> 00:27:49,160 Speaker 1: time when you're on a ship that can travel at 463 00:27:49,200 --> 00:27:51,160 Speaker 1: the speed of light or in the case of Star Trek, 464 00:27:51,640 --> 00:27:55,439 Speaker 1: magically going faster than the speed of light, and we 465 00:27:55,480 --> 00:27:58,639 Speaker 1: won't even get into warp speed. It all is crazy. 466 00:27:58,680 --> 00:28:02,200 Speaker 1: But and being able to use that and somehow related 467 00:28:02,280 --> 00:28:05,680 Speaker 1: to making sense on time passing on planets or space 468 00:28:05,680 --> 00:28:09,440 Speaker 1: stations or whatever, that's a huge mess. But it's also 469 00:28:09,520 --> 00:28:12,200 Speaker 1: outside of our episode, so we'll just leave it at that. 470 00:28:12,720 --> 00:28:15,760 Speaker 1: We don't notice the effects of special relativity in most 471 00:28:15,800 --> 00:28:18,119 Speaker 1: of our day to day lives because we are not 472 00:28:18,240 --> 00:28:21,119 Speaker 1: traveling fast enough relative to each other for it to 473 00:28:21,160 --> 00:28:24,800 Speaker 1: be a real factor most of the time. But it 474 00:28:24,840 --> 00:28:28,159 Speaker 1: does get even more weird. Were it possible to build 475 00:28:28,200 --> 00:28:31,160 Speaker 1: a spaceship that could travel at the speed of light, 476 00:28:31,720 --> 00:28:34,480 Speaker 1: and you were to take this sort of trip to 477 00:28:34,560 --> 00:28:38,320 Speaker 1: an outside observer, time would appear to stop for you 478 00:28:38,520 --> 00:28:42,720 Speaker 1: aboard your spaceship. Now if assuming this was even possible, 479 00:28:43,000 --> 00:28:45,680 Speaker 1: you would still experience time in your own frame of 480 00:28:45,720 --> 00:28:48,400 Speaker 1: reference as per normal, but your friend back on Earth 481 00:28:48,560 --> 00:28:51,640 Speaker 1: would see that it looked like you were frozen in time. However, 482 00:28:51,800 --> 00:28:54,520 Speaker 1: this is a mood point. Matter cannot travel at the 483 00:28:54,560 --> 00:28:58,680 Speaker 1: speed of light, so it's more of a thought experiment anyway. However, 484 00:28:59,000 --> 00:29:03,520 Speaker 1: we can actually det time dilation with extremely accurate time 485 00:29:03,520 --> 00:29:07,720 Speaker 1: measurement devices like atomic clocks. In fact, we've done it 486 00:29:08,280 --> 00:29:14,040 Speaker 1: in experiments. Scientists have synchronized two atomic clocks, and these 487 00:29:14,120 --> 00:29:18,160 Speaker 1: atomic clocks keep incredibly accurate time down to a matter 488 00:29:18,240 --> 00:29:23,040 Speaker 1: of nanoseconds, and a nanosecond is one billion of a second. 489 00:29:23,240 --> 00:29:27,000 Speaker 1: So one clock was kept stationary, you know, relatively speaking, 490 00:29:27,200 --> 00:29:31,000 Speaker 1: here on Earth. The other traveled aboard a high speed aircraft, 491 00:29:31,240 --> 00:29:33,800 Speaker 1: and at the end of the experiment they compared the 492 00:29:33,920 --> 00:29:37,320 Speaker 1: two clocks against each other, and the one that was 493 00:29:37,360 --> 00:29:41,160 Speaker 1: aboard the aircraft had measured less time than the one 494 00:29:41,240 --> 00:29:45,520 Speaker 1: that stayed on the ground on Earth, less time passed 495 00:29:45,880 --> 00:29:49,080 Speaker 1: on that aircraft relatively the amount of time passing on 496 00:29:49,160 --> 00:29:52,320 Speaker 1: the ground. It wasn't just that one clock was moving 497 00:29:52,360 --> 00:29:55,440 Speaker 1: more slowly than the other. Literally less time was passing 498 00:29:56,280 --> 00:29:59,840 Speaker 1: in reference to the other point of from the perspective 499 00:30:00,080 --> 00:30:03,080 Speaker 1: of the other point of reference, that is, the difference 500 00:30:03,160 --> 00:30:07,360 Speaker 1: was right in line with Einstein's calculations. Now, as we'll see, 501 00:30:07,560 --> 00:30:09,480 Speaker 1: this ends up being an important point when we get 502 00:30:09,480 --> 00:30:12,040 Speaker 1: to satellites. But we can't just jump on that yet. 503 00:30:12,080 --> 00:30:16,120 Speaker 1: We do need to take into consideration general relativity. So, 504 00:30:16,200 --> 00:30:19,120 Speaker 1: as I mentioned, special relativity only looks at frames of 505 00:30:19,160 --> 00:30:21,840 Speaker 1: reference that are in a constant and consistent motion with 506 00:30:21,840 --> 00:30:24,280 Speaker 1: regard to one another. There could be no change in 507 00:30:24,280 --> 00:30:28,240 Speaker 1: direction or speed because that introduces accelerative forces and that 508 00:30:28,320 --> 00:30:32,680 Speaker 1: changes things. So to take acceleration into account, Einstein proposed 509 00:30:32,720 --> 00:30:36,120 Speaker 1: his theory of general relativity ten years after his theory 510 00:30:36,200 --> 00:30:39,400 Speaker 1: of special relativity, so this would be nineteen fifteen for 511 00:30:39,440 --> 00:30:42,760 Speaker 1: those who are keeping track. This theory would incorporate the 512 00:30:42,800 --> 00:30:47,720 Speaker 1: force of gravity into Einstein's work, which means factoring in acceleration. 513 00:30:48,000 --> 00:30:51,680 Speaker 1: So in this theory, Einstein introduced the equivalence principle, which 514 00:30:51,840 --> 00:30:55,040 Speaker 1: says that gravity pulling in one direction is equivalent to 515 00:30:55,120 --> 00:30:59,280 Speaker 1: acceleration in another direction. So we can actually experience this. 516 00:30:59,520 --> 00:31:02,400 Speaker 1: It's easy to remember and imagine. Imagine getting on an 517 00:31:02,400 --> 00:31:05,720 Speaker 1: elevator and it's going up, and as it goes up, 518 00:31:05,760 --> 00:31:09,760 Speaker 1: you feel that sense of increased gravity pulling down on 519 00:31:09,880 --> 00:31:14,040 Speaker 1: you as the elevator accelerates. When the elevator is going down, 520 00:31:14,600 --> 00:31:17,760 Speaker 1: you feel a sense of decreased gravity as the elevator 521 00:31:17,760 --> 00:31:22,000 Speaker 1: accelerates downward. So gravity and acceleration are equivalent, which means 522 00:31:22,080 --> 00:31:25,240 Speaker 1: that it can also affect our measurements of space and time. 523 00:31:25,800 --> 00:31:30,920 Speaker 1: Einstein hypothesized that gravity was warping space time itself. Take 524 00:31:31,040 --> 00:31:36,920 Speaker 1: something that's really massive, like a huge dense star, that 525 00:31:36,960 --> 00:31:40,920 Speaker 1: would warp space time around it through its gravity, and 526 00:31:40,960 --> 00:31:44,760 Speaker 1: we can even observe this scientifically. Scientists have measured light 527 00:31:45,200 --> 00:31:50,120 Speaker 1: that has curved around massive stars. This is called gravitational lensing. 528 00:31:50,760 --> 00:31:53,440 Speaker 1: Now here's another thing that gets a bit confusing. The 529 00:31:53,480 --> 00:31:57,800 Speaker 1: effects of gravity on time mean that time passes differently 530 00:31:57,880 --> 00:32:01,520 Speaker 1: for objects in orbit when taken in reference to time 531 00:32:01,560 --> 00:32:06,800 Speaker 1: passing on Earth itself. Time passes faster in orbit than 532 00:32:06,880 --> 00:32:09,880 Speaker 1: it does on Earth. Now, again, this is a frame 533 00:32:09,920 --> 00:32:12,560 Speaker 1: of reference thing, because if you were on a spaceship 534 00:32:12,760 --> 00:32:16,480 Speaker 1: in orbit, your experience of time would feel exactly the 535 00:32:16,480 --> 00:32:19,400 Speaker 1: way it does when you are on Earth. It's only 536 00:32:19,480 --> 00:32:23,120 Speaker 1: when we look at this from two frames of reference 537 00:32:23,520 --> 00:32:25,960 Speaker 1: that we see how it doesn't match up. So what 538 00:32:26,040 --> 00:32:28,520 Speaker 1: does this all mean for satellites. Well, it means that 539 00:32:28,560 --> 00:32:32,240 Speaker 1: satellites in orbit have a couple of different relativistic effects 540 00:32:32,320 --> 00:32:35,160 Speaker 1: going on in our frame of reference here on Earth, 541 00:32:35,440 --> 00:32:39,400 Speaker 1: satellites are traveling faster than we are to maintain orbit, 542 00:32:39,680 --> 00:32:42,280 Speaker 1: which means that if we compare the passing of time 543 00:32:42,400 --> 00:32:46,200 Speaker 1: in each frame of reference, time would pass faster for 544 00:32:46,360 --> 00:32:50,680 Speaker 1: us than for the satellite. However, due to the gravitational 545 00:32:50,760 --> 00:32:53,800 Speaker 1: effect on space time, we also know that something in 546 00:32:53,960 --> 00:32:57,960 Speaker 1: orbit will have time passed faster for that thing then 547 00:32:58,000 --> 00:33:00,480 Speaker 1: we would experience here on Earth. So it's the opposite 548 00:33:00,560 --> 00:33:03,240 Speaker 1: of the effect of special relativity in a way, and 549 00:33:03,280 --> 00:33:06,920 Speaker 1: the effects of special relativity and general relativity don't actually 550 00:33:06,960 --> 00:33:10,320 Speaker 1: cancel each other out, which means ultimately that time on 551 00:33:10,360 --> 00:33:13,200 Speaker 1: a satellite and time down here on Earth are not 552 00:33:13,400 --> 00:33:16,239 Speaker 1: syncd up with reference to one another, and for some 553 00:33:16,320 --> 00:33:20,440 Speaker 1: types of satellites that's a problem. I'll explain more after 554 00:33:20,480 --> 00:33:32,360 Speaker 1: we take this quick break. To understand why relativity is 555 00:33:32,400 --> 00:33:36,400 Speaker 1: important with certain satellites, Let's talk about the Global Positioning 556 00:33:36,480 --> 00:33:40,280 Speaker 1: System or GPS. Now, this is the satellite system that 557 00:33:40,400 --> 00:33:42,800 Speaker 1: provides data back to Earth that makes it possible to 558 00:33:42,840 --> 00:33:46,960 Speaker 1: get precise coordinates using a GPS receiver. So how does 559 00:33:47,040 --> 00:33:50,000 Speaker 1: that work? Well, here on Earth, you could get a 560 00:33:50,120 --> 00:33:56,320 Speaker 1: very imprecise idea of your general coordinates through uh trilateration 561 00:33:56,840 --> 00:33:59,840 Speaker 1: using signals from cell phone towers. This works on a 562 00:34:00,040 --> 00:34:03,760 Speaker 1: fairly simple principle. So we know that the radio signals 563 00:34:03,920 --> 00:34:07,160 Speaker 1: sent to and from cell phones travel at essentially the 564 00:34:07,160 --> 00:34:10,960 Speaker 1: speed of light. So if a cell phone tower broadcasts 565 00:34:11,000 --> 00:34:14,239 Speaker 1: out a short command that just requests your phone to 566 00:34:14,320 --> 00:34:18,200 Speaker 1: respond back with a quick response a ping. In other words, 567 00:34:18,800 --> 00:34:21,160 Speaker 1: the amount of time it would take for the ping 568 00:34:21,200 --> 00:34:23,919 Speaker 1: to reach the cell tower could be used to work 569 00:34:24,000 --> 00:34:27,600 Speaker 1: backward and figure out how far away the phone is 570 00:34:27,840 --> 00:34:30,440 Speaker 1: from that cell phone tower. Because you know the speed 571 00:34:30,480 --> 00:34:33,319 Speaker 1: of travel, right is the speed of light, so you 572 00:34:33,360 --> 00:34:36,040 Speaker 1: also know how much time it took. That means you 573 00:34:36,040 --> 00:34:38,799 Speaker 1: can work backward to figure out the distance between those 574 00:34:38,840 --> 00:34:44,399 Speaker 1: two points. However, that's just a distance, there's no direction there. Now, 575 00:34:44,440 --> 00:34:47,560 Speaker 1: if you did this with multiple cell towers, the collective 576 00:34:47,640 --> 00:34:49,799 Speaker 1: data from those towers could be used to get a 577 00:34:49,880 --> 00:34:53,200 Speaker 1: rough estimate of where the phone is. So let's imagine 578 00:34:53,280 --> 00:34:56,040 Speaker 1: we've got a map, and on that map we've got 579 00:34:56,080 --> 00:35:00,200 Speaker 1: three cell towers A, B, n C. You can see 580 00:35:00,239 --> 00:35:03,359 Speaker 1: exactly where each one is. And let's say that you've 581 00:35:03,400 --> 00:35:06,920 Speaker 1: got a phone that's located somewhere within the broadcast range 582 00:35:07,000 --> 00:35:10,680 Speaker 1: of those three cell towers. Each tower sends a ping 583 00:35:10,680 --> 00:35:13,799 Speaker 1: to your phone, your phone responds with a ping back, 584 00:35:13,920 --> 00:35:17,960 Speaker 1: and you are given the amount of distance between your 585 00:35:18,000 --> 00:35:21,919 Speaker 1: phone and each of those three towers. Well, Tower as 586 00:35:22,000 --> 00:35:26,400 Speaker 1: result says that you are a mile away from Tower A, 587 00:35:26,840 --> 00:35:29,920 Speaker 1: so you actually have to draw a full circle around 588 00:35:30,000 --> 00:35:33,680 Speaker 1: Tower A to represent all the possible points you could 589 00:35:33,719 --> 00:35:35,759 Speaker 1: be that are one mile away from Tower A. So 590 00:35:35,840 --> 00:35:40,480 Speaker 1: you're drawing a mile radius around Tower A. Tower B 591 00:35:40,640 --> 00:35:44,400 Speaker 1: responds that you're within one point five miles of Tower B, 592 00:35:44,800 --> 00:35:46,640 Speaker 1: so you have to draw a circle around Tower B 593 00:35:46,800 --> 00:35:49,759 Speaker 1: to represent all the points where you could be that 594 00:35:49,800 --> 00:35:52,160 Speaker 1: are a mile and a half away from it. Now, 595 00:35:52,920 --> 00:35:55,000 Speaker 1: the circle from tower B in the circle from Tower 596 00:35:55,040 --> 00:35:58,400 Speaker 1: A should intersect each other at two points, but that 597 00:35:58,480 --> 00:36:01,040 Speaker 1: means you could be at either of those two points, right, 598 00:36:01,160 --> 00:36:03,759 Speaker 1: you could be an either overlap, So you don't have 599 00:36:03,880 --> 00:36:07,439 Speaker 1: enough information yet. By coordinating with tower C, and let's 600 00:36:07,440 --> 00:36:10,400 Speaker 1: say that one tells you you're within two miles, you 601 00:36:10,440 --> 00:36:13,520 Speaker 1: can draw a third circle, and the point where all 602 00:36:13,640 --> 00:36:18,040 Speaker 1: three circles would meet would be your general location. It's 603 00:36:18,080 --> 00:36:21,160 Speaker 1: not incredibly precise, but it does give you an idea 604 00:36:21,200 --> 00:36:25,520 Speaker 1: of where you are. The GPS constellation of satellites does 605 00:36:25,600 --> 00:36:27,759 Speaker 1: something similar, only we have to think of this in 606 00:36:27,880 --> 00:36:32,080 Speaker 1: terms of three dimensional space rather than a two dimensional map. 607 00:36:32,560 --> 00:36:36,080 Speaker 1: So a satellite sends out a high frequency, low power 608 00:36:36,239 --> 00:36:40,440 Speaker 1: radio signal and receivers pick that signal up. The receiver, 609 00:36:40,760 --> 00:36:43,759 Speaker 1: let's say it's your smartphone, doesn't have to send data 610 00:36:43,880 --> 00:36:46,320 Speaker 1: back up to the satellite, which is good because I 611 00:36:46,320 --> 00:36:49,560 Speaker 1: would be an enormous drain on your smartphones power. So 612 00:36:49,640 --> 00:36:53,600 Speaker 1: really it's just listening for these signals. Now, the receiver 613 00:36:53,640 --> 00:36:57,920 Speaker 1: and satellite both run the same digital pattern relative to 614 00:36:58,239 --> 00:37:01,560 Speaker 1: a specific time stamp. It's easy if we think of 615 00:37:01,560 --> 00:37:04,279 Speaker 1: this as midnight. So let's say that midnight hits and 616 00:37:04,360 --> 00:37:08,560 Speaker 1: this particular digital pattern starts both on the satellite and 617 00:37:08,960 --> 00:37:11,920 Speaker 1: the receiver, so they're both running the exact same pattern. 618 00:37:12,239 --> 00:37:15,240 Speaker 1: The satellite beams out a signal carrying this digital pattern. 619 00:37:15,520 --> 00:37:18,399 Speaker 1: The satellite is far away, so it takes a little time, 620 00:37:18,600 --> 00:37:20,440 Speaker 1: you know, not much, but a little time for that 621 00:37:20,520 --> 00:37:23,960 Speaker 1: signal to get to your receiver. And the lag between 622 00:37:24,040 --> 00:37:27,600 Speaker 1: the pattern that's playing on your receiver and the signal 623 00:37:28,040 --> 00:37:31,120 Speaker 1: of that same pattern coming in from the satellite tells 624 00:37:31,160 --> 00:37:34,920 Speaker 1: the receiver how far away it is from that particular satellite. 625 00:37:34,960 --> 00:37:37,759 Speaker 1: Because again we know that the signal is moving at 626 00:37:37,800 --> 00:37:40,440 Speaker 1: the speed of the transmission itself, and that's the speed 627 00:37:40,440 --> 00:37:43,520 Speaker 1: of light, and that's a constant. So now the receiver 628 00:37:43,600 --> 00:37:46,600 Speaker 1: knows how far away it is from that one satellite. 629 00:37:47,120 --> 00:37:50,520 Speaker 1: And because the orbits of these satellites are predictable, the 630 00:37:50,560 --> 00:37:53,640 Speaker 1: receiver has a record of where that satellite should be 631 00:37:53,760 --> 00:37:56,800 Speaker 1: relative to the your surface. Occasionally we have to tweak 632 00:37:56,960 --> 00:38:00,840 Speaker 1: that record because stuff like gravity can pull a satellite 633 00:38:00,840 --> 00:38:03,400 Speaker 1: slightly out of position over time, so that actually is 634 00:38:03,440 --> 00:38:06,520 Speaker 1: something that has to be addressed on occasion. Now this 635 00:38:06,600 --> 00:38:10,680 Speaker 1: receiver will do this with at least four satellites. The 636 00:38:10,800 --> 00:38:14,880 Speaker 1: why four and not three, and I gave the three 637 00:38:14,880 --> 00:38:18,480 Speaker 1: cell phone tower examples. Well, it's because the clocks on 638 00:38:18,640 --> 00:38:21,960 Speaker 1: satellites and the clock that's running on the device that 639 00:38:22,040 --> 00:38:25,080 Speaker 1: the receiver is built into may not be in and 640 00:38:25,120 --> 00:38:29,520 Speaker 1: really aren't truly synchronized. And the intersection of four spheres 641 00:38:29,680 --> 00:38:34,680 Speaker 1: of distance like these four spheres represent the various ranges 642 00:38:34,719 --> 00:38:38,200 Speaker 1: that these satellites are finding themselves in. With regard to 643 00:38:38,239 --> 00:38:43,680 Speaker 1: this receiver can only intersect at one point. That's the 644 00:38:43,719 --> 00:38:47,680 Speaker 1: only place they could all intersect. So if a GPS 645 00:38:47,719 --> 00:38:50,279 Speaker 1: receiver's clock is not matching up to the clocks on 646 00:38:50,320 --> 00:38:53,279 Speaker 1: the satellites, there will be no intersection at all, and 647 00:38:53,320 --> 00:38:55,640 Speaker 1: the receiver will say, well, I can't find an intersection, 648 00:38:55,719 --> 00:38:58,120 Speaker 1: so that I know that means my clock is off 649 00:38:58,280 --> 00:39:01,520 Speaker 1: from all the other clocks, and it will then adjust 650 00:39:01,600 --> 00:39:04,239 Speaker 1: its own clock to be an alignment so that the 651 00:39:04,280 --> 00:39:07,920 Speaker 1: four spheres have a point of intersection and that is 652 00:39:08,080 --> 00:39:11,400 Speaker 1: your location on Earth now. In order for our receivers 653 00:39:11,440 --> 00:39:13,799 Speaker 1: to be able to do this, the accuracy of the 654 00:39:13,840 --> 00:39:17,960 Speaker 1: atomic clocks aboard those GPS satellites has to be accurate 655 00:39:18,040 --> 00:39:23,360 Speaker 1: within twenty to thirty nanoseconds. And remember a nanosecond is 656 00:39:23,360 --> 00:39:28,000 Speaker 1: one billionth of a second. That is an astiunding level 657 00:39:28,040 --> 00:39:31,400 Speaker 1: of accuracy. And because these satellites are in motion and 658 00:39:31,480 --> 00:39:35,440 Speaker 1: they are also affected by Earth's gravity, they are subject 659 00:39:35,440 --> 00:39:39,239 Speaker 1: to the effects of special and general relativity, and this 660 00:39:39,320 --> 00:39:42,480 Speaker 1: means we actually have to make calculations to take that 661 00:39:42,680 --> 00:39:47,560 Speaker 1: into account. Now, according to special relativity and the relative 662 00:39:47,600 --> 00:39:50,560 Speaker 1: speeds of satellites to a fixed point on the surface 663 00:39:50,600 --> 00:39:54,240 Speaker 1: of the Earth, we would expect the atomic clock aboard 664 00:39:54,280 --> 00:39:59,000 Speaker 1: that satellite to register seven fewer micro seconds per day 665 00:39:59,040 --> 00:40:01,919 Speaker 1: than a clock on Earth because these satellites are moving 666 00:40:01,960 --> 00:40:06,319 Speaker 1: through space faster than we are, relatively speaking, So that 667 00:40:06,360 --> 00:40:09,160 Speaker 1: means from our frame of reference, time is passing more 668 00:40:09,239 --> 00:40:14,160 Speaker 1: slowly on that satellite than it does here on Earth. Ah. 669 00:40:14,200 --> 00:40:18,640 Speaker 1: But general relativity comes into play too, and general relativity 670 00:40:18,680 --> 00:40:22,920 Speaker 1: tells us that the Earth's gravity warps space time around 671 00:40:22,920 --> 00:40:27,080 Speaker 1: our planet. And one of general relativity's predictions is that 672 00:40:27,160 --> 00:40:31,040 Speaker 1: a clock closer to a massive object, so like a 673 00:40:31,120 --> 00:40:35,920 Speaker 1: clock here on Earth, will take more slowly than a 674 00:40:36,040 --> 00:40:40,320 Speaker 1: clock that is further out from that same massive object. 675 00:40:40,640 --> 00:40:43,440 Speaker 1: So the closer the clock is to the massive object, 676 00:40:43,480 --> 00:40:47,440 Speaker 1: the less time it will experience it will measure compared 677 00:40:47,480 --> 00:40:49,919 Speaker 1: to a clock this further away, which is crazy, right. 678 00:40:50,640 --> 00:40:55,319 Speaker 1: So taking only general relativity into account, we would see 679 00:40:55,320 --> 00:40:58,080 Speaker 1: that a clock aboard one of these satellites would register 680 00:40:58,560 --> 00:41:02,200 Speaker 1: more time having past on that satellite than a clock 681 00:41:02,400 --> 00:41:06,000 Speaker 1: here on Earth, meaning from our frame of reference, time 682 00:41:06,080 --> 00:41:09,680 Speaker 1: is actually passing faster on those satellites than it does 683 00:41:09,920 --> 00:41:13,320 Speaker 1: here for us. This would come out to about forty 684 00:41:13,320 --> 00:41:16,319 Speaker 1: five micro seconds a day, meaning that at the end 685 00:41:16,360 --> 00:41:19,279 Speaker 1: of day one, the clock aboard that satellite would be 686 00:41:19,360 --> 00:41:22,479 Speaker 1: ahead of a clock here on Earth by forty five 687 00:41:22,600 --> 00:41:26,719 Speaker 1: micro seconds, and this would continue day after day, with 688 00:41:26,880 --> 00:41:30,400 Speaker 1: the gap growing wider every single day. Now, when we 689 00:41:30,480 --> 00:41:36,000 Speaker 1: bring both special and general relativity together into consideration, we 690 00:41:36,160 --> 00:41:38,719 Speaker 1: see that they don't just cancel each other out right, 691 00:41:39,040 --> 00:41:42,279 Speaker 1: because we've got that seven micro second lag due to 692 00:41:42,320 --> 00:41:45,760 Speaker 1: special relativity, but we have the forty five micro second 693 00:41:45,960 --> 00:41:49,799 Speaker 1: surge due to general relativity. So in the end we're 694 00:41:49,800 --> 00:41:54,080 Speaker 1: looking at a thirty eight micro second difference per day 695 00:41:54,120 --> 00:41:56,840 Speaker 1: between a clock on a satellite and a clock here 696 00:41:56,920 --> 00:42:00,040 Speaker 1: on Earth. The clocks on the satellites will get a 697 00:42:00,080 --> 00:42:02,440 Speaker 1: head of similar clocks here on Earth by thirty eight 698 00:42:02,480 --> 00:42:06,719 Speaker 1: microseconds every single day. And while a microsecond is a 699 00:42:06,840 --> 00:42:09,239 Speaker 1: very small amount of time, I mean we're talking at 700 00:42:09,239 --> 00:42:12,479 Speaker 1: a level that we don't typically experience. We don't think 701 00:42:12,480 --> 00:42:16,120 Speaker 1: of time in microseconds for our day to day lives. However, 702 00:42:16,560 --> 00:42:21,120 Speaker 1: thirty eight microseconds is equal to thirty eight thousand nanoseconds, 703 00:42:21,440 --> 00:42:24,320 Speaker 1: and if you're looking for an accuracy of around twenty 704 00:42:24,360 --> 00:42:28,600 Speaker 1: to thirty nanoseconds, this becomes an enormous problem if we 705 00:42:28,680 --> 00:42:31,799 Speaker 1: don't take it into account. And this brings us background 706 00:42:31,800 --> 00:42:33,800 Speaker 1: to something I mentioned at the top of the show. 707 00:42:34,520 --> 00:42:38,000 Speaker 1: We know that Einstein was right about relativity because we 708 00:42:38,080 --> 00:42:41,879 Speaker 1: have to account for it with technology like GPS. If 709 00:42:41,920 --> 00:42:45,200 Speaker 1: we didn't take it into account, if we didn't factor 710 00:42:45,280 --> 00:42:49,120 Speaker 1: in the effects of relativity, our GPS wouldn't work for 711 00:42:49,239 --> 00:42:52,920 Speaker 1: very long at all. Our technology proves that the science 712 00:42:53,080 --> 00:42:56,080 Speaker 1: is real, or else the tech would fail at what 713 00:42:56,160 --> 00:42:59,239 Speaker 1: it needs to do. Now. In general, I think that's 714 00:42:59,280 --> 00:43:01,279 Speaker 1: a great let us And to take home, there are 715 00:43:01,320 --> 00:43:04,400 Speaker 1: a lot of voices out there that call science into question, 716 00:43:04,960 --> 00:43:07,520 Speaker 1: and some of them are more outlandish than others. A 717 00:43:07,560 --> 00:43:11,080 Speaker 1: person who is passionately and sincerely arguing that the Earth 718 00:43:11,200 --> 00:43:14,680 Speaker 1: is flat seems pretty far out there for me because 719 00:43:14,840 --> 00:43:17,600 Speaker 1: so much of our technology we've built upon and we 720 00:43:17,640 --> 00:43:21,480 Speaker 1: rely upon wouldn't work if that were true. Even if 721 00:43:21,520 --> 00:43:25,920 Speaker 1: you can't experience something directly, such as having a meaningful 722 00:43:26,120 --> 00:43:30,239 Speaker 1: experience of time dilation, a ton of the stuff we 723 00:43:30,360 --> 00:43:33,719 Speaker 1: do experience on a day to day basis is affected 724 00:43:33,760 --> 00:43:36,920 Speaker 1: by this stuff, and it proves the existence and also 725 00:43:37,040 --> 00:43:40,480 Speaker 1: the benefits of having the scientific method. Now give a 726 00:43:40,520 --> 00:43:44,000 Speaker 1: little side note on GPS to kind of wrap this up. 727 00:43:44,040 --> 00:43:47,560 Speaker 1: The original GPS configuration came out of a United States 728 00:43:47,600 --> 00:43:51,360 Speaker 1: Department a defense project. The original purpose was to provide 729 00:43:51,400 --> 00:43:55,880 Speaker 1: positioning information for government and military, but specifically the United 730 00:43:55,880 --> 00:43:58,400 Speaker 1: States and its allies, and for that reason, the U 731 00:43:58,480 --> 00:44:02,520 Speaker 1: S Government wished to restrict access to this technology. The 732 00:44:02,640 --> 00:44:04,920 Speaker 1: general line of thought was that it would be better 733 00:44:05,280 --> 00:44:07,600 Speaker 1: if the U. S didn't allow tech that could, you know, 734 00:44:08,160 --> 00:44:12,400 Speaker 1: give precise coordinates for stuff like military bases or the 735 00:44:12,400 --> 00:44:15,880 Speaker 1: position of various military units to people who didn't belong 736 00:44:15,960 --> 00:44:19,480 Speaker 1: to those divisions. So, as a matter of national security, 737 00:44:19,760 --> 00:44:24,239 Speaker 1: the US guarded this technology civilian receivers. So if you 738 00:44:24,239 --> 00:44:26,880 Speaker 1: went out and you bought a GPS receiver, you could 739 00:44:26,920 --> 00:44:31,719 Speaker 1: get public GPS signals. But the United States was purposefully 740 00:44:31,920 --> 00:44:37,040 Speaker 1: instituting a policy called selective availability, which was an intentional 741 00:44:37,200 --> 00:44:42,719 Speaker 1: degradation of public GPS signals. They were introducing errors on 742 00:44:43,000 --> 00:44:47,440 Speaker 1: purpose so that GPS receivers couldn't get an accurate location. 743 00:44:47,480 --> 00:44:52,319 Speaker 1: It limited accuracy to around fifty meters horizontally in a 744 00:44:52,360 --> 00:44:56,000 Speaker 1: hundred meters vertically, and effectively, that meant that you wouldn't 745 00:44:56,040 --> 00:44:59,920 Speaker 1: really know your precise coordinates. You certainly couldn't use a 746 00:45:00,040 --> 00:45:04,440 Speaker 1: GPS receiver as a turn by turn directions tool because 747 00:45:04,480 --> 00:45:07,200 Speaker 1: you wouldn't even necessarily show up on the right street. 748 00:45:07,840 --> 00:45:10,239 Speaker 1: You wouldn't know if you were approaching your turn or 749 00:45:10,239 --> 00:45:12,960 Speaker 1: if you had already passed it. It was it was 750 00:45:13,040 --> 00:45:15,520 Speaker 1: not practical for that. It was only in the year 751 00:45:15,600 --> 00:45:19,240 Speaker 1: two thousand, when US President Bill Clinton directed the government 752 00:45:19,320 --> 00:45:23,760 Speaker 1: to end selective availability, that civilian GPS receivers could actually 753 00:45:23,800 --> 00:45:27,320 Speaker 1: get accurate data. And that's what made the modern GPS 754 00:45:27,400 --> 00:45:31,760 Speaker 1: receivers and stuff like our phones possible. So before two thousand, 755 00:45:31,960 --> 00:45:34,840 Speaker 1: GPS receivers didn't work very well for the average person, 756 00:45:35,320 --> 00:45:38,160 Speaker 1: but it wasn't because the technology was bad or that 757 00:45:38,239 --> 00:45:41,239 Speaker 1: the science was wrong. It worked that way, or if 758 00:45:41,239 --> 00:45:44,680 Speaker 1: you prefer it, it didn't work properly on purpose. And 759 00:45:44,760 --> 00:45:48,200 Speaker 1: that wraps up this episode about relativity and why it's 760 00:45:48,239 --> 00:45:51,239 Speaker 1: important with technology, and it's not just satellite tech, but 761 00:45:51,280 --> 00:45:53,960 Speaker 1: that's a big one, and it also ends up being 762 00:45:54,040 --> 00:45:56,920 Speaker 1: a big thorn in the side for science fiction authors 763 00:45:56,960 --> 00:46:00,399 Speaker 1: who want to write about interstellar travel at ser than 764 00:46:00,480 --> 00:46:04,879 Speaker 1: light speeds, because you have to start finding alternative explanations 765 00:46:04,920 --> 00:46:08,480 Speaker 1: for how that's possible, because we we've come up against 766 00:46:08,480 --> 00:46:12,440 Speaker 1: these limits that Einstein predicted, and so far his predictions 767 00:46:12,440 --> 00:46:14,920 Speaker 1: have held true. So in order to travel faster than 768 00:46:14,960 --> 00:46:16,960 Speaker 1: the speed of light, you do have to create something 769 00:46:17,040 --> 00:46:21,839 Speaker 1: like warp drive, which theoretically warps space around you, So 770 00:46:21,960 --> 00:46:26,560 Speaker 1: rather than traveling faster than light, you're decreasing the distance 771 00:46:26,640 --> 00:46:30,399 Speaker 1: between your point of origin and your destination. It would 772 00:46:30,400 --> 00:46:32,280 Speaker 1: be kind of like taking a map of the United 773 00:46:32,320 --> 00:46:35,359 Speaker 1: States and saying I'm going to travel from Atlanta to 774 00:46:35,480 --> 00:46:38,880 Speaker 1: Los Angeles, from one coast to the other, but instead 775 00:46:38,880 --> 00:46:41,719 Speaker 1: of drawing a line from Atlanta to l A, you 776 00:46:41,800 --> 00:46:44,319 Speaker 1: just fold the map so that the two dots are 777 00:46:44,360 --> 00:46:46,360 Speaker 1: next to each other, and then you draw a line 778 00:46:46,440 --> 00:46:49,160 Speaker 1: that way. That's how warp speed is supposed to work, 779 00:46:49,280 --> 00:46:51,279 Speaker 1: because it's the only way you can get around the 780 00:46:51,320 --> 00:46:53,600 Speaker 1: fact that you can't really go faster than the speed 781 00:46:53,600 --> 00:46:57,000 Speaker 1: of light. But that's a topic for another show. If 782 00:46:57,040 --> 00:46:59,840 Speaker 1: you guys have suggestions for future topics I should tackle, 783 00:47:00,120 --> 00:47:02,960 Speaker 1: please let me know. Send me a message on Twitter. 784 00:47:03,200 --> 00:47:06,439 Speaker 1: The handle is text stuff H s W and I'll 785 00:47:06,440 --> 00:47:15,719 Speaker 1: talk to you again really soon y. Text Stuff is 786 00:47:15,719 --> 00:47:18,920 Speaker 1: an I Heart Radio production. For more podcasts from I 787 00:47:19,000 --> 00:47:22,600 Speaker 1: Heart Radio, visit the i heart Radio app, Apple Podcasts, 788 00:47:22,719 --> 00:47:24,720 Speaker 1: or wherever you listen to your favorite shows.