1 00:00:04,440 --> 00:00:13,000 Speaker 1: Welcome to Tech Stuff, a production from iHeartRadio. Hey therein 2 00:00:13,160 --> 00:00:16,800 Speaker 1: Welcome to Tech Stuff, I'm your host, Jonathan Strickland. I'm 3 00:00:16,800 --> 00:00:20,200 Speaker 1: an executive producer with iHeartRadio, and how the tech are you. 4 00:00:20,920 --> 00:00:23,720 Speaker 1: We have an episode that originally published on July first, 5 00:00:23,760 --> 00:00:28,120 Speaker 1: twenty twenty. It's called It's All Relative And when I 6 00:00:28,160 --> 00:00:31,479 Speaker 1: was a kid, I was convinced that Einstein's theories were 7 00:00:31,560 --> 00:00:36,160 Speaker 1: these super complicated explanations of the universe that really had 8 00:00:36,200 --> 00:00:39,960 Speaker 1: no real intersection with my daily life. But as it 9 00:00:40,000 --> 00:00:43,879 Speaker 1: turns out, without an understanding of relativity, a lot of 10 00:00:43,880 --> 00:00:48,040 Speaker 1: the technology we rely upon wouldn't work properly. And it's 11 00:00:48,080 --> 00:00:55,240 Speaker 1: fascinating stuff. Hope you enjoy. The hertz unit refers to 12 00:00:55,320 --> 00:00:59,280 Speaker 1: the number of repeated phenomena over the course of a second. 13 00:00:59,720 --> 00:01:03,400 Speaker 1: So well, imagine that you're dribbling a basketball, so that 14 00:01:03,520 --> 00:01:06,520 Speaker 1: the ball goes from your hand to the ground back 15 00:01:06,600 --> 00:01:09,759 Speaker 1: up to your hand once per second. Well, you could 16 00:01:09,760 --> 00:01:14,440 Speaker 1: describe your dribbling as being one hurts in frequency one 17 00:01:14,520 --> 00:01:18,399 Speaker 1: full cycle per second, up down, up. Now, if you 18 00:01:18,440 --> 00:01:21,759 Speaker 1: dribbled twice as fast, so that the ball went up, down, 19 00:01:21,920 --> 00:01:25,039 Speaker 1: up two full times per second, then it would be 20 00:01:25,319 --> 00:01:29,280 Speaker 1: two hurts. Well, we can describe lots of stuff with 21 00:01:29,440 --> 00:01:32,120 Speaker 1: the unit hurts. We use it to describe sounds, in 22 00:01:32,160 --> 00:01:36,360 Speaker 1: which case we're talking about the frequency at which stuff vibrates. 23 00:01:37,000 --> 00:01:40,880 Speaker 1: Typical human hearing spans a range of frequencies that at 24 00:01:40,920 --> 00:01:43,800 Speaker 1: the low end is at twenty hurts. That represents the 25 00:01:43,920 --> 00:01:46,600 Speaker 1: lowest pitches of sounds. You get to go those deep 26 00:01:46,720 --> 00:01:50,600 Speaker 1: bass notes. That's around the twenty hurts of area, and 27 00:01:50,640 --> 00:01:53,000 Speaker 1: then it goes all the way up to twenty kill 28 00:01:53,000 --> 00:01:57,040 Speaker 1: a hurts or twenty thousand hurts. That represents the very 29 00:01:57,120 --> 00:02:01,200 Speaker 1: highest pitches that people can typically hear, and those frequencies 30 00:02:01,400 --> 00:02:05,600 Speaker 1: correlate to how quickly stuff is vibrating back and forth. Now, 31 00:02:05,680 --> 00:02:08,120 Speaker 1: when it comes to us hearing things, we usually mean 32 00:02:08,240 --> 00:02:12,160 Speaker 1: that we're talking about the vibrations and fluctuation and air pressure, 33 00:02:12,400 --> 00:02:15,800 Speaker 1: and those fluctuations and air pressure interact with our ear drums. 34 00:02:16,520 --> 00:02:18,880 Speaker 1: But we can use hurts to talk about all sorts 35 00:02:18,919 --> 00:02:22,840 Speaker 1: of stuff, including the processor speed of a CPU. In 36 00:02:22,880 --> 00:02:25,480 Speaker 1: that case, we're really talking about the number of clock 37 00:02:25,720 --> 00:02:29,240 Speaker 1: cycles per second, So you get it. This is a 38 00:02:29,320 --> 00:02:32,720 Speaker 1: description of the frequency of the number of times a 39 00:02:32,760 --> 00:02:35,960 Speaker 1: certain thing happens like within a second. And I also 40 00:02:36,040 --> 00:02:39,320 Speaker 1: explained that we measure the rate at which we can 41 00:02:39,440 --> 00:02:43,240 Speaker 1: send data using the term bits. A bit is a 42 00:02:43,280 --> 00:02:46,640 Speaker 1: basic unit of digital information, and when we talk about computers, 43 00:02:46,880 --> 00:02:49,560 Speaker 1: we're talking about bits in the form of a zero 44 00:02:49,840 --> 00:02:54,040 Speaker 1: or a one binary information, just like your basic two 45 00:02:54,080 --> 00:02:58,080 Speaker 1: way physical switch has two positions off or on. So 46 00:02:58,160 --> 00:03:00,480 Speaker 1: if you hear a term like kill a bit, that 47 00:03:00,560 --> 00:03:04,200 Speaker 1: means one thousand bits, and a megabit is one million bits, 48 00:03:04,240 --> 00:03:09,120 Speaker 1: and a gigabit would be one billion bits. Likewise, megabits 49 00:03:09,200 --> 00:03:12,919 Speaker 1: per second tells us how many million bits can move 50 00:03:13,040 --> 00:03:16,280 Speaker 1: from one point to another per second over that connection. 51 00:03:16,760 --> 00:03:19,840 Speaker 1: So if you've got a one hundred megabit per second connection, 52 00:03:20,520 --> 00:03:24,040 Speaker 1: theoretically it would mean that up to one hundred million 53 00:03:24,120 --> 00:03:29,040 Speaker 1: bits can transfer across that communication channel per second, though 54 00:03:29,160 --> 00:03:32,040 Speaker 1: that's not how it works out most of the time, 55 00:03:32,120 --> 00:03:35,040 Speaker 1: but that's a matter for a different episode. I didn't 56 00:03:35,080 --> 00:03:39,320 Speaker 1: mention that this is different from something like megabytes. So 57 00:03:39,440 --> 00:03:42,640 Speaker 1: a byte is a unit that consists of eight bits. 58 00:03:43,480 --> 00:03:46,440 Speaker 1: And this gets confusing because we often describe stuff like 59 00:03:46,520 --> 00:03:50,600 Speaker 1: file sizes in terms of bytes, but transfer speeds in 60 00:03:50,760 --> 00:03:54,000 Speaker 1: terms of bits. So let's say that you do have 61 00:03:54,080 --> 00:03:57,720 Speaker 1: that one hundred megabits per second download speed, and you 62 00:03:57,800 --> 00:04:01,360 Speaker 1: want to download a one hundred megabyte file, well, that 63 00:04:01,440 --> 00:04:05,240 Speaker 1: means it's not going to take one second. It's going 64 00:04:05,320 --> 00:04:08,160 Speaker 1: to take eight seconds to download the file, because a 65 00:04:08,200 --> 00:04:12,280 Speaker 1: megabyte is eight times larger than a megabit. And actually 66 00:04:12,840 --> 00:04:15,640 Speaker 1: even that is a little bit misleading because in computer 67 00:04:15,680 --> 00:04:19,000 Speaker 1: memory terms, we typically look at units of memory based 68 00:04:19,040 --> 00:04:23,120 Speaker 1: on powers of two rather than powers of ten. So 69 00:04:23,160 --> 00:04:27,159 Speaker 1: instead of a kilobyte being one thousand bytes, it's actually 70 00:04:27,160 --> 00:04:31,240 Speaker 1: one thy twenty four bytes. And there's no standardization in 71 00:04:31,279 --> 00:04:35,040 Speaker 1: the tech industry, so sometimes people will say a kilobyte 72 00:04:35,160 --> 00:04:38,479 Speaker 1: and they mean one thousand bytes. Sometimes they'll say killobyte 73 00:04:38,480 --> 00:04:41,680 Speaker 1: and they mean one thy twenty four bytes, and you 74 00:04:41,720 --> 00:04:44,320 Speaker 1: will want to tear your hair out, and then you'll 75 00:04:44,320 --> 00:04:46,880 Speaker 1: look like I do, I'm bald if you didn't know. 76 00:04:47,160 --> 00:04:50,440 Speaker 1: But this episode isn't about the peculiarities of our naming 77 00:04:50,480 --> 00:04:54,359 Speaker 1: conventions and the computer information age. Instead, I wanted to 78 00:04:54,360 --> 00:04:58,640 Speaker 1: tackle something else that affects everything really, but in particular, 79 00:04:59,040 --> 00:05:00,839 Speaker 1: we really had to suss it out in order to 80 00:05:00,839 --> 00:05:04,440 Speaker 1: make certain types of satellites work properly, and this is 81 00:05:04,440 --> 00:05:08,280 Speaker 1: the concept of relativity. So in this episode, we're really 82 00:05:08,320 --> 00:05:11,720 Speaker 1: going to learn why an understanding of relativity is important 83 00:05:11,920 --> 00:05:16,040 Speaker 1: if we want our certain satellite technologies to work, and 84 00:05:16,080 --> 00:05:19,000 Speaker 1: it serves as a great reminder that technology is only 85 00:05:19,040 --> 00:05:22,840 Speaker 1: really possible through an understanding of science. You can think 86 00:05:22,880 --> 00:05:26,960 Speaker 1: of tech as the physical manifestation of our understanding of 87 00:05:27,000 --> 00:05:30,560 Speaker 1: scientific principles, and that means if we were wrong in 88 00:05:30,600 --> 00:05:34,760 Speaker 1: our understanding of science, the technology shouldn't really work. So 89 00:05:34,839 --> 00:05:37,680 Speaker 1: in a way, you can think of technology that works 90 00:05:37,960 --> 00:05:41,719 Speaker 1: as evidence that the scientific method is a darn good formula. 91 00:05:42,400 --> 00:05:45,200 Speaker 1: Since we're talking about relativity, it means we're going to 92 00:05:45,240 --> 00:05:49,680 Speaker 1: be talking about a real Einstein today. His name was Einstein, 93 00:05:50,200 --> 00:05:54,240 Speaker 1: which is convenient. But before we get to Einstein, we 94 00:05:54,360 --> 00:05:59,760 Speaker 1: have Galileo Galileo Galileo figure Ro. Wait No, I'm sorry, 95 00:05:59,800 --> 00:06:04,720 Speaker 1: wait that's Bohemian Rhapsody. I meant Galileo Galilei. This. Galileo 96 00:06:05,080 --> 00:06:08,920 Speaker 1: made an observation that if you've got two observers moving 97 00:06:08,960 --> 00:06:12,280 Speaker 1: at a constant speed and direction, so they're moving at 98 00:06:12,279 --> 00:06:15,120 Speaker 1: the same velocity, they will get the same results for 99 00:06:15,200 --> 00:06:19,440 Speaker 1: any experiment that involves moving stuff around a mechanical experiment. 100 00:06:20,160 --> 00:06:23,960 Speaker 1: This is easier to understand if we use an example, 101 00:06:24,279 --> 00:06:27,479 Speaker 1: and I like one that my colleague Robert Lamb used 102 00:06:27,520 --> 00:06:30,960 Speaker 1: when he wrote about relativity for HowStuffWorks dot com back 103 00:06:31,000 --> 00:06:33,919 Speaker 1: in the day. He used an example of a train 104 00:06:34,400 --> 00:06:38,240 Speaker 1: and a scientific ping pong ball. All right, so imagine 105 00:06:38,279 --> 00:06:40,800 Speaker 1: you've got a scientist who's standing in the middle of 106 00:06:40,839 --> 00:06:44,320 Speaker 1: an aisle on a moving train, and the train is 107 00:06:44,360 --> 00:06:47,200 Speaker 1: moving at a steady speed in a straight line, so 108 00:06:47,279 --> 00:06:51,839 Speaker 1: there are no active forces of acceleration going on here. Remember, 109 00:06:52,080 --> 00:06:56,440 Speaker 1: acceleration describes a force that involves a change in velocity, 110 00:06:56,520 --> 00:06:59,359 Speaker 1: so that either means a change in direction or a 111 00:06:59,440 --> 00:07:03,720 Speaker 1: change in speed, or both. But in this case constant 112 00:07:03,720 --> 00:07:09,120 Speaker 1: speed constant direction. Robert used nice round numbers in his examples, 113 00:07:09,240 --> 00:07:11,600 Speaker 1: so he suggested that the train is moving at one 114 00:07:11,640 --> 00:07:14,840 Speaker 1: hundred miles per hour. Well it's not round. If we 115 00:07:14,880 --> 00:07:16,680 Speaker 1: go to the metric system, that would be one hundred 116 00:07:16,720 --> 00:07:20,200 Speaker 1: and sixty one kilometers per hour. If the train stays 117 00:07:20,320 --> 00:07:23,160 Speaker 1: steady to the scientist, it will feel as if that 118 00:07:23,240 --> 00:07:27,160 Speaker 1: scientist is actually just standing still, just anywhere, and we're 119 00:07:27,320 --> 00:07:31,120 Speaker 1: conveniently ignoring an emotion that would happen due to irregularities 120 00:07:31,160 --> 00:07:33,800 Speaker 1: with the train's wheels or the train tracks or anything 121 00:07:33,880 --> 00:07:36,720 Speaker 1: like that. And if this is hard for you to imagine, 122 00:07:36,920 --> 00:07:39,760 Speaker 1: just think about how you feel when you're standing still 123 00:07:39,920 --> 00:07:43,360 Speaker 1: or sitting still or laying down here on Earth. We 124 00:07:43,520 --> 00:07:47,040 Speaker 1: know the Earth is moving through space. It is a 125 00:07:47,160 --> 00:07:51,160 Speaker 1: body in motion, but when we are still relative to 126 00:07:51,200 --> 00:07:55,240 Speaker 1: the Earth itself, we don't feel that motion. Assuming there's 127 00:07:55,280 --> 00:07:57,960 Speaker 1: not some other weird event going on, like an earthquake, 128 00:07:58,000 --> 00:08:01,760 Speaker 1: which is something separate. But back to our hypothetical train, 129 00:08:02,280 --> 00:08:06,680 Speaker 1: the scientist tosses the ping pong ball down the aisle. Now, 130 00:08:06,760 --> 00:08:10,720 Speaker 1: from the scientist's perspective, this ping pong ball will travel 131 00:08:10,760 --> 00:08:14,480 Speaker 1: at whatever speed they threw it at. Robert actually suggests 132 00:08:14,560 --> 00:08:17,960 Speaker 1: a relatively gentle toss of five miles per hour or 133 00:08:18,000 --> 00:08:21,720 Speaker 1: eight kilometers per hour. The ping pong ball would bounce 134 00:08:21,840 --> 00:08:24,360 Speaker 1: down the aisle, just as it would if the scientists 135 00:08:24,360 --> 00:08:26,440 Speaker 1: were to toss the ball on a train that isn't 136 00:08:26,480 --> 00:08:30,720 Speaker 1: moving at all, or on just flat ground. However, let's 137 00:08:30,760 --> 00:08:34,280 Speaker 1: say we have a second observer who's not on the train. 138 00:08:34,320 --> 00:08:36,640 Speaker 1: They're standing off to the side, and they can see 139 00:08:36,720 --> 00:08:39,880 Speaker 1: through the train. To this person, it will appear as 140 00:08:39,960 --> 00:08:43,520 Speaker 1: if the ping pong ball is moving very fast. Indeed, 141 00:08:43,880 --> 00:08:47,800 Speaker 1: relative to this stationary observer, the ping pong ball will 142 00:08:47,800 --> 00:08:49,760 Speaker 1: appear to move at the speed at which it was 143 00:08:49,840 --> 00:08:53,600 Speaker 1: thrown in addition to the speed of the train itself. 144 00:08:53,960 --> 00:08:56,160 Speaker 1: So if we take the two figures, we would get 145 00:08:56,320 --> 00:08:58,959 Speaker 1: one hundred five miles per hour or one hundred and 146 00:08:59,000 --> 00:09:05,600 Speaker 1: sixty nine per hour. This is called a Galilean transformation. Alternatively, 147 00:09:05,880 --> 00:09:08,040 Speaker 1: if the scientists were throwing the ping pong ball in 148 00:09:08,120 --> 00:09:11,080 Speaker 1: the opposite direction of the train's travel, so they're facing 149 00:09:11,280 --> 00:09:13,600 Speaker 1: toward the back of the train, it would appear to 150 00:09:13,679 --> 00:09:16,880 Speaker 1: this second observer the ping pong ball was moving at 151 00:09:16,880 --> 00:09:20,280 Speaker 1: a slightly slower speed than the overall train was, whereas 152 00:09:20,320 --> 00:09:23,040 Speaker 1: to the scientist on board, the ping pong ball would 153 00:09:23,080 --> 00:09:25,920 Speaker 1: still be traveling at that five mile per hour speed. 154 00:09:26,640 --> 00:09:30,720 Speaker 1: So this is where the term relativity comes into play. 155 00:09:31,120 --> 00:09:36,120 Speaker 1: The effects observed are relative to the perspective of the observer. 156 00:09:36,640 --> 00:09:40,319 Speaker 1: It's all based on the reference frame of that observer. 157 00:09:40,960 --> 00:09:43,280 Speaker 1: If you're on the train, then you're just looking at 158 00:09:43,280 --> 00:09:46,360 Speaker 1: a ping pong ball bouncing at a relatively slow speed 159 00:09:46,400 --> 00:09:48,920 Speaker 1: down the aisle. If you're not on the train, the 160 00:09:48,960 --> 00:09:52,480 Speaker 1: ping pong ball is moving quite fast, so it's all relative. 161 00:09:53,160 --> 00:09:56,440 Speaker 1: Isaac Newton would follow along and say, yeah, mate, this 162 00:09:56,520 --> 00:09:59,000 Speaker 1: all tracks. I don't know why he talked like that. 163 00:09:59,640 --> 00:10:02,920 Speaker 1: In his Laws of Motion, Newton stated that these laws 164 00:10:02,960 --> 00:10:06,200 Speaker 1: of motion should hold in an inertial frame as well 165 00:10:06,240 --> 00:10:09,320 Speaker 1: as reference frame that was moving at a constant velocity 166 00:10:09,400 --> 00:10:12,400 Speaker 1: relative to the inertial frame. An inertial frame, by the way, 167 00:10:12,760 --> 00:10:14,800 Speaker 1: is just a frame of reference in which there are 168 00:10:14,960 --> 00:10:18,160 Speaker 1: zero net forces acting upon it, so that there are 169 00:10:18,200 --> 00:10:20,960 Speaker 1: no forces of acceleration in play. So in our example, 170 00:10:21,120 --> 00:10:23,679 Speaker 1: the train that we talked about, that would be our 171 00:10:23,760 --> 00:10:28,280 Speaker 1: inertial frame. All of this is fairly intuitive, but then 172 00:10:28,320 --> 00:10:32,200 Speaker 1: we get to something really tricky. Einstein would establish that 173 00:10:32,280 --> 00:10:34,880 Speaker 1: the speed of light in a vacuum is the fastest 174 00:10:34,920 --> 00:10:38,040 Speaker 1: speed in our universe. Nothing can go faster than that. 175 00:10:38,520 --> 00:10:40,640 Speaker 1: But hey, what if you're on a train that's traveling 176 00:10:40,679 --> 00:10:43,199 Speaker 1: one hundred miles per hour and you're facing forward, you're 177 00:10:43,200 --> 00:10:46,080 Speaker 1: facing the direction of travel, and then you have a 178 00:10:46,120 --> 00:10:50,199 Speaker 1: flashlight and you turn on the flashlight. Well, doesn't that 179 00:10:50,280 --> 00:10:53,520 Speaker 1: mean you should perform a Galileean transformation on this and 180 00:10:53,559 --> 00:10:56,760 Speaker 1: say the light from that flashlight in your hands is 181 00:10:56,760 --> 00:10:59,480 Speaker 1: actually traveling at the normal speed of light on board 182 00:10:59,480 --> 00:11:03,520 Speaker 1: the train. But also get that boost of the trains travel, 183 00:11:03,559 --> 00:11:05,439 Speaker 1: so it should be the speed of light plus one 184 00:11:05,520 --> 00:11:08,800 Speaker 1: hundred miles per hour. Doesn't that make sense? While according 185 00:11:08,800 --> 00:11:11,960 Speaker 1: to actual experiments performed before Einstein would come around to 186 00:11:12,000 --> 00:11:16,000 Speaker 1: explain things, the answer was Nope, doesn't look like it 187 00:11:16,040 --> 00:11:20,559 Speaker 1: works that way. Scientists Edward Morley and Albert A. Michelson 188 00:11:20,840 --> 00:11:24,560 Speaker 1: created an experiment to measure the speed of light back 189 00:11:24,640 --> 00:11:27,760 Speaker 1: in eighteen eighty seven, and actually they were looking for 190 00:11:27,840 --> 00:11:31,360 Speaker 1: something else. They were looking for evidence of a hypothetical 191 00:11:31,400 --> 00:11:37,480 Speaker 1: substance called luminiferous ether. Say why, all right, we'll stick 192 00:11:37,520 --> 00:11:41,800 Speaker 1: with me, because in a way this does make sense. Okay, 193 00:11:41,920 --> 00:11:45,720 Speaker 1: So on Earth we see waves traveling through a medium, right, 194 00:11:45,880 --> 00:11:49,200 Speaker 1: Like if you look out in the ocean, you can 195 00:11:49,320 --> 00:11:52,920 Speaker 1: see actual waves in the water, and the water is 196 00:11:52,960 --> 00:11:57,360 Speaker 1: a physical medium through which these waves travel. Sound can't 197 00:11:57,520 --> 00:12:01,120 Speaker 1: travel in space because space is effect actively a vacuum. 198 00:12:01,400 --> 00:12:04,480 Speaker 1: The particles that are in space are so far apart 199 00:12:04,480 --> 00:12:07,080 Speaker 1: from one another that there's no way for the vibration 200 00:12:07,240 --> 00:12:11,400 Speaker 1: of one particle to come into contact and affect another particle. 201 00:12:11,760 --> 00:12:14,840 Speaker 1: So sound can't travel. Sound travels through the propagation of 202 00:12:14,960 --> 00:12:18,600 Speaker 1: vibrational waves. And if your stuff isn't in contact with 203 00:12:18,640 --> 00:12:20,960 Speaker 1: each other, there's no way for them to have that 204 00:12:21,040 --> 00:12:24,120 Speaker 1: wave propagate. So there has to be some sort of 205 00:12:24,320 --> 00:12:29,120 Speaker 1: medium like air or solid surfaces or something in order 206 00:12:29,160 --> 00:12:33,680 Speaker 1: for sound travel. Well, if that's the case, said the 207 00:12:33,679 --> 00:12:37,160 Speaker 1: folks of the time, then stuff like light must need 208 00:12:37,200 --> 00:12:39,800 Speaker 1: some sort of medium to travel through, right. I mean 209 00:12:39,840 --> 00:12:42,320 Speaker 1: sound has to have something. Light must have something too. 210 00:12:43,160 --> 00:12:46,040 Speaker 1: Light can definitely travel through space. I mean, that's how 211 00:12:46,040 --> 00:12:49,000 Speaker 1: we can see anything, because light from the Sun travels 212 00:12:49,040 --> 00:12:52,400 Speaker 1: through space to hit the Earth. So the light has 213 00:12:52,440 --> 00:12:55,160 Speaker 1: to be moving through some sort of medium we cannot 214 00:12:55,240 --> 00:13:01,079 Speaker 1: observe directly. This hypothetical medium was the aforementioned maniferous ether. 215 00:13:01,760 --> 00:13:05,600 Speaker 1: But assuming this ether existed at all, it had to 216 00:13:05,600 --> 00:13:08,960 Speaker 1: be pretty darn special because we can't feel it, we 217 00:13:09,040 --> 00:13:13,400 Speaker 1: can't detect it, it creates no observable effects, So if 218 00:13:13,440 --> 00:13:16,480 Speaker 1: it were real, it had to be unlike pretty much 219 00:13:16,520 --> 00:13:20,200 Speaker 1: anything else we had discovered up to that point. Now, 220 00:13:20,440 --> 00:13:24,640 Speaker 1: let's assume that the universe is filled with this ether stuff. 221 00:13:25,040 --> 00:13:28,640 Speaker 1: The question rises, how the heck does the ether interact 222 00:13:28,720 --> 00:13:31,080 Speaker 1: with all the physical stuff that's in the universe, the 223 00:13:31,120 --> 00:13:36,400 Speaker 1: actual matter and also energy. After all, the bodies in 224 00:13:36,559 --> 00:13:40,360 Speaker 1: space like stars, planets, moons and all that other stuff. 225 00:13:40,640 --> 00:13:44,160 Speaker 1: All of that is moving, none of it is standing still, 226 00:13:44,440 --> 00:13:48,040 Speaker 1: and if it is moving, it would presumably disturb this 227 00:13:48,360 --> 00:13:51,960 Speaker 1: ether medium, right. I mean, if you move your hand 228 00:13:52,200 --> 00:13:55,040 Speaker 1: through a pool of water, you are disturbing that water. 229 00:13:55,080 --> 00:13:58,080 Speaker 1: You're making currents and eddies. So it was thought that 230 00:13:58,360 --> 00:14:01,600 Speaker 1: the motion of all these elements in space would disturb 231 00:14:01,720 --> 00:14:05,240 Speaker 1: the ether in some way, and hypothetically there would be 232 00:14:05,280 --> 00:14:09,440 Speaker 1: some sort of ether wind. But if there were a wind, 233 00:14:09,920 --> 00:14:13,520 Speaker 1: then presumably the speed of light would be affected depending 234 00:14:13,640 --> 00:14:17,640 Speaker 1: upon the wind's direction in relation to the light's direction. 235 00:14:18,040 --> 00:14:21,000 Speaker 1: So think of a really windy day in the real world. 236 00:14:21,400 --> 00:14:25,000 Speaker 1: If you're walking against a very very tough wind, like 237 00:14:25,040 --> 00:14:27,920 Speaker 1: a gale force wind, you have to power through it 238 00:14:27,960 --> 00:14:31,480 Speaker 1: to keep moving forward. Now, if you're walking with the wind, 239 00:14:31,840 --> 00:14:33,640 Speaker 1: like the wind is to your back and pushing you, 240 00:14:34,040 --> 00:14:36,760 Speaker 1: then you get a big boost. Well, the same thing 241 00:14:36,880 --> 00:14:40,840 Speaker 1: should be happening with light if ether wind were real, 242 00:14:41,480 --> 00:14:44,880 Speaker 1: and so Mickelson and Morley devised a gadget that would 243 00:14:44,960 --> 00:14:49,720 Speaker 1: split light into two beams, directing those beams down different paths, 244 00:14:50,000 --> 00:14:53,400 Speaker 1: using mirrors in different directions, and seeing if those two 245 00:14:53,400 --> 00:14:56,640 Speaker 1: beams of light would hit an eyepiece at different times. 246 00:14:56,680 --> 00:15:00,760 Speaker 1: The thought being well, one of these directions would theoretically 247 00:15:00,840 --> 00:15:03,680 Speaker 1: be in the same direction as the ether wind, and 248 00:15:03,760 --> 00:15:06,560 Speaker 1: one would be at a cross direction of ether wind, 249 00:15:06,800 --> 00:15:08,720 Speaker 1: So we should see a difference in the amount of 250 00:15:08,760 --> 00:15:12,040 Speaker 1: time it takes for the light from this one source 251 00:15:12,240 --> 00:15:15,360 Speaker 1: that's been split into two to arrive at an eyepiece. 252 00:15:16,320 --> 00:15:21,080 Speaker 1: But that's not what they found. They observed no such effect. 253 00:15:21,240 --> 00:15:23,600 Speaker 1: So if there were such a thing as ether, the 254 00:15:23,640 --> 00:15:27,120 Speaker 1: stuff wasn't giving either a boost or a drag on 255 00:15:27,280 --> 00:15:30,400 Speaker 1: light itself. No matter what. The light was traveling at 256 00:15:30,400 --> 00:15:33,480 Speaker 1: a constant speed, which turned out to be approximately one 257 00:15:33,560 --> 00:15:36,480 Speaker 1: hundred eighty six thousand miles per second or around three 258 00:15:36,560 --> 00:15:40,400 Speaker 1: hundred thousand kilometers per second. Now that flew in the 259 00:15:40,440 --> 00:15:44,760 Speaker 1: face of classic Newtonian physics clearly. With the example of 260 00:15:44,800 --> 00:15:47,040 Speaker 1: the ping pong ball and the train, the ping pong 261 00:15:47,080 --> 00:15:50,320 Speaker 1: ball has to be traveling faster than the train it's on. 262 00:15:50,400 --> 00:15:52,480 Speaker 1: I mean, that just makes sense. If you were standing 263 00:15:52,560 --> 00:15:54,880 Speaker 1: on the top of the very front of the train 264 00:15:55,320 --> 00:15:58,040 Speaker 1: and then you threw the ping pong ball, and we 265 00:15:58,120 --> 00:16:01,560 Speaker 1: ignore stuff like wind resistant, the ping pong ball would 266 00:16:01,640 --> 00:16:03,920 Speaker 1: land ahead of the train, So it has to be 267 00:16:04,000 --> 00:16:07,240 Speaker 1: going faster. So what the heck was so special about 268 00:16:07,360 --> 00:16:10,120 Speaker 1: light and what was going on? Well, this was one 269 00:16:10,120 --> 00:16:13,240 Speaker 1: of the great mysteries that Albert Einstein set his mind 270 00:16:13,280 --> 00:16:16,240 Speaker 1: to unraveling, and it formed the basis of one of 271 00:16:16,280 --> 00:16:19,360 Speaker 1: his great theories of relativity. And this would be the 272 00:16:19,360 --> 00:16:23,000 Speaker 1: theory of special relativity, which poses that the laws of 273 00:16:23,040 --> 00:16:26,640 Speaker 1: physics are in the same in all inertial frames of references. 274 00:16:27,240 --> 00:16:28,960 Speaker 1: And that means the speed of light will be the 275 00:16:28,960 --> 00:16:33,400 Speaker 1: same for all observers, regardless of their relative perspectives. It 276 00:16:33,440 --> 00:16:36,760 Speaker 1: doesn't matter the context. The speed of light is the 277 00:16:36,800 --> 00:16:40,080 Speaker 1: speed of light. Now, there's an implication to this theory 278 00:16:40,440 --> 00:16:43,520 Speaker 1: that really got people scratching their heads. If the speed 279 00:16:43,520 --> 00:16:47,240 Speaker 1: of light is absolutely constant, that would mean that stuff 280 00:16:47,400 --> 00:16:51,480 Speaker 1: like distance and time are not. And as a heck 281 00:16:51,520 --> 00:16:54,480 Speaker 1: of a brain teaser, when we come back, we'll explore 282 00:16:54,520 --> 00:17:06,080 Speaker 1: this more. Let's imagine that you live half a mile 283 00:17:06,200 --> 00:17:09,760 Speaker 1: away from a lovely park, and it's a half mile 284 00:17:09,800 --> 00:17:12,600 Speaker 1: away in the morning, it's a half mile away. At night, 285 00:17:13,240 --> 00:17:15,720 Speaker 1: it's a half mile away. On a Tuesday, it's a 286 00:17:15,760 --> 00:17:19,639 Speaker 1: half mile away. On a Saturday. Half a mile is 287 00:17:19,720 --> 00:17:24,040 Speaker 1: half a mile, right, it's a reliable constant in our lives. 288 00:17:24,119 --> 00:17:27,280 Speaker 1: If it weren't, we could never give directions to anywhere 289 00:17:27,320 --> 00:17:30,639 Speaker 1: because all the measurements and landmarks would change all the time, 290 00:17:30,920 --> 00:17:34,120 Speaker 1: and our world wouldn't make sense the way it does 291 00:17:34,160 --> 00:17:38,159 Speaker 1: to us now. So in our individual experiences, in our 292 00:17:38,280 --> 00:17:42,480 Speaker 1: day to day lives, stuff like distance seems pretty darn 293 00:17:42,560 --> 00:17:47,560 Speaker 1: reliable and fixed. So how dare Einstein come along with 294 00:17:47,600 --> 00:17:51,400 Speaker 1: this theory of special relativity at nineteen oh five and say, well, yeah, 295 00:17:51,440 --> 00:17:55,560 Speaker 1: but see, the speed of light is really the true constant, 296 00:17:55,920 --> 00:17:59,560 Speaker 1: and for that to work, time and distance or space, 297 00:17:59,640 --> 00:18:04,960 Speaker 1: in other word, words, must be somewhat mutable. Einstein positive 298 00:18:05,160 --> 00:18:09,400 Speaker 1: that there is no absolute frame of reference in our universe, 299 00:18:09,640 --> 00:18:12,679 Speaker 1: which means there is no place in the universe that 300 00:18:12,840 --> 00:18:17,480 Speaker 1: is totally stationary. Everything is moving, which means all motion 301 00:18:17,760 --> 00:18:20,919 Speaker 1: is relative. You can't really talk about moving except in 302 00:18:20,960 --> 00:18:24,959 Speaker 1: reference to some other moving thing. So even as we 303 00:18:25,160 --> 00:18:28,879 Speaker 1: sit still and try to meditate, we do so on 304 00:18:28,920 --> 00:18:32,879 Speaker 1: a planet that is hurtling through space. We are in motion. 305 00:18:33,200 --> 00:18:36,399 Speaker 1: We're all moving through space and time, and we all 306 00:18:36,440 --> 00:18:40,560 Speaker 1: have a frame of reference, and each frame of reference 307 00:18:40,920 --> 00:18:44,320 Speaker 1: is just as legitimate as every other frame of reference, 308 00:18:45,080 --> 00:18:48,520 Speaker 1: or I guess you could say, if everybody's super, nobody is. 309 00:18:49,320 --> 00:18:52,520 Speaker 1: I guess I've watched The Incredibles too many times. Well, anyway, 310 00:18:52,560 --> 00:18:56,400 Speaker 1: this particular nineteen oh five theory is called special relativity 311 00:18:56,560 --> 00:19:01,800 Speaker 1: because Einstein's explanation only covered special cases, that being when 312 00:19:02,040 --> 00:19:05,600 Speaker 1: two inertial frames are in constant motion with regard to 313 00:19:05,640 --> 00:19:08,720 Speaker 1: one another, and there can be no acceleration, so the 314 00:19:08,760 --> 00:19:10,919 Speaker 1: motion had to be in a straight line at a 315 00:19:11,000 --> 00:19:14,679 Speaker 1: constant speed. A change in direction or speed would be 316 00:19:14,800 --> 00:19:18,080 Speaker 1: an acceleration, and to cover those instances we would have 317 00:19:18,080 --> 00:19:20,600 Speaker 1: to wait a decade for Einstein to work out his 318 00:19:20,720 --> 00:19:24,320 Speaker 1: theory of general relativity. We'll get to that, but we've 319 00:19:24,359 --> 00:19:27,280 Speaker 1: got a lot more to say about special relativity. So 320 00:19:27,400 --> 00:19:30,400 Speaker 1: Einstein was taking a different approach to the results of 321 00:19:30,440 --> 00:19:33,879 Speaker 1: the experiments done by people like Michelson and Morley. The 322 00:19:33,920 --> 00:19:38,080 Speaker 1: scientific world at large was essentially saying, well, this can't 323 00:19:38,119 --> 00:19:40,720 Speaker 1: be right. These results can't be right. There must be 324 00:19:40,800 --> 00:19:44,320 Speaker 1: something wrong with the experiment or the equipment, because we're 325 00:19:44,440 --> 00:19:48,000 Speaker 1: sure this theory is correct and that ether is there. 326 00:19:48,600 --> 00:19:51,439 Speaker 1: Einstein was taking a totally different perspective. He was saying, 327 00:19:52,080 --> 00:19:56,400 Speaker 1: if we assume the experiments are producing accurate results, then 328 00:19:56,440 --> 00:19:59,760 Speaker 1: it stands to reason that the prevailing theory is flawed 329 00:20:00,080 --> 00:20:02,600 Speaker 1: and we have to figure out what the real explanation is. 330 00:20:03,040 --> 00:20:05,360 Speaker 1: And this is one of those important points in science. 331 00:20:05,920 --> 00:20:09,520 Speaker 1: It's that if your results in your experiment don't meet 332 00:20:09,560 --> 00:20:14,639 Speaker 1: your hypothesis, it's very possible that your hypothesis is wrong. 333 00:20:14,960 --> 00:20:17,960 Speaker 1: Now you need to do multiple experiments to find out 334 00:20:18,520 --> 00:20:20,919 Speaker 1: and to test your equipment make sure there's not any 335 00:20:21,280 --> 00:20:24,520 Speaker 1: errors there that could be causing the issues. But it 336 00:20:24,560 --> 00:20:27,440 Speaker 1: does mean that you need to re examine that hypothesis, 337 00:20:27,960 --> 00:20:32,080 Speaker 1: and at this time the scientific community wasn't really doing that, 338 00:20:32,720 --> 00:20:37,200 Speaker 1: so Einstein did away with the ether. His explanation suggested 339 00:20:37,240 --> 00:20:41,520 Speaker 1: that our observable universe has four dimensions, not that there 340 00:20:41,520 --> 00:20:44,760 Speaker 1: can only be four dimensions, but rather there are four 341 00:20:44,800 --> 00:20:52,320 Speaker 1: dimensions we can detect and observe, and these would be up, down, left, right, forward, backward, 342 00:20:52,760 --> 00:20:57,520 Speaker 1: and then the fourth dimension, which is time. Collectively, those 343 00:20:57,560 --> 00:21:01,280 Speaker 1: three dimensions are space. The fourth dimension is time, and 344 00:21:01,320 --> 00:21:06,320 Speaker 1: we get the space time continuum, this intrinsic relationship between 345 00:21:06,359 --> 00:21:10,000 Speaker 1: space and time or space time continuum, which also gives 346 00:21:10,080 --> 00:21:13,280 Speaker 1: us dozens of Star Trek episodes that would use it 347 00:21:13,320 --> 00:21:15,919 Speaker 1: as shorthand, for things are about to get really weird. 348 00:21:16,600 --> 00:21:20,120 Speaker 1: Einstein positive that the speed of light is measured as 349 00:21:20,240 --> 00:21:23,399 Speaker 1: constant in all frames of reference. And let's think for 350 00:21:23,480 --> 00:21:27,199 Speaker 1: a second. What we mean by speed. Speed is a 351 00:21:27,240 --> 00:21:31,000 Speaker 1: description of how much distance can be covered per unit 352 00:21:31,119 --> 00:21:34,080 Speaker 1: of time. So a speed of one hundred miles per 353 00:21:34,080 --> 00:21:37,080 Speaker 1: hour means that in one hour's time we will cover 354 00:21:37,160 --> 00:21:40,439 Speaker 1: a distance of one hundred miles. That's very obvious. But 355 00:21:41,040 --> 00:21:44,240 Speaker 1: if the speed of light is constant for all frames 356 00:21:44,320 --> 00:21:48,040 Speaker 1: of reference, regardless of how those frames are moving relative 357 00:21:48,080 --> 00:21:51,520 Speaker 1: to each other, that must mean something about space and 358 00:21:51,800 --> 00:21:55,680 Speaker 1: or time is a little wonky. And let's think about 359 00:21:55,720 --> 00:21:58,920 Speaker 1: our train experiment again. If you are aboard a train 360 00:21:59,320 --> 00:22:01,600 Speaker 1: moving at a move one hundred miles per hour in 361 00:22:01,640 --> 00:22:04,120 Speaker 1: a straight line, and you toss a ping pong ball 362 00:22:04,160 --> 00:22:06,919 Speaker 1: straight up in the air, well, it's gonna go straight 363 00:22:07,000 --> 00:22:09,240 Speaker 1: up and come right back down to your hand in 364 00:22:09,320 --> 00:22:12,960 Speaker 1: a nice vertical line. From an outside observer who isn't 365 00:22:12,960 --> 00:22:15,199 Speaker 1: on the train, it would look a little differently. You 366 00:22:15,200 --> 00:22:18,040 Speaker 1: would throw the ball up at one point relative to 367 00:22:18,080 --> 00:22:20,720 Speaker 1: this outside observer, and the ball would appear to move 368 00:22:20,760 --> 00:22:24,200 Speaker 1: not just vertically, but horizontally before coming back down. Now, 369 00:22:24,240 --> 00:22:27,640 Speaker 1: if we repeat this experiment but we use light, we 370 00:22:27,680 --> 00:22:30,760 Speaker 1: really see how it gets confusing. Okay, so now you're 371 00:22:30,800 --> 00:22:34,640 Speaker 1: on a train, but it's going really fast, like let's say, 372 00:22:34,720 --> 00:22:38,080 Speaker 1: half the speed of light. But the speed and direction 373 00:22:38,200 --> 00:22:41,240 Speaker 1: are constant. So you're on this train. You don't feel 374 00:22:41,480 --> 00:22:45,320 Speaker 1: any acceleration forces because you're moving at a constant speed 375 00:22:45,920 --> 00:22:48,760 Speaker 1: and in a constant direction, so your velocity remains the same. 376 00:22:49,280 --> 00:22:51,560 Speaker 1: In fact, if there were no windows on the train, 377 00:22:51,640 --> 00:22:53,400 Speaker 1: you wouldn't even be able to tell that the train 378 00:22:53,520 --> 00:22:55,800 Speaker 1: was moving at all. So let's say you've got a 379 00:22:55,840 --> 00:22:58,679 Speaker 1: laser pointer and you've got a mirror on the ceiling 380 00:22:58,760 --> 00:23:01,720 Speaker 1: of the train and a foton detector on the floor 381 00:23:01,720 --> 00:23:04,439 Speaker 1: of the train. You shoot the laser up at the mirror, 382 00:23:04,680 --> 00:23:07,680 Speaker 1: it reflects off the mirror, and then it comes back 383 00:23:07,680 --> 00:23:10,560 Speaker 1: down and hits the detector on the floor, and it 384 00:23:10,760 --> 00:23:13,360 Speaker 1: registers how long it took the light to travel from 385 00:23:13,400 --> 00:23:16,280 Speaker 1: your laser pointer to hit the detector. And to you, 386 00:23:16,640 --> 00:23:19,600 Speaker 1: the laser makes a vertical line. All that makes sense, right, 387 00:23:19,640 --> 00:23:23,000 Speaker 1: you can imagine that, But for our outside observer who's 388 00:23:23,000 --> 00:23:25,280 Speaker 1: not on the train, it would appear as though the 389 00:23:25,359 --> 00:23:29,040 Speaker 1: laser were actually traveling at a diagonal up to that mirror, 390 00:23:29,280 --> 00:23:32,600 Speaker 1: and then a diagonal back down toward the detector. So 391 00:23:33,119 --> 00:23:35,679 Speaker 1: for one observer, the one on the train, we have 392 00:23:35,720 --> 00:23:39,320 Speaker 1: a straight line. It's vertical up down. For the second 393 00:23:39,400 --> 00:23:42,280 Speaker 1: observer off the train, we have an angled path, sort 394 00:23:42,320 --> 00:23:44,160 Speaker 1: of like how a billiard ball can hit the side 395 00:23:44,160 --> 00:23:46,240 Speaker 1: of a pool table and bounce off at an angle. 396 00:23:47,000 --> 00:23:50,400 Speaker 1: But this creates an apparent paradox. The path viewed by 397 00:23:50,600 --> 00:23:52,960 Speaker 1: you on the train is a straight line, and by 398 00:23:53,000 --> 00:23:56,600 Speaker 1: definition that is the shortest distance between two points. The 399 00:23:56,640 --> 00:23:59,119 Speaker 1: path observed by the person who is not on the 400 00:23:59,160 --> 00:24:02,320 Speaker 1: train is an angled line, and by definition that has 401 00:24:02,359 --> 00:24:05,520 Speaker 1: to be longer. The speed of light is constant in 402 00:24:05,560 --> 00:24:09,080 Speaker 1: both cases, but the distance is different between the two 403 00:24:09,080 --> 00:24:13,040 Speaker 1: points of reference. And because speed is distance divided by time, 404 00:24:13,359 --> 00:24:16,359 Speaker 1: if the distance is different, the time must also be 405 00:24:16,520 --> 00:24:22,240 Speaker 1: different between those two points of reference. Crazy This brings 406 00:24:22,320 --> 00:24:25,440 Speaker 1: us to the concept of time dilation. It also, by 407 00:24:25,440 --> 00:24:29,760 Speaker 1: the way, can affect distance. The faster an object gets, 408 00:24:30,280 --> 00:24:34,679 Speaker 1: the more squished it gets. So if you had this 409 00:24:34,840 --> 00:24:37,480 Speaker 1: train and you were to get up to near the 410 00:24:37,520 --> 00:24:40,800 Speaker 1: speed of light, the train to an outside observer would 411 00:24:40,800 --> 00:24:44,840 Speaker 1: appear to be shorter than it normally would be to 412 00:24:44,920 --> 00:24:48,640 Speaker 1: anyone inside the train, the dimensions would remain exactly the same. 413 00:24:49,000 --> 00:24:52,040 Speaker 1: You would not suddenly see a shorter train. It wouldn't 414 00:24:52,040 --> 00:24:54,600 Speaker 1: be like you were in that compressor scene in Star Wars. 415 00:24:54,960 --> 00:24:57,239 Speaker 1: The train would appear to be normal only from an 416 00:24:57,280 --> 00:25:00,400 Speaker 1: outside observer who is not traveling at that speed, when 417 00:25:00,440 --> 00:25:05,800 Speaker 1: it appeared that the train itself was getting squished shorter. Likewise, 418 00:25:06,240 --> 00:25:09,960 Speaker 1: the faster something goes with respect to some other point 419 00:25:09,960 --> 00:25:13,760 Speaker 1: of reference that's important, the more quickly time appears to 420 00:25:13,800 --> 00:25:17,920 Speaker 1: pass for those at the other point of reference. Or alternatively, 421 00:25:18,240 --> 00:25:22,199 Speaker 1: the more slowly time seems to pass for the fast 422 00:25:22,280 --> 00:25:25,320 Speaker 1: moving thing from the frame of reference of the person 423 00:25:25,320 --> 00:25:28,720 Speaker 1: who's not moving fast. This gets really clunky. I know, 424 00:25:28,800 --> 00:25:31,160 Speaker 1: it gets confusing. So let's talk about space travels some more, 425 00:25:31,160 --> 00:25:34,680 Speaker 1: because examples actually make this way easier to explain. All right, 426 00:25:34,720 --> 00:25:37,720 Speaker 1: So let's say you've built a spaceship and this spaceship 427 00:25:37,760 --> 00:25:41,159 Speaker 1: can go wicked fast, like eighty percent of the speed 428 00:25:41,160 --> 00:25:44,200 Speaker 1: of light, and you're gonna go on a year long 429 00:25:44,320 --> 00:25:48,040 Speaker 1: jaunt out in space, and your best friend is hanging 430 00:25:48,119 --> 00:25:51,640 Speaker 1: back on Earth. Now we now have our two frames 431 00:25:51,680 --> 00:25:54,360 Speaker 1: of reference. We have the spaceship, and then we have 432 00:25:54,400 --> 00:25:59,080 Speaker 1: the person on Earth. So let's ignore accelerative forces for 433 00:25:59,160 --> 00:26:02,199 Speaker 1: the moment because we're gonna have to just focus on 434 00:26:02,240 --> 00:26:04,920 Speaker 1: special relativity. We'll get to general relativity in a moment. 435 00:26:05,320 --> 00:26:08,880 Speaker 1: So you're in your spaceship. You're zooming around at eighty 436 00:26:08,920 --> 00:26:11,320 Speaker 1: percent the speed of light, and for you, time is 437 00:26:11,359 --> 00:26:15,040 Speaker 1: passing normally. The seconds feel like seconds, minutes feel like minutes, 438 00:26:15,080 --> 00:26:17,640 Speaker 1: hours feel like hours, et cetera. And you're on there 439 00:26:17,640 --> 00:26:21,880 Speaker 1: for a full year. Back on Earth, time is passing normally. 440 00:26:21,920 --> 00:26:24,320 Speaker 1: For your best friend who's just hanging out on Earth, 441 00:26:24,400 --> 00:26:28,000 Speaker 1: they feel their seconds pass like seconds. They're minutes passing minutes, 442 00:26:28,040 --> 00:26:31,120 Speaker 1: and so on. However, when we look at the two 443 00:26:31,160 --> 00:26:34,880 Speaker 1: of you in reference to one another, something unusual happens. 444 00:26:35,200 --> 00:26:37,280 Speaker 1: So to your best friend on Earth, it looks like 445 00:26:37,359 --> 00:26:41,720 Speaker 1: time is passing very slowly for you aboard your spaceship. 446 00:26:42,160 --> 00:26:44,800 Speaker 1: To you on your spaceship, it looks like time is 447 00:26:44,840 --> 00:26:48,560 Speaker 1: passing super fast for your friend back on Earth. So 448 00:26:48,640 --> 00:26:50,879 Speaker 1: when you do get back to Earth a year later 449 00:26:51,040 --> 00:26:53,800 Speaker 1: than the two of you enter the same point of reference, 450 00:26:54,359 --> 00:26:57,840 Speaker 1: things are weird. From your perspective, you've only aged a 451 00:26:57,920 --> 00:27:00,000 Speaker 1: year because you spend a year aboard your SPA ship, 452 00:27:00,520 --> 00:27:02,399 Speaker 1: but a little more than a year and a half 453 00:27:02,640 --> 00:27:05,760 Speaker 1: has passed on Earth while you were gone. Your calendars 454 00:27:05,800 --> 00:27:08,960 Speaker 1: wouldn't line up anymore. The faster you go relative to 455 00:27:09,000 --> 00:27:13,199 Speaker 1: your frame of reference, the more pronounced the time dilation. Now, 456 00:27:13,240 --> 00:27:15,040 Speaker 1: I do want to be clear about this, it's not 457 00:27:15,119 --> 00:27:19,120 Speaker 1: really correct to say that as speed increases time slows down. 458 00:27:19,480 --> 00:27:22,480 Speaker 1: You have to always relay this in terms of having 459 00:27:22,560 --> 00:27:26,520 Speaker 1: another frame of reference, because within a single frame of reference, 460 00:27:26,760 --> 00:27:30,560 Speaker 1: time just passes normally. There's no difference. By the way, 461 00:27:30,920 --> 00:27:34,240 Speaker 1: This is also why star dates in the Star Trek 462 00:27:34,320 --> 00:27:37,600 Speaker 1: universe don't make a whole lot of sense. They tried 463 00:27:37,680 --> 00:27:42,800 Speaker 1: to retroactively make it make sense. But keeping time when 464 00:27:42,840 --> 00:27:45,240 Speaker 1: you're on a ship that can travel at the speed 465 00:27:45,240 --> 00:27:47,800 Speaker 1: of light or in the case of Star Trek, magically 466 00:27:47,840 --> 00:27:51,359 Speaker 1: going faster than the speed of light and we won't 467 00:27:51,400 --> 00:27:54,399 Speaker 1: even get into warp speed at all, is crazy. But 468 00:27:55,400 --> 00:27:58,040 Speaker 1: being able to use that and somehow relate it to 469 00:27:58,080 --> 00:28:01,720 Speaker 1: making sense on time passing on planets or space stations 470 00:28:01,760 --> 00:28:05,560 Speaker 1: or whatever. That's a huge mess. But it's also outside 471 00:28:05,560 --> 00:28:07,760 Speaker 1: of our episode, so we'll just leave it at that. 472 00:28:08,400 --> 00:28:11,440 Speaker 1: We don't notice the effects of special relativity in most 473 00:28:11,440 --> 00:28:13,760 Speaker 1: of our day to day lives, because we are not 474 00:28:13,920 --> 00:28:16,800 Speaker 1: traveling fast enough relative to each other for it to 475 00:28:16,840 --> 00:28:20,479 Speaker 1: be a real factor most of the time. But it 476 00:28:20,520 --> 00:28:23,800 Speaker 1: does get even more weird. Were it possible to build 477 00:28:23,840 --> 00:28:26,800 Speaker 1: a spaceship that could travel at the speed of light, 478 00:28:27,400 --> 00:28:30,159 Speaker 1: and you were to take this sort of trip to 479 00:28:30,200 --> 00:28:33,879 Speaker 1: an outside observer, time would appear to stop for you 480 00:28:34,200 --> 00:28:38,400 Speaker 1: aboard your spaceship. Now if assuming this was even possible, 481 00:28:38,680 --> 00:28:41,320 Speaker 1: you would still experience time in your own frame of 482 00:28:41,360 --> 00:28:44,080 Speaker 1: reference as per normal, but your friend back on Earth 483 00:28:44,240 --> 00:28:47,320 Speaker 1: would see that it looked like you were frozen in time. However, 484 00:28:47,480 --> 00:28:50,160 Speaker 1: this is a moot point. Matter cannot travel at the 485 00:28:50,200 --> 00:28:54,360 Speaker 1: speed of light, so it's more of a thought experiment anyway. However, 486 00:28:54,640 --> 00:28:59,120 Speaker 1: we can actually detect time dilation with extremely accurate time 487 00:28:59,200 --> 00:29:03,360 Speaker 1: measurement device like atomic clocks. In fact, we've done it 488 00:29:03,960 --> 00:29:09,640 Speaker 1: in experiments. Scientists have synchronized two atomic clocks, and these 489 00:29:09,800 --> 00:29:13,840 Speaker 1: atomic clocks keep incredibly accurate time down to a matter 490 00:29:13,880 --> 00:29:18,360 Speaker 1: of nanoseconds, and a nanosecond is one billionth of a second, 491 00:29:18,880 --> 00:29:22,640 Speaker 1: So one clock was kept stationary, you know, relatively speaking, 492 00:29:22,840 --> 00:29:26,680 Speaker 1: here on Earth. The other traveled aboard a high speed aircraft, 493 00:29:26,880 --> 00:29:29,440 Speaker 1: and at the end of the experiment they compared the 494 00:29:29,560 --> 00:29:33,000 Speaker 1: two clocks against each other, and the one that was 495 00:29:33,000 --> 00:29:36,840 Speaker 1: aboard the aircraft had measured less time than the one 496 00:29:36,880 --> 00:29:41,120 Speaker 1: that stayed on the ground on Earth. Less time passed 497 00:29:41,520 --> 00:29:44,480 Speaker 1: on that aircraft relative to the amount of time passing 498 00:29:44,600 --> 00:29:47,680 Speaker 1: on the ground. It wasn't just that one clock was 499 00:29:47,720 --> 00:29:50,600 Speaker 1: moving more slowly than the other. Literally less time was 500 00:29:50,680 --> 00:29:54,840 Speaker 1: passing in reference to the other point of from the 501 00:29:54,880 --> 00:29:58,240 Speaker 1: perspective of the other point of reference, that is, the 502 00:29:58,280 --> 00:30:02,520 Speaker 1: difference was right in line with Einstein's calculations. Now, as 503 00:30:02,560 --> 00:30:04,880 Speaker 1: we'll see, this ends up being an important point when 504 00:30:04,920 --> 00:30:07,160 Speaker 1: we get to satellites. But we can't just jump on 505 00:30:07,240 --> 00:30:11,680 Speaker 1: that yet. We do need to take into consideration general relativity. So, 506 00:30:11,840 --> 00:30:14,800 Speaker 1: as i mentioned, special relativity only looks at frames of 507 00:30:14,800 --> 00:30:17,479 Speaker 1: reference that are in a constant and consistent motion with 508 00:30:17,520 --> 00:30:19,920 Speaker 1: regard to one another. There could be no change in 509 00:30:19,960 --> 00:30:23,920 Speaker 1: direction or speed because that introduces accelerative forces and that 510 00:30:24,000 --> 00:30:28,320 Speaker 1: changes things. So to take acceleration into account. Einstein proposed 511 00:30:28,320 --> 00:30:31,800 Speaker 1: his theory of general relativity ten years after his theory 512 00:30:31,840 --> 00:30:35,080 Speaker 1: of special relativity, so this would be nineteen fifteen For 513 00:30:35,120 --> 00:30:38,440 Speaker 1: those who are keeping track, This theory would incorporate the 514 00:30:38,480 --> 00:30:43,280 Speaker 1: force of gravity into Einstein's work, which means factoring in acceleration. 515 00:30:43,640 --> 00:30:47,360 Speaker 1: So in this theory, Einstein introduced the equivalence principle, which 516 00:30:47,520 --> 00:30:50,720 Speaker 1: says that gravity pulling in one direction is equivalent to 517 00:30:50,800 --> 00:30:54,920 Speaker 1: acceleration in another direction. So we can actually experience this. 518 00:30:55,160 --> 00:30:58,040 Speaker 1: It's easy to remember and imagine. Imagine getting on an 519 00:30:58,080 --> 00:31:01,360 Speaker 1: elevator and it's going up, and as it goes up, 520 00:31:01,400 --> 00:31:05,440 Speaker 1: you feel that sense of increased gravity pulling down on 521 00:31:05,520 --> 00:31:09,720 Speaker 1: you as the elevator accelerates. When the elevator is going down, 522 00:31:10,240 --> 00:31:13,400 Speaker 1: you feel a sense of decreased gravity as the elevator 523 00:31:13,440 --> 00:31:17,720 Speaker 1: accelerates downward. So gravity and acceleration are equivalent, which means 524 00:31:17,720 --> 00:31:20,960 Speaker 1: that it can also affect our measurements of space and time. 525 00:31:21,480 --> 00:31:26,560 Speaker 1: Einstein hypothesized that gravity was warping space time itself. Take 526 00:31:26,680 --> 00:31:32,560 Speaker 1: something that's really massive, like a huge dense star, that 527 00:31:32,600 --> 00:31:36,560 Speaker 1: would warp space time around it through its gravity, and 528 00:31:36,600 --> 00:31:40,400 Speaker 1: we can even observe this scientifically, scientists have measured light 529 00:31:40,840 --> 00:31:45,800 Speaker 1: that has curved around massive stars. This is called gravitational lensing. 530 00:31:46,400 --> 00:31:49,120 Speaker 1: Now here's another thing that gets a bit confusing. The 531 00:31:49,160 --> 00:31:53,480 Speaker 1: effects of gravity on time mean that time passes differently 532 00:31:53,560 --> 00:31:57,200 Speaker 1: for objects in orbit when taken in reference to time 533 00:31:57,280 --> 00:32:01,280 Speaker 1: passing on Earth itself, time pass this is faster in 534 00:32:01,520 --> 00:32:05,120 Speaker 1: orbit than it does on Earth. Now, again, this is 535 00:32:05,160 --> 00:32:07,520 Speaker 1: a frame of reference thing, because if you were on 536 00:32:07,560 --> 00:32:11,400 Speaker 1: a spaceship in orbit, your experience of time would feel 537 00:32:11,520 --> 00:32:14,120 Speaker 1: exactly the way it does when you are on Earth. 538 00:32:14,440 --> 00:32:18,040 Speaker 1: It's only when we look at this from two frames 539 00:32:18,080 --> 00:32:20,840 Speaker 1: of reference that we see how it doesn't match up. 540 00:32:21,360 --> 00:32:23,840 Speaker 1: So what does this all mean for satellites. Well, it 541 00:32:23,840 --> 00:32:26,440 Speaker 1: means that satellites in orbit have a couple of different 542 00:32:26,480 --> 00:32:30,400 Speaker 1: relativistic effects going on. In our frame of reference here 543 00:32:30,400 --> 00:32:34,120 Speaker 1: on Earth, satellites are traveling faster than we are to 544 00:32:34,240 --> 00:32:37,440 Speaker 1: maintain orbit, which means that if we compare the passing 545 00:32:37,480 --> 00:32:40,960 Speaker 1: of time in each frame of reference, time would pass 546 00:32:41,200 --> 00:32:45,280 Speaker 1: faster for us than for the satellite. However, due to 547 00:32:45,320 --> 00:32:49,000 Speaker 1: the gravitational effect on space time, we also know that 548 00:32:49,080 --> 00:32:52,160 Speaker 1: something in orbit will have time pass faster for that 549 00:32:52,680 --> 00:32:55,360 Speaker 1: thing than we would experience here on Earth. So it's 550 00:32:55,400 --> 00:32:58,560 Speaker 1: the opposite of the effect of special relativity in a way, 551 00:32:58,800 --> 00:33:01,720 Speaker 1: and the effects of special relie relativity and general relativity 552 00:33:01,800 --> 00:33:05,280 Speaker 1: don't actually cancel each other out, which means ultimately that 553 00:33:05,440 --> 00:33:08,440 Speaker 1: time on a satellite and time down here on Earth 554 00:33:08,560 --> 00:33:11,560 Speaker 1: are not syncd up with reference to one another. And 555 00:33:11,600 --> 00:33:15,360 Speaker 1: for some types of satellites that's a problem. I'll explain 556 00:33:15,440 --> 00:33:27,000 Speaker 1: more after we take this quick break to understand why 557 00:33:27,080 --> 00:33:30,880 Speaker 1: relativity is important with certain satellites, let's talk about the 558 00:33:30,960 --> 00:33:35,240 Speaker 1: Global Positioning System or GPS. Now, this is the satellite 559 00:33:35,320 --> 00:33:37,920 Speaker 1: system that provides data back to Earth that makes it 560 00:33:37,960 --> 00:33:42,080 Speaker 1: possible to get precise coordinates using a GPS receiver. So 561 00:33:42,160 --> 00:33:45,240 Speaker 1: how does that work? Well, here on Earth, you could 562 00:33:45,320 --> 00:33:49,960 Speaker 1: get a very imprecise idea of your general coordinates through 563 00:33:50,640 --> 00:33:55,320 Speaker 1: a trilateration using signals from cell phone towers. This works 564 00:33:55,320 --> 00:33:58,440 Speaker 1: on a fairly simple principle. So we know that the 565 00:33:58,560 --> 00:34:02,200 Speaker 1: radio signals sent to and from cell phones travel at 566 00:34:02,360 --> 00:34:05,080 Speaker 1: essentially the speed of light. So if a cell phone 567 00:34:05,120 --> 00:34:09,520 Speaker 1: tower broadcasts out a short command that just requests your 568 00:34:09,560 --> 00:34:12,960 Speaker 1: phone to respond back with a quick response a ping. 569 00:34:13,160 --> 00:34:15,879 Speaker 1: In other words, the amount of time it would take 570 00:34:16,000 --> 00:34:18,920 Speaker 1: for the ping to reach the cell tower could be 571 00:34:19,000 --> 00:34:22,200 Speaker 1: used to work backward and figure out how far away 572 00:34:22,600 --> 00:34:25,400 Speaker 1: the phone is from that cell phone tower. Because you 573 00:34:25,440 --> 00:34:27,759 Speaker 1: know the speed of travel, right is the speed of light, 574 00:34:28,280 --> 00:34:31,279 Speaker 1: so you also know how much time it took. That 575 00:34:31,360 --> 00:34:33,719 Speaker 1: means you can work backward to figure out the distance 576 00:34:33,840 --> 00:34:38,200 Speaker 1: between those two points. However, that's just a distance, there's 577 00:34:38,239 --> 00:34:41,360 Speaker 1: no direction there. Now, if you did this with multiple 578 00:34:41,360 --> 00:34:44,920 Speaker 1: cell towers, the collective data from those towers could be 579 00:34:44,960 --> 00:34:47,440 Speaker 1: used to get a rough estimate of where the phone is. 580 00:34:47,920 --> 00:34:50,600 Speaker 1: So let's imagine we've got a map, and on that 581 00:34:50,680 --> 00:34:54,480 Speaker 1: map we've got three cell towers A, B, and C. 582 00:34:55,320 --> 00:34:58,479 Speaker 1: You can see exactly where each one is. And let's 583 00:34:58,480 --> 00:35:01,399 Speaker 1: say that you've got a phone that located somewhere within 584 00:35:01,440 --> 00:35:05,480 Speaker 1: the broadcast range of those three cell towers. Each tower 585 00:35:05,560 --> 00:35:08,799 Speaker 1: sends a ping to your phone, Your phone responds with 586 00:35:08,840 --> 00:35:12,120 Speaker 1: a ping back, and you are given the amount of 587 00:35:12,160 --> 00:35:15,959 Speaker 1: distance between your phone and each of those three towers. Well, 588 00:35:16,880 --> 00:35:21,200 Speaker 1: Tower a's result says that you are a mile away 589 00:35:21,360 --> 00:35:24,160 Speaker 1: from Tower A, so you actually have to draw a 590 00:35:24,200 --> 00:35:28,640 Speaker 1: full circle around Tower A to represent all the possible 591 00:35:28,680 --> 00:35:30,799 Speaker 1: points you could be that are one mile away from 592 00:35:30,800 --> 00:35:35,680 Speaker 1: Tower A, So you're drawing a mile radius around Tower A. 593 00:35:35,719 --> 00:35:39,440 Speaker 1: Tower B responds that you're within one point five miles 594 00:35:39,480 --> 00:35:41,720 Speaker 1: of Tower B, so you have to draw a circle 595 00:35:41,719 --> 00:35:44,920 Speaker 1: around Tower B to represent all the points where you 596 00:35:44,920 --> 00:35:46,600 Speaker 1: could be that are a mile and a half away 597 00:35:46,600 --> 00:35:49,840 Speaker 1: from it. Now, the circle from tower B in the 598 00:35:49,880 --> 00:35:53,360 Speaker 1: circle from Tower A should intersect each other at two points, 599 00:35:53,840 --> 00:35:55,799 Speaker 1: but that means you could be at either of those 600 00:35:55,840 --> 00:35:59,000 Speaker 1: two points. Right, you could be at either overlap, so 601 00:35:59,040 --> 00:36:02,239 Speaker 1: you don't have enough information yet. By coordinating with tower C, 602 00:36:02,760 --> 00:36:05,160 Speaker 1: and let's say that one tells you you're within two miles, 603 00:36:05,960 --> 00:36:08,960 Speaker 1: you can draw a third circle, and the point where 604 00:36:09,000 --> 00:36:12,800 Speaker 1: all three circles would meet would be your general location. 605 00:36:13,440 --> 00:36:16,440 Speaker 1: It's not incredibly precise, but it does give you an 606 00:36:16,520 --> 00:36:20,719 Speaker 1: idea of where you are. The GPS constellation of satellites 607 00:36:20,840 --> 00:36:23,279 Speaker 1: does something similar, only we have to think of this 608 00:36:23,320 --> 00:36:26,680 Speaker 1: in terms of three dimensional space rather than a two 609 00:36:26,800 --> 00:36:30,799 Speaker 1: dimensional map. So a satellite sends out a high frequency, 610 00:36:31,120 --> 00:36:34,960 Speaker 1: low power radio signal and receivers pick that signal up. 611 00:36:35,560 --> 00:36:38,840 Speaker 1: The receiver, let's say it's your smartphone, doesn't have to 612 00:36:38,880 --> 00:36:41,640 Speaker 1: send data back up to the satellite, which is good 613 00:36:41,719 --> 00:36:44,680 Speaker 1: because i'd be an enormous drain on your smartphone's power. 614 00:36:45,120 --> 00:36:48,840 Speaker 1: So really it's just listening for these signals. Now, the 615 00:36:48,880 --> 00:36:53,400 Speaker 1: receiver and satellite both run the same digital pattern relative 616 00:36:53,520 --> 00:36:57,080 Speaker 1: to a specific time stamp. It's easy if we think 617 00:36:57,120 --> 00:36:59,760 Speaker 1: of this as midnight. So let's say that midnight hits 618 00:36:59,800 --> 00:37:02,840 Speaker 1: and and this particular digital pattern starts both on the 619 00:37:02,880 --> 00:37:07,040 Speaker 1: satellite and the receiver, so they're both running the exact 620 00:37:07,080 --> 00:37:10,040 Speaker 1: same pattern. The satellite beams out a signal carrying this 621 00:37:10,120 --> 00:37:13,399 Speaker 1: digital pattern. The satellite is far away, so it takes 622 00:37:13,400 --> 00:37:15,480 Speaker 1: a little time, you know, not much, but a little 623 00:37:15,480 --> 00:37:18,200 Speaker 1: time for that signal to get to your receiver. And 624 00:37:18,280 --> 00:37:21,920 Speaker 1: the lag between the pattern that's playing on your receiver 625 00:37:22,400 --> 00:37:25,399 Speaker 1: and the signal of that same pattern coming in from 626 00:37:25,440 --> 00:37:29,040 Speaker 1: the satellite tells the receiver how far away it is 627 00:37:29,200 --> 00:37:32,239 Speaker 1: from that particular satellite, because again we know that the 628 00:37:32,360 --> 00:37:35,360 Speaker 1: signal is moving at the speed of the transmission itself, 629 00:37:35,360 --> 00:37:37,640 Speaker 1: and that's the speed of light, and that's a constant. 630 00:37:38,280 --> 00:37:40,480 Speaker 1: So now the receiver knows how far away it is 631 00:37:40,680 --> 00:37:44,520 Speaker 1: from that one satellite. And because the orbits of these 632 00:37:44,640 --> 00:37:48,040 Speaker 1: satellites are predictable, the receiver has a record of where 633 00:37:48,160 --> 00:37:51,759 Speaker 1: that satellite should be relative to your surface. Occasionally we 634 00:37:51,840 --> 00:37:55,239 Speaker 1: have to tweak that record because stuff like gravity can 635 00:37:55,480 --> 00:37:58,239 Speaker 1: pull a satellite slightly out of position over time, so 636 00:37:58,480 --> 00:38:00,359 Speaker 1: that actually is something that has to be a rest 637 00:38:00,480 --> 00:38:03,920 Speaker 1: on occasion. Now, this receiver will do this with at 638 00:38:04,040 --> 00:38:08,719 Speaker 1: least four satellites the Y four and not three, and 639 00:38:08,880 --> 00:38:13,000 Speaker 1: I gave the three cell phone tower examples. Well, it's 640 00:38:13,040 --> 00:38:16,760 Speaker 1: because the clocks on satellites and the clock that's running 641 00:38:16,800 --> 00:38:19,719 Speaker 1: on the device that the receiver is built into may 642 00:38:19,760 --> 00:38:24,040 Speaker 1: not be and really aren't truly synchronized. And the intersection 643 00:38:24,120 --> 00:38:29,280 Speaker 1: of for spheres of distance like these four spheres representing 644 00:38:29,280 --> 00:38:32,879 Speaker 1: the various ranges that these satellites are finding themselves in 645 00:38:33,080 --> 00:38:38,560 Speaker 1: with regard to this receiver can only intersect at one point. 646 00:38:39,000 --> 00:38:42,799 Speaker 1: That's the only place they could all intersect. So if 647 00:38:42,800 --> 00:38:45,480 Speaker 1: a GPS receiver's clock is not matching up to the 648 00:38:45,480 --> 00:38:48,600 Speaker 1: clocks on the satellites, there will be no intersection at all. 649 00:38:48,840 --> 00:38:51,280 Speaker 1: And the receiver will say, well, I can't find an intersection, 650 00:38:51,400 --> 00:38:53,760 Speaker 1: so that I know that means my clock is off 651 00:38:53,920 --> 00:38:57,200 Speaker 1: from all the other clocks, and it will then adjust 652 00:38:57,280 --> 00:38:59,840 Speaker 1: its own clock to be an alignment so that the 653 00:39:00,120 --> 00:39:03,560 Speaker 1: or spheres have a point of intersection and that is 654 00:39:03,760 --> 00:39:07,080 Speaker 1: your location on Earth. Now, in order for our receivers 655 00:39:07,080 --> 00:39:09,480 Speaker 1: to be able to do this, the accuracy of the 656 00:39:09,520 --> 00:39:13,600 Speaker 1: atomic clocks aboard those GPS satellites has to be accurate 657 00:39:13,680 --> 00:39:18,960 Speaker 1: within twenty to thirty nanoseconds. And remember a nanosecond is 658 00:39:19,000 --> 00:39:23,680 Speaker 1: one billionth of a second. That is an astounding level 659 00:39:23,719 --> 00:39:27,040 Speaker 1: of accuracy. And because these satellites are in motion and 660 00:39:27,120 --> 00:39:31,080 Speaker 1: they are also affected by Earth's gravity, they are subject 661 00:39:31,120 --> 00:39:34,880 Speaker 1: to the effects of special and general relativity, and this 662 00:39:35,000 --> 00:39:38,120 Speaker 1: means we actually have to make calculations to take that 663 00:39:38,360 --> 00:39:43,200 Speaker 1: into account. Now, according to special relativity and the relative 664 00:39:43,239 --> 00:39:46,280 Speaker 1: speeds of satellites to a fixed point on the surface 665 00:39:46,280 --> 00:39:49,799 Speaker 1: of the Earth, we would expect the atomic clock aboard 666 00:39:49,920 --> 00:39:54,839 Speaker 1: that satellite to register seven fewer microseconds per day than 667 00:39:54,880 --> 00:39:57,799 Speaker 1: a clock on Earth because these satellites are moving through 668 00:39:57,840 --> 00:40:02,320 Speaker 1: space faster than we are, relatively speaking, so that means 669 00:40:02,320 --> 00:40:05,400 Speaker 1: from our frame of reference, time is passing more slowly 670 00:40:05,600 --> 00:40:09,759 Speaker 1: on that satellite than it does here on Earth. Ah. 671 00:40:09,880 --> 00:40:14,319 Speaker 1: But general relativity comes into play too, and general relativity 672 00:40:14,360 --> 00:40:18,600 Speaker 1: tells us that the Earth's gravity warps space time around 673 00:40:18,600 --> 00:40:22,759 Speaker 1: our planet. And one of general relativity's predictions is that 674 00:40:22,840 --> 00:40:26,719 Speaker 1: a clock closer to a massive object, so like a 675 00:40:26,800 --> 00:40:31,640 Speaker 1: clock here on Earth, will tick more slowly than a 676 00:40:31,719 --> 00:40:35,920 Speaker 1: clock that is further out from that same massive object. 677 00:40:36,280 --> 00:40:39,080 Speaker 1: So the closer the clock is to the massive object, 678 00:40:39,160 --> 00:40:43,120 Speaker 1: the less time it will experience it will measure compared 679 00:40:43,120 --> 00:40:45,560 Speaker 1: to a clock that's further away, which is crazy, right. 680 00:40:46,280 --> 00:40:50,960 Speaker 1: So taking only general relativity into account, we would see 681 00:40:50,960 --> 00:40:53,760 Speaker 1: that a clock aboard one of these satellites would register 682 00:40:54,239 --> 00:40:57,920 Speaker 1: more time having passed on that satellite than a clock 683 00:40:58,040 --> 00:41:01,640 Speaker 1: here on Earth, meaning for our frame of reference, time 684 00:41:01,719 --> 00:41:05,400 Speaker 1: is actually passing faster on those satellites than it does 685 00:41:05,560 --> 00:41:08,880 Speaker 1: here for us. This would come out to about forty 686 00:41:09,000 --> 00:41:12,040 Speaker 1: five microseconds a day, meaning that at the end of 687 00:41:12,160 --> 00:41:15,520 Speaker 1: day one, the clock aboard that satellite would be ahead 688 00:41:15,600 --> 00:41:19,120 Speaker 1: of a clock here on Earth by forty five microseconds, 689 00:41:19,400 --> 00:41:23,000 Speaker 1: and this would continue day after day, with the gap 690 00:41:23,120 --> 00:41:26,680 Speaker 1: growing wider every single day. Now, when we bring both 691 00:41:26,880 --> 00:41:32,279 Speaker 1: special and general relativity together into consideration, we see that 692 00:41:32,360 --> 00:41:35,200 Speaker 1: they don't just cancel each other out right, because we've 693 00:41:35,200 --> 00:41:39,319 Speaker 1: got that seven microsecond lag due to special relativity, but 694 00:41:39,400 --> 00:41:43,920 Speaker 1: we have the forty five microsecond surge due to general relativity. 695 00:41:44,200 --> 00:41:46,960 Speaker 1: So in the end, we're looking at a thirty eight 696 00:41:47,080 --> 00:41:51,480 Speaker 1: microsecond difference per day between a clock on a satellite 697 00:41:51,560 --> 00:41:54,680 Speaker 1: and a clock here on Earth. The clocks on the 698 00:41:54,680 --> 00:41:57,439 Speaker 1: satellites will get ahead of similar clocks here on Earth 699 00:41:57,480 --> 00:42:00,960 Speaker 1: by thirty eight microseconds every single day. And while a 700 00:42:01,000 --> 00:42:04,040 Speaker 1: microsecond is a very small amount of time, I mean 701 00:42:04,160 --> 00:42:07,480 Speaker 1: we're talking at a level that we don't typically experience. 702 00:42:07,520 --> 00:42:10,279 Speaker 1: We don't think of time in microseconds for our day 703 00:42:10,320 --> 00:42:14,360 Speaker 1: to day lives. However, thirty eight microseconds is equal to 704 00:42:14,440 --> 00:42:18,160 Speaker 1: thirty eight thousand nanoseconds, and if you're looking for an 705 00:42:18,200 --> 00:42:22,640 Speaker 1: accuracy of around twenty to thirty nanoseconds, this becomes an 706 00:42:22,880 --> 00:42:26,040 Speaker 1: enormous problem if we don't take it into account. And 707 00:42:26,120 --> 00:42:28,640 Speaker 1: this brings us back round to something I mentioned at 708 00:42:28,640 --> 00:42:31,920 Speaker 1: the top of the show. We know that Einstein was 709 00:42:32,000 --> 00:42:35,000 Speaker 1: right about relativity because we have to account for it 710 00:42:35,200 --> 00:42:39,480 Speaker 1: with technology like GPS. If we didn't take it into account, 711 00:42:39,600 --> 00:42:43,160 Speaker 1: if we didn't factor in the effects of relativity, our 712 00:42:43,239 --> 00:42:46,920 Speaker 1: GPS wouldn't work for very long at all. Our technology 713 00:42:47,080 --> 00:42:50,359 Speaker 1: proves that the science is real, or else the tech 714 00:42:50,680 --> 00:42:53,880 Speaker 1: would fail at what it needs to do now. In general, 715 00:42:54,320 --> 00:42:56,799 Speaker 1: I think that's a great lesson to take home. There 716 00:42:56,880 --> 00:42:59,200 Speaker 1: are a lot of voices out there that call science 717 00:42:59,280 --> 00:43:02,840 Speaker 1: into questions, and some of them are more outlandish than others, 718 00:43:03,080 --> 00:43:06,760 Speaker 1: a person who's passionately and sincerely arguing that the Earth 719 00:43:06,840 --> 00:43:10,320 Speaker 1: is flat seems pretty far out there for me, because 720 00:43:10,520 --> 00:43:13,279 Speaker 1: so much of our technology we've built upon and we 721 00:43:13,320 --> 00:43:17,160 Speaker 1: rely upon wouldn't work if that were true. Even if 722 00:43:17,160 --> 00:43:21,640 Speaker 1: you can't experience something directly, such as having a meaningful 723 00:43:21,800 --> 00:43:25,920 Speaker 1: experience of time dilation, a ton of the stuff we 724 00:43:26,000 --> 00:43:29,360 Speaker 1: do experience on a day to day basis is affected 725 00:43:29,400 --> 00:43:32,520 Speaker 1: by this stuff, and it proves the existence and also 726 00:43:32,719 --> 00:43:36,040 Speaker 1: the benefits of having the scientific method. Now I'll give 727 00:43:36,080 --> 00:43:39,040 Speaker 1: a little side note on GPS to kind of wrap 728 00:43:39,120 --> 00:43:42,440 Speaker 1: this up. The original GPS configuration came out of a 729 00:43:42,520 --> 00:43:46,480 Speaker 1: United States Department a defense project. The original purpose was 730 00:43:46,520 --> 00:43:51,080 Speaker 1: to provide positioning information for government and military, but specifically 731 00:43:51,120 --> 00:43:53,600 Speaker 1: the United States and its allies, and for that reason, 732 00:43:53,800 --> 00:43:57,520 Speaker 1: the US government wished to restrict access to this technology. 733 00:43:58,120 --> 00:44:00,640 Speaker 1: The general line of thought was that it be better 734 00:44:00,960 --> 00:44:03,279 Speaker 1: if the US didn't allow tech that could, you know, 735 00:44:03,800 --> 00:44:08,040 Speaker 1: give precise coordinates for stuff like military bases or the 736 00:44:08,080 --> 00:44:11,560 Speaker 1: position of various military units to people who didn't belong 737 00:44:11,640 --> 00:44:15,160 Speaker 1: to those divisions. So, as a matter of national security, 738 00:44:15,400 --> 00:44:19,880 Speaker 1: the US guarded this technology civilian receivers. So if you 739 00:44:19,920 --> 00:44:22,520 Speaker 1: went out and you bought a GPS receiver, you could 740 00:44:22,560 --> 00:44:27,400 Speaker 1: get public GPS signals, but the United States was purposefully 741 00:44:27,600 --> 00:44:32,719 Speaker 1: instituting a policy called selective availability, which was an intentional 742 00:44:32,880 --> 00:44:38,359 Speaker 1: degradation of public GPS signals. They were introducing errors on 743 00:44:38,640 --> 00:44:43,040 Speaker 1: purpose so that GPS receivers couldn't get an accurate location. 744 00:44:43,160 --> 00:44:48,000 Speaker 1: It limited accuracy to around fifty meters horizontally and one 745 00:44:48,040 --> 00:44:51,640 Speaker 1: hundred meters vertically, and effectively that meant that you wouldn't 746 00:44:51,719 --> 00:44:55,640 Speaker 1: really know your precise coordinates. You certainly couldn't use a 747 00:44:55,680 --> 00:45:00,000 Speaker 1: GPS receiver as a turn by turn directions tool because 748 00:45:00,160 --> 00:45:02,840 Speaker 1: you wouldn't even necessarily show up on the right street. 749 00:45:03,480 --> 00:45:05,920 Speaker 1: You wouldn't know if you were approaching your turn or 750 00:45:05,920 --> 00:45:08,640 Speaker 1: if you had already passed it. It was it was 751 00:45:08,719 --> 00:45:11,200 Speaker 1: not practical for that. It was only in the year 752 00:45:11,239 --> 00:45:14,880 Speaker 1: two thousand, when US President Bill Clinton directed the government 753 00:45:14,960 --> 00:45:19,399 Speaker 1: to end selective availability, that civilian GPS receivers could actually 754 00:45:19,440 --> 00:45:23,000 Speaker 1: get accurate data. And that's what made the modern GPS 755 00:45:23,040 --> 00:45:27,480 Speaker 1: receivers and stuff like our phones possible. So before two thousand, 756 00:45:27,640 --> 00:45:30,520 Speaker 1: GPS receivers didn't work very well for the average person, 757 00:45:31,000 --> 00:45:33,799 Speaker 1: but it wasn't because the technology was bad, or that 758 00:45:33,920 --> 00:45:36,880 Speaker 1: the science was wrong it worked that way, or if 759 00:45:36,920 --> 00:45:40,319 Speaker 1: you prefer it, it didn't work properly on purpose. And 760 00:45:40,440 --> 00:45:43,839 Speaker 1: that wraps up this episode about relativity and why it's 761 00:45:43,880 --> 00:45:46,880 Speaker 1: important with technology, and it's not just satellite tech, but 762 00:45:46,920 --> 00:45:49,680 Speaker 1: that's a big one, and it also ends up being 763 00:45:49,719 --> 00:45:52,560 Speaker 1: a big thorn in the side for science fiction authors 764 00:45:52,600 --> 00:45:56,000 Speaker 1: who want to write about interstellar travel at faster than 765 00:45:56,080 --> 00:45:59,840 Speaker 1: light speeds, because you have to start finding alternative X 766 00:46:00,200 --> 00:46:04,120 Speaker 1: nations for how that's possible, because we've come up against 767 00:46:04,120 --> 00:46:08,080 Speaker 1: these limits that Einstein predicted, and so far his predictions 768 00:46:08,080 --> 00:46:10,560 Speaker 1: have held true. So in order to travel faster than 769 00:46:10,600 --> 00:46:12,560 Speaker 1: the speed of light, you do have to create something 770 00:46:12,760 --> 00:46:17,440 Speaker 1: like warp drive, which theoretically warps space around you. So 771 00:46:17,600 --> 00:46:22,240 Speaker 1: rather than traveling faster than light, you're decreasing the distance 772 00:46:22,280 --> 00:46:26,080 Speaker 1: between your point of origin and your destination. It would 773 00:46:26,080 --> 00:46:27,920 Speaker 1: be kind of like taking a map of the United 774 00:46:27,960 --> 00:46:31,000 Speaker 1: States and saying I'm going to travel from Atlanta to 775 00:46:31,120 --> 00:46:34,520 Speaker 1: Los Angeles, from one coast to the other, but instead 776 00:46:34,560 --> 00:46:37,600 Speaker 1: of drawing a line from Atlanta to LA you just 777 00:46:37,760 --> 00:46:40,239 Speaker 1: fold the map so that the two dots are next 778 00:46:40,239 --> 00:46:42,560 Speaker 1: to each other, and then you draw a line that way. 779 00:46:42,960 --> 00:46:45,399 Speaker 1: That's how warp speed is supposed to work, because it's 780 00:46:45,400 --> 00:46:47,400 Speaker 1: the only way you can get around the fact that 781 00:46:47,440 --> 00:46:49,600 Speaker 1: you can't really go faster than the speed of light. 782 00:46:50,520 --> 00:46:53,080 Speaker 1: But that's a topic for another show. If you guys 783 00:46:53,120 --> 00:46:56,439 Speaker 1: have suggestions for future topics I should tackle, please let 784 00:46:56,480 --> 00:46:59,320 Speaker 1: me know. Send me a message on Twitter. The handle 785 00:46:59,400 --> 00:47:04,399 Speaker 1: is text hsw and I'll talk to you again really soon. 786 00:47:10,600 --> 00:47:15,240 Speaker 1: Tech Stuff is an iHeartRadio production. For more podcasts from iHeartRadio, 787 00:47:15,560 --> 00:47:19,279 Speaker 1: visit the iHeartRadio app, Apple Podcasts, or wherever you listen 788 00:47:19,320 --> 00:47:20,400 Speaker 1: to your favorite shows.