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