WEBVTT - Rerun: It's All Relative 0:00:04.440 --> 0:00:13.000 Welcome to Tech Stuff, a production from iHeartRadio. Hey therein 0:00:13.160 --> 0:00:16.800 Welcome to Tech Stuff, I'm your host, Jonathan Strickland. I'm 0:00:16.800 --> 0:00:20.200 an executive producer with iHeartRadio, and how the tech are you. 0:00:20.920 --> 0:00:23.720 We have an episode that originally published on July first, 0:00:23.760 --> 0:00:28.120 twenty twenty. It's called It's All Relative And when I 0:00:28.160 --> 0:00:31.479 was a kid, I was convinced that Einstein's theories were 0:00:31.560 --> 0:00:36.160 these super complicated explanations of the universe that really had 0:00:36.200 --> 0:00:39.960 no real intersection with my daily life. But as it 0:00:40.000 --> 0:00:43.879 turns out, without an understanding of relativity, a lot of 0:00:43.880 --> 0:00:48.040 the technology we rely upon wouldn't work properly. And it's 0:00:48.080 --> 0:00:55.240 fascinating stuff. Hope you enjoy. The hertz unit refers to 0:00:55.320 --> 0:00:59.280 the number of repeated phenomena over the course of a second. 0:00:59.720 --> 0:01:03.400 So well, imagine that you're dribbling a basketball, so that 0:01:03.520 --> 0:01:06.520 the ball goes from your hand to the ground back 0:01:06.600 --> 0:01:09.759 up to your hand once per second. Well, you could 0:01:09.760 --> 0:01:14.440 describe your dribbling as being one hurts in frequency one 0:01:14.520 --> 0:01:18.399 full cycle per second, up down, up. Now, if you 0:01:18.440 --> 0:01:21.759 dribbled twice as fast, so that the ball went up, down, 0:01:21.920 --> 0:01:25.039 up two full times per second, then it would be 0:01:25.319 --> 0:01:29.280 two hurts. Well, we can describe lots of stuff with 0:01:29.440 --> 0:01:32.120 the unit hurts. We use it to describe sounds, in 0:01:32.160 --> 0:01:36.360 which case we're talking about the frequency at which stuff vibrates. 0:01:37.000 --> 0:01:40.880 Typical human hearing spans a range of frequencies that at 0:01:40.920 --> 0:01:43.800 the low end is at twenty hurts. That represents the 0:01:43.920 --> 0:01:46.600 lowest pitches of sounds. You get to go those deep 0:01:46.720 --> 0:01:50.600 bass notes. That's around the twenty hurts of area, and 0:01:50.640 --> 0:01:53.000 then it goes all the way up to twenty kill 0:01:53.000 --> 0:01:57.040 a hurts or twenty thousand hurts. That represents the very 0:01:57.120 --> 0:02:01.200 highest pitches that people can typically hear, and those frequencies 0:02:01.400 --> 0:02:05.600 correlate to how quickly stuff is vibrating back and forth. Now, 0:02:05.680 --> 0:02:08.120 when it comes to us hearing things, we usually mean 0:02:08.240 --> 0:02:12.160 that we're talking about the vibrations and fluctuation and air pressure, 0:02:12.400 --> 0:02:15.800 and those fluctuations and air pressure interact with our ear drums. 0:02:16.520 --> 0:02:18.880 But we can use hurts to talk about all sorts 0:02:18.919 --> 0:02:22.840 of stuff, including the processor speed of a CPU. In 0:02:22.880 --> 0:02:25.480 that case, we're really talking about the number of clock 0:02:25.720 --> 0:02:29.240 cycles per second, So you get it. This is a 0:02:29.320 --> 0:02:32.720 description of the frequency of the number of times a 0:02:32.760 --> 0:02:35.960 certain thing happens like within a second. And I also 0:02:36.040 --> 0:02:39.320 explained that we measure the rate at which we can 0:02:39.440 --> 0:02:43.240 send data using the term bits. A bit is a 0:02:43.280 --> 0:02:46.640 basic unit of digital information, and when we talk about computers, 0:02:46.880 --> 0:02:49.560 we're talking about bits in the form of a zero 0:02:49.840 --> 0:02:54.040 or a one binary information, just like your basic two 0:02:54.080 --> 0:02:58.080 way physical switch has two positions off or on. So 0:02:58.160 --> 0:03:00.480 if you hear a term like kill a bit, that 0:03:00.560 --> 0:03:04.200 means one thousand bits, and a megabit is one million bits, 0:03:04.240 --> 0:03:09.120 and a gigabit would be one billion bits. Likewise, megabits 0:03:09.200 --> 0:03:12.919 per second tells us how many million bits can move 0:03:13.040 --> 0:03:16.280 from one point to another per second over that connection. 0:03:16.760 --> 0:03:19.840 So if you've got a one hundred megabit per second connection, 0:03:20.520 --> 0:03:24.040 theoretically it would mean that up to one hundred million 0:03:24.120 --> 0:03:29.040 bits can transfer across that communication channel per second, though 0:03:29.160 --> 0:03:32.040 that's not how it works out most of the time, 0:03:32.120 --> 0:03:35.040 but that's a matter for a different episode. I didn't 0:03:35.080 --> 0:03:39.320 mention that this is different from something like megabytes. So 0:03:39.440 --> 0:03:42.640 a byte is a unit that consists of eight bits. 0:03:43.480 --> 0:03:46.440 And this gets confusing because we often describe stuff like 0:03:46.520 --> 0:03:50.600 file sizes in terms of bytes, but transfer speeds in 0:03:50.760 --> 0:03:54.000 terms of bits. So let's say that you do have 0:03:54.080 --> 0:03:57.720 that one hundred megabits per second download speed, and you 0:03:57.800 --> 0:04:01.360 want to download a one hundred megabyte file, well, that 0:04:01.440 --> 0:04:05.240 means it's not going to take one second. It's going 0:04:05.320 --> 0:04:08.160 to take eight seconds to download the file, because a 0:04:08.200 --> 0:04:12.280 megabyte is eight times larger than a megabit. And actually 0:04:12.840 --> 0:04:15.640 even that is a little bit misleading because in computer 0:04:15.680 --> 0:04:19.000 memory terms, we typically look at units of memory based 0:04:19.040 --> 0:04:23.120 on powers of two rather than powers of ten. So 0:04:23.160 --> 0:04:27.159 instead of a kilobyte being one thousand bytes, it's actually 0:04:27.160 --> 0:04:31.240 one thy twenty four bytes. And there's no standardization in 0:04:31.279 --> 0:04:35.040 the tech industry, so sometimes people will say a kilobyte 0:04:35.160 --> 0:04:38.479 and they mean one thousand bytes. Sometimes they'll say killobyte 0:04:38.480 --> 0:04:41.680 and they mean one thy twenty four bytes, and you 0:04:41.720 --> 0:04:44.320 will want to tear your hair out, and then you'll 0:04:44.320 --> 0:04:46.880 look like I do, I'm bald if you didn't know. 0:04:47.160 --> 0:04:50.440 But this episode isn't about the peculiarities of our naming 0:04:50.480 --> 0:04:54.359 conventions and the computer information age. Instead, I wanted to 0:04:54.360 --> 0:04:58.640 tackle something else that affects everything really, but in particular, 0:04:59.040 --> 0:05:00.839 we really had to suss it out in order to 0:05:00.839 --> 0:05:04.440 make certain types of satellites work properly, and this is 0:05:04.440 --> 0:05:08.280 the concept of relativity. So in this episode, we're really 0:05:08.320 --> 0:05:11.720 going to learn why an understanding of relativity is important 0:05:11.920 --> 0:05:16.040 if we want our certain satellite technologies to work, and 0:05:16.080 --> 0:05:19.000 it serves as a great reminder that technology is only 0:05:19.040 --> 0:05:22.840 really possible through an understanding of science. You can think 0:05:22.880 --> 0:05:26.960 of tech as the physical manifestation of our understanding of 0:05:27.000 --> 0:05:30.560 scientific principles, and that means if we were wrong in 0:05:30.600 --> 0:05:34.760 our understanding of science, the technology shouldn't really work. So 0:05:34.839 --> 0:05:37.680 in a way, you can think of technology that works 0:05:37.960 --> 0:05:41.719 as evidence that the scientific method is a darn good formula. 0:05:42.400 --> 0:05:45.200 Since we're talking about relativity, it means we're going to 0:05:45.240 --> 0:05:49.680 be talking about a real Einstein today. His name was Einstein, 0:05:50.200 --> 0:05:54.240 which is convenient. But before we get to Einstein, we 0:05:54.360 --> 0:05:59.760 have Galileo Galileo Galileo figure Ro. Wait No, I'm sorry, 0:05:59.800 --> 0:06:04.720 wait that's Bohemian Rhapsody. I meant Galileo Galilei. This. Galileo 0:06:05.080 --> 0:06:08.920 made an observation that if you've got two observers moving 0:06:08.960 --> 0:06:12.280 at a constant speed and direction, so they're moving at 0:06:12.279 --> 0:06:15.120 the same velocity, they will get the same results for 0:06:15.200 --> 0:06:19.440 any experiment that involves moving stuff around a mechanical experiment. 0:06:20.160 --> 0:06:23.960 This is easier to understand if we use an example, 0:06:24.279 --> 0:06:27.479 and I like one that my colleague Robert Lamb used 0:06:27.520 --> 0:06:30.960 when he wrote about relativity for HowStuffWorks dot com back 0:06:31.000 --> 0:06:33.919 in the day. He used an example of a train 0:06:34.400 --> 0:06:38.240 and a scientific ping pong ball. All right, so imagine 0:06:38.279 --> 0:06:40.800 you've got a scientist who's standing in the middle of 0:06:40.839 --> 0:06:44.320 an aisle on a moving train, and the train is 0:06:44.360 --> 0:06:47.200 moving at a steady speed in a straight line, so 0:06:47.279 --> 0:06:51.839 there are no active forces of acceleration going on here. Remember, 0:06:52.080 --> 0:06:56.440 acceleration describes a force that involves a change in velocity, 0:06:56.520 --> 0:06:59.359 so that either means a change in direction or a 0:06:59.440 --> 0:07:03.720 change in speed, or both. But in this case constant 0:07:03.720 --> 0:07:09.120 speed constant direction. Robert used nice round numbers in his examples, 0:07:09.240 --> 0:07:11.600 so he suggested that the train is moving at one 0:07:11.640 --> 0:07:14.840 hundred miles per hour. Well it's not round. If we 0:07:14.880 --> 0:07:16.680 go to the metric system, that would be one hundred 0:07:16.720 --> 0:07:20.200 and sixty one kilometers per hour. If the train stays 0:07:20.320 --> 0:07:23.160 steady to the scientist, it will feel as if that 0:07:23.240 --> 0:07:27.160 scientist is actually just standing still, just anywhere, and we're 0:07:27.320 --> 0:07:31.120 conveniently ignoring an emotion that would happen due to irregularities 0:07:31.160 --> 0:07:33.800 with the train's wheels or the train tracks or anything 0:07:33.880 --> 0:07:36.720 like that. And if this is hard for you to imagine, 0:07:36.920 --> 0:07:39.760 just think about how you feel when you're standing still 0:07:39.920 --> 0:07:43.360 or sitting still or laying down here on Earth. We 0:07:43.520 --> 0:07:47.040 know the Earth is moving through space. It is a 0:07:47.160 --> 0:07:51.160 body in motion, but when we are still relative to 0:07:51.200 --> 0:07:55.240 the Earth itself, we don't feel that motion. Assuming there's 0:07:55.280 --> 0:07:57.960 not some other weird event going on, like an earthquake, 0:07:58.000 --> 0:08:01.760 which is something separate. But back to our hypothetical train, 0:08:02.280 --> 0:08:06.680 the scientist tosses the ping pong ball down the aisle. Now, 0:08:06.760 --> 0:08:10.720 from the scientist's perspective, this ping pong ball will travel 0:08:10.760 --> 0:08:14.480 at whatever speed they threw it at. Robert actually suggests 0:08:14.560 --> 0:08:17.960 a relatively gentle toss of five miles per hour or 0:08:18.000 --> 0:08:21.720 eight kilometers per hour. The ping pong ball would bounce 0:08:21.840 --> 0:08:24.360 down the aisle, just as it would if the scientists 0:08:24.360 --> 0:08:26.440 were to toss the ball on a train that isn't 0:08:26.480 --> 0:08:30.720 moving at all, or on just flat ground. However, let's 0:08:30.760 --> 0:08:34.280 say we have a second observer who's not on the train. 0:08:34.320 --> 0:08:36.640 They're standing off to the side, and they can see 0:08:36.720 --> 0:08:39.880 through the train. To this person, it will appear as 0:08:39.960 --> 0:08:43.520 if the ping pong ball is moving very fast. Indeed, 0:08:43.880 --> 0:08:47.800 relative to this stationary observer, the ping pong ball will 0:08:47.800 --> 0:08:49.760 appear to move at the speed at which it was 0:08:49.840 --> 0:08:53.600 thrown in addition to the speed of the train itself. 0:08:53.960 --> 0:08:56.160 So if we take the two figures, we would get 0:08:56.320 --> 0:08:58.959 one hundred five miles per hour or one hundred and 0:08:59.000 --> 0:09:05.600 sixty nine per hour. This is called a Galilean transformation. Alternatively, 0:09:05.880 --> 0:09:08.040 if the scientists were throwing the ping pong ball in 0:09:08.120 --> 0:09:11.080 the opposite direction of the train's travel, so they're facing 0:09:11.280 --> 0:09:13.600 toward the back of the train, it would appear to 0:09:13.679 --> 0:09:16.880 this second observer the ping pong ball was moving at 0:09:16.880 --> 0:09:20.280 a slightly slower speed than the overall train was, whereas 0:09:20.320 --> 0:09:23.040 to the scientist on board, the ping pong ball would 0:09:23.080 --> 0:09:25.920 still be traveling at that five mile per hour speed. 0:09:26.640 --> 0:09:30.720 So this is where the term relativity comes into play. 0:09:31.120 --> 0:09:36.120 The effects observed are relative to the perspective of the observer. 0:09:36.640 --> 0:09:40.319 It's all based on the reference frame of that observer. 0:09:40.960 --> 0:09:43.280 If you're on the train, then you're just looking at 0:09:43.280 --> 0:09:46.360 a ping pong ball bouncing at a relatively slow speed 0:09:46.400 --> 0:09:48.920 down the aisle. If you're not on the train, the 0:09:48.960 --> 0:09:52.480 ping pong ball is moving quite fast, so it's all relative. 0:09:53.160 --> 0:09:56.440 Isaac Newton would follow along and say, yeah, mate, this 0:09:56.520 --> 0:09:59.000 all tracks. I don't know why he talked like that. 0:09:59.640 --> 0:10:02.920 In his Laws of Motion, Newton stated that these laws 0:10:02.960 --> 0:10:06.200 of motion should hold in an inertial frame as well 0:10:06.240 --> 0:10:09.320 as reference frame that was moving at a constant velocity 0:10:09.400 --> 0:10:12.400 relative to the inertial frame. An inertial frame, by the way, 0:10:12.760 --> 0:10:14.800 is just a frame of reference in which there are 0:10:14.960 --> 0:10:18.160 zero net forces acting upon it, so that there are 0:10:18.200 --> 0:10:20.960 no forces of acceleration in play. So in our example, 0:10:21.120 --> 0:10:23.679 the train that we talked about, that would be our 0:10:23.760 --> 0:10:28.280 inertial frame. All of this is fairly intuitive, but then 0:10:28.320 --> 0:10:32.200 we get to something really tricky. Einstein would establish that 0:10:32.280 --> 0:10:34.880 the speed of light in a vacuum is the fastest 0:10:34.920 --> 0:10:38.040 speed in our universe. Nothing can go faster than that. 0:10:38.520 --> 0:10:40.640 But hey, what if you're on a train that's traveling 0:10:40.679 --> 0:10:43.199 one hundred miles per hour and you're facing forward, you're 0:10:43.200 --> 0:10:46.080 facing the direction of travel, and then you have a 0:10:46.120 --> 0:10:50.199 flashlight and you turn on the flashlight. Well, doesn't that 0:10:50.280 --> 0:10:53.520 mean you should perform a Galileean transformation on this and 0:10:53.559 --> 0:10:56.760 say the light from that flashlight in your hands is 0:10:56.760 --> 0:10:59.480 actually traveling at the normal speed of light on board 0:10:59.480 --> 0:11:03.520 the train. But also get that boost of the trains travel, 0:11:03.559 --> 0:11:05.439 so it should be the speed of light plus one 0:11:05.520 --> 0:11:08.800 hundred miles per hour. Doesn't that make sense? While according 0:11:08.800 --> 0:11:11.960 to actual experiments performed before Einstein would come around to 0:11:12.000 --> 0:11:16.000 explain things, the answer was Nope, doesn't look like it 0:11:16.040 --> 0:11:20.559 works that way. Scientists Edward Morley and Albert A. Michelson 0:11:20.840 --> 0:11:24.560 created an experiment to measure the speed of light back 0:11:24.640 --> 0:11:27.760 in eighteen eighty seven, and actually they were looking for 0:11:27.840 --> 0:11:31.360 something else. They were looking for evidence of a hypothetical 0:11:31.400 --> 0:11:37.480 substance called luminiferous ether. Say why, all right, we'll stick 0:11:37.520 --> 0:11:41.800 with me, because in a way this does make sense. Okay, 0:11:41.920 --> 0:11:45.720 So on Earth we see waves traveling through a medium, right, 0:11:45.880 --> 0:11:49.200 Like if you look out in the ocean, you can 0:11:49.320 --> 0:11:52.920 see actual waves in the water, and the water is 0:11:52.960 --> 0:11:57.360 a physical medium through which these waves travel. Sound can't 0:11:57.520 --> 0:12:01.120 travel in space because space is effect actively a vacuum. 0:12:01.400 --> 0:12:04.480 The particles that are in space are so far apart 0:12:04.480 --> 0:12:07.080 from one another that there's no way for the vibration 0:12:07.240 --> 0:12:11.400 of one particle to come into contact and affect another particle. 0:12:11.760 --> 0:12:14.840 So sound can't travel. Sound travels through the propagation of 0:12:14.960 --> 0:12:18.600 vibrational waves. And if your stuff isn't in contact with 0:12:18.640 --> 0:12:20.960 each other, there's no way for them to have that 0:12:21.040 --> 0:12:24.120 wave propagate. So there has to be some sort of 0:12:24.320 --> 0:12:29.120 medium like air or solid surfaces or something in order 0:12:29.160 --> 0:12:33.680 for sound travel. Well, if that's the case, said the 0:12:33.679 --> 0:12:37.160 folks of the time, then stuff like light must need 0:12:37.200 --> 0:12:39.800 some sort of medium to travel through, right. I mean 0:12:39.840 --> 0:12:42.320 sound has to have something. Light must have something too. 0:12:43.160 --> 0:12:46.040 Light can definitely travel through space. I mean, that's how 0:12:46.040 --> 0:12:49.000 we can see anything, because light from the Sun travels 0:12:49.040 --> 0:12:52.400 through space to hit the Earth. So the light has 0:12:52.440 --> 0:12:55.160 to be moving through some sort of medium we cannot 0:12:55.240 --> 0:13:01.079 observe directly. This hypothetical medium was the aforementioned maniferous ether. 0:13:01.760 --> 0:13:05.600 But assuming this ether existed at all, it had to 0:13:05.600 --> 0:13:08.960 be pretty darn special because we can't feel it, we 0:13:09.040 --> 0:13:13.400 can't detect it, it creates no observable effects, So if 0:13:13.440 --> 0:13:16.480 it were real, it had to be unlike pretty much 0:13:16.520 --> 0:13:20.200 anything else we had discovered up to that point. Now, 0:13:20.440 --> 0:13:24.640 let's assume that the universe is filled with this ether stuff. 0:13:25.040 --> 0:13:28.640 The question rises, how the heck does the ether interact 0:13:28.720 --> 0:13:31.080 with all the physical stuff that's in the universe, the 0:13:31.120 --> 0:13:36.400 actual matter and also energy. After all, the bodies in 0:13:36.559 --> 0:13:40.360 space like stars, planets, moons and all that other stuff. 0:13:40.640 --> 0:13:44.160 All of that is moving, none of it is standing still, 0:13:44.440 --> 0:13:48.040 and if it is moving, it would presumably disturb this 0:13:48.360 --> 0:13:51.960 ether medium, right. I mean, if you move your hand 0:13:52.200 --> 0:13:55.040 through a pool of water, you are disturbing that water. 0:13:55.080 --> 0:13:58.080 You're making currents and eddies. So it was thought that 0:13:58.360 --> 0:14:01.600 the motion of all these elements in space would disturb 0:14:01.720 --> 0:14:05.240 the ether in some way, and hypothetically there would be 0:14:05.280 --> 0:14:09.440 some sort of ether wind. But if there were a wind, 0:14:09.920 --> 0:14:13.520 then presumably the speed of light would be affected depending 0:14:13.640 --> 0:14:17.640 upon the wind's direction in relation to the light's direction. 0:14:18.040 --> 0:14:21.000 So think of a really windy day in the real world. 0:14:21.400 --> 0:14:25.000 If you're walking against a very very tough wind, like 0:14:25.040 --> 0:14:27.920 a gale force wind, you have to power through it 0:14:27.960 --> 0:14:31.480 to keep moving forward. Now, if you're walking with the wind, 0:14:31.840 --> 0:14:33.640 like the wind is to your back and pushing you, 0:14:34.040 --> 0:14:36.760 then you get a big boost. Well, the same thing 0:14:36.880 --> 0:14:40.840 should be happening with light if ether wind were real, 0:14:41.480 --> 0:14:44.880 and so Mickelson and Morley devised a gadget that would 0:14:44.960 --> 0:14:49.720 split light into two beams, directing those beams down different paths, 0:14:50.000 --> 0:14:53.400 using mirrors in different directions, and seeing if those two 0:14:53.400 --> 0:14:56.640 beams of light would hit an eyepiece at different times. 0:14:56.680 --> 0:15:00.760 The thought being well, one of these directions would theoretically 0:15:00.840 --> 0:15:03.680 be in the same direction as the ether wind, and 0:15:03.760 --> 0:15:06.560 one would be at a cross direction of ether wind, 0:15:06.800 --> 0:15:08.720 So we should see a difference in the amount of 0:15:08.760 --> 0:15:12.040 time it takes for the light from this one source 0:15:12.240 --> 0:15:15.360 that's been split into two to arrive at an eyepiece. 0:15:16.320 --> 0:15:21.080 But that's not what they found. They observed no such effect. 0:15:21.240 --> 0:15:23.600 So if there were such a thing as ether, the 0:15:23.640 --> 0:15:27.120 stuff wasn't giving either a boost or a drag on 0:15:27.280 --> 0:15:30.400 light itself. No matter what. The light was traveling at 0:15:30.400 --> 0:15:33.480 a constant speed, which turned out to be approximately one 0:15:33.560 --> 0:15:36.480 hundred eighty six thousand miles per second or around three 0:15:36.560 --> 0:15:40.400 hundred thousand kilometers per second. Now that flew in the 0:15:40.440 --> 0:15:44.760 face of classic Newtonian physics clearly. With the example of 0:15:44.800 --> 0:15:47.040 the ping pong ball and the train, the ping pong 0:15:47.080 --> 0:15:50.320 ball has to be traveling faster than the train it's on. 0:15:50.400 --> 0:15:52.480 I mean, that just makes sense. If you were standing 0:15:52.560 --> 0:15:54.880 on the top of the very front of the train 0:15:55.320 --> 0:15:58.040 and then you threw the ping pong ball, and we 0:15:58.120 --> 0:16:01.560 ignore stuff like wind resistant, the ping pong ball would 0:16:01.640 --> 0:16:03.920 land ahead of the train, So it has to be 0:16:04.000 --> 0:16:07.240 going faster. So what the heck was so special about 0:16:07.360 --> 0:16:10.120 light and what was going on? Well, this was one 0:16:10.120 --> 0:16:13.240 of the great mysteries that Albert Einstein set his mind 0:16:13.280 --> 0:16:16.240 to unraveling, and it formed the basis of one of 0:16:16.280 --> 0:16:19.360 his great theories of relativity. And this would be the 0:16:19.360 --> 0:16:23.000 theory of special relativity, which poses that the laws of 0:16:23.040 --> 0:16:26.640 physics are in the same in all inertial frames of references. 0:16:27.240 --> 0:16:28.960 And that means the speed of light will be the 0:16:28.960 --> 0:16:33.400 same for all observers, regardless of their relative perspectives. It 0:16:33.440 --> 0:16:36.760 doesn't matter the context. The speed of light is the 0:16:36.800 --> 0:16:40.080 speed of light. Now, there's an implication to this theory 0:16:40.440 --> 0:16:43.520 that really got people scratching their heads. If the speed 0:16:43.520 --> 0:16:47.240 of light is absolutely constant, that would mean that stuff 0:16:47.400 --> 0:16:51.480 like distance and time are not. And as a heck 0:16:51.520 --> 0:16:54.480 of a brain teaser, when we come back, we'll explore 0:16:54.520 --> 0:17:06.080 this more. Let's imagine that you live half a mile 0:17:06.200 --> 0:17:09.760 away from a lovely park, and it's a half mile 0:17:09.800 --> 0:17:12.600 away in the morning, it's a half mile away. At night, 0:17:13.240 --> 0:17:15.720 it's a half mile away. On a Tuesday, it's a 0:17:15.760 --> 0:17:19.639 half mile away. On a Saturday. Half a mile is 0:17:19.720 --> 0:17:24.040 half a mile, right, it's a reliable constant in our lives. 0:17:24.119 --> 0:17:27.280 If it weren't, we could never give directions to anywhere 0:17:27.320 --> 0:17:30.639 because all the measurements and landmarks would change all the time, 0:17:30.920 --> 0:17:34.120 and our world wouldn't make sense the way it does 0:17:34.160 --> 0:17:38.159 to us now. So in our individual experiences, in our 0:17:38.280 --> 0:17:42.480 day to day lives, stuff like distance seems pretty darn 0:17:42.560 --> 0:17:47.560 reliable and fixed. So how dare Einstein come along with 0:17:47.600 --> 0:17:51.400 this theory of special relativity at nineteen oh five and say, well, yeah, 0:17:51.440 --> 0:17:55.560 but see, the speed of light is really the true constant, 0:17:55.920 --> 0:17:59.560 and for that to work, time and distance or space, 0:17:59.640 --> 0:18:04.960 in other word, words, must be somewhat mutable. Einstein positive 0:18:05.160 --> 0:18:09.400 that there is no absolute frame of reference in our universe, 0:18:09.640 --> 0:18:12.679 which means there is no place in the universe that 0:18:12.840 --> 0:18:17.480 is totally stationary. Everything is moving, which means all motion 0:18:17.760 --> 0:18:20.919 is relative. You can't really talk about moving except in 0:18:20.960 --> 0:18:24.959 reference to some other moving thing. So even as we 0:18:25.160 --> 0:18:28.879 sit still and try to meditate, we do so on 0:18:28.920 --> 0:18:32.879 a planet that is hurtling through space. We are in motion. 0:18:33.200 --> 0:18:36.399 We're all moving through space and time, and we all 0:18:36.440 --> 0:18:40.560 have a frame of reference, and each frame of reference 0:18:40.920 --> 0:18:44.320 is just as legitimate as every other frame of reference, 0:18:45.080 --> 0:18:48.520 or I guess you could say, if everybody's super, nobody is. 0:18:49.320 --> 0:18:52.520 I guess I've watched The Incredibles too many times. Well, anyway, 0:18:52.560 --> 0:18:56.400 this particular nineteen oh five theory is called special relativity 0:18:56.560 --> 0:19:01.800 because Einstein's explanation only covered special cases, that being when 0:19:02.040 --> 0:19:05.600 two inertial frames are in constant motion with regard to 0:19:05.640 --> 0:19:08.720 one another, and there can be no acceleration, so the 0:19:08.760 --> 0:19:10.919 motion had to be in a straight line at a 0:19:11.000 --> 0:19:14.679 constant speed. A change in direction or speed would be 0:19:14.800 --> 0:19:18.080 an acceleration, and to cover those instances we would have 0:19:18.080 --> 0:19:20.600 to wait a decade for Einstein to work out his 0:19:20.720 --> 0:19:24.320 theory of general relativity. We'll get to that, but we've 0:19:24.359 --> 0:19:27.280 got a lot more to say about special relativity. So 0:19:27.400 --> 0:19:30.400 Einstein was taking a different approach to the results of 0:19:30.440 --> 0:19:33.879 the experiments done by people like Michelson and Morley. The 0:19:33.920 --> 0:19:38.080 scientific world at large was essentially saying, well, this can't 0:19:38.119 --> 0:19:40.720 be right. These results can't be right. There must be 0:19:40.800 --> 0:19:44.320 something wrong with the experiment or the equipment, because we're 0:19:44.440 --> 0:19:48.000 sure this theory is correct and that ether is there. 0:19:48.600 --> 0:19:51.439 Einstein was taking a totally different perspective. He was saying, 0:19:52.080 --> 0:19:56.400 if we assume the experiments are producing accurate results, then 0:19:56.440 --> 0:19:59.760 it stands to reason that the prevailing theory is flawed 0:20:00.080 --> 0:20:02.600 and we have to figure out what the real explanation is. 0:20:03.040 --> 0:20:05.360 And this is one of those important points in science. 0:20:05.920 --> 0:20:09.520 It's that if your results in your experiment don't meet 0:20:09.560 --> 0:20:14.639 your hypothesis, it's very possible that your hypothesis is wrong. 0:20:14.960 --> 0:20:17.960 Now you need to do multiple experiments to find out 0:20:18.520 --> 0:20:20.919 and to test your equipment make sure there's not any 0:20:21.280 --> 0:20:24.520 errors there that could be causing the issues. But it 0:20:24.560 --> 0:20:27.440 does mean that you need to re examine that hypothesis, 0:20:27.960 --> 0:20:32.080 and at this time the scientific community wasn't really doing that, 0:20:32.720 --> 0:20:37.200 so Einstein did away with the ether. His explanation suggested 0:20:37.240 --> 0:20:41.520 that our observable universe has four dimensions, not that there 0:20:41.520 --> 0:20:44.760 can only be four dimensions, but rather there are four 0:20:44.800 --> 0:20:52.320 dimensions we can detect and observe, and these would be up, down, left, right, forward, backward, 0:20:52.760 --> 0:20:57.520 and then the fourth dimension, which is time. Collectively, those 0:20:57.560 --> 0:21:01.280 three dimensions are space. The fourth dimension is time, and 0:21:01.320 --> 0:21:06.320 we get the space time continuum, this intrinsic relationship between 0:21:06.359 --> 0:21:10.000 space and time or space time continuum, which also gives 0:21:10.080 --> 0:21:13.280 us dozens of Star Trek episodes that would use it 0:21:13.320 --> 0:21:15.919 as shorthand, for things are about to get really weird. 0:21:16.600 --> 0:21:20.120 Einstein positive that the speed of light is measured as 0:21:20.240 --> 0:21:23.399 constant in all frames of reference. And let's think for 0:21:23.480 --> 0:21:27.199 a second. What we mean by speed. Speed is a 0:21:27.240 --> 0:21:31.000 description of how much distance can be covered per unit 0:21:31.119 --> 0:21:34.080 of time. So a speed of one hundred miles per 0:21:34.080 --> 0:21:37.080 hour means that in one hour's time we will cover 0:21:37.160 --> 0:21:40.439 a distance of one hundred miles. That's very obvious. But 0:21:41.040 --> 0:21:44.240 if the speed of light is constant for all frames 0:21:44.320 --> 0:21:48.040 of reference, regardless of how those frames are moving relative 0:21:48.080 --> 0:21:51.520 to each other, that must mean something about space and 0:21:51.800 --> 0:21:55.680 or time is a little wonky. And let's think about 0:21:55.720 --> 0:21:58.920 our train experiment again. If you are aboard a train 0:21:59.320 --> 0:22:01.600 moving at a move one hundred miles per hour in 0:22:01.640 --> 0:22:04.120 a straight line, and you toss a ping pong ball 0:22:04.160 --> 0:22:06.919 straight up in the air, well, it's gonna go straight 0:22:07.000 --> 0:22:09.240 up and come right back down to your hand in 0:22:09.320 --> 0:22:12.960 a nice vertical line. From an outside observer who isn't 0:22:12.960 --> 0:22:15.199 on the train, it would look a little differently. You 0:22:15.200 --> 0:22:18.040 would throw the ball up at one point relative to 0:22:18.080 --> 0:22:20.720 this outside observer, and the ball would appear to move 0:22:20.760 --> 0:22:24.200 not just vertically, but horizontally before coming back down. Now, 0:22:24.240 --> 0:22:27.640 if we repeat this experiment but we use light, we 0:22:27.680 --> 0:22:30.760 really see how it gets confusing. Okay, so now you're 0:22:30.800 --> 0:22:34.640 on a train, but it's going really fast, like let's say, 0:22:34.720 --> 0:22:38.080 half the speed of light. But the speed and direction 0:22:38.200 --> 0:22:41.240 are constant. So you're on this train. You don't feel 0:22:41.480 --> 0:22:45.320 any acceleration forces because you're moving at a constant speed 0:22:45.920 --> 0:22:48.760 and in a constant direction, so your velocity remains the same. 0:22:49.280 --> 0:22:51.560 In fact, if there were no windows on the train, 0:22:51.640 --> 0:22:53.400 you wouldn't even be able to tell that the train 0:22:53.520 --> 0:22:55.800 was moving at all. So let's say you've got a 0:22:55.840 --> 0:22:58.679 laser pointer and you've got a mirror on the ceiling 0:22:58.760 --> 0:23:01.720 of the train and a foton detector on the floor 0:23:01.720 --> 0:23:04.439 of the train. You shoot the laser up at the mirror, 0:23:04.680 --> 0:23:07.680 it reflects off the mirror, and then it comes back 0:23:07.680 --> 0:23:10.560 down and hits the detector on the floor, and it 0:23:10.760 --> 0:23:13.360 registers how long it took the light to travel from 0:23:13.400 --> 0:23:16.280 your laser pointer to hit the detector. And to you, 0:23:16.640 --> 0:23:19.600 the laser makes a vertical line. All that makes sense, right, 0:23:19.640 --> 0:23:23.000 you can imagine that, But for our outside observer who's 0:23:23.000 --> 0:23:25.280 not on the train, it would appear as though the 0:23:25.359 --> 0:23:29.040 laser were actually traveling at a diagonal up to that mirror, 0:23:29.280 --> 0:23:32.600 and then a diagonal back down toward the detector. So 0:23:33.119 --> 0:23:35.679 for one observer, the one on the train, we have 0:23:35.720 --> 0:23:39.320 a straight line. It's vertical up down. For the second 0:23:39.400 --> 0:23:42.280 observer off the train, we have an angled path, sort 0:23:42.320 --> 0:23:44.160 of like how a billiard ball can hit the side 0:23:44.160 --> 0:23:46.240 of a pool table and bounce off at an angle. 0:23:47.000 --> 0:23:50.400 But this creates an apparent paradox. The path viewed by 0:23:50.600 --> 0:23:52.960 you on the train is a straight line, and by 0:23:53.000 --> 0:23:56.600 definition that is the shortest distance between two points. The 0:23:56.640 --> 0:23:59.119 path observed by the person who is not on the 0:23:59.160 --> 0:24:02.320 train is an angled line, and by definition that has 0:24:02.359 --> 0:24:05.520