WEBVTT - Rerun: It's All Relative 0:00:04.400 --> 0:00:07.800 Welcome to tech Stuff, a production from I Heart Radio. 0:00:12.440 --> 0:00:15.440 Hey there, and welcome to tech Stuff. I'm your host, 0:00:15.600 --> 0:00:18.720 Jonathan Strickland. I'm an executive producer with I Heart Radio. 0:00:18.920 --> 0:00:22.720 And how the tech are you. Well, I'm still on vacation, y'all. 0:00:23.040 --> 0:00:25.560 I'll be back soon. But in the meantime, we have 0:00:25.640 --> 0:00:29.640 an episode that originally published on July one, twenty. It's 0:00:29.680 --> 0:00:32.960 called It's All Relative. And when I was a kid, 0:00:33.000 --> 0:00:37.120 I was convinced that Einstein's theories were the these super 0:00:37.240 --> 0:00:41.800 complicated explanations of the universe that really had no real 0:00:42.000 --> 0:00:44.840 intersection with my daily life. But as it turns out, 0:00:44.880 --> 0:00:48.920 without an understanding of relativity, a lot of the technology 0:00:49.000 --> 0:00:53.400 we rely upon wouldn't work properly. It's fascinating stuff. I 0:00:53.479 --> 0:01:00.000 hope you enjoy. The hurts unit refers to the numb 0:01:00.120 --> 0:01:03.640 or of repeated phenomena over the course of a second. 0:01:04.080 --> 0:01:07.959 So imagine that you're dribbling a basketball, so that the 0:01:08.000 --> 0:01:11.040 ball goes from your hand to the ground back up 0:01:11.080 --> 0:01:14.560 to your hand once per second. Well, you could describe 0:01:14.640 --> 0:01:19.119 your dribbling as being one hurts in frequency, one full 0:01:19.200 --> 0:01:23.119 cycle per second. Up down, up, Now, if you dribbled 0:01:23.160 --> 0:01:26.119 twice as fast, so that the ball went up down 0:01:26.280 --> 0:01:29.520 up two full times per second, then there would be 0:01:29.680 --> 0:01:33.640 two hurts. Well, we can describe lots of stuff with 0:01:33.760 --> 0:01:36.480 the unit hurts. We use it to describe sounds, in 0:01:36.480 --> 0:01:40.720 which case we're talking about the frequency at which stuff vibrates. 0:01:41.360 --> 0:01:45.200 Typical human hearing spans a range of frequencies that at 0:01:45.240 --> 0:01:48.160 the low end is that twenty hurts. That represents the 0:01:48.240 --> 0:01:50.680 lowest pitches of sounds. So you can think of those 0:01:50.680 --> 0:01:54.760 deep bass notes. That's around the twenty hurts of area uh, 0:01:54.800 --> 0:01:57.000 and then it goes all the way up to twenty 0:01:57.120 --> 0:02:01.360 killer hurts or twenty thousand hurts. That represents the very 0:02:01.440 --> 0:02:05.480 highest pitches that people can typically here, And those frequencies 0:02:05.760 --> 0:02:10.000 correlate to how quickly stuff is vibrating back and forth. Now, 0:02:10.000 --> 0:02:12.440 when it comes to us hearing things, we usually mean 0:02:12.600 --> 0:02:16.520 that we're talking about the vibrations and fluctuation and air pressure, 0:02:16.760 --> 0:02:20.160 and those fluctuations and air pressure interact with our ear drums. 0:02:20.840 --> 0:02:23.240 But we can use hurts to talk about all sorts 0:02:23.280 --> 0:02:27.160 of stuff, including the processor speed of a CPU. In 0:02:27.200 --> 0:02:29.799 that case, we're really talking about the number of clock 0:02:30.040 --> 0:02:33.560 cycles per second, so you get it. This is a 0:02:33.639 --> 0:02:37.040 description of the frequency of the number of times a 0:02:37.120 --> 0:02:40.320 certain thing happens, like within a second. And I also 0:02:40.400 --> 0:02:43.720 explained that we measure the rate at which we can 0:02:43.760 --> 0:02:47.600 send data using the term bits. A bit is a 0:02:47.600 --> 0:02:51.000 basic unit of digital information, and when we talk about computers, 0:02:51.200 --> 0:02:53.920 we're talking about bits in the form of a zero 0:02:54.200 --> 0:02:58.400 or a one binary information, just like your basic two 0:02:58.400 --> 0:03:02.480 way physical switch has two positions off or on. So 0:03:02.520 --> 0:03:04.840 if you hear a term like kill a bit, that 0:03:04.880 --> 0:03:08.519 means one thousand bits, and a megabit is one million bits, 0:03:08.560 --> 0:03:13.519 and a gigabit would be one billion bits. Likewise, megabits 0:03:13.560 --> 0:03:17.280 per second tells us how many million bits can move 0:03:17.400 --> 0:03:20.720 from one point to another per second over that connection. 0:03:21.120 --> 0:03:24.239 So if you've got a one hundred megabit per second connection, 0:03:24.840 --> 0:03:28.400 theoretically it would mean that up to one hundred million 0:03:28.480 --> 0:03:33.360 bits can transfer across that communication channel per second, though 0:03:33.520 --> 0:03:36.400 that's not how it works out most of the time, 0:03:36.440 --> 0:03:39.360 but that's a matter for a different episode. I didn't 0:03:39.400 --> 0:03:43.640 mention that this is different from something like megabytes. So 0:03:43.760 --> 0:03:47.000 a bite is a unit that consists of eight bits, 0:03:47.840 --> 0:03:50.760 and this gets confusing because we often describe stuff like 0:03:50.840 --> 0:03:55.000 file sizes in terms of bites, but transfer speeds in 0:03:55.120 --> 0:03:58.280 terms of bits. So let's say that you do have 0:03:58.400 --> 0:04:01.840 that one hundred megabits person, I can download speed, and 0:04:02.000 --> 0:04:05.600 you want to download a one hundred megabyte file, Well, 0:04:05.600 --> 0:04:09.440 that means it's not going to take one second. It's 0:04:09.440 --> 0:04:12.520 gonna take eight seconds to download the file, because a 0:04:12.520 --> 0:04:16.640 megabyte is eight times larger than a megabit. And actually 0:04:17.160 --> 0:04:19.919 even that is a little bit misleading because in computer 0:04:20.040 --> 0:04:23.320 memory terms, we typically look at units of memory based 0:04:23.360 --> 0:04:27.440 on powers of two rather than powers of ten. So 0:04:27.480 --> 0:04:31.040 instead of a killer byte being one thousand bytes, it's 0:04:31.080 --> 0:04:35.400 actually one thousand twenty four bytes. And there's no standardization 0:04:35.520 --> 0:04:38.760 in the tech industry, so sometimes people will say a 0:04:38.839 --> 0:04:41.920 kill a byte and they mean one thousand bytes. Sometimes 0:04:41.920 --> 0:04:43.960 they'll say kill a byte and they mean one thousand 0:04:44.040 --> 0:04:47.160 twenty four bytes, and you will want to tear your 0:04:47.200 --> 0:04:50.280 hair out, and then you'll look like I do, I'm 0:04:50.320 --> 0:04:52.880 bald if you didn't know. But this episode isn't about 0:04:52.880 --> 0:04:57.880 the peculiarities of our naming conventions and the computer information age. Instead, 0:04:58.200 --> 0:05:02.080 I wanted to tackle something else. It affects everything, really, 0:05:02.160 --> 0:05:04.680 but in particular we really had to suss it out 0:05:04.760 --> 0:05:08.000 in order to make certain types of satellites work properly. 0:05:08.279 --> 0:05:11.320 And this is the concept of relativity. So in this 0:05:11.360 --> 0:05:14.599 episode we're really going to learn why an understanding of 0:05:14.600 --> 0:05:19.320 relativity is important if we want our certain satellite technologies 0:05:19.360 --> 0:05:22.159 to work, and it serves as a great reminder that 0:05:22.240 --> 0:05:26.400 technology is only really possible through an understanding of science. 0:05:26.760 --> 0:05:30.200 You can think of tech as the physical manifestation of 0:05:30.240 --> 0:05:34.080 our understanding of scientific principles, and that means if we 0:05:34.080 --> 0:05:37.760 were wrong in our understanding of science, the technology shouldn't 0:05:37.800 --> 0:05:40.680 really work. So in a way, you can think of 0:05:40.800 --> 0:05:44.720 technology that works as evidence that the scientific method is 0:05:44.760 --> 0:05:48.800 a darned good formula. Since we're talking about relativity, it 0:05:48.839 --> 0:05:52.160 means we're gonna be talking about a real Einstein today. 0:05:52.320 --> 0:05:57.159 His name was Einstein, which is convenient. But before we 0:05:57.200 --> 0:06:03.680 get to Einstein, we have Galileo Galileo, Galileo Figaro. Wait no, 0:06:03.760 --> 0:06:08.320 I'm sorry, Wait that's Bohemian Rhapsody. I meant Galileo galile This. 0:06:08.440 --> 0:06:12.680 Galileo made an observation that if you've got two observers 0:06:13.000 --> 0:06:16.480 moving at a constant speed and direction, so they're moving 0:06:16.520 --> 0:06:19.320 at the same velocity, they will get the same results 0:06:19.400 --> 0:06:23.800 for any experiment that involves moving stuff around a mechanical experiment. 0:06:24.520 --> 0:06:28.280 This is easier to understand if we use an example, 0:06:28.640 --> 0:06:31.839 and I like one that my colleague Robert Lamb used 0:06:31.880 --> 0:06:34.800 when he wrote about relativity for how Stuff Works dot 0:06:34.800 --> 0:06:37.800 Com back in the day. He used an example of 0:06:37.839 --> 0:06:41.760 a train and a scientific ping pong ball. Alright, so 0:06:42.120 --> 0:06:45.000 imagine you've got a scientist who's standing in the middle 0:06:45.040 --> 0:06:48.360 of an aisle on a moving train, and the train 0:06:48.560 --> 0:06:51.320 is moving at a steady speed in a straight line, 0:06:51.440 --> 0:06:56.160 so there are no active forces of acceleration going on here. Remember, 0:06:56.400 --> 0:07:00.880 acceleration describes a force that involves a chain and velocities. 0:07:01.000 --> 0:07:04.120 That other means a change in direction or a change 0:07:04.160 --> 0:07:08.440 in speed or both, but in this case constant speed 0:07:08.880 --> 0:07:13.520 constant direction. Robert used nice round numbers in his examples, 0:07:13.560 --> 0:07:15.920 so he suggested that the train is moving at one 0:07:16.320 --> 0:07:19.280 miles per hour. Well it's not round. If we go 0:07:19.360 --> 0:07:22.840 to the metric system, that would be one kilometers per hour. 0:07:23.360 --> 0:07:26.800 If the train stays steady to the scientist, it will 0:07:26.840 --> 0:07:29.560 feel as if that scientist is actually just standing still, 0:07:29.800 --> 0:07:33.720 just anywhere, and we're conveniently ignoring an emotion that would 0:07:33.720 --> 0:07:36.960 happen due to irregularities with the trains wheels or the 0:07:36.960 --> 0:07:39.680 train tracks or anything like that. And if this is 0:07:39.720 --> 0:07:42.360 hard for you to imagine, just think about how you 0:07:42.440 --> 0:07:46.040 feel when you're standing still or sitting still or laying down. 0:07:46.240 --> 0:07:50.160 Here on Earth. We know the Earth is moving through space. 0:07:50.800 --> 0:07:53.680 It is a body in motion, but when we are 0:07:54.040 --> 0:07:58.640 still relative to the Earth itself, we don't feel that motion. 0:07:58.960 --> 0:08:02.320 Assuming there's not mother weird event going on like an earthquake, 0:08:02.360 --> 0:08:06.120 which is something separate. But back to our hypothetical train, 0:08:06.640 --> 0:08:11.000 the scientist tosses the ping pong ball down the aisle. Now, 0:08:11.080 --> 0:08:15.080 from the scientist's perspective, this ping pong ball will travel 0:08:15.120 --> 0:08:18.840 at whatever speed they threw it at. Robert actually suggests 0:08:18.880 --> 0:08:22.320 a relatively gentle toss of five miles per hour or 0:08:22.320 --> 0:08:26.040 eight kilometers per hour. The ping pong ball would bounce 0:08:26.200 --> 0:08:28.680 down the aisle, just as it would if the scientists 0:08:28.680 --> 0:08:30.800 were to toss the ball on a train that isn't 0:08:30.800 --> 0:08:35.079 moving at all, or on just flat ground. However, let's 0:08:35.080 --> 0:08:38.640 say we have a second observer who's not on the train. 0:08:38.679 --> 0:08:41.040 They're standing off to the side, and they can see 0:08:41.080 --> 0:08:44.280 through the train. To this person, it will appear as 0:08:44.320 --> 0:08:47.880 if the ping pong ball is moving very fast. Indeed, 0:08:48.200 --> 0:08:52.120 relative to this stationary observer, the ping pong ball will 0:08:52.160 --> 0:08:54.120 appear to move at the speed at which it was 0:08:54.160 --> 0:08:57.960 thrown in addition to the speed of the train itself. 0:08:58.320 --> 0:09:00.800 So if we take the two figures, we get one 0:09:00.920 --> 0:09:03.960 hundred five miles per hour or a hundred sixty nine 0:09:04.000 --> 0:09:09.920 kilometers per hour. This is called a Galilean transformation. Alternatively, 0:09:10.240 --> 0:09:12.400 if the scientists were throwing the ping pong ball in 0:09:12.440 --> 0:09:15.440 the opposite direction of the trains travel, so they're facing 0:09:15.600 --> 0:09:17.920 towards the back of the train, it would appear to 0:09:18.000 --> 0:09:21.040 this second observer that the ping pong ball was moving 0:09:21.120 --> 0:09:24.040 at a slightly slower speed than the overall train was, 0:09:24.200 --> 0:09:27.080 whereas to the scientist on board, the ping pong ball 0:09:27.160 --> 0:09:30.280 would still be traveling at that five mile per hour speed. 0:09:30.960 --> 0:09:35.400 So this is where the term relativity comes into play. 0:09:35.480 --> 0:09:40.480 The effects observed are relative to the perspective of the observer. 0:09:41.000 --> 0:09:44.680 It's all based on the reference frame of that observer. 0:09:45.280 --> 0:09:47.640 If you're on the train, then you're just looking at 0:09:47.640 --> 0:09:50.680 a ping pong ball bouncing at a relatively slow speed 0:09:50.720 --> 0:09:53.280 down the aisle. If you're not on the train, the 0:09:53.320 --> 0:09:56.840 ping pong ball is moving quite fast, so it's all relative. 0:09:57.480 --> 0:10:00.800 Isaac Newton would follow along and say, yeah, mate, this 0:10:00.840 --> 0:10:03.320 old tracks. I don't know why I talked like that. 0:10:04.040 --> 0:10:07.280 In his Laws of Motion, Newton stated that these laws 0:10:07.320 --> 0:10:10.800 emotions should hold in an inertial frame as well as 0:10:10.880 --> 0:10:13.680 a reference frame that was moving at a constant velocity 0:10:13.720 --> 0:10:16.800 relative to the inertial frame. And inertial frame, by the way, 0:10:17.120 --> 0:10:19.160 is just a frame of reference in which there are 0:10:19.280 --> 0:10:22.480 zero net forces acting upon it, so that there are 0:10:22.520 --> 0:10:25.280 no forces of acceleration in play. So in our example, 0:10:25.480 --> 0:10:28.040 the train that we talked about, that would be our 0:10:28.080 --> 0:10:32.640 inertial frame. All of this is fairly intuitive, but then 0:10:32.679 --> 0:10:36.560 we get to something really tricky. Einstein would establish that 0:10:36.640 --> 0:10:39.240 the speed of light in a vacuum is the fastest 0:10:39.240 --> 0:10:43.160 speed in our universe. Nothing can go faster than that. Hey, 0:10:43.160 --> 0:10:45.760 what if you're on the train that's traveling one per 0:10:45.840 --> 0:10:48.959 hour and you're facing forward, you're facing the direction of travel, 0:10:49.440 --> 0:10:52.280 and then you have a flashlight and you turn on 0:10:52.440 --> 0:10:55.560 the flashlight. Well, doesn't that mean you should perform a 0:10:55.600 --> 0:10:59.360 Galilean transformation on this and say the light from that 0:10:59.400 --> 0:11:02.600 flashlight in your hands is actually traveling at the normal 0:11:02.640 --> 0:11:06.000 speed of light on board the train, but also get 0:11:06.040 --> 0:11:08.400 that boost of the trains travel, So it should be 0:11:08.400 --> 0:11:11.320 the speed of light plus one miles per hour. Doesn't 0:11:11.320 --> 0:11:15.040 that make sense? Well, according to actual experiments performed before 0:11:15.080 --> 0:11:19.640 Einstein would come around to explain things, the answer was Nope, 0:11:19.640 --> 0:11:23.400 doesn't look like it works that way. Scientists Edward Morley 0:11:23.440 --> 0:11:27.840 and Albert A. Michelson created an experiment to measure the 0:11:27.840 --> 0:11:31.400 speed of light back in seven and actually they were 0:11:31.400 --> 0:11:34.800 looking for something else. They were looking for evidence of 0:11:34.800 --> 0:11:41.400 a hypothetical substance called luminiferous ether. Say what, all right, 0:11:41.440 --> 0:11:44.680 We'll stick with me, because in a way this does 0:11:44.760 --> 0:11:48.760 make sense. Okay, So on Earth we see waves traveling 0:11:48.800 --> 0:11:52.200 through a medium, right, Like if you look out in 0:11:52.240 --> 0:11:55.959 the ocean, you can see actual waves in the water, 0:11:56.360 --> 0:11:59.200 and the water is a physical medium through which these 0:11:59.200 --> 0:12:04.000 waves travel. Sound can't travel in space because space is 0:12:04.080 --> 0:12:08.040 effectively a vacuum. The particles that are in space are 0:12:08.080 --> 0:12:10.800 so far apart from one another there's no way for 0:12:10.840 --> 0:12:14.240 the vibration of one particle to come into contact and 0:12:14.280 --> 0:12:18.079 affect another particle, so sound can't travel. Sound travels through 0:12:18.080 --> 0:12:22.160 the propagation of vibrational waves, and if your stuff isn't 0:12:22.200 --> 0:12:24.520 in contact with each other, there's no way for them 0:12:24.559 --> 0:12:27.640 to have that wave propagate. So there has to be 0:12:27.720 --> 0:12:32.200 some sort of medium like air or solid surfaces or 0:12:32.320 --> 0:12:37.120 something in order for sound travel. Well, if that's the case, 0:12:37.480 --> 0:12:40.679 said the folks of the time, then stuff like light 0:12:41.040 --> 0:12:43.760 must need some sort of medium to travel through, right. 0:12:43.880 --> 0:12:45.960 I mean sound has to have something. Light must have 0:12:46.040 --> 0:12:50.040 something too. Light can definitely travel through space. I mean 0:12:50.040 --> 0:12:52.520 that's how we can see anything, because light from the 0:12:52.559 --> 0:12:56.160 Sun travels through space to hit the Earth. So the 0:12:56.240 --> 0:12:58.920 light has to be moving through some sort of medium 0:12:58.960 --> 0:13:04.040 we cannot observe directly. This hypothetical medium was the aforementioned 0:13:04.200 --> 0:13:09.600 luminiferous ether. But assuming this ether existed at all, it 0:13:09.640 --> 0:13:12.839 had to be pretty darn special because we can't feel it, 0:13:13.200 --> 0:13:17.440 we can't detect it, it creates no observable effects, So 0:13:17.600 --> 0:13:20.520 if it were real, it had to be unlike pretty 0:13:20.600 --> 0:13:24.520 much anything else we had discovered up to that point. Now, 0:13:24.800 --> 0:13:29.040 let's assume that the universe is filled with this ether stuff. 0:13:29.360 --> 0:13:33.000 The question rises, how the heck does the ether interact 0:13:33.040 --> 0:13:35.440 with all the physical stuff that's in the universe, the 0:13:35.440 --> 0:13:40.760 actual matter and also energy. After all, the bodies in 0:13:40.880 --> 0:13:44.720 space like stars, planets, moons, and all that other stuff. 0:13:44.960 --> 0:13:48.559 All of that is moving, none of it is standing still, 0:13:48.800 --> 0:13:52.400 and if it is moving, it would presumably disturb this 0:13:52.679 --> 0:13:56.520 ether medium, right. I mean, if you move your hand 0:13:56.559 --> 0:13:59.360 through a pool of water, you are disturbing that water. 0:13:59.440 --> 0:14:02.560 You're making currents and eddies. So it was thought that 0:14:02.640 --> 0:14:06.000 the motion of all these elements in space would disturb 0:14:06.080 --> 0:14:09.600 the ether in some way, and hypothetically there would be 0:14:09.679 --> 0:14:13.760 some sort of ether wind. But if there were a wind, 0:14:14.240 --> 0:14:17.920 then presumably the speed of light would be affected depending 0:14:18.000 --> 0:14:22.080 upon the wind's direction in relation to the lights direction. 0:14:22.400 --> 0:14:25.360 So think of a really windy day in the real world. 0:14:25.720 --> 0:14:29.320 If you're walking against a very very tough wind, like 0:14:29.360 --> 0:14:32.240 a gale force wind, you have to power through it 0:14:32.280 --> 0:14:35.800 to keep moving forward. Now, if you're walking with the wind, 0:14:36.160 --> 0:14:38.040 like the wind is to your back and pushing you, 0:14:38.360 --> 0:14:41.120 then you get a big boost. Well, the same thing 0:14:41.200 --> 0:14:45.160 should be happening with light if ether wind were real, 0:14:45.800 --> 0:14:49.280 and so Mickelson and Morley devised a gadget that would 0:14:49.280 --> 0:14:53.520 split light into two beams, directing those beams down different 0:14:53.560 --> 0:14:57.520 paths using mirrors in different directions, and seeing if those 0:14:57.560 --> 0:15:01.000 two beams of light would hit an eyepiece at different times, 0:15:01.040 --> 0:15:05.120 the thought being well, one of these directions would theoretically 0:15:05.160 --> 0:15:08.000 be in the same direction as the ether wind, and 0:15:08.120 --> 0:15:10.880 one would be at a cross direction of ether wind. 0:15:11.160 --> 0:15:13.120 So we should see a difference in the amount of 0:15:13.120 --> 0:15:16.400 time it takes for the light from this one source 0:15:16.600 --> 0:15:19.720 that's been split into two to arrive at an eyepiece. 0:15:20.680 --> 0:15:25.440 But that's not what they found. They observed no such effect. 0:15:25.560 --> 0:15:27.960 So if there were such a thing as ether, the 0:15:28.000 --> 0:15:31.440 stuff wasn't giving either a boost or a drag on 0:15:31.640 --> 0:15:34.720 light itself. No matter what. The light was traveling at 0:15:34.760 --> 0:15:37.760 a constant speed, which turned out to be approximately one 0:15:38.520 --> 0:15:41.640 six thousand miles per second or around three hundred thousand 0:15:41.680 --> 0:15:45.320 kilometers per second. Now that flew in the face of 0:15:45.440 --> 0:15:49.400 classic Newtonian physics clearly. With the example of the ping 0:15:49.440 --> 0:15:52.000 pong ball and the train, the ping pong ball has 0:15:52.080 --> 0:15:54.960 to be traveling faster than the train it's on. I mean, 0:15:55.000 --> 0:15:57.200 that just makes sense. If you were standing on the 0:15:57.240 --> 0:15:59.920 top of the very front of the train, and then 0:16:00.040 --> 0:16:03.160 you through the ping pong ball, and we ignore stuff 0:16:03.200 --> 0:16:06.680 like wind resistance, the ping pong ball would land ahead 0:16:06.720 --> 0:16:09.120 of the train, so it has to be going faster. 0:16:09.600 --> 0:16:12.280 So what the heck was so special about light and 0:16:12.320 --> 0:16:14.680 what was going on? Well, this was one of the 0:16:14.720 --> 0:16:18.480 great mysteries that Albert Einstein's that is mine to unraveling, 0:16:18.760 --> 0:16:21.120 and it formed the basis of one of his great 0:16:21.200 --> 0:16:24.280 theories of relativity. And this would be the theory of 0:16:24.400 --> 0:16:28.000 special relativity, which poses that the laws of physics are 0:16:28.000 --> 0:16:31.760 in the same in all inertial frames of references. And 0:16:31.800 --> 0:16:33.560 that means the speed of light will be the same 0:16:33.600 --> 0:16:38.160 for all observers, regardless of their relative perspectives. It doesn't 0:16:38.200 --> 0:16:41.440 matter the context. The speed of light is the speed 0:16:41.440 --> 0:16:44.840 of light. Now, there's an implication to this theory that 0:16:44.960 --> 0:16:47.920 really got people scratching their heads. If the speed of 0:16:48.000 --> 0:16:51.760 light is absolutely constant, that would mean that stuff like 0:16:51.920 --> 0:16:55.920 distance and time are not. And as a heck of 0:16:55.920 --> 0:16:59.280 a brain teaser, when we come back, we'll explore this more. 0:17:07.920 --> 0:17:11.360 Let's imagine that you live half a mile away from 0:17:11.359 --> 0:17:14.520 a lovely park, and it's a half mile away in 0:17:14.560 --> 0:17:17.760 the morning, it's a half mile away. At night, it's 0:17:17.800 --> 0:17:20.359 a half mile away. On a Tuesday, it's a half 0:17:20.400 --> 0:17:24.320 mile away. On a Saturday. Half a mile is half 0:17:24.359 --> 0:17:28.360 a mile, right, it's a reliable constant in our lives. 0:17:28.440 --> 0:17:31.600 If it weren't, we could never give directions to anywhere 0:17:31.680 --> 0:17:34.960 because all the measurements and landmarks would change all the time, 0:17:35.240 --> 0:17:38.440 and our world wouldn't make sense the way it does 0:17:38.480 --> 0:17:42.520 to us now. So in our individual experiences, in our 0:17:42.600 --> 0:17:46.800 day to day lives, stuff like distance seems pretty darn 0:17:46.880 --> 0:17:51.919 reliable and fixed. So how dare Einstein come along with 0:17:51.960 --> 0:17:55.760 this theory of special relativity in nineteen o five and say, well, yeah, 0:17:55.760 --> 0:17:59.879 but see, the speed of light is really the true constant, 0:18:00.280 --> 0:18:03.920 and for that to work, time and distance or space 0:18:04.000 --> 0:18:09.600 in other words, must be somewhat mutable. Einstein positive that 0:18:09.680 --> 0:18:13.760 there is no absolute frame of reference in our universe, 0:18:13.960 --> 0:18:17.040 which means there is no place in the universe that 0:18:17.200 --> 0:18:21.919 is totally stationary. Everything is moving, which means all motion 0:18:22.119 --> 0:18:25.280 is relative. You can't really talk about moving except in 0:18:25.320 --> 0:18:29.280 reference to some other moving thing. So even as we 0:18:29.520 --> 0:18:33.199 sit still and try to meditate, we do so on 0:18:33.280 --> 0:18:37.320 a planet that is hurtling through space. We are in motion. 0:18:37.520 --> 0:18:40.680 We're all moving through space and time, and we all 0:18:40.760 --> 0:18:44.920 have a frame of reference, and each frame of reference 0:18:45.280 --> 0:18:48.720 is just as legitimate as every other frame of reference 0:18:49.400 --> 0:18:51.960 or I guess you could say, if everybody is super, 0:18:52.160 --> 0:18:56.880 nobody is. I guess I've watched The Incredibles too many times. Well, anyway, 0:18:56.920 --> 0:19:00.720 this particular nineteen o five theory is called special relativity 0:19:00.920 --> 0:19:06.240 because Einstein's explanation only covered special cases, that being when 0:19:06.359 --> 0:19:09.959 two inertial frames are in constant motion with regard to 0:19:10.000 --> 0:19:13.080 one another, and there can be no acceleration, so the 0:19:13.119 --> 0:19:15.280 motion had to be in a straight line at a 0:19:15.320 --> 0:19:19.080 constant speed. A change in direction or speed would be 0:19:19.119 --> 0:19:22.399 an acceleration, and to cover those instances we would have 0:19:22.440 --> 0:19:25.000 to wait a decade for Einstein to work out his 0:19:25.080 --> 0:19:28.680 theory of general relativity. We'll get to that, but we've 0:19:28.680 --> 0:19:31.679 got a lot more to say about special relativity. So 0:19:31.760 --> 0:19:34.760 Einstein was taking a different approach to the results of 0:19:34.800 --> 0:19:38.199 the experiments done by people like Michelson and Morley. The 0:19:38.280 --> 0:19:42.440 scientific world at large was essentially saying, well, this can't 0:19:42.440 --> 0:19:45.080 be right. These results can't be right. There must be 0:19:45.119 --> 0:19:48.680 something wrong with the experiment or the equipment, because we're 0:19:48.760 --> 0:19:52.359 sure this theory is correct and that ether is there. 0:19:52.920 --> 0:19:55.800 Einstein was taking a totally different perspective. He was saying, 0:19:56.440 --> 0:20:00.720 if we assume the experiments are producing accurate result, then 0:20:00.760 --> 0:20:04.080 it stands to reason that the prevailing theory is flawed 0:20:04.400 --> 0:20:07.000 and we have to figure out what the real explanation is. 0:20:07.359 --> 0:20:09.720 And this is one of those important points in science. 0:20:10.240 --> 0:20:13.840 It's that if your results in your experiment don't meet 0:20:13.880 --> 0:20:19.080 your hypothesis, it's very possible that your hypothesis is wrong. 0:20:19.280 --> 0:20:22.399 Now you need to do multiple experiments to find out 0:20:22.840 --> 0:20:25.480 and to test your equipment make sure there's not any 0:20:25.600 --> 0:20:28.879 errors there that could be causing the issues. But it 0:20:28.920 --> 0:20:31.760 does mean that you need to re examine that hypothesis, 0:20:32.320 --> 0:20:36.440 and at this time the scientific community wasn't really doing that, 0:20:37.080 --> 0:20:41.560 so Einstein did away with the ether. His explanation suggested 0:20:41.600 --> 0:20:45.880 that our observable universe has four dimensions, not that there 0:20:45.880 --> 0:20:49.080 can only be four dimensions, but rather there are four 0:20:49.119 --> 0:20:56.720 dimensions we can detect and observe, and these would be up, down, left, right, forward, backward, 0:20:57.119 --> 0:21:01.920 and then the fourth dimension, which is time. Collectively, those 0:21:01.920 --> 0:21:05.640 three dimensions are space. The fourth dimension is time, and 0:21:05.680 --> 0:21:10.639 we get the space time continuum, this intrinsic relationship between 0:21:10.680 --> 0:21:14.600 space and time or spacetime continuum, which also gives us 0:21:15.480 --> 0:21:17.800 dozens of Star Trek episodes that would use it as 0:21:17.800 --> 0:21:21.520 shorthand for things are about to get really weird. Einstein 0:21:21.600 --> 0:21:25.119 positive that the speed of light is measured as constant 0:21:25.160 --> 0:21:28.320 in all frames of reference. And let's think for a second. 0:21:28.600 --> 0:21:32.280 What we mean by speed. Speed is a description of 0:21:32.320 --> 0:21:36.000 how much distance can be covered per unit of time. 0:21:36.520 --> 0:21:39.479 So a speed of one miles per hour means that 0:21:39.560 --> 0:21:42.199 in one hour's time we will cover a distance of 0:21:42.240 --> 0:21:46.000 one hundred miles. That's very obvious. But if the speed 0:21:46.000 --> 0:21:50.080 of light is constant for all frames of reference, regardless 0:21:50.200 --> 0:21:53.000 of how those frames are moving relative to each other, 0:21:53.640 --> 0:21:57.399 that must mean something about space and or time is 0:21:57.440 --> 0:22:01.399 a little wonky. And let's think about our train experiment again. 0:22:01.960 --> 0:22:04.600 If you are aboard a train moving at a smooth 0:22:04.640 --> 0:22:07.679 one hour in a straight line, and you toss a 0:22:07.720 --> 0:22:10.440 ping pong ball straight up in the air, well, it's 0:22:10.440 --> 0:22:12.840 gonna go straight up and come right back down to 0:22:12.880 --> 0:22:16.120 your hand in a nice vertical line. From an outside 0:22:16.119 --> 0:22:18.720 observer who isn't on the train, it would look a 0:22:18.760 --> 0:22:21.240 little differently. You would throw the ball up at one 0:22:21.280 --> 0:22:24.480 point relative to this outside observer, and the ball would 0:22:24.480 --> 0:22:27.560 appear to move not just vertically, but horizontally before coming 0:22:27.560 --> 0:22:30.639 back down. Now, if we repeat this experiment, but we 0:22:30.760 --> 0:22:34.200 use light, we really see how it gets confusing. Okay, 0:22:34.240 --> 0:22:37.840 so now you're on a train, but it's going really fast, 0:22:38.119 --> 0:22:41.320 like let's say, half the speed of light, but the 0:22:41.400 --> 0:22:44.640 speed and direction are constant. So you're on this train. 0:22:44.680 --> 0:22:48.480 You don't feel any acceleration forces because you're moving at 0:22:48.480 --> 0:22:52.320 a constant speed and a constant direction, so your velocity 0:22:52.359 --> 0:22:55.320 remains the same. In fact, if there were no windows 0:22:55.359 --> 0:22:57.240 on the train, you wouldn't even be able to tell 0:22:57.240 --> 0:22:59.760 that the train was moving at all. So let's say 0:22:59.760 --> 0:23:02.520 you've a laser pointer and you've got a mirror on 0:23:02.600 --> 0:23:05.600 the ceiling of the train and a photon detector on 0:23:05.640 --> 0:23:08.200 the floor of the train. You shoot the laser up 0:23:08.200 --> 0:23:11.320 at the mirror, it reflects off the mirror, and then 0:23:11.359 --> 0:23:14.360 it comes back down and hits the detector on the floor, 0:23:14.600 --> 0:23:17.080 and it registers how long it took the light to 0:23:17.119 --> 0:23:20.280 travel from your laser pointer to hit the detector. And 0:23:20.359 --> 0:23:23.159 to you, the laser makes a vertical line. All that 0:23:23.200 --> 0:23:25.960 makes sense, right, you can imagine that, But for our 0:23:26.080 --> 0:23:29.080 outside observer who's not on the train, it would appear 0:23:29.160 --> 0:23:32.040 as though the laser were actually traveling at a diagonal 0:23:32.359 --> 0:23:35.240 up to that mirror and then a diagonal back down 0:23:35.359 --> 0:23:39.080 towards the detector. So for one observer, the one on 0:23:39.119 --> 0:23:42.080 the train, we have a straight line. It's vertical up down. 0:23:42.600 --> 0:23:45.520 For the second observer off the train, we have an 0:23:45.560 --> 0:23:48.040 angled path, sort of like how a billiard ball can 0:23:48.119 --> 0:23:50.000 hit the side of a pool table and bounce off 0:23:50.000 --> 0:23:53.719 at an angle. But this creates an apparent paradox. The 0:23:53.760 --> 0:23:57.000 path viewed by you on the train is a straight line, 0:23:57.040 --> 0:24:00.359 and by definition that is the shortest distance between two points. 0:24:00.840 --> 0:24:03.320 The path observed by the person who is not on 0:24:03.359 --> 0:24:06.359 the train is an angled line, and by definition that 0:24:06.440 --> 0:24:09.639 has to be longer. The speed of light is constant 0:24:09.720 --> 0:24:13.200