WEBVTT - It's All Relative 0:00:04.400 --> 0:00:07.760 Welcome to tex Stuff, a production from I Heart Radio. 0:00:12.039 --> 0:00:14.680 Hey there, and welcome to tech Stuff. I'm your host, 0:00:14.800 --> 0:00:17.880 Jonathan Strickland. I'm an executive producer with I Heart Radio 0:00:18.000 --> 0:00:21.919 and I love all things tech. And in our last episode, 0:00:22.000 --> 0:00:27.320 I explained how communications satellites send information via radio waves, 0:00:27.800 --> 0:00:30.720 which is why we talked about signals from such things 0:00:30.760 --> 0:00:34.800 in terms like hurts. The hurts unit refers to the 0:00:34.920 --> 0:00:38.680 number of repeated phenomena over the course of a second. 0:00:39.159 --> 0:00:43.040 So imagine that you're dribbling a basketball so that the 0:00:43.080 --> 0:00:46.120 ball goes from your hand to the ground back up 0:00:46.159 --> 0:00:49.639 to your hand once per second. Well, you could describe 0:00:49.720 --> 0:00:54.200 your dribbling as being one hurts in frequency one full 0:00:54.280 --> 0:00:58.240 cycle per second, up, down, up. Now, if you dribbled 0:00:58.240 --> 0:01:01.600 twice as fast, so that the all went up, down, up, 0:01:01.680 --> 0:01:06.520 two full times per second, then it would be two hurts. Well, 0:01:06.760 --> 0:01:09.679 we can describe lots of stuff with the unit hurts. 0:01:10.000 --> 0:01:12.200 We use it to describe sounds, in which case we're 0:01:12.200 --> 0:01:17.200 talking about the frequency at which stuff vibrates. Typical human 0:01:17.240 --> 0:01:20.600 hearing spans a range of frequencies that at the low 0:01:20.720 --> 0:01:24.319 end is that twenty hurts. That represents the lowest pitches 0:01:24.520 --> 0:01:26.880 of sounds. So you can think of those deep base notes. 0:01:26.920 --> 0:01:30.240 That's around the twenty hurts of area uh, and then 0:01:30.480 --> 0:01:32.880 it goes all the way up to twenty killer hurts 0:01:33.040 --> 0:01:37.480 or twenty thousand hurts. That represents the very highest pitches 0:01:37.560 --> 0:01:41.360 that people can typically here, and those frequencies correlate to 0:01:41.400 --> 0:01:45.240 how quickly stuff is vibrating back and forth. Now, when 0:01:45.240 --> 0:01:47.920 it comes to us hearing things, we usually mean that 0:01:48.240 --> 0:01:51.600 we're talking about the vibrations and fluctuation and air pressure, 0:01:51.840 --> 0:01:55.240 and those fluctuations and air pressure interact with our ear drums. 0:01:55.920 --> 0:01:58.320 But we can use hurts to talk about all sorts 0:01:58.320 --> 0:02:02.000 of stuff, including the pros sessor speed of a CPU. 0:02:02.120 --> 0:02:04.520 In that case, we're really talking about the number of 0:02:04.560 --> 0:02:08.080 clock cycles per second, So you get it. This is 0:02:08.560 --> 0:02:11.959 a description of the frequency of the number of times 0:02:12.000 --> 0:02:15.040 a certain thing happens, like within a second. And I 0:02:15.120 --> 0:02:18.280 also explained that we measure the rate at which we 0:02:18.560 --> 0:02:22.519 can send data using the term bits. A bit is 0:02:22.560 --> 0:02:25.240 a basic unit of digital information, and when we talk 0:02:25.280 --> 0:02:28.480 about computers, we're talking about bits in the form of 0:02:28.480 --> 0:02:32.520 a zero or a one binary information, just like your 0:02:32.560 --> 0:02:36.880 basic two way physical switch has two positions off or on. 0:02:37.400 --> 0:02:39.320 So if you hear a term like kill a bit, 0:02:39.760 --> 0:02:42.799 that means one thousand bits, and a megabit is one 0:02:42.880 --> 0:02:47.560 million bits, and a gigabit would be one billion bits. Likewise, 0:02:47.960 --> 0:02:52.040 megabits per second tells us how many million bits can 0:02:52.120 --> 0:02:55.800 move from one point to another per second over that connection. 0:02:56.200 --> 0:02:59.320 So if you've got a one hundred megabit per second connection, 0:03:00.040 --> 0:03:03.480 theoretically it would mean that up to one hundred million 0:03:03.560 --> 0:03:08.440 bits can transfer across that communication channel per second, though 0:03:08.600 --> 0:03:11.480 that's not how it works out most of the time, 0:03:11.520 --> 0:03:14.400 but that's a matter for a different episode. I didn't 0:03:14.440 --> 0:03:18.760 mention that this is different from something like megabytes. So 0:03:18.800 --> 0:03:22.040 a byte is a unit that consists of eight bits. 0:03:22.880 --> 0:03:25.840 And this gets confusing because we often describe stuff like 0:03:25.919 --> 0:03:30.079 file sizes in terms of bytes, but transfer speeds in 0:03:30.200 --> 0:03:33.359 terms of bits. So let's say that you do have 0:03:33.480 --> 0:03:37.160 that one hundred megabits per second download speed, and you 0:03:37.240 --> 0:03:40.800 want to download a one hundred megabyte file, Well, that 0:03:40.840 --> 0:03:44.760 means it's not going to take one second. It's gonna 0:03:44.800 --> 0:03:48.160 take eight seconds to download the file because a megabyte 0:03:48.240 --> 0:03:52.480 is eight times larger than a megabit. And actually even 0:03:52.520 --> 0:03:55.880 that is a little bit misleading because in computer memory terms, 0:03:56.280 --> 0:03:59.240 we typically look at units of memory based on powers 0:03:59.360 --> 0:04:03.000 of two rather than powers of ten. So instead of 0:04:03.000 --> 0:04:06.800 a killer bite being one thousand bites, it's actually one 0:04:06.840 --> 0:04:10.760 thousand twenty four bites. And there's no standardization in the 0:04:10.800 --> 0:04:14.160 tech industry. So sometimes people will say a kill a 0:04:14.240 --> 0:04:17.320 bite and they mean one thousand bites. Sometimes they'll say 0:04:17.400 --> 0:04:20.160 kill a bite and they mean one thousand, twenty four bites, 0:04:20.680 --> 0:04:23.320 And you will want to tear your hair out and 0:04:23.360 --> 0:04:25.880 then you'll look like I do, I'm bald if you 0:04:25.880 --> 0:04:29.200 didn't know. But this episode isn't about the peculiarities of 0:04:29.240 --> 0:04:33.359 our naming conventions and the computer information age. Instead, I 0:04:33.400 --> 0:04:37.320 wanted to tackle something else that affects everything really, but 0:04:37.400 --> 0:04:39.840 in particular, we really had to suss it out in 0:04:40.000 --> 0:04:43.480 order to make certain types of satellites work properly. And 0:04:43.520 --> 0:04:46.920 this is the concept of relativity. So in this episode 0:04:47.200 --> 0:04:50.280 we're really going to learn why an understanding of relativity 0:04:50.400 --> 0:04:54.839 is important if we want our certain satellite technologies to work, 0:04:55.360 --> 0:04:58.120 and it serves as a great reminder that technology is 0:04:58.160 --> 0:05:02.080 only really possible through an understanding of science. You can 0:05:02.080 --> 0:05:06.240 think of tech as the physical manifestation of our understanding 0:05:06.279 --> 0:05:09.799 of scientific principles, and that means if we were wrong 0:05:09.880 --> 0:05:13.599 in our understanding of science, the technology shouldn't really work. 0:05:14.080 --> 0:05:16.640 So in a way, you can think of technology that 0:05:16.720 --> 0:05:20.360 works as evidence that the scientific method is a darned 0:05:20.360 --> 0:05:24.320 good formula. Since we're talking about relativity, it means we're 0:05:24.360 --> 0:05:27.919 gonna be talking about a real Einstein today. His name 0:05:28.279 --> 0:05:33.200 was Einstein, which is convenient. But before we get to Einstein, 0:05:33.600 --> 0:05:39.440 we have Galileo Galileo, Galileo Figaro. Wait no, I'm sorry, Wait, 0:05:39.520 --> 0:05:44.760 that's Bohemian Rhapsody. I meant Galileo galile This. Galileo made 0:05:44.760 --> 0:05:48.480 an observation that if you've got two observers moving at 0:05:48.520 --> 0:05:51.760 a constant speed and direction, so they're moving at the 0:05:51.800 --> 0:05:54.840 same velocity, they will get the same results for any 0:05:54.839 --> 0:05:59.760 experiment that involves moving stuff around a mechanical experiment. This 0:06:00.080 --> 0:06:03.960 is easier to understand if we use an example, and 0:06:04.080 --> 0:06:07.120 I like one that my colleague Robert Lamb used when 0:06:07.160 --> 0:06:10.120 he wrote about relativity for how Stuff Works dot Com 0:06:10.160 --> 0:06:13.000 back in the day. He used an example of a 0:06:13.040 --> 0:06:16.840 train and a scientific ping pong ball. All right, so 0:06:17.200 --> 0:06:20.080 imagine you've got a scientist who's standing in the middle 0:06:20.120 --> 0:06:23.400 of an aisle on a moving train, and the train 0:06:23.640 --> 0:06:26.400 is moving at a steady speed in a straight line, 0:06:26.520 --> 0:06:31.240 so there are no active forces of acceleration going on here. Remember, 0:06:31.440 --> 0:06:35.799 acceleration describes a force that involves a change in velocity, 0:06:35.880 --> 0:06:38.760 so that other means a change in direction or a 0:06:38.839 --> 0:06:43.080 change in speed or both. But in this case constant 0:06:43.160 --> 0:06:48.599 speed constant direction. Robert used nice round numbers in his examples, 0:06:48.640 --> 0:06:51.000 so he suggested that the train is moving at one 0:06:51.360 --> 0:06:54.359 miles per hour. Well it's not round. If we go 0:06:54.440 --> 0:06:56.680 to the metric system, that would be one sixty one 0:06:56.760 --> 0:07:01.120 kilometers per hour. If the train stays stead to the scientist, 0:07:01.600 --> 0:07:03.680 it will feel as if that scientist is actually just 0:07:03.800 --> 0:07:08.440 standing still, just anywhere, and we're conveniently ignoring an emotion 0:07:08.480 --> 0:07:11.760 that would happen due to irregularities with the trains wheels 0:07:11.840 --> 0:07:14.400 or the train tracks or anything like that. And if 0:07:14.440 --> 0:07:16.960 this is hard for you to imagine, just think about 0:07:17.080 --> 0:07:20.080 how you feel when you're standing still, or sitting still 0:07:20.280 --> 0:07:23.800 or laying down Here on Earth. We know the Earth 0:07:23.880 --> 0:07:27.520 is moving through space. It is a body in motion, 0:07:27.840 --> 0:07:31.640 but when we are still relative to the Earth itself, 0:07:32.280 --> 0:07:35.320 we don't feel that motion. Assuming there's not some other 0:07:35.600 --> 0:07:38.760 weird event going on, like an earthquake, which is something separate, 0:07:39.400 --> 0:07:43.360 but back to our hypothetical train, the scientist tosses the 0:07:43.440 --> 0:07:48.160 ping pong ball down the aisle. Now, from the scientist's perspective, 0:07:48.560 --> 0:07:51.720 this ping pong ball will travel at whatever speed they 0:07:51.760 --> 0:07:55.440 threw it at. Robert actually suggests a relatively gentle toss 0:07:55.520 --> 0:07:58.840 of five miles per hour or eight kilometers per hour. 0:07:59.360 --> 0:08:02.400 The ping pong ball would bounce down the aisle, just 0:08:02.520 --> 0:08:04.440 as it would if the scientists were to toss the 0:08:04.480 --> 0:08:07.040 ball on a train that isn't moving at all, or 0:08:07.160 --> 0:08:11.160 on just flat ground. However, let's say we have a 0:08:11.240 --> 0:08:14.520 second observer who's not on the train. They're standing off 0:08:14.560 --> 0:08:16.960 to the side and they can see through the train. 0:08:17.440 --> 0:08:19.880 To this person, it will appear as if the ping 0:08:19.960 --> 0:08:24.080 pong ball is moving very fast. Indeed, relative to this 0:08:24.240 --> 0:08:27.840 stationary observer, the ping pong ball will appear to move 0:08:27.920 --> 0:08:31.040 at the speed at which it was thrown in addition 0:08:31.240 --> 0:08:34.040 to the speed of the train itself. So if we 0:08:34.120 --> 0:08:37.160 take the two figures, we get one hundred five miles 0:08:37.160 --> 0:08:40.440 per hour or a hundred sixty nine kilometers per hour. 0:08:41.120 --> 0:08:46.000 This is called a Galilean transformation. Alternatively, if the scientists 0:08:46.000 --> 0:08:48.760 were throwing the ping pong ball in the opposite direction 0:08:48.840 --> 0:08:51.280 of the trains travel, so they're facing towards the back 0:08:51.320 --> 0:08:54.240 of the train, it would appear to this second observer 0:08:54.400 --> 0:08:56.760 that the ping pong ball was moving at a slightly 0:08:56.800 --> 0:08:59.920 slower speed than the overall train was, whereas to the 0:09:00.000 --> 0:09:02.800 scientist on board, the ping pong ball would still be 0:09:02.880 --> 0:09:07.200 traveling at that five mile per hour speed. So this 0:09:07.320 --> 0:09:11.199 is where the term relativity comes into play. The effects 0:09:11.200 --> 0:09:16.280 observed are relative to the perspective of the observer. It's 0:09:16.320 --> 0:09:20.520 all based on the reference frame of that observer. If 0:09:20.559 --> 0:09:22.800 you're on the train, then you're just looking at a 0:09:22.800 --> 0:09:26.000 ping pong ball bouncing at a relatively slow speed down 0:09:26.000 --> 0:09:28.559 the aisle. If you're not on the train, the ping 0:09:28.640 --> 0:09:31.920 pong ball is moving quite fast, so it's all relative. 0:09:32.520 --> 0:09:35.800 Isaac Newton would follow along and say, yeah, mate, this 0:09:35.920 --> 0:09:38.400 all tracks. I don't know why I talked like that. 0:09:39.120 --> 0:09:42.360 In his Laws of Motion, Newton stated that these laws 0:09:42.360 --> 0:09:45.880 emotions should hold in an inertial frame as well as 0:09:45.960 --> 0:09:48.720 a reference frame that was moving at a constant velocity 0:09:48.800 --> 0:09:51.640 relative to the inertial frame and inertial frame by the 0:09:51.640 --> 0:09:54.040 way is just a frame of reference in which there 0:09:54.080 --> 0:09:57.400 are zero net forces acting upon it, so that there 0:09:57.400 --> 0:10:00.360 are no forces of acceleration in play. So in our example, 0:10:00.559 --> 0:10:03.120 the train that we talked about, that would be our 0:10:03.160 --> 0:10:07.720 inertial frame. All of this is fairly intuitive, but then 0:10:07.760 --> 0:10:11.640 we get to something really tricky. Einstein would establish that 0:10:11.679 --> 0:10:14.280 the speed of light in a vacuum is the fastest 0:10:14.320 --> 0:10:17.520 speed in our universe. Nothing can go faster than that. 0:10:17.920 --> 0:10:20.040 But hey, what if you're on the train that's traveling 0:10:20.080 --> 0:10:23.480 one hour and you're facing forward, you're facing the direction 0:10:23.520 --> 0:10:26.440 of travel, and then you have a flashlight and you 0:10:26.600 --> 0:10:30.160 turn on the flashlight. Well, doesn't that mean you should 0:10:30.200 --> 0:10:33.960 perform a Galilean transformation on this and say the light 0:10:34.040 --> 0:10:37.120 from that flashlight in your hands is actually traveling at 0:10:37.200 --> 0:10:39.840 the normal speed of light on board the train. But 0:10:39.960 --> 0:10:43.120 also get that boost of the trains travel, so it 0:10:43.120 --> 0:10:45.839 should be the speed of light plus one miles per hour. 0:10:46.040 --> 0:10:49.760 Doesn't that make sense? Well, according to actual experiments performed 0:10:49.760 --> 0:10:53.160 before Einstein would come around to explain things, the answer 0:10:53.320 --> 0:10:57.439 was Nope, doesn't look like it works that way. Scientists 0:10:57.679 --> 0:11:02.160 Edward Morley and Albert A. Michelson created an experiment to 0:11:02.440 --> 0:11:06.280 measure the speed of light back in and actually they 0:11:06.280 --> 0:11:09.720 were looking for something else. They were looking for evidence 0:11:09.800 --> 0:11:16.480 of a hypothetical substance called luminiferous ether. Say what, all right, 0:11:16.520 --> 0:11:19.760 We'll stick with me, because in a way this does 0:11:19.840 --> 0:11:23.800 make sense. Okay, So on Earth we see waves traveling 0:11:23.880 --> 0:11:27.240 through a medium, right, Like if you look out in 0:11:27.280 --> 0:11:31.040 the ocean, you can see actual waves in the water, 0:11:31.440 --> 0:11:34.280 and the water is a physical medium through which these 0:11:34.280 --> 0:11:39.080 waves travel. Sound can't travel in space because space is 0:11:39.120 --> 0:11:43.079 effectively a vacuum. The particles that are in space are 0:11:43.160 --> 0:11:45.760 so far apart from one another that there's no way 0:11:45.800 --> 0:11:49.199 for the vibration of one particle to come into contact 0:11:49.240 --> 0:11:53.000 and affect another particle. So sound can't travel. Sound travels 0:11:53.000 --> 0:11:56.920 through the propagation of vibrational waves. And if your stuff 0:11:57.000 --> 0:11:59.320 isn't in contact with each other, there's no way for 0:11:59.400 --> 0:12:02.520 them to have that wave propagate. So there has to 0:12:02.559 --> 0:12:07.080 be some sort of medium like air or solid surfaces 0:12:07.200 --> 0:12:11.720 or something in order for sound travel. Well, if that's 0:12:11.760 --> 0:12:15.200 the case, said the folks of the time, then stuff 0:12:15.240 --> 0:12:18.840 like light must need some sort of medium to travel through, right, 0:12:18.920 --> 0:12:21.000 I mean sound has to have something Light must have 0:12:21.120 --> 0:12:25.079 something too. Light can definitely travel through space. I mean, 0:12:25.120 --> 0:12:27.600 that's how we can see anything, because light from the 0:12:27.640 --> 0:12:31.240 Sun travels through space to hit the Earth. So the 0:12:31.320 --> 0:12:34.000 light has to be moving through some sort of medium 0:12:34.000 --> 0:12:39.120 we cannot observe directly. This hypothetical medium was the aforementioned 0:12:39.280 --> 0:12:44.679 luminiferous ether. But assuming this ether existed at all, it 0:12:44.720 --> 0:12:47.920 had to be pretty darn special because we can't feel it, 0:12:48.280 --> 0:12:52.520 we can't detect it. It creates no observable effects. So 0:12:52.640 --> 0:12:55.600 if it were real, it had to be unlike pretty 0:12:55.679 --> 0:12:59.520 much anything else we had discovered up to that point. Now, 0:12:59.800 --> 0:13:04.079 let's assume that the universe is filled with this ether stuff. 0:13:04.440 --> 0:13:08.080 The question rises, how the heck does the ether interact 0:13:08.120 --> 0:13:10.480 with all the physical stuff that's in the universe, the 0:13:10.520 --> 0:13:15.840 actual matter and also energy. After all the bodies in 0:13:15.960 --> 0:13:19.760 space like stars, planets, moons, and all that other stuff, 0:13:20.040 --> 0:13:23.680 all of that is moving, none of it is standing still, 0:13:23.880 --> 0:13:27.480 and if it is moving, it would presumably disturb this 0:13:27.760 --> 0:13:31.599 ether medium, right. I mean, if you move your hand 0:13:31.600 --> 0:13:34.439 through a pool of water, you are disturbing that water. 0:13:34.520 --> 0:13:37.600 You're making currents and eddies. So it was thought that 0:13:37.720 --> 0:13:41.040 the motion of all these elements in space would disturb 0:13:41.160 --> 0:13:44.640 the ether in some way, and hypothetically there would be 0:13:44.720 --> 0:13:48.800 some sort of ether wind. But if there were a wind, 0:13:49.320 --> 0:13:53.000 then presumably the speed of light would be affected depending 0:13:53.080 --> 0:13:57.160 upon the wind's direction in relation to the lights direction. 0:13:57.480 --> 0:14:00.440 So think of a really windy day in the real world. 0:14:00.800 --> 0:14:04.400 If you're walking against a very very tough wind, like 0:14:04.440 --> 0:14:07.320 a gale force wind, you have to power through it 0:14:07.360 --> 0:14:10.880 to keep moving forward. Now, if you're walking with the wind, 0:14:11.240 --> 0:14:13.120 like the wind is to your back and pushing you, 0:14:13.440 --> 0:14:16.160 then you get a big boost. Well, the same thing 0:14:16.280 --> 0:14:20.240 should be happening with light if ether wind were real, 0:14:20.880 --> 0:14:24.320 and so Michelson and Morley devised a gadget that would 0:14:24.360 --> 0:14:29.160 split light into two beams, directing those beams down different paths, 0:14:29.440 --> 0:14:32.760 using mirrors in different directions, and seeing if those two 0:14:32.840 --> 0:14:36.080 beams of light would hit an eyepiece at different times. 0:14:36.120 --> 0:14:40.160 The thought being well, one of these directions would theoretically 0:14:40.240 --> 0:14:43.080 be in the same direction as the ether wind, and 0:14:43.160 --> 0:14:45.960 one would be at a cross direction of ether wind. 0:14:46.240 --> 0:14:48.160 So we should see a difference in the amount of 0:14:48.200 --> 0:14:51.440 time it takes for the light from this one source 0:14:51.680 --> 0:14:54.800 that's been split into two to arrive at an eyepiece. 0:14:55.720 --> 0:15:00.520 But that's not what they found. They observed no such effect. 0:15:00.640 --> 0:15:03.040 So if there were such a thing as ether, the 0:15:03.080 --> 0:15:06.520 stuff wasn't giving either a boost or a drag on 0:15:06.720 --> 0:15:09.800 light itself. No matter what. The light was traveling at 0:15:09.800 --> 0:15:12.840 a constant speed, which turned out to be approximately one 0:15:13.320 --> 0:15:16.320 eighty six thousand miles per second or around three hundred 0:15:16.360 --> 0:15:20.160 thousand kilometers per second. Now that flew in the face 0:15:20.280 --> 0:15:24.280 of classic Newtonian physics clearly. With the example of the 0:15:24.280 --> 0:15:26.720 ping pong ball and the train, the ping pong ball 0:15:26.840 --> 0:15:29.720 has to be traveling faster than the train it's on. 0:15:29.800 --> 0:15:31.840 I mean, that just makes sense. If you were standing 0:15:31.960 --> 0:15:34.280 on the top of the very front of the train 0:15:34.760 --> 0:15:37.440 and then you throw the ping pong ball, and we 0:15:37.480 --> 0:15:41.000 ignore stuff like wind resistance, the ping pong ball would 0:15:41.040 --> 0:15:43.280 land ahead of the train, so it has to be 0:15:43.400 --> 0:15:46.680 going faster. So what the heck was so special about 0:15:46.760 --> 0:15:49.560 light and what was going on? Well, this was one 0:15:49.560 --> 0:15:52.640 of the great mysteries that Albert Einstein said his mind 0:15:52.680 --> 0:15:55.640 to unraveling, and it formed the basis of one of 0:15:55.680 --> 0:15:58.800 his great theories of relativity, and this would be the 0:15:58.800 --> 0:16:02.440 theory of special relativity, which poses that the laws of 0:16:02.480 --> 0:16:06.080 physics are in the same in all inertial frames of references, 0:16:06.680 --> 0:16:08.360 and that means the speed of light will be the 0:16:08.400 --> 0:16:12.800 same for all observers, regardless of their relative perspectives. It 0:16:12.840 --> 0:16:16.200 doesn't matter the context. The speed of light is the 0:16:16.240 --> 0:16:19.440 speed of light. Now, there's an implication to this theory 0:16:19.840 --> 0:16:22.920 that really got people scratching their heads. If the speed 0:16:22.960 --> 0:16:26.640 of light is absolutely constant, that would mean that stuff 0:16:26.720 --> 0:16:30.920 like distance and time are not. And as a heck 0:16:30.920 --> 0:16:33.920 of a brain teaser, when we come back, we'll explore 0:16:33.960 --> 0:16:44.480 this more. Let's imagine that you live half a mile 0:16:44.600 --> 0:16:48.520 away from a lovely park, and it's a half mile away. 0:16:48.520 --> 0:16:51.040 In the morning, it's a half mile away. At night, 0:16:51.680 --> 0:16:54.160 it's a half mile away. On a Tuesday, it's a 0:16:54.160 --> 0:16:58.080 half mile away on a Saturday. Half a mile is 0:16:58.160 --> 0:17:02.440 half a mile, right, It's a reliable constant in our lives. 0:17:02.520 --> 0:17:05.680 If it weren't, we could never give directions to anywhere 0:17:05.760 --> 0:17:09.080 because all the measurements and landmarks would change all the time, 0:17:09.320 --> 0:17:12.520 and our world wouldn't make sense the way it does 0:17:12.560 --> 0:17:16.600 to us now. So in our individual experiences, in our 0:17:16.680 --> 0:17:20.879 day to day lives, stuff like distance seems pretty darn 0:17:20.960 --> 0:17:26.000 reliable and fixed. So how dare Einstein come along with 0:17:26.040 --> 0:17:29.840 this theory of special relativity in nineteen o five and say, well, yeah, 0:17:29.880 --> 0:17:34.000 but see, the speed of light is really the true constant, 0:17:34.359 --> 0:17:38.000 and for that to work, time and distance or space, 0:17:38.080 --> 0:17:43.679 in other words, must be somewhat mutable. Einstein positive that 0:17:43.760 --> 0:17:47.840 there is no absolute frame of reference in our universe, 0:17:48.040 --> 0:17:51.119 which means there is no place in the universe that 0:17:51.280 --> 0:17:56.000 is totally stationary. Everything is moving, which means all motion 0:17:56.200 --> 0:17:59.359 is relative. You can't really talk about moving except in 0:17:59.400 --> 0:18:03.400 reference to some other moving thing. So even as we 0:18:03.600 --> 0:18:07.280 sit still and try to meditate, we do so on 0:18:07.359 --> 0:18:11.400 a planet that is hurtling through space. We are in motion. 0:18:11.600 --> 0:18:14.760 We're all moving through space and time, and we all 0:18:14.840 --> 0:18:19.000 have a frame of reference, and each frame of reference 0:18:19.359 --> 0:18:22.800 is just as legitimate as every other frame of reference. 0:18:23.520 --> 0:18:27.000 Or I guess you could say, if everybody's super nobody is. 0:18:27.720 --> 0:18:30.960 I guess I've watched The Incredibles too many times. Well, anyway, 0:18:31.000 --> 0:18:34.800 this particular nineteen o five theory is called special relativity 0:18:35.000 --> 0:18:40.320 because Einstein's explanation only covered special cases, that being when 0:18:40.440 --> 0:18:44.040 two inertial frames are in constant motion with regard to 0:18:44.080 --> 0:18:47.159 one another, and there can be no acceleration, so the 0:18:47.200 --> 0:18:49.359 motion had to be in a straight line at a 0:18:49.400 --> 0:18:53.160 constant speed. A change in direction or speed would be 0:18:53.200 --> 0:18:56.480 an acceleration, and to cover those instances we would have 0:18:56.520 --> 0:18:59.080 to wait a decade for Einstein to work out his 0:18:59.160 --> 0:19:02.760 theory of general relativity. We'll get to that, but we've 0:19:02.800 --> 0:19:05.800 got a lot more to say about special relativity. So 0:19:05.840 --> 0:19:08.840 Einstein was taking a different approach to the results of 0:19:08.880 --> 0:19:12.280 the experiments done by people like Michelson and Morley. The 0:19:12.359 --> 0:19:16.520 scientific world at large was essentially saying, well, this can't 0:19:16.520 --> 0:19:19.159 be right. These results can't be right. There must be 0:19:19.200 --> 0:19:22.800 something wrong with the experiment or the equipment, because we're 0:19:22.840 --> 0:19:26.440 sure this theory is correct and that ether is there. 0:19:27.000 --> 0:19:29.879 Einstein was taking a totally different perspective. He was saying, 0:19:30.520 --> 0:19:34.800 if we assume the experiments are producing accurate results, then 0:19:34.840 --> 0:19:38.200 it stands to reason that the prevailing theory is flawed 0:19:38.520 --> 0:19:41.080 and we have to figure out what the real explanation is. 0:19:41.480 --> 0:19:43.800 And this is one of those important points in science. 0:19:44.320 --> 0:19:47.920 It's that if your results in your experiment don't meet 0:19:47.960 --> 0:19:53.160 your hypothesis, it's very possible that your hypothesis is wrong. 0:19:53.359 --> 0:19:56.399 Now you need to do multiple experiments to find out 0:19:56.920 --> 0:19:59.560 and to test your equipment make sure there's not any 0:19:59.680 --> 0:20:02.760 error is there that could be causing the issues. But 0:20:02.840 --> 0:20:05.840 it does mean that you need to re examine that hypothesis, 0:20:06.400 --> 0:20:10.520 and at this time the scientific community wasn't really doing that, 0:20:11.160 --> 0:20:15.639 so Einstein did away with the ether. His explanation suggested 0:20:15.680 --> 0:20:19.960 that our observable universe has four dimensions, not that there 0:20:19.960 --> 0:20:23.160 can only be four dimensions, but rather there are four 0:20:23.200 --> 0:20:30.800 dimensions we can detect and observe, and these would be up, down, left, right, forward, backward, 0:20:31.200 --> 0:20:36.000 and then the fourth dimension, which is time. Collectively, those 0:20:36.000 --> 0:20:39.720 three dimensions are space. The fourth dimension is time, and 0:20:39.760 --> 0:20:44.719 we get the space time continuum, this intrinsic relationship between 0:20:44.760 --> 0:20:48.680 space and time or spacetime continuum, which also gives us 0:20:49.560 --> 0:20:51.840 dozens of Star Trek episodes that would use it as 0:20:51.880 --> 0:20:55.600 shorthand for things are about to get really weird. Einstein 0:20:55.680 --> 0:20:59.200 posited that the speed of light is measured as constant 0:20:59.240 --> 0:21:02.440 in all freems of reference. And let's think for a second. 0:21:02.680 --> 0:21:06.359 What we mean by speed. Speed is a description of 0:21:06.400 --> 0:21:10.119 how much distance can be covered per unit of time. 0:21:10.600 --> 0:21:13.399 So a speed of one hundred miles per hour means 0:21:13.440 --> 0:21:16.120 that in one hour's time, we will cover a distance 0:21:16.200 --> 0:21:19.760 of one hundred miles. That's very obvious. But if the 0:21:19.800 --> 0:21:23.400 speed of light is constant for all frames of reference, 0:21:23.480 --> 0:21:27.080 regardless of how those frames are moving relative to each other, 0:21:27.720 --> 0:21:31.480 that must mean something about space and or time is 0:21:31.520 --> 0:21:35.480 a little wonky. And let's think about our train experiment again. 0:21:36.040 --> 0:21:38.679 If you are aboard a train moving at a smooth 0:21:38.720 --> 0:21:41.280 one miles per hour in a straight line, and you 0:21:41.359 --> 0:21:44.320 toss a ping pong ball straight up in the air, well, 0:21:44.359 --> 0:21:46.800 it's gonna go straight up and come right back down 0:21:46.840 --> 0:21:49.760 to your hand in a nice vertical line. From an 0:21:49.760 --> 0:21:52.760 outside observer who isn't on the train, it would look 0:21:52.760 --> 0:21:55.040 a little differently. You would throw the ball up at 0:21:55.119 --> 0:21:58.320 one point relative to this outside observer, and the ball 0:21:58.320 --> 0:22:01.359 would appear to move not just vertically, but horizontally before 0:22:01.400 --> 0:22:04.560 coming back down. Now, if we repeat this experiment but 0:22:04.640 --> 0:22:08.280 we use light, we really see how it gets confusing. Okay, 0:22:08.320 --> 0:22:11.919 so now you're on a train, but it's going really fast, 0:22:12.200 --> 0:22:15.399 like let's say half the speed of light, but the 0:22:15.480 --> 0:22:18.720 speed and direction are constant. So you're on this train. 0:22:18.800 --> 0:22:22.560 You don't feel any acceleration forces because you're moving at 0:22:22.560 --> 0:22:26.400 a constant speed and a constant direction, so your velocity 0:22:26.440 --> 0:22:29.400 remains the same. In fact, if there were no windows 0:22:29.440 --> 0:22:31.320 on the train, you wouldn't even be able to tell 0:22:31.359 --> 0:22:33.840 that the train was moving at all. So let's say 0:22:33.840 --> 0:22:36.520 you've got a laser pointer and you've got a mirror 0:22:36.520 --> 0:22:39.480 on the ceiling of the train and a photon detector 0:22:39.600 --> 0:22:42.000 on the floor of the train. You shoot the laser 0:22:42.160 --> 0:22:45.240 up at the mirror, it reflects off the mirror, and 0:22:45.280 --> 0:22:47.720 then it comes back down and hits the detector on 0:22:47.800 --> 0:22:50.800 the floor, and it registers how long it took the 0:22:50.880 --> 0:22:53.920 light to travel from your laser pointer to hit the detector, 0:22:54.280 --> 0:22:57.120 and to you, the laser makes a vertical line. All 0:22:57.160 --> 0:22:59.760 that makes sense, right, you can imagine that, But for 0:23:00.000 --> 0:23:02.760 are outside observer who's not on the train, it would 0:23:02.760 --> 0:23:05.439 appear as though the laser were actually traveling at a 0:23:05.520 --> 0:23:08.880 diagonal up to that mirror and then a diagonal back 0:23:09.000 --> 0:23:12.960 down towards the detector. So for one observer, the one 0:23:13.040 --> 0:23:15.560 on the train, we have a straight line. It's vertical 0:23:15.720 --> 0:23:19.280 up down. For the second observer off the train, we 0:23:19.359 --> 0:23:21.720 have an angled path, sort of like how a billiard 0:23:21.720 --> 0:23:23.440 ball can hit the side of a pool table and 0:23:23.560 --> 0:23:27.199 bounce off at an angle. But this creates an apparent paradox. 0:23:27.680 --> 0:23:30.399 The path viewed by you on the train is a 0:23:30.440 --> 0:23:33.440 straight line, and by definition, that is the shortest distance 0:23:33.480 --> 0:23:36.760 between two points. The path observed by the person who 0:23:36.880 --> 0:23:39.639 is not on the train is an angled line, and 0:23:39.680 --> 0:23:42.439 by definition that has to be longer. The speed of 0:23:42.520 --> 0:23:46.159 light is constant in both cases, but the distance is 0:23:46.240 --> 0:23:49.960 different between the two points of reference, And because speed 0:23:50.080 --> 0:23:53.160 is distance divided by time, if the distance is different, 0:23:53.240 --> 0:23:57.000 the time must also be different between those two points 0:23:57.040 --> 0:24:01.919 of reference. Crazy This brings us to the concept of 0:24:02.000 --> 0:24:05.840