Speaker 1: Welcome to tex Stuff, a production from I Heart Radio.
Speaker 1: Hey there, and welcome to tech Stuff. I'm your host,
Speaker 1: Jonathan Strickland. I'm an executive producer with I Heart Radio
Speaker 1: and I love all things tech. And in our last episode,
Speaker 1: I explained how communications satellites send information via radio waves,
Speaker 1: which is why we talked about signals from such things
Speaker 1: in terms like hurts. The hurts unit refers to the
Speaker 1: number of repeated phenomena over the course of a second.
Speaker 1: So imagine that you're dribbling a basketball so that the
Speaker 1: ball goes from your hand to the ground back up
Speaker 1: to your hand once per second. Well, you could describe
Speaker 1: your dribbling as being one hurts in frequency one full
Speaker 1: cycle per second, up, down, up. Now, if you dribbled
Speaker 1: twice as fast, so that the all went up, down, up,
Speaker 1: two full times per second, then it would be two hurts. Well,
Speaker 1: we can describe lots of stuff with the unit hurts.
Speaker 1: We use it to describe sounds, in which case we're
Speaker 1: talking about the frequency at which stuff vibrates. Typical human
Speaker 1: hearing spans a range of frequencies that at the low
Speaker 1: end is that twenty hurts. That represents the lowest pitches
Speaker 1: of sounds. So you can think of those deep base notes.
Speaker 1: That's around the twenty hurts of area uh, and then
Speaker 1: it goes all the way up to twenty killer hurts
Speaker 1: or twenty thousand hurts. That represents the very highest pitches
Speaker 1: that people can typically here, and those frequencies correlate to
Speaker 1: how quickly stuff is vibrating back and forth. Now, when
Speaker 1: it comes to us hearing things, we usually mean that
Speaker 1: we're talking about the vibrations and fluctuation and air pressure,
Speaker 1: and those fluctuations and air pressure interact with our ear drums.
Speaker 1: But we can use hurts to talk about all sorts
Speaker 1: of stuff, including the pros sessor speed of a CPU.
Speaker 1: In that case, we're really talking about the number of
Speaker 1: clock cycles per second, So you get it. This is
Speaker 1: a description of the frequency of the number of times
Speaker 1: a certain thing happens, like within a second. And I
Speaker 1: also explained that we measure the rate at which we
Speaker 1: can send data using the term bits. A bit is
Speaker 1: a basic unit of digital information, and when we talk
Speaker 1: about computers, we're talking about bits in the form of
Speaker 1: a zero or a one binary information, just like your
Speaker 1: basic two way physical switch has two positions off or on.
Speaker 1: So if you hear a term like kill a bit,
Speaker 1: that means one thousand bits, and a megabit is one
Speaker 1: million bits, and a gigabit would be one billion bits. Likewise,
Speaker 1: megabits per second tells us how many million bits can
Speaker 1: move from one point to another per second over that connection.
Speaker 1: So if you've got a one hundred megabit per second connection,
Speaker 1: theoretically it would mean that up to one hundred million
Speaker 1: bits can transfer across that communication channel per second, though
Speaker 1: that's not how it works out most of the time,
Speaker 1: but that's a matter for a different episode. I didn't
Speaker 1: mention that this is different from something like megabytes. So
Speaker 1: a byte is a unit that consists of eight bits.
Speaker 1: And this gets confusing because we often describe stuff like
Speaker 1: file sizes in terms of bytes, but transfer speeds in
Speaker 1: terms of bits. So let's say that you do have
Speaker 1: that one hundred megabits per second download speed, and you
Speaker 1: want to download a one hundred megabyte file, Well, that
Speaker 1: means it's not going to take one second. It's gonna
Speaker 1: take eight seconds to download the file because a megabyte
Speaker 1: is eight times larger than a megabit. And actually even
Speaker 1: that is a little bit misleading because in computer memory terms,
Speaker 1: we typically look at units of memory based on powers
Speaker 1: of two rather than powers of ten. So instead of
Speaker 1: a killer bite being one thousand bites, it's actually one
Speaker 1: thousand twenty four bites. And there's no standardization in the
Speaker 1: tech industry. So sometimes people will say a kill a
Speaker 1: bite and they mean one thousand bites. Sometimes they'll say
Speaker 1: kill a bite and they mean one thousand, twenty four bites,
Speaker 1: And you will want to tear your hair out and
Speaker 1: then you'll look like I do, I'm bald if you
Speaker 1: didn't know. But this episode isn't about the peculiarities of
Speaker 1: our naming conventions and the computer information age. Instead, I
Speaker 1: wanted to tackle something else that affects everything really, but
Speaker 1: in particular, we really had to suss it out in
Speaker 1: order to make certain types of satellites work properly. And
Speaker 1: this is the concept of relativity. So in this episode
Speaker 1: we're really going to learn why an understanding of relativity
Speaker 1: is important if we want our certain satellite technologies to work,
Speaker 1: and it serves as a great reminder that technology is
Speaker 1: only really possible through an understanding of science. You can
Speaker 1: think of tech as the physical manifestation of our understanding
Speaker 1: of scientific principles, and that means if we were wrong
Speaker 1: in our understanding of science, the technology shouldn't really work.
Speaker 1: So in a way, you can think of technology that
Speaker 1: works as evidence that the scientific method is a darned
Speaker 1: good formula. Since we're talking about relativity, it means we're
Speaker 1: gonna be talking about a real Einstein today. His name
Speaker 1: was Einstein, which is convenient. But before we get to Einstein,
Speaker 1: we have Galileo Galileo, Galileo Figaro. Wait no, I'm sorry, Wait,
Speaker 1: that's Bohemian Rhapsody. I meant Galileo galile This. Galileo made
Speaker 1: an observation that if you've got two observers moving at
Speaker 1: a constant speed and direction, so they're moving at the
Speaker 1: same velocity, they will get the same results for any
Speaker 1: experiment that involves moving stuff around a mechanical experiment. This
Speaker 1: is easier to understand if we use an example, and
Speaker 1: I like one that my colleague Robert Lamb used when
Speaker 1: he wrote about relativity for how Stuff Works dot Com
Speaker 1: back in the day. He used an example of a
Speaker 1: train and a scientific ping pong ball. All right, so
Speaker 1: imagine you've got a scientist who's standing in the middle
Speaker 1: of an aisle on a moving train, and the train
Speaker 1: is moving at a steady speed in a straight line,
Speaker 1: so there are no active forces of acceleration going on here. Remember,
Speaker 1: acceleration describes a force that involves a change in velocity,
Speaker 1: so that other means a change in direction or a
Speaker 1: change in speed or both. But in this case constant
Speaker 1: speed constant direction. Robert used nice round numbers in his examples,
Speaker 1: so he suggested that the train is moving at one
Speaker 1: miles per hour. Well it's not round. If we go
Speaker 1: to the metric system, that would be one sixty one
Speaker 1: kilometers per hour. If the train stays stead to the scientist,
Speaker 1: it will feel as if that scientist is actually just
Speaker 1: standing still, just anywhere, and we're conveniently ignoring an emotion
Speaker 1: that would happen due to irregularities with the trains wheels
Speaker 1: or the train tracks or anything like that. And if
Speaker 1: this is hard for you to imagine, just think about
Speaker 1: how you feel when you're standing still, or sitting still
Speaker 1: or laying down Here on Earth. We know the Earth
Speaker 1: is moving through space. It is a body in motion,
Speaker 1: but when we are still relative to the Earth itself,
Speaker 1: we don't feel that motion. Assuming there's not some other
Speaker 1: weird event going on, like an earthquake, which is something separate,
Speaker 1: but back to our hypothetical train, the scientist tosses the
Speaker 1: ping pong ball down the aisle. Now, from the scientist's perspective,
Speaker 1: this ping pong ball will travel at whatever speed they
Speaker 1: threw it at. Robert actually suggests a relatively gentle toss
Speaker 1: of five miles per hour or eight kilometers per hour.
Speaker 1: The ping pong ball would bounce down the aisle, just
Speaker 1: as it would if the scientists were to toss the
Speaker 1: ball on a train that isn't moving at all, or
Speaker 1: on just flat ground. However, let's say we have a
Speaker 1: second observer who's not on the train. They're standing off
Speaker 1: to the side and they can see through the train.
Speaker 1: To this person, it will appear as if the ping
Speaker 1: pong ball is moving very fast. Indeed, relative to this
Speaker 1: stationary observer, the ping pong ball will appear to move
Speaker 1: at the speed at which it was thrown in addition
Speaker 1: to the speed of the train itself. So if we
Speaker 1: take the two figures, we get one hundred five miles
Speaker 1: per hour or a hundred sixty nine kilometers per hour.
Speaker 1: This is called a Galilean transformation. Alternatively, if the scientists
Speaker 1: were throwing the ping pong ball in the opposite direction
Speaker 1: of the trains travel, so they're facing towards the back
Speaker 1: of the train, it would appear to this second observer
Speaker 1: that the ping pong ball was moving at a slightly
Speaker 1: slower speed than the overall train was, whereas to the
Speaker 1: scientist on board, the ping pong ball would still be
Speaker 1: traveling at that five mile per hour speed. So this
Speaker 1: is where the term relativity comes into play. The effects
Speaker 1: observed are relative to the perspective of the observer. It's
Speaker 1: all based on the reference frame of that observer. If
Speaker 1: you're on the train, then you're just looking at a
Speaker 1: ping pong ball bouncing at a relatively slow speed down
Speaker 1: the aisle. If you're not on the train, the ping
Speaker 1: pong ball is moving quite fast, so it's all relative.
Speaker 1: Isaac Newton would follow along and say, yeah, mate, this
Speaker 1: all tracks. I don't know why I talked like that.
Speaker 1: In his Laws of Motion, Newton stated that these laws
Speaker 1: emotions should hold in an inertial frame as well as
Speaker 1: a reference frame that was moving at a constant velocity
Speaker 1: relative to the inertial frame and inertial frame by the
Speaker 1: way is just a frame of reference in which there
Speaker 1: are zero net forces acting upon it, so that there
Speaker 1: are no forces of acceleration in play. So in our example,
Speaker 1: the train that we talked about, that would be our
Speaker 1: inertial frame. All of this is fairly intuitive, but then
Speaker 1: we get to something really tricky. Einstein would establish that
Speaker 1: the speed of light in a vacuum is the fastest
Speaker 1: speed in our universe. Nothing can go faster than that.
Speaker 1: But hey, what if you're on the train that's traveling
Speaker 1: one hour and you're facing forward, you're facing the direction
Speaker 1: of travel, and then you have a flashlight and you
Speaker 1: turn on the flashlight. Well, doesn't that mean you should
Speaker 1: perform a Galilean transformation on this and say the light
Speaker 1: from that flashlight in your hands is actually traveling at
Speaker 1: the normal speed of light on board the train. But
Speaker 1: also get that boost of the trains travel, so it
Speaker 1: should be the speed of light plus one miles per hour.
Speaker 1: Doesn't that make sense? Well, according to actual experiments performed
Speaker 1: before Einstein would come around to explain things, the answer
Speaker 1: was Nope, doesn't look like it works that way. Scientists
Speaker 1: Edward Morley and Albert A. Michelson created an experiment to
Speaker 1: measure the speed of light back in and actually they
Speaker 1: were looking for something else. They were looking for evidence
Speaker 1: of a hypothetical substance called luminiferous ether. Say what, all right,
Speaker 1: We'll stick with me, because in a way this does
Speaker 1: make sense. Okay, So on Earth we see waves traveling
Speaker 1: through a medium, right, Like if you look out in
Speaker 1: the ocean, you can see actual waves in the water,
Speaker 1: and the water is a physical medium through which these
Speaker 1: waves travel. Sound can't travel in space because space is
Speaker 1: effectively a vacuum. The particles that are in space are
Speaker 1: so far apart from one another that there's no way
Speaker 1: for the vibration of one particle to come into contact
Speaker 1: and affect another particle. So sound can't travel. Sound travels
Speaker 1: through the propagation of vibrational waves. And if your stuff
Speaker 1: isn't in contact with each other, there's no way for
Speaker 1: them to have that wave propagate. So there has to
Speaker 1: be some sort of medium like air or solid surfaces
Speaker 1: or something in order for sound travel. Well, if that's
Speaker 1: the case, said the folks of the time, then stuff
Speaker 1: like light must need some sort of medium to travel through, right,
Speaker 1: I mean sound has to have something Light must have
Speaker 1: something too. Light can definitely travel through space. I mean,
Speaker 1: that's how we can see anything, because light from the
Speaker 1: Sun travels through space to hit the Earth. So the
Speaker 1: light has to be moving through some sort of medium
Speaker 1: we cannot observe directly. This hypothetical medium was the aforementioned
Speaker 1: luminiferous ether. But assuming this ether existed at all, it
Speaker 1: had to be pretty darn special because we can't feel it,
Speaker 1: we can't detect it. It creates no observable effects. So
Speaker 1: if it were real, it had to be unlike pretty
Speaker 1: much anything else we had discovered up to that point. Now,
Speaker 1: let's assume that the universe is filled with this ether stuff.
Speaker 1: The question rises, how the heck does the ether interact
Speaker 1: with all the physical stuff that's in the universe, the
Speaker 1: actual matter and also energy. After all the bodies in
Speaker 1: space like stars, planets, moons, and all that other stuff,
Speaker 1: all of that is moving, none of it is standing still,
Speaker 1: and if it is moving, it would presumably disturb this
Speaker 1: ether medium, right. I mean, if you move your hand
Speaker 1: through a pool of water, you are disturbing that water.
Speaker 1: You're making currents and eddies. So it was thought that
Speaker 1: the motion of all these elements in space would disturb
Speaker 1: the ether in some way, and hypothetically there would be
Speaker 1: some sort of ether wind. But if there were a wind,
Speaker 1: then presumably the speed of light would be affected depending
Speaker 1: upon the wind's direction in relation to the lights direction.
Speaker 1: So think of a really windy day in the real world.
Speaker 1: If you're walking against a very very tough wind, like
Speaker 1: a gale force wind, you have to power through it
Speaker 1: to keep moving forward. Now, if you're walking with the wind,
Speaker 1: like the wind is to your back and pushing you,
Speaker 1: then you get a big boost. Well, the same thing
Speaker 1: should be happening with light if ether wind were real,
Speaker 1: and so Michelson and Morley devised a gadget that would
Speaker 1: split light into two beams, directing those beams down different paths,
Speaker 1: using mirrors in different directions, and seeing if those two
Speaker 1: beams of light would hit an eyepiece at different times.
Speaker 1: The thought being well, one of these directions would theoretically
Speaker 1: be in the same direction as the ether wind, and
Speaker 1: one would be at a cross direction of ether wind.
Speaker 1: So we should see a difference in the amount of
Speaker 1: time it takes for the light from this one source
Speaker 1: that's been split into two to arrive at an eyepiece.
Speaker 1: But that's not what they found. They observed no such effect.
Speaker 1: So if there were such a thing as ether, the
Speaker 1: stuff wasn't giving either a boost or a drag on
Speaker 1: light itself. No matter what. The light was traveling at
Speaker 1: a constant speed, which turned out to be approximately one
Speaker 1: eighty six thousand miles per second or around three hundred
Speaker 1: thousand kilometers per second. Now that flew in the face
Speaker 1: of classic Newtonian physics clearly. With the example of the
Speaker 1: ping pong ball and the train, the ping pong ball
Speaker 1: has to be traveling faster than the train it's on.
Speaker 1: I mean, that just makes sense. If you were standing
Speaker 1: on the top of the very front of the train
Speaker 1: and then you throw the ping pong ball, and we
Speaker 1: ignore stuff like wind resistance, the ping pong ball would
Speaker 1: land ahead of the train, so it has to be
Speaker 1: going faster. So what the heck was so special about
Speaker 1: light and what was going on? Well, this was one
Speaker 1: of the great mysteries that Albert Einstein said his mind
Speaker 1: to unraveling, and it formed the basis of one of
Speaker 1: his great theories of relativity, and this would be the
Speaker 1: theory of special relativity, which poses that the laws of
Speaker 1: physics are in the same in all inertial frames of references,
Speaker 1: and that means the speed of light will be the
Speaker 1: same for all observers, regardless of their relative perspectives. It
Speaker 1: doesn't matter the context. The speed of light is the
Speaker 1: speed of light. Now, there's an implication to this theory
Speaker 1: that really got people scratching their heads. If the speed
Speaker 1: of light is absolutely constant, that would mean that stuff
Speaker 1: like distance and time are not. And as a heck
Speaker 1: of a brain teaser, when we come back, we'll explore
Speaker 1: this more. Let's imagine that you live half a mile
Speaker 1: away from a lovely park, and it's a half mile away.
Speaker 1: In the morning, it's a half mile away. At night,
Speaker 1: it's a half mile away. On a Tuesday, it's a
Speaker 1: half mile away on a Saturday. Half a mile is
Speaker 1: half a mile, right, It's a reliable constant in our lives.
Speaker 1: If it weren't, we could never give directions to anywhere
Speaker 1: because all the measurements and landmarks would change all the time,
Speaker 1: and our world wouldn't make sense the way it does
Speaker 1: to us now. So in our individual experiences, in our
Speaker 1: day to day lives, stuff like distance seems pretty darn
Speaker 1: reliable and fixed. So how dare Einstein come along with
Speaker 1: this theory of special relativity in nineteen o five and say, well, yeah,
Speaker 1: but see, the speed of light is really the true constant,
Speaker 1: and for that to work, time and distance or space,
Speaker 1: in other words, must be somewhat mutable. Einstein positive that
Speaker 1: there is no absolute frame of reference in our universe,
Speaker 1: which means there is no place in the universe that
Speaker 1: is totally stationary. Everything is moving, which means all motion
Speaker 1: is relative. You can't really talk about moving except in
Speaker 1: reference to some other moving thing. So even as we
Speaker 1: sit still and try to meditate, we do so on
Speaker 1: a planet that is hurtling through space. We are in motion.
Speaker 1: We're all moving through space and time, and we all
Speaker 1: have a frame of reference, and each frame of reference
Speaker 1: is just as legitimate as every other frame of reference.
Speaker 1: Or I guess you could say, if everybody's super nobody is.
Speaker 1: I guess I've watched The Incredibles too many times. Well, anyway,
Speaker 1: this particular nineteen o five theory is called special relativity
Speaker 1: because Einstein's explanation only covered special cases, that being when
Speaker 1: two inertial frames are in constant motion with regard to
Speaker 1: one another, and there can be no acceleration, so the
Speaker 1: motion had to be in a straight line at a
Speaker 1: constant speed. A change in direction or speed would be
Speaker 1: an acceleration, and to cover those instances we would have
Speaker 1: to wait a decade for Einstein to work out his
Speaker 1: theory of general relativity. We'll get to that, but we've
Speaker 1: got a lot more to say about special relativity. So
Speaker 1: Einstein was taking a different approach to the results of
Speaker 1: the experiments done by people like Michelson and Morley. The
Speaker 1: scientific world at large was essentially saying, well, this can't
Speaker 1: be right. These results can't be right. There must be
Speaker 1: something wrong with the experiment or the equipment, because we're
Speaker 1: sure this theory is correct and that ether is there.
Speaker 1: Einstein was taking a totally different perspective. He was saying,
Speaker 1: if we assume the experiments are producing accurate results, then
Speaker 1: it stands to reason that the prevailing theory is flawed
Speaker 1: and we have to figure out what the real explanation is.
Speaker 1: And this is one of those important points in science.
Speaker 1: It's that if your results in your experiment don't meet
Speaker 1: your hypothesis, it's very possible that your hypothesis is wrong.
Speaker 1: Now you need to do multiple experiments to find out
Speaker 1: and to test your equipment make sure there's not any
Speaker 1: error is there that could be causing the issues. But
Speaker 1: it does mean that you need to re examine that hypothesis,
Speaker 1: and at this time the scientific community wasn't really doing that,
Speaker 1: so Einstein did away with the ether. His explanation suggested
Speaker 1: that our observable universe has four dimensions, not that there
Speaker 1: can only be four dimensions, but rather there are four
Speaker 1: dimensions we can detect and observe, and these would be up, down, left, right, forward, backward,
Speaker 1: and then the fourth dimension, which is time. Collectively, those
Speaker 1: three dimensions are space. The fourth dimension is time, and
Speaker 1: we get the space time continuum, this intrinsic relationship between
Speaker 1: space and time or spacetime continuum, which also gives us
Speaker 1: dozens of Star Trek episodes that would use it as
Speaker 1: shorthand for things are about to get really weird. Einstein
Speaker 1: posited that the speed of light is measured as constant
Speaker 1: in all freems of reference. And let's think for a second.
Speaker 1: What we mean by speed. Speed is a description of
Speaker 1: how much distance can be covered per unit of time.
Speaker 1: So a speed of one hundred miles per hour means
Speaker 1: that in one hour's time, we will cover a distance
Speaker 1: of one hundred miles. That's very obvious. But if the
Speaker 1: speed of light is constant for all frames of reference,
Speaker 1: regardless of how those frames are moving relative to each other,
Speaker 1: that must mean something about space and or time is
Speaker 1: a little wonky. And let's think about our train experiment again.
Speaker 1: If you are aboard a train moving at a smooth
Speaker 1: one miles per hour in a straight line, and you
Speaker 1: toss a ping pong ball straight up in the air, well,
Speaker 1: it's gonna go straight up and come right back down
Speaker 1: to your hand in a nice vertical line. From an
Speaker 1: outside observer who isn't on the train, it would look
Speaker 1: a little differently. You would throw the ball up at
Speaker 1: one point relative to this outside observer, and the ball
Speaker 1: would appear to move not just vertically, but horizontally before
Speaker 1: coming back down. Now, if we repeat this experiment but
Speaker 1: we use light, we really see how it gets confusing. Okay,
Speaker 1: so now you're on a train, but it's going really fast,
Speaker 1: like let's say half the speed of light, but the
Speaker 1: speed and direction are constant. So you're on this train.
Speaker 1: You don't feel any acceleration forces because you're moving at
Speaker 1: a constant speed and a constant direction, so your velocity
Speaker 1: remains the same. In fact, if there were no windows
Speaker 1: on the train, you wouldn't even be able to tell
Speaker 1: that the train was moving at all. So let's say
Speaker 1: you've got a laser pointer and you've got a mirror
Speaker 1: on the ceiling of the train and a photon detector
Speaker 1: on the floor of the train. You shoot the laser
Speaker 1: up at the mirror, it reflects off the mirror, and
Speaker 1: then it comes back down and hits the detector on
Speaker 1: the floor, and it registers how long it took the
Speaker 1: light to travel from your laser pointer to hit the detector,
Speaker 1: and to you, the laser makes a vertical line. All
Speaker 1: that makes sense, right, you can imagine that, But for
Speaker 1: are outside observer who's not on the train, it would
Speaker 1: appear as though the laser were actually traveling at a
Speaker 1: diagonal up to that mirror and then a diagonal back
Speaker 1: down towards the detector. So for one observer, the one
Speaker 1: on the train, we have a straight line. It's vertical
Speaker 1: up down. For the second observer off the train, we
Speaker 1: have an angled path, sort of like how a billiard
Speaker 1: ball can hit the side of a pool table and
Speaker 1: bounce off at an angle. But this creates an apparent paradox.
Speaker 1: The path viewed by you on the train is a
Speaker 1: straight line, and by definition, that is the shortest distance
Speaker 1: between two points. The path observed by the person who
Speaker 1: is not on the train is an angled line, and
Speaker 1: by definition that has to be longer. The speed of
Speaker 1: light is constant in both cases, but the distance is
Speaker 1: different between the two points of reference, And because speed
Speaker 1: is distance divided by time, if the distance is different,
Speaker 1: the time must also be different between those two points
Speaker 1: of reference. Crazy This brings us to the concept of
Speaker 1: time dilation. It also, by the way, can affect distance.
Speaker 1: The faster and object gets, the more squished it gets.
Speaker 1: So if you had this train and you were to
Speaker 1: get up to near the speed of light, the train
Speaker 1: to an outside observer would appear to be shorter than
Speaker 1: it normally would be. To anyone inside the train, the
Speaker 1: dimensions would remain exactly the same. You would not suddenly
Speaker 1: see a shorter train. It wouldn't be like you were
Speaker 1: in that compressor scene in Star Wars. The train would
Speaker 1: appear to be normal. Only from an outside observer who
Speaker 1: is not traveling at that speed would it appear that
Speaker 1: the train itself was getting squished shorter. Likewise, the faster
Speaker 1: something goes with respect to some other point of reference
Speaker 1: that's important, the more quickly time appears to pass for
Speaker 1: those at the other point of reference, or alternatively, the
Speaker 1: more slowly time seems to pass for the fast moving
Speaker 1: thing from the frame of reference of the person who's
Speaker 1: not moving fast. This gets really clunky. I know, it
Speaker 1: gets confusing. So let's talk about space travel some more,
Speaker 1: because examples actually make this way easier to explain. All right,
Speaker 1: So let's say you've built a spaceship and this spaceship
Speaker 1: can go wicked fast, like eight percent of the speed
Speaker 1: of light, and you're gonna go on a year long
Speaker 1: jaunt out in space, and your best friend is hanging
Speaker 1: back on Earth. Now we now have our two frames
Speaker 1: of reference. We have the spaceship and then we have
Speaker 1: the person on Earth. So let's ignore accelerative forces for
Speaker 1: the moment, because we're gonna have to just focus on
Speaker 1: special relativity. We'll get to general relativity in a moment.
Speaker 1: So you're in your spaceship, You're zooming around at the
Speaker 1: speed of light, and for you, time is passing normally.
Speaker 1: The seconds feel like seconds, minutes feel like minutes, hours
Speaker 1: feel like hours, etcetera. And you're on there for a
Speaker 1: full year. Back on Earth, time is passing normally. For
Speaker 1: your best friend who's just hanging out on Earth, they
Speaker 1: feel their seconds passed like seconds, their minutes passing minutes,
Speaker 1: and so on. However, when we look at the two
Speaker 1: of you in reference to one another, something unusual happens.
Speaker 1: So to your best friend on Earth, it looks like
Speaker 1: time is passing very slowly for you aboard your spaceship.
Speaker 1: To you on your spaceship, it looks like time is
Speaker 1: passing super fast for your friend back on Earth. So
Speaker 1: when you do get back to Earth a year later
Speaker 1: than the two of you enter the same point of reference,
Speaker 1: things are weird. From your perspective, You've only aged a
Speaker 1: year because you spend a year aboard your space ship,
Speaker 1: but a little more than a year and a half
Speaker 1: has passed on Earth while you were gone. Your calendars
Speaker 1: wouldn't line up anymore. The faster you go relative to
Speaker 1: your frame of reference, the more pronounced the time dilation. Now,
Speaker 1: I do want to be clear about this. It's not
Speaker 1: really correct to say that as speed increases, time slows down.
Speaker 1: You have to always relay this in terms of having
Speaker 1: another frame of reference, because within a single frame of reference,
Speaker 1: time just passes normally. There's no difference. By the way.
Speaker 1: This is also why star dates in the Star Trek
Speaker 1: universe don't make a whole lot of sense. They try
Speaker 1: to retroactively make it makes sense. But keeping time when
Speaker 1: you're on a ship that can travel at the speed
Speaker 1: of light or in the case of Star Trek, magically
Speaker 1: going faster than the speed of light, and we won't
Speaker 1: even get into warp speed, it all is crazy. But
Speaker 1: being able to use that and somehow related to making
Speaker 1: sense on time passing on planets or space stations or whatever,
Speaker 1: that's a huge mess. But it's also outside of our episode,
Speaker 1: so we'll just leave it at that. We don't notice
Speaker 1: the effects of special relativity in most of our day
Speaker 1: to day lives because we are not traveling fast enough
Speaker 1: relative to each other for it to be a real
Speaker 1: factor most of the time. But it does get even
Speaker 1: more yeared. Were it possible to build a spaceship that
Speaker 1: could travel at the speed of light and you were
Speaker 1: to take this sort of trip to an outside observer,
Speaker 1: time would appear to stop for you aboard your spaceship Now,
Speaker 1: if assuming this was even possible, you would still experience
Speaker 1: time in your own frame of reference as per normal,
Speaker 1: but your friend back on Earth would see that it
Speaker 1: looked like you were frozen in time. However, this is
Speaker 1: a mood point. Matter cannot travel at the speed of light,
Speaker 1: so it's more of a thought experiment anyway. However, we
Speaker 1: can actually detect time dilation with extremely accurate time measurement
Speaker 1: devices like atomic clocks. In fact, we've done it in experiments.
Speaker 1: Scientists have synchronized two atomic clocks, and these atomic clocks
Speaker 1: keep incredibly accurate time down to a matter of nanoseconds,
Speaker 1: and a nanosecond is one billionth of a second. So
Speaker 1: one clock was kept stationary a relatively speaking, here on Earth.
Speaker 1: The other traveled aboard a high speed aircraft. And at
Speaker 1: the end of the experiment they compared the two clocks
Speaker 1: against each other, and the one that was aboard the
Speaker 1: aircraft had measured less time than the one that stayed
Speaker 1: on the ground on Earth. Less time passed on that
Speaker 1: aircraft relatively the amount of time passing on the ground.
Speaker 1: It wasn't just that one clock was moving more slowly
Speaker 1: than the other. Literally, less time was passing in reference
Speaker 1: to the other point of from the perspective of the
Speaker 1: other point of reference. That is, the difference was right
Speaker 1: in line with Einstein's calculations. Now, as we'll see, this
Speaker 1: ends up being an important point when we get to satellites.
Speaker 1: But we can't just jump on that yet. We do
Speaker 1: need to take into consideration general relativity. So, as I mentioned,
Speaker 1: special relativity only looks at frames of reference that are
Speaker 1: in a constant and consistent motion with regard to one another.
Speaker 1: There could be no change in direction or speed because
Speaker 1: that introduces accelerative forces and that changes things. So to
Speaker 1: take acceleration into account, Einstein proposed his theory of general
Speaker 1: relativity ten years after his theory of special relativity, so
Speaker 1: this would be nineteen fifteen for those who are keeping track.
Speaker 1: This theory would incorporate the force of gravity into Einstein's work,
Speaker 1: which means factoring in acceleration. So in this theory, Einstein
Speaker 1: introduced the equivalence principle, which says that gravity pulling in
Speaker 1: one direction is equivalent to acceleration in another direction. So
Speaker 1: we can actually experience this. It's easy to remember and imagine.
Speaker 1: Imagine getting on an elevator and it's going up, and
Speaker 1: as it goes up, you feel that sense of increased
Speaker 1: gravity pulling down on you as the elevator accelerates. When
Speaker 1: the elevator is going down, you feel a sense of
Speaker 1: decreased gravity as the elevator accelerates downward. So gravity and
Speaker 1: acceleration are equivalent, which means that it can also affect
Speaker 1: our measurements of space and time. Einstein hypothesized that gravity
Speaker 1: was warping spacetime itself. Take something that's really massive, like
Speaker 1: a huge dense star, that would warp spacetime around it
Speaker 1: through its gravity, and we can even observe this scientifically.
Speaker 1: Scientists have measured light that has curved around massive stars.
Speaker 1: This is called gravitational lensing. Now here's another thing that
Speaker 1: gets a bit confusing. The effects of gravity on time
Speaker 1: mean that time passes differently for objects in orbit when
Speaker 1: taken into reference to time passing on Earth itself, time
Speaker 1: passes faster in orbit than it does on Earth. Now, again,
Speaker 1: this is a frame of reference thing, because if you
Speaker 1: were on a spaceship in orbit, your experience of time
Speaker 1: would feel exactly the way it does when you are
Speaker 1: on Earth. It's only when we look at this from
Speaker 1: two frames of reference that we see how it doesn't
Speaker 1: match up. So what does this all mean for satellites, Well,
Speaker 1: it means that satellites in orbit have a couple of
Speaker 1: different relativistic effects going on. In our frame of reference
Speaker 1: here on Earth, satellites are traveling faster than we are
Speaker 1: to maintain orbit, which means that if we compare the
Speaker 1: passing of time in each frame of reference, time would
Speaker 1: pass faster for us than for the satellite. However, due
Speaker 1: to the gravitational effect on space time, we also know
Speaker 1: that something in orbit will have time passed faster for
Speaker 1: that thing than we would experience here on Earth. So
Speaker 1: it's the opposite of the effect of special relativity in
Speaker 1: a way, and the effects of special relativity and general
Speaker 1: relativity don't actually cancel each other out, which means ultimately
Speaker 1: that time on a satellite and time down here on
Speaker 1: Earth are not syncd up with reference to one another,
Speaker 1: and for some types of satellites that's a problem. I'll
Speaker 1: explain more after we take this quick break. To understand
Speaker 1: why relativity is important with certain satellites, let's talk about
Speaker 1: the Global Positioning System or GPS. Now, this is the
Speaker 1: satellite system that provides data back to Earth that makes
Speaker 1: it possible to get precise coordinates using a GPS receiver.
Speaker 1: So how does that work? Well, here on Earth, you
Speaker 1: could get a very imprecise idea of your general coordinates
Speaker 1: through UH trilateration using signals from cell phone towers. This
Speaker 1: works on a fairly simple principle. So we know that
Speaker 1: the radio signals sent to and from cell phones travel
Speaker 1: at essentially the speed of light. So if a cell
Speaker 1: phone tower broadcasts out a short command that just requests
Speaker 1: your phone to respond back with a quick response a ping.
Speaker 1: In other words, the amount of time it would take
Speaker 1: for the pain to reach the cell tower could be
Speaker 1: used to work backward and figure out how far away
Speaker 1: the phone is from that cell phone tower. Because you
Speaker 1: know the speed of travel, right is the speed of light,
Speaker 1: so you also know how much time it took. That
Speaker 1: means you can work backward to figure out the distance
Speaker 1: between those two points. However, that's just a distance, there's
Speaker 1: no direction there. Now, if you did this with multiple
Speaker 1: cell towers, the collective data from those towers could be
Speaker 1: used to get a rough estimate of where the phone is.
Speaker 1: So let's imagine we've got a map and on that map,
Speaker 1: we've got three cell towers A, B, n C. You
Speaker 1: can see exactly where each one is. And let's say
Speaker 1: that you've got a phone that's located somewhere within the
Speaker 1: broadcast range of those three cell towers. Each tower sends
Speaker 1: a ping to your phone, your phone responds with a
Speaker 1: ping back, and you are given the amount of distance
Speaker 1: between your phone and each of those three towers. Well,
Speaker 1: Tower as result says that you are a mile away
Speaker 1: from Tower A, So you actually have to draw a
Speaker 1: full circle around Tower A to represent all the possible
Speaker 1: points you could be that are one mile away from
Speaker 1: Tower A. So you're drawing a mile radius around Tower A.
Speaker 1: Tower B responds that you're within one point five miles
Speaker 1: of Tower B, so you have to draw a circle
Speaker 1: around Tower B to represent all the points where you
Speaker 1: could be that are a mile and a half away
Speaker 1: from it. Now, the circle from Tower B in the
Speaker 1: circle from Tower A should intersect each other at two points,
Speaker 1: but that means you could be at either of those
Speaker 1: two points, right, You could be at either overlap, So
Speaker 1: you don't have enough information yet. By coordinating with Tower C,
Speaker 1: and let's say that one tells you you're within two miles.
Speaker 1: You can draw a third circle, and the point where
Speaker 1: all three circles would meet would be your general location.
Speaker 1: It's not incredibly precise, but it does give you an
Speaker 1: idea of where you are. The GPS constellation of satellites
Speaker 1: does something similar, only we have to think of this
Speaker 1: in terms of three dimensional space rather than a two
Speaker 1: dimensional map. So a satellite sends out a high frequency,
Speaker 1: low power radio signal and receivers pick that signal up.
Speaker 1: The receiver, let's say it's your smartphone, doesn't have to
Speaker 1: send data back up to the satellite, which is good
Speaker 1: because I would be an enormous drain on your smartphones power.
Speaker 1: So really it's just listening for these signals. Now, the
Speaker 1: receiver and satellite both run the same digital pattern relative
Speaker 1: to a specific time stamp. It's easy if we think
Speaker 1: of this as midnight. So let's say that midnight hits
Speaker 1: and this particular digital pattern starts both on the satellite
Speaker 1: and the receiver, so they're both running the exact same pattern.
Speaker 1: The satellite beams out of signal carrying this digital pattern.
Speaker 1: The satellite is far away, so it takes a little time,
Speaker 1: you know, not much, but a little time for that
Speaker 1: signal to get to your receiver, and the lag between
Speaker 1: the pattern that's playing on your receiver and the signal
Speaker 1: of that same pattern coming in from the satellite tells
Speaker 1: the receiver how far away it is from that particular satellite,
Speaker 1: because again we know that the signal is moving at
Speaker 1: the speed of the transmission itself, and that's the speed
Speaker 1: of light, and that's a constant. So now the receiver
Speaker 1: knows how far away it is from that one satellite.
Speaker 1: And because the orbits of these satellites are predictable, the
Speaker 1: receiver has a record of where that satellite should be
Speaker 1: relative to the your surface. Occasionally we have to tweak
Speaker 1: that record because stuff like gravity can pull a satellite
Speaker 1: slightly out of position over time, so that actually is
Speaker 1: something that has to be addressed on occasion. Now, this
Speaker 1: receiver will do this with at least four satellites the
Speaker 1: y four and not three, and I gave the three
Speaker 1: cell phone tower examples. Well, it's because the clocks on
Speaker 1: satellites and the clock that's running on the device that
Speaker 1: the receiver is built into may not be in and
Speaker 1: really aren't truly synchrono eyes and the intersection of four
Speaker 1: spheres of distance like these four spheres represent the various
Speaker 1: ranges that these satellites are finding themselves in. With regard
Speaker 1: to this, receiver can only intersect at one point. That's
Speaker 1: the only place they could all intersect. So if a
Speaker 1: GPS receiver's clock is not matching up to the clocks
Speaker 1: on the satellites, there will be no intersection at all,
Speaker 1: and the receiver will say, well, I can't find an intersection,
Speaker 1: so that I know that means my clock is off
Speaker 1: from all the other clocks, and it will then adjust
Speaker 1: its own clock to be an alignment so that the
Speaker 1: four spheres have a point of intersection and that is
Speaker 1: your location on Earth. Now. In order for our receivers
Speaker 1: to be able to do this, the accuracy of the
Speaker 1: atomic clocks aboard those GPS satellites has to be accurate
Speaker 1: within twenty to thirty nanoseconds. And remember a nanosecond is
Speaker 1: one billionth of a second. That is an a Downding
Speaker 1: level of accuracy. And because these satellites are in motion
Speaker 1: and they are also affected by Earth's gravity, they are
Speaker 1: subject to the effects of special and general relativity, and
Speaker 1: this means we actually have to make calculations to take
Speaker 1: that into account. Now, according to special relativity and the
Speaker 1: relative speeds of satellites to a fixed point on the
Speaker 1: surface of the Earth, we would expect the atomic clock
Speaker 1: aboard that satellite to register seven fewer micro seconds per
Speaker 1: day than a clock on Earth because the satellites are
Speaker 1: moving through space faster than we are, relatively speaking. So
Speaker 1: that means from our frame of reference, time is passing
Speaker 1: more slowly on that satellite than it does here on Earth. Ah.
Speaker 1: But general relativity comes into play too, and general relativity
Speaker 1: tells us that the Earth's gravity warps space time around
Speaker 1: our planet. And one of general relativity's predictions is that
Speaker 1: a clock closer to a massive object, so like a
Speaker 1: clock here on Earth, will take more slowly than a
Speaker 1: clock that is further out from that same massive object.
Speaker 1: So the closer the clock is to the massive object,
Speaker 1: the less time it will experience it will measure compared
Speaker 1: to o clock this further away, which is crazy right.
Speaker 1: So taking only general relativity into account, we would see
Speaker 1: that a clock aboard one of these satellites would register
Speaker 1: more time having passed on that satellite than a clock
Speaker 1: here on Earth, meaning from our frame of reference, time
Speaker 1: is actually passing faster on those satellites than it does
Speaker 1: here for us, this would come out to about forty
Speaker 1: five micro seconds a day, meaning that at the end
Speaker 1: of day one, the clock aboard that satellite would be
Speaker 1: ahead of a clock here on Earth by forty five
Speaker 1: micro seconds, and this would continue day after day, with
Speaker 1: the gap growing wider every single day. Now, when we
Speaker 1: bring both special and general relativity together into consideration, we
Speaker 1: see that they don't just cancel each other out right,
Speaker 1: because we've got that seven microsecond lag due to special relativity,
Speaker 1: but we have the forty five microsecond surge due to
Speaker 1: general relativity. So in the end, we're looking at a
Speaker 1: thirty eight microsecond difference per day between a clock on
Speaker 1: a satellite and a clock here on Earth. The clocks
Speaker 1: on the satellites will get ahead of similar clocks here
Speaker 1: on Earth by thirty eight microseconds every single day. And
Speaker 1: while a microsecond is a very small amount of time,
Speaker 1: I mean we're talking at a level that we don't
Speaker 1: typically experience. We don't think of time in microseconds for
Speaker 1: our day to day lives. However, thirty eight microseconds is
Speaker 1: equal to thirty eight thousand nanoseconds, and if you're looking
Speaker 1: for an accuracy of around twenty to thirty nanoseconds. This
Speaker 1: becomes an enormous problem if we don't take it into account.
Speaker 1: And this brings us background to something I mentioned at
Speaker 1: the top of the show. We know that Einstein was
Speaker 1: right about relativity because we have to account for it
Speaker 1: with technology like GPS. If we didn't take it into account,
Speaker 1: if we didn't factor in the effects of relativity, our
Speaker 1: GPS wouldn't work for very long at all. Our technology
Speaker 1: proves that the science is real, or else the tech
Speaker 1: would fail at what it needs to do now. In general,
Speaker 1: I think that's a great lesson to take home. There
Speaker 1: are a lot of voices out there that call science
Speaker 1: into question, and some of them are more outlandish than others.
Speaker 1: A person who is passionately and sincerely arguing that the
Speaker 1: Earth is flat seems pretty far out there for me,
Speaker 1: because so much of our technology we've built upon and
Speaker 1: we rely upon wouldn't work if that were true. Even
Speaker 1: if you can't experience something directly, such as having a
Speaker 1: meaningful experience of time dilation, a ton of the stuff
Speaker 1: we do experience on a day to day basis is
Speaker 1: affected by this stuff, and it proves the existence and
Speaker 1: also the benefits of having the scientific method. Now give
Speaker 1: a little side note on GPS to kind of wrap
Speaker 1: this up. The original GPS configuration came out of a
Speaker 1: United States Department a defense project. The original purpose was
Speaker 1: to provide positioning information for government and military, but specifically
Speaker 1: the United States and its allies, and for that reason,
Speaker 1: the U S Government wished to restrict access to this technology.
Speaker 1: The general line of thought was that it would be
Speaker 1: better if the U S didn't allow tech that could,
Speaker 1: you know, give precise coordinates for stuff like military bases
Speaker 1: or the position of various military units to people who
Speaker 1: didn't belong to those divisions. So, as a matter of
Speaker 1: national security, the US guarded this technology civilian receivers. So
Speaker 1: if you went out and you bought a GPS receiver,
Speaker 1: you could get public GPS signals. But the United States
Speaker 1: was purposefully instituting a policy called selective availability, which was
Speaker 1: an intentional degradation of public GPS signals. They were introducing
Speaker 1: errors on purpose so that GPS receivers couldn't get an
Speaker 1: accurate location. It limited accuracy to around fifty meters horizontally
Speaker 1: in a hundred meters vertically and effectively, that meant that
Speaker 1: you wouldn't really know your precise coordinates. You certainly couldn't
Speaker 1: use a GPS receiver as a turn by turn directions
Speaker 1: tool because you wouldn't even necessarily show up on the
Speaker 1: right street. You wouldn't know if you were approaching your
Speaker 1: turn or if you had already passed it. It was
Speaker 1: it was not practical for that. It was only in
Speaker 1: the year two thousand, when US President Bill Clinton directed
Speaker 1: the government to end selective availability that civilian GPS receivers
Speaker 1: could actually get accurate data. And that's what made the
Speaker 1: modern GPS receivers and stuff like our phones possible. So
Speaker 1: before two thousand, GPS receivers didn't work very well for
Speaker 1: the average person, but it wasn't because the technology was
Speaker 1: bad or that the science was wrong. It worked that way,
Speaker 1: or if you prefer it, it didn't work properly on purpose.
Speaker 1: And that wraps up this episode about relativity and why
Speaker 1: it's important with technology, and it's not just satellite tech,
Speaker 1: but that's a big one, and it also ends up
Speaker 1: being a big thorn in the side for science fiction
Speaker 1: authors who want to write about interstellar travel at faster
Speaker 1: than light speeds because you have to start finding alternative
Speaker 1: explanations for how that's possible, because we we've come up
Speaker 1: against these limits that Einstein predicted, and so far his
Speaker 1: predictions have held true. So in order to travel faster
Speaker 1: than the speed of light, you do have to create
Speaker 1: something like warp drive, which theoretically warps space around you.
Speaker 1: So rather than traveling faster than light, you're decreasing the
Speaker 1: distance betweening your point of origin and your destination. It
Speaker 1: would be kind of like taking a map of the
Speaker 1: United States and saying I'm going to travel from Atlanta
Speaker 1: to Los Angeles, from one coast to the other, but
Speaker 1: instead of drawing a line from Atlanta to l A,
Speaker 1: you just fold the map so that the two dots
Speaker 1: are next to each other, and then you draw a
Speaker 1: line that way. That's how warp speed is supposed to work,
Speaker 1: because it's the only way you can get around the
Speaker 1: fact that you can't really go faster than the speed
Speaker 1: of light. But that's a topic for another show. If
Speaker 1: you guys have suggestions for future topics I should tackle,
Speaker 1: please let me know. Send me a message on Twitter.
Speaker 1: The handle is tech stuff hs W and I'll talk
Speaker 1: to you again really soon. Text Stuff is an I
Speaker 1: heart Radio production. For more podcasts from my heart Radio,
Speaker 1: visit the i heart Radio app, Apple Podcasts, or wherever
Speaker 1: you listen to your favorite shows. Two