Speaker 1: Welcome to tech 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 how the tech are you. Well, I'm still on vacation, y'all.
Speaker 1: I'll be back soon. But in the meantime, we have
Speaker 1: an episode that originally published on July one, twenty. It's
Speaker 1: called It's All Relative. And when I was a kid,
Speaker 1: I was convinced that Einstein's theories were the these super
Speaker 1: complicated explanations of the universe that really had no real
Speaker 1: intersection with my daily life. But as it turns out,
Speaker 1: without an understanding of relativity, a lot of the technology
Speaker 1: we rely upon wouldn't work properly. It's fascinating stuff. I
Speaker 1: hope you enjoy. The hurts unit refers to the numb
Speaker 1: or 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 ball went up down
Speaker 1: up two full times per second, then there would be
Speaker 1: two hurts. Well, we can describe lots of stuff with
Speaker 1: the unit hurts. We use it to describe sounds, in
Speaker 1: which case we're talking about the frequency at which stuff vibrates.
Speaker 1: Typical human hearing spans a range of frequencies that at
Speaker 1: the low end is that twenty hurts. That represents the
Speaker 1: lowest pitches of sounds. So you can think of those
Speaker 1: deep bass notes. That's around the twenty hurts of area uh,
Speaker 1: and then it goes all the way up to twenty
Speaker 1: killer hurts or twenty thousand hurts. That represents the very
Speaker 1: highest pitches that people can typically here, And those frequencies
Speaker 1: correlate to how quickly stuff is vibrating back and forth. Now,
Speaker 1: when it comes to us hearing things, we usually mean
Speaker 1: that 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 processor speed of a CPU. In
Speaker 1: that case, we're really talking about the number of clock
Speaker 1: cycles per second, so you get it. This is a
Speaker 1: description of the frequency of the number of times a
Speaker 1: certain thing happens, like within a second. And I also
Speaker 1: explained that we measure the rate at which we can
Speaker 1: send data using the term bits. A bit is a
Speaker 1: basic unit of digital information, and when we talk about computers,
Speaker 1: we're talking about bits in the form of a zero
Speaker 1: or a one binary information, just like your basic two
Speaker 1: way physical switch has two positions off or on. So
Speaker 1: if you hear a term like kill a bit, that
Speaker 1: means one thousand bits, and a megabit is one million bits,
Speaker 1: and a gigabit would be one billion bits. Likewise, megabits
Speaker 1: per second tells us how many million bits can move
Speaker 1: 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 bite 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 bites, but transfer speeds in
Speaker 1: terms of bits. So let's say that you do have
Speaker 1: that one hundred megabits person, I can download speed, and
Speaker 1: you want to download a one hundred megabyte file, Well,
Speaker 1: that means it's not going to take one second. It's
Speaker 1: gonna take eight seconds to download the file, because a
Speaker 1: megabyte is eight times larger than a megabit. And actually
Speaker 1: even that is a little bit misleading because in computer
Speaker 1: memory terms, we typically look at units of memory based
Speaker 1: on powers of two rather than powers of ten. So
Speaker 1: instead of a killer byte being one thousand bytes, it's
Speaker 1: actually one thousand twenty four bytes. And there's no standardization
Speaker 1: in the tech industry, so sometimes people will say a
Speaker 1: kill a byte and they mean one thousand bytes. Sometimes
Speaker 1: they'll say kill a byte and they mean one thousand
Speaker 1: twenty four bytes, and you will want to tear your
Speaker 1: hair out, and then you'll look like I do, I'm
Speaker 1: bald if you didn't know. But this episode isn't about
Speaker 1: the peculiarities of our naming conventions and the computer information age. Instead,
Speaker 1: I wanted to tackle something else. It affects everything, really,
Speaker 1: but in particular we really had to suss it out
Speaker 1: in order to make certain types of satellites work properly.
Speaker 1: And this is the concept of relativity. So in this
Speaker 1: episode we're really going to learn why an understanding of
Speaker 1: relativity is important if we want our certain satellite technologies
Speaker 1: to work, and it serves as a great reminder that
Speaker 1: technology is only really possible through an understanding of science.
Speaker 1: You can think of tech as the physical manifestation of
Speaker 1: our understanding of scientific principles, and that means if we
Speaker 1: were wrong in our understanding of science, the technology shouldn't
Speaker 1: really work. So in a way, you can think of
Speaker 1: technology that works as evidence that the scientific method is
Speaker 1: a darned good formula. Since we're talking about relativity, it
Speaker 1: means we're gonna be talking about a real Einstein today.
Speaker 1: His name was Einstein, which is convenient. But before we
Speaker 1: get to Einstein, we have Galileo Galileo, Galileo Figaro. Wait no,
Speaker 1: I'm sorry, Wait that's Bohemian Rhapsody. I meant Galileo galile This.
Speaker 1: Galileo made an observation that if you've got two observers
Speaker 1: moving at a constant speed and direction, so they're moving
Speaker 1: at the same velocity, they will get the same results
Speaker 1: for any experiment that involves moving stuff around a mechanical experiment.
Speaker 1: This is easier to understand if we use an example,
Speaker 1: and I like one that my colleague Robert Lamb used
Speaker 1: when he wrote about relativity for how Stuff Works dot
Speaker 1: Com back in the day. He used an example of
Speaker 1: a train and a scientific ping pong ball. Alright, 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 chain and velocities.
Speaker 1: That other means a change in direction or a change
Speaker 1: in speed or both, but in this case constant speed
Speaker 1: 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 kilometers per hour.
Speaker 1: If the train stays steady to the scientist, it will
Speaker 1: feel as if that scientist is actually just standing still,
Speaker 1: just anywhere, and we're conveniently ignoring an emotion that would
Speaker 1: happen due to irregularities with the trains wheels or the
Speaker 1: train tracks or anything like that. And if this is
Speaker 1: hard for you to imagine, just think about how you
Speaker 1: feel when you're standing still or sitting still or laying down.
Speaker 1: Here on Earth. We know the Earth is moving through space.
Speaker 1: It is a body in motion, but when we are
Speaker 1: still relative to the Earth itself, we don't feel that motion.
Speaker 1: Assuming there's not mother weird event going on like an earthquake,
Speaker 1: which is something separate. But back to our hypothetical train,
Speaker 1: the scientist tosses the ping pong ball down the aisle. Now,
Speaker 1: from the scientist's perspective, this ping pong ball will travel
Speaker 1: at whatever speed they threw it at. Robert actually suggests
Speaker 1: a relatively gentle toss of five miles per hour or
Speaker 1: eight kilometers per hour. The ping pong ball would bounce
Speaker 1: down the aisle, just as it would if the scientists
Speaker 1: were to toss the ball on a train that isn't
Speaker 1: moving at all, or on just flat ground. However, let's
Speaker 1: say we have a second observer who's not on the train.
Speaker 1: They're standing off to the side, and they can see
Speaker 1: through the train. To this person, it will appear as
Speaker 1: if the ping pong ball is moving very fast. Indeed,
Speaker 1: relative to this stationary observer, the ping pong ball will
Speaker 1: appear to move at the speed at which it was
Speaker 1: thrown in addition to the speed of the train itself.
Speaker 1: So if we take the two figures, we get one
Speaker 1: hundred five miles per hour or a hundred sixty nine
Speaker 1: kilometers per hour. This is called a Galilean transformation. Alternatively,
Speaker 1: if the scientists were throwing the ping pong ball in
Speaker 1: the opposite direction of the trains travel, so they're facing
Speaker 1: towards the back of the train, it would appear to
Speaker 1: this second observer that the ping pong ball was moving
Speaker 1: at a slightly slower speed than the overall train was,
Speaker 1: whereas to the scientist on board, the ping pong ball
Speaker 1: would still be traveling at that five mile per hour speed.
Speaker 1: So this is where the term relativity comes into play.
Speaker 1: The effects observed are relative to the perspective of the observer.
Speaker 1: It's all based on the reference frame of that observer.
Speaker 1: If you're on the train, then you're just looking at
Speaker 1: a ping pong ball bouncing at a relatively slow speed
Speaker 1: down the aisle. If you're not on the train, the
Speaker 1: ping 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: old 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 way,
Speaker 1: is just a frame of reference in which there are
Speaker 1: zero net forces acting upon it, so that there are
Speaker 1: 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. Hey,
Speaker 1: what if you're on the train that's traveling one per
Speaker 1: hour and you're facing forward, you're facing the direction of travel,
Speaker 1: and then you have a flashlight and you turn on
Speaker 1: the flashlight. Well, doesn't that mean you should perform a
Speaker 1: Galilean transformation on this and say the light from that
Speaker 1: flashlight in your hands is actually traveling at the normal
Speaker 1: speed of light on board the train, but also get
Speaker 1: that boost of the trains travel, So it should be
Speaker 1: the speed of light plus one miles per hour. Doesn't
Speaker 1: that make sense? Well, according to actual experiments performed before
Speaker 1: Einstein would come around to explain things, the answer was Nope,
Speaker 1: doesn't look like it works that way. Scientists Edward Morley
Speaker 1: and Albert A. Michelson created an experiment to measure the
Speaker 1: speed of light back in seven and actually they were
Speaker 1: looking for something else. They were looking for evidence of
Speaker 1: 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 there's no way for
Speaker 1: the vibration of one particle to come into contact and
Speaker 1: affect another particle, so sound can't travel. Sound travels through
Speaker 1: the propagation of vibrational waves, and if your stuff isn't
Speaker 1: in contact with each other, there's no way for them
Speaker 1: to have that wave propagate. So there has to be
Speaker 1: some sort of medium like air or solid surfaces or
Speaker 1: something in order for sound travel. Well, if that's the case,
Speaker 1: said the folks of the time, then stuff like light
Speaker 1: 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 Mickelson and Morley devised a gadget that would
Speaker 1: split light into two beams, directing those beams down different
Speaker 1: paths using mirrors in different directions, and seeing if those
Speaker 1: two 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: six thousand miles per second or around three hundred thousand
Speaker 1: kilometers per second. Now that flew in the face of
Speaker 1: classic Newtonian physics clearly. With the example of the ping
Speaker 1: pong ball and the train, the ping pong ball has
Speaker 1: to be traveling faster than the train it's on. I mean,
Speaker 1: that just makes sense. If you were standing on the
Speaker 1: top of the very front of the train, and then
Speaker 1: you through the ping pong ball, and we ignore stuff
Speaker 1: like wind resistance, the ping pong ball would land ahead
Speaker 1: of the train, so it has to be going faster.
Speaker 1: So what the heck was so special about light and
Speaker 1: what was going on? Well, this was one of the
Speaker 1: great mysteries that Albert Einstein's that is mine to unraveling,
Speaker 1: and it formed the basis of one of his great
Speaker 1: theories of relativity. And this would be the theory of
Speaker 1: special relativity, which poses that the laws of physics are
Speaker 1: in the same in all inertial frames of references. And
Speaker 1: that means the speed of light will be the same
Speaker 1: for all observers, regardless of their relative perspectives. It doesn't
Speaker 1: matter the context. The speed of light is the speed
Speaker 1: of light. Now, there's an implication to this theory that
Speaker 1: really got people scratching their heads. If the speed of
Speaker 1: light is absolutely constant, that would mean that stuff like
Speaker 1: distance and time are not. And as a heck of
Speaker 1: a brain teaser, when we come back, we'll explore this more.
Speaker 1: Let's imagine that you live half a mile away from
Speaker 1: a lovely park, and it's a half mile away in
Speaker 1: the morning, it's a half mile away. At night, it's
Speaker 1: a half mile away. On a Tuesday, it's a half
Speaker 1: mile away. On a Saturday. Half a mile is half
Speaker 1: 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 is super,
Speaker 1: nobody is. 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 result, 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: errors there that could be causing the issues. But it
Speaker 1: 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: positive that the speed of light is measured as constant
Speaker 1: in all frames 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 miles per hour means that
Speaker 1: in one hour's time we will cover a distance of
Speaker 1: one hundred miles. That's very obvious. But if the speed
Speaker 1: of light is constant for all frames of reference, regardless
Speaker 1: 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 hour in a straight line, and you toss a
Speaker 1: ping pong ball straight up in the air, well, it's
Speaker 1: gonna go straight up and come right back down to
Speaker 1: your hand in a nice vertical line. From an outside
Speaker 1: observer who isn't on the train, it would look a
Speaker 1: little differently. You would throw the ball up at one
Speaker 1: point relative to this outside observer, and the ball would
Speaker 1: appear to move not just vertically, but horizontally before coming
Speaker 1: back down. Now, if we repeat this experiment, but we
Speaker 1: 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 a laser pointer and you've got a mirror on
Speaker 1: the ceiling of the train and a photon detector on
Speaker 1: the floor of the train. You shoot the laser up
Speaker 1: at the mirror, it reflects off the mirror, and then
Speaker 1: it comes back down and hits the detector on the floor,
Speaker 1: and it registers how long it took the light to
Speaker 1: travel from your laser pointer to hit the detector. And
Speaker 1: to you, the laser makes a vertical line. All that
Speaker 1: makes sense, right, you can imagine that, But for our
Speaker 1: outside observer who's not on the train, it would appear
Speaker 1: as though the laser were actually traveling at a diagonal
Speaker 1: up to that mirror and then a diagonal back down
Speaker 1: towards the detector. So for one observer, the one on
Speaker 1: the train, we have a straight line. It's vertical up down.
Speaker 1: For the second observer off the train, we have an
Speaker 1: angled path, sort of like how a billiard ball can
Speaker 1: hit the side of a pool table and bounce off
Speaker 1: at an angle. But this creates an apparent paradox. The
Speaker 1: path viewed by you on the train is a straight line,
Speaker 1: and by definition that is the shortest distance between two points.
Speaker 1: The path observed by the person who is not on
Speaker 1: the train is an angled line, and by definition that
Speaker 1: has to be longer. The speed of light is constant
Speaker 1: in both cases, but the distance is different between the
Speaker 1: two points of reference. And because speed is distance divided
Speaker 1: by time, if the distance is different, the time must
Speaker 1: also be different between those two points of reference. Crazy
Speaker 1: This brings us to the concept of time dilation. It also,
Speaker 1: by the way, can affect distance. The faster and object gets,
Speaker 1: the more squished it gets. So if you had this
Speaker 1: train and you were to get up to near the
Speaker 1: speed of light, the train to an outside observer would
Speaker 1: appear to be shorter than it normally would be to
Speaker 1: anyone inside the train, the dimensions would remain exactly the same.
Speaker 1: You would not suddenly see a shorter train. It wouldn't
Speaker 1: be like you were in that compressor scene in Star Wars.
Speaker 1: The train would a to be normal. Only from an
Speaker 1: outside observer who is not traveling at that speed would
Speaker 1: it appear that the train itself was getting squished shorter. Likewise,
Speaker 1: the faster something goes with respect to some other point
Speaker 1: of reference that's important, the more quickly time appears to
Speaker 1: pass for those at the other point of reference. Or alternatively,
Speaker 1: the more slowly time seems to pass for the fast
Speaker 1: moving thing from the frame of reference of the person
Speaker 1: who's not moving fast. This gets really clunky. I know,
Speaker 1: it 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 of the speed of light,
Speaker 1: and you're gonna go on a year long jaunt out
Speaker 1: in space, and your best friend is hanging back on Earth.
Speaker 1: Now we now have our two frames of reference. We
Speaker 1: have the spaceship and then we have the person on Earth.
Speaker 1: So let's ignore accelerative forces for the moment, because we're
Speaker 1: going to have to just focus on special relativity. We'll
Speaker 1: get to general relativity in a moment. So you're in
Speaker 1: your spaceship. You're zooming around at the speed of light,
Speaker 1: and for you, time is passing normally. The seconds feel
Speaker 1: like seconds, minutes feel like minutes, hours feel like hours, etcetera.
Speaker 1: And you're on there for a full year. Back on Earth,
Speaker 1: time is passing normally. For your best friend who's just
Speaker 1: hanging out on Earth, they feel their seconds passed like seconds,
Speaker 1: their minutes passing minutes, and so on. However, when we
Speaker 1: look at the two of you in reference to one another,
Speaker 1: something unusual happens. So to your best friend on Earth,
Speaker 1: it looks like time is passing very slowly for you
Speaker 1: aboard your spaceship. To you on your spaceship, it looks
Speaker 1: like time is passing super fast for your friend back
Speaker 1: on Earth. So when you do get back to Earth
Speaker 1: a year later than the two of you enter the
Speaker 1: same point of reference, things are weird. Your perspective, you've
Speaker 1: only aged a year because you spend a year aboard
Speaker 1: your spaceship, but a little more than a year and
Speaker 1: a half has passed on Earth while you were gone.
Speaker 1: Your calendars wouldn't line up anymore. The faster you go
Speaker 1: relative to your frame of reference, the more pronounced the
Speaker 1: time dilation. Now, I do want to be clear about this,
Speaker 1: it's not really correct to say that as speed increases
Speaker 1: time slows down. You have to always relay this in
Speaker 1: terms of having another frame of reference, because within a
Speaker 1: single frame of reference, time just passes normally. There's no difference.
Speaker 1: By the way. This is also why star dates in
Speaker 1: the Star Trek universe don't make a whole lot of sense.
Speaker 1: They try to retroactively make it makes sense. But keeping
Speaker 1: time when you're on a ship that can travel at
Speaker 1: the speed of light or in the case of Star Trek,
Speaker 1: magically going faster than the speed of light, and we
Speaker 1: won't even get into warp speed. It all is crazy.
Speaker 1: But and being able to use that and somehow related
Speaker 1: to making sense on time passing on planets or space
Speaker 1: stations or whatever, that's a huge mess. But it's also
Speaker 1: outside of our episode, so we'll just leave it at that.
Speaker 1: We don't notice the effects of special relativity in most
Speaker 1: of our day to day lives because we are not
Speaker 1: traveling fast enough relative to each other for it to
Speaker 1: be a real factor most of the time. But it
Speaker 1: does get even more weird. Were it possible to build
Speaker 1: a spaceship that could travel at the speed of light,
Speaker 1: and you were to take this sort of trip to
Speaker 1: an outside observer, time would appear to stop for you
Speaker 1: aboard your spaceship. Now if assuming this was even possible,
Speaker 1: you would still experience time in your own frame of
Speaker 1: reference as per normal, but your friend back on Earth
Speaker 1: would see that it looked like you were frozen in time. However,
Speaker 1: this is a mood point. Matter cannot travel at the
Speaker 1: speed of light, so it's more of a thought experiment anyway. However,
Speaker 1: we can actually det time dilation with extremely accurate time
Speaker 1: measurement devices like atomic clocks. In fact, we've done it
Speaker 1: in experiments. Scientists have synchronized two atomic clocks, and these
Speaker 1: atomic clocks keep incredibly accurate time down to a matter
Speaker 1: of nanoseconds, and a nanosecond is one billion of a second.
Speaker 1: So one clock was kept stationary, you know, relatively speaking,
Speaker 1: here on Earth. The other traveled aboard a high speed aircraft,
Speaker 1: and at the end of the experiment they compared the
Speaker 1: two clocks against each other, and the one that was
Speaker 1: aboard the aircraft had measured less time than the one
Speaker 1: that stayed on the ground on Earth, less time passed
Speaker 1: on that aircraft relatively the amount of time passing on
Speaker 1: the ground. It wasn't just that one clock was moving
Speaker 1: more slowly than the other. Literally less time was passing
Speaker 1: in reference to the other point of from the perspective
Speaker 1: of the other point of reference, that is, the difference
Speaker 1: was right in line with Einstein's calculations. Now, as we'll see,
Speaker 1: this ends up being an important point when we get
Speaker 1: to satellites. But we can't just jump on that yet.
Speaker 1: We do need to take into consideration general relativity. So,
Speaker 1: as I mentioned, special relativity only looks at frames of
Speaker 1: reference that are in a constant and consistent motion with
Speaker 1: regard to one another. There could be no change in
Speaker 1: direction or speed because that introduces accelerative forces and that
Speaker 1: changes things. So to take acceleration into account, Einstein proposed
Speaker 1: his theory of general relativity ten years after his theory
Speaker 1: of special relativity, so this would be nineteen fifteen for
Speaker 1: those who are keeping track. This theory would incorporate the
Speaker 1: force of gravity into Einstein's work, which means factoring in acceleration.
Speaker 1: So in this theory, Einstein introduced the equivalence principle, which
Speaker 1: says that gravity pulling in one direction is equivalent to
Speaker 1: acceleration in another direction. So we can actually experience this.
Speaker 1: It's easy to remember and imagine. Imagine getting on an
Speaker 1: elevator and it's going up, and as it goes up,
Speaker 1: you feel that sense of increased gravity pulling down on
Speaker 1: you as the elevator accelerates. When the elevator is going down,
Speaker 1: you feel a sense of decreased gravity as the elevator
Speaker 1: accelerates downward. So gravity and acceleration are equivalent, which means
Speaker 1: that it can also affect our measurements of space and time.
Speaker 1: Einstein hypothesized that gravity was warping space time itself. Take
Speaker 1: something that's really massive, like a huge dense star, that
Speaker 1: would warp space time around it through its gravity, and
Speaker 1: we can even observe this scientifically. Scientists have measured light
Speaker 1: that has curved around massive stars. This is called gravitational lensing.
Speaker 1: Now here's another thing that gets a bit confusing. The
Speaker 1: effects of gravity on time mean that time passes differently
Speaker 1: for objects in orbit when taken in reference to time
Speaker 1: passing on Earth itself. Time passes faster in orbit than
Speaker 1: it does on Earth. Now, again, this is a frame
Speaker 1: of reference thing, because if you were on a spaceship
Speaker 1: in orbit, your experience of time would feel exactly the
Speaker 1: way it does when you are on Earth. It's only
Speaker 1: when we look at this from two frames of reference
Speaker 1: that we see how it doesn't match up. So what
Speaker 1: does this all mean for satellites. Well, it means that
Speaker 1: satellites in orbit have a couple of different relativistic effects
Speaker 1: going on in our frame of reference here on Earth,
Speaker 1: satellites are traveling faster than we are to maintain orbit,
Speaker 1: which means that if we compare the passing of time
Speaker 1: in each frame of reference, time would pass faster for
Speaker 1: us than for the satellite. However, due to the gravitational
Speaker 1: effect on space time, we also know that something in
Speaker 1: orbit will have time passed faster for that thing then
Speaker 1: we would experience here on Earth. So it's the opposite
Speaker 1: of the effect of special relativity in a way, and
Speaker 1: the effects of special relativity and general relativity don't actually
Speaker 1: cancel each other out, which means ultimately that time on
Speaker 1: a satellite and time down here on Earth are not
Speaker 1: syncd up with reference to one another, and for some
Speaker 1: types of satellites that's a problem. I'll explain more after
Speaker 1: we take this quick break. To understand why relativity is
Speaker 1: important with certain satellites, Let's talk about the Global Positioning
Speaker 1: System or GPS. Now, this is the satellite system that
Speaker 1: provides data back to Earth that makes it possible to
Speaker 1: get precise coordinates using a GPS receiver. So how does
Speaker 1: that work? Well, here on Earth, you could get a
Speaker 1: very imprecise idea of your general coordinates through uh trilateration
Speaker 1: using signals from cell phone towers. This works on a
Speaker 1: fairly simple principle. So we know that the radio signals
Speaker 1: sent to and from cell phones travel at essentially the
Speaker 1: speed of light. So if a cell phone tower broadcasts
Speaker 1: out a short command that just requests your phone to
Speaker 1: respond back with a quick response a ping. In other words,
Speaker 1: the amount of time it would take for the ping
Speaker 1: to reach the cell tower could be used to work
Speaker 1: backward and figure out how far away the phone is
Speaker 1: from that cell phone tower. Because you know the speed
Speaker 1: of travel, right is the speed of light, so you
Speaker 1: also know how much time it took. That means you
Speaker 1: can work backward to figure out the distance between those
Speaker 1: two points. However, that's just a distance, there's no direction there. Now,
Speaker 1: if you did this with multiple cell towers, the collective
Speaker 1: data from those towers could be used to get a
Speaker 1: rough estimate of where the phone is. So let's imagine
Speaker 1: we've got a map, and on that map we've got
Speaker 1: three cell towers A, B, n C. You can see
Speaker 1: exactly where each one is. And let's say that you've
Speaker 1: got a phone that's located somewhere within the broadcast range
Speaker 1: of those three cell towers. Each tower sends a ping
Speaker 1: to your phone, your phone responds with a ping back,
Speaker 1: and you are given the amount of distance between your
Speaker 1: phone and each of those three towers. Well, Tower as
Speaker 1: result says that you are a mile away from Tower A,
Speaker 1: so you actually have to draw a full circle around
Speaker 1: Tower A to represent all the possible points you could
Speaker 1: be that are one mile away from Tower A. So
Speaker 1: you're drawing a mile radius around Tower A. Tower B
Speaker 1: responds that you're within one point five miles of Tower B,
Speaker 1: so you have to draw a circle around Tower B
Speaker 1: to represent all the points where you could be that
Speaker 1: are a mile and a half away from it. Now,
Speaker 1: the circle from tower B in the circle from Tower
Speaker 1: A should intersect each other at two points, but that
Speaker 1: means you could be at either of those two points, right,
Speaker 1: you could be an either overlap, So you don't have
Speaker 1: enough information yet. By coordinating with tower C, and let's
Speaker 1: say that one tells you you're within two miles, you
Speaker 1: can draw a third circle, and the point where all
Speaker 1: three circles would meet would be your general location. It's
Speaker 1: not incredibly precise, but it does give you an idea
Speaker 1: of where you are. The GPS constellation of satellites does
Speaker 1: something similar, only we have to think of this in
Speaker 1: terms of three dimensional space rather than a two dimensional map.
Speaker 1: So a satellite sends out a high frequency, low power
Speaker 1: radio signal and receivers pick that signal up. The receiver,
Speaker 1: let's say it's your smartphone, doesn't have to send data
Speaker 1: back up to the satellite, which is good because I
Speaker 1: would be an enormous drain on your smartphones power. So
Speaker 1: really it's just listening for these signals. Now, the receiver
Speaker 1: and satellite both run the same digital pattern relative to
Speaker 1: a specific time stamp. It's easy if we think of
Speaker 1: this as midnight. So let's say that midnight hits and
Speaker 1: this particular digital pattern starts both on the satellite and
Speaker 1: the receiver, so they're both running the exact same pattern.
Speaker 1: The satellite beams out a 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: why 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 synchronized. And the intersection of four spheres
Speaker 1: of distance like these four spheres represent the various ranges
Speaker 1: that these satellites are finding themselves in. With regard to
Speaker 1: this receiver can only intersect at one point. That's the
Speaker 1: only place they could all intersect. So if a GPS
Speaker 1: receiver's clock is not matching up to the clocks on
Speaker 1: the satellites, there will be no intersection at all, and
Speaker 1: 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 astiunding level
Speaker 1: of accuracy. And because these satellites are in motion and
Speaker 1: they are also affected by Earth's gravity, they are subject
Speaker 1: to the effects of special and general relativity, and this
Speaker 1: means we actually have to make calculations to take that
Speaker 1: into account. Now, according to special relativity and the relative
Speaker 1: speeds of satellites to a fixed point on the surface
Speaker 1: of the Earth, we would expect the atomic clock aboard
Speaker 1: that satellite to register seven fewer micro seconds per day
Speaker 1: than a clock on Earth because these satellites are moving
Speaker 1: through space faster than we are, relatively speaking, So that
Speaker 1: means from our frame of reference, time is passing more
Speaker 1: 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 a 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 past 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 micro second lag due to
Speaker 1: special relativity, but we have the forty five micro second
Speaker 1: surge due to general relativity. So in the end we're
Speaker 1: looking at a thirty eight micro second difference per day
Speaker 1: between a clock on a satellite and a clock here
Speaker 1: on Earth. The clocks on the satellites will get a
Speaker 1: head of similar clocks here on Earth by thirty eight
Speaker 1: microseconds every single day. And while a microsecond is a
Speaker 1: very small amount of time, I mean we're talking at
Speaker 1: a level that we don't typically experience. We don't think
Speaker 1: of time in microseconds for our day to day lives. However,
Speaker 1: thirty eight microseconds is equal to thirty eight thousand nanoseconds,
Speaker 1: and if you're looking for an accuracy of around twenty
Speaker 1: to thirty nanoseconds, this becomes an enormous problem if we
Speaker 1: don't take it into account. And this brings us background
Speaker 1: to something I mentioned at the top of the show.
Speaker 1: We know that Einstein was right about relativity because we
Speaker 1: have to account for it with technology like GPS. If
Speaker 1: we didn't take it into account, if we didn't factor
Speaker 1: in the effects of relativity, our GPS wouldn't work for
Speaker 1: very long at all. Our technology proves that the science
Speaker 1: is real, or else the tech would fail at what
Speaker 1: it needs to do. Now. In general, I think that's
Speaker 1: a great let us And to take home, there are
Speaker 1: a lot of voices out there that call science into question,
Speaker 1: and some of them are more outlandish than others. A
Speaker 1: person who is passionately and sincerely arguing that the Earth
Speaker 1: is flat seems pretty far out there for me because
Speaker 1: so much of our technology we've built upon and we
Speaker 1: rely upon wouldn't work if that were true. Even if
Speaker 1: you can't experience something directly, such as having a meaningful
Speaker 1: experience of time dilation, a ton of the stuff we
Speaker 1: do experience on a day to day basis is affected
Speaker 1: by this stuff, and it proves the existence and also
Speaker 1: the benefits of having the scientific method. Now give a
Speaker 1: little side note on GPS to kind of wrap this up.
Speaker 1: The original GPS configuration came out of a United States
Speaker 1: Department a defense project. The original purpose was to provide
Speaker 1: positioning information for government and military, but specifically the United
Speaker 1: States and its allies, and for that reason, the U
Speaker 1: S Government wished to restrict access to this technology. The
Speaker 1: general line of thought was that it would be better
Speaker 1: if the U. S didn't allow tech that could, you know,
Speaker 1: give precise coordinates for stuff like military bases or the
Speaker 1: position of various military units to people who didn't belong
Speaker 1: to those divisions. So, as a matter of national security,
Speaker 1: the US guarded this technology civilian receivers. So if you
Speaker 1: went out and you bought a GPS receiver, you could
Speaker 1: get public GPS signals. But the United States was purposefully
Speaker 1: instituting a policy called selective availability, which was an intentional
Speaker 1: degradation of public GPS signals. They were introducing errors on
Speaker 1: purpose so that GPS receivers couldn't get an accurate location.
Speaker 1: It limited accuracy to around fifty meters horizontally in a
Speaker 1: hundred meters vertically, and effectively, that meant that you wouldn't
Speaker 1: really know your precise coordinates. You certainly couldn't use a
Speaker 1: GPS receiver as a turn by turn directions tool because
Speaker 1: you wouldn't even necessarily show up on the right street.
Speaker 1: You wouldn't know if you were approaching your turn or
Speaker 1: if you had already passed it. It was it was
Speaker 1: not practical for that. It was only in the year
Speaker 1: two thousand, when US President Bill Clinton directed the government
Speaker 1: to end selective availability, that civilian GPS receivers could actually
Speaker 1: get accurate data. And that's what made the modern GPS
Speaker 1: receivers and stuff like our phones possible. So before two thousand,
Speaker 1: GPS receivers didn't work very well for the average person,
Speaker 1: but it wasn't because the technology was bad or that
Speaker 1: the science was wrong. It worked that way, or if
Speaker 1: you prefer it, it didn't work properly on purpose. And
Speaker 1: that wraps up this episode about relativity and why it's
Speaker 1: important with technology, and it's not just satellite tech, but
Speaker 1: that's a big one, and it also ends up being
Speaker 1: a big thorn in the side for science fiction authors
Speaker 1: who want to write about interstellar travel at ser than
Speaker 1: light speeds, because you have to start finding alternative explanations
Speaker 1: for how that's possible, because we we've come up against
Speaker 1: these limits that Einstein predicted, and so far his predictions
Speaker 1: have held true. So in order to travel faster than
Speaker 1: the speed of light, you do have to create something
Speaker 1: like warp drive, which theoretically warps space around you, So
Speaker 1: rather than traveling faster than light, you're decreasing the distance
Speaker 1: between your point of origin and your destination. It would
Speaker 1: be kind of like taking a map of the United
Speaker 1: States and saying I'm going to travel from Atlanta to
Speaker 1: Los Angeles, from one coast to the other, but instead
Speaker 1: of drawing a line from Atlanta to l A, you
Speaker 1: just fold the map so that the two dots are
Speaker 1: next to each other, and then you draw a line
Speaker 1: 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 text stuff H s W and I'll
Speaker 1: talk to you again really soon y. Text Stuff is
Speaker 1: an I Heart Radio production. For more podcasts from I
Speaker 1: Heart Radio, visit the i heart Radio app, Apple Podcasts,
Speaker 1: or wherever you listen to your favorite shows.