Speaker 1: Get in touch with technology with tech Stuff from how
Speaker 1: stuff Works dot com. Hey everybody, and welcome to tech Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with
Speaker 1: How Stuff Works in my Heart Radio, and I love
Speaker 1: all things tech. If you're wondering why I said it
Speaker 1: that way, is because I was watching my producer Tari,
Speaker 1: who likes to try and lip sync as I do
Speaker 1: my intro, and sometimes I tried to throw her off
Speaker 1: on purpose. And you, guys, get to enjoy the fruits
Speaker 1: of my labor. You also are going to get to
Speaker 1: enjoy a classic episode of tech Stuff because I'm still
Speaker 1: on vacation and by now I'm sure I'm deep in
Speaker 1: Harry Potter World probably, So this classic episode is all
Speaker 1: about Howlego works. This was the facility that detected gravitational
Speaker 1: waves a few years ago, which was a big, big
Speaker 1: deal in the science world. It went from talking about
Speaker 1: a hypothetical effect to detecting said hypothetical effect does proving
Speaker 1: it's not just hypothetical. So I hope you enjoy this
Speaker 1: classic episode. The Ligo Observatory had picked up a gravitational wave,
Speaker 1: and this was huge news around the world and in
Speaker 1: case you were wondering, what the heck is this news
Speaker 1: all about? How did they pick up that gravitational wave?
Speaker 1: What what exactly is the technology powering our sensors to
Speaker 1: detect this stuff? How does it all work? That's what
Speaker 1: this episode is all about. So this was the very
Speaker 1: first time anyone had been able to measure a gravitational
Speaker 1: wave directly. So today we're gonna talk all about what
Speaker 1: that means and how it happened. Now, to begin with,
Speaker 1: we need to lay some groundwork and to to really
Speaker 1: get an understanding what gravitational waves are. So gravitational waves, ultimately,
Speaker 1: we're one of the predictions made by a certain Albert
Speaker 1: Einstein with this theory of general relativity. So in that theory,
Speaker 1: Einstein presented this idea that our universe is filled with spacetime.
Speaker 1: If you're a fan of science fiction, you have undoubtedly
Speaker 1: come across that term star trek is all about the
Speaker 1: space time continuum, and that you've got to be careful.
Speaker 1: You could rip a hole in the fabric of space time.
Speaker 1: As far as we know, that's not really that possible. Um,
Speaker 1: I mean, black holes could sort of be that maybe,
Speaker 1: But at any rate, spacetime itself. Is this calling it
Speaker 1: stuff is probably the wrong way of putting it. But
Speaker 1: it is like a fabric and mass hangs inside this fabric.
Speaker 1: And by mass, i'm talking about stuff like stars or
Speaker 1: even an entire solar systems or galaxies that hang in
Speaker 1: this fabric, and just like you would see in a
Speaker 1: two dimensional display, Uh, it ends up curving the brick
Speaker 1: around the mass. Uh. We often talk about this in
Speaker 1: terms of a very simple example that's easy to imagine. Uh.
Speaker 1: You get some sort of stretchy material. Often you'll just
Speaker 1: hear someone say, okay, get a trampoline. You've got a trampoline,
Speaker 1: and you put a big, heavy bowling ball on the trampoline.
Speaker 1: So that bowling ball is going to deform the trampoline surface.
Speaker 1: It's no longer going to be straight. It's going to
Speaker 1: end up curving around the bowling ball to some extent,
Speaker 1: creating kind of a dimple where the bowling ball has
Speaker 1: has created this impression inside the trampoline, and as long
Speaker 1: as the bowling ball is there, that impression is going
Speaker 1: to stay. This is sort of the like the way
Speaker 1: spacetime curves around giant masses like stars and black holes,
Speaker 1: things like that. Of course, we have to remember that
Speaker 1: spacetime is actually four dimensional, not a two dimensional thing
Speaker 1: like a trampoline. I mean, I know that trampolines technically
Speaker 1: have three dimensions, but we're really looking at a surface,
Speaker 1: so it's more like a two dimensional plane. In reality,
Speaker 1: In spacetime it's four dimensional because you've got the three
Speaker 1: spatial dimensions plus time, and that is a little difficult
Speaker 1: to get your head around. But that's why we tend
Speaker 1: to look at this two dimensional example. It's a lot
Speaker 1: easier for us to imagine. So let's go a little
Speaker 1: further with that analogy to kind of talk about gravity.
Speaker 1: See Einstein proposed that gravity was a manifestation of this
Speaker 1: curved space time. And if we take that trampoline example,
Speaker 1: Let's say that you have a regular trampoline. You haven't
Speaker 1: put the bowling ball on there yet, so it's a
Speaker 1: nice flat surface, and you have a marble, and you
Speaker 1: roll the marble across the surface of the trampoline. So
Speaker 1: if there's nothing else there, and if the trampoline is level,
Speaker 1: if the surfaces level, the marble should just roll in
Speaker 1: the straight line from one side of the trampoline to
Speaker 1: the other. No problem. Now, let's say you put that big,
Speaker 1: heavy bowling ball on the trampoline. It creates that dimple,
Speaker 1: and then you try and roll the marble across the
Speaker 1: trampoline surface. Well, now that dim bowl is going to
Speaker 1: end up affecting the pathway of the marble. It's going
Speaker 1: to start to spiral inward toward the bowling ball. Ultimately
Speaker 1: it'll end up making contact with the bowling ball. And
Speaker 1: Einstein said, that's essentially what gravity is. It's that you've
Speaker 1: got these large masses that curves spacetime to the extent
Speaker 1: that smaller masses are spiraling inward toward the large mass.
Speaker 1: It's just happening on a scale that's much much, much
Speaker 1: larger than any bowling ball marble example. But that this
Speaker 1: isn't essentially what we see when we see planets orbiting
Speaker 1: a sun, or we see a moon orbiting a planet,
Speaker 1: or we see star systems orbiting a galaxy, you know,
Speaker 1: the center of a galaxy. And uh, it's all because
Speaker 1: of this curve spacetime. Now, all of that already is
Speaker 1: pretty heavy stuff. And keep in mind, there was not
Speaker 1: really any way to directly observe this. It was mostly
Speaker 1: the the uh just just Einstein using logic to work
Speaker 1: all this out and math logic and math, and ultimately
Speaker 1: it fit with what we saw of the universe. But
Speaker 1: we weren't able to test a lot of this. But
Speaker 1: then it gets even more mind blowing because now we
Speaker 1: have to get to gravitational waves. So Einstein said that
Speaker 1: if a mass were large enough and either changed shape
Speaker 1: rapidly enough, or it changed its movement in some way,
Speaker 1: uh really really quickly, it would cause ripples of space
Speaker 1: time to move outward from that event at the speed
Speaker 1: of light. And those ripples are what we call gravitational waves,
Speaker 1: which are different from gravity waves. By the way, I
Speaker 1: have been known to accidentally say gravity waves instead of
Speaker 1: gravitational waves. But the two are different things. A gravity
Speaker 1: wave is a wave that exists because of gravity. In
Speaker 1: other words, it's a physical wave of some sort of
Speaker 1: fluid system, whether it's atmosphere or or water or some
Speaker 1: other liquid. Uh. That's a gravity wave on a planet's surface.
Speaker 1: It's not the same thing as a gravitational wave, which
Speaker 1: is really a ripple of space time and like I said,
Speaker 1: it moves outward from that event at the speed of
Speaker 1: light um and stuff that could cause significant gravitational waves.
Speaker 1: Things that would be big enough for us to potentially
Speaker 1: pick up here on Earth if we had the right equipment,
Speaker 1: would include things like two black holes orbiting or colliding
Speaker 1: with one another, which in fact, that was the event
Speaker 1: that we were able to pick up with the ligo facilities,
Speaker 1: and I'll talk about those in just a bit. But
Speaker 1: there could be other stuff too, like neutron stars orbiting
Speaker 1: one another fast enough would generate gravitational waves, or a
Speaker 1: supernova explosion would create one as well. And each of
Speaker 1: these events give off a huge amount of energy, and
Speaker 1: some of the energy gets converted into making these gravitational waves.
Speaker 1: So one takeaway from this prediction something that Einstein said
Speaker 1: would happen is that an event that produces gravitational waves
Speaker 1: is an event in which energy is being lost, So
Speaker 1: you would expect to see less energy within that system
Speaker 1: afterward than before. Uh. And it would be a hundred
Speaker 1: years from the time of publication of the theory of
Speaker 1: general relativity to the time when scientists announced that they
Speaker 1: had detected a gravitational wave directly. And that's because gravitational
Speaker 1: waves are devilishly difficult to detect. And that's some alliteration
Speaker 1: for you right there. So gravitational waves are invisible. They
Speaker 1: don't emit any sort of electromagnetic radiation, so we can't
Speaker 1: see them. We can't detect them with radio detectors, nothing
Speaker 1: like that. Uh And that makes it pretty tricky to
Speaker 1: figure out where they are. But they do just pass
Speaker 1: through the universe. They don't get absorbed or scattered the
Speaker 1: way electromagnetic radiation does. If you hold up a mirror
Speaker 1: and light hits the mirror, light will bounce off the mirror.
Speaker 1: That's not the case with gravitational waves. They pass right through. Uh.
Speaker 1: So it's a very different thing than electromagnetic radiation. UM.
Speaker 1: And while they're generated from enormous events, the gravitational waves
Speaker 1: aren't very strong. By the time they get to Earth.
Speaker 1: They are pretty weak, so weak that you would need
Speaker 1: an incredibly sensitive tool in order to pick them up.
Speaker 1: And also you have to be searching at the right time,
Speaker 1: because if the event that generated the gravitational waves happened
Speaker 1: a billion years ago, but the location is four billion
Speaker 1: light years from Earth, then we would have to wait
Speaker 1: another three billion years for those gravitational waves to get
Speaker 1: to us, because again, they travel at the speed of light.
Speaker 1: That's their limit, So you have to be at the
Speaker 1: right place at the right time to pick these things
Speaker 1: up and uh, and in some cases you might argue
Speaker 1: that that's incredibly fortuitous. Although to be fair, it looks
Speaker 1: like the events that could generate gravitational waves happened pretty
Speaker 1: frequently throughout the universe. But the universe is huge, so
Speaker 1: if they're happening far away, far enough away, it will
Speaker 1: take a very long time for that information to get
Speaker 1: to us. So before the announcement on February eleven, sixteen,
Speaker 1: scientists had observed phenomena that supported the existence of gravitational waves,
Speaker 1: but we're not direct observations of a gravitational wave. Here's
Speaker 1: an example. A pair of astronomers in Puerto Rico in
Speaker 1: the nineteen seventies noticed that there was a binary pulsar
Speaker 1: system and they went back to the theory of general
Speaker 1: relativity because this was a sort of system that would
Speaker 1: be exactly the type to generate gravitational waves according to
Speaker 1: the predictions from general relativity, and because general relativity predicted, hey,
Speaker 1: if it can create gravitational waves, it's going to lose
Speaker 1: energy over time, they ended up coming up with the
Speaker 1: hypothesis that well, over time, this binary pulsar system should
Speaker 1: start to slow down because it's it's losing energy. It
Speaker 1: can't keep up at the speed it's going. So they
Speaker 1: decided to keep an eye on it. And by keeping
Speaker 1: an eye on it, I mean they continue to observe
Speaker 1: this pulstar system over the course of eight years, and
Speaker 1: by the end of the eight year period, they were
Speaker 1: comparing the findings they were observing to the predictions made
Speaker 1: by general relativity, and they were matching up. It was
Speaker 1: it was unfolding exactly the way Einstein predicted it should
Speaker 1: unfold based upon his theory of general relativity, which is
Speaker 1: incredible when you think about it, that the observations are
Speaker 1: matching up so neatly against the predictions. Uh, you know,
Speaker 1: it just shows how how keenly aware Einstein was of
Speaker 1: how our universe appears to work. Keeping in mind the
Speaker 1: general relativity. While an amazing idea collection of ideas, really
Speaker 1: it doesn't encompass everything we know, right, it doesn't. It
Speaker 1: doesn't really address quantum mechanics, for example, at least not
Speaker 1: in a way that incorporates it with classical physics. But
Speaker 1: based upon what it did cover, it seems like it
Speaker 1: was an incredibly accurate theory. Alright, so this was really
Speaker 1: considered strong but indirect support of gravitational waves because again
Speaker 1: the astronomers didn't observe gravitational waves directly. They couldn't see
Speaker 1: them or detect them, but they could see the effects,
Speaker 1: and again it was matching up with the predictions made
Speaker 1: from general relativity, So it was good indirect evidence that
Speaker 1: gravitational waves existed. Then there was an event a couple
Speaker 1: of years ago that you might have heard about, when
Speaker 1: a team of researchers working on the BICEP two telescope,
Speaker 1: which is in an Antarctica, had announced that they thought
Speaker 1: they might have discovered evidence of gravitational waves that supported
Speaker 1: a hypothesis called cosmic inflation. That's a lot of information
Speaker 1: right there, so let me explain what all that means.
Speaker 1: Cosmic inflation is a hypothesis that relates to the Big
Speaker 1: Bang theory. So with a Big Bang theory, you've got
Speaker 1: this event in which the universe undergoes a period of
Speaker 1: rapid expansion. Cosmic inflation is kind of that rapid expansion
Speaker 1: on steroids. The idea being that well, when we look
Speaker 1: at our universe and we look at the the what
Speaker 1: we can observe, it appears that our observations don't quite
Speaker 1: match up with what we would expect if we had
Speaker 1: uh just steady expansion since the Big Bang. In other words,
Speaker 1: we look at all the information we have available to us,
Speaker 1: and it looks to us that it doesn't quite match up.
Speaker 1: Something's got to be wrong. Well. One possible explanation is
Speaker 1: that surely after the Big Bang, and I'm by shortly,
Speaker 1: I mean tend to the negative thirty six power seconds
Speaker 1: after the Big Bang. So you take a ten, you
Speaker 1: put a decimal point behind the tin, then you move
Speaker 1: the decimal point to the left thirty six times, then
Speaker 1: you put seconds behind that. We're talking a fraction of
Speaker 1: a fraction of a fraction of a second. The universe
Speaker 1: underwent massive expansion, and it only lasted from from that
Speaker 1: point to about ten to the negative thirty third power
Speaker 1: or thirty second power seconds, So again an instant. It's
Speaker 1: it's completely unimaginable, at least for myself, how short an
Speaker 1: amount of time this was. But that's how how quickly
Speaker 1: the universe expanded, uh significantly, and then it slowed, but
Speaker 1: it continued to expand. Now if in fact cosmic inflation
Speaker 1: is correct, it solves a lot of the problems we
Speaker 1: have between the what we observe of today and what
Speaker 1: we believe happened with the Big Bang um and reconciles
Speaker 1: those differences. If cosmic inflation is wrong, then something else
Speaker 1: that we believe is wrong. Right. It means that what
Speaker 1: we observe either isn't representative of reality somehow we're not
Speaker 1: getting a big enough picture to understand it, or that
Speaker 1: the Big Bang theory itself is flawed in some fundamental way.
Speaker 1: We'll be back with more about HOWLEGO works in just
Speaker 1: a second, but first let's take a quick break. So
Speaker 1: the BICEP two team, what they were looking for was
Speaker 1: some evidence of gravitational waves that would have been generated
Speaker 1: during the Big Bang. This would end up supporting the
Speaker 1: cosmic inflation hypothesis, and the way they did this was
Speaker 1: they were looking at the cosmic microwave background or c MB. Now,
Speaker 1: the cosmic microwave background emerged about three thousand years after
Speaker 1: the Big Bang. This was still a period where the
Speaker 1: universe was so dense that light could not pass through it.
Speaker 1: It was dark and dense, but the cosmic microwave background
Speaker 1: formed around that time. And the hypothesis stated, well, gravitational
Speaker 1: waves would have affected the cosmic microwave background, polarizing some
Speaker 1: of those uh, some of those particles really particles, but
Speaker 1: some of the energy polarizing some of the cosmic microwave
Speaker 1: background in such a way that if you were to
Speaker 1: observe it, you could see the effect of a gravitational
Speaker 1: wave passing through the CMB. Uh. And then as the
Speaker 1: universe expand expanded rather uh, that that mark would also expand.
Speaker 1: It's kind of like imagine leaving a fingerprint on some
Speaker 1: sort of stretchy material and then stretching that material out.
Speaker 1: The fingerprint is still there. It's deformed, but still there.
Speaker 1: That's what the Bicept two team was looking for, was
Speaker 1: this pattern in the CMB that would indicate that gravitational
Speaker 1: waves from the Big Bang had passed through, and if
Speaker 1: they found that, that would be a huge support for
Speaker 1: cosmic inflation. And in the spring often they announced that
Speaker 1: they believed they had found such evidence, and they also
Speaker 1: invited other researchers to take a look at their data
Speaker 1: and see if it was verifiable or maybe they overlooked something.
Speaker 1: And in the fall often another team said we're sorry,
Speaker 1: but it looks to us like space dust might have
Speaker 1: created a false positive that what you thought it was
Speaker 1: the polarized CMB that you had been looking for was
Speaker 1: actually just space dust that's not actually part of the CMB.
Speaker 1: And uh so that ended up kind of putting the
Speaker 1: dampener on the whole celebration of finding gravitational waves to
Speaker 1: support cosmic inflation. But even if it was completely verified,
Speaker 1: even if BICEP two had irrefutable evidence that they had
Speaker 1: found the presence of gravitational waves through a uh you know,
Speaker 1: the way it affected the CNB, even then that's not
Speaker 1: direct detection. It's still indirect. You're looking at the way
Speaker 1: it's affected something else. So uh, you know, again, we're
Speaker 1: still not discovering one. And and part of that is
Speaker 1: that BICEP two is a telescope. It's looking at through
Speaker 1: the electromagnetic spectrum. And again, gravitational waves don't show up
Speaker 1: that way. So no telescope would help you find a
Speaker 1: gravitational wave directly. You might be able to find how
Speaker 1: it affected something else, but not the wave itself. Now
Speaker 1: that's not the case with the ligo observatories. Actually it's
Speaker 1: technically one observatory, but it has four different facilities, two
Speaker 1: detectors UH and to research facilities that are all part
Speaker 1: of the LIGO Observatory. LEGO itself is an acronym and
Speaker 1: it stands for Laser Interferometer Gravitational Wave Observatory. So it's
Speaker 1: a pair of giant detectors built on the surface of
Speaker 1: the Earth. One is located in Hanford, Washington, the other
Speaker 1: is in Livingstone, Louisiana. Now they're about just a little
Speaker 1: under two thousand miles apart, or just over three thousand
Speaker 1: kilometers apart from each other, and that's really important. I'll
Speaker 1: explain why in a little bit. So to understand how
Speaker 1: they work, we also have to talk about something else
Speaker 1: that gravitational waves do as they pass through space. They
Speaker 1: stretch and compress space itself. So again, if you were
Speaker 1: to if you were to take a piece of elastic,
Speaker 1: Let's say you've got a rubber band, a nice thick
Speaker 1: rubber band, and you cut it so that it's just
Speaker 1: one strip. When you pull on that rubber band, it
Speaker 1: stretches along the line where you're applying force, So it
Speaker 1: stretches in that direction, in the perpendicular direction, ninety degrees
Speaker 1: from where you're pulling it compresses, it gets more narrow,
Speaker 1: and then when you let it return to its normal shape,
Speaker 1: it gets you know, the long part ends up getting
Speaker 1: shorter and the narrow part ends of getting wider as
Speaker 1: a result, gravitational waves do this to reality. They do
Speaker 1: this to actual space. They stretch and compress, and it
Speaker 1: happens several times as the wave oscillates through. Really I
Speaker 1: should just say as the wave passes through rather than oscillates. Uh,
Speaker 1: the distortion oscillates, but the wave passes through. So that
Speaker 1: means the actual distance changes between two points as the
Speaker 1: gravitational wave passes through that area. So if we were
Speaker 1: to magnify this effect, and I mean magnify it to
Speaker 1: a ludicrous degree, you would be able to see it.
Speaker 1: You would actually be able to witness this. You could
Speaker 1: stand ten feet away from someone else and when the
Speaker 1: gravitational wave passes through, it would make it look like
Speaker 1: the two of you suddenly got further away and then
Speaker 1: closer to each other, and then further away and closer
Speaker 1: to each other, even though you haven't moved anywhere, because
Speaker 1: the distance itself is stretching and compressing. So why don't
Speaker 1: we see that? I mean, if the celestial events that
Speaker 1: produce gravitational waves happen on the order of something like
Speaker 1: every fifteen minutes. Why are we all noticing this whibbly
Speaker 1: wobbly effect. Well, it's because the actual distortion that happens
Speaker 1: here on Earth is much much much smaller in magnitude,
Speaker 1: so much more, so much smaller that it's difficult to
Speaker 1: even explain. But if you were to have a supernova
Speaker 1: explode in the Milky Way galaxy, in our galaxy, the
Speaker 1: gravitational waves generated by that explosion would maybe be powerful
Speaker 1: enough to distort the distance between the Earth and the
Speaker 1: Sun by about the diameter of a hydrogen atom, so
Speaker 1: not noticeable to any degree, not at least to human senses.
Speaker 1: So if you were to even go on a smaller scale,
Speaker 1: let's say that you you pick two points that are
Speaker 1: a kilometer apart here on the surface of the Earth,
Speaker 1: the amount of distortion would be equivalent to a few
Speaker 1: thousands of the diameter of a proton. So you're talking
Speaker 1: about a sub atomic particle, and just a tiny, tiny,
Speaker 1: tiny fraction of that sub atomic particles diameter would be
Speaker 1: the amount of distortion that would happen across a kilometer
Speaker 1: worth of distance here on Earth. Again, that means it's
Speaker 1: so small that it's incredibly difficult to detect, so much
Speaker 1: so that Einstein himself I was pretty sure we would
Speaker 1: never be able to directly detect gravitational waves because he
Speaker 1: could not imagine a system that would be sensitive enough
Speaker 1: to pick up such a minute change, a distortion that's
Speaker 1: happening so quickly because it's a fraction of a second,
Speaker 1: and it's so small as to be unnoticeable. So the
Speaker 1: other problem here is not just that it's such a
Speaker 1: very tiny effect that lasts a short amount of time.
Speaker 1: It's also that a lot of other stuff could create
Speaker 1: false positives. You can have incredibly sensitive instrumentation, but if
Speaker 1: that instrument is really really sensitive, any sort of interference
Speaker 1: could set off and you could end up getting false readings.
Speaker 1: So a change in air pressure or temperature, or seismic activity,
Speaker 1: even a heavy truck driving nearby could set off false results.
Speaker 1: So you have to come up with a really clever
Speaker 1: way to measure distortion, to limit vibration, and to eliminate
Speaker 1: the chance that it was a false positive. And Lego
Speaker 1: is the answer to all of that. So the Lego
Speaker 1: Observatory is actually the result of decades of collaborative work
Speaker 1: among different scientific research centers and international bodies and universities,
Speaker 1: and all started back in nineteen seventy nine. That's when
Speaker 1: the National Science Foundation approved funds for cal Tech and
Speaker 1: m i T to develop laser interferometer research and development.
Speaker 1: And a few years later, in nineteen eighty three, Caltech
Speaker 1: and m i T submitted a proposal for a kilometer
Speaker 1: scale detector. Uh but keep in mind, all right, so
Speaker 1: nineteen seventy nine you get the funding for R and
Speaker 1: D three, there's the submission of a proposal for a
Speaker 1: kilometer scale detector. There wouldn't be approval for a detector
Speaker 1: until nineteen nine, so almost a decade later, and which
Speaker 1: turns out was probably okay, because we really didn't have
Speaker 1: the technological ability to detect things on a scale small
Speaker 1: enough to register a gravitational wave the first place. But
Speaker 1: but still, you know, a decade's delay before you even
Speaker 1: get approval is still pretty rough. Construction didn't begin until
Speaker 1: the inauguration of the Ligo Observatory took place in nineteen
Speaker 1: but even then that didn't mean that the the observatory
Speaker 1: was online collecting data. It didn't do that until two
Speaker 1: thousand two, and here's the kicker. Eventually scientists came to
Speaker 1: the conclusion that this Ligo observatory was not sensitive enough
Speaker 1: to detect gravitational waves. That despite the fact that it
Speaker 1: was this large UH detector or pair of large detectors,
Speaker 1: actually because again one in Louisiana one in Washington, it
Speaker 1: wasn't sensitive enough to be effective. So it was not
Speaker 1: quite back to the drawing board. But it didn't mean
Speaker 1: that they had to think about how they would upgrade
Speaker 1: these facilities so that they could be sensitive and off
Speaker 1: to pick up a gravitational wave. So in two Ligo
Speaker 1: went offline to undergo a big overhaul, and it took
Speaker 1: four years of construction and testing to get it into
Speaker 1: shape and another year to set it up for new observations,
Speaker 1: which means that it wasn't until twenty fifteen that it
Speaker 1: was ready to come back online. By now it was
Speaker 1: called the Advanced Ligo Observatory, and it began collecting data
Speaker 1: in September. Literally days after it had come online, it
Speaker 1: picked up a gravitational wave. So that's pretty phenomenal that
Speaker 1: just a couple of days, just a few days really
Speaker 1: after it had been turned on again in we got
Speaker 1: a hit. So it was incredibly exciting. So how did
Speaker 1: this happen? How does it actually work? Well, we have
Speaker 1: to take a look at what interferometers are all about.
Speaker 1: An interferometer uses a technique in which electromagnetic wave are
Speaker 1: superimposed on one another in order to get information. Now,
Speaker 1: Ligo does this with a laser beam because it's a
Speaker 1: laser interferometer, and the laser beam gets shot through a
Speaker 1: beam splitter and the beams, the two beams that result
Speaker 1: go down too long vacuum tubes, so both of the
Speaker 1: Lego detectors are in an l shape. So you've got
Speaker 1: these long, long vacuum tubes that extend two and a
Speaker 1: half miles or about four kilometers out from the crux
Speaker 1: from the the angle where they meet up and each
Speaker 1: one is you know, they're both the same length. They
Speaker 1: have to be exactly the same length. And the way
Speaker 1: this works is that, uh, kind of behind the crux,
Speaker 1: you've got a laser that shoots out a beam of
Speaker 1: light to a beam splitter. The splitter does exactly what
Speaker 1: it sounds like it does. It splits the beam into
Speaker 1: two separate beams with with alternating canceling wavelengths. I guess
Speaker 1: I should say, so the the troughs and peaks on
Speaker 1: one match up with the peaks and troughs of the other.
Speaker 1: That's really important when we get a little further down
Speaker 1: the line here. So one of those two beams goes
Speaker 1: down one branch of this l shaped detector. The other
Speaker 1: beam goes down the other branch. And keep in mind,
Speaker 1: like I said, both of these branches are exactly the
Speaker 1: same length two and a half miles or four kilometers.
Speaker 1: When the laser gets to the end, they hit a mirror.
Speaker 1: Each beam hits a mirror, they come back to the
Speaker 1: point of origin. And because the two laser beams have
Speaker 1: these uh these counteracting wave lengths, they cancel each other out.
Speaker 1: So the peaks on one cancel out the troughs of
Speaker 1: the other, and vice versa. That means that no light
Speaker 1: gets emitted through the system. And it's important because there's
Speaker 1: actually a light detector that's part of this system as well.
Speaker 1: It's looking for any sign of laser light, because a
Speaker 1: sign of laser light would say that something has changed somehow.
Speaker 1: The distances between these or the distances represented by these
Speaker 1: two vacuum tubes has changed and that would be indicative
Speaker 1: of an event like a gravitational wave moving through. So
Speaker 1: if any light shines through, you know something has happened. Essentially,
Speaker 1: it says that there's a mismatch in the lengths of
Speaker 1: the vacuum tubes themselves. So when a gravitational wave passes through,
Speaker 1: one vacuum tube will get shorter while the other gets longer.
Speaker 1: And that's because the two tubes are offset by ninety degrees,
Speaker 1: so one is going to be along one side of
Speaker 1: the wave and that will lengthen the other will be
Speaker 1: along uh will be perpendicular to that and will shorten
Speaker 1: as a result. And this means that the lasers will
Speaker 1: have different distance says to travel down, So the laser
Speaker 1: traveling the shorter distance takes less time to get back
Speaker 1: to the crux. The laser going down the longer distance
Speaker 1: takes more time. And even though this is only happening
Speaker 1: within a fraction of a second, it's long enough for
Speaker 1: us to be able to detect the difference. And it
Speaker 1: also means that those wave lengths don't match up anymore,
Speaker 1: they don't cancel each other out anymore, so some of
Speaker 1: that laser light gets admitted to the light detector, which
Speaker 1: then indicates what's going on. It knows which which one
Speaker 1: of the branches was short versus long, and knows how
Speaker 1: long it happened, and knows how much it oscillated back
Speaker 1: and forth, because obviously this is continuing as these as
Speaker 1: the gravitational wave moves through, So you collect a lot
Speaker 1: of data in a short amount of time. And we're
Speaker 1: talking like teeny tiny slices of a second as we're
Speaker 1: getting all this information, which is pretty incredible. You guys,
Speaker 1: this topic is heavy because of gravitational lads, get it.
Speaker 1: So let's take a quick break. So once you get
Speaker 1: all that data, you can then analyze it. Actually, more importantly,
Speaker 1: before you analyze it, you have to verify it. Now.
Speaker 1: This is why it's important that there are two detectors,
Speaker 1: and it's also important that they are so far apart,
Speaker 1: like three tho kilometers apart from each other. That's because
Speaker 1: if you get a blip on one of them, if
Speaker 1: it's a true gravitational wave, you should also get a
Speaker 1: blip on the other one. And because gravitational waves move
Speaker 1: at the speed of light, there should be a slight
Speaker 1: difference in time when both detectors pick up on this
Speaker 1: gravitational wave somewhere right around ten milliseconds or less. In
Speaker 1: the case of the one that was detected back in
Speaker 1: the fall of two thousand fifteen but not announced until
Speaker 1: two thousand sixteen, it hit the Louisiana detector first, and
Speaker 1: seven milliseconds later it hit the Washington detector, So that
Speaker 1: was indicative of something like a gravitational wave as opposed
Speaker 1: to some local event that would have caused interference and
Speaker 1: created a false positive. If an earthquake had happened in Washington,
Speaker 1: then the facility may have may have picked something up,
Speaker 1: but you wouldn't expect to see it in Louisiana because
Speaker 1: it was a localized event. Same thing is true if
Speaker 1: something had happened in Louisiana. So by seeing it happen
Speaker 1: at both within this ten millisecond time frame meant that
Speaker 1: it was a very good candidate for a gravitational wave
Speaker 1: passing through. And that's exactly what happened. Um. It was
Speaker 1: a home run in the first ending of the game,
Speaker 1: or even really the first ad bat of the game.
Speaker 1: It's like your first player steps up on the first
Speaker 1: day of baseball and knocks a home run, and that
Speaker 1: defines the moment the season. Really, that's that's the equivalent
Speaker 1: of what we saw here on a scientific thick basis.
Speaker 1: So the the The other thing I want to talk
Speaker 1: about was how LEGO tries to minimize the possibility of
Speaker 1: detecting a false positive in the first place. So, yeah,
Speaker 1: false positives are something that that they worry about, and
Speaker 1: the fact that there are two detectors helps minimize that.
Speaker 1: But even so, you want to eliminate the possibility of
Speaker 1: a false positive so that you're not constantly sifting through
Speaker 1: noise looking for a signal. Do you want to minimize
Speaker 1: noise as much as possible. So Lego does this through
Speaker 1: using combinations of active and passive UH vibration reduction systems.
Speaker 1: One thing that they do is they remove the air
Speaker 1: from the tubes. That is why their vacuum tubes. They
Speaker 1: remove the air for two reasons. One, they don't want
Speaker 1: any sound passing through the chambers. Sound could possibly interfere
Speaker 1: with the measurements. Sound would impact the mirrors, and even
Speaker 1: a small impact would be enough to cause a problem
Speaker 1: when you're measuring this laser. For one thing, they're looking
Speaker 1: at distances. When they're measuring the changes between the two branches.
Speaker 1: You know, I mentioned that one's getting longer, one's getting smaller.
Speaker 1: The distances they're looking at are very very tiny. We're
Speaker 1: talking ten to the negative nineteenth power meters. So again
Speaker 1: you take the number ten, you move a decimal place
Speaker 1: nineteen times to the left of that, and you put
Speaker 1: meters at the end. That's the distance that these lasers
Speaker 1: are are measuring the distortion and distance. So it's very
Speaker 1: very very tiny, and something as simple as sound could
Speaker 1: change that. So you can't have any sound in these
Speaker 1: vacuum tubes. You've got to get the air out. Also,
Speaker 1: air can absorb and uh and and scatter laser light,
Speaker 1: which would interfere with the experiment as well, So you've
Speaker 1: got to get air out now dawn to the vibration
Speaker 1: reduction systems. So the active isolation system is meant to
Speaker 1: weed out the majority of vibration, and it's active because
Speaker 1: it is actively working against any vibration it encounters. You've
Speaker 1: got sensors that detect vibration, they send commands to force
Speaker 1: actuators that move in opposition to the vibration. So it's
Speaker 1: kind of like noise canceling headphones. If you if you
Speaker 1: put on a pair of noise canceling headphones. What they're
Speaker 1: supposed to do is pick up any incoming sound and
Speaker 1: then generate sound waves that are in direct opposition of
Speaker 1: the incoming sound, so that you get a cancelation effect.
Speaker 1: That's the same thing that these active systems are trying
Speaker 1: to do at Ligo, except instead of it just being sound,
Speaker 1: it's really any vibration. Although I guess you could argue
Speaker 1: that any vibration really is sound, so it's kind of
Speaker 1: a moot point. But anyway, they're actively trying to counteract
Speaker 1: that vibration. But then you've got the passive system. This
Speaker 1: is the suspension system for the mirrors, and this is
Speaker 1: you know, the next step. So you've eliminated a huge
Speaker 1: percentage of the vibration at this point, but that's not
Speaker 1: good enough. You need to eliminate as much as close
Speaker 1: to the vibration as you possibly can. So next we
Speaker 1: look at the suspension system of Ligos mirrors, and they
Speaker 1: are at the base of a four pendulum system. Meaning
Speaker 1: imagine you've got a string and it ends in a
Speaker 1: in a pendulum. A weight a mass of some sort,
Speaker 1: and it has to be a mass of significant size,
Speaker 1: so that it will it'll um resist moving. It's the
Speaker 1: law of inertia, you know. UH. An object at rest
Speaker 1: tends to stay at rest, so it will end up
Speaker 1: absorbing a lot of vibration and minimizing it on the
Speaker 1: other end. So you've got that first pendulum, that's pendulum
Speaker 1: number one. From that you suspend angelum number two. So
Speaker 1: already you're getting fewer vibrations because pendulum number one is
Speaker 1: picking them up. What vibrations do manage to pass through
Speaker 1: start to get picked up by pendulum number two, and
Speaker 1: again the law of inertia means that it will dampen
Speaker 1: a lot of that vibration. Then you've got pendulum number three,
Speaker 1: and then beneath that you finally have the mirror, which
Speaker 1: is forts or about eighty eight pounds worth of mirror. UH.
Speaker 1: And hopefully after the active impassive systems have all taken
Speaker 1: care of the vibration, nothing else is getting to that mirror.
Speaker 1: By the way, you can actually test this out yourself,
Speaker 1: if you like, by uh, getting four strings that are
Speaker 1: all equal length, and some washers, some nice heavy washers.
Speaker 1: Tie a washer at the end of the string of
Speaker 1: the first string. Then tie a washer um so that
Speaker 1: one end of the string connects to washer number one.
Speaker 1: One end of the string connects to washer number two,
Speaker 1: and so on and so fourth. And if you hold
Speaker 1: it up and you start shaking your hand holding the string,
Speaker 1: you'll notice that the washer at the top moves more
Speaker 1: than the second washer, which moves more than the third,
Speaker 1: and by the time you get down to the fourth one,
Speaker 1: it's not moving much at all because it's been the
Speaker 1: vibrations have been dampened by the previous pendulums, and that's
Speaker 1: the principle of this passive system, So that helps eliminate
Speaker 1: a lot of that vibration. Uh, without those dampening systems
Speaker 1: in place, the two ligo detectors would be picking up
Speaker 1: a lot of noise, and since we're still not really
Speaker 1: sure how often gravitational waves passed through the Earth, that
Speaker 1: would be a problem. Now. Between two thousand and two
Speaker 1: and two thousand and ten, with the early version of LEGO,
Speaker 1: they didn't pick up any gravitational waves at all, which
Speaker 1: we think is because the detectors weren't sensitive enough. We
Speaker 1: think that's the reason, but an alternative reason could be
Speaker 1: that gravitational waves aren't as frequent as we think they are.
Speaker 1: That they don't pass through the Earth as frequently as
Speaker 1: we might otherwise believe. However, the opposite could be true.
Speaker 1: We could have way more gravitational waves passing through Earth
Speaker 1: than we had anticipated. Some of them may be so
Speaker 1: faint that even this advanced LIGO system cannot pick it up.
Speaker 1: There are already plans to upgrade LIGO again, and there
Speaker 1: are other ligo observatory systems that will that are in
Speaker 1: development now that will also listening for gravitational waves. And
Speaker 1: listen tends to be the way most people refer to it,
Speaker 1: like you're listening for this universal vibration moving through the Earth.
Speaker 1: So because it was only a few days after they
Speaker 1: came online, a lot of people are thinking that gravitational
Speaker 1: waves are probably fairly common. Otherwise, it was just extraordinarily
Speaker 1: lucky that we picked it up just days or the
Speaker 1: observatory was online again. The one that we did pick
Speaker 1: up was one point three billion light years away, which
Speaker 1: means that the event happened one point three billion years ago.
Speaker 1: That event being two black holes colliding with one another
Speaker 1: to form a solitary black hole mass in the UH.
Speaker 1: In the process, it vaporized about three solar masses worth
Speaker 1: of of mass I guess, which is a huge amount
Speaker 1: to think about being converted into energy, and the gravitational
Speaker 1: waves emanated from there at the speed of light, so
Speaker 1: one point three billion years later, Earth, which was one
Speaker 1: point three billion light years away, picked him up. So
Speaker 1: in a way, it was incredibly lucky. But if this
Speaker 1: happens more frequently than we we originally believed, we might
Speaker 1: see that this is not an uncommon event. It's very
Speaker 1: possible that there are things we cannot see in the universe,
Speaker 1: ears that create gravitational waves. So in other words, it's
Speaker 1: stuff that does not give off electromagnetic radiation at all,
Speaker 1: but it does create gravitational waves, meaning that we now
Speaker 1: have the capacity to detect things that otherwise would have
Speaker 1: remained completely undetectable by us. So one of the many
Speaker 1: reasons why this discovery is so exciting it opens up
Speaker 1: brand new science. It creates a new discipline of science,
Speaker 1: gravitational astronomy, which can really get going now because it's
Speaker 1: not that different from when the telescope was invented. Before
Speaker 1: the telescope, astronomy was pretty limited. You could map out
Speaker 1: astrological bodies when you were way back in the day
Speaker 1: before the science of astronomy had really gotten going. Once
Speaker 1: you started figuring out the difference between mythology and science,
Speaker 1: then astronomy really takes over. You could map out where
Speaker 1: these different bodies go, You could figure out which ones
Speaker 1: are must be planets versus stars, but you couldn't really
Speaker 1: gather a lot more information than that. You can still
Speaker 1: get an impressive amount of data just from observing with
Speaker 1: the naked eye, but the telescope opened up a whole
Speaker 1: new world of study, and this gravitational wave detector system
Speaker 1: has opened up a similar, all new world that was
Speaker 1: not accessible by us until this year real really late,
Speaker 1: last year late. So we might end up discovering things
Speaker 1: that we've never been able to observe before. Will also
Speaker 1: likely be able to study all sorts of cool stuff,
Speaker 1: like how fast is the universe expanding, how much dark
Speaker 1: energy is in our universe. We might learn more about
Speaker 1: black holes already. The gravitational wave detected by the by
Speaker 1: ligo has given us the strongest direct evidence of black holes. Um,
Speaker 1: I guess I should say indirect evidence because it's the
Speaker 1: gravity waves generated by the black holes. But uh, not
Speaker 1: that we ever doubted the existence of black holes. But
Speaker 1: this is yet more evidence and supported them. So it's
Speaker 1: really an exciting time. We could end up learning all
Speaker 1: sorts of stuff, stuff that we can't even anticipate right now,
Speaker 1: and that's why it's such a big deal. I also
Speaker 1: think that LEGO is just an incredibly elegant way of
Speaker 1: detecting something that otherwise is impossible for us to see
Speaker 1: or feel or experience. And it's incredibly simple, at least
Speaker 1: on the principle of it. The technology itself is very
Speaker 1: complicated because it has to be so sensitive to detect
Speaker 1: these very tiny changes in distance and time, but the
Speaker 1: principle behind it is elegant, and I mean, you don't
Speaker 1: get much more simple than a ninety degree angle. That's
Speaker 1: pretty bare bones there, but a very clever way of
Speaker 1: detecting something that I Stein believed was going to be
Speaker 1: beyond our ability to ever experience. So now we have
Speaker 1: a revolutionary new way to examine the universe. We have
Speaker 1: no way of knowing what sort of stuff we might
Speaker 1: learn as a result, which is incredibly exciting. And it's
Speaker 1: all due to some lasers, some beam splitters, and some mirrors,
Speaker 1: and since we're already looking at lots of different organizations
Speaker 1: building their own ligo observatories and also increasing the capacity
Speaker 1: or or at least the sensitivity of the current ligo system.
Speaker 1: Who knows what we're going to see next. And that
Speaker 1: wraps up this classic episode of tech Stuff Howlego Works.
Speaker 1: I hope you guys enjoyed it. If you have any
Speaker 1: suggestions for future episodes of tech Stuff, send me an email.
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