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