Archives for July 2016

>> Here we go!
[? Blackalicious rapping Chemical Calisthenics ?]
? Neutron, proton, mass defect, lyrical oxidation, yo irrelevant
? Mass spectrograph, pure electron volt, atomic energy erupting
? As I get all open on betatron, gamma rays thermo cracking
? Cyclotron and any and every mic
? You’re on trans iridium, if you’re always uranium
? Molecules, spontaneous combustion, pow
? Law of de-fi-nite pro-por-tion, gain-ing weight
? I’m every element around

>> Regina Barber DeGraaff: Welcome to Spark Science where we explore stories of human curiosity. I’m Regina Barber DeGraaff, Astrophysicist and proud Washingtonian. For today’s episode, we took a tour of the LIGO observatory alongside Western Washington University students in Hanford, Washington.
LIGO stands for Laser Interferometer Gravitational-Wave Observatory. On September 14th, 2015, the LIGO sites at Hanford and Livingston, Louisiana simultaneously detected gravitational waves. Before we go any further, let’s listen to a description of gravitational waves from Piled Higher and Deeper Comics, also known as PHD Comics.
>> What is a gravitational wave? It’s a ripple in the fabric of space and time. Imagine that space is a giant sheet of rubber. Things that have mass cause that rubber sheet to bend like a bowling ball on a trampoline. The more mass, the more that space gets bent and distorted by gravity.
Gravitational waves are produced whenever masses accelerate changing the distortion of space. Everything with mass and/or energy can make gravitational waves. Now, gravity is very weak in the scale of other forces in the universe so you need something really, really massive moving very, very fast to make the big ripples that we can detect.
How would you observe a ripple in space? If the space between you and me stretched or compressed, we wouldn’t notice it if we had make marks on our metaphorical rubber sheet because these marks would also get stretched further apart. But there is one ruler that doesn’t get stretched, one made using the speed of light. If the space between two points gets stretched, then light will take longer to go from one point to the other. And, if the space gets squeezed, light takes less time to cross the two points.
This is where the LIGO experiment comes in. It has four kilometer long tunnels and uses lasers to measure the changes in the distance between the ends of the tunnels. When a gravitational wave comes through, it stretches space in one direction and squeezes space in the other direction.
By measuring the interference of the lasers as they bounce between the different points, physicists can measure very precisely whether the space in between has stretched or compressed and the precision needed is incredible. To detect a gravitational wave, you need to be able to tell when something changes in length by a few parts in 10 to the 23. The effect of a gravitational wave is so miniscule and easily confused with random noise, you need a smart data analysis technique.
>> Regina Barber DeGraaff: LIGO has been trying to make an instrument that is sensitive enough to detect gravitational waves since the 1970s. As a former student and faculty member of various universities in Washington, I have seen scientists struggle to work towards detection for decades. Once the latest detection upgrade happened in 2015, dreams became a reality.
At the end of our tour, Spark Science intern, Lia Cook, will ask questions from our listeners. If there are any questions you would like us to ask our guests on future shows, please follow us on our SparkScienceNow Facebook and Twitter accounts for upcoming show information and send us your questions. Without further ado, let’s listen to Dale Ingram, the Education and Outreach Coordinator at LIGO – Hanford Observatory.
>> Dale Ingram: This — so you can see the initial LIGO optics sitting on the table over there. That’s a single wire loop suspension and they turn the stocks in so that the mirror is basically mobilized in there. So when the 5th graders that visit us bump the table, it doesn’t knock the mirror off the wire.
This is where our suspension technology has gone in terms of doing the upgrade where you don’t just use a single stage suspension, but this is a four-stage suspension. And this one, which we use in four places, the four vacuum chambers that form the boundaries of the long arms, this one is two layers deep also. You have a main chain of masses hanging in the front and then a reaction chain of four more masses hanging in the rear. And that’s so you can isolate both parts of it actuation system that puts the corrective forces on the masses.
So the way — the primary technology that LIGO uses to put forces on the masses to keep them sitting still and to keep them at the proper angle is to put — well, like that mirror over there. The mirror has little, tiny permanent magnets glued onto it in five places where the magnet is in close proximity to a coil of wire. And then you electrify the coil to magnetize the coil and now you can put a magnetic force on the suspended mass. And that’s most of what you’ve got going on in here. But, unlike the initial LIGO version where the — what we call the voice coils, those copper coils — were mounted right to the cage and so they weren’t isolated from any vibrations that would be making the cage hum. Here, you’re able to mount the voice coils on suspended masses and then have those communicate with the permanent magnets that are also on suspended masses.
So it gives you a quieter actuation strategy and then you get the benefit of the additional passive isolation because, instead of just having a single pendulum, you’ve got this cascade of pendulums.
So this was a prototype. They never put a mirror in it. In the production units, you would have the mirror down at the bottom and then this would be a glass mass also and then these glass fibers would connect the stage three glass mass to the stage four mirror and suspending the mirror by glass from glass gives you better control of the thermal noise that’s one of our three principle noise sources across our frequency spectrum.
But you can tell, from the visual comparison, that this one is about 10 times bigger than that one. It’s 10 times heavier. It takes up 10 times more room in your computing system because of all the additional inputs and outputs that you’ve got to the thing. It’s much harder to construct so that you can get the masses aligned properly. It’s more challenging to test. It’s more challenging to install. But we wouldn’t have seen that black hole signal without it I don’t think.
So these were put together — we’re going to walk by this middle building over here in a few moments. That’s where these structures were assembled after the parts were shipped to the site from — the suspension parts mainly came from the UK . And then all the parts have to get cleaned and baked individually and then hermetically sealed in wrapping, and then taken over to the assembly building. And then, in clean rooms, in bunny suits, people who bear the odor of mechanical and electrical engineers did most of the assembly work. And then the testing. And then you install it. Get it all lined up. And then people like Sheela go into the control room and start pushing buttons to make it behave properly.
OK. Out we go. We’re going to be outside for a little while. We’ll stop in several locations and I’ll prattle at you a bit. And then we’re going to go back inside the main building.
>> Ladies and gentlemen, we have detected gravitational waves. We did it!
[Applause]
[? A Capella Science singing LIGO Feel that Space ?]

? And I know they could be testing me
? The data might be wrong
? A preplanned concocted recipe
? And played up all along
? But at least my graphs are beautiful
? With sigma 5.1
? This I know
? This I know

>> Regina Barber DeGraaff: Welcome back to Spark Science where we are on location at LIGO in Hanford, Washington.
>> Dale Ingram: So — especially in the upgrade, you’ve got this really high-quality vibration isolation in there that’s intended to make the detector just feel like it’s freely floating in outer space and not subject to a lot of local forces that are sloshing it around. Nonetheless, just to not complicate life any further than it needs to be complicated, we try to take some pains to minimize the human generated seismic noise that would exist because you’ve got people and vehicles moving around the site.
So this — these heat pumps keep the room cool that’s in the middle of the building that contains the Beowulf cluster, one of the clusters that we us in LIGO for data analysis. So there’s a room pretty much dead center in here that has about 250 rack-mounted PCs all etherneted together and then a bunch of servers and redundant disk storage and so forth. And with — if somebody logs onto the cluster and really taxes it pretty hard with a big analysis job, then you really belch out a lot of heat in there. So there’s a total of something like 36 tons of air conditioning in the room to keep the room cool. And then this is part of the circulation system for that.
But you can see down at the feet of these things, they’re on springs. So all of the rotating machinery that we mount — and that’s heat pumps, other HVAC stuff, compressors, etc. etc. — we have to mechanically isolate all of that from the ground just to try and keep the seismic signal in the ground a little bit cleaner.
We do a lot of school field trips here and especially when the weather gets warmer, the children get tired of the fact that we make them walk so much [laughing]. And that’s — you know, if you ask the question, “Why is this building 800 feet away from that one?” I’m told — you all wonder, you know, after a few years, what becomes LIGO urban myth — they sent Auto out of that building and they asked him to walk every 100 feet and stop and start jumping up and down. And they were looking at him both on the seismometer data that you can see in the control room and then the interferometer also.
And, by the time he got over here, he was jumping up and down and they couldn’t see him. They said, “OK, Ado, you can put the building there.”
[Laughter]
So that gives a nice before, you know, when the garbage truck comes on Tuesday morning, which is quite heavy and it throws the dumpster contents over its head and makes a little earthquake. That’s confined to this area and that just helps us keep the ground cleaner over there.
We don’t have the luxury of being as much spread out at Livingston. The equivalent of this building is much closer to the corner station. But they have some different rules for traffic down there and it ends up working OK.
>> I have a question. I know it gets windy out here. Does the vibrations from the wind affect the buildings?
>> Dale Ingram: Yes. Yes.
[Laughter]
So what do I tell them, Sheela? It’s like above 25 miles an hour then we’re in trouble? What’s the threshold these days?
>> Yeah. If it’s above — if it’s above 20 you can definitely see it.
>> Above 20 [laughing].
>> But we can still operate as long as there’s no storms on the ocean. Like if there’s waves on the ocean [inaudible]. We can’t handle both [inaudible] at the same time. So if we had just wind of 25, we’d probably be OK. But 40 or something, it’s over.
>> We’re done for the day. Time to wrap it up.
>> Dale Ingram: So the three natural issues that, in the current era, would be the most likely to cost us running time would be seismic waves from distant large earthquakes, or close large earthquakes if you had the misfortune of having one close — but like just yesterday there was a magnitude six and a half or seven that went off somewhere down by Mexico. And something like that would keep us down probably for a couple hours because you get this stuff coming through at about a 10th of a hertz. That just makes it — we can’t put enough force on the meters using the actuators to obligate them to sit still in the face of all the slosh from the seismic waves. So we’ll — we just can’t get the detector going.
High winds the same way. They push on the buildings. That tilts the buildings and tilts the ground underneath the buildings and then tilts the chamber that the mirror is sitting in. And then the ocean wave affect that Sheela mentioned, if that’s the — if there’s no earthquakes going off and the wind’s not blowing hard, then usually we can win the battle with the seismicity from the ocean waves. But then, if you get wind on top of that, it’s — things get too shaky and we might be down for a while.
[? A Capella Science singing LIGO Feel that Space ?]
? They told me don’t worry about it
? Analyze the chirp and
? No more
? They told me be careful
? And doubt it
? But I’ve seen a merger
? Of black hole-ole-ole-oles!

? LIGO feels when space is rippling through
? With a wave of
? Gravitation

? LIGO feels when space is rippling due
? To a tensor
? Perturbation
>> Regina Barber DeGraaff: Welcome back to Spark Science where we are listening to LIGO tour guide, Dale Ingram, talk about gravitational waves.
>> Dale Ingram: Now, when you see the long arms of the detector outside of the buildings, this is what you’re looking at, these 12 foot long concrete enclosures we call them that were cast in Richland and then trucked out here. You bulldozed, compressed the flat 1.5 mile long paths for the beam tube and then poured the concrete slab along those paths, mounted the beam tube on the slab, and then just set the covers on top of the slab merely to provide protection for the beam tube.
And we don’t do — there’s no lights in the tunnel. There’s no heating. There’s mice in there and snakes and it’s definitely like the dark underbelly of LIGO. But we don’t really care because the beam tube sits in there and the light carries — the tube carries the light back and forth or houses the light on its journey.
Now you can see on the tube section here that there’s a bellow section welded into it. So this creature is why we don’t have to worry about any temperature control in the tube. You got a 2.5 mile long piece of welded steal that’s going to want to get a lot longer when the weather gets hot and then shrink when it gets cool. So the flexible bellows absorbs that stretching and shrinking and doesn’t stress the ends of the detector where the vacuum chambers are.
Three millimeter steal. It was — you know, sheet metal that was about this wide. They did this work over in Pasco. It was Chicago Bridge and Iron that had the contract. So they would roll the steal into the tube and then a robot would do the weld. And then they would weld the stiffening rings on to help the tube stay nice and round. It’ll actually sag under its own weight without the help of the stiffening rings. And, you know, the pressure is one trillionth on the inside of what it is on the outside so you got to hold the thing nice and round.
Steal alloy number 3-0-4, which I think is some kind of sort of special low hydrogen recipe, but we’ll be getting hydrogen out of it as long as it sits out here. I should pause for questions or comments about plumbing related issues.
>> So what’s the diameter of the enclosure that you put under vacuum?
>> Dale Ingram: Well, that’s — yeah. That’s the tube that runs all — the entire length of each arm. And then inside the buildings most of the tubing that connects the vacuum chambers is a little bit fatter than that, but comparable to it. So if you just do a quick and dirty calculation that takes the volume of the beam tube and then the volume of the vacuum chambers, it’s about 10,000 cubic meters that we have to keep down at 10 to the minus 9 torr.
>> How do you do that? Like what — like how big are your pumps?
>> Dale Ingram: Well, the only really taxing part of that operation was at the beginning when you built it and then pumped it down the first time. The long arms are still holding the vacuum that was applied to them 18 years ago. Right? And as long as your stuff doesn’t leak, it all works out OK.
Other than the outgassing that requires you to run the pumps. Now, like everything else you hear Sheela and I say, that’s a little bit of a lie because we just spent more than four years having a number of vacuum chambers open in the buildings. And, when the chambers open, you’ve got purge air on going through the inside that’s very dry and over pressured. So you’re always having an outward sweep of air. Nonetheless, when human beings go crawl around in the vacuum chamber, even though they’re all bunny suited up, they leave some water in there through sweat.
And so you can tell by looking at these residual gas analyzers, when you close the system back up, that the chamber is a little bit contaminated because human beings were in there.
So we have these enormous gate valves. When we have chambers open, we can drop the valves to wall off the long arms so that they don’t get vented. You vent the chambers. Take the door off. Go in there. Do the work. Come back out. You got to pump down the chambers and, depending on the volume that was open and how long it was open, you might have to pump for anything from two weeks to six weeks. And you do that in stages. So we have scroll pumps just kind of conventional big, beefy vacuum pumps, noisy, that take you from atmosphere down to a torr down to maybe a 10th of a torr, somewhere in that region.
Once you get down to about a 10th of a torr, then we use these magnetically levitating turbo pumps that are crazy. Right? They go at like 30 to 50 thousand RPMs. And you run those for a length of time that takes you from 10 to the minus one down to 10 to the minus six. When you get to 10 to the minus six or 10 to the minus seven, then you open the valves and let the ion pumps do the rest.
And then, once you get back down to where you want to be, you just watch it real closely to make sure there’s no leaks around the flanges of the doors or any smaller flanges that you had taken off to mount cameras on the view ports. There’s lots of places where it can leak because you’ve got zillions of bolts on the flanges. But Kyle is pretty good at keeping an eye on that stuff and we’ve had no significant problems with the vacuum system here.
In Livingston, we did have a problem. So, when you first built LIGO and you got the beam tube baked and pumped down and all of that infrastructure was ready, they wrapped the entire five miles of the tube in insulation to provide a little bit of noise mitigation so the tube wouldn’t vibrate so much from, you know, environmental noise. And then the mice crawled into the insulation and set up residence in there. Which we’ve always known. I mean, there’s like Avogadro’s number of mice per square mile in here.
[Laughter]
But some of the mice were adventurous, you know, like Magellan and so they crawled through the insulation up to the top and then they started living on top of the tube. And they would urinate and the urine was eating at the welds. So we sprung a couple of very tiny leaks in the tube in Louisiana. And they thought it was to be blamed on the mice. It ends up that that might have been part of the problem, but another part of the problem is that we had some leakage around one of the gate valves too. So they built this kind of sarcophagus thing around the gate valve to provide a second seal around it.
But, in the process of doing the leak hunting, they had to pull all the insulation off. And we did the same thing here because we didn’t know how big of a problem was here. We don’t get cable, but we were at a friend’s house years ago and they had this show on there like called The World’s Dirtiest Job or something with the guy who now like advertises getting tires at the Ford dealership, whatever his name is. This definitely would have qualified. I mean, we had contractors out here pulling off eight kilometers of mouse infested fiberglass insulation. Like that’s your dream [laughing].
So the tube is naked now in the enclosure. And we have another team of people who are out here washing the whole thing. And they’re just about done. When they get done and it’s all kind of spiffed up and cleaned and adequately sealed, we’ll probably coat it again with something else. But it’s going to have to be mouse proof.
But part of it also is figuring out how to best cope with the circumstances that Mother Nature gives you at the site, how to keep the mice out the of instrument, how to keep the moths out of the instrument. So we were really worried about this. You’re doing the upgrade. You’ve got vacuum chambers open. And there’s moths getting into the instrument floor. And if one of those goes into the vacuum system and stays in there, and then you pull the vacuum, vaporized moth. Right? And then you end up with moth molecules landing on the surface of the mirror and then LIGO doesn’t work.
So it’s this kind of funny just odd-ball sort of circumstance, but it was a significant concern. And so you got to figure out — you know, it’s part of the problem solving in LIGO. How do you make sure you don’t get a moth inside the detector?
That’s not my favorite bug story. My favorite bug story is that Rick Savage, who at the time was kind of our principle main laser system scientist, he gets on an airplane and he flies down to Livingston because he’s got a week or two of work to do down there. This was during one of our science runs either in the 5th or the 6th science run. He gets down there and the interferometers breaks, which is not uncommon. But what was a little bit uncommon in this case is the operator — the whole like three or four operators over the series of several shifts — they couldn’t fix it.
And they isolated the problem to something with the laser system. And you know, this is like auto mechanic work. Right? Trying to diagnose what’s the symptom versus what’s the problem. So they’re working, working, working, and, you know, we’re all getting uptight, right, because we’re supposed to be producing data and the instrument is down for like two days. That’s a really big deal.
So, finally, they said, “Look, we’ve got to get Rick back here. We don’t know what in the world is wrong with this thing.” So they call him in Livingston. He gets on a plane. While he’s in the air, they figure it out. You got a periscope down at the end of the laser table so the light at table height hits the periscope mirror, gets reflected up, and then hits the other periscope mirror and gets reflected through a light pipe, through a window, in a vacuum chamber, and then it’s into the vacuum. A bug had crawled across the periscope mirror and gotten fried on the mirror.
[Laughter]
And, at that point, the beam is still just a millimeter or two. Right? And it turns out you cannot detect gravitational waves with bug guts on the periscope mirror. So then you got to go in and the mirror actually cracked I think from the heating because, you know, you’re shining an infrared laser beam on a bug and the bug absorbs a lot more than the glass does. All right. Let’s keep going.
[? A Capella Science singing LIGO Feel that Space ?]
? Vacuum sealed interferometer ?
? An L 5-mile long ?
? Split a laser, bounce 300 times ?
? Compare the distance gone ?
? One built in Louisiana and one more in Washington ?
? That’s LIGO ?
? Yeah LIGO ?

? A billion lightyear journey to cover ?
? Then it hit the Fabry-Perot ?
? Lengthening one leg then the other ?
? Making fringes dance on to dio-o-o-ode! ?

>> So I’ve got a question about the laser.
>> Dale Ingram: Uh-huh.
>> What type of laser are you using? Is it a diode laser or is it a gas type laser?
>> Dale Ingram: It is not a gas laser. It’s a solid state, continuous wave, neodymium mag laser. Diode laser. But it’s staged. There’s a two watt oscillator and then a 35 watt amplifier and then a — like a 150 watt oscillator on the far side of that. And it’s basically a — so you generate this really, really pure two watt light and you boost it up to a few dozen watts and then you boost it up to a couple hundred. And — and, as the power of the beam increases, it’s not get noisier. That’s the magic of it. It’s about the best light that anybody knows how to make.
>> What’s the peak wavelength?
>> Dale Ingram: The wavelength is 1.064 nanometers in the IR. And we need that number not to change at all [laughing]. Because fluctuations either in frequency or amplitude can make you think you’re seeing gravitational waves at the output. So we place a big — you know, people ask us all the time, “Wouldn’t you be better served to use a like visible or UV because, you know, the fringe is going to be narrower and, inherently, that would make you more sensitive?” It wouldn’t make you more sensitive if you could get light at those shorter wavelengths as good as what we can make in the IR and that’s not the case. That 1.06 nanometer light has a really long history in high precision work because it’s just rock solid stable.
Now, back to LIGO, the ground under your feet is shaking about 10 to the minus seven meters per second. That varies seasonally because of the seismic effect of ocean waves. But that’s — that level of ground motion is about 12 orders of magnitude above what the detector has to be able to sort out in terms of length changes. So that’s how much of this stuff you’ve got to filter out of the machine.
What we learned — what we’ve learned over the last year is that, if the detector is running and the wind moves up to like 30 or 35 miles an hour, the detector will probably stay operational, the light will stay resonant in the machine, but, if you lose lock, if you drop the resonant condition and the wind is still blowing that hard, it’s really hard to get the detector back on. Because you don’t have all the control signals. When we’re all the way up, we’ve got this entire array of control signals that help the instrument stay stable in terms of orchestrating the servo loops. When you lose lock, a lot of those signals go away and that just increases the challenge of trying to get back to your operate state.

[? A Capella Science singing LIGO Feel that Space ?]
? LIGO feels when space is rippling through ?
? With a wave of ?
? Gravitation ?

? LIGO feels when space is rippling through ?
? To a tensor ?
? Perturbation ?

? LIGO feels when space is rippling through ?
? From an ancient ?
? Amalgamation ?

? LIGO feels that space because it’s crew ?
? Gave it seismic ?
? Isolation ?

>> Regina Barber DeGraaff: Welcome back to Spark Science where we are on location at LIGO in Hanford, Washington.
>> Dale Ingram: This is the principle control station here behind me. So I think what we’ll do is just start up here and make a circuit around the walls of the room. So the light gets cleaned up on the mode cleaner, makes it through the power recycling cavity — in the power recycling cavity, the beam expands from a millimeter or two in diameter up to something that’s like the diameter of a pineapple can — and then you’re at the beam splitter. The light comes off the beam splitter, goes through the backs of what we call the inner test masses, down to the ends, reflects 200 or 300 times between the mirrors that are spaced by four kilometers along the arms. Then you get some power leaking back to the beam splitter, some of which then comes out the output arm where we have this signal extraction cavity. And then the output mode cleaner that does the final clean-up on the light before it comes out and is measured on the photo diodes.
So, in the interferometer, if you count all of the reflections that the light undergoes, it encounters pieces of glass hundreds of times and that causes some mode impurities to crop up, what some of our people call “junk light,” that kind of clouds your ability to read out the interference pattern. So this optical cavity right at the end of the instrument basically strips out the junk and gives you this nice pure beam that has the interference fringe in it.
The light comes out a little hole right here, works its way down the laser table. So the light gets reflected up through the periscope and then sent through a pipe where it goes into the first vacuum chamber, passes into the second vacuum chamber — so this is your vibration isolation platform. All of those spring and mass passive isolators are out of the instrument now and they’ve been replaced by these things that act like noise counseling headphones that have onboard sensors that measure the local noise and then those sensor signals are part of servo loops that direct the action of force actuators to cancel out that noise and leave the optical table sitting really, really still.
And then you have these multiple stage suspension that are clamped to the optical table so you get even more isolation passively from the multiple suspension stages. And then you have the permanent magnet electromagnetic actuators in the suspensions to do additional position and angle control of the mirrors.
And all of that stuff is orchestrated through orchestrated through feedback and we can sit in here and monitor the behavior of those servo loops, or change the filtering in the servo loops or actually change the composition of the loop itself using the digital controls. And then the light gets processed by the interferometer, gets multiplied in power to a significant extent because of all the resonance of light that happens in the various cavities. This is the last vacuum chamber along the beamline and that is the output mode cleaner. That’s the unit that resonates the light out of the detector — the light that’s transmitted out of the OMC after the junk has been filtered out of it — lands on sensing photo diodes back here that are basically the readout of the gravitational signal.
The leisure enclosure is just on the other side of this wall. And then the light works its way from left to right up to the beam splitter. And then, on all the TV screens, you just have multiple readouts of detector data channels and then some environmental monitors as well.
So the idea of the control room is that you walk in from the hall and you look around and, within the span of about a minute, you can figure out the key features of what the environment is doing today and what the detector is doing today. And then, when you sit down at one of these work stations, you have access to hundreds and hundreds of graphical interfaces that allow you, not just to read out the status of detector channels, but to actually interact with filter banks and other variable settings in the instrument hardware.
And you were thinking for about the last 20 minutes, “This guy never stops talking.”
[Laughter]
But I’m actually going to stop now and let you ask questions. Yes?
>> So I’m from Spark Science. So, from Jeff, he asks, how much raw data does LIGO generate every day?
>> Dale Ingram: About a terabyte.
>> What percentage of this raw data is released to the Einstein At-Home Citizens Science Project?
>> Dale Ingram: That is a very good question. So the reason that we collect roughly a terabyte a day is that we are not only archiving the gravitational wave channel, but a whole — but thousands of other instrument channels and then hundreds of environmental channels as well. So the data format that we use we call “frames” and a frame is basically like a grid where you have maybe 32 or 64 seconds of data — I’m not sure what the length of the frame is these days — and then all of the channels that you have collected over that span of time — so that whole chunk of data is called a frame — and we include in the frame all of these auxiliary channels and environmental channels that are necessary for signal confirmation, and to really understand what the behavior of the detector was.
But for gravitational wave analysis, such as for the Einstein At-Home effort, you really only need the gravitational wave channel. And it’s not the gravitational wave channel that comes straight out of the instrument. We call in the strain channel, which has some processing and some calibration on it. So, if you’re subscribing to Einstein at home, you’re really only looking at the strain data. And the code that your computer is running is analyzing that strain dataset for this particular signature that might be associated with neutron star pulsars.
Now, that’s a very computing intensive process. That’s why we have to have everybody donating their unused computer cycles to contribute to this Einstein At-Home effort. It really speeds up our ability to look for pulsar signals in our data. But you’re only getting a small fraction of the full frame data that LIGO collects through that system.
>> How is the data analyzed by Einstein At-Home participants used in research or projects?
>> Dale Ingram: There’s really nothing different about the Einstein At-Home circumstance than the analysis circumstance that led to the black hole in spiral announcement. But the difference is that, to do the pulsar search, you really need a lot of computing cycles because there’s so many templates that you have to run to compare to the data. Because you have to have that pulsar waveform. You have to have that template in there. But then you have to vary the template over many, many different frequencies and many, many different sky positions.
So it’s a relatively massive computing problem because of all the iterations due to the sky positions and the possible frequencies that that signal could exist. So that just means we’ve got to have a lot of computers. We could do the analysis of the September signal with the clusters that we have access to outside of the general public, but we can’t do that for the pulsar search. We’ve got to borrow yours just to have enough cycles to be able to get the job done.
>> And in, from Taylor, what instruments were used to discover gravitational waves?
>> Dale Ingram: We have to be a little bit careful with the use of the word “discover.” We try not to say that we have “discovered” gravitational waves. What we have discovered is what appears to be the first instance of a binary pair of black holes and the gravitational wave emission from that system. But the — the first — in my view, kind of the first smoking gun, in terms of the physical reality of gravitational waves and the measurement of that kind of signal, was from radio astronomy. It was two radio astronomers at the Arecibo Telescope collecting data in the ’70s in an effort to continued then — actually continues today — they identified these two neutron stars that are orbiting each other we about an eight hour period, and one of them is a pulsar, a radio pulsar.
So, on the Arecibo radio telescope, you can see the blip — you know, from the radio beacon of the pulsar and, from the frequency changes in the blip, you can see how the orbital dynamics of that pair of neutron stars was changing. And it was changing basically in a way that totally agrees with the prediction that general relativity makes for that kind of system if it’s emitting gravitational waves. Their orbit is decaying in a way that agrees with what GR says if you assume that the system is radiating gravitational waves.
So they won the Nobel Prize for that in 1993 for that discovery. It’s Pulse and Taylor. And, if I were to use the word “discover,” I would attach that to their finding. But, what you don’t have with the Wholeson Taylor [sp?] circumstance is basically the ability to read the gravitational wave signal directly, which is what LIGO wants to do.
So, in terms of direct detection where the signal is, you know, causing a behavior in the detector itself, that would be LIGO and these two huge interferometers.
Now, the Virgo detector in Italy, it was not running at the time LIGO detected our signal in mid September because they are still in their upgrade program. They’re moving closer to finishing it. We’re hoping that Virgo will join LIGO for the second run that we launch, which will be mid-summer or late summer. And if that interferometer, along with the two LIGO interferometers, if the three of us are able to pick up the same signal, then you’re sky pointing to the source of the gravitational wave gets a lot better.
>> How often do events that produce gravitational waves occur?
>> Dale Ingram: Well, if you consider the entire universe, which is an enormously big place, they’re probably going off regularly. Right? I mean, 100 — well, 50, 60, 70 years ago, if you asked somebody how often do supernovae go off, what would they have said? Once ever 10 years? Once every, you know — go out to the edge of the local group of galaxies. You know? Maybe a few a century?
Now we know that, you know, they go off at least once a day. But, in order to see them daily, you’ve got to look way out there [laughing]. Which now the optical people can do.
So presumably, you could make a statement kind of like that for gravitational wave sources. If you could go out to a ball of space that’s 10 billion lightyears in radius, you’d probably pick up signals pretty regularly. So we’re limited by the reach of the interferometers. We think that the September event occurred about a billion light years away. And it was loud enough that we think we could go further than that and still pick up the signal, but not hugely further.
I don’t know if we would be sensitive to an event that was five billion light years away. So that’s one of the questions that we’re very interested to gain more insight on going forward. We know we got the big one in September. Sheela pointed out that much tinier one that happened about a month later. We’re still analyzing the remainder of the data from that run. About 2/3 of the data from the run is still under analysis. We’ll see if anything gets claimed from that dataset.
And then we start running again in the summer. We go for four or six mammoths and we see what shows up there. I think — you know, I think our people are hopeful over the next couple years and when we’re in operating mode, we might pick up signals maybe monthly. But whatever that number turns out to be, it’s going to be based on the reach of the detectors out into space.
So LIGO always wants to improve the sensitivity of the machine so we can see further out into space so we can more events.
>> What implications do gravitational waves have on modern day physics and technology?
>> Dale Ingram: The implications for modern day physics are related, I would say, to tests of general relativity. That’s one thing I’ve consistently heard people in LIGO say over the years. Why are you doing this?
One reason is we’re really interested to see how general relativity holds up in the gravitationally nutty environment of the inspiral of a pair of black holes. Based on the September event, it appears that it holds up reasonably well. Like Einstein got it right again.
But there’s more work to be done there. And then I think another dimension of the physics and astrophysics is the possibility that there might be other kinds of bodies out there that might have the capability to produce gravitational waves and maybe we haven’t really imagined what those bodies could be like.
So people talk about quark stars. You know, you’ve got neutron stars. They’re kind of a known quantity. Do you have quark stars? Are they out there? Are there other, you know, unusual bodies that you could get gravitational waves from that maybe you’re not getting light from that you could gain some insight into?
So there’s issues like that on the physics side. On the technology side, it’s this. Right? I mean, that’s the world’s highest performing laser system along with the installations and the other gravitational wave detectors around the world in terms of amplitude and frequency stability relative to the power that it produces. You know, nobody knew how to make that 15 years ago. Why do we know how to make it now? And it’s a German company that knows how to make it. Because LIGO needed it and Virgo needed it.
So the unusual performance requirements that the gravitational wave detectors carry for the successful doing of our science means you’ve got to develop new, cutting edge technology to make the — to allow the detectors to be sensitive enough. So — and there’s spinoffs, you know. On the advance LIGO website, there’s 12 little stories about technology spinoffs that have come from the science and engineering that’s gone into LIGO. More of that is to come. Those two dimensions I would say.
>> And then what new discoveries can scientists make using gravitational waves?
>> Dale Ingram: There’s four categories of sources that LIGO — that our collaboration is kind of organized around. Inspirals, these unmodeled events that we call “bursts” and you can kind of include the inspirals in the bursts to a degree. But you have, you know, two bodies going like this, spinning around each other. You have a body exploding in something like a supernova. That could produce some signal. You have continuous sources. That would be your pulsars, you neutron star pulsars sitting there spinning. And, if there’s a bump on the pulsar somewhere, it’ll make gravitational waves.
And then somebody asked in the auditorium about primordial gravitational waves. You know, the gravitational wave signature from the Big Bang. Or the gravitational wave rumble, the gravitational wave backdrop of the universe that’s kind of the collection of all these sources that have gone off over such a long period of time down at a very low level.
So the people in our collaboration that are in those working groups, they can tell you stories about what they think those signals ought to be like. You know, we have expectations for what those signals will be like and what those signals will tell us.
I think the big question to a lot of our scientists is, “What are we going to measure that’s going to completely surprise us?” You know? And we don’t know the answer to that question. But that’s the marvelous nature of that question. Is there the potential that you could discover something from doing this science that’s going to really blow our minds? Like, “Wow. We never expected that.”
And I heard one of our scientists say a couple weeks ago that the black hole inspiral, as cool as it was, kind of sort of turned out the way we expected based on what general relativity says for how that event should go. And that’s marvelous. We have no complaints about that whatsoever. But how cool is it going to be when some signal shows up in the machines that you know is a gravitational wave signal, but you have know idea what caused it and now you have to figure out what is the nature of that source? That could be really cool.
>> So I have three more questions. One is from Hans and he asks, “Since a photon of light was frozen in boron a few years ago, does that mean that the speed of light is not consistent? For example, does the light being bent around the edge of an event horizon on a black hole slow down?”
>> Dale Ingram: I don’t know. I can tell you that I have not heard our scientists say anything different over the last two years about issues related to the speed of light than the things that customarily get said that you all are familiar with. So the particular instance that’s referred to in the question, I think our people are aware of that, but it has not caused our people to think differently about how light behaves or what the speed of light means in the broader context of physics than what has been the traditional view.
Some of you are aware that several years ago this finding was announced of neutrinos going faster than the speed of light. So I asked one of our people his thoughts about that and he basically said, “Give them a little bit of time and they’ll figure out what went haywire,” and that turned out to be the case. You know, it was kind of an electronics issue.
And that’s not to say that people in LIGO or elsewhere in physics have minds that are closed to the possibility that there may be something freaky associated with the speed of light. I don’t think that there’s evidence to date that suggests a revision of our thinking is necessary.
>> The last question from me. So I was wondering if you could explaining gravitational waves in layman’s terms.
>> Dale Ingram: So you know what an earthquake is.
>> Yes.
>> Dale Ingram: You got a fault line sitting there. Slip. And that slippage, that shaking, produces energy that then ripples out through the ground in a wave like way. That’s what gravitational waves are. The difference is that it’s not the ground that’s slipping. It’s something like two black holes crashing into each other or orbiting each other and then crashing into each other. And the waves that travel outward from that event are not moving through any material medium. They’re waves of the emptiness of space itself.
>> OK.
>> Dale Ingram: They’re spacequakes. Gravitational waves are the waves you get from spacequakes. We could talk about this stuff longer than you want to listen to it, I can guarantee you that. But that will be better than [inaudible].
[Applause]
[? A Capella Science singing LIGO Feel that Space ?]
? This event’s power is enormous ?
? Fifty universes of suns ?
? We had indirect clues before this ?
? All you GR haters, you were wrong-o-o-ong ?
? LIGO feels when space is rippling through ?

>> Regina Barber DeGraaff: Today’s episode, LIGO and the Fabric of Space, was recorded on location in Hanford, Washington with the help of Spark Science Student Correspondent, Lia Cook, LIGO Tour Guide, Dale Ingram, and Western Washington University physics students. A special thanks to Western Washington University Women in Physics. This show was recorded by Nathan Miller and produced and edited by Nathan Miller and Regina Barber DeGraaff. Our theme music is “Chemical Calisthenics” by Blackalicious and the feature song today is “LIGO Feel That Space, the Weekend Parody” by A Capella Science.
[?Blackalicious rapping Chemical Calisthenics ?]

? Lead, gold, tin, iron, platinum, zinc, when I rap you think
? Iodine nitrate activate
? Red geranium, the only difference is I transmit sound
? Balance was unbalanced then you add a little talent in
? Careful, careful with those ingredients
? They could explode and blow up if you drop them
? And they hit the ground

[End of podcast.]