Gravitational Waves Exist
February 11, 2016 8:12 AM   Subscribe

 
From the second link: Word of LIGO’s success was met by hosannas in the scientific community, albeit with the requisite admonishments of the need for confirmation or replication.

Uh, isn't this premature then, if there's only one known instance of this occurring?
posted by Brandon Blatcher at 8:17 AM on February 11, 2016


The first person to see the results was named Marco Drago? This has "origin story" written all over it.
posted by Etrigan at 8:22 AM on February 11, 2016 [33 favorites]


Um, I think if you look at the previous post you will see that gravity is just a myth.
posted by Rock Steady at 8:24 AM on February 11, 2016 [3 favorites]


Uh, isn't this premature then, if there's only one known instance of this occurring?
We already gave the 1993 Nobel Prize for showing gravitational waves existed. This is just the first direct detection. It's also looking exactly as we expected it to.

As Matt Strassler put it earlier the really amazing thing is people pulled off such an incredible challenge.
posted by edd at 8:24 AM on February 11, 2016 [5 favorites]


Still from the second link:
Detailed analysis of its form told a tale of Brobdingnagian activities in a far corner of the universe: the last waltz of a pair of black holes shockingly larger than astrophysicists had been expecting.

One of them was 36 times as massive as the sun, the other 29. As they approached the end, at half the speed of light, they were circling each other 250 times a second.

And then the ringing stopped as the two holes coalesced into a single black hole, a trapdoor in space with the equivalent mass of 62 suns. All in a fifth of a second, Earth time.
All in the fifth of a second. That sounds terrifying, but at least if it every happened near Earth, we'd never know.
posted by Brandon Blatcher at 8:25 AM on February 11, 2016 [22 favorites]


Very cool that this was known by so many but didn't leak. With all the long pieces and explanatory videos already about it, it had to be embargoed for at least a week, I'd think. Very neat stuff.
posted by jmccw at 8:26 AM on February 11, 2016 [2 favorites]


Listen to the chirp.

Look at the waveform.

And here's the peer reviewed paper. (Although PRL crashed under load - there's a first!)

It is beautiful. Just beautiful.
posted by RedOrGreen at 8:27 AM on February 11, 2016 [13 favorites]


Uh, isn't this premature then, if there's only one known instance of this occurring?

The signal was detected at both LIGO sites, hundreds of miles apart. There aren't other events yet, but with the same signal at 2 sites, the confidence is high enough that they can have every right to claim credit for the discovery.
posted by chimaera at 8:28 AM on February 11, 2016 [4 favorites]


For those watching this in real time, there is an ongoing NSF livestream that I assume will be converted to an archival video once it's over (it's still running live as I type this). Similarly there is a local (to me, anyway) MIT announcement talk that just started. This is a big enough deal that MIT sent out a campus-wide email this morning announcing it. I've been here for 20 years and I've never seen that happen before.
posted by range at 8:28 AM on February 11, 2016 [7 favorites]


jmccw: I'd been hearing rumours for some time, although they only really solidified in the last fortnight, with numbers on it surfacing over the last week.
posted by edd at 8:29 AM on February 11, 2016 [3 favorites]


Yeah science!
posted by malocchio at 8:30 AM on February 11, 2016 [1 favorite]


Us electromagnetic spectrum observers (a distinction we haven't needed till today!) got the notification telegram on September 14th. It is really amazing that it stayed as quiet as it did, all things considered.
posted by RedOrGreen at 8:31 AM on February 11, 2016 [12 favorites]


For the ignorant such as myself, what is the significance of this? Why is it being hailed as such a huge discovery?
posted by Sangermaine at 8:33 AM on February 11, 2016 [1 favorite]


I don't think it's really a huge discovery. It's the demonstration of an entirely new technology for observing the universe.
posted by edd at 8:34 AM on February 11, 2016 [1 favorite]


Everything that we perceive - till today - is mediated by electromagnetic radiation. Light, radio waves, X-rays - all part of the EM spectrum. This is a whole new observational window on the universe - sort of like discovering that you have ears in addition to eyes.

We've known these gravity waves exist for a long time, and indirectly confirmed them with binary pulsars. This is the first *direct* detection.
posted by RedOrGreen at 8:37 AM on February 11, 2016 [28 favorites]


RedOrGreen: coughneutrinoscough ;-)
posted by edd at 8:38 AM on February 11, 2016 [5 favorites]


Phil Plait did a really solid lay-person write up as well.
posted by Think_Long at 8:40 AM on February 11, 2016 [5 favorites]


From the NYT article: "Three solar masses worth of energy were vaporized in a storm of gravitational waves"

Ok, that's an incredibly amount of energy. Is that kind of energy destructive to objects (planets, stars, etc.)?
posted by Hactar at 8:41 AM on February 11, 2016 [2 favorites]


> coughneutrinoscough ;-)

(Yep, the highest ratio of PhD theses to detected events. Should have added that [*].)
posted by RedOrGreen at 8:42 AM on February 11, 2016 [1 favorite]


I thought I felt something weird around the middle of September.
posted by Rock Steady at 8:46 AM on February 11, 2016 [8 favorites]


Uh, isn't this premature then, if there's only one known instance of this occurring?

There are two detectors, one in Washington State and one in Louisiana. They both saw the signal, and it's a dead fit to theoretical.

This is in some ways a really boring result. "Oh, look, Einstein was right *again!*" But the sensitivity they needed to detect something so absurdly energetic as two black holes merging is just staggering. I know a guy on the LIGO team, he described the first run as "We knew the world was noisy, but we had no idea how noisy!" They're measuring things to 1 part in 1021. Digging that small a signal out of a very noisy world is just amazing.

The question is can we get that measurability down a few more exponents? Each one we do both increases the range of detection and increases the events we can detect. This event was two black holes merging, which is, gravity wise, about as loud as it gets. It may be that only space based detectors will be able to drop the noise floor enough to gain significant sensitivity -- and the ESA has launched a mission to test one possible way of building a space-based gravity telescope. The hard part isn't putting them in orbit, it's measuring the distance between them incredibly precisely *and* understand what part of that is actually the satellites moving with respect to each other and which is actually a gravity wave signal.

If we can make it work, we get two things -- vastly longer detector arms and vastly less noise.
posted by eriko at 8:47 AM on February 11, 2016 [14 favorites]


🌊🌊🌊🌊🌊🌊🌊
posted by TedW at 8:49 AM on February 11, 2016 [2 favorites]


I thought I felt something weird around the middle of September.

Your username changed briefly to Rock Quiveringslightly, but no one noticed.
posted by Etrigan at 8:49 AM on February 11, 2016 [7 favorites]


Sean Carroll's blog post had a nice perspective on "Oh, look, Einstein was right *again!*".
The fact that Einstein’s prediction has turned out to be right is an enormously strong testimony to the power of science in general, and physics in particular, to describe our natural world. Einstein didn’t know about black holes; he didn’t even know about lasers, although it was his work that laid the theoretical foundations for both ideas.
I'm grateful to Nicola Twilley for doing such a great job of science journalism for the New Yorker. It's a great article for the layman, humanizing the challenge of this kind of science. It helps the team had a few months to prepare the announcement and press. Good for them!
posted by Nelson at 8:51 AM on February 11, 2016 [17 favorites]


It's the demonstration of an entirely new technology for observing the universe.

I would argue that this is, in no small sense, pretty much the definition of Huge Discovery.
posted by aramaic at 8:51 AM on February 11, 2016 [4 favorites]


On the amount of energy generated:
“The total power output of gravitational waves during the brief collision was 50 times greater than all of the power put out by all the of the stars in the universe put together,” said Kip Thorne of Caltech, one of LIGO’s founders. “It’s unbelievable.” [source]
posted by bouvin at 8:52 AM on February 11, 2016 [8 favorites]


I love the fact we built two of these giant detectors because, you know, statistical significance.
posted by Dean358 at 8:56 AM on February 11, 2016 [2 favorites]


So, this Laser Interferometer Gravitational-Wave Observatory; you say it vibrates?
posted by yhbc at 8:57 AM on February 11, 2016 [30 favorites]


Dean358: it's more to help get a direction on where the signal came from. It's also why we want more up and running, to improve that.
posted by edd at 8:57 AM on February 11, 2016 [4 favorites]


I did my PhD in GW instrument science & my other half is still in the LSC and worked on the analysis of this event. I could hardly be more thrilled and more proud.
posted by norabelle at 8:59 AM on February 11, 2016 [48 favorites]


Bill Watterson was almost right: scientific progress actually goes "Bloop!"
posted by qcubed at 9:01 AM on February 11, 2016 [11 favorites]


How accurately do we know where this black hole is?
posted by thedward at 9:02 AM on February 11, 2016


I love the fact we built two of these giant detectors because, you know, statistical significance.

You have to protect against the possibility of Jake Busey blowing the first one up.
posted by Etrigan at 9:03 AM on February 11, 2016 [11 favorites]


thedward: Not accurately at all; with two detectors they could confine things to a large swath of the Southern sky (hundreds of square degrees). With new detectors coming online they should be able to localize things much better.

The distance is similarly uncertain; equivalent to looking ~1.3 billion light years, but that number is uncertain at the ~40% level.
posted by janewman at 9:06 AM on February 11, 2016 [1 favorite]


This is super exciting and super awesome and I am mostly incoherent with glee about it.

Fortunately a bunch of my friends are way more coherent and wrote some great explainers that you can add to Phil's from up above, like Nadia Drake's for National Geographic and Matthew Francis for The Atlantic.

I love that LIGO wasn't quiet enough so they had to shield it even more to make the souped-up "advanced LIGO".

I'll echo Sean Carroll: It's stunning that we've once again observed something that Einstein predicted. I was lucky enough to get to live through the earlier huge demonstration of Bose-Einstein condensates in a dilute gas of atoms. norabelle, I'm so thrilled and jealous that you're getting the same thing.
posted by sgranade at 9:09 AM on February 11, 2016


While I'm squeeing about, here: have an explanation of the difference between gravity waves and gravitational waves. LIGO detected the latter.
posted by sgranade at 9:12 AM on February 11, 2016 [2 favorites]


It's pretty incredible that the earth's surface is stable enough to support these extremely long and rigid tubes with only minimal fluctuation. They must have some type of incredible vibration dampening technology.
posted by Think_Long at 9:13 AM on February 11, 2016


I'm really dismayed to see that the New Yorker has bought into this cockamamie pseudoscience:

"The pipes are so long—nearly two and a half miles—that they have to be raised from the ground by a yard at each end, to keep them lying flat as Earth curves beneath them."
posted by Zerowensboring at 9:16 AM on February 11, 2016 [4 favorites]




So does this bring us back to a view of space/time as sort of a luminous ether and/or a medium that exists independent of extended bodies? If space/time propagates waves, it's not a void, it's got some kind of substance to it, independent of any physically extended bodies. It's been a long time since I tried to wrap my head around the special and general theories of relativity, so I may be confused here, but what does this mean for our understanding of space/time? It seems like this result isn't compatible with the idea that space doesn't exist independently of extended bodies. Physicists of MeFi: Am I understanding this result right? Does this make space/time a medium for wave propagation, like the old luminous ether idea, or what?
posted by saulgoodman at 9:25 AM on February 11, 2016


"The pipes are so long—nearly two and a half miles—that they have to be raised from the ground by a yard at each end, to keep them lying flat as Earth curves beneath them."

Yeah, my back-of-the-envelope calculation gives me a foot raise at each end, not a yard (assuming it's resting on the ground at the midpoint of each pipe).

Although, seriously, I'm sure they're suspended in some sort of super-dampening coil system or whatever to avoid picking up local trucks and such, and of course nowhere outside of a salt flat is the ground perfectly flat, so it's probably not noticeable at all.

Also: yay gravitational waves!
posted by math at 9:26 AM on February 11, 2016 [1 favorite]


I believe this is also the first time we've directly observed a black hole. We've been able to imply their existence and presence by looking at things like accretion discs and stars orbiting around the supermassive black hole in the galactic center, but LIGO has seen the merger of these two black holes directly.
posted by eriko at 9:26 AM on February 11, 2016 [4 favorites]


It's an astonishing piece of engineering - and it's not just that it's detected GW. It's not a detector, it's an observatory. I'm not quite so sure that the secret was that well-kept as the story has it; I talked to some Advanced LIGO computational guys towards the end of last year and it was clear that they were excited and confident about something... and it was LIGO, so it wasn't going to be about a change in the dessert menu in the canteen.

They said nothing. They didn't have to.

Now, where's the plan for how to do it at home with a couple of LEDs and an Arduino, eh?
posted by Devonian at 9:29 AM on February 11, 2016 [2 favorites]


“I don’t remember how it happened, but we shared the hotel room that night,” Weiss said. They sat at a tiny table, filling sheet after sheet of paper with sketches and equations. Thorne, who was raised Mormon, drank Dr Pepper

The math life is raw as hell
posted by Greg Nog at 9:30 AM on February 11, 2016 [32 favorites]


OKliGO?
posted by butterstick at 9:34 AM on February 11, 2016


saulgoodman: it's no change from the relativity of the last hundred years - e.g. Einstein's views and other such reading you can follow on from there.
posted by edd at 9:34 AM on February 11, 2016 [3 favorites]


Yeah, my back-of-the-envelope calculation gives me a foot raise at each end, not a yard (assuming it's resting on the ground at the midpoint of each pipe).

Are you assuming both pipes lie along Great Circles?
posted by jamjam at 9:41 AM on February 11, 2016


The total power output of gravitational waves during the brief collision was 50 times greater than all of the power put out by all the of the stars in the universe put together...

And yet that caused a ripple in the detectors of about the width of a proton.
posted by CheeseDigestsAll at 9:44 AM on February 11, 2016 [3 favorites]


saulgoodman: Does this make space/time a medium for wave propagation, like the old luminous ether idea, or what?

Yes and no: yes, waves move through the structure of spacetime, but no, it's not really related to the old luminiferous aether. Luminiferous aether theory said that there had to be some kind of medium to carry light waves around. But it turns out that you can't have a kind of aether that would meet all the physical criteria.

There is a structure to space and time. We see it in how the universe is expanding, and in how the ripples that LIGO detected consist of space expanding and contracting. Back in the day, Einstein talked about a "relativistic aether" to distinguish it from the electromagnetic aether, but that way of thinking died out pretty quickly.
posted by sgranade at 9:44 AM on February 11, 2016 [2 favorites]


Though I guess that wouldn't matter...
posted by jamjam at 9:44 AM on February 11, 2016


A quick swag using the numbers in the article gives me the result that if you were standing 2000 light years from the colliding black holes, you might start to feel your skin tingle.
posted by RobotVoodooPower at 9:44 AM on February 11, 2016 [2 favorites]


Thorne, who was raised Mormon, drank Dr Pepper

The math life is raw as hell

I want to say that Dr Pepper was what Feynman was noted for drinking after he became teetotal, but I can't remember if that's actually right. Is it?
posted by howfar at 9:47 AM on February 11, 2016


They're measuring things to 1 part in 1021. Digging that small a signal out of a very noisy world is just amazing.

In ten years this kind of signal processing will be routinely done by $5 chips inside Internet modems to deliver terabit speeds over copper wiring designed to transmit voice-only audio and installed a hundred years ago.

I can't decide whether that makes me excited or fills me with despair.
posted by flabdablet at 9:48 AM on February 11, 2016 [3 favorites]


If you want to see the actual technical drawings of the vibration damping systems that the mirrors are mounted on, it's in the LSC public document repository here.

The instruments are extraordinary works of audacity, imagination and ingenuity. For every single thing that goes into the detector, people have asked 'how can we make that better?' and 'how can we control that?'. They are really lovely machines. I did four whole years studying the amount of measurement noise that would be contributed by the thermally induced vibrations of a particular type mirror coating and a particular way of joining bits of glass together. Every single component has been looked into in that kind of detail.
posted by norabelle at 9:50 AM on February 11, 2016 [40 favorites]


(Although PRL crashed under load - there's a first!)

For those who can't get through to Physical Review Letters, the LIGO collaboration has it on their public server.
posted by Johnny Assay at 9:50 AM on February 11, 2016 [2 favorites]


does this bring us back to a view of space/time as sort of a luminous ether and/or a medium that exists independent of extended bodies?

No. It tells us more about how those bodies interact.
posted by flabdablet at 9:51 AM on February 11, 2016


I should go back to Hactar's comment on how dangerous a gravitational wave might be. If I recall correctly the strain caused by a gravitational wave varies as 1/r (not the usual 1/r2 for intensities of waves, as it's an amplitude instead). You can probably hand-wave the expected effect from there, but I'm not too sure how you calculate gravitational wave interaction cross sections and such. The black holes concerned were about 1014 times further from us than the Sun though, so the strain at that distance would have been 10-7, which doesn't seem much, and that would have been a very close distance.
posted by edd at 9:51 AM on February 11, 2016


Congrats to those involved in this detection, it's really spectacular. And LIGO's just warming up, not yet at design sensitivity. Plus there's Virgo and a detector in Japan and possibly one in India. Not to mention LISA in space.

A rare case when it's not actually possible to be overexcited.

Also very cool to see is that the peer reviewed paper is already out (well, except the APS website is so hammered that I had to get it from a friend instead -- on edit thanks to Johnny Assay for a more stable link!). What a fantastic operation.
posted by nat at 9:52 AM on February 11, 2016 [1 favorite]


Oh I also have a science question if someone can let me know-- the ringdown in their signal, how close does it let them probe the details of the merger? (I know it seems to match simulations quite well, but is there a good way to quantify e.g. which quasinormal modes they can see in the ringdown, or to what curvature this tests GR?)
posted by nat at 9:57 AM on February 11, 2016 [1 favorite]


Science being a process of incremental improvement, I trust that none of the people involved in this project has unfortunate preferences in shirts.
posted by flabdablet at 9:57 AM on February 11, 2016 [6 favorites]


I want to say that Dr Pepper was what Feynman was noted for drinking after he became teetotal, but I can't remember if that's actually right. Is it?

It sounds about right, I mean it's like the most famous soda with a PhD
posted by Greg Nog at 9:59 AM on February 11, 2016 [26 favorites]


nat: There's this paper on GR tests from the event which might have the hardcore quasi-normal gnarly details for you.
posted by norabelle at 10:00 AM on February 11, 2016 [2 favorites]


Digging that small a signal out of a very noisy world is just amazing.

from a 'behind the scenes' look :P
"Long before you get to the observatory, drivers are asked to slow down to 10 mph to reduce vibrations."

I believe this is also the first time we've directly observed a black hole.

from the liveblog!
"Worth noting that, in addition to finding gravitational waves, this is also the first observation of a binary black hole merger."
posted by kliuless at 10:01 AM on February 11, 2016 [3 favorites]


So space/time does seem to have a structure independent of extended bodies, at least. Thanks for the explanatory replies. Good clarification about luminous ether having been a theoretical medium for light propagation; forgot that. Thought the idea was more generally that space wasn't simply void but had an independent substance. Unless I'm mistaken, there was some doubt about the possibility of space/time having extension in the absence of extended bodies at one time. It's great to see such a clear experimental confirmation (assuming the results hold up) that space/time has an independent physical structure, if I'm understanding that much right. Also: black holes!
posted by saulgoodman at 10:04 AM on February 11, 2016


There's also a nice short description of this story (with some key figures from the journal article) on astrobites at Opening Our Ears to the Universe.
posted by sedna17 at 10:06 AM on February 11, 2016


It sounds about right, I mean it's like the most famous soda with a PhD

Only because Mr. Pibb had his degree taken away by a bunch of suits in some so-called "trademark infringement" lawsuit. Somehow Dr. Thunder avoided this fate, perhaps he went to an institution that stood behind his degree.
posted by Copronymus at 10:14 AM on February 11, 2016 [7 favorites]


Are you assuming both pipes lie along Great Circles?

Yes! All pipes (that lie on the surface of the earth and are not pointing up or down) are along Great Circles.
posted by math at 10:29 AM on February 11, 2016 [2 favorites]


When the LIGO prototype was installed at MIT, it got very good at tracking the positions and movements of trains on the MBTA Red Line. Urban legend has it that it was the inspiration for live train and bus tracking apps.

Okay, so I just created that urban legend. But it deserves to exist.
posted by ocschwar at 10:52 AM on February 11, 2016 [8 favorites]


You have to protect against the possibility of Jake Busey blowing the first one up.


Luckily, Jake Busey is much easier to detect than gravitational waves. Dude is so pale, he practically glows in the dark. He's got to be giving off some kind of radiation.
posted by TheWhiteSkull at 10:58 AM on February 11, 2016 [2 favorites]


Luckily, Jake Busey is much easier to detect than gravitational waves.

You say that, but have you checked under your bed lately?
posted by Etrigan at 11:00 AM on February 11, 2016 [2 favorites]


I had a fox do it yesterday. All clear.
posted by TheWhiteSkull at 11:02 AM on February 11, 2016 [4 favorites]


So, if I'm understanding this correctly, when a gravitational wave passes through my body, then one part of my body is in a different time and space from another? That I am literally in two times and places at once? And everything that surrounds me is, as well, for a shimmeringly brief moment?

How marvelous and strange, to have one's paradigms challenged so well.
posted by the matching mole at 11:08 AM on February 11, 2016


It's more like your body is stretched in a cartoon-like manner, but on an infinitesimal scale that isn't detectable unless you use lasers, 5 miles of evacuated tubing, precise algorithms and optical hardware, et cetera.
posted by explosion at 11:14 AM on February 11, 2016 [3 favorites]


the matching mole: I wouldn't put it like that. All the bits of your body are in different places from the rest obviously. A gravitational wave would just change the distances between different bits a tiny tiny amount.
posted by edd at 11:16 AM on February 11, 2016


edd, as a follow up, how close would you (or, say a small planet) have to be to the black holes to actually be damaged by the gravitational strain created?
posted by Hactar at 11:22 AM on February 11, 2016


Hactar: I wouldn't be terribly confident in working that out. I'm not all that sure of my earlier comment - not quite my field and just basing it on bits I've picked up on in various seminars and so on mainly.
posted by edd at 11:28 AM on February 11, 2016


Astounding how simple the idea for this detector is, and how amazing the lengths to bring that simple idea to life. Needing to filter out wolf howls to "hear" stars crash mashes my poetical buttons.
posted by joeyh at 11:48 AM on February 11, 2016 [8 favorites]


It's kind of a cliche, but it's true; it's just astounding to think of a young man sitting in a dull patent office a hundred years ago, working out the shape of the entire universe with just a pen and paper and his brain.
posted by tavella at 11:58 AM on February 11, 2016 [10 favorites]


My lay understanding is that the reason why our proof of gravity waves has been inferential is because they generally don't produce spectacular luminous effects in the same way that quantum mechanics governs supernovae or electromagnetism kicks plasma around. Astronomers knew that tight binaries lost energy. But they couldn't actually see what that energy was doing (other than tweaking orbits) before now. Gravity waves offered a good fit to explain the observations.

And there was a remote possibility that General Relativity was wrong, demanding a radically different theory of gravity to explain the observations.
posted by CBrachyrhynchos at 12:08 PM on February 11, 2016


The total power output of gravitational waves during the brief collision was 50 times greater than all of the power put out by all the of the stars in the universe put together...

Do what, now?
posted by valkane at 12:11 PM on February 11, 2016 [2 favorites]


The total power output of gravitational waves during the brief collision was 50 times greater than all of the power put out by all the of the stars in the universe put together...

It's a somewhat misleading factoid. Power is defined as energy/time so if you reduce the time to a fraction of a second you're going to increase the power. I also suspect that gravitational energy and electromagnetic energy probably can't be compared in this way.
posted by CBrachyrhynchos at 12:20 PM on February 11, 2016 [2 favorites]


The observed black holes were 35(+5-4) and 29(+4-4) solar masses, and the output from the merger was a black hole of 62(+4-4) solar masses. They infer that 3.0(+0.5-0.5) solar masses were converted into energy (E=mc^2) and radiated out as gravitational waves within a millisecond or so.

Our sun fuses hydrogen to helium and the tiny bit of mass converted to energy is enough to power it for billions of years. Add up the power output of all the stars in the entire universe, and this event briefly (very briefly) outshone all of them put together, but in a band that we'd never been able to observe directly before.
posted by RedOrGreen at 12:22 PM on February 11, 2016 [9 favorites]


As an aside, the paper in PRL is shockingly readable, a model of clarity.

They can afford to do that because they have a dozen other more technical companion pieces appearing today, but the primary paper lays out the overview, all the effects they considered, and a very straightforward assessment of what it means.

If you have even a modest technical background, it's worth taking a look at it. Try the first link on this page.
posted by RedOrGreen at 12:25 PM on February 11, 2016 [6 favorites]


I think the 'brief period' was the duration of the detected chirp, not just the instant when the two black holes merged. They were spiralling in towards each other because they were losing so much energy due to gravitational waves, and that acceleration increased the rate of loss, so the final moment of impact wouldn't have imparted very much more acceleration. Although i can't get my head around what would actually have happened to the shape of the horizons when they touched and shared their internal space-time systems. Would there be near-instantaneous deceleration from luminal speeds? In which case, perhaps the bulk of the GW energy loss came at that point.

On the other hand, we did hear that chirp for a good long time, relatively speaking. I think I'd better read the paper...

(Ah, yes, looks from the paper that the bulk of the energy was radiated in around 250ms...)
posted by Devonian at 12:40 PM on February 11, 2016


> I think the 'brief period' was the duration of the detected chirp, not just the instant when the two black holes merged.

Ah, yes, this is correct. The paper says the peak luminosity was 200(+30-20) M_sun c^2 per second - that's 0.2 solar masses converted to gravitational radiation per millisecond at the peak. (Not all 3 solar masses in one millisecond, like I mistakenly said above.)
posted by RedOrGreen at 12:47 PM on February 11, 2016


To put it another way: turning a flashlight on and picking it up from the floor involves similar quantities of power (on the cosmic scale of black hole mergers.) We tend to underestimate the energies involved in mass just being mass moving around in spacetime.
posted by CBrachyrhynchos at 12:53 PM on February 11, 2016


Only because Mr. Pibb had his degree taken away by a bunch of suits in some so-called "trademark infringement" lawsuit.

Sorry, this is just wrong. Pibb never graduated:

"Mr. Pibb is the replica of Dr Pepper. But it’s the bullshit replica because dude didn’t even get his degree!"

Source: Hedberg
posted by Zerowensboring at 1:07 PM on February 11, 2016


Thorne, who was raised Mormon, drank Dr Pepper

Dr Pepper has caffeine, supposedly more than Coke, just saying...

also, starting in the 90s it's been fairly difficult to do a PhD in theoretical general relativity in the US. the only funded active groups were doing numerical analysis of black hole collisions. gr was supposed to be subsumed by string theory. so, if super LIGO ends up opening up a menagerie of gr events, their isn't a large culture of people doing fundamental gr theoretical work.
posted by ennui.bz at 1:10 PM on February 11, 2016


Our sun fuses hydrogen to helium and the tiny bit of mass converted to energy is enough to power it for billions of years. Add up the power output of all the stars in the entire universe, and this event briefly (very briefly) outshone all of them put together, but in a band that we'd never been able to observe directly before.

To give you the idea of the magnitude of the energy release -- it is as much energy as the Sun, at its current luminosity, would radiate in 15 trillion years. That's, for all intents, 1000 times the age of the Universe itself.
posted by eriko at 1:22 PM on February 11, 2016 [2 favorites]


Thorne, who was raised Mormon, drank Dr Pepper

Dr Pepper has caffeine, supposedly more than Coke, just saying...


There is no Mormon restriction on caffeine, just "hot" drinks. Since the two most popular hot drinks (coffee and tea) contain caffeine it is assumed that it is the caffeine (even amoung Mormons). Actually, Mormons tend to drink enormous amounts of diet coke for some reason.
posted by 445supermag at 1:31 PM on February 11, 2016 [1 favorite]


How accurately do we know where this black hole is?

that's a good question and, as far as i can tell, the paper doesn't answer it completely. the given distance is 410+160/-180 Mpc. the +160/-180 are the "typical" errors, so you can see that even in distance the errors are pretty big (it's like saying something is 400 miles away, give or take 200 miles). but there doesn't seem to be any attempt at all to calculate the angular position. at a minimum, they must know the rough direction (which half of the sky) from the delay between the two detectors (the signal arrived first at one, then the other about 7ms later).

also, people are talking about 30 solar mass black holes being unusual. but there's a possible selection effect (which again i don't see discussed in the paper) - it may be that this signal is a particularly suitable one for the system to detect, and so was seen because it was easier to see, not because it is particularly representative of events in general.

ps that distance is a redshift of about 0.09.
posted by andrewcooke at 1:38 PM on February 11, 2016


So, uh, the paper talks about early attempts to detect gravitational waves using:

"Weber and his resonant mass detectors in the 1960s [23], followed by an international network of cryogenic resonant detectors"

... so a large number of these detectors might be used in a cascade? And if something went wrong with them, there might be a resonance cascade?
posted by danhon at 1:57 PM on February 11, 2016


andrewcooke: in the announcement video there was a banana-shaped set of contours roughly overlapping the Magellanic Clouds for the position. I haven't got a decent view of that since though.
posted by edd at 2:03 PM on February 11, 2016 [1 favorite]


You know, Cooper could have just told Murph that he loves her like a regular father would have.
posted by radwolf76 at 2:15 PM on February 11, 2016 [1 favorite]


> in the announcement video there was a banana-shaped set of contours roughly overlapping the Magellanic Clouds for the position

With just two detectors, the localization is pretty poor, and the EM observers were initially given a long narrow strip of interest that wound across both the northern and southern sky.

The "banana" will show up in the EM follow up papers, none of which are posted yet, but I see that the neutrino follow up is posted online, and they show that uncertainty region in their Figure 1. Compared to typical fields of view, that's a YUUUUUGE chunk of sky. (It's a neutrino non-detection, by the way, nothing to get excited about.)
posted by RedOrGreen at 2:17 PM on February 11, 2016 [3 favorites]


The total power output of gravitational waves during the brief collision was 50 times greater than all of the power put out by all the of the stars in the universe put together...

That's a lot of energy.

Do we know what form that energy ultimately takes? And would black holes themselves be able to absorb gravitational waves?

If the energy stays in the form of gravitational waves, but of diminishing amplitude as they spread through the universe and greater wavelength as well as lesser amplitude as the universe expands, does that mean we could look at the fabric of space-time itself as a pink noise palimpsest of gravitational waves of all wavelengths with an upper limit established by the dimensions of the universe itself?
posted by jamjam at 2:24 PM on February 11, 2016 [1 favorite]


"No verified email" - hmmm. Are we sure this Einstein guy is a legitimate researcher?
posted by Wordshore at 2:25 PM on February 11, 2016 [5 favorites]


jamjam: energy in GR is... complicated. But broadly, gravitational waves don't couple much to the rest of the universe and are just going to stay as they are for the most part.

There's actually a fair background at certain frequencies from not long after the Big Bang. We think.
posted by edd at 2:31 PM on February 11, 2016


> does that mean we could look at the fabric of space-time itself as a pink noise palimpsest of gravitational waves of all wavelengths with an upper limit established by the dimensions of the universe itself?

Yes, that's pretty close to what we expect, although the longest wavelengths are not quite that long. Cosmology gets too complicated for me at those early epochs, but with pulsar timing, for example, we expect to detect the stochastic background of gravitational waves from merging supermassive black holes at nanoHertz frequencies. (Look at this image, for example, to see how the different bands line up.)

Sean Carroll's post linked upthread is a good one.
posted by RedOrGreen at 2:42 PM on February 11, 2016 [1 favorite]


How accurately do we know where this black hole is?

LIGO is getting a lot of signal. Some of that signal is noise which can be modelled because it is of terrestrial origin. The thing with colliding black holes is that it's something which may be relatively common when galaxies collide and it's a tractable (just barely) problem to theoretically analyse, so it's possible to look for collision events in the mess of LIGO data. The question is: how much of that signal is actual gravitational wave events and not noise? So, the more important thing is "what" rather than "where."
posted by ennui.bz at 2:48 PM on February 11, 2016


Are we sure this Einstein guy is a legitimate researcher?

Dude doesn't even have a middle name. Pi Day, pffft.
posted by lazycomputerkids at 3:20 PM on February 11, 2016 [1 favorite]


Actually, Mormons tend to drink enormous amounts of diet coke for some reason

You don't seem to find too many people who just drink a little Diet Coke from time to time. It's none, or all day long, with Diet Coke.
posted by thelonius at 3:26 PM on February 11, 2016 [3 favorites]


ONCE upon a time, there lived a man who was fascinated by the phenomenon of gravity.
Roger W. Babson?
posted by thelonius at 3:34 PM on February 11, 2016


So, when something mysteriously fell off the table and my husband said it was because we were having a high-gravity day--he was right?
posted by SLC Mom at 3:40 PM on February 11, 2016 [1 favorite]


“Humor Scientists Rush to Discover First Gravitational Waves Your Mom Joke,” Jim Hodgson, The Atlanta Banana, 11 February 2016
posted by ob1quixote at 4:26 PM on February 11, 2016 [4 favorites]


For a fraction of a second, the distance between the atoms in your body expanded and contracted by an impossibly small amount. They jiggled a bit. The displacement involved was an order of magnitude smaller than the size of the atoms themselves. The event that caused this happened 1.3 billion years ago. The ripple passed through the earth at the speed of light on September 14th of last year and kept right on going. You were scratching absently at an itch on your leg when it happened and for some reason you had the Golden Girls theme song stuck in your head, though you no longer remember this.
posted by dephlogisticated at 4:52 PM on February 11, 2016 [9 favorites]


For a fraction of a second, the distance between the atoms in your body expanded and contracted by an impossibly small amount. They jiggled a bit.

Is energy from the gravitational wave transferred to the atoms as a result of this "jiggling?"
posted by JackFlash at 5:00 PM on February 11, 2016


Is energy from the gravitational wave transferred to the atoms as a result of this "jiggling?"
Yes, but not much.
posted by sjswitzer at 5:14 PM on February 11, 2016 [1 favorite]


in theory yes. in practice, the signal was at about 100Hz. sine these waves travel with the speed of light, that means the wavelength is 3 million metres. so if you think of a wave that's 3,000 km long, it's practically flat - incredibly flat - at the scale of your body. so there's very little energy lost.

and add to that the constant factor involved (G) is tiny too...

i'm not sure i've explained that very well. imagine a boat. on boat-sized waves it's bouncing around all over damn place - lots of energy passed from the wave to the boat. but when the waves are the size of a million boats in length, then it's going up and down so smoothly the boat doesn't "see" the wave at all, and very little energy is lost).
posted by andrewcooke at 5:16 PM on February 11, 2016 [1 favorite]


For the ignorant such as myself, what is the significance of this? Why is it being hailed as such a huge discovery?

We should be able to use this method to observe events a billionth of a billionth of a billionth of a billionth of a second after the big bang.
posted by walrus at 5:21 PM on February 11, 2016 [2 favorites]


The "banana" will show up in the EM follow up papers

I love this website!
posted by eriko at 6:14 PM on February 11, 2016 [2 favorites]


For the ignorant such as myself, what is the significance of this? Why is it being hailed as such a huge discovery?

Numerous applications. I imagine one would be observing how often black holes collide in the observable universe, which would generate and fine tune cosmology and astronomy models.
posted by sebastienbailard at 7:14 PM on February 11, 2016


Side note: whats a good physics book to read? I loved reading Brian Greene's stuff years ago. What now? This shit is cool
posted by MisantropicPainforest at 7:17 PM on February 11, 2016


recent askme with science books - i don't think anything being discussed here is particularly new, except for the detection itself.
posted by andrewcooke at 7:32 PM on February 11, 2016 [1 favorite]


It's amazing that the frequencies in the chirp are in the audible range, emanating from an object 60 times the mass of the Sun. "Strong-field, high-velocity regime" indeed! This is a big day for General Relativity.
posted by mubba at 8:31 PM on February 11, 2016


It's getting pretty weird.

The Fermi Gamma Ray follow-up team is reporting (PDF preprint) "the presence of a weak transient source 0.4 s after the GW event was detected, with a false alarm probability of 0.0022. This weak transient lasting 1 s does not appear connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. Its localization is ill-constrained but consistent with the direction of GW150914. ... If the [gamma ray] transient is associated with GW150914, this electromagnetic signal from a stellar mass black hole binary merger is unexpected."

"Unexpected" is a modest way to phrase it, I guess. (Of course it's probably just coincidence.)
posted by RedOrGreen at 9:59 PM on February 11, 2016 [3 favorites]


Bill Watterson was almost right: scientific progress actually goes "Bloop!"

No, that was the cracking of an ice shelf as it breaks up from Antarctica. Nothing to do with scientific progress at all. You're thinking of the Transmogrifier
or something.
posted by sebastienbailard at 11:46 PM on February 11, 2016


This Ligo postdoc's blog post is a good account of what it was like to see the signal and what it means.
posted by sebastienbailard at 12:28 AM on February 12, 2016


What an amazing achievement! They've literally been working on this for longer than I've been alive, and now... total vindication! They actually detected a vibration less than the width of a proton! And now they've got the apparatus sensitive enough there'll no doubt be many more detections to come...
posted by Kevin Street at 1:42 AM on February 12, 2016


I know there’s a lot to read about this everywhere but I liked this collection of short and straightforward articles on this on The Conversation (starting here), all written by researchers and academics. I browsed through a few and found them more interesting and at the same time approachable than long journalistic-style pieces, at least.
posted by bitteschoen at 2:17 AM on February 12, 2016 [2 favorites]


I've decided to get ahead of the curve:

Gravitational Waves are a phony liberal plot!

Follow the money!

A bunch of so-called scientists invented these "waves" to get grant dollars and cushy university jobs!

"Wave" goodbye to your tax dollars!

etc.
posted by Chitownfats at 6:08 AM on February 12, 2016 [4 favorites]


I've been wondering about having two instruments. There's lots of advantages to that approach, but was it necessary for eliminating a site-specific spurious reading? They've tried to isolate the instruments from trucks, seismic events, etc.. But how many things did they see that looked like a signal at one site but not at the other?

That blog post by postdoc Christopher Berry is great. It's the second post that talks about how the biggest concern for the result not being correct was that some human deliberately sabotaged the instrument. Either the injection team or a rogue saboteur. They're confident in their science and engineering; it's their fellow scientists they don't quite trust :-)

Bonus link: Gravitational Wave Detectors and Sources, by Berry and others. It visualizes detection possibilities for gravity waves at different energy and frequency. LIGO is built to detect low frequency, very high energy gravitational waves that come from colliding black holes. There are other detectors like the space-based eLISA that will detect gravitational waves from other sources with higher frequencies, etc.

If I read the chart right, LIGO can theoretically just detect gravitational waves from pulsars. Are these pulsars we also can observe in the electromagnetic spectrum?
posted by Nelson at 6:45 AM on February 12, 2016


I find Hactar posting on this topic to be eponyawesome.
posted by ZeusHumms at 6:59 AM on February 12, 2016


> I've been wondering about having two instruments... how many things did they see that looked like a signal at one site but not at the other?

The paper says they calculate their noise background by first shifting the time series at the two detectors by more than the light travel time across them (~10 ms) and then cross-correlating the series.

If I try this with ASCII art, say the actual series looks like this as a function of time:
D1: 011012000101017898701010103001010012030100
D2: 000101400101789870101010143200010102004010

If you time shift the D2 series by more than 15 milliseconds (either way) and then do the cross correlation, you can guarantee that any "hits" will be spurious, because it is either chance coincidence or something traveling much slower than c. But you will still get hits when a real GW event ("78987") lines up with a noise spike ("432") at the other detector. So your estimate of the background false positive rate will be *worse* than what it really is.

They show plots of these detection statistic curves - the event they reported yesterday really blows the curve. It is a ridiculous outlier on their plots, and they estimate a chance occurrence probability of once in 22,500 years of operation. (Or 1 in 203,000 years, if you account for the waveform specifics.)

The second most significant event (briefly mentioned in the paper, so no embargo) has a false alarm probability of once every 2.3 years. Not too bad, but I guarantee that they are so (SO) relieved that they didn't have to make their big announcement based on that event!

> LIGO can theoretically just detect gravitational waves from pulsars. Are these pulsars we also can observe in the electromagnetic spectrum?

Yes, if you have something massive and spinning but not perfectly spherical, it would radiate gravitational waves. A neutron star spins, and it is massive, and it is observed to slow down because it radiates energy, and we don't see all of that radiated energy in the EM spectrum for pulsars. In the old LIGO days (LIGO-1 or pre-LIGO or non-Advanced-LIGO or whatever they're calling it now), they published papers about how their non-detections meant that the Crab pulsar was not radiating all its energy loss in the form of gravitational waves, else they'd have seen it. But that meant that they could constrain the departure from a perfect sphere, and limit the height of mountains on the Crab pulsar.

(Like all things related to neutron stars, the "mountains" are ridiculously out there - we are talking about centimeter-sized mountains. At the outrageous max. Gravity is weird in the strong field regime.)
posted by RedOrGreen at 9:47 AM on February 12, 2016 [7 favorites]


eLISA would work at lower frequencies than LIGO.
posted by edd at 1:12 PM on February 12, 2016 [1 favorite]


It's amazing that the frequencies in the chirp are in the audible range

Apparently LIGO's range is 30–7000 Hz, so anything it is able to detect is going to be audible. I don't mean to dispute the amazingness of it, though - it's mind boggling to think of stellar phenomena happening on that time scale.

Let's see. If each of the two bodies makes a peak when it's whizzing past, a 250Hz wave would mean they were orbiting each other at 125 Hz. According to Wolfram Alpha, a 60 M black hole has a Schwarzschild radius of 175 km. I seem to recall you're not supposed to be able to see what happens inside the event horizon, so wouldn't that mean that the last we heard, the 250Hz wave, would've been at that radius? But going around a 175km radius circle 125 times a second makes for a linear velocity something just shy of half the speed of light!

On one hand, that seems unreasonably fast for something with mass.
On the other hand, I just looked up rotating black holes, and am realizing that in this context, I have no idea what's reasonable or not, including all of that above napkin math. Can someone with a better understanding of stuff like frame-dragging help me out here?
posted by aubilenon at 3:18 PM on February 12, 2016 [1 favorite]


Someone else asked this above, and now I'm wondering too -- do such powerful gravitational waves have any practical effect in the real world? Ie, if you were in the solar system where these two were combining, would you feel anything at all? What does 3 suns worth of gravitational waves look like close up?
posted by tavella at 4:25 PM on February 12, 2016


Ah, found a description from Gizmodo:

"Now assume that we are 2 m (~6.5 ft) tall and floating outside the black holes at a distance equal to the Earth’s distance to the Sun. I estimate that you would feel alternately squished and stretched by about 165 nm (your height changes by more than this through the course of the day due to your vertebrae compressing while you are upright). This is more than survivable."

It's hard to get my mind around that much mass going into energy and meaning so little to the real world!
posted by tavella at 4:30 PM on February 12, 2016 [2 favorites]


aubilenon: the final black hole has rotation 0.67, in units that range from 0 (not spinning) to 1 (the maximum spin a black hole can have; proportional to the mass squared).

So it's spinning about two thirds as much as it possibly could be spinning.

In somewhat useful units, that's angular momentum = .67 G M^2/c, where M is the mass, G is gravitational constant, and c is speed of light.

Regarding tavella's comment-- yeah, gravity is *weak*. Sort of startling.
posted by nat at 5:25 PM on February 12, 2016


This is super-cool: Signal Processing with GW150914 Open Data. A Python Notebook that demonstrates analyzing the LIGO sensor data for yourself, converting the raw data into spectrogram plots and playable sound files.
posted by Nelson at 7:17 AM on February 13, 2016 [2 favorites]




The instruments are extraordinary works of audacity, imagination and ingenuity. For every single thing that goes into the detector, people have asked 'how can we make that better?' and 'how can we control that?'. They are really lovely machines. I did four whole years studying the amount of measurement noise that would be contributed by the thermally induced vibrations of a particular type mirror coating and a particular way of joining bits of glass together. Every single component has been looked into in that kind of detail.

there's a nice writeup by natalie wolchover in quanta, which links to this interview with gabriela gonzález that i found really interesting:
How is it possible to detect a length of less than one-ten-thousandth of the diameter of a proton?

The way I described it, it sounds simple. It’s a beam splitter, a laser and two mirrors. But there are thousands and thousands of things that need to be controlled. The distance is always changing because the mirrors are moving. We need a lot of tricks to make sure the atomic motion, the Brownian motion, of these mirrors does not limit us too much. This all has to be done in a vacuum. You are counting photons and there is a quantum uncertainty in the number of photons. The very hard work in the field has been reducing those sources of noise to get the sensitivity that we have now.

Is that the difference between the initial LIGO and Advanced LIGO?

It’s amazing, because if you look at it from the outside, it looks the same. It’s the same observatory, the same vacuum chambers. But on the inside, everything is different. We have a laser that’s 10 times as powerful, with more stabilization and more features. In initial LIGO, we had mirrors hanging from a single suspension, which in turn was hanging from “shock absorbers” to reduce seismic noise. In Advanced LIGO, we have mirrors in a quadruple suspension hanging from an active seismic isolation system. It’s a system that has lots of sensors and pushers — we call them actuators — that cancel the noise. So they measure the way the ground is moving and then they cancel it.

How much of the universe will Advanced LIGO be able to observe?

We refer to the sensitivity of our detectors by how sensitive they are to binary neutron star systems. With initial LIGO we could detect these systems up to 20 megaparsecs away. [A megaparsec is about 3.3 million light-years.] Now we can see 60, 70, sometimes even 80 megaparsecs away. But we think that Advanced LIGO detectors should, with all the bells and whistles, reach 200 megaparsecs.

And will this sensitivity allow Advanced LIGO to detect gravitational waves?

With a sensitivity of 200 megaparsecs in two detectors, we expect a rate of tens of events per year. If we are at 150 megaparsecs, then we might see a few a year. But that’s already more than one!
the interview was in october :P

oh and from carroll's list of 'five big targets in particle physics/gravitation/cosmology' for the decade...
  1. Discover the Higgs boson.
  2. Directly detect gravitational waves.
  3. Directly observe dark matter.
  4. Find evidence of inflation (e.g. tensor modes) in the CMB.
  5. Discover a particle not in the Standard Model.
re: #3 (and #5?), here's frank wilczek on axions: "The experimental search for axions continues on several fronts. Two of the most promising experiments are aimed at detecting the axion fluid. One of them, ADMX (Axion Dark Matter eXperiment) uses specially crafted, ultrasensitive antennas to convert background axions into electromagnetic pulses. The other, CASPEr (Cosmic Axion Spin Precession Experiment) looks for tiny wiggles in the motion of nuclear spins, which would be induced by the axion fluid. Between them, these difficult experiments promise to cover almost the entire range of possible axion masses. Do axions exist? We still don't know for sure. Their existence would bring the story of time's reversible arrow to a dramatic, satisfying conclusion, and very possibly solve the riddle of the dark matter, to boot. The game is afoot."
posted by kliuless at 11:11 PM on February 13, 2016 [2 favorites]


Several solar masses were lost to energy in the gravitational waves. So something escaped from a black hole, seemingly! Granted, the energy is still in the gravitational regime, but it's still radiating away and, though small, it has (just barely perceptible) effects on the rest of the universe.

Is this lost mass attributable to relativistic effects of the black holes' extreme velocity rather than to their rest masses (none of which is lost)? I've not seen anyone comment on this aspect of it.
posted by sjswitzer at 1:55 PM on February 14, 2016


It seems like it would have to be energy lost from the relativistic mass, although I'm not an expert. The waves are being generated by a rotating, asymmetric system. If the rotation stops, so does the radiation, which implies that the energy being radiated is taken from the rotational energy. Also, the energy lost this way causes orbital decay, which even more strongly implies the same.

Because of that, I don't think it is energy escaping from a black hole - the energy radiated is present in the two-body system, not the black hole per se. Once the black holes merge, there's a brief window of time when energy continued to radiate, until the resulting body reached full symmetry, at which point it would stop.

See Hawking radiation for a more straightforward (but theoretical) case of energy escaping from a black hole.
posted by vibratory manner of working at 3:22 PM on February 14, 2016 [1 favorite]


Also, the energy lost this way causes orbital decay, which even more strongly implies the same.
It sure does. Thanks for pointing that out!
posted by sjswitzer at 7:30 PM on February 14, 2016


Bit late to return, but yes sjswitzer - it can come out of the black hole mass, but there's a limit to how much black holes can radiate away this way, and these sorts of processes don't need the quantum mechanical stuff that Hawking radiation does. The Penrose process is another example of that sort of thing.

The limit on how much can disappear is a consequence of the Area Theorem - the total area of the black hole event horizons can't decrease. This is ignoring Hawking radiation. The author of the theorem can be let off for not knowing about Hawking radiation at the time he came up with it, because the author is Hawking.
posted by edd at 6:00 AM on February 19, 2016


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