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Gravitational waves detected by LIGO
- brnie4d1kt4tr 11y agoPost something not the telegraph. Seriously, the only thing this article is says: Physicists and astronomers are agog. On Thursday, experimenters will report the first detection of a phenomenon that has been long predicted: bursts of gravitational waves generated by cosmic collisions of black holes. That is NOT a report, that's someone guessing what the report will be. There's not a single quote from anyone remotely involved in the project. This is a piece of shit summary of a wikipedia entry on LIGO with a clickbait headline. fucking SAGE
- ck2 11y agoI supposed for now it's impossible to detect the source or even general direction of such waves? Are gravitational waves also limited to the same speed as light? Wait, is it the actual fabric of space that is "waving" ? Whoa. ps. fun fact "razzmatazz" appears in google less than a million times
- brnie4d1kt4tr 11y agoYou can get the direction of such waves by looking at 2 experiments at once, or experiments with 3-d mirror arrangements instead of 2-d ones. Yes, the existance of grav waves is only possible if they travel at some top speed, which is presumed to be the speed of light.
- joolze 11y agoyou can determine direction with multiple experiments, or with 3d mirror arrangements, see LISA and yes, they can only exist if they travel at the speed of light. it's a major test of the limiting speed of light.
- MereInterest 11y agoMultiple experiments wouldn't help very much, because it will be a new source each time. When two black holes merge, it is only during the final few seconds that very large gravitational waves are emitted.
- evanb 11y agoI believe gp meant multiple laser interferometers, not multiple gravitational-wave-emitting events.
- kryptiskt 11y agoIt's possible, there are three detectors hundreds of miles from each other, so they can use triangulation to get a fairly accurate read of the source.
- yanowitz 11y agoIt's two detectors, each of which has two tunnels at right angles to each other (and generate an interference pattern when a gravity wave distorts the tunnels length).
- kryptiskt 11y agoOops, I meant two.
- SideburnsOfDoom 11y agoI'm no expert, but wouldn't you need an extremely long baseline to triangulate on distant stars? I mean, too long to fit on planet earth?
- kryptiskt 11y agoOnly if your interested in the distance, parallax measurements do that by measuring when the Earth in on different sides of the sun. If you're only after direction you can measure the time skew between signal hitting detector one and two.As you know the speed (same as light), and that the wavefront is parallel, you have a pretty good idea where in the sky the wave came from.
- SideburnsOfDoom 11y agoFor the first case, you would need a signal that lasts for at least half a year. Does that cover two black holes merging?
- davrosthedalek 11y agoWell, technically, they black holes circle each other for billion of years. So with instruments sensitive enough, you could do that. Unfortunately, LIGO and the others are only sensitive enough to see the last few parts of a second, when the signal is strongest.
- MereInterest 11y agoThe general direction may be possible, but the source itself would not be. The compression is smallest parallel to the direction of the wave's travel, and is largest perpendicular to the direction of the wave's travel. LIGO measures a change in the difference between the lengths of the two arms, ad so it would be more sensitive to waves moving along one of the arms. It would not be at all sensitive to waves that are moving perpendicular to both arms. Since there are two such facilities, located on different parts of the Earth, they may be able to compare the relative size measured by each facility, and narrow down a part of the sky. Since the facilities are relatively close to each other (only 2000 miles, 30 degrees along Earth's circumference), the margin of error would be very large. Ideally, to localize the direction, you would have three facilities, each located at 90 degrees away from the other two, so that you have one facility "pointed" in each direction. Even then, it would only be able to narrow it down to 2 possible origins, as the direction of travel of the wave would not be measurable. Anything that carries information is limited to the speed of light. Gravitational waves carry information about the location of the merging black holes, and so they are limited to the speed of light. If anything that carried information were to travel faster than the speed of light, it would break causality, because you could find some frame of reference in which the effect happened before the cause. And yes, it is spacetime itself that is vibrating.
- OscarCunningham 11y agoHow exactly is "speed of light" defined when the spacetime is moving in the precisely the region in which we are trying to measure the speed of light?
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- dantillberg 11y agoIf at the same time* we were to observe a supernova via other telescopes, that would give a pretty good indication. :) *: And this would also possibly serve to answer another question -- do gravitational waves travel at precisely the speed of light? (also, I'd be interested in hearing about neutrino detectors -- how closely (if nonzero) to the speed of light do neutrinos travel?)
- spacehome 11y agoYes, gravity waves travel at lightspeed, at least if you buy into general relativity's tensor equations. Neutrinos have rest mass and move slower than light. We know this because neutrinos change their flavor in transit, meaning they experience the passage of time, something that would not be possible if they had no rest mass and traveled at light speed. https://en.wikipedia.org/wiki/Neutrino_oscillation https://en.wikipedia.org/wiki/Neutrino_oscillation Nobody knows how much slower, but they must be moving almost light speed because we see neutrinos from supernova collapse before we see the light emission. (The light emission from supernovae is delayed by several hours, because it takes that long to heat up the gas around the collapsed core before it can radiate out.) https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions
- antome 11y agoAny idea on what the certainty is for these results? 5 Sigma?
- brnie4d1kt4tr 11y agothis is a rumor
- hcrisp 11y agoRumored to be 5.1. https://news.ycombinator.com/item?id=11073020 https://news.ycombinator.com/item?id=11073020
- cshimmin 11y ago> On Thursday, experimenters will report the first detection of a phenomenon that has been long predicted So... this is news before news? I.e. rumor. LIGO is not scheduled to announce results for another 3.5 hrs.
- agentgt 11y agoIf it is a rumor it's probably on very good authority. The author appears to be extremely reputable.
- deleted 11y ago[deleted]
- apsec112 11y agoThe author is Sir Martin Rees, the leading astronomer in the UK (Astronomer Royal), and former president of the Royal Society. It's not some random journalist. https://en.wikipedia.org/wiki/Martin_Rees https://en.wikipedia.org/wiki/Martin_Rees
- lmm 11y agoHe's The Right Honourable Lord Rees these days.
- michaelhoffman 11y agoIt's common for journalists to be told science news before an official announcement if they agree not to publish on it until afterward. This is called an embargo.
- kbart 11y agoOh come on, can't you wait few more hours for an official announcement? It's the third (to my count) "announcement of announcement" today.
- ebbv 11y agoI think articles coming out ahead of the announcement, explaining to the general public what the announcement means is actually really helpful. Then more people who might be interested can turn in to the announcement itself.
- dwightgunning 11y agoI agree. It's just the click-baiting that irks me.
- trymas 11y agoyou can do everything for sweet sweet internet points.
- alexburton 11y agoFor publishers it's sweet, sweet internet munies.
- jug 11y agoIn other news, Perl 6 is done! ;)
- __mbm__ 11y agoFor the official announcement, where you'll hear all of the sound bytes you'll be reading later today, you can get to the livestream from Caltech's website here https://www.caltech.edu/ https://www.caltech.edu/ Starts in 2 minutes.
- joolze 11y agoPost something not the telegraph. Seriously, the only thing this article is says: Physicists and astronomers are agog. On Thursday, experimenters will report the first detection of a phenomenon that has been long predicted: bursts of gravitational waves generated by cosmic collisions of black holes. That is NOT a report, that's someone guessing what the report will be. There's not a single quote from anyone remotely involved in the project. This is a piece of shit summary of a wikipedia entry on LIGO with a clickbait headline. SAGE
- apsec112 11y agoThe second paragraph, immediately afterwards, says: "Sadly it is not unknown for hyped-up scientific claims to be mistaken or exaggerated - claims of particles going faster than light, gravitational waves from the big bang, and so forth. I count myself a hard-to-convince sceptic. But what is being claimed will be the culmination of literally decades of effort by scientists and engineers with high credentials, and this time I expect to be fully convinced." ie., Sir Martin Rees (the author), one of the most famous astronomers in the world, is putting his credibility behind this. That matters.
- graycat 11y agoYou are a very skeptical, no BS, tough nut to crack kind of guy. Good! I like that! HN, the Internet, the world needs much more of that. Such high standards make at least some of HN a crown jewel of the Internet place. Still, back to common, ordinary, reality, Sir Rees does have a lot of credibility.
- merraksh 11y agoLive stream at https://www.youtube.com/watch?v=zyo4DFr4D4I https://www.youtube.com/watch?v=zyo4DFr4D4I
- roddux 11y agoHeadline should read: Telegraph reporter jumps gun for ad revenue
- apsec112 11y agoThe author is Sir Martin Rees, one of the most accomplished astronomers in the world, not a Telegraph reporter. https://en.wikipedia.org/wiki/Martin_Rees https://en.wikipedia.org/wiki/Martin_Rees
- db48x 11y agoThese two statements are not mutually exclusive.
- apsec112 11y agoPer Googling site:telegraph.co.uk "by sir martin rees", Rees has written one piece for the Telegraph before, in 2013. He doesn't seem to write for other news outlets (although he has written a book), and if he has any background as a journalist, Wikipedia doesn't mention it. Calling him a "reporter" seems quite silly.
- db48x 11y agoIf you report on current events, you're a reporter. Regardless, the substantive portion of the statement is 'jumps the gun for ad revenue'.
- realo 11y agoMy friends invite me to dinner sometimes. They make the meal. That does not make them chefs, or cooks by profession. At best we can say they cooked that particular meal. Being a journalist or reporter by profession is one thing. Saying that someone who wrote a single news article is a reporter seems to be an abusive usage of the word. At best we could say that he reported that particular event. Just saying...
- amelius 11y agoWouldn't it be much more spectacular if these waves were not detected?
- dantillberg 11y agoIf they were not detected, that wouldn't necessarily say much unless you could demonstrate certainly that they also should have been. In which case, yes. Though, in actuality, the physics of gravitational waves have been indirectly observed previously [0], so it's not like it's still entirely in the realm of hypothesis. [0]: The Hulse–Taylor binary pulsar: https://en.wikipedia.org/wiki/PSR_B1913%2B16 https://en.wikipedia.org/wiki/PSR_B1913%2B16
- MereInterest 11y agoAt the moment, it would tell us more about cosmology than about the underlying physics, were we not to detect the gravitational waves. We expect gravitational waves to be emitted from two black holes as they orbit very close to each other, just before they merge. From general relativity, we know how big of gravitational waves to expect. However, we don't know how many such black hole mergers occur in nearby space. LIGO can only measure gravitational waves down to a certain strength, and so we can only detect waves that are caused by black hole mergers within some distance of Earth. Predictions of how many such mergers occur vary wildly, depending on the assumptions in the model. (I don't have exact numbers, and would appreciate if anyone does have the numbers.) If we did not detect gravitational waves, I would use that as a lower bound of the number of black hole mergers, rather than as a breaking of general relativity.
- olympus 11y agoNot observing any gravitational waves wouldn't prove that gravitational waves didn't exist, so there wouldn't be nearly as much fuss and news articles written. Imagine the press release: "Jury still out on existence of gravitational waves: LIGO not sensitive enough/ Is LIGO a gazillion dollar waste?." So while if someone were able to PROVE that gravitational waves didn't exist that would be pretty spectacular because it would upend decades of scientific research and cause us to rethink relativity. But this is still pretty spectacular in it's own right. The predictions that physicists make are made by examining mathematical models that are only partially vetted. Some parts of the models remain theoretical because we don't have instruments sensitive enough to measure their predictions (we are talking about energies on a ridiculous tiny scale here). Finally we have invested millions on an instrument that is sensitive enough and it confirms (to the best of its ability) that we were on the right track. This is a great relief to the scientists that they don't have to go back to the drawing board and rethink all their models, plus it is a great victory for predictions made before the age of computers.
- madaxe_again 11y agoI'm am really confused as to how Martin Rees has written such a poor article. He's bloody Astronomer Royal. I suspect a ghostwriter. a) Gravitational waves do NOT "shake the mirrors". They make spacetime contract in orthogonal directions around and within the beam tube (and of course elsewhere) thus causing the light to travel a tiny bit further in the tube, thus causing interference by moving the two beams out of phase. b) As I posted the other day - what about Virgo? What about GEO600? I feel really sorry for the scientists who've spent decades working on this as part of a global collaboration to now have LIGO take all of the credit for this discovery.
- bloat 11y agoa) He says just that, three paragraphs before he uses the shorthand "shakes" - which is in quotes, indicating the inaccuracy of the usage.
- madaxe_again 11y agoTrue, but it's a poor analogy. I've read many of his books - and it feels like this got editorialised or ghostwritten into "wrong" - he is usually a precise and excellent explainer of complex concepts.
- nevir 11y agoMaybe he makes mistakes, or has trouble explaining some concepts, from time to time?
- ebbv 11y ago> I feel really sorry for the scientists who've spent decades working on this as part of a global collaboration to now have LIGO take all of the credit for this discovery. You might as well say the same thing about CERN and the Higgs. That's how credit for discoveries works. You can't just give it to "the whole scientific community" so you pick the most specific attribution that makes sense.
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- feider 11y ago"This is why it’s been crucial to have two similar detectors separated by nearly 2,000 miles - one in Washington State, the other in Louisiana - and to seek events that show up in both detectors, thereby ruling out effects caused by local seismic events, passing trucks, and so forth." Sounds like a good old survival bias ;) Seriously though, what is confidence interval in LIGO?
- olympus 11y agoThe standard for physics reporting on things like this is "five sigma" or that the test statistic in their hypothesis test must be greater than 5. Since this is a one-tailed test, this corresponds to a p-value smaller than 0.00000029, so the chances of being wrong are about 1 in 3.5 million. This isn't a "confidence interval" like you were asking about, but I think that it answers what you meant to ask. Let me know if you wanted something else.
- feider 11y agoThanks, that pretty much explained what I was after.
- bakhy 11y agoi want to take my upvote away from this. seeing the title, i foolishly thought that the conference already took place, and just clicked before reading and seeing that the title is a lie. :/
- deleted 11y ago[deleted]
- ww520 11y agoThis is huge. The amount of precise measurement went into it is remarkable.
- sgrytoyr 11y agoHow do they measure (not just calculate, if I understand this correctly) "a distance less than a millionth of the size of a single atom"? That sounds very difficult to do with equipment that is presumably made of atoms.
- mclightning 11y agoYou can probably use sub-atomic features of atoms to do sub-atomic measurements. For example their electromagnetic fields may be shifting depending on distance to another atom or another field. PS: I am no physicist.
- bbrazil 11y agohttps://en.wikipedia.org/wiki/Michelson_interferometer https://en.wikipedia.org/wiki/Michelson_interferometer Basically fire two lasers at right angles to each other at mirrors, and see the pattern when they bounce back.
- dekhn 11y agoBTW, you can build your own Michelson interferometer (when it was first constructed, it was a technical marvel, involving a large hunk of metal floating on mercury, deep down in a building, and even then the experiment was affected by subtle vibrations): https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6635 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=66...
- Velox 11y agoWhen light interferes with itself it creates a "pattern". When the light beams are out of phase, the interference pattern is different. The gravitational waves basically minutely increase the distance that one of the beams travels and causes it to go out of phase with the other, thus changing the interference pattern.
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- anotheryou 11y agowild speculation or a broken press embargo? press conference is streamed in an hour here: https://youtu.be/zyo4DFr4D4I https://youtu.be/zyo4DFr4D4I
- ascorbic 11y agoThe live stream has moved, and has now started here: https://www.youtube.com/watch?v=c7293kAiPZw https://www.youtube.com/watch?v=c7293kAiPZw
- pavanky 11y agoThanks! I was stuck at the other stream wondering when it was going to start.
- srikar 11y agoLink to research paper here: https://news.ycombinator.com/item?id=11080678 https://news.ycombinator.com/item?id=11080678
- kkamperschroer 11y agoA useful layman's explanation of gravitational waves and the LIGO experiement: https://www.youtube.com/watch?v=1Tstyqz2g7o https://www.youtube.com/watch?v=1Tstyqz2g7o
- deleted 11y ago[deleted]
- lobster_johnson 11y agoAs an aside, it's hilarious that the announcement was spoiled by Twitter pic of the backroom marzipan cake posted 8 minutes before the announcement: https://twitter.com/marckuchner/status/697802191873114112 https://twitter.com/marckuchner/status/697802191873114112.
- amelius 11y agoShouldn't we have multiple detectors, to determine which direction the waves are coming from? (Like an antenna array can also be direction-specific using computational techniques). Or are these detectors already directionally sensitive?
- Steuard 11y agoLIGO is based on two detectors, one in Louisiana and one in Washington. With those, according to today's talk, we can get a rough idea of the direction of the source: it was in the southern sky, vaguely in the direction of the Magellanic Clouds. Once some of the other planned experiments come online over the next few years, they expect to be able to localize sources to within 5-10 degrees on the sky. (Or so I just heard from the press conference.)