Talk:LIGO

Untitled
We need to add a subsection with a description of the interferometers and how its possible for them to measure such small distances.

Two things strike me about this summary. First, how do the detection facilities account for the overwhelmingly powerful effects of even very minor earthquakes that occur every day at multiple locations around the earth?
 * Multiple detectors in several locations of same cosmic event. Allows one to subtract local noise. (Not just earthquakes, this experiment detects slamming doors.) Someone who knows more, add more. GangofOne 07:00, 7 August 2005 (UTC)

Second, the last paragraph of this summary is a thinly disguised plagarism of the LIGO-detectors web summary. If I pulled that in my work it would be ixney-on-hombre if you catch my drift...maybe someone with a good technical grasp of this could re-write it in a more "original" context instead of rewording a website summary. - JS 6-10-05

I added an external link on discussion of vibration and interference.

I have a question, what is "Diameter 	4000 m" supposed to mean? LIGO has two arms forming an 'L', their lengths are 4000m. So wouldn't it be more precise if you put it "Radius 4000 m"? Or just write "Arm length 4000m"? — Preceding unsigned comment added by InsideYaBrain (talk • contribs) 17:12, 23 April 2013 (UTC)

ligo
I have a question on why study the gravitational waves? What do we gain from it?? User:Sjml9




 * Why did Maxwell waste his time studying Electromagnetism. Everyone knew it wasn't good for anything back in 1864.
 * Actually, although you weren't taught it in either high school or college, Maxwell's development of what are now known as Maxwell's equations was far more important than any other single event (or group of events) in the 19th century! The Mexican-American War&mdash;trivial. The American Civil War; in spite of what you were taught&mdash;trivial. The abolition of slavery in much of the world; well that's a little more important, but still small shakes compared to Maxwell's equations.
 * Maxwell's equations, developed in 1864, set the stage for electric lights powered by AC current, radio, television, computers, space flight, and almost everything we consider routine today. You'd still live in a world lit by fire without Maxwell's equations!
 * No one can assure you we're not wasting our time and money looking for gravitational waves. But your great-grandchildren (who will think your life was as primitive as you think your great-grandparents lives were) will live in a different world than you can even imagine.
 * Williamborg 03:52, 1 July 2006 (UTC)


 * And finally, I must admit I've been awaiting with some impatience the experimenters publication of some discovery. Once we actually detect gravitational waves we'll get some sense of the significance of the event...


 * Hmm, I'm not sure any of these replies actually answer the user's question. The study of gravitational waves are needded to explain and/or confirm a number of phenomenon more directly. Some are entirely hypothetical, others only indirectly observed. This part from the article, recently updated by me thanks to a great online lecture by Kip Thorne himself (co-founder of LIGO), should help answer your question: -- Northgrove 05:34, 1 January 2007 (UTC)


 * The following text, below, is a copy of a post I found around the internet somewhere. I would like the answer to this also, so I copy post it here, to be mulled over, digested and hopefully, answered! --87.115.10.14 (talk) 07:05, 19 January 2008 (UTC)

Just getting back to LIGO for a while (sorry if this isn't strictly on topic), I understand that two long laser beams, at 90 degrees to each other, split from one laser source originally by a semi-silvered mirror, are re-combined at a sensitive detector to see whether their wave forms are cancelling or reinforcing. A passing gravity wave will sequentially lengthen and shorten the wavelength of only one of these light beams because the space-time continuum is distorted in only the direction of travel of the gravity wave. This, it is assumed, will cause the interference of the two laser beams to vary also - causing a variation in the light level measured at the detector.

I still don't see why LIGO will work because a gravity wave is indiscriminate in the way it distorts things. Everything is embedded in our 4-space, including the laser light waves lying along the direction taken by the gravity wave. As the gravity wave compresses and then dilates space-time, the LIGO tube and the laser beam within it will compress and dilate in perfect synchrony. Even the human observers' heads will compress and dilate as the gravity wave passes! The number of light waves per unit length of the LIGO tube (the laser wavelength) will appear unchanged because the actual physical length of the tube will shorten and lengthen as the light waves do, and as the eyeballs of the experimenters do too. If the waves of the re-united beams were re-inforcing peak-to-peak before the gravity wave arrived, they will remain peak-to-peak as the gravity wave passes through also. This alteration in the length of the tube, or arm, of the LIGO experiment, together with the variation in the wavelength of the laser beam, will be completely undetectable for that reason. It's not a case of the gravity waves being too weak to detect, their influence is universal within our frame of reference and therefore cannot be directly detected .. by definition!

The above is the way I see the situation. But dozens of scientists have spent billions of dollars designing LIGO, so I have to conclude I'm completely incorrect in my reasoning.

Can anyone tell me how you can measure a distortion of space-time (4-space) if you, and every tool you use to measure the distortion, including light, are part of the same space-time being distorted? ???

The key concept is tidal effect. 66.27.66.182 (talk) 06:53, 6 February 2009 (UTC)

"Billions of dollars" above is a bit exaggerated. $365 million was spent building LIGO. I don't know the cost of subsequent improvements or the operating budgets, but I would estimate the total US investment remains under $0.5 billion. —Preceding unsigned comment added by 192.220.217.1 (talk) 19:44, 21 July 2010 (UTC)

The article describes the operation of LIGO as being very sensitive but otherwise standard interferometry between the two arms of the interferometer. However as noted above things are more subtle because not only the arms but also the propagating light in the interferometer is sensitive to a change in space time caused by the gravitational waves and depend on the tidal effect. It would be good if the article explains/compute the phase shift between the two beams and has a good reference. Unfortunately I don't have one.

RogierBrussee (talk) 13:21, 2 August 2010 (UTC)


 * There is an excellent video of an introductory lecture on LIGO physics by professor Alan Weinstein of Caltech: http://elmer.caltech.edu/ph237/week12/week12.html —Preceding unsigned comment added by 131.215.115.31 (talk) 20:58, 13 December 2010 (UTC)


 * I am not sure if video of lecture by professor Alan Weinstein is intended to cover the issue of the arms and the light both being affected by the gravitational waves in ways that might be expected to cancel each other out, but it does not seem to (I have not looked at the video, just the set of slides provided). I think this issue is important enough to have a section of it's own, so I have started one: see "Change interferometer arms and change in light might be expected to cancel each other out - an answer" below. FrankSier (talk) 15:46, 6 March 2017 (UTC)

observations

 * Should the two GW observations be mentioned in the summary?

The article contains the statement "But if and when even one verified gravitational wave event is observed by any of the worldwide detectors, it will be a truly exciting moment for all astronomers and astrophysicists worldwide who have waited so long for such an event to be seen." If this is true, then the newly added statement "In February 2007 a short gamma ray burst, GRB070201 which came from the direction of the Andromeda Galaxy, failed to be observed by LIGO. This was significant as it ruled out the Andromeda Galaxy as the location of the event." is not correct. since LIGO has not been able able to demonstrate detection of any verifyable gravity waves. So I have modified the sentense to reflect this. Blufox (talk) 12:29, 23 January 2008 (UTC)

You can't measure God, heretics.

This section states "Equivalently, this is a relative change in distance of approximately one part in 10^21." This statement needs to be explained. As stated it is not clear.

1 attometre
This does not pertain to this article, but the article on 1 attometre references LIGO, and I want to make sure it has its facts straight. Has LIGO actually reached 1 attometre sensitivity, or is that its target? Could someone who knows this please check the article. Pulu (talk) 06:58, 12 November 2008 (UTC)

Dubious
Note that 1 mi ≠ 1.600 km. Provide a reference for which of the two numbers is correct, then convert it properly. Gene Nygaard (talk) 13:48, 5 January 2009 (UTC)
 * The other issue to be settled is, from the POV of astronomical measurement, which is the more relevant description of separation: the distance along an arc from Louisiana to Washington or the direct Euclidian distance through a bit of the earth's crust? 96.237.148.44 (talk) 22:56, 11 February 2009 (UTC)
 * The relevant distance is the three-dimensional Euclidean one, because GWs don't care if they travel through the Earth. The distance between the vertices of the LIGO interferometers is 3002km; I converted that to 1865 miles. 74.212.144.98 (talk) 19:52, 16 March 2009 (UTC)
 * It is mostly not the physical distance, but the rotation due to the curvature of the earth. That determines the polarization of the detectable waves. Separate from that, is the direction of the arms. One thought was to make them close to the same, allowing for detection consensus. Detecting different polarizations increases the chance of detecting something. The distance between them, and signal time difference, gives one angle for determining direction. Gah4 (talk) 05:45, 6 April 2022 (UTC)
 * As for 1mi vs. 1.600km, astronomy often has measurements where within a factor of 1000 is considered close. I suspect 1.6km/mi is close enough. Gah4 (talk) 05:45, 6 April 2022 (UTC)
 * It is mostly not the physical distance, but the rotation due to the curvature of the earth. That determines the polarization of the detectable waves. Separate from that, is the direction of the arms. One thought was to make them close to the same, allowing for detection consensus. Detecting different polarizations increases the chance of detecting something. The distance between them, and signal time difference, gives one angle for determining direction. Gah4 (talk) 05:45, 6 April 2022 (UTC)
 * As for 1mi vs. 1.600km, astronomy often has measurements where within a factor of 1000 is considered close. I suspect 1.6km/mi is close enough. Gah4 (talk) 05:45, 6 April 2022 (UTC)
 * As for 1mi vs. 1.600km, astronomy often has measurements where within a factor of 1000 is considered close. I suspect 1.6km/mi is close enough. Gah4 (talk) 05:45, 6 April 2022 (UTC)
 * As for 1mi vs. 1.600km, astronomy often has measurements where within a factor of 1000 is considered close. I suspect 1.6km/mi is close enough. Gah4 (talk) 05:45, 6 April 2022 (UTC)

Einstein@home
The home-computer discovery with references 7 and 8 is not really relevant because it is a discovery of a pulsar using radio data, not gravitational waves. 99.38.163.5 (talk) 02:45, 9 September 2010 (UTC)

1999 promise
In this 1999 Physics Today article LIGO Director Barry Barish and Rainer Weiss state: "After LIGO's first data run, we plan to interleave subsequent searches with a series of detector upgrades that promise to lead to ever-enhanced sensitivity, making the direct detection of gravitational waves a reality within the next decade." I think this is far more reliable source than Rana Adhikari's dubious private communication (to whom?) referenced in the WP article ("In 2004, it was reported that theorists estimated the chances of an unambiguous direct detection by 2010 at one in six."). Actually (as documented here) Adhikari stated in 2007: "I tell students they're lucky [...]. They're getting in at the right time -- it's right before we see something." Well ... .

LIGO Australia dead, LIGO India under consideration
Apparently Australia was unable to raise the funds, much less than by the October 1 deadline.

However, there was interest from India, and apparently there is the potential to locate a third interferometer there:
 * U.S. gravitational wave detection experiment looking at India as a possible site
 * 2011 NSF Review of LIGO-India Effort
 * Boost for India's hopes to host gravity wave detector

I don't have time to properly wikify this information, so I'm dumping it here for use by anyone who does. 71.41.210.146 (talk) 21:33, 28 October 2011 (UTC)

comment
is it fair to say, that after several years, and at least 360 million tax dollars, there are no ( 0 ) results worth reporting on ? That is to say, the LIGO has not detected any (any) gravity waves ? I don't want to sound like an antiscience wierdo, but if you spend 400 million dollars or so, and get nothing out of it, I think taht is worth commenting on, and the LIGO people should have a defense. — Preceding unsigned comment added by 68.236.121.54 (talk) 21:46, 31 July 2012 (UTC)

I have the same concern. The article needs to say clearly that for all the experimental work - there have been zero detections of gravity waves; none, nada, zip. — Preceding unsigned comment added by 98.234.101.123 (talk) 02:18, 23 January 2013 (UTC)

LIGO is a scientific project. The primary purpose for conducting scientific experiments is to expand human knowledge. Thousands of undergrads, grad students, post-docs, and professors have benefitted substantially from their association with LIGO, and have gone on to do more or less important scientific work and taught others how to do science. LIGO has expanded scientific understanding of optics and signal processing; It's shortsighted to ignore these side benefits, which have been achieved with great economy when one considers the the relative expense to employ 1000 people for 20 years in industry. — Preceding unsigned comment added by 131.215.115.31 (talk) 21:52, 30 July 2015 (UTC)
 * Negative results in scientific research are just as important as positive ones. LIGO has spared us any murky claim of detection, based on creative statistics, of the kind common in other realms of physics. Sincere thanks for that and keep up the good work. — Preceding unsigned comment added by 217.162.119.154 (talk) 04:37, 10 October 2015 (UTC)
 * Not quite fair writing this in 2020, but there are graphs showing sensitivity, what can be discovered, and how likely. I am pretty sure that the original LIGO detection rate was within expectations. It could detect black hole mergers up to a certain distance from earth, where the expected number was low, but with plans for increase in sensitivity (and so larger distance) later. Gah4 (talk) 20:08, 25 June 2020 (UTC)
 * Not quite fair writing this in 2020, but there are graphs showing sensitivity, what can be discovered, and how likely. I am pretty sure that the original LIGO detection rate was within expectations. It could detect black hole mergers up to a certain distance from earth, where the expected number was low, but with plans for increase in sensitivity (and so larger distance) later. Gah4 (talk) 20:08, 25 June 2020 (UTC)
 * Not quite fair writing this in 2020, but there are graphs showing sensitivity, what can be discovered, and how likely. I am pretty sure that the original LIGO detection rate was within expectations. It could detect black hole mergers up to a certain distance from earth, where the expected number was low, but with plans for increase in sensitivity (and so larger distance) later. Gah4 (talk) 20:08, 25 June 2020 (UTC)

dead link
In the Notes section

^ "LIGO Sheds Light on Cosmic Event". 2007-12-20. Retrieved 2007-12-21.

points to http://mr.caltech.edu/media/Press_Releases/PR13084.html which redirects to the useless http://www.caltech.edu/content/press

From the text it is unclear what exactly the non-detection demonstrates.

Is there some working link to the referenced article or to some other explanation of the event somehow related to the detector?--Dobrichev (talk) 13:40, 11 January 2013 (UTC)

incomplete statement
The statement "... gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10−18 m ..." does not mention what the magnitude of the gravitational waves are at their origin -- i.e., whether they are created due to two blackholes colliding or two asteroids colliding. - Subh83 (talk &#124; contribs) 10:40, 23 June 2013 (UTC)

Does the "Dyson approach" obviate the need for "Advanced LIGO"?
Detecting gravity waves through analysis of the earth's seismic data is apparently nine orders of magnitide more sensitive than LIGO. So why bother building Advanced LIGO (which will be only one order of magnitude more sensitive)? 199.46.199.232 (talk) 23:34, 14 March 2014 (UTC)

What's the ESA decision on NGO?
From the article: "A decision by ESA on the proposal is expected for November 2013"

So, what's the decision? Shouldn't the article be updated? 96.32.186.207 (talk) 06:42, 2 April 2014 (UTC)

geez where is the excitement about engineering
am i the only kid who would like a section like ligo can detect teh equivalent of 1/1000 of human hair distance change between earth and sun..or the sensitivity of ligo is great, ordianry metaphors fail  — Preceding unsigned comment added by 50.49.131.230 (talk) 03:06, 3 January 2015 (UTC)

Matters of style and substance
Since there seems to be some confusion on the part of an IP user, let me point out MOS:BOLD, specifically the guideline
 * "Do not use boldface for emphasis in article text."

However, this stylistic issue is perhaps secondary to a more substantial apparent misunderstanding of science in general and LIGO in particular. The stylistically inappropriate boldface is being used to emphasize that LIGO has not yet detected gravitational waves. I believe this emphasis is intended to imply that LIGO has therefore failed in its mission, but such an implication would be incorrect. My understanding, as a non-expert, is that LIGO has met or exceeded its design goals. Therefore either observation or non-observation of gravitational wave signals provides new and valuable information about the frequency of astrophysical events predicted to generate such signals, precisely what LIGO is supposed to produce.

Finally, I would request that the IP user refrain from accusing me of vandalism per WP:GOODFAITH. Cheers, David Schaich Talk/Cont 19:54, 6 September 2015 (UTC)

PS. As a mea culpa, I should not have used rollback to fix the issues discussed above. I'm not yet used to this feature, and only belatedly realized that further edit summaries after my first might have benefited the IP user. Sorry about that, David Schaich Talk/Cont 20:29, 6 September 2015 (UTC)

Future unclear
LIGO-India's section is unclear to me. The first paragraph claims the "designs and hardware" for one of the two "Advanced LIGO detectors" will be installed in India. The second paragraph mentions the network of three detectors formed by linking LIGO and Virgo observatories, and discusses the benefit of adding a fourth site.

But the third paragraph begins with "The NSF was willing to permit this relocation". What is being relocated where? The hardware for one of the two advanced US-based LIGO detectors? The original Australian plans? The fourth paragraph appears to clarify that one of the US detectors will be relocated - is that it? It's as if there's something missing or mis-ordered in the four paragraphs that could help avoid confusing the reader. -84user (talk) 04:54, 27 September 2015 (UTC)


 * It may be a problem with chronology and/or need to update. Cheers, BatteryIncluded (talk) 20:45, 27 September 2015 (UTC)


 * i find it quite painful to read this article because of mixed up chronological order, mixing current state with past and future in the same paragraphs. even the introduction is following this mixed up pattern. can we change the structure a little bit to fix this? --ThurnerRupert (talk) 03:44, 15 February 2016 (UTC)

credits, credits
User:BatteryIncluded, thanks for your hint, i did not clue into really looking at this long list of authors before. but at the same time i'd love to make the story a little less abstract, and include information that a real person needs to do work to spot something, and marco drago was lucky to see it. to somehow describe that there are data feeds, alerts, checking happens around the world, around the clock. also missing is that parts of ligo come from different areas of the world, this is a truely international effort, besides of course the fact that every american taxpayer contributed one or two dollars to it at least. --ThurnerRupert (talk) 05:36, 13 February 2016 (UTC)
 * My concern is that he is being promoted in Wikipedia to the degree that to the casual reader he looks like the "discoverer". In fact it is a factoid, and it is so, that his Biography/article was labeled as non-notable and proposed for deletion. I have no problem with his single mention in the proper article subsection, but spamming other Wikipedia articles is another.  Keep the perspective. Cheers, BatteryIncluded (talk) 05:48, 13 February 2016 (UTC)

Laser power
According to this official source, laser power on entering interferometer is 200 Watts, not 20 Watts as shown on the image in the article and written in the text of the article. I think, this should be corrected. Illustr (talk) 21:02, 18 April 2016 (UTC)


 * I was talking with Sheila Rowan earlier this week, and she mentioned that in 2015 Advanced LIGO used only a small fraction of their total possible input laser power. Increasing the amount of power coming in from the laser is one of the ways they expect to become more sensitive this year and in the near future.  Checking arXiv:1602.03837, I see (at the bottom of page 3) "20 W of laser input".  So I think 20W is the correct number currently being used, even though 200W may be the theoretical peak that they'll try to reach in the future. David Schaich Talk/Cont 17:11, 23 April 2016 (UTC)


 * Thank you, this makes it clear. Illustr (talk) 12:29, 24 April 2016 (UTC)

Location
United States of America, not even mentioned. Stop the European jealously and censorship.


 * Hm. The locations are in Benton County, Washington and Livingston Parish, Louisiana, where 99.9% of United States citizens do NOT live, so the statement above could be considered 99.9% misleading.
 * LIGO is a truly international scientific consortium, financed and staffed globally. The VIRGO detector in Italy increases the effective angular sensitivity by approximately a factor of 10.  A third LIGO, in India real soon now, will increase sensitivity further.  The idea was championed and developed by German physicist Rainier Weiss and Scottish physicist Ron Drevers, and was implemented by thousands of geniuses worldwide.
 * I'm proud to live in the USA that welcomes and enables genius from the entire planet, and collaborates with all nations in the exploration of the universe. And I'm proud to personally contribute to similar international collaborations.  It is sad that many of my fellow citizens never accomplished anything more significant than being born here, but it is never too late to learn a practical skill and improve the world (or at least your county, state, or nation) with it.
 * BTW, it is amusing that the location given in the sidebar is accurate to 30 centimeters; this appears to be the center of the beam crossings at each site. Thanks to TobinFricke for the exacting detail, a personal example of the global collaboration that makes LIGO so spectacular! KeithLofstrom (talk) 19:20, 27 September 2018 (UTC)

Plagiarism
The second paragraph under the "History" section:

"Prototype interferometric gravitational wave detectors (interferometers) were built in the late 1960s by Robert L. Forward and colleagues at Hughes Research Laboratories (with mirrors mounted on a vibration isolated plate rather than free swinging), and in the 1970s (with free swinging mirrors between which light bounced many times) by Weiss at MIT, and then by Heinz Billing and colleagues in Garching Germany, and then by Ronald Drever, James Hough and colleagues in Glasgow, Scotland."

seems way too close to the following paragraph in its cite:

"Prototype interferometric gravitational wave detectors (“interferometers”) were built in the late 1960s by Robert Forward and colleagues at Hughes Research Laboratories (with mirrors mounted on a vibration isolated plate rather than free swinging), and in the 1970s (with free swinging mirrors between which light bounced many times) by Weiss at MIT, and then by Hans Billing and colleagues in Garching Germany, and then by Ronald Drever, James Hough and colleagues in Glasgow Scotland." — Preceding unsigned comment added by 82.45.253.129 (talk) 14:50, 19 July 2016 (UTC)

Section Operations illustration
The figure shown in the section Operation does not match with the configuration of LIGO. That confuses the reader.

https://www.ligo.caltech.edu/video/ligo20160211v6 explains clearly that the unperturbed interferometer is tuned tot a dark fringe. Perturbations, e.g. a gravitational wave, cause periodic light fringes.

The illustration tells just the opposite. In frame 1 the recombined reflected beams should extinguish each other.

Since the illustration does not match the LIGO operation it should be edited or removed. The animation in the link above (also available on YouTube) shows the variable response to a gravitational wave. That explains LIGO far better. — Preceding unsigned comment added by Janallerddeboer (talk • contribs) 13:44, 5 February 2017 (UTC)
 * As well as I understand, whichever one it tunes to, it locks to. That is, instead of measuring the change in brightness, you measure the change in mirror position to stay in the same point of the fringe. The point where brightness would change faster is halfway, but I didn't look up how they do it. Gah4 (talk) 20:14, 25 June 2020 (UTC)
 * As well as I understand, whichever one it tunes to, it locks to. That is, instead of measuring the change in brightness, you measure the change in mirror position to stay in the same point of the fringe. The point where brightness would change faster is halfway, but I didn't look up how they do it. Gah4 (talk) 20:14, 25 June 2020 (UTC)

Change interferometer arms and change in light might be expected to cancel each other out - an answer
The interferometer tube and the light both get stretched by the gravitational wave so how come anything observable happens?

This Youtube The (apparent) Absurdity of Detecting Gravitational Waves brings this issue up and at least attempts to answer it, at 5 mins 22 seconds in. (The addition of 'apparent' in the title is mine, in case anyone thinks this is some anti-science.)

The explanation is something to do with timing, and I don't entirely understand it, and it is possibly over-simplified, but maybe one needs to be a professor of physics to really understand it.

One might not expect Youtube to be a good source, but the person being interviewed is Rana Adhikari, Professor of Physics, Caltech.

I think that this issue is worth putting the article, but could do with further thought and/or expertise. FrankSier (talk) 15:34, 6 March 2017 (UTC)


 * I have now found a mention on a/the LIGO website: and I think it is saying that the crucial things are that it is not the wavelength of the light that matters, but the timing of the light, and the fact that "gravitational waves do NOT change the speed of light". I take this to mean that the length of the arms really does change as far as the light is concerned. (So this is different than the sort of length change considered in Special Relativity, where the length of something depends on the velocity of the observer.)


 * Also, the Youtube I mentioned earlier mentions that the time period (ie inverse of frequency) of the particular gravitational waves detected so far are much longer than the transit time of the light, so the lengths of the arms do not change much during one light transit. FrankSier (talk) 16:27, 6 March 2017 (UTC)

This article "If light waves are stretched by gravitational waves, how can we use light as a ruler to detect gravitational waves?" by Peter Saulson, originally published in 1997, does a good job of answering this question. I'm not a regular editor so could someone check if it is a suitable reference and include it if acceptable please. George Dishman (talk) 13:02, 8 November 2017 (UTC)

Sensitivity to 10,000 times smaller than a proton over 4 km
I came here looking for information about the sensitivity of LIGO. But there are almost no absolute figures in the article. It says "2 times more sensitive", "10 times more sensitive" etc - but "more sensitive than what?"/

There's one point where the article talks about a sensitivity of 1 part in 10^21 at 100 Hz over 4 km. It then says this is equivalent to a thousandth of the width of a proton. But the cites are to academic papers and not directly for that particular fact. The LIGO website itself says under Facts:


 * "LIGO is designed to detect a change in distance between its mirrors 1/10,000th the width of a proton! This is equivalent to measuring the distance to the nearest star to an accuracy smaller than the width of a human hair!"

Immediately before that it says
 * "to measure a motion 10,000 times smaller than an atomic nucleus (the smallest measurement ever attempted by science)..."

Since the atomic nucleus of hydrogen consists of a single proton then the two are compatible but I thought proton was the more precise. Could say alternatively "smallest atomic nucleus".

I thought this should be mentioned in the introduction too. It helps the lay reader to realize quite how minute the changes are right away, if they thought "gravitational waves" as like waves on the sea, say. No these are tiny movements. I hope that change is accepted, I know sometimes the lede paragraphs on wikipedia can be the result of long battles but there is nothing about it on this talk page so I thought I'd just be bold and edit it.

The main question then is whether the mention of a thousandth of the width of a proton later in the page should be edited to match. If so - what's the reason - is LIGO ten times more sensitive than it used to be, or is there something different about the way it is calculated, or just a mistake? Well a proton has charge radius of 0.8751(61)× 10−15 m. And 1 in 1021 over 4 km multiplied by 10000 gives 10000×4000×10-21 or 4× 10−14, which is larger than the charge diameter of a proton and even multiplied by 1000, it's still double the charge diameter of a proton. So the later statement must be false as it is internally inconsistent, unless I'm missing something or made a mistake in this calculation - but I don't know how to correct it without reading the papers - does anyone know the answer? Robert Walker (talk) 12:37, 24 August 2017 (UTC)
 * Sometimes things are accurate enough. As I note below, the latitude/longitude give an accuracy down to 0.3m/1ft for something that is at least 4km across. Being a quantum object, the diameter of a proton is somewhat fuzzy. (Which doesn't mean someone won't give it to six digits.) The mirror movement detection is frequency sensitive. Should they give it at the most sensitive frequency? Some average? Using a proton or nucleus is something people can think about, even if it isn't all that close, just close enough.Gah4 (talk) 20:52, 26 June 2020 (UTC)
 * Sometimes things are accurate enough. As I note below, the latitude/longitude give an accuracy down to 0.3m/1ft for something that is at least 4km across. Being a quantum object, the diameter of a proton is somewhat fuzzy. (Which doesn't mean someone won't give it to six digits.) The mirror movement detection is frequency sensitive. Should they give it at the most sensitive frequency? Some average? Using a proton or nucleus is something people can think about, even if it isn't all that close, just close enough.Gah4 (talk) 20:52, 26 June 2020 (UTC)


 * The current graph of LIGO shows the sensitivity at 200Hz to be somewhat better than 10-23: https://www.ligo.org/science/Publication-GW170814/images/figure1.png — Preceding unsigned comment added by 50.1.214.5 (talk) 02:55, 22 February 2021 (UTC)
 * That's noise not sensitivity, and it's 10-23/sqrt(Hz). To convert this to a frequency-independent strain you need the frequency and the duration of the noise. And then you still need to consider that a signal needs a reasonable signal to noise ratio (i.e. much larger than 1). This is (another) reason the 10-21 shouldn't be given with too much precision - it depends on the signal, the acceptable background rate and so on. A nearby neutron star merger can be detected with smaller strain than a larger black hole merger simply because it's a longer signal. --mfb (talk) 08:57, 22 February 2021 (UTC)

Blind spots
Do any of the references talk about the blind spots of the detectors? Tayste (edits) 03:49, 18 October 2017 (UTC)


 * The reference I added two sections above includes full polar diagrams. That's probably more detailed than most people would want though. George Dishman (talk) 13:23, 8 November 2017 (UTC)

Fabry-Perot interferometer performance
The article mentions briefly that LIGO uses the Fabry-Perot type of interferometer and provides a link to Wikipedia's page on that topology, but although that page gives a comprehensive analysis of their behaviour for a fixed structure and variable wavelength, it doesn't address the way LIGO works with fixed monochromatic illumination and variable arm length. This thesis gives a comprehensive analysis of the way the cavities perform in LIGO. I would suggest including at least Figure 1 would be of benefit (if this is an acceptable source) and it would make clearer how the shorter arms mention in the penultimate sentence in the section on observatories produce the same response at frequencies above around 200Hz but half the response below that. [p.s. On trying to make the Fabry-Perot link internal, I got an error message saying %E2 was illegal, but the link was copied from the address bar of the page, is WP breaking its own rules?] George Dishman (talk) 13:22, 8 November 2017 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified one external link on LIGO. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20060721201701/http://elmer.tapir.caltech.edu/ph237/CourseMaterials.html to http://elmer.tapir.caltech.edu/ph237/CourseMaterials.html

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 13:11, 14 December 2017 (UTC)

6th gravitational wave detected
On Nov. 15, 2017, LIGO detected its 6th gravitational wave, GW170608. https://www.ligo.org/detections.php

This wiki only mentions the 5 gravitational waves found. Please update! Whisperjunkie (talk) 06:16, 28 February 2018 (UTC)

What's $420m between friends?
By mid-September 2015 "the world's largest gravitational-wave facility" completed a 5-year US $200-million overhaul at a total cost of $620 million.

So I'm guessing that supplementary Girl Guide cookies sold like hot cakes over the specified time period? &mdash; MaxEnt 22:17, 17 July 2018 (UTC)

Outer space
The article seems to be missing that LIGO was for a while in the budgeting stage going to be in outer space! Because it was thought that they would need to be away from noise sources, and that the lasers would have to be very very long. It would have been massively expensive, and tediously hard to get set up. Someone came along and figured out that LIGO done on terra firma was possible, as long as all the noise could be budgeded properly, detected and then cancelled out. The success of LIGO is mainly because of sensing noise sources and cancelling them out. -Inowen (nlfte) 09:04, 7 September 2018 (UTC)
 * LIGO was never intended to be in space, you are probably thinking of LISA. That was cancelled but is now being worked on as eLISA. George Dishman (talk) 21:48, 17 September 2018 (UTC)

O3 run: dates
The article still thinks the O3 run is in the future... I would update it but I don't find clear dates. They stopped publishing candidate events at a rapid rate early June (source), but such a short observation run sounds implausible. The same issue applies to Virgo interferometer which doesn't even know about that observation run. --mfb (talk) 13:13, 28 June 2019 (UTC)
 * It started on 1 April, I've updated the article. Absolutelypuremilk (talk) 14:25, 28 June 2019 (UTC)
 * They started publishing new candidates again! I wonder what caused the gap. --mfb (talk) 02:04, 13 July 2019 (UTC)

LIGO Voyager mirror: Error in text?
The text says that (a) it will use a silicon mirror and (b) that silicon will be transparent to the light. A bulk transparent material can't work as mirror. The reference discusses a silicon mirror, but says nothing about transparency. Pure silicon does have a high transmission rate for 1500 nm if it is not too thick. Will it get a mirror coating? Why would the transparency be relevant then? --mfb (talk) 11:11, 7 September 2019 (UTC)

building
Does anyone know when the LIGO building was completed? That is, not necessarily the stuff inside, but just the empty building. Gah4 (talk) 20:19, 25 June 2020 (UTC)

accuracy
The longitude-latitude for the LIGO facilities are given to 0.01", or about 0.3m (1ft) in distance. For something that is at least 4km across, that seems excessively accurate. Where is that point?  Maybe the intersection of the two arms might be nice. Gah4 (talk) 20:33, 25 June 2020 (UTC)
 * I checked Hanford and it seems to point to the intersection of the arms. Removing one digit doesn't change that visibly, removing another digit puts the marker notably away from it. --mfb (talk) 14:05, 26 June 2020 (UTC)
 * That sounds about right. One digit less would be 3m/10ft, and two digits 30m/100ft. The parking lot would be good for car navigation systems. I have found before the coordinates for a university to this accuracy, where there isn't a place to indicate.  The presidents office?  But as they say, X marks the spot!  Gah4 (talk) 20:41, 26 June 2020 (UTC)
 * That sounds about right. One digit less would be 3m/10ft, and two digits 30m/100ft. The parking lot would be good for car navigation systems. I have found before the coordinates for a university to this accuracy, where there isn't a place to indicate.  The presidents office?  But as they say, X marks the spot!  Gah4 (talk) 20:41, 26 June 2020 (UTC)
 * That sounds about right. One digit less would be 3m/10ft, and two digits 30m/100ft. The parking lot would be good for car navigation systems. I have found before the coordinates for a university to this accuracy, where there isn't a place to indicate.  The presidents office?  But as they say, X marks the spot!  Gah4 (talk) 20:41, 26 June 2020 (UTC)

Any photos of mirrors or inner workings?
A machine this important deserves to be shown-off. Doesn't anyone have any photos of the mirrors? the laser?

How about a design diagram illustrating how the mirrors are suspended so they don't vibrate? Noleander (talk) 23:27, 11 October 2020 (UTC)
 * LigoMirror.jpg is the best I have. This is the one for public viewing in the lobby of LIGO Hanford. Gah4 (talk) 06:21, 6 April 2022 (UTC)
 * LigoMirror.jpg is the best I have. This is the one for public viewing in the lobby of LIGO Hanford. Gah4 (talk) 06:21, 6 April 2022 (UTC)

Awards
Approximately 1000 members of the LIGO Scientific Collaboration shared the following prizes in common for significant contributions to astrophysics:


 * 2017: Princess of Asturias Award In Technical and Scientific Research
 * 2017: Einstein Prize
 * 2016: Gruber Cosmology Prize
 * 2016: Breakthrough Prize in Fundamental Physics  — Preceding unsigned comment added by 50.1.214.5 (talk) 02:45, 22 February 2021 (UTC)

Update needed on sensitivity improvements
This line references a future time that has now passed. This should be updated based on the actual progress at LIGO.

"Its sensitivity will be further enhanced until it reaches design sensitivity around 2021."

--Chowlab92 (talk) 02:09, 24 January 2022 (UTC)

polarization
This one gives some explanation on the quadrupole source of gravitational waves, and especially on their polarization. This one a little more detail, and more equations. Gah4 (talk) 06:31, 6 April 2022 (UTC)

First light
First light seems to be an astronomy term. As well as I know, it applies, even though it isn't an optical detector. That is, it should apply. Might ask an astronomer, though. Gah4 (talk) 04:19, 28 September 2023 (UTC)
 * It's generally used for images taken by telescopes. LIGO doesn't detect light and it doesn't take images. Searching for 'LIGO "first light"' produces tons of unrelated articles about multi-messenger astronomy (detecting electromagnetic signals together with gravitational waves). I don't find any article talking about "first light" for LIGO. The infobox still shows the entry because the template for telescopes uses "service entry" and displays it as "first light" - which is fine for optical telescopes but weird for gravitational wave detectors. --mfb (talk) 12:43, 28 September 2023 (UTC)
 * I suspect physicists would also use it for radio telescopes, as it is still photons, though not visible. Even more likely for IR telescopes, again not visible but maybe also light. I am trying to find a WP:RS one way or the other. Note that Second sound isn't actually sound, though that doesn't seem to bother anyone. Gah4 (talk) 00:25, 29 September 2023 (UTC)
 * OK, WP:RS number one says first sound based on the audio frequency output from the detector. Or, it seems to me, that GW couples to mechanical vibrations. Early (unsuccessful) GW detectors tried to measure vibrational modes of large masses. Gah4 (talk) 01:53, 29 September 2023 (UTC)
 * Now, WP:RS number two says YES. (In all caps.) That it applies to the first detected signal from any astronomical instrument. That is, in a more generalized sense than you might expect. Gah4 (talk) 03:00, 29 September 2023 (UTC)
 * OK, WP:RS number one says first sound based on the audio frequency output from the detector. Or, it seems to me, that GW couples to mechanical vibrations. Early (unsuccessful) GW detectors tried to measure vibrational modes of large masses. Gah4 (talk) 01:53, 29 September 2023 (UTC)
 * Now, WP:RS number two says YES. (In all caps.) That it applies to the first detected signal from any astronomical instrument. That is, in a more generalized sense than you might expect. Gah4 (talk) 03:00, 29 September 2023 (UTC)
 * Now, WP:RS number two says YES. (In all caps.) That it applies to the first detected signal from any astronomical instrument. That is, in a more generalized sense than you might expect. Gah4 (talk) 03:00, 29 September 2023 (UTC)