Talk:LIGO

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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)[reply]

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.

ligo

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

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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—trivial. The American Civil War; in spite of what you were taught—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)[reply]

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)[reply]

Predicted significant emissions of gravitational waves are expected from binary inspiral systems (collisions and coalescences of neutron stars or black holes), supernova collapses of stellar cores (which form neutron stars and black holes), rotations of neutron stars with deformed crusts, and the remnants of gravitational radiation created by the birth of the universe. The observatory may in theory also observe more exotic currently hypothetical phenomenon, such as gravitational waves caused by oscillating cosmic strings or colliding domain walls. Since the early 1990s, interferometer physicists have believed that technology is at the point where detection of gravitational waves—of significant astrophysical interest—is possible.

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)[reply]

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)[reply]

"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)[reply]

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)[reply]

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)[reply]

observations

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)[reply]

You can't measure God, heretics.

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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:

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)[reply]

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.