Talk:Gravitational wave/Archive 1

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Spooky action

Does "spooky action at a distance" have anything to do with gravitation radiation? I though gravity waves travelled at (or near) c? Isn't spooky action to do with quantum entanglement? miterdale 14:13, 25 Jun 2004 (UTC)

Gravitation radiation has very little to do with quantum entanglement. Also a lot of the assertions in the article were factually wrong.

Roadrunner 16:34, 25 Jun 2004 (UTC)

(William M. Connolley 17:39, 25 Jun 2004 (UTC)) Not at all sure I believe this dipole/quadrupole stuff, especially since someone can't spell quadrupole.

Note: I rewrote larger parts of it in July 2004. I hope I deleted every such stuff. Gravitaional radiation has in fact little to do with entanglement or spooky action on a distance. Simon A. 15:49, 16 Oct 2004 (UTC)

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What about an orbital cosmic ray gravitic wave detector? lysdexia 11:37, 16 Oct 2004 (UTC)

Yes, that is planned and called the LISA project. I think it is mentioned in the article, albeit only briefly. Simon A. 15:49, 16 Oct 2004 (UTC)

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Where has it: "been proposed that certain conductors, especially superconductors, could be made to emit gravitational waves in the laboratory"? If we're talking about this:[1] kook's theories then this mention needs to be removed post haste, because then it's complete pseudoscience. --Deglr6328 04:42, 6 Dec 2004 (UTC)

• No reply->removed.--Deglr6328 19:44, 12 Dec 2004 (UTC)

---

Although the idea is far-fetched, some astronomers already dream of […] gravity phones to communicate via gravity waves across p-branes.

To be sure, astronomers probably have all sorts of exciting dreams. Still, I would like to propose against recording them in Wikipedia in general, and this article in particular.
—Herbee 13:51, 2005 Apr 12 (UTC)

References

Might want to remove the first reference, which is actually about gravity waves, not gravitational waves, and shouldn't be necessary in this page. If nobody objects, it will go... --Iridia 02:30, May 15, 2005 (UTC)

Expert

Ok so I guess I am kind of an expert here. I am a graduate student in large gravity (theory) group at a large university. But I have nothing to do with any actual measurement experiments. My advisor is very well known in gravity.

So looking over the article it seems ok. There are a few factual errors. There are also some places with big words that could use some better explaination for the casual reader. I think gravity waves should be accessable to the casual reader on up to the advanced reader.

I am going to clean over this and make minor corrections. Then I will add a section deriving the gravitational wave from the flat metric and explain what it is and what it means. And I will probably add a paragraph comparing it to E&M radiation and talk more about the Weyl tensor.(CHF 08:40, 27 October 2005 (UTC))

Ok I gave the article a good cleaning. It took more work than I thought. Next I think some derivations might be valuable to physics students. (CHF 11:24, 27 October 2005 (UTC))

Nice job! And long over due. A true encyclopedia treatment and very accesible. DV8 2XL 12:19, 27 October 2005 (UTC)

Thanks. I think I am pretty much done, at least for the parts that I am knowledgable in.(CHF 13:16, 27 October 2005 (UTC))

Hi, CHF, good to see someone taking an interest in this. I had a buncha stuff in mind when I added the flag, which I should have listed in a todo list. I wanted to see a much more discussion at a higher level later in the article, as part of WikiProject GTR, a project which is still in its incipient stages. One thing which has not yet been addressed is the distinction between the linearized theory of the generation of gravitational radiation (with links to multipoles, far-fields, weak-fields) and exact solutions such as pp-waves which are or will be extensively discussed in Category:Exact solutions in general relativity.

Content

Hi all. The articles linearized gravity and linearised Einstein field equations may be worth a quick perusal to decide exactly where certain derivations should be. The derivation given here (or part of it, at least) is in the linearised EFE article; I planned to go into that in more detail, but server problems put an end to that idea. As there is no point in having duplicate derivations, can we come to an agreement over which article should have the derivation ? Thanks. ---Mpatel (talk) 09:22, 29 October 2005 (UTC)

I don't know. I am torn. But I do think that the linearized gravity would need other derivations as well. There is more to linearized gravity than this one derivation. And this article still needs the derivations of the monopole, dipole, quadropole stuff. Personally I see no problem with duplication. (CHF)

"Also, because gravitational waves are so weak (and thus difficult to detect), objects opaque to light are often transparent to gravitational radiation." Objects are transparent to gravitational radiation because the waves are weak? --24.94.189.89 14:13, 2 November 2005 (UTC)

Sources of Gravitational Waves

Someone changed the paragraph to read

In gravity, an object's quadropole moment must be changing in time for it to radiate. This means that a single moving mass (monopole) will not radiate unless it "has bumps" and is spinning. A pair of orbiting masses is kind of like a very bumpy, spinning mass, so they may radiate. A changing monopole moment will not radiate due to the conservation of translational energy-momentum. The changing dipole moment will not radiate due to the conservation of angular momentum. But the changing quadropole moment will radiate gravitational waves. The system will lose energy due to this process. Much as a speeding charge decelerates as it radiates, the gravitational system will spin down as it radiates.

It was right, but this is completely wrong. "Bumps" don't do anything and neither does spinning. Changing quadropole moment - learn it, understand it.

Please don't edit stuff you aren't sure about. Pick up a book and be sure.(CHF 10:24, 8 November 2005 (UTC))

Good grief. In the past I've often tried to explain this in newsgroup posts, and have frequently been dismayed to see how badly people lacking the standard math/physics training often misunderstand what I (or others) wrote. Ineed, the textbooks by Carroll and by Schutz both offer excellent presentations of quadrupole radiation, but both suffer from notational quirks which can and have misled some well-intentioned but not very well-prepared readers. (To be fair, both authors are of course writing for well-prepared students, and quite properly so.)

Sigh... this is an important and often misunderstood topic. I've been making noises for some time about writing one or more articles on multipole moments in gtr, e.g. distinguishing between "Weyl multipoles", which bear an obvious relation to multipoles in Newtonian gravitation, and the various relativistic multipole moments (known to be equivalent under favorable circumstances). But right now I'm rather discouraged about the future of WP (see the sad history of Albert Einstein).---CH (talk) 22:38, 9 November 2005 (UTC)

I'd like to appologize for that. (CHF 14:36, 14 February 2006 (UTC))

Last two sections

Removed "trivia" since these topics are in fact extremely important. Alas, these two sections are seriously misleading in various ways. This entire section is so misleading it should be removed entirely:

Gravitational waves differ markedly from electromagnetic waves in that electromagnetic waves can be derived exactly from Maxwell's equations. However gravitational waves, as a linear, spin-2 wave, as they are often thought of are only perturbations to certain space-time geometries. In other words, classically there are always linear, spin-1 E&M waves, but there are never linear, spin-2 gravitational waves. There are still wave-like fluctuations, but in general things are nonlinear, as is always the case in General Relativity. This is one of the reasons there may be no graviton.

The thing that is analogous to electromagnetic radiation is the Weyl curvature, not the linear, spin-2 wave.

Thinking of the graviton as something which might "exist" is not, I think, fruitful. Better to think of it as a theoretical concept useful in some ways, but having serious limitations. Much like spacetime is undeniably useful, even essential for formulating metric theories of spacetime, but according to some approaches to a possible quantum theory of gravity, ultimately this is a seriously misleading notion. But I hesitate to say that the concepts which are put forth to replace it are things which might "exist"; rather, they might be conceptually useful under more extreme conditions where the spacetime concept is no longer useful.

I think the author of the last sentence might have been trying to compare Ricci (or Einstein) and Weyl curvature. Ricci curvature is directly proportional to the immediate presence of energy-momentum; Weyl curvature can propagate as a wave, and all that. But of course, in gtr, exact EM waves exist (see monochromatic electromagnetic plane wave for an example) and the immediate presence of EM field energy at various events "causes" Ricci curvature there.

As for "always non-linear", I would avoid using that language. Sometimes general relativity does admit linear superposition. In particular, two pp-waves traveling in the same direction can be linear superimposed.

In static Weyl vacuums, there is a simple formula for superimposing an arbitrary Weyl vacuum and a line mass. It is possible to write down a general formula, but this is not very useful. The fact that this special case is so simple reflects the symmetry group of the class of Weyl vacuums (transformations taking a Weyl vacuum to a new Weyl vacuum, or even the same one but in a different chart). CH

Deleted nonsense

To whoever wrote this:

Our solar system can not radiate very much gravitational radiation because the planets are mostly on the same plane of orbit with spins aligned to that plane. And even if this were not the case, the gravitational forces in our solar system are very weak with the exception of Mercury and the Sun.

FYI, spins aligned with the orbital plane or not has nothing to do with the quadrupole moment formula giving the most elementary estimate of the power (energy per unit time) radiating by a binary system such as Mercury, Sun.---CH 00:04, 20 December 2005 (UTC)

Spin-spin interactions can make the orbits more stable (decay slower) if they have a certain alignment (both up or one up and one down (but pointing in a little in both cases)). But, yeah it won't totally stop the radiation. (CHF 14:41, 14 February 2006 (UTC))

To whoever wrote this:

The thing that is analogous to electromagnetic radiation is the Weyl curvature, not the linear, spin-2 wave.

This doesn't even make sense. Maybe you were confusing the linearized gtr approximate treatment of weak gravitational radiation with the real McCoy? See the textbooks by Carrol, Stephani, Schutz, and MTW for some excellent discussion of analogies of weak-field gravitational radiation with EM radiation. Analogies with strong-field radiation also exist but are harder to explain, so let's get the simple stuff right first. ---CH 00:17, 20 December 2005 (UTC)

(LOL) Now I recall that I wrote the second paragraph I quoted! That is, I wrote it in on this talk page--- and then someone else added that sentence to the article without the context! This illustrates the point that context is everything: if you yank meaningful sentences from another users writings and insert them randomly into an article, you are likely to turn sense into nonsense, in addition to disrupting the flow of ideas in the article.---CH 13:30, 21 December 2005 (UTC)

Detection

The section Detection in the current version is very badly written. I started to try to improve it, but threw up my hands. Surely the WP community can do better than this! See the expository papers listed at Relativity on the World Wide Web for some excellent sources you can use. ---CH

Derivation

This section needs a new introduction clarifying that this "derivation" involves the linearized approximation. Indeed, this is a linearized perturbation of Minkowski vacuum. ---CH 00:20, 20 December 2005 (UTC)

One part in 10²¹, not 10^{&minus 21}

Hi, 24.61.41.56, thanks for noticing the wrong sign. Someone other than myself keeps putting in the incorrect minus sign, and I don't know why that is attributed to me (I don't even use that syntax!). Whoever you are, do you see that one part in ten expresses the ratio one:ten? So one part in 10²¹ is what we want here.---CH 10:29, 23 December 2005 (UTC)

FWIW, apparently this happened when I tried to revert to a previous version, and didn't notice that version contained the mistaken sign.---CH 10:52, 23 December 2005 (UTC)

Production of gravitational radiation

139.184.30.17, you wrote A gravity wave arises due to density changes in a fluid. But this claim is not only ambiguous, it is incorrect under either interpretation:

• density perturbations do not always produce gravitational radiation (consider a spherically pulsating star)
• gravitational radiation will be produced by any source having a time varying quadrupole moment tensor (or time-varying higher multipoles), regardless of whether the source contains a fluid (consider a bar rotating about an axis orthgonal to its symmetry axis).

Please do not edit this article if you do not have your facts straight, OK? TIA---CH 10:37, 23 December 2005 (UTC)

Please accept my apologies!

Ooops, I get it, you said "gravity wave", not "gravitational wave". However, since this article is about gravitational waves, I'll try to replace that explanation with a link to the appropriate article. Also, my reversion fixed another problem in which someone replaced "distant events" (correct) with "massive events (nonsensical). Sorry for falsely accusing you!---CH 10:43, 23 December 2005 (UTC)

On second thought, I think the link to Gravity wave should suffice. ---CH 10:48, 23 December 2005 (UTC)

Possibly inappropriate links

This paper is apparenlty an unpublished comparison of gravitational radiation in various theories, which I haven't read, but the fact that it is unpublished may be a warning sign:

• Gravitational Radiation by Warren F. Davis

—Preceding unsigned comment added by Hillman (talk • contribs) 13:39, 24 December 2005

(Sorry all, I did indeed forget to sign my own comment, so I just signed after the fact.---CH 08:53, 6 May 2006 (UTC))

Before gratuitously flagging a "warning sign" about this paper, I would suggest that the writer take the trouble to read it or, :at the least, exert himself sufficiently to learn something of the paper's origin. It is, in fact, a slightly edited version of :my MIT Ph.D. thesis. It passed muster at MIT; it ought to pass muster here!

--- Warren F. Davis, Ph.D.

—Preceding unsigned comment added by Wfdavis (talk • contribs) 21:12, 23 March 2006

Please take no offense, Warren, but if your thesis was published shouldn't you also have sent it to the arXiv? If you had so (and it's probably not too late, if this is a recent thesis), I would almost certainly have seen it and at least skimmed it. With experience (if you choose to hang around WP for very long), I think you will soon learn why we old timers react with suspicion to links to personal webpages! (Now I'm curious--- why wouldn't you put up your Ph.D. thesis at your academic website? Oh well, send it to the arXiv; I look forward to reading it. Well, more likely skimming it...)

BTW, you can sign and datestamp your comments simply by typing ~~~~ (four tildes) at the end of your future comments.---CH 08:53, 6 May 2006 (UTC)

More linkspam and POV pushing

Anon 130.184.88.44 (University of Arkansas at Fayetteville) added several links within the body of the article to a cranky website promoting alleged proprietary "technology", [2]. These links were embedded in text promoting claims about high frequency gravitational radiation which must be regarded as fringe at best. Such edits are somewhere between linkspam and POV pushing and are deprecated. ---CH 19:18, 3 March 2006 (UTC)

Improvement urgently needed

Wrt User:Miserlou's addition of {{fact}} flag, gravitational waves do carry energy in general relativity, and this has been been proven long ago, but the current version is not quite right in what it says about this and many other matters. Caveat emptor.---CH 22:38, 17 April 2006 (UTC)

Someone apparently queried this oddly phrased statement: Just as an electromagnetic wave has electric and magnetic components, so too does a gravitational wave have gravitoelectric and gravitomagnetic components. A "+" wave has an "X" gravitomagnetic component, and vice versa. I certainly wouldn't put it like that, and I haven't seen anything in the literature phrased like that. Possibly whoever wrote it was thinking of the case of vacuum pp waves, wherein for a plus polarized wave the electrogravitic and magnetogravitic tensors, taken wrt a family of Rosen observers (certain inertial observers with purely transverse expansion) with spatial basis vectors "aligned" with the wave, look like

$E[{\vec {X}}]_{{\hat {a}}{\hat {b}}}=\left[{\begin{matrix}0&0&0\\0&\alpha &0\\0&0&-\alpha \end{matrix}}\right],\;\;B[{\vec {X}}]_{{\hat {a}}{\hat {b}}}=\left[{\begin{matrix}0&0&0\\0&0&\alpha \\0&\alpha &0\end{matrix}}\right]$

whereas for a cross polarized wave, these look like

$E[{\vec {X}}]_{{\hat {a}}{\hat {b}}}=\left[{\begin{matrix}0&0&0\\0&0&\beta \\0&\beta &0\end{matrix}}\right],\;\;B[{\vec {X}}]_{{\hat {a}}{\hat {b}}}=\left[{\begin{matrix}0&0&0\\0&\beta &0\\0&0&-\beta \end{matrix}}\right]$

where $\alpha ,\;\beta$ are appropriate functions. But I have never seen these called gravitomagnetic components and gravitoelectric components.

Every time I look at this article, it seems to be in worse shape, which tends to discourage any plans to try to improve it, unfortunately. ---CH 08:26, 6 May 2006 (UTC)

My recent rework

I've made some drastic edits recently to arrange things in a way that non-experts (like myself) will find more accessible than it was before. There were a lot of parenthetical remarks that didn't seem to contribute much, and a lot of digressions that, while interesting, destroyed the flow of the article. If anyone wants to reinstate material I deleted, please consider re-adding it rather than reverting my changes. --Doradus 17:30, 9 May 2006 (UTC)

Thanks. I was just about to say its still a "sprawling mess" :-/ but at least you are trying. Someone asked for citations to pseudotensors and gravitational radiation: recently there have been a ton of arXiv eprints on pseudotensors. Some years ago, Bel superenergy tensor was also popular for gravitational plane waves. ---CH 03:34, 12 June 2006 (UTC)

Hmm... lemme try to make a more helpful critique :-/ The basic reason this is a sprawling mess is that WP desperately needs good articles on various topics, or already has articles, on which this article should draw rather than reinventing the wheel:

1. multipoles (separate articles on conventional multipoles in Newtonian gravitation, linked to electrostatics &c., and on relativistic multipoles, linked to related notions)
2. weak fields in gtr
3. far fields in gtr
4. LIGO

I'd like to write these myself, but arguing with idgits over work I've already done is taking all my time.---CH 03:38, 12 June 2006 (UTC)

Todo list

As a courtesy, I have removed the "expert" items from the todo list. I am leaving WP and doubt anyone else will know how to implement the suggested improvements since this was mostly a note to myself.

While I never extensively edited this article, and mostly hadn't the heart to monitor it, since I feel it is rather awful and concerns a subject dear to my heart, from time to time I make more or less specific suggestions in this talk page. Sadly, I am now abandoning this article to its fate.

Good luck to all students in your search for information, regardless!---CH 00:09, 1 July 2006 (UTC)

Detection section

Some conflicting information in the "difficulties of detection" section. Frequencies do not seem to be accurate, at least compared to Hawking's estimates cited earlier in the article (probably near the introduction)

Quantum gravity, wave-particle aspects, and graviton

This is a page about GRAVITATIONAL WAVES. And suddendly, this paragraph is obviously about GRAVITY. Confusion in some minds? see https://kn0l.wordpress.com/la-gravite-est-elle-instantanee/ (in french) — Preceding unsigned comment added by 163.47.106.116 (talk) 01:12, 12 January 2017 (UTC)

Einstein’s Field Equations in Wave Form

In the Advanced Mathematics section, could someone kindly provide a reference to a proof of the claim that solutions of $\Box {\bar {h}}^{\alpha \beta }=-16\pi \tau ^{\alpha \beta }$ are waves traveling with velocity $1$?

Leonard Huang (talk) 19:36, 25 February 2017 (UTC)

External links

Dr Baker Jr's collaborator's work in HFGW finds a reference in the main article. His site GravWaves has a detailed account of the history and development of GW research. He is a pioneer in the HFGW field, however, this article is not restricted to LFGW; the article is called Gravitational waves. The US patents form an integral part of the technology researched to find applications for HFGW; therefore, they are very relevant for a general reader. The edits which added the links were started months back by another editor and there was no objection by the current editors who were very much observant even then. Now, why this war-like situation? In a Wikipedia article, a general account of the subject is given which includes technology and other educative pages from the internet. GW is a developing field, hence, all possibilities and potentials are to be respected and presented. Please, enlighten me, how taking away technology possibilities of HFGW would enrich the article? My request is to give what I discussed here a thought. Thanks User:Mandot —Preceding undated comment added 11:42, 13 September 2017 (UTC)

Where has it been reported in reliable sources WP:RS to achieve notability WP:N? Weburbia (talk) 11:56, 13 September 2017 (UTC)

A story in Hindustan Times by Manoj Sharma (talk) User:Mandot —Preceding undated comment added 12:21, 13 September 2017 (UTC)

References

Abusive language in Edit summary of External links

All editors watching this page please note that User:Deacon Vorbis is repeatedly indulging in abusive language usage on Edit summary. You may see the recent edits and reverts. The link of a US patent was added by me more than 2 months back. Nobody objected to it, there are more than 350 editors watching this page. Today, I noticed a group of editors led by User:Deacon Vorbis arbitrarily deciding that the link does not belong here. It is a US patent of a relevant technology also reported in national newspapers. It teaches a method to modulate the invariant mass of an object which creates gravitational waves. Why shouldn't it belong here? The man who holds a patent has a Wikipedia page on his works. The use of obscene and abusive words clearly show bias of this group of editors. They are behaving like dictators who suddenly decide to remove some relevant links in a motivated manner. The use of abusive language by Wikipedia editors has indeed lowered the dignity of Wikipedia Cottonmother —Preceding undated comment added 14:19, 13 September 2017 (UTC)

First, see the definition at wikt:my ass#Interjection. While it's mildly vulgar, it's by no means abusive. As well, the patent links (as well as the the company link) are promotional and do not belong on the page; see WP:ELNO for more info. The fact that they went unnoticed for a couple months is irrelevant to their appropriateness. In fact, I was alerted to it by a rather dubious comment made on a phys.org article, so I decided to investigate. Moreover, the patents constitute WP:FRINGE material and so also don't belong.

While I appreciate your confidence in my influence, I can assure you that I lead no other editors, let alone a whole group! --Deacon Vorbis (talk) 14:48, 13 September 2017 (UTC)

Going by your logic, even LIGO findings are fringe, as they are unconfirmed and repeatedly challenged by many. As another user pointed out above, this field is still getting defined. A US patent by known researchers is as good as LIGO findings -- unless you count money invested. I find your "investigations" and judgement as motivated. It is indeed uncanny that you took such offense and started using unmentionable body-part expletives; and then suddenly to rescue you, 3 more editors showed up repeatedly. When I edited and added the Pal patent link on 12 July 2017, it was deleted by some unregistered user on 14 July 2017, very soon it was reinstated back immediately by user:TwoTwoHello. This fact clearly shows that the link was being observed by many editors and was found good enough; therefore, contrary to your assertions, my edit of 12 July 2017 did not go unnoticed at all, rather it was approved by the community. You are now trying to hide behind false modesty. Your extreme reaction in using expletives brands you as a dubious editor with a motivated following. Rest of the editors may comment. Therefore the edit shall be undone. I am sorry, you may soon find yourself isolated in a Quixotic corner. Cottonmother — Preceding unsigned comment added by Cottonmother (talk • contribs) 15:57, 13 September 2017 (UTC)

Please sign your talk page comments with four tildes: ~~~~.

First, I have to say that asses are most definitely not unmentionable. I mention them all the time in fact. And we all have one (even if we shouldn't go waving them around). Moreover, my use of "my ass" is hardly extreme, nor does it mark me as "dubious" (whatever that means), nor does it give me a motivated following (whatever that means, too).

Second, I'm confused about your LIGO comments; they're really irrelevant to the discussion at hand, which is the appropriateness of the links in question. Please read WP:PATENTS for some more info here. That doesn't apply exactly, since these are external links rather than sources, but it does give some good insight into why they're not appropriate.

Third, your link was not deleted by an IP and restored by TwoTwoHello. The IP's edit was merely a small bit of vandalism which was undone by TwoTwoHello. Your claim is demonstrably false. The fact that it wasn't noticed at the time is irrelevant to its appropriateness now. --Deacon Vorbis (talk) 16:24, 13 September 2017 (UTC)

Pray, tell me in clear terms why "they" are not appropriate? From your statement no.2, "That doesn't apply exactly, since these are external links rather than sources, but it does give some good insight into why they're not appropriate." Wikipedia is replete with references to patents, as links and otherwise. If the referred IP address link removal was a small bit of vandalism, going by that logic, you folks are repeatedly indulging in the same vandalism of the same amount, and a whole series of it. To top it all, you are reporting my edits as an act of war. I accept that you people have formed a group to assault a valid edit. However, I repeatedly request you not to act as ring leaders. These times are very testy; there is no point in venting LIGO's frustration on a user. If you accuse something of being from the fringe, then you also know even Big Bang came from the fringe. — Preceding unsigned comment added by Cottonmother (talk • contribs) 17:03, 13 September 2017 (UTC)

Are you saying that you have a WP:COI here?TR 17:53, 13 September 2017 (UTC)

(edit conflict) Per WP:ELNO #13, this patent shouldn't be included in the external link section of the article. It possibly could be included in the article itself as long as WP:PATENTS is satisfied and it's not just thrown in for the sake of it. — nihlus kryik  (talk) 17:57, 13 September 2017 (UTC)

That about covers it, but my own take is they are not good references, being primary sources, and not good external links, being legalistic technical gobbledygook, intended for lawyers as much as scientists. Certainly of no interest to the typical reader of one of our articles. The only time a patent should be linked to is when it is the discussed in the article, so its relevance is established, and properly sourced.--JohnBlackburne^words_deeds 18:33, 13 September 2017 (UTC)

"Mathematics" section

The current mathematics section is somewhat of a relic of an old version of this page from before any experimental confirmation of the topic. Since then this page has grown significantly, and has become of interest to a much wider audience. I think it might be better to relegate the rather technical (and textbooky) material of this section to other more relevant pages. What do others think?TR 15:08, 22 September 2017 (UTC)

The article should presumably be split. The "textbooky" material is simplified to the point of being misleading. Historically, the linearized solutions had a bad reputation, and not just because it was unclear if they were physical or coordinate. Consider the "elevator light" paradox. Fix, relative to a freely falling elevator, an electric charge. Does it radiate, as per Maxwell? Yes, from outside the elevator, no from inside. The resolution is that the equivalence principle is purely local, but radiation is global. Linearized gravity is appropriate for analyzing detector response, but it isn't very good for the generation and prediction of actual gravitational waveforms. 129.68.81.72 (talk) 18:18, 24 September 2017 (UTC)

Linearized gravity already exists as an article and covers most of the content of the "mathematics" section here anyway. Any additional content can be merged there.TR 21:52, 24 September 2017 (UTC)

No, the additional content, generation/prediction, would be fully non-linear. Adding it to linearized gravity would make no sense. 129.68.81.72 (talk) 23:05, 24 September 2017 (UTC)

Radiation pattern of binary system

It would be helpful if the article described the radiation pattern of the binary systems discussed. The purple diagram shows omnidirectional radiation in the orbital plane. From symmetry, I would guess this was +polarized. Can this radiate angular momentum? Is there also circular-polarized radiation in the polar directions? If so, is the power radiation pattern a sphere (isotropic)? Is the angular-momentum radiation pattern a doughnut, a sphere or a dumbbell? Thanks, --catslash (talk) 18:52, 25 September 2017 (UTC)

I think going in to this would be too much detail for this particular article. (This would be more suitable for something like binary black hole, or something...). To answer your questions:

1. Yes on the equator the waves have a "+" polarization.
2. Yes, this can (and does) radiate angular momentum.
3. Away, from the equator there is a mix of polarizations. At he poles you get something close to circular polarization.
4. The power radiation spectrum is not isotropic but varies across the sphere. Typically this pattern is expanded in spin-weighted spherical harmonics of spin weight -2. The dominant modes are l=|m|=2 modes. Plotting the squares of these should give you a good idea of the angular distribution on the sphere.
5. The distribution of the angular momentum emission is almost identical.

Hope this helps.TR 13:00, 26 September 2017 (UTC)

Many thanks for such a clear and comprehensive answer. --catslash (talk) 13:37, 26 September 2017 (UTC)

Secondary effects

An anonymous comment under the Talk:Gravitational wave/Archive 5#Poincaré first predicted gravitational waves before Einstein section above says "Gravitational waves don't produce any gravity or gravitational effects." Is this true? Surely if gravitational waves carry energy they must create a gravitational effect of their own? Not detectable in front of the wave, any more than a sonic boom can be heard in front of the aircraft producing it, but detectable behind and to the sides. If this is not the case, the overall curvature of space-time would change every time black holes collide, which appears absurd. Do these secondary gravitational effects contribute materially to the question of dark matter, or is the cumulative effect of billions of years worth of waves still negligible?--Keith Edkins ( Talk ) 17:25, 9 October 2017 (UTC)

Only part of an answer, but once a gravitational wave passes, then space can be permanently shifted (expanded). Each time black holes collide they give out about 5% of there mass in waves. If there are heirarchical mergers, say 27 in a row, a black hole 35,000,000 times bigger is made and 75% is radiated as gravitational waves. So it could appear as hot dark "matter". But already pulsar observations have ruled out such a high level of low frequency waves. But not only that, for every particle acceleration or photon emission there will also be a gravitation wave. These however will be extremely minute and high frequency. Graeme Bartlett (talk) 11:53, 10 October 2017 (UTC)

I agree with Keith Edkins that gravitational waves must transport mass-energy just as a photon does, and when absorbed by a system they increase the mass of that system, and furthermore as Keith suggests they constitute mass within intergalactic space, possibly explaining some fraction of "missing mass" observations. It should be possible to do a back-of-envelope calculation of the extent of mass (baryonic matter) acceleration from the big bang to present and determine the amount of mass-energy generated in gravitational radiation and see if this is of the same order as CDM mass estimates. I do not know why Graeme Bartlett calls this "hot dark matter" or why quasar observations "rule out" such an effect. I also expect that absorption of gravitational waves by orbiting systems should cause them to outspiral.

Spope3 (talk) 01:15, 11 November 2017 (UTC)

If there was enough gravitational waves out there, there would be some mass, and possibly gravitational effects. \It would be dark and free flowing, and thus "hot". See https://arxiv.org/abs/1310.4569 for the use of pulsar timing to put a limit on the magnitude of gravitational waves there are out there. An article here is Pulsar timing array. Graeme Bartlett (talk) 08:22, 18 January 2018 (UTC)

Graeme Bartlett - thanks. I agree on the definition of "hot". Thanks. I think the pulsar timing measurements are not indicative of the mass-energy of the gravitons that comprise the GWB; they instead measure the strain cause by such waves between the instrument and the pulsar. These will be very different when there are a large number of small sources contributing to the GWB. Sources that contribute to the strain may combine destructively, whereas the mass-energy of any one graviton is always positive and so these combine additively. Simplistically I would expect the mass-energy to scale with the number of sources, and the magnitude of the strain with the square root of this number. Spope3 (talk) 21:57, 12 February 2018 (UTC)

The pulsar timing is only sensitive to the really low frequency waves, perhaps from supermassive black hole mergers. It is very difficult to absorb gravitational waves, and the average orbiting system will absorb very little. Also the existing detectors are not sensitive to those really low frequencies or high supersonic frequencies either. But they already rule out a certain level of power in the audio frequency range. Graeme Bartlett (talk) 03:56, 13 February 2018 (UTC)

Yes, there's no question that there are negative results from the pulsar timing study you referenced (Shannon) and also more extensive studies from the NanoGrav Collaboration (Mingarelli - here: https://arxiv.org/abs/1508.03024 ). The question is what is being ruled out. As I described above, at some point the central limit theorem figures into the negative outcome -- the GWB as measured by strain is combination of a large number of sources and so does not measure directly the mass-energy in the background. The link between these two is model-dependent. This is described in much more detail in Mingarelli - sections 1.2 and 1.3 of the introduction. But yes the results are so far negatvie. Spope3 (talk) 19:00, 14 February 2018 (UTC)

Directional sensitivity of the Interferometer ?

The interferometer has two perpendicular arms, so when the wavefront of a passing gravitational wave is parallel to one arm and perpendicular to the other (as shown in the illustration), then the instrument is sensitive to the passing of the wave. Per the current text, this "is precisely the motion to which an interferometer is most sensitive". But what happens to the sensitivity if the wave happens to come from an equal (45 degree) angle to both arms? Would a wave from this direction be detectable at all? Is there some trigonometric relation between the sensitivity and angles between 0 and 45 degrees ? Similarly, what about a wave perpendicular to both arms, i.e. a wavefront parallel to the plane spanned by the two arms? Would a wave from this direction be detectable at all? I think the article could be expanded to cover such limitations. Further, I am guessing one reason interferometers suitable for detecting gravitational waves are being built on different parts of the Earth is exactly to try to avoid such blind (or deaf?) spots. Some information related to this would also be interesting. Lastly, I am thinking that the (millisecond scale) delay between the detections in different interferometers is what allows for the (coarse) localization of the source of the wave. This additional advantage of having multiple, well separated detectors would also be good to point out. Thanks! Lklundin (talk) 20:05, 21 October 2017 (UTC)

I read that direction can also be established by the time difference when the wave hits separate detectors (separate locations). That is one of the additional attractiveness of having India-Ligo (Indian Initiative in Gravitational-wave Observations) go online "far" from the USA and European detectors. Cheers, BatteryIncluded (talk) 20:14, 21 October 2017 (UTC)

It is harder to visualize than dipole fields like EM waves. You can see from the polarization videos that it is most sensitive when the axes are parallel to the detector axes. That is, the + mode is detected, while the 45 degree rotated X mode is not. Coming from other directions, it depends on the components along the axes. Gah4 (talk) 09:41, 1 July 2020 (UTC)

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Gravitational wave astronomy

In this section: The sources of gravitational waves described above are in the low-frequency end of the gravitational-wave spectrum (10−7 to 105 Hz). An astrophysical source at the high-frequency end of the gravitational-wave spectrum (above 105 Hz and probably 1010 Hz) generates[clarification needed] relic gravitational waves that are theorized to be faint imprints of the Big Bang like the cosmic microwave background.[54]

It seems to me that high and low frequency ranges are mentioned incorrectly. The "waves described above" are in the high-frequency end; gravitational waves originating form the Big Bang have long wavelengths, low frequencies. Bookaneer (talk) 12:22, 3 November 2017 (UTC)

Effects of Passing, probable error

In the Effects of Passing section of this page, there is a paraphrased reference to LIGO's sensitivity that compares it to measuring the distance between us and the nearest star to an accuracy of one human hair. That is the *limit* of LIGO's ability to sense the gravity waves, but it is not necessarily the actual size of the waves. Unless gravity waves AND the sensitivity of LIGO are exactly identical, this section needs corrected. — Preceding unsigned comment added by 40.0.40.10 (talk) 08:13, 7 November 2017 (UTC)

Completely agree. There isn't enough here to say why there shouldn't be doubt about the whole phenomenon if the measurements are essentially beyond anything conventionally considered measurable, like e.g. quarks. Quarks are flatly stated to be undetectable. This apparently is in the same domain. At some point, in consideration of the huge sums of public money that are spent on these things, a better job of explaining them, including to yourselves, will be in order. I am dubious of the current model of gravitation, of gravitational waves, quarks, etc. because they present the image of science that has veered off from a need confirm reality and instead live within theory as if it were.

That is to say there isn't enough here, wiki isn't everything so will look elsewhere in re why an effect that is comparable to measuring a quark should be confirmation of gravity waves. 98.4.124.117 (talk) 06:52, 15 April 2018 (UTC)

This is confusing. Waves are commonly described by wavelength. That is, we say size when we should say wavelength. In the case of electromagnetic waves, there is no ambiguity. Gravitational waves have a wavelength, and also an amplitude, where the latter can also be given as a length ratio, or given an interferometer arm length, the amplitude is a length, but unrelated to wavelength. Gah4 (talk) 09:46, 1 July 2020 (UTC)

Proof

Are the recent laser interferometer tests proof of a '"fabric" of reality," and is this simple three-word term, as are the two main ideas in it, aside from being a nice title for a book, rather or not quite eloquent and useful in the way of describing where gravitational waves live and their effects? Regards, Inowen (nlfte) 00:52, 18 January 2018 (UTC)

"Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation"

This part is junk. Either the writer means gravitational waves are a kind of radiation, which they arent; they are distortions in spacetime, or energy within gravitation waves is transformed in accord with a gravitational principle, which is technical and does not belong in the introduction. -Inowen (nlfte) 02:39, 12 September 2018 (UTC)

This does look OK to me. Just as light being a distortion in the electromagnetic field, does not preclude it from being radiation. Graeme Bartlett (talk) 00:57, 17 September 2018 (UTC)

Are gravitational waves real?

Moved to Wikipedia:Reference desk/Archives/Science/2018 November 5#Are gravitational waves real?

The article leaves no doubt that gravitational waves as "disturbances of spacetime" are real, at least since they have been discovered experimentally (by measurement). I admit that the LIGO experiment has measured real effects; but did these effects say to the experimenter "Hello, here we are, and we are disturbances of spacetime"? I doubt this. Rather the identification of the measured effects as demonstrating the existence of "gravitational waves in the sense of Einstein's general relativity" evidently requires to presuppose Einstein's theory which predicts the existence of spacetime and of these waves as disturbances of it. Without the presupposed ART nobody would ever have understood some unidentified waves in this very sense. The suspicion then is well-founded that the identification results from a logical mistake, say of begging the question, and therefore is unjustified. Ed Dellian2003:D2:9703:5941:A81D:7A1B:AD26:ABD0 (talk) 11:39, 5 November 2018 (UTC)

Discussion moved; please continue there. –Deacon Vorbis (carbon • videos) 15:32, 5 November 2018 (UTC)

Is this a real controversy that should be included in the article? Tom Ruen (talk) 13:06, 4 December 2018 (UTC)

• The LIGO collaboration must respond to gravitational wave criticism 31 October 2018
• Danish physicists claim to cast doubt on detection of gravitational waves 10/31/2018

FWIW - Seems, more recently, in December 2018, a relevant report was published in Quanta Magazine - in any case - Enjoy! :) Drbogdan (talk) 14:09, 2 January 2019 (UTC)

References

There's a well known saying that starts off with, "If it quacks like a duck..." Cloudswrest (talk) 15:01, 2 January 2019 (UTC)

More specifically, the waves are in the audio frequency range, so we could actually hear them. In the case of black holes spiraling in, there is a frequency pattern that is easily measured and compared to the theory. Gah4 (talk) 09:50, 1 July 2020 (UTC)

Time Dilation

This article should cover the expected effects on gravitational time dilation, not just space. 77.86.117.208 (talk) 09:48, 13 November 2018 (UTC)

Moving Gravitational wave to Gravitational radiation for better understanding

Hello everyone. As mentioned in the title, such operation would alter the meaning a bit and most importantly, suit the definition of the article nowadays such as: "In physics, gravitational radiation refers to the wave (or its quantum, gravitons) of the gravitational field, propagating (radiating) through space, carrying gravitational radiant energy." I would like to hear anyone's reply. Dominic3203 (talk) 09:25, 30 January 2019 (UTC)

Langrangian point between colliding black holes

A Lagrangian point exists midway between two equal masses where their gravitational field cancel. I see no sign of cancellation between the black holes persisting in the simulation video. Is this correct? DroneB (talk) 20:41, 7 May 2019 (UTC)

"Gravitational wave memory effect" - ok (or not ok) to include?

Apparently, recently added text/refs re a "Gravitational wave memory effect" (see copy of edit below) has been reverted as "not useful to include" - others may (or may not) agree - Comments Welcome from other editors - in any case - Enjoy! :) Drbogdan (talk) 15:30, 8 May 2019 (UTC)

Copied, in part, from "Gravitational wave - diff - 05/08/2019"

---Gravitational wave memory effect--- Gravitational waves may interact with matter causing a gravitational wave memory effect, a permanent (and measurable) record of displacement, regarded byresearchers as persistent gravitational wave observables. One measurable example of such an effect is a geodesic deviation allowing for arbitrary acceleration; another, a holonomy observable; and finally, a particular procedure based on a spinning test particle.

(Note: some references below may contain duplicated content)

References

This is essentially just a headline, full of MOS:JARGON, with no context. There's no indication that this is meaningful or important work. This sort of trawling of science news sites to report on current research just isn't helpful, in fact I'd go so far as to say it's actively harmful – it bloats articles with irrelevant information. –Deacon Vorbis (carbon • videos) 15:54, 8 May 2019 (UTC)

In my opinion that revert was completely irrational [unnecessary]. Your edits were very constructive, supported by 3 excellent sources, and well described in the edit history. I have restored them all but soon after this one of the Wikipedians reverted them again. However, your edits and reverts are as valid as his. So you have every right to defend your position.

Vikom ^talk 02:20, 14 May 2019 (UTC)

I can tell by your use of bold text that you must be serious about your comment. However, from wikt:irrational:, "1. Not rational; unfounded or nonsensical." You may not agree with me, but that doesn't justify your calling my revert "irrational", since I clearly spelled out my reasons above. Furthermore, there was no description in the edit history; it was merely a copy/paste of the text added to the article, which is rarely helpful. But even still, what's in the edit history is meaningless for what's in the article, so I don't know why you even brought that up. Finally, you haven't addressed the objections I raised initially, so I can't meaningfully respond. However, if you'd like to make any suggestions that begin to address the objections I had, then I'd be happy to listen. –Deacon Vorbis (carbon • videos) 02:52, 14 May 2019 (UTC)

Oops, my fault. I have not noticed your previous comment. Please, give me some time. I must go out now. As for "irrational", I have gone too far. I am sorry (see my correction). Vikom ^talk 17:50, 14 May 2019 (UTC)

@Deacon Vorbis: There are many sources on the subject, but let's check only one of them. This synopsis was meant to be understandable for non-physicists, but was published by the American Physical Society, which is the world's second largest organization of physicists. So the source is very reliable, and can support information in our article, which is not for physicists. An average reader can read that "Researchers predict the existence of three new long-lived signatures of gravitational waves, [...] Those objects don’t return to their original configurations after the waves pass, creating a “persistent” effect that scientists could potentially measure." Wow, amazing! But the existence of this phenomenon is only a prediction. On the other hand theoretical predictions in physics are a very important part of physics itself. The Higgs boson is a good example. In other words a known hypothetical phenomenon also deserves mentioning in Wikipedia. Probably for most readers even a short mention about "the memory effect" would be enough to satisfy their curiosity. After all, Wikipedia is not a textbook. But if we do not mention of this phenomenon at all, the reader may feel disappointed with Wikipedia when they encounters such information on the Internet, maybe on an amateur blog. Your wrote: "There's no indication that this is meaningful or important work.". Probably you are right. Now, the choice is yours. I will not restore those reverted edits again.

Vikom ^talk 02:35, 15 May 2019 (UTC)

@Drbogdan: Why don't you join the discussion? Vikom ^talk 17:31, 15 May 2019 (UTC)

@Vikom: Thank you for your comments - and suggestion - seems my original post above, and related comments by others (so far) covers most of my own thinking at the moment - however - if further considerations arise, I may post further of course - currently busy with establishing better coordinates for several Mars-related image maps, including {{Mars map}} and related - and the new Microarchitectural Data Sampling article - nonetheless, Comments Welcome from others on this particular topic - Thanks again - and - Enjoy! :) Drbogdan (talk) 17:55, 15 May 2019 (UTC)

Worthy reference?

FWIW - worthy recent reference (in some way?) for this (or related) article? - seems clear - and well written - Comments Welcome - in any case - Enjoy! :) Drbogdan (talk) 14:59, 30 July 2019 (UTC)

@Drbogdan: Did you even read the article?

Of course, all of this is just preliminary at this point. The LIGO collaboration has yet to announce a definitive detection of any type, and the IceCube event may turn out to be either a foreground, unrelated neutrino or a spurious event entirely. No electromagnetic signal has been announced, and there might not be one at all.

See also WP:NOTNEWS and Betteridge's law of headlines (the latter of which isn't definitive, but man, it should set off some major alarm bells). –Deacon Vorbis (carbon • videos) 15:27, 30 July 2019 (UTC)

@Deacon Vorbis: Yes - one of the passages in the article that stood out to me => "... a gamma-ray signal arrived nearly at the same exact time as the gravitational waves, with less than a 2-second difference in arrival time. Across a journey of more than 100 million light-years, that one measurement both confirmed that gravitational waves and electromagnetic waves travel at the same speed to within 15 significant digits ..." - which seemed to be related to one of my own earlier discussions at => "Talk:GW170817#Can GRB and GW detection times for same event be different?" - others may find other statements in the article that may be of interest, but that statement is of interest to me at the moment - in any case - Enjoy! :) Drbogdan (talk) 16:15, 30 July 2019 (UTC)

References

Wrong definition

1. "Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses" Because any movement in Kepler mechanics is result of gravity, it means that any mass movement generates gravitational waves. Isn't better to write that gravitational waves are result of mass M repeatable movement when dM≠0 or dR≠0 in any point of its trajectory, where R is a distance to foci?

2. According to https://en.wikipedia.org/wiki/Radiation and https://en.wikipedia.org/wiki/Conservation_of_energy any radiating system loses energy. It is good when we speak about merger of two black holes but certainly is not right in case of Earth that still orbits Sun. So we must choose one of two: gravitational waves aren't radiation or Earth orbiting Sun doesn't generate gravitational waves (that means that definition of gravitation waves is wrong).

3. "Gravitational waves are disturbances in the curvature of spacetime" means that gravitational waves are changing of gravitational field, so it (mass and gravitational field) is similar to electric charge and electric field and means that according to https://en.wikipedia.org/wiki/Conservation_of_energy , movement of source of the field changes field at the same time that means that any changing of gravitational field aka "gravitational waves" occurs instantly and hasn't "speed" (this is difference between "field" and "radiation"). 178.140.161.126 (talk) 15:35, 30 July 2019‎ (UTC)

Consider that the photon is the propagators of the electromagnetic field. We normally think of creating them by accelerating charges, as that makes radio transmitters work, and then they have the appropriate frequency. Consider two non-accelerating charges just sitting there. Theory says that photons are going back and forth, between them, but we won't measure them the way we measure radio waves. Similarly, presumably gravitons (the quantum particle of the gravitational wave) go back and forth between non-accelerating masses, which can also be described as gravitational waves. Gah4 (talk) 09:59, 1 July 2020 (UTC)

There are two definitions of gravitational waves -

1. The variation of the intensity of gravity as apparent from a binary system. This is nothing special. As the binary stars orbit one another, the very slight variation in distance between each star and an observer causes the intensity of gravity to change. The frequency of the gravitational wave is 2 times the orbital frequency. It has been known for centuries that distance affects the intensity of gravity. This is the type of gravitational waves that have been detected.

2. The propagation wave of gravity, similar to the electromagnetic wave. Such a wave would be emitted by anything with mass, accelerating or not. This type of wave has been predicted but never detected.

LeeMcLoughlinScientist (talk) 18:44, 14 October 2022 (UTC)

It is well known that electric dipoles, commonly in the shape of dipole antennas, generate EM waves. It is also well known that quantum mechanics quantizes the EM wave into photons. So, oscillating dipoles create photons. But photons are the carriers of the EM field, and so are also there in the case of static fields. Theory says that they are there, but we can't individually measure them. And gravitational waves are also quantized, with the graviton, but we also don't have the ability to detect them. We don't detect the wave or photon nature of static electric fields, but we know that they are there. It doesn't seem surprising that we don't detect a wave or graviton nature to gravity, even though we know it is there. Gah4 (talk) 08:00, 15 October 2022 (UTC)

Electric dipoles (or any antenna) propagate photons as EM waves yes and that's because it is necessary for EM waves to propagate at a frequency. The clue is in the name, 'EM'. The force is two forces rolled in to one. The frequency determines how often the electric force and the magnetic force peak in turn.

With gravity, no frequency is necessary. It is a single force. Gravitons would be propagated steadily (presumably at the speed of light). Gravitational waves exist only as an oscillating intensity of gravity from a binary system, directly caused by the oscillating geometry and distance of the binary system as it orbits. LeeMcLoughlinScientist (talk) 09:57, 15 October 2022 (UTC)

But quantum mechanics, and especially Wave–particle duality, says that waves go along with particles. So, even in the case of a static field, there have to be gravitons and gravitational waves. Gah4 (talk) 17:13, 15 October 2022 (UTC)

A wave is a property of something, it can't be an entity in itself. Particles are just that, partlicles. And so a wave can be a property of particles. As I said before, photons must have a frequency/wavelength because that determines how fast the electric and magnetic forces peak in turn. Gravitons are not like photons. Photons carry two forces (E and M) but gravity is singular. It doesn't require a frequency. Gravitons can propagate flat with no frequency. If gravity had a frequency then there would be different energies of gravity for different frequency. This is not consistent with observations. LeeMcLoughlinScientist (talk) 19:24, 16 October 2022 (UTC)

E and M are two different ways, in special relativity, of looking at the same force. Photons are wave packets, an appropriately localized disturbance in the EM field, and quantized by quantum mechanics. We only get to see a small part of the spectrum of gravitational waves, which is a good thing. (To see more, you need to be very close to a black hole.) Particles are not just particles, but a result of quantum mechanics and quantization. Radio waves are still, theoretically, photons, but we can't count them individually. We still know that they are there. Gah4 (talk) 00:07, 17 October 2022 (UTC)

Speed of gravitational waves

In the article's very first sentence today, it claims that gravity waves 'propagate as waves outward from their source at the speed of light.'

That's an important assertion, and much may hang on it. But I found no citations to support it (none immediately follow it). Also unclear: is this a purely theoretical assertion? else what empirical evidence is there to support it? Supporting evidence needs to be cited; a discussion in the article would be welcome. Thanks, and the *only* reply I seek is clarification of the article. Twang (talk) 17:38, 7 January 2020 (UTC)

I suspect that, yes, it is based on theory, but then so is all of gravitational waves. As well as I know it, interactions mediated by particles with mass have short(er) range, and those without mass have infinite range. That was, for example, used to predict the mass of the pion. There is discussion in the photon article about the mass of the photon. If it has mass, then light doesn't travel at the speed of light. I suspect that the physics changes if you give the graviton mass, but that is as close as I know it. More details are discussed in graviton. Gah4 (talk) 21:45, 2 July 2020 (UTC)

LIGO and other gravitational wave detectors are accurately timed. By comparing the time of arrival at each of the detectors, and assuming the speed of light, one can triangulate the direction of the source. Followup optical surveys in some cases have corroborated the direction of the source. Cloudswrest (talk) 19:16, 6 July 2020 (UTC)

Yes. But I suspect that if they were, say 0.999c that those timing them wouldn't see the difference. Well, maybe if they can be identified optically, so an actual direction could be compared. Gah4 (talk) 21:42, 6 July 2020 (UTC)

Previously someone copied from: Talk:GW170817#Can GRB and GW detection times for same event be different?. It is probably worth linking here, but not copying. Gah4 (talk) 16:16, 8 July 2020 (UTC)

@Gah4: - Thank you for posting the link - seems better after all - my further relevant comment (not WP:CWW) => BRIEF Followup - according to the current lede (8 July 2020) in the Speed of gravity article => In the relativistic sense, the "speed of gravity" refers to the speed of a gravitational wave, which, as predicted by general relativity and confirmed by observation of the GW170817 neutron star merger, is the same speed as the speed of light (c). - hope this helps in some way - iac - Stay Safe and Healthy !! - Drbogdan (talk) 16:51, 8 July 2020 (UTC)

UPDATE: Seems a gravitational wave may arrive before a light wave in some related instances, according to a recent science report. - Drbogdan (talk) 13:01, 26 October 2023 (UTC)

References

Difference between spacetime and gravity

The article should include an explanation of the difference between spacetime and gravity. In the rod&bead experiment it is unclear why the gravitational waves would affect just the beads along the rod and not the space housing the atoms of the rod itself (and therefore the rod) as well. Gravitational waves are disturbances in spacetime, why affect and move just the beads and not the space housing the atoms of the rod (and the space anywhere the rod may be attached for that matter)? 86.93.208.34 (talk) 00:49, 12 May 2020 (UTC)

45 degrees

There is the phrase: polarizations of a gravitational wave are 45 degrees apart with a {{cn}}. If you look at the polarization videos, you can see that, in the same way that dipole waves have polarizations 90 degrees apart, quadrupole waves polarizations are 45 degrees apart. Rotating 90 degrees, results in the same signal (though with a phase shift). I suppose it would be nice to have a reference, though, but it is pretty much obvious for a quadrupole field. Gah4 (talk) 10:02, 1 July 2020 (UTC)

It does seem self-evidently true, provided it is admitted that wave-front involves a quarupolar oscillation. There is already a {{cn}} tag on the statement that the wave does have this form (in the second paragraph of the Effects of passing section). catslash (talk) 22:49, 1 July 2020 (UTC)

I see one for no motion in the direction of propagation. That is, a transverse not longitudinal wave. The quadrupole claim looks like it cites Einstein, though I didn't follow the link. Gah4 (talk) 00:13, 2 July 2020 (UTC)

According to WP:CITEFOOT (last paragraph), an in-line citation placed at the very end of a paragraph may relate to the entire paragraph. I assumed (perhaps erroneously) that the same was true for a {{cn}}. catslash (talk) 15:50, 2 July 2020 (UTC)

I have wondered about this for a long time, mostly when finding {{cn}} not discussed in talk, and which I don't think are needed. I usually assume it is the last sentence, but even that is often enough ambiguous. (There might be more than one statement in a sentence that could need citing.) It seems to me less a problem for in-line citation. You can always look at the reference and see what it says. In the case of {{cn}}, there is no reference to look at to see what it doesn't say. I suppose a whole paragraph could need {{cn}}, but most often it should be a specific claim. Gah4 (talk) 18:07, 2 July 2020 (UTC)

There is another edit related to polarization, and the edit summary links to this one. It isn't so well explained there, but you can see quadrupole oscillation in the linear case, that it oscillates between x and y directions. The orthogonal polarization then oscillates between the x+y and x-y directions, that is, 45 degree rotated. You can also see that circular polarized results from adding the two linear polarizations with a 90 degree phase delay. The LIGO detectors detect strain (polarization) along the two interferometer axes, and not when it is 45 degree rotated. In the 45 degree case, the two arms will stretch/shrink in phase, for no difference. This came up in laying out the two LIGO centers. (Besides the change due to change in longitude.) One choice was to make them 45 degrees apart, such that one would detect one polarization, and the other one the other. But that (mostly) doesn't allow for confirming detection. So the two detect pretty much the same polarization, and so miss half the events. But as more get built, they have different polarizations to detect, in addition to changes from longitude. Gah4 (talk) 10:50, 28 January 2022 (UTC)

square degree or steradian?

The article uses the non-SI square degree for how well the direction can be determined, instead of the SI steradian. Should we also give the SI unit? Gah4 (talk) 13:35, 8 July 2020 (UTC)

I mean, sure, I don't see why not, although I was surprised to find that {{convert}} doesn't handle solid angle (that I could find). It might be worth adding there rather than doing by hand. Even more useful to a casual reader, though, might be to note that this is about 0.15% of the total sky, or about 320 times the area covered by a full moon. –Deacon Vorbis (carbon • videos) 13:53, 8 July 2020 (UTC)

But {{convert}} will tell you the apparent age of your dog that you got 42 fortnights (0.23 dog years) ago! –Deacon Vorbis (carbon • videos) 13:59, 8 July 2020 (UTC)

It seems that there is a proposal for angle units, and suggestion, not yet proposal, for solid angle. I added to the suggestion. Gah4 (talk) 15:25, 8 July 2020 (UTC)

redshift

The section on redshift has a few {{citation needed}}, and I might see if I can find some. In the case of light, redshift is useful as we can compare spectral lines to known lines, and compute the redshift. In the case of GW, there are no spectral lines, so there is nothing to compare. Presumably the physics requires it, but it doesn't seem so useful. Gah4 (talk) 01:53, 26 November 2020 (UTC)

3 space-probe laser interferometric array for very long primordial gravitational wave detection

Earth-sized interferometry isn't big enough for very long primordial gravitational wave detection (it has a cut-off [frequency limit]). Write more. Ask NASA and CNSA (physicists are friendly).

future missions — Preceding unsigned comment added by 2A02:587:411F:F7D5:D013:D83D:B586:E11E (talk) 17:26, 30 April 2021 (UTC)

One basic citation needeed

Which is the scientific document that expressed first loud and clear that "Gravitational waves are (disturbances in the curvature of spacetime,) generated by accelerated masses (, that propagate as waves)"? Yoxxa (talk) 12:03, 12 June 2021 (UTC)

Someone mentioned this one in a recent edit summary. Does that help? Gah4 (talk) 10:53, 28 January 2022 (UTC)

Mathematical error in wording?

Would a physicist like to confirm that this sentence from the article is true – or correct it? "The magnitude of this effect decreases in proportion to the inverse distance from the source." I think that sentence contains a subtle double-negative; literally, it means that a gravitational wave grows as it propagates. I would have expected something like, "The magnitude of this effect is inversely proportional to the distance from the source." Also, I want a gold star for noticing this. Wegesrand (talk) 17:42, 7 April 2022 (UTC)

Went to the cited source (which says, "As with all radiation fields, the amplitude of the gravitational waves falls off as r^–1 far from the source"[sic]) and corrected the sentence myself. That'll be two stars, please. Wegesrand (talk) 10:23, 19 April 2022 (UTC)

I think it was fine, but I do see the confusion. One that I have known a long time, if A is half as fast as B, then A is slower. A is also twice as slow. But is twice as fast the same as half as slow? But I think the original one is fine. Proportional is proportional, inverse is inverse, and distance is distance. There is no other meaning. Gah4 (talk) 05:55, 22 April 2022 (UTC)