Talk:Gravitational wave/Archive 5

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May 2009 Clarification request

There's a May 2009 clarification request by User Cesiumfrog in the 'Astrophysics and Gravitational section'. It was discussed at the time in 2 sections above (now archived to here and here) by 2 users (both now banned), but not fixed. As we are expecting that this article will need to be cleaned up for ITN purposes by Thursday, I've left a request on Cesiumfrog's Talk page asking him/her to give more detail about what it is that he/she wants clarified.Tlhslobus (talk) 20:57, 9 February 2016 (UTC)

If we continue to get no details from Cesiumfrog, does anybody know what to do about this (I don't)? Tlhslobus (talk) 03:27, 11 February 2016 (UTC)

Re: Orbital lifetime limits from gravitational radiation

I don't understand the reasoning behind this statement, "The Earth will break apart from tidal forces if it orbits closer than a few radii from the Sun. This would form a ring around the Sun and instantly stop the emission of gravitational waves", specifically the word "instantly". Is there some theoretical lower limit of a mass, below which gravitational waves are not emanated when it moves? Just because the hypothetical Earth in this situation has broken up, does not mean its mass has vanished. Certainly, waves from each of the individual post-breakup particles will carry far less energy than did the whole Earth. Also, because of the roughly circular distribution of the particles and their proximity to one another, the waves will tend to merge and cancel, thus making their detection from a significant distance much more challenging. But the total mass and average orbital speed of particles proximately post-breakup will be the same as the Earth had immediately prior to the breakup, so should the total amount of energy being gravitationally radiated away not also be the same?108.13.99.101 (talk) 23:16, 10 February 2016 (UTC)

I edited the sentence, thanks. The use of 'instantly' didn't make much sense, it would take some time after breakup for the matter to form a disk with a symmetric mass distribution. Gap9551 (talk) 23:26, 10 February 2016 (UTC)

To Do List is from 2005, needs updating or deleting

The 'To do list' currently at the top of this page was created sometime in 2005, and has seemingly not been changed since, even tho many, most, or all the items on it have probably been adequately addressed. So can somebody who understands this subject and/or our ITN quality standards a lot better than me please either update it or delete it - otherwise it's liable to be a source of misdirected effort and/or a cause of unnecessary delay in getting this item posted to ITN if and when the rumoured announcement later today leads to an ITN posting request. Tlhslobus (talk) 03:47, 11 February 2016 (UTC)

I've now added a warning to this effect at the bottom of the list and also as near the top as I could manage. (If at first you can't see the warnings you may have to click on the 'refresh' command at the top of the list.) Tlhslobus (talk) 04:32, 11 February 2016 (UTC)

LIGO 2016 success!!

Here is the report on today's announcement: http://www.nsf.gov/news/news_summ.jsp?cntn_id=137628 100.15.120.162 (talk) 16:18, 11 February 2016 (UTC)

They possibly managed to find an evidence for the existence of those waves, but it requires more verification. There are some critical responses from diverse institutes, so is it really accurate to include the existence of g waves as a fact here ? --95.115.172.215 (talk) 17:02, 11 February 2016 (UTC)

References 1, 7, 57 and 58 should probably be removed, and replaced by reference 8 (the discovery PRL paper) plus a pointer to the LIGO 'Scientific Summary' (semi-technical account) at https://www.ligo.caltech.edu/system/media_files/binaries/301/original/detection-science-summary.pdf ... and the surrounding text adjusted in each case. NormanGray (talk) 17:28, 11 February 2016 (UTC)

Aaarg! Sorry, I've messed up the reference to the LIGO article, not sure exactly how. I moved the 2016 LIGO detection text to the rear of the section from the front. The reason being it seemed not to be consistent in date order. 80.189.172.184 (talk) 18:26, 11 February 2016 (UTC)

No worries, I fixed the format. Cheers, BatteryIncluded (talk) 18:28, 11 February 2016 (UTC)

Isn't is great that gravitational waves were detected exactly one hundred years from when Einstein predicted them in 1916? Titus III (talk) 23:49, 11 February 2016 (UTC)

Updates to other pages, per the LIGO news

Pages are being updated pretty rapidly, but these are pages that still may need to be updated due to the recent news:

• Tests of general relativity#Direct detection of gravitational waves
• Timeline of astronomy
• Introduction to general relativity, a featured article
• History of technology ("LIGO is trying to detect gravitational waves")
• Observational astronomy ("that may capture events")
• GEO600#Joint science run with LIGO ("it is hoped that they will perhaps reveal the arrival at Earth of two unambiguous bursts of gravitational waves")

If a page doesn't need any changes, or if the needed changes are made, please feel free to edit my comment to cross that page off. Cheers, --Hirsutism (talk) 18:29, 11 February 2016 (UTC)

Wave solutions

Now that it is in the news, I looked at this page and was surprised that it does not refer to the key item from 1959 on plane solutions [1] . I will not meddle with this page, but whoever likes to, please update with some history. Robinson is still alive, and is probably drinking and celebrating right now. Gravity, gravy, etc. (talk) 19:36, 11 February 2016 (UTC)

Use of the word Prediction

I am puzzled by the use of the word prediction in the article to talk about Albert Einstein's theory. According to Merriam-Webster's definition of the word prediction it is "a statement about what will happen or might happen in the future" or "the act of saying what will happen in the future". Einstein did not say that Gravitational Waves would exist or be found in the future. He theorized about them which according to Merriam-Webster's definition of the word theorize which means "to think of or suggest ideas about what is possibly true or real" I think it would be much more accurate in describing Einstein role in the existence of Gravitational Waves. He understood them and explained them, he didn't say "in a future time scientists will find Gravitational Waves". — Preceding unsigned comment added by 151.33.78.149 (talk) 09:55, 12 February 2016 (UTC)

You should read the articles Scientific theory and Predictive power. Einstein's theory predicted a number of things, and one prediction was that we would be able to detect gravitational waves, but this couldn't be done until we developed the technology to do so. The theory also predicted what the correct value would be for the bending of light around massive objects (see Gravitational lensing but this wasn't proved until 1919. Predictive power is one of the hallmarks of a good scientific theory. Richerman (talk) 11:07, 12 February 2016 (UTC)

I think it may be more accurate to write Einstein theorized gravitational waves exist. The ability to make accurate predictions of future events(Neils Bohr) is a validation of a theory.

According to the literature, it is very safe and accurate to say that he predicted them: see Google Scholar and Google Books. - DVdm (talk) 15:02, 12 February 2016 (UTC)

Please take a look at Scientific method; The best hypotheses lead to predictions. Cheers, BatteryIncluded (talk) 15:28, 12 February 2016 (UTC)

Is this correct? Einstein created a theory of general relativity(a hypotheses), then Einstein created a prediction that gravitational waves exist as a consequence of the theory.CuriousMind01 (talk) 16:05, 12 February 2016 (UTC)

Yes it is. The theory was published in 1915 and he predicted gravitational waves in 1916 - see:[2]. Richerman (talk) 19:57, 12 February 2016 (UTC)

You are right, that definition of the term 'prediction' is different from how the term is used in science. Gap9551 (talk) 20:07, 12 February 2016 (UTC)

The word prediction seems to be used with 2 different meanings:

1. The dictionary meaning :"a statement about what will happen or might happen in the future" where conducting an experiment to measure if prediction X will occur with values V +/- uncertainty U, at a time T in the future. The experiment is designed to test predictions of future events based on a hypotheses.

2. an alternate meaning: theorizing something exists now, and predicts the something will be actually be found and detected and measured in the future as used in Google Scholar. CuriousMind01 (talk) 01:30, 13 February 2016 (UTC)

Gravitons?

The article doesn't talk about gravitons. I'm curious if LIGO measuring these gravity waves, connected to general relativity, can tell us anything about quantum theory? Tom Ruen (talk) 14:41, 12 February 2016 (UTC)

Gravitational wave observation and Graviton both say something about the new upper limit. But maybe it could be mentioned here too. Gap9551 (talk) 20:04, 12 February 2016 (UTC)

I see at Gravitational_wave_observation#Gravitons. That's good. Tom Ruen (talk) 21:57, 12 February 2016 (UTC)

Effects of passing

The section of the article titled "Effects of passing" states:.

The effects of a passing gravitational wave can be visualized by imagining a perfectly flat region of spacetime with a group of motionless test particles lying in a plane (e.g′., the surface of a computer screen)." This description is ignorant of Relativity. A 2D space-time diagram has one axis for space and one axis for time, so particles can only be shown in a straight line, not a ring as is being discussed in that section. The diagram also has no time axis. The author seems to think that space-time is just a fancy way of saying "space". 1.75.240.2 (talk) 09:06, 13 February 2016 (UTC)

I don't think there's a problem. The visualization refers to a 2D spatial subspace of simultaneity of 4D spacetime. If the latter is flat, then the former is also flat. - DVdm (talk) 15:03, 13 February 2016 (UTC)

The intent behind the video was to depict apparent motion in free-falling test particles in 2 spatial dimensions, with time indicated on the viewer’s watch (and with wave moving normal to the spatial plane shown). Illustration instead with a 3-rd time axis is certainly possible, but would be more difficult to envision. Relativity doesn’t really have anything to do with the depiction.

What is probably bothering you at least subconsciously is a deceptive feature of the video. The video really doesn’t show test particles moving as viewed looking down from points above on a plane directly above the particles. Instead, the particles’ motion is seen relative to a fixed point in the loop center. The particles’ apparent motion is not invariant across their plane even though the wave passing through is constant in this plane at any given time.

What the video depicts is actually a little bizarre. It shows only what an observer at the center of the loop of particles sees by timing photons reflected off the test particles. Another observer would also center loops of particles, but would they would be displaced from the original depiction. David in Cincinnati (talk) 15:14, 17 February 2016 (UTC)

Space distortions

Can anyone explain this animation [3] from space.com, showing two orbital black holes, and a rainbow colored stretched surface below, which bends downwards for mass, but after 0:40 it bents upwards on the orthogonal directions of the black holes. Is the bending upwards implying some sort of "spacial contraction" (versus ordinary gravity expansion of space, slowing of time) or otherwise a "repulsive gravity force" (like the traditional tabletop model of gravity on a curved surface) or something else? What is gravity doing in those "upward" domains? Tom Ruen (talk) 17:02, 13 February 2016 (UTC)

Are gravitational waves more like sound or light?

I realized the gravitational waves could be longitudinal wave (like sound), or transverse wave (like light), or could be both! I'd assume gravitational waves are more like sound, with space-time compression/distortions, but this article talks about polarization, which suggests transverse waves. It seems like this wave-nature is something that can be clarified in this article. Tom Ruen (talk) 00:42, 17 February 2016 (UTC)

Here's one answer [4] "Gravitational waves are transverse waves but they are not dipole transverse waves like most electromagnetic waves, they are quadrupole waves. They simultaneously squeeze and stretch matter in two perpendicular directions." Tom Ruen (talk) 00:46, 17 February 2016 (UTC)

To confirm and edit

1. Are gravitational waves due to an intense gravitational source (such as the GW150914 system) "self-redshifted" by the gravitational field of the object itself? (ie does the object act on its own gravitational waves, for example by space-time distorting, causing the waves to be affected)

I think this would have some effect. However, in simulations/calculations, properties of the gravitational wave are worked out at infinity, and hence this is already taken into account — BobQQ (talk)

1. Is "redshifting" the correct term or the term actually used for gravitational wave frequency shifts?

Yes. It is used in [5] for cosmological redshifting. — BobQQ (talk) 15:46, 17 February 2016 (UTC)

1. Do we have good cites for these kinds of properties of GWs?

FT2 ^{(Talk | email)} 10:38, 17 February 2016 (UTC)

Looks like we do for the second, but I don't know for the first. — BobQQ (talk) 15:46, 17 February 2016 (UTC)

To the first question, in a strong/dynamic gravitational field there may not necessarily be locally well defined notions of frequency. Hence since the source frequencies are not well defined, the question becomes what do you mean by redshift. That being being said, like EM waves, GW do experience a frequency shift due to travelling out of a "gravitational potential" or relative motion.

As to your last question, I am not even sure you could call these "properties of GWs". Hence it is not clear they should be commented on here. (For comparison, electromagnetic wave does not mention redshift either.)TR 15:00, 18 February 2016 (UTC)

Do the Photons with their Orbital Angular Momentum Radiate gravitational Waves?

From the Wikipedia pages we find that: 1. “ Systems that have nonzero energy but zero rest mass, such as photons moving in a single direction, do not have ‘center-of-mass’ frames, because there is no frame in which they have zero net momentum. They always possess a net momentum magnitude that is equal to their energy divided by the speed of light. 2. The angular momentum of light is a vector quantity that expresses the amount of dynamical rotation present in the electromagnetic field of the light. Indeed, a beam of light, while traveling approximately in a straight line, can also be rotating (or “spinning”, or “twisting”) around its own axis. This rotation, while not visible to the naked eye, can be revealed by the interaction of the light beam with matter, as shown in the figure below: The total angular momentum of light and matter is conserved in time. But there are actually two distinct forms of rotation of a light beam, one involving its polarization and the other its wave-front shape. These two forms of rotation are hence associated with two distinct forms of angular momentum, respectively named (i) light spin angular momentum (SAM) and (ii) light orbital angular momentum (OAM).” From the above statements it appears that a photon moving in straight line with an orbital angular momentum, as shown in a picture in the Wikipedia page, is likely to radiate gravitational waves. What is the opinion of the expert editors? Question from: Hasmukh K. Tank 117.228.140.245 (talk) 15:46, 24 February 2016 (UTC)

Actually any electromagnetic radiation will have an association gravitational wave. The EM wave distorts space. Gravitational waves can also carry angular momentum. I will look for a reference for you. Graeme Bartlett (talk) 05:52, 7 March 2016 (UTC)

Dear Friend, Please find the references. Based on the references we can understand and partly explain the 'cosmological red-shift' in terms of extra galactic light loosing energy because of gravitational waves radiation. Hasmukh K. Tank, 117.229.15.132 (talk) 17:02, 4 April 2016 (UTC)

Clarification needed

At present the article reads: "If the dumbbell spins like a wheel on an axle, it will not radiate gravitational waves; if it tumbles end over end, as in the case of two planets orbiting each other, it will radiate gravitational waves. The heavier the dumbbell, and the faster it tumbles, the greater is the gravitational radiation it will give off. In an extreme case, such as when the two weights of the dumbbell are massive stars like neutron stars or black holes, orbiting each other quickly, then significant amounts of gravitational radiation would be given off."

The first line makes little sense: "If the dumbbell spins like a wheel on an axle, it will not radiate gravitational waves; if it tumbles end over end, as in the case of two planets orbiting each other, it will radiate gravitational waves." If the dumbbell spins like a wheel on an axle that is the same like "it tumbles end over end." So, that is not well expressed.

The second part: "The heavier the dumbbell, and the faster it tumbles, the greater is the gravitational radiation it will give off. In an extreme case, such as when the two weights of the dumbbell are massive stars like neutron stars or black holes, orbiting each other quickly, then significant amounts of gravitational radiation would be given off." That implies that simply by tumbling it is somehow radiating energy from some source. What is the source of that energy? I suspect, but am uncertain, that the energy is the result of the change of the potential energy of the two masses as they spiral into each other. If that is not the source of energy then what is it? Mass and energy that enters the critical radius of a black hole is there to stay forever with the exception of the extraction of energy associated with the spin energy of each BH through the Penrose Process. But the Penrose Process is not the source of the gravitational energy and the orbit of the masses about each other does not magically create energy. The only source of energy I see here is due to the decrease of Potential Energy as a result of their spiralling into each other. Potential Energy results in an increase of the kinetic energy of the BH and some of that PE is carried away in the form of gravitational waves. Zedshort (talk) 14:39, 6 March 2016 (UTC)

How about you pick up a book? (Instead of asking variants of the same question over and over again.)TR 14:44, 6 March 2016 (UTC)

Support. -BatteryIncluded (talk) 15:37, 6 March 2016 (UTC)

How about you understand the idea of an encyclopedia written by volunteers that is very incomplete, and poorly written to such a degree that the ideas are poorly expressed. Did I step on your territory? Pardon me, I'll be sure not to do that again, provided you tell me where your territory lies. When I get a response that is complete, concise and intelligible I will be satisfied and not post such questions. In the meantime such questions might prompt an improvement to the article. By they way, do you know how thuggish you sound? Zedshort (talk) 16:59, 6 March 2016 (UTC)

Disagree with revert

I disagree with this revert of my edit. "We must align this article with the electromagnetic radiation article" is not an acceptable reason for a blanket revert, and I disagree with the premise. There is no good reason why the presentation here should align closely with that other article, and even if that were so that would not justify all of the changes that were reverted in this edit.--Srleffler (talk) 06:08, 9 March 2016 (UTC)

I agree. Moreover I strongly object to the phrasing "Gravitational waves are radiant energy". Besides the obvious grammatical issue, there is the blatant problem of treating energy as a "something" rather than a quantity.TR 12:46, 9 March 2016 (UTC)

Why don't gravitational waves devoured by a black hole?

Gravitational waves because of two black holes merge was detected, but why not being sucked? 星耀晨曦 (talk) 06:42, 10 March 2016 (UTC)

some of the waves will have been absorbed by the black holes in the merger. The modelling takes this into consideration. But most escapes out into space around the black holes. Black holes will be about the only way to stop gravitational waves, but you cannot surround yourself with a sphere of black holes, otherwise you would be inside an ever bigger one. Graeme Bartlett (talk) 11:15, 10 March 2016 (UTC)

I was even thinking that if you could time reverse the gravitational waves given out by a binary black hole merger, you could split a single back hole back into two. I don't know if this is theoretically possible, it certainly is not practical. Graeme Bartlett (talk) 11:18, 10 March 2016 (UTC)

That sounds as if it would violate the area law.TR 15:28, 10 March 2016 (UTC)

IMO, photons have mass, gravitons do not. BatteryIncluded (talk) 17:41, 10 March 2016 (UTC)

Wikipedia seems to have no mention of this "area law". Perhaps we need to include it somewhere. I was not talking gravitons, but gravitational waves, which do indeed carry energy. So a volume of space with gravitational waves in it will appear to have mass in it. From the photon page: "The photon has zero rest mass". Graeme Bartlett (talk) 00:28, 11 March 2016 (UTC)

The "area law" is also known as the second law of black hole mechanics.TR 08:45, 11 March 2016 (UTC)

That page section could do with some simpler explanations, including calling it an "area law". It would be violated by a black hole de-merger, but only with the expenditure of much energy, and a very unlikely situation. Graeme Bartlett (talk) 02:58, 12 March 2016 (UTC)

Agreed, with the quality of that page. It could do with quite a bit of work. Having given your idea some thought, I think the problematic bit is that the time reverse of a black hole is a white hole. White holes occur automatically in eternal black hole solutions. In particular, many of the calculations used for the description of BH binaries contain (fictious) white hole horizons in their past. The natural boundary conditions on these is that there is nothing coming out of them (similar to assuming no radiation coming from past null infinity). However, the time reversal of the merger that you suggest would have GW radiation coming out of the past white hole horizon. Preparing the system to have a certain profile of GWs coming in from past infinity is as you said unpractical, it is impossible to prepar the system such that the correct waves are coming out of the white hole. This is what makes the suggested scenario impossible.TR 12:24, 12 March 2016 (UTC)

Both electromagnetic and gravitational radiation carry energy, and so have similar gravitational mass-energy properties. They also both follow null geodesics and so have would be considered to have zero rest mass. The case of gravitational waves is more complicated because of the difficulty of separating them from the background curvature and hence defining an energy-momentum tensor. — BobQQ (talk) 14:31, 11 March 2016 (UTC)

Andre Lichnérowicz

has given the most axiomatic and complete description of gravitational waves, Annali di Matematica Pura & Appl. 4 [1960] p 1-95 "Ondes et Radiation Électromagnétiques et Gravitationelles en Relativité Générale", although in an old-fashioned way with indices instead of basis-free. It should be included in the bibliography! — Preceding unsigned comment added by 72.77.197.12 (talk) 14:28, 19 March 2016 (UTC)

Sound barrier vs luminal (speed of light barrier)

No particle is able to travel faster than the speed of light, but usually briefly space chunks themselves at extreme conditions (for example during big bangs or black hole mergers). During the normalization process all quantum information is emitted subluminally (under the light-speed limit) but biased polarization statistics reveal the event.

Omitted reference of Einstein

As far as I can see the following reference is omitted:

Einstein A.& Rosen N, On gravitational waves, J. Franklin Inst. vol.223, 1937 43-54

Also the reference to Einstein 1918 is repeated as refs 3 and 32. I would make the changes myself but how to do it? JFB80 (talk) 13:37, 13 May 2016 (UTC)

 Done. Please verify that I placed On gravitational waves at the most appropriate location. Thanks, BatteryIncluded (talk) 14:04, 13 May 2016 (UTC)

Thanks. Maybe you could also put in that reference to Lichnerowicz mentioned in a previous comment above (last but one). JFB80 (talk) 05:50, 16 May 2016 (UTC)

Claims of superluminal propagation of gravitational waves

So I came across this paper claiming that the upper limit on gravitational wave propagation is 1.7c. http://arxiv.org/abs/1602.04188 Does anyone know if there is a critique or rebuttal to this paper anywhere, or could someone tell me how this paper is wrong? Thanks. — Preceding unsigned comment added by 96.50.27.58 (talk) 01:53, 25 June 2016 (UTC)

Nothing wrong with the paper as far as I can see. It just states direct experimental upper limits on speed of gravitational wave propagation, assuming no underlying models with Lorentz symmetry and come up with 1.7c. In models with Lorentz symmetry we have c as the universal speed limit of course. — Preceding unsigned comment added by Sharanbngr (talk • contribs) 15:57, 13 September 2016 (UTC)

Poincaré first predicted gravitational waves before Einstein

In 1905 Henri Poincaré first predicted gravitational waves ondes gravifiques emanating from a body and propagating at the speed of light as being required by the formalism of spacetime.

This must be included in this Wikipedia article. — Preceding unsigned comment added by 173.65.234.214 (talk) 13:22, 30 June 2016 (UTC)

References

That is completely right, but Poincares prediction was in the context of special relativity, since general relativity has not been invented in 1905! — Preceding unsigned comment added by 130.133.155.68 (talk) 09:31, 2 July 2016 (UTC)

I agree with you. It is the same gravitational wave, it can be seen in both special and general relativity. — Preceding unsigned comment added by 173.65.234.214 (talk) 14:15, 2 July 2016 (UTC)

NO, Poincarré is talking about GRAVITY, the propagation of GRAVITY, it's supposed speed of propagation, according to Laplace, etc. He is NOT talking about "gravitationnal waves". Different subjects. In "ondes gravifique" the adjective "gravifique" means "that PRODUCE gravity". Gravitationnal waves don't produce any gravity or gravitationnal effects. They ORIGINATE from a gravitationnal situation i.e. accelerations. The sound of moving leaves in a tree doesn't produce wind. — Preceding unsigned comment added by 163.47.106.116 (talk) 00:24, 13 January 2017 (UTC)

dark matter and gravitational waves

All matter (atoms, stars etc.) emit gravitational waves (usually undetectably negligible). All stars emit gravitational waves in a galaxy (at much lower levels than a black hole merger event), and that energy is absorbed by other stars more and more in relation to the distance from the galactic core. Of course that idea is moronic, but in Wikipedia we should mention all ideas, if it is silly like that one we should analyze that the provided energy wouldn't be enough. Censorship doesn't help! — Preceding unsigned comment added by 2A02:587:4109:5C00:3102:EF8:C9E5:D035 (talk) 17:36, 16 September 2016 (UTC)

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