# Talk:Gravitational wave

 To-do list for Gravitational wave: class="todo-box" colspan="2" style="Template:Talk other border:1px dotted gray; padding: 2px 4px;" |To-do list is empty: remove {{to do}} tag or click on edit to add an item.

## Mathematics

The equation given as the full Einstein equation in the Mathematics section is incorrect, see http://en.wikipedia.org/wiki/Einstein_field_equations for the full equation. The one given is actually just the linearised version, see http://en.wikipedia.org/wiki/Linearized_Einstein_field_equations for a version of it. — Preceding unsigned comment added by 67.220.7.72 (talk) 02:41, 8 February 2012 (UTC)

## TStein's Radiation from other sources

Since one of the Hulse-Taylor binary stars is a pulsar, why isn't it possible that the orbit is decaying because of radio emission (electromagnetic radiation) and not gravitational wave emission (gravitational radiation)?Lestrade (talk) 00:40, 15 February 2009 (UTC)Lestrade

It would be a scandal of the utmost highest order if not only the original authors of the theory but all subsequent generations of scientist since then would commit such an elementary blunder. I suspect that net effect of any recoil due to its radio emission would cancel out during a revolution. Then again I truly know nothing about this field. TStein (talk) 05:40, 16 February 2009 (UTC)

It is acknowledged by scientists that the orbital rate of pulsars is slowed by electromagnetic radiation. Professor Virginia Trimble wrote that "gravitational radiation is less important than electromagnetic in slowing down the Crab and other pulsars." (Sky & Telescope, October 1987, p. 367) Lestrade (talk) 18:35, 17 February 2009 (UTC)Lestrade

Pulsars are neutron stars. In speaking of the pulsar's orbit, Clifford Will stated that "there are some residual frictional forces between the neutron star and the surrounding medium that do tend to slow it down… "(Was Einstein Right?, Ch. 10, p. 183). Will even explicitly attributed the slowing of the Crab pulsar to "friction between it and the surrounding medium" (op. cit., p. 185). However, instead of attributing the orbital decay of the Hulse-Taylor binary stars' orbit to known, familiar, detectable causes such as friction or electromagnetic radiation, scientists prefer to claim that the cause is the unknown, unfamiliar, undetectable radiation of gravitational waves. Supposedly, this is because the rate of orbital decay exactly matches the amount predicted in Einstein's equations.Lestrade (talk) 04:17, 18 February 2009 (UTC)Lestrade

## Other explanations

I would like to add the following information to the article. It seems to me that this information might be considered important by someone other than myself.

The rate of decrease of the orbital period of the Hulse-Taylor binary system is explained by the loss of energy due to gravitational radiation. The "observed decrease…agrees with the value…due to loss of energy via gravitational waves as predicted by the general relativistic formula for quadrupole radiation…. The agreement between observed and calculated general relativistic values…is better than 1%."[1] It is admitted, though, that the orbital decay may be the effect of other causes. "Other conceivable causes of orbital period decrease: tidal energy dissipation, other forms of energy loss, changes of orbital period by acceleration due to a third body, etc., have also been studied."[2]

This whole article is disgustingly POV. Gravitational waves are just a theory. They need to be actually measured in nature before they get the kind fact-y treatment given here. A layman would read this article and think they are fact. 2001:470:1F04:3DF:0:0:0:2 (talk) 20:42, 5 June 2013 (UTC)

## Analogy

This whole topic of gravitational waves is based on the unstated assumption, possibly incorrect and false, that gravitation is almost completely analogous to electromagnetism. If I include this judgment in the article, will it be regarded as my own subjective opinion and therefore be deleted? I assume that everyone knows that this fundamental, tacit assumption is the basis of most scientists' beliefs today about gravitation.Lestrade (talk) 02:40, 22 February 2009 (UTC)Lestrade

I don't see what you mean. The theory of gravitational waves is based on general relativity, not on an analogy with electromagnetism. General relativity happens to be mathematically similar to electromagnetism and the waves are correspondingly similar, but there are also differences, the biggest being that gravitational radiation has no dipole component. No assumption of similarity to electromagnetism goes into these calculations. -- BenRG (talk) 16:07, 24 February 2009 (UTC)

I give up. If Michael Berry's explanation.[3] isn't sufficient, then there is no hope of further communication.Lestrade (talk) 18:41, 24 February 2009 (UTC)Lestrade

No need to give up yet. The idea that all forces at a distance must travel by some sort of wave is a fundamental physics that I don't think can be denied. (Unless you believe that the force travels instantly.) I can see BenRG's point that the analogy can be taken too far, though. I don't think that quotation implies anything near as complex as what he implies but I can see where it might cause problems, unnecessarily. (All forces at a distance must travel in waves not just E&M and gravitational forces). Further I don't see why a lengthy quotation is needed to make a simple point. Quotations of that sort begs the reader to think that you are basing your argument merely on the authority of the person quoted. TStein (talk) 23:29, 24 February 2009 (UTC)
I think you're both missing the point. Berry says that an analogy with electromagnetism suggests that gravitational waves probably exist. That's true, it does suggest that. That's totally different from a claim that the concept of gravitational waves is "based on [that] unstated assumption, possibly incorrect and false". The idea is that you make a guess based on an analogy, then you go and check the guess, and it turns out to be right or wrong. In this case, right. Once you've checked it, the fact that you were originally inspired by an analogy no longer matters. The analogy is not the basis for the belief. -- BenRG (talk) 01:32, 25 February 2009 (UTC)

My concern was that credulous Wikipedia readers would thoughtlessly accept the hypothesis that gravitation exists as waves in a field as though it was an established fact . Scientists used that model successfully for electromagnetism and have applied it to gravitation. If gravitation is not a field of waves, however, then we will never understand it because we will have stopped considering alternative models. I considered Michael Berry's words to give a very clear insight into the way that gravitation is studied at present. Besides, I have experienced one too many deletions and the straw has broken the camel's back. It is a characteristic of Wikipedia that any one person can perform a deletion and prevent valuable content from appearing. At present, I don't have the stomach for arguing and giving explanations to people who are set to oppose whatever I might say. Lestrade (talk) 00:20, 25 February 2009 (UTC)Lestrade

Einstein wrote his General Theory of Relativity when he thought that gravitation is similar to or equivalent to electromagnetism. As a result, he interpreted his equations as being representative of radiating waves, travelling at precisely 299,792,458 m/s, that are caused by matter in motion. A few years later, the equivalence of gravitation and electromagnetism was not accepted by scientists. However, the analogy of gravitation and electromagnetism is accepted today by most scientists. The Wikipedia article also presumes this analogy and assumes that gravitation has the same qualities as electromagnetism. It is generally informative when unstated assumptions are clearly declared. By doing so, the reader is aware that the article has a presumptive bias or slant. This clear and open awareness allows the reader to think for him– or herself and not be influenced surreptitiously. For this reason, the tacit assumption that gravitation is analogous to electromagnetism, in that it consists of radiating waves that are caused by matter in motion, should be made explicit for the benefit of readers. It should be clear that the article is based on a presumption, not on facts that can be taken for granted.Lestrade (talk) 16:16, 13 May 2009 (UTC)Lestrade
Lestrade is correct, theology must be identified when it is invoked. However he misunderstands the theory of electromagnetism and gravitational radiation. Electromagnetic raditation comes from ACCELERATED charges, and gravitational radiation is presumed to originate from ACCELERATED masses. To be more accurate, the acceleration must vary in direction or with time. This is the jerk factor or third derivative of position. Charges or masses in unaccelerated motion do not radiate.Trojancowboy (talk) 18:24, 13 May 2009 (UTC)

Why are you using the noun "theology"? This is not a religious discussion, nor is it a metaphysical discussion. I suspect that you are trying to be dismissive. Your statement illustrates the reason that gravitation is assumed to be analogous to electromagnetism. Please note that I said "analogous" and not "equivalent." The analogy is that both electromagnetism and gravitation are partially similar because they both consist of radiation, travelling at precisely 299,792,458 m/s, that results from an acceleration[4]. This analogy tacitly underlies all current thinking about gravitation. It is entirely possible that this presumed analogy is incorrect.71.245.114.30 (talk) 15:05, 14 May 2009 (UTC)Lestrade

## Talk page footnotes

1. Ciufolini and Wheeler, Gravitation and Inertia, Ch. 3, p. 147
2. C.M. Will, Theory and Experiment in Gravitational Physics, rev. ed. (Cambridge University Press, Cambridge, 1993)
3. According to Sir Michael Berry, "The analogy between gravitation and electromagnetism … suggests that gravitational waves should exist, which transmit with speed c effects of the acceleration of masses, just as electromagnetic waves transmit the effects of the acceleration of charges." (Principles of cosmology and gravitation, 3.5.)
4. Ibid.

## grav waves perhaps detected in 1987

http://arxivblog.com/?p=1271
http://arxiv.org/abs/0903.0252 --Wongba (talk) 21:52, 4 March 2009 (UTC)

## 1 in 10^-20 ?

The article says that the measured effect of gravitational waves on Earth, "will never be much more than 1 in 10^(-20)". Is this correct? Surely that would be a very large effect. Should this say "1 in 10^(20)"?

--Thom2002 (talk) 18:57, 16 March 2009 (UTC)

## Equational existence

In the section on power generated in the earth-sun sytem, it is claimed that "Substituting these values into the above equation gives about 200 watts of power radiated by the Earth-Sun system in the form of gravitational waves." These 200 watts exist in an equation but cannot be shown to exist in real experience. The reason is simply that, in stubborn resistance to the wishes and desires of physicists, gravitational waves have never been detected. Is there a brave physicist who will admit this for the benefit of earnest Wikipedia readers?Lestrade (talk) 04:26, 22 April 2009 (UTC)Lestrade

The sentence you quote only asserts that an equation that is part of a scientific theory yields a certain numerical result if appropriate numbers are supplied for the mass of the sun and the mass of the earth, etc. The calculated numerical value is significant because, for one thing, 200 watts of energy is the equivalent of one of the larger incandescent light bulbs used in homes. They are easy to see from a few hundred meters away, but from even someplace as close as the moon it would be a very faint signal. A gravitational wave that would cross space from the vicinity of another star, diminished by the r squared rule, and still be powerful enough to agitate our crude instruments would have to be a very major event. P0M (talk) 04:52, 22 April 2009 (UTC)

In other words, the 200 watts of power could very well be a mathematical fiction. Why does the article dogmatically make statements as though the power radiation is a fact? We all want Kip Thorne to be found correct and to win all of his bets with other scientists, but it might serve Wikipedia better if speculations are expressed as speculations instead of as facts.Lestrade (talk) 23:17, 28 April 2009 (UTC)Lestrade

## Power radiated by the earth sun system

I reverted to an older edit of this section Power radiated by the earth sun system because it was a whole lot clearer than the last edit. For example, the last edit included angular frequency (denoted omega) in the equation without saying what it meant. The article used to be written in such a way that most of it could have been understood by anyone with a knowledge of basic math and physics but lately editors have been using the article to show off their own knowledge. Lucretius (talk) 22:38, 22 April 2009 (UTC)

Thanks. I think that the intention of scientific articles in Wikipedia should always be to support the people who do not already understand the content. Writers like Einstein and Heisenberg always did an excellent job, when writing for the general public, of not saying anything that could mislead the questing high school student, and also explaining all that could be explained without bringing in higher math, jargon of the field, etc. We should try to live up to their examples. P0M (talk) 23:00, 22 April 2009 (UTC)

Lucretius is absolutely right about clarity. The previous formula incorporating omega was nearly useless. However, he erred in substituting pi for 5. The total amount of energy in the earths orbit was grossly in error and I added references. When the orbit drops, the orbital speed increases. This doubles the final amount of the drop to subtract the correct amount of energy lost. Further, the rate of energy loss increases dramatically by the inverse cube of the radius as it drops.Trojancowboy (talk) 23:29, 23 April 2009 (UTC)

I've had this discussion before with Moble, now archived. He included Pi on the authority of Kip Thorne (see archive 6 November 2006). I had found another source that listed 5 instead but MOBle is much more erudite about gravitational theory than I am and so we stayed with his (and Thorne's) preference for Pi. Also MOBle argued that the energy for radiation comes basically from the kinetic energy and not from gravitational P.E. (see archive 29 Nov. 2006). I don't know how erudite you are, Trojancowboy, but MOBle convinced me that he was the expert and I happily accepted his advice - the article as it now stands is almost entirely his work and I think he did a great job. I haven't undone your edit but I did revise it to clear up a few things. I don't really care if it's Pi or 5 or if it's 200 or 300 Watts just so long as we don't burden the argument with unnecessary detail - we're dealing with approximations. Lucretius (talk) 04:12, 24 April 2009 (UTC)

Kip Thorne was wrong about pi. It is especially important for an encyclopedia to be right. R and omega are related by the 3/2 rule, the square of a planets period is proportional to the cube of its mean distance from the sun. Solving for omega in terms of G, R, and the two masses gives exactly the formula that I used. Pi never enters in. Both formulas give exactly the same result but the first requires both R and omega. My reference confims it. The formula can also be expressed in terms of omega alone but the result is quite cumbersome. It involves the 7/3 power of G, the square of the product of the masses, the 2/3 power of the sum of the masses, and 10/3 power of omega. It is almost as useless as the original formula.
I also derived the formula for lifetime of an orbit, which varies as the fourth power of the radius and inversely as the product of the masses and the sum of the masses. Take a one solar mass star orbiting the 2 million solar mass black hole at the Galactic Center in a 1,000 second orbit. It has a lifetime of 20 years. I encourage confirmation of these matters by knowledgeable editors.Trojancowboy (talk) 21:38, 24 April 2009 (UTC)

It worries me a bit when you say you 'derived' a formula for the lifetime of an orbit and I don't think you can simply dismiss Kip Thorne as 'wrong'. But I agree that the article needs overseeing by 'knowledgeable editors' and I concede that the Pi attributed to Thorne does seem to represent a minority view. Lucretius (talk) 23:40, 28 April 2009 (UTC)

MTW has 5, not π (equation 36.16, page 988). It also gives a formula for the decay of the radius as a function of time (36.17, same page), which is ${\displaystyle R=R_{0}(1-t/\tau _{0})^{1/4}}$, where ${\displaystyle \tau _{0}={\tfrac {5}{256}}{\tfrac {c^{5}}{G^{3}}}{\tfrac {{R_{0}}^{4}}{M_{1}M_{2}(M_{1}+M_{2})}}}$. Using that I get 20 years in Trojancowboy's example (though I used the Newtonian formula for the radius, which may have been a mistake since it's only a few Schwarzschild radii). For the Earth–Sun system I get 1·1023 years, or 8·1012 times the current age of the universe. Note the decay time is exactly 1/4 of the estimate you get by assuming constant dR/dt, which (I assume) is why the decay time currently in the article is four times larger. -- BenRG (talk) 00:04, 30 April 2009 (UTC)

.......

A previous post from Lucretius is on point and I second the motion:
There is no democracy in mathematics, you are either right or wrong. Pi and 5 are not the same thing in a formula.  ::BenRG is correct but his formula is unnecessarily complex. This is exactly what I got and will post the short derivation here soon.
I think that I made a calculation error in earth's orbit lifetime even though I did it twice. I will fix it soon and add some realistic binary orbits to the article.Trojancowboy (talk) 21:08, 30 April 2009 (UTC)

re-worded the perceived outcome of what would happen to the earth before its orbital energy was radiated away, seemed an odd sentence, but left everything else the same. Indomei (talk) 07:56, 20 June 2009 (UTC)

## Page Rename

I added an important comparison to electromagnetic radiation in the introduction and it needs a lot more work. I came to this article to calculate some binary star radiation and found it nearly useless for that purpose. One of the problems is that many authors in the literature use different units such as chirp mass and reduced mass. This entire article should be understandable by someone who has studied calculus.

This page should be renamed "Gravitational Radiation". The term "gravity wave" is almost NEVER used in physics or astronomy. That term should be redirected. I would like comment on this rename.Trojancowboy (talk) 21:14, 30 April 2009 (UTC)

Sorry but I don't think the comparison to em radiation is very helpful so early in the article. Poor Joe Blow comes to the article to find out what gravitational radiation is all about and suddenly he finds he's getting a lecture on em radiation. Moreover the difference between em and gravitational radiation is one of the great stumbling blocks to a unified theory and I don't think we should be trying to understand one in terms of the other since that suggests original research. The use of simple formulae is empowering for ordinary readers and I think these should feature in a popular encyclopaedia as much as possible BUT I'm worried when you talk about devising simple formulae for complex physical processes and I'd rather you used something from the literature. I don't care what you name the article - a gravitational wave by any other name would feel as slight. Lucretius

I say that the EM comparison is essential since everyone understands the concept of radio waves and antennas. It adds to understanding rather than obscuring it. Did you find my comparison to be unclear? I had to study for hours to reach the level of understanding that I cleared up in a small paragraph.Trojancowboy (talk) 23:25, 30 April 2009 (UTC)

I don't want to keep throwing a damp blanket over your fire but - a) Not everyone understands radio waves and antennas; b) statements like the strongest em radiation is produced by antennas... are wrong unless accompanied by technical qualifications that confuse the issue; c) an article on g radiation should not be introduced with a lecture on em radiation. For these reasons, I found your latest edit confusing. Lucretius (talk) 23:46, 30 April 2009 (UTC)

How could my explanation be made less confusing? The only electromagnetic radiation stronger than that coming from antennas is lightning strikes and cyclotrons. Were you aware of the connection between EM Waves and Gravitational Waves? I say that most people are not.
I just realized that collections of binary stars whose orbits have been synchronized in period and phase can make a DIRECTIONAL gravitational wave antenna. Maybe I should patent the idea. That may be the only way to get LIGO to work and justify all of the tax money. Somebody needs to advise the aliens on the other stars to tune up their GR transmitter and point it our way.
We need to enlarge this discussion and take a survey. Trojancowboy (talk) 00:50, 1 May 2009 (UTC)

You say that the strongest em radiation comes from antennas but the strongest gravitational radiation comes from binary stars - don't stars radiate em energy? Also you are clearly using the article to promote your own ideas and that's a recipe for trouble. Lucretius (talk) 02:34, 1 May 2009 (UTC)

The strongest radio wave radiation comes from antennas. The sun radiates about 50 megawatts per meter squared in the IR/visible light/UV but only microwatts or less per meter squared in the radio region. Megawatts per meter squared are radiated by antennas. Lasers are beyond the scope of the article. All of my contributions are readily cited in the literature.
Take a look at the orbital animation and improvements.Trojancowboy (talk) 02:52, 1 May 2009 (UTC)

## What if the Earth Was Electrically Bound to the Sun?

Your antenna analogy really makes no sense. There is no gravitational dipole radiation—the first term in the radiation from an antenna, the one that dominates in practice, isn't there at all in the gravitational case. If the Earth–Sun system were electromagnetically instead of gravitationally bound then the radiated power would be enormously larger, F v4 / 3 c3 ≈ 1014 W if I calculated correctly. Gravitational radiation is weaker because the gravitational field is not like the electromagnetic field. -- BenRG (talk) 12:56, 1 May 2009 (UTC)

BenRG is mistaken. Masses in an highly eccentric orbit have STRONG dipole radiation. It occurs in a pulse ONCE per revolution at the near point. PSR B1913+16 is a classic example but it is too far away to be spotted by any conceivable GR detector. The distance between the equal mass neutron stars vary from one solar radii to five and its period is about 8 hours. It has dipole, quadrapole, hexapole, octapole and 2*n higherpole radiation when its pulse is expanded by Fourier transform. A lightning strike also has these modes in the EM spectrum. Such highly eccentric orbits do not last very long on a cosmic time scale because they become circularized. They then only emit quadrapole radiation. They can last for millions of years however, which makes them rare.Trojancowboy (talk) 19:21, 1 May 2009 (UTC)

Be that as it may, I just calculated that the radiated energy from the Earth-Sun system would be around 1012 times larger if the system was electrically instead of gravitationally bound. I assume I wasn't mistaken about that? So the paragraph you wrote, which claims that gravitational radiation is like electromagnetic radiation but is weak because the radiating systems are typically small compared to the wavelength of the radiation, is awfully misleading, isn't it? The wavelength in this scenario is one light year in both the gravitational and electromagnetic cases; the ratio of the wavelength to the size of the system is the same in both cases. The factor of 1012 is due to a difference between vector and tensor field theories. It's due to gravitation being, in this situation, not like electromagnetism. Right? The Earth-Sun system is used as an example later in the article, so I think this matters.

Kindly inform us what charge you assigned to the sun and earth. Did you assume that each was a conductive sphere of their present radius? Did you consider the 333,000:1 difference in mass and the 1:4 difference in density? What formula did you use? It seems to me that you can ignore corona and arcing for the purposes of this calculation.Trojancowboy (talk) 15:44, 3 May 2009 (UTC)

MTW says outright that there is no gravitational dipole radiation of any sort (§36.1), and the reason they give makes sense to me (it follows from conservation of linear and angular momentum). I am, nevertheless, prepared to believe that there's some tricky way in which general relativity has something that can be called dipole radiation, but I'm going to have to see a source for that; I'm not going to take your word for it. Whether or not GTR has dipole radiation of some kind, you can't naively compare radiated power in electromagnetism and gravitation because their predictions do not agree. Obviously they are similar theories, but this isn't one of the ways in which they're similar. -- BenRG (talk) 22:37, 1 May 2009 (UTC)

I don't expect anybody to take my word for anything. I expect them to merely listen and then use their own eyes. Maxwell's equations are beyond my field of expertise but I think that the radiation from an earth electrically bound to the sun is exactly the same as when gravitationally bound, 200 Watts. Let us get an expert to confirm this. You fail to note that the dimension of the antenna is 500 light seconds, the time that it takes light from the sun to reach the earth. The wavelength of the radiation is 1/2 light year since it is quadrapole. (2 cycles per year) The antenna dimension is one part in 31,000 of the wavelength.
This problem is related to the ultraviolet catastrophe before Planck discovered his constant. This Wiki link is very poor for the history of it. The UV Castrophe resulted from the prediction that the electron of the hydrogen atom would inspiral in microseconds from EM radiation in the UV region. It hasn't happened yet because angular momentum is quantitized. BTW, the electron orbital speed is c/137, just like a solar mass star approaching a black hole. Its rotation frequency is in the ultraviolet frequency band. We are way beyond the quantum world here. The frequency here is 1/15,000,000 cycles per second. To my knowledge, the lowest frequency antenna ever built was at 72 cycles per second in Michigan for Navy submarine communications. It was hundreds of miles of underground wire driven with tens of megawatts and radiating a few watts (dipole).
This reference explains something about dipole GR calculations.Gravitational radiation back-reaction They are to be done anytime that the orbits are not perfectly circular. Hyperbolic passes generate a pulse of GR with an infinite number of poles. (harmonics if you will) It is like putting a square wave on a half wave antenna. It works perfectly well and radiates 1st, 3rd, 5th, etc harmonics. (directional patterns change with harmonic number) Eliptical orbits generate dipole radiation to various degrees and higher order 2n poles as well.
Circular orbits generate only quadrapole radiation at twice the revolution frequency. They are the limiting case of eliptical orbits. Parabolic orbits are the other limiting case of eliptical orbits. Hyperbolic orbits are likely a case by themselves. Flyby velocity of parabolic orbits is limited to the escape velocity at the limb. Flyby velocity of hyperbolic orbits is limited to the speed of light. They generate the most intense radiation.
If I did the calculation correctly, a sun grazing pass by an 100 mile diameter rocky comet would generate a strain pulse of ~10-25 smeared out over an hour. This is at least four orders of magnitude below the detection threshhold of LISA. It takes something the size of Mercury to be detectable under those conditions. LIGO would never see anything because its frequency response does not go down low enough.Trojancowboy (talk) 03:20, 2 May 2009 (UTC)
Here is a relevant paper, published 2007, according to which there is NO dipolar gravitational radiation in Einstein's theory: page 3904 (Pdf page 14) from 'Gravitational Waves' by Kostas Kokkotas in Acta Physica Polonica Vol 38, No.12 2007:[1]. It provides a very good overview of the whole subject and should be a reference point for editors of this Wiki article. Lucretius (talk) 02:46, 5 May 2009 (UTC)

## GR Believers and GR Deniers

It is also possible to assert that "there is no gravitational radiation." This is the case because the whole concept of the gravitational wave may be merely the result of the misleading use of analogy. Scientists assume that gravitation is like electromagnetism.Lestrade (talk) 15:25, 1 May 2009 (UTC)Lestrade

It is curious that Einstein initially believed in Gravitational Radiation and then decided in later life that it didn't exist. He is held up to be a saint. The moral of the story is that he didn't know what he was talking about in at least at one point in his life. This is a lesson to those in Ivory Towers. Perhaps Lestrade will explain the shrinkage of binary neutron star orbits for us.Trojancowboy (talk) 19:21, 1 May 2009 (UTC)
As noted above, in the "Other explanations" section, Clifford Will asserted that "Other conceivable causes of orbital period decrease: tidal energy dissipation, other forms of energy loss, changes of orbital period by acceleration due to a third body, etc., have also been studied." (C.M. Will, Theory and Experiment in Gravitational Physics, rev. ed. (Cambridge University Press, Cambridge, 1993)) Lestrade (talk) 19:31, 1 May 2009 (UTC)Lestrade
I would be honored to see your calculations on PSR B1913+16. GR accounts for the loss to about 6 decimal places. It seems to me that your causes would be lucky to get the right order of magnitude, let alone the first decimal place. If you can do it to 6 decimal places, you are assured of a Nobel prize.Trojancowboy (talk) 19:46, 1 May 2009 (UTC)

## Commons categories

Have I understood the distinction between Gravity wave and Gravitational wave correctly in my assigning of media to the Commons categories Commons:Category:Gravity waves and Commons:Category:Gravitational waves? Specifically, Gravity wave talks about hydrodynamic waves and fluids and I am unsure whether that also applies to the particle ripples seen in the rings of Saturn. I am also asking this at Talk:Gravity wave#Commons categories. 84user (talk) 12:51, 1 May 2009 (UTC)

You done good. It looks to me like all graphics in both areas are in the correct category. This page will likely be renamed "Gravitational radiation" to eliminate the confusion.Trojancowboy (talk) 15:45, 1 May 2009 (UTC)

## Enough of this

Trojancowboy, there is no future in the kind of edits you are making. Wikipedia is a co-operative venture but you seem to be flying about on a kind of automatic pilot. I thank you for correcting the formula I cut and pasted into the article but almost all your edits since then have been unhelpful and they will be undone by other editors - unco-operative edits do not survive the test of time in a venture like this. Lucretius (talk) 22:49, 1 May 2009 (UTC) Also please note comment by BenRG above. Lucretius (talk) 23:22, 1 May 2009 (UTC)

Trojancowboy, I'm going to revert your edits to the Introduction. Antennas are not the strongest source of em radiation except within a very limited set of criteria. Dipolar gravitational radiation is (at best) a highly uncharacteristic form of gravitational radiation. You don't introduce a subject by dwelling on highly unusual or specific cases. Lucretius (talk) 22:47, 2 May 2009 (UTC)

I've now re-edited the Introduction to meet the needs of an encyclopaedia article, which is to make itself understood by as many people as possible. I've looked at some other recent changes that are in desperate need of rephrasing, such as this gem from Power radiated by Orbiting Bodies (italics mine):

At this rate, it would take 3.12 x 1013 times more than the current age of the Universe for the Earth to fall into the Sun. Actually it would happen four times faster than this because the process would accelerate as the earth got closer to the sun. (Far worse things are predicted to happen long before then!)

We should never 'publish' drafts like that in such a key article as this. Lucretius (talk) 22:20, 3 May 2009 (UTC)

I've revised the section Effects of a passing gravitational wave as this was littered with debris from numerous past edits. Lucretius (talk) 05:29, 4 May 2009 (UTC)

I've revised the section Power radiated by Orbiting Bodies to remove some problems with its presentation. I've kept Trojancowboy's math except for his estimate of the time it takes for two neutron stars to spiral into each other - that can be presented in a later section although personally I think orbit duration lies outside the scope of the article. I've also rounded off some numbers. I love the animated graphics introduced by Trojancowboy and I'm sure contributions like that will help attract readers to Wiki. Lucretius (talk) 00:49, 5 May 2009 (UTC)

I requested a custom graphic from the author User:Zhatt yesterday but have received no reply. It would be for dissimilar mass objects in an elliptical orbit.Trojancowboy (talk) 02:55, 6 May 2009 (UTC)
The graphics author has been contacted and is trying to find time to do the needed orbits.Trojancowboy (talk) 18:35, 6 May 2009 (UTC)

## Astrophysics and gravitational waves

Under Astrophysics and gravitational waves User:Cesiumfrog has correctly flagged this following paragraph for clarification. It needs to be expanded and clarified by an expert.

"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.[6] At these high frequencies it is potentially possible that the sources may be “man made”[1] that is, gravitational waves generated and detected in the laboratory.[7][8]"

Trojancowboy (talk) 02:51, 6 May 2009 (UTC)

Regarding this disputed paragraph - it has been a source of dispute before. I tracked it as far back as May 11 2007 when it was restored by Ems57cva - he restored it on the grounds that it was mentioned in an article High-Frequency Gravitational Waves (an article however that now redirects to Gravitational Wave). The paragraph was deleted again by ScienceApologist, an editor very pro-active in stamping out bogus science (though sometimes he goes a bit too far in my opinion). The paragraph looks to me like a crazy combination of different sources that could be legitimate separately - it should be deleted on suspicion and the onus is then on the author to justify its inclusion. Lucretius (talk) 00:00, 7 May 2009 (UTC)

## High Frequency Gravitational Waves

You can view this deleted page at [High Frequency Gravitational Waves]. That deleted page is identical to [A Prospective on High-Frequency Gravitational Waves]. I don't know who copied who. This is my first exposure to plagarism. I am not qualified to evaluate what is bogus from what is real. However, the Chinese are working in this area and that at least should be studied.Trojancowboy (talk) 02:45, 7 May 2009 (UTC)

Yes this is interesting. It looks like the merger with this article was a deliberate attempt to squash the original article. The original article is well referenced and it's clearly based on the Pdf you've uncovered - unfortunately the author of the Pdf has listed no organizational affiliations and therefore his paper lacks authority. I guess that's why it was squashed. Lucretius (talk) 05:10, 7 May 2009 (UTC)

As you can see from [GravWave® LLC TEAM] , Robert Baker is no fool. It is clear that the page concerned is based on his paper which was not presented until September, 2007. It likely existed in a similar form before then. User:Cesiumfrog questioned the passage and may be related to User:Csblack who started the page concerned on 3 May, 2007. Over the following week it grew to its final length in about 20 edits. Csblack's last edit was 24 August, 2007. Cesiumfrog's first edit was on 26 May, 2008 and he is currently active.

I have read the paper from which the Wiki page was copied. It does not appear to be fringe physics. It contains this passage:

"A formulation of the quadrupole that is easily related to the orbital motion of binary stars or black holes, rotating rods, laboratory HFGW generation, etc. is based upon the jerk or shake of mass (time rate of change of acceleration) and is derived by Baker (2006) as P = (1.76x10^-52)*(2r*Df/Dt)^2 W (1) where P is the power of the GWs, r is the distance between two masses, m, Df is a change in force, N, over the time interval Dt, s, that is, the jerk or shake of the two masses, such as the change in centrifugal force with time as masses move around each other on a circular orbit. Please recognize, however, that Δf need NOT be a gravitational force (please see Einstein,1916; Infeld quoted by Weber 1964, p. 97; Grishchuk 1974)."

I did not bother putting the equation in nice form for this talk page. With great difficulty, I checked it out. With a factor of four error it becomes the equation for gravitational radiation power in this article. That equation is beyond dispute and is referenced in many places. It is likely that factor of 4 is my error, because of quadrapole versus dipole radiation. His version of the equation takes care of spinning bars, revolving dumbbells and other man made forms of radiation as well as astonomical sources. It takes quite an expert to derive that equation.

His formula for converting radiated gravitational wave power to strain is likely correct as well. This paper should be carefully studied. This is still no excuse for Csblack to copy the paper verbatim. I wonder how much more of this article is similarly plagarized. Deleting the page concerned was like throwing the baby out with the bathwater because it was crying. BTW, as a general rule, a Yahoo search for a single sentence will usually locate a document on the web. It would be nice for a volunteer to check this article for plagarism.

Baker no longer slops at the public trough and is heavily involved in patents on man made gravitational radiation. He has associated with the free energy crowd but that may be the way he gets money and publicity, see [Interviews ] . However Robert Bussard, of Blessed Memory, was interviewed by the same guy and he was not a nut. I have studied Bussard carefully.

You should keep in mind that 100 years ago, the learned professors told the Wright Brothers that powered flight was impossible. Two high school dropouts were better physicists and mathematicians than the former.

Yes I agree that the baby should not have been thrown out with the bathwater - mainstream science looks like any other POV when it is defended so ruthlessly. On the other hand, innovative science doesn't need help from Wikipedia and it looks as if Baker and others can manage well enough without free publicity here. If their ideas have any value, they'll be back later. Lucretius (talk) 21:59, 7 May 2009 (UTC)

## Confusion on Rotating Bodies

Now a different matter - your latest edit to Introduction merely repeats an error that I removed. Gravitational waves are not always generated by accelerated masses - a spinning sphere or disc has orbital acceleration but it doesn't necessarily generate waves. You should revert to my previous edit - that a disturbance in spacetime is generated when things move in a certain way. The rest of the article demonstrates what this means. Lucretius (talk) 00:00, 7 May 2009 (UTC)

This is a valid point and has been fixed.Trojancowboy (talk) 02:13, 7 May 2009 (UTC)

Sorry but you haven't fixed it. I quote from your edit (italics mine):

Objects which are accelerated by other objects generate a disturbance in spacetime which spreads like ripples on the surface of a pond.

In fact the surface of a sphere is made of point-like objects that don't radiate even though they are accelerated. So how is the latest edit an improvement?

You need to understand also that a paragraph is like a cobweb - cutting one thread dislocates many others. Edits to a paragraph cut through a 'semantic web' and they can cause the paragraph to lose coherence. You might as well scrap my edit of Introduction and start again. My edit was aimed at a wide audience; your use of concepts such as 'acceleration' and mechanical 'strain' are aimed at a more technically capable audience. Our combined edits result in a paragraph that doesn't really know where it is going. You should either revert to my edit or rewrite the Introduction from the ground up. Lucretius (talk) 04:37, 7 May 2009 (UTC)

I've now rewritten the Introduction again. Hopefully that will be the last edit of the section for some time.Lucretius (talk) 01:42, 8 May 2009 (UTC)
The redo is good. BTW, four objects of equal mass revolving around their center of mass do NOT radiate gravitational waves. Each opposing pair radiates out of phase waves which cancel. This is not true for an odd number of objects. Such orbits are eventually unstable and degenerate, which makes them of theoretical interest only. This is why a spinning sphere does not emit gravitational radiation.Trojancowboy (talk) 01:13, 8 May 2009 (UTC)

That's a fascinating bit of info and you should add it to Sources of gravitational radiation as part of the list of objects that do/don't radiate - preferably with a reference. Lucretius (talk) 02:24, 8 May 2009 (UTC)

That is a rainy day project with another dozen just like it. Fires need to be put out first.Trojancowboy (talk) 14:37, 8 May 2009 (UTC)

## Plagiarism

There is massive copying to or from h ttp://encyclopedia.stateuniversity.com/pages/9072/gravitational-radiation.html Introduction, The effects of a passing gravitational wave, Sources of gravitational waves, Gravitational wave detectors. There is no attribution either way. The culprit needs to be found. This is a Wiki blacklisted hyperlink, whatever that means. You will have to patch the URL back together to view it.Trojancowboy (talk) 01:14, 8 May 2009 (UTC)

On further research about half of this article is copied verbatum from the Cambridge Enclopedia Volume 31, see h ttp://encyclopedia.stateuniversity.com/collection/31/Cambridge-Encyclopedia.html . Patch this URL back together to view the page. This was done to avoid the Wikipedia Spam blacklist. Who knows what to do now? This part of the article is obcure and hard to understand anyway and should be rewritten.Trojancowboy (talk) 14:34, 8 May 2009 (UTC)

That site copied its article from here. Lucretius (talk) 22:11, 8 May 2009 (UTC)
I was barking up the wrong tree. This is a scam on-line university degree site. Their WhoIs is masked by Go Daddy and they should be shut down. As you can see at h ttp://encyclopedia.stateuniversity.com/pages/9073/gravitational-redshift.html , they have copied the page gravitational redshift as well. Their html is incompetent with first letter overwrite and all equations are missing. My guess is that they are required to credit Wikipedia. Most likely the Cambridge Encyclopedia can go after them as well. I am going to report it but this may already be known. Previously GoDaddy instantly shut down a website that I reported for another unrelated matter. Trojancowboy (talk) 22:55, 8 May 2009 (UTC)

## Total Orbital Energy and Orbit Lifetime

I'm wondering about some of the recent edits. For example: However, the total energy of the Earth orbiting the Sun (kinetic energy plus gravitational potential energy) is about 1.14 x 1036 joules. I assume that you added Gravitational potential rather than Gravitational potential energy. Or did you mean something else by 'total energy'? I'm also not convinced that orbit duration should be part of this article. Lucretius (talk) 22:34, 8 May 2009 (UTC)

Gravitational potential energy is the energy released if the earth were to fall to the surface of the sun. Kinetic energy is the energy in the earth's orbital motion relative to the sun. The later energy is about 1/400 as much. Orbit lifetime is essential to understand the problems with detection. Lifetime of the earth's orbit is of academic interest only. The remark "far worse things are predicted to happen long before then!" was not my doing. It sounds a bit corny to me but User:Lestrade must be kept happy.
Binary star orbit lifetime is the bread and butter of gravitational radiation detectors. Inspiral cannot be understood without it. This confusion will be fixed soon. I spent a lot of time on the plagarism issue which interfered with finishing this part. Trojancowboy (talk) 23:12, 8 May 2009 (UTC)

Gravitational potential energy is a negative value and I don't think you can derive radiated energy from it. As for "far worse things" - I like that bit and that's why I keep sticking it back in. Lucretius (talk) 00:05, 9 May 2009 (UTC)

Gravitational potential energy is a positive with respect to the surface of the sun. You have to have a velocity of about c/500 at the surface of the sun to reach the earth's orbit. The sum of both it and the orbital energy is the amount of energy which has to be lost to gravitational radiation to bring the earth's orbit to the surface of the sun. This occurs during the inspiral time. Keep in mind that the section concerned is not finished.Trojancowboy (talk) 00:45, 9 May 2009 (UTC)

I keep wondering where the radiated energy comes from and I know you can't say it comes from potential energy. The argument about swapping signs at the surface of the sun is mathematically convenient I guess but the fact remains that gravitational potential energy is negative and it can't be a source of radiated energy. So I'm still wondering where this total energy comes from. Lucretius (talk) 02:05, 9 May 2009 (UTC)

When you coast down a hill on your bicycle, your brake gets hot. That is gravitational potential energy being turned into heat. The energy dissipated in the brake in Joules is (bike {plus rider) mass in kilograms*9.81 Newtons) * hill height in meters. This is force times distance. Gravitational potential energy is turned into gravitational radiation as the orbit shrinks. Orbital energy actually increases as the orbit shrinks and the earth speeds up. For an orbit just over the sun's surface, GPE is 0 and orbital energy is maximum. Orbital speed there is about c/700. Half the original total of orbital energy of the earth is present in the sun grazing orbit. The other half has been lost to GR. This is a dangerous experiment to perform because of the 5500 Kelvin surface temperature. See Specific orbital energy. BTW, mu there is confusing, it should be changed to "G*m".Trojancowboy (talk) 02:47, 9 May 2009 (UTC)

As far as I know the heat in the brakes is kinetic energy. The kinetic energy doesn't come from gravitational potential energy but from the effects on the bike of the gravitational field. When you talk about total energy I think it should be made clear that you mean the total energy radiated by the Earth when it spirals into the Sun - this would remove any issues about the origin of the radiated energy, which is a thorny topic. Lucretius (talk) 05:45, 9 May 2009 (UTC)

When you ride up a hill, the energy that you produce is stored in the earth's gravitational field. When you come down, that same energy is given up by the field in the form of heat in your brakes. If you don't use the brakes, it is stored in your velocity and instantly released in heat when you wipe out at the bottom. There is even a tiny amount of gravitational radiation then.
A tiny object orbiting a large object at 1.5 radii from the latter's center has equal amounts of kinetic and gravitational potential energy. In the case of the sun, the orbital velocity 0.5 radii above its surface is c/840 and each energy is 64*109 Joules/kg. This is amount of energy in the orbital velocity or the amount of energy released if the object were to be dropped from the orbit to the surface. Gasoline has only about 1/1200 of this energy density. Such velocities can only be reached by solar sail. Present day nuclear rockets will not work.Trojancowboy (talk) 01:12, 10 May 2009 (UTC)
I am utterly fascinated with Lucretius's statement "Gravitational potential energy is a negative value." It seems to me that the article would be greatly improved if there was an amplification of this statement.Lestrade (talk) 13:13, 12 May 2009 (UTC)Lestrade

## Mass of Gravitational Fields

The Earth's gravitational field is not affected by other bodies in it - that's why all objects fall at the same speed within the Earth's gravitational field. Hence it makes no sense to talk about other bodies storing their energy in the Earth's field. Gravitational potential energy isn't physical material and therefore physical waves can't be derived from it. The issue isn't easy and it's best to avoid it in the article - total energy should be understood as total energy radiated during the inspiral and not as an energy-reserve located somewhere - because it's so hard to know exactly where it is located. Lucretius (talk) 03:31, 10 May 2009 (UTC)

The earth doesn't have a gravitational field, there's just one gravitational field shared by all matter. Gravitational potential energy is stored in the gravitational field. I don't understand what you mean by "Gravitational potential energy isn't physical material and therefore physical waves can't be derived from it." Waves are no more physical than potential energy as far as I can see. They're just different configurations of the field. -- BenRG (talk) 22:21, 11 May 2009 (UTC)
The earth's gravitational field contains the Gravitational binding energy which is 2.26Template:E Joules. Just like an electric field or a photon, it has mass by the e=mc^2 relation. The gravitational field mass is 2.5Template:E kg which is the mass of a cube of water 13.5 km on a side. Most of this mass is in the space within a few radii above the earth's surface.
This is negligible with respect to the earth's mass but not quite so in the case of the sun. There it is ~ 1 part in 1.2 million of the sun's mass. In the case of a neutron star, the mass of its gravitational field is 1/11 of its mass. (mass=sun, radius=10 km)Trojancowboy (talk) 23:55, 11 May 2009 (UTC)
The Earth's gravitational field is not affected by other bodies in it - that's why all objects fall at the same speed within the Earth's gravitational field. The field is affected by other bodies in it. It works by simple vector addition. Hence it makes no sense to talk about other bodies storing their energy in the Earth's field. No, this is incorrect. In Newtonian gravity, the gravitational field carries a a negative energy density proportional to the square of the field. Gravitational potential energy isn't physical material and therefore physical waves can't be derived from it. Not sure what you're getting at here. Of course energy is never physical material. The issue isn't easy and it's best to avoid it in the article - total energy should be understood as total energy radiated during the inspiral and not as an energy-reserve located somewhere - because it's so hard to know exactly where it is located. In general, it's hard to know exactly where energy is located. That's a general fact about energy. Anyway, none of your comments here have anything to do with relativity, and they don't show competence with nonrelativistic physics.--76.167.77.165 (talk) 03:10, 20 October 2009 (UTC)

Kinetic energy is the energy of movement and it can be readily converted into a wave. Gravitational potential energy is the energy of position and its conversion into waves is not a direct or self-evident physical process - it requires the intervention of a force. There are some theories that identify gravitational potential energy with dark energy but that's mere speculation. Otherwise, gravitational potential energy is simply a useful idea. My point is simply this - if 'total energy' is the total energy radiated by the Earth's inspiral, why do we need to source the energy in potential energy or even kinetic energy? However, I'm glad that you are keeping a watch over this article, BenRG, and I concede that you are better qualified to do that than I am Lucretius (talk) 01:08, 12 May 2009 (UTC)

Dark energy is irrelevent here. I have read speculation that it is simply a huge number of undetected solar mass black holes. You should study Gravitational binding energy. Half the mass of the electron is the mass of its electric field. See Classical electron radius, although this article has its limits.Trojancowboy (talk) 02:00, 12 May 2009 (UTC)
The distinction between kinetic energy and potential energy is a valid one in nonrelativistic Newtonian physics. It ceases to be a clear distinction in classical electromagnetism. It is not a useful distinction in general relativity. Lucretius, you're out of your depth here.--76.167.77.165 (talk) 03:12, 20 October 2009 (UTC)

Gravitational binding energy is energy stored rather than energy expended and this begins to make more sense. However the physical process by which this energy is released in waves is surely an aspect of quantum gravity and I think this also is murky territory. I return yet again to the only point I have been trying to make all this time - if 'total energy' is the total energy radiated by the Earth's inspiral, why do we need to source the energy in potential energy or kinetic energy or even binding energy? The energy source is just too problematic. My point about dark energy was illustrative. Lucretius (talk) 02:17, 12 May 2009 (UTC)

You make a good point that I will clarify in the article. Energy from the gravitational field is split into two parts. Half is radiated in gravitational waves. The other half goes into kinetic energy of the orbiting bodies. This is exactly the extra speed needed for them to orbit at the reduced radius.Trojancowboy (talk) 02:22, 12 May 2009 (UTC)

Don't forget to supply your references. I think you are going to have trouble deriving the energy of the gravitational waves from the binding energy of the Sun-Earth system. I think angular momentum offers a better understanding of sources - the angular momentum carried off by the waves comes from the angular momentum of the Earth's orbit around the sun and this diminishes along with the orbit. Whereas all this talk of radiated energy introduces a really difficult question - which energy reserve is being depleted? Lucretius (talk) 03:53, 12 May 2009 (UTC)

This energy comes from the reduction of the energy in the earth's gravitational field. The energy lost by the gravitational field of the sun is much less, 1 part in 333,000. Half of this energy goes into increasing the earth's orbital speed, and the other half is radiated in the form of gravity waves. They carry away exactly the same amount of angular momentum as is lost by the earth when its orbit decays. This will be made clear in the article when time permits.Trojancowboy (talk) 15:48, 13 May 2009 (UTC)

If Earth's kinetic energy is half of the radiated field energy then that field energy must be the negative of negative gravitational potential energy. That suggests that the radiated energy is gravitational binding energy but, according to my reading of that article, the Earth's binding energy has nothing to do with the Sun (except for increases in Earth's mass due to thermal energy and orbital speed). My doubts will be silenced when you provide a credible reference, clearly sourcing gravitational radiation in the energy of the field. Also, I'm wondering if the ratio of power to kinetic energy 2:1 is a bit like a ratio of oranges to lemons - they are clearly very different things. In fact the ratio of rs adiated energy/kinetic energy suggests that orbits are quantized, same as electron orbits, which is getting into quantum gravity research, it seems to me. The article is supposed to report established theory not venture into speculation. I really appreciate your willingness to discuss issues and this should lead to a better article. Lucretius (talk) 01:33, 14 May 2009 (UTC)

Your statement is not correct. The INCREASE in the energy of the earth's orbital motion (kinetic energy) is EQUAL to the amount of gravitation radiation emitted. The DECREASE in gravitation potential energy of the earth is TWICE that of either of the two. You were pointed to several wiki articles on elementary celestial mechanics. This is covered in the later part of first year college astronomy.Trojancowboy (talk) 16:50, 14 May 2009 (UTC)

I was merely rephrasing your argument - kinetic energy and radiated gravitational energy are equal and they both come from the field energy. Thus the ratio of this field energy to kinetic energy is 2:1. I called this field energy 'radiated field energy' to distinguish it from the field energy that is still stored and available for use. I made the point that this 'radiated field energy' must be gravitational binding energy that has been released (i.e. the negative of gravitational potential energy). I'm a complete amateur in these things and I've never tried to hide that but the problem here is not my ignorance. The problem is the lack of literature on the sourcing of gravitational waves - otherwise you would have quoted it by now surely. You need to find a reputable author who sources gravitational waves. Otherwise the article should avoid the issue. Here is a link to a site that discusses the difficulty of locating energy within a gravitational system [2]. Lucretius (talk) 01:22, 15 May 2009 (UTC)

Lucretius, Trojancowboy is correct on this point, in the semiclassical limit where it makes sense to distinguish between kinetic and gravitational energy.--76.167.77.165 (talk) 03:18, 20 October 2009 (UTC)

There seems to be a lot of confusion here about the distinction between kinetic energy and potential energy. There is no useful distinction of this kind to be made in general relativity. There's a good discussion of this, at a fairly elementary level, in ch. 3 of Taylor and Wheeler, Exploring Black Holes. In general, the equivalence principle implies that there can be no well-defined local energy density in general relativity; see any good discussion of linearized gravity for this, e.g., Rindler or Carroll.--76.167.77.165 (talk) 03:16, 20 October 2009 (UTC)

## Archiving Time

This page is over two years long and overdue for archiving. Most of it is of historical interest only. Who can do this?Trojancowboy (talk) 01:16, 10 May 2009 (UTC)

I agree that the page is too long and most of it should be archived. Lucretius (talk) 03:34, 10 May 2009 (UTC)

I archived oldest discussions.Trojancowboy (talk) 02:26, 11 May 2009 (UTC)

## Existence of Gravitational Waves

Regarding Trojancowboy's remark that "User Lestrade must be kept happy," I must comment that User Lestrade will be happy if the article on Gravitational wave communicates the truth, not certain people's wishes and hopes. We might wish that there are gravitational waves and we might hope that they will be discovered. It is permissible, however, to state that there is a difference between what exists and what we hope exists, regardless of contemporary consensus. If we are going to assume that Einstein's equations have proved with final certainty that gravitational waves exist in the experienced world, regardless of the failure to detect them directly, then we should be able to provide definite public readable support for that assumption. A citation or two would be appreciated.Lestrade (talk) 18:47, 11 May 2009 (UTC)

I am sorry about the false attribution of that remark to you. You make a perfectly valid point. Gravitational waves have NOT been proved to exist because no receiver has ever detected them. On the other hand, LIGO can detect them only with a dose of good luck. It is not sensitive enough in the required frequency range. There is a perfectly understandable reason that gravitational radiation has not been detected. If LISA fails to find it, evidence will be strong that it does not exist. Pulsar measurements agree with the predictions of Gravitational Radiation equations precisely.
I have no quarrel with either the Gravity Wave Deniers or the Gravity Wave Believers. I like the theory that an angel is retarding the orbit of PSR 1913+16. This theory is perfectly consistant with observation and the mathematics is much simpler. How that angel keeps such good time has not been explained to me. Presumedly, an angel is assigned to each pulsar binary system. Let the observations settle the manner. It is worth noting that the Ether Deniers like Einstein won out over the Ether Believers. It could happen in gravitational radiation.Trojancowboy (talk) 19:22, 11 May 2009 (UTC)

The Ether Deniers have not won. The Ether Believers won when they baptized their poor Ether as a reborn Spacetime Continuum and had it behave in public as though it is a Vector field Plenum.Lestrade (talk) 13:27, 12 May 2009 (UTC)Lestrade

Professor Clifford Will of Washington University was serious enough about this topic to list "[o]ther conceivable causes of orbital period decrease: tidal energy dissipation, other forms of energy loss, changes of orbital period by acceleration due to a third body, etc." in his Theory and Experiment in Gravitational Physics, published by Cambridge University Press in 1993. We are the poorer for his having written "etc." instead of listing even more possible causes of binary pulsar orbital decay. His writing was not facetious and gravitational wave is not a facetious topic. It may be taken seriously by anyone who is interested in gravitation and who is not disposed to eagerly accept the explanations that are current and popular.Lestrade (talk) 16:53, 12 May 2009 (UTC)Lestrade

Just like I said, eccentric orbits generate DIPOLE radiation, see [Proposed Supermassive Blackhole System in 3C66B] . This paper is a good background for this article.

Therefore, hyperbolic passes generate a one time pulse of GR, similar to the impulse function in electronics. Highly eccentric orbits generate a burst of GR at their periapsis and nearly nothing at their apoapsis. Eccentric orbits have an infinite number of harmonics starting at the frequency of rotation of the orbit. Trojancowboy (talk) 19:59, 13 May 2009 (UTC)

Trojancowboy, I think you're mistaken here. You can't have gravitational dipole radiation, basically because gravitational dipoles don't exist. The quote doesn't say anything about dipole radiation.--76.167.77.165 (talk) 03:21, 20 October 2009 (UTC)

## Does Gravtitional Radiation Convey Linear Momemtum?

User:Decora has correctly flagged this statement as dubious:

. See the reference in the text for the dubious flag. My guess is that this is impossible unless GR is directional. Antenna arrays or searchlights indeed do carry off linear momentum but there are no reflectors for GR or unsymmetrical directional patterns of radiation.

This section requires the attention of an expert. Who took down the expert needed flag? Perhaps the real problem is that we have too many experts who do not know their limitations.Trojancowboy (talk) 16:05, 14 May 2009 (UTC)

There is a published document here Gravitational Recoil Velocities supporting the thesis that gravitational waves carry off linear momentum. Regarding your calculation of the total energy of the Sun-Earth system and your knowledge about which kinds of energy are turned into gravitational waves, you might want to read this Physics Forums. Regarding your comment about too many experts - I agree. Lucretius (talk) 05:41, 15 May 2009 (UTC)

The Physics Forum was of little value. Conversation there boils down to how many angels can fit on the head of a pin. The Gravitational Recoil was dynamite however. It must be digested and written up for the article.

I had heard of black hole mergers supposedly generating enough recoil to eject one of the stars from the galaxy. It turns out that this is from DIRECTIONAL gravitational radiation. Large black holes with a mass ratio of 3 to 1 can cause the merged black hole to be ejected from the galaxy at 0.1% of the speed of light. This directional GR occurs at the moment of merger. If the holes are of equal mass, no directional GR is produced. If one is much greater than the other, directional GR is produced at the moment of merger but recoil is negligible.

The paper didn't say so but it appears to me that the source of the directional GR is due to the larger black hole absorbing most of the GR. Most of the GR going toward the smaller black hole flies on by it and escapes into space. As a result, the big black hole experiences directional thrust from absorbing the GR as the smaller black hole is merging with it.

See the link below debunking detection of High Frequency GR. If I crunched the numbers correctly, a neutron star will REFLECT GR in the neighborhood of 1,000 cycles per second and below. Black holes absorb it totally and generate only half the recoil as a neutron star would for the same GR power. In other words, gravity wave radars would only be able to see neutron stars. Black holes only absorb GR and anything less dense than a neutron star is transparent to it. There will be more on this topic later. That expert has his work cut out for him.Trojancowboy (talk) 00:12, 17 May 2009 (UTC)

I have repeatedly given you the links to Wiki articles which explain elementary orbital mechanics. This stuff is 325 years old. The source of orbital decay is not my theory, it is simply plugging in numbers to first year astronomy orbital equations. There are hundreds of papers written by fools, in fact, the vast majority.

Dipole radiation is well established by those who understand GR. It occurs ONLY in eccentric or hyperbolic orbits. User:Lestrade's buddy Clifford Will has a book with a chapter on it, see http://www.amazon.com/gp/product/0521439736/ref=sip_pdp_dp_0 . BTW, Will is a GR Believer not a GR Denier. This is contrary to what his champion would have us believe. It is likely that dipole is the dominant radiation over quadrapole and hexapole.

No combination of 2nd and 4th harmonics can create a waveform which repeats once per orbit. Eccentric orbits generate odd harmonics as well as even ones. Circular orbits generate only even harmonics.Trojancowboy (talk) 02:20, 17 May 2009 (UTC)

Unfortunately statements like There are hundreds of papers written by fools, in fact, the vast majority and Dipole radiation is well established by those who understand GR are the reason why I don't want to work with you. I don't make substantive edits to a highly technical article like this but I can and do make changes in presentation that can be very helpful in establishing an article. But I won't help establish the edits of somebody as challenging as you are. Lucretius (talk) 03:24, 17 May 2009 (UTC)

The question of whether gravitational waves carry momentum (they do) has nothing to do with the question of whether gravitational dipole radiation exists (it doesn't). Re the momentum, see Rindler, Relativity: Special, General, and Cosmological, Oxford, 2001, pp. 333-334. Re the nonexistence of dipole radiation, see p. 332 of the same book.--76.167.77.165 (talk) 03:28, 20 October 2009 (UTC)

## High Frequency GR and Fringe Science

I have previously mentioned [A Prospective on High-Frequency Gravitational Waves] by Robert Baker which I have had a little time to study. Baker knows the basics and derived several interesting verstions of different equations which I have confirmed to be both usefull and correct. He then goes into a far fetched proposal about a fractal membrane and other pie in the sky concepts. This quote is extracted from that paper in our article:

Baker has been trying to get Federal funding for detection of HFGR for eventual use as a see thru the earth radar, submarine communications, time transmissions, and directed weapons. The federal government commissioned the following study of the National Security implications of this technology at [High Frequency Gravitational Waves]. It seems to debunk the theory that such waves can be detected in the laboratory or used for any practical purpose. It is claimed there that many of Baker's calculations are off by MANY orders of magnitude.

We need to tread very carefully here to avoid making Wikipedia a laughing stock. I have seen many Wikipedia articles without references which were quite sound and many others full of references which were bogus. The ultimate is an expert editor with good references.Trojancowboy (talk) 23:58, 15 May 2009 (UTC)

Długosz (talk) 22:46, 5 February 2010 (UTC)

## Animated image improvement

This is regarding the animated images with the black backgrounds: As I age, it is getting harder for me to see small or narrow red foreground objects against a black background. I can see the cross marking the center in the diagrams, but not the circles representing the orbits. Can someone change these images to improve the contrast? Maybe a lighter shade of red, or thicker lines marking the circles? (Also, consider SVG format.) Thanks. 206.53.193.156 (talk) SlowJog (talk) 16:30, 21 May 2009 (UTC)

Does anyone know whether it is possible to do movies with SVG? P0M (talk) 08:23, 22 May 2009 (UTC)
It is possible to do animations with SVG. 206.53.196.126 SlowJog (talk) 23:51, 22 May 2009 (UTC)

User:SlowJog is absolutely correct and it is not because his eyes are getting tired. I have contacted the original author of these graphics to rectify these and other problems. According to Scalable Vector Graphics, SVG files can be animated but Internet Explorer will not work with SVG. This would make them essentially useless on the web. As far as I know, only gif files are practical for animation on the web. Trojancowboy (talk) 02:14, 27 May 2009 (UTC)

The way Wikipedia works, users do not see the actual SVG image. The system apparently generates png images on the fly, show them on the screen for the user, and then, I guess, it saves only the SVG.
That may be on account of the viewers who use Internet Explorer. My browser shows SVG just fine.
For the time being, the best solution would probably be to just fix the GIF animation. P0M (talk) 20:21, 27 May 2009 (UTC)
Then, I agree. I wasn't aware of the Internet Explorer limitation. SlowJog (talk) 23:15, 5 June 2009 (UTC)

I believe the animation does not show a pure quadrupole oscillation, otherwise the masses that are rotated 45° from the polarisation directions would not be moved. (See www.gravity.uwa.edu.au/docs/review.pdf page 6) Perhaps a superposition of both polarizations? HolyMole23 (talk) 19:18, 15 June 2009 (UTC)

## Orbital Drag from Gravitational Radiation

The formula for gravitational radiation power radiated by objects in binary circular orbits in terms of the distance between them can be reworked in terms of their velocity. If v is the sum of their velocities relative to their center of mass, the power is:

${\displaystyle {\frac {dE}{dt}}=-{\frac {32}{5c^{5}G}}{\frac {(m_{1}m_{2})^{2}}{(m_{1}+m_{4})^{4}}}\ v^{10}}$ .

The earth's velocity relative to the sun is 3Template:E m/s which gives the standard 200 Watts of GR power. The drag produced by this GR is 6.6Template:E Newtons which corresponds to about 1/6 of the weight of a sheet of printer paper. By comparision, the solar radiation pressure is 5.67Template:E Newtons, or the weight of a cube of water 38.6 meters on a side. This assumes complete absorption of the 1337 Watts per square meter of the earth's cross section.

For an opposite extreme, take a pair of solar mass white dwarfs orbiting with a total velocity of 1.18Template:E m/s (1,000 second orbital period). Their total drag is 1.09Template:E N or the weight of a cube of water 1,037 kilometers on a side.

Are such trivia useful for the article? Trojancowboy (talk) 22:48, 27 May 2009 (UTC)

## Polarization mode

If a gravitational wave is a ripple in spacetime, is it both transverse and longitudinal, as are all other ripples? General Relativity predicts only transverse gravitational waves. If a gravitational wave has a longitudinal component, then General Relativity is wrong.Lestrade (talk) 15:27, 30 May 2009 (UTC)Lestrade

I think you're taking the ripple analogy a little too far there. 98.207.130.36 (talk) 22:25, 28 August 2010 (UTC)

## Non-undulational gravitation

Gravitation does not necessarily propagate in waves. Waves only occur if one mass oscillates or rotates in relation to another mass. As a result of the movement, the distance between the masses alternately increases and decreases. As a result, the gravitation between the masses periodically varies. If neither mass is in motion relative to the other, the gravitation between them is steady and constant, not wavelike. The article might give the impression that gravitation waves are the only form of gravitation, so I will attempt to include this information in the article.Lestrade (talk) 14:33, 31 May 2009 (UTC)Lestrade

## Making waves

I can create gravitational waves by moving one mass forward and backward in relation to another mass. Isn't this true?Lestrade (talk) 13:22, 16 June 2009 (UTC)Lestrade

## Reflection, refraction, diffraction

Three of the basic properties of waves, yet the article does not mention one. If gravitational waves differ fundamentally from other waves that is of interest and should be dealt with in the article. Harrylentil (talk) 09:23, 24 August 2009 (UTC)Harrylentil

If I am understanding correctly, gravitational radiation has a spin of 2 while electromagnetic radiation has a spin of 1. Can gravitational radiation decay into two electromagnetic waves making it even harder to detect gravity waves?

Reddwarf2956 (talk) 16:27, 2 September 2009 (UTC)

## Astrophysics and gravitational waves

Could anyone answer for me the following question: Can gravitational wave pass through a black hole? Thanks! —Preceding unsigned comment added by Earthandmoon (talkcontribs) 10:55, 15 October 2009 (UTC)

A black hole will absorb all radiation including gravitational. When it absorbs a gravitational wave, it vibrates like a bowl of jelly. Eventually it quiets down. This vibration cannot be seen outside the event horizon.

Trojancowboy (talk) 00:28, 9 January 2010 (UTC)

## Possibly mistake

There is an equation in the article

     ${\displaystyle \int \,\tau ^{ij}(t-r,{\vec {x}}')\,d^{3}x'=\int \,x'^{i}x'^{j}\nabla _{k}\nabla _{l}\tau ^{kl}(t-r,{\vec {x}}')\,d^{3}x'\ ,}$



Shouldn't be:

    ${\displaystyle \int \,\tau ^{ij}(t-r,{\vec {x}}')\,d^{3}x'=(1/2)\int \,x'^{i}x'^{j}\nabla _{k}\nabla _{l}\tau ^{kl}(t-r,{\vec {x}}')\,d^{3}x'\ ,}$


? —Preceding unsigned comment added by 188.33.187.104 (talk) 02:13, 16 December 2009 (UTC)

## Variable Gravitational Field not the same as Waves

An important distinction that I find nowhere in this article thus far is this:

   the distiction between a gravitational wave and a time-varying gravitational field.


That, in turn, begs the question of how, under ideal circumstances, one might detect and measure one and the other.

If I'm standing on the Earth's surface, with the Sun and Moon under my feet, I will feel slightly heavier than if the Sun and Moon are overhead: a difference in the strength of the net gravitational field upon a test mass can be measured as a difference in force. If, on the other hand, one is confined to a closed capsule in space, and a massive object sweeps by, the increasing gravitational field translates into an acceleration that cannot be perceived from inside the capsule (Einsteins' Equivalence Principle) except if the gravitational field has a spatial gradient strong enough to cause tidal forces inside the capsule. Such tidal forces are what keeps Jupiter's moon Io volcanically active [4] as it experiences a time-varying gravitational field from Jupiter and the other major moons.

It therefore behooves us to explain on what basis one would believe or assume that gravitational waves can stretch and compress a heavenly body without performing work (and, therefore, being absorbed and turned into heat).

Under Does Gravitational Radiation Convey Linear Momentum? Trojancowboy claims:

   If I crunched the numbers correctly, a neutron star will REFLECT GR in the neighborhood of 1,000 cycles per second and below.
...
Black holes only absorb GR and anything less dense than a neutron star is transparent to it.


Fjados (talk) 20:55, 22 December 2009 (UTC)

## Gertsenshtein Effect

I can't find any information on the Gertsenshtein Effect on Wikipedia, and Google returns mostly copies of the above-mentioned HFGW topic and its debunkers. No where do I find a discussion of how this effect works.
Długosz (talk) 23:01, 5 February 2010 (UTC)

## Explanation in addition to discussion

How do the particles start oscillating when the gravitational wave passes? Do they ride the wave? Second I keep reading about tides induced by gravity; how does that result in pulling things closer together? I have a feeling that these sound like really dumb questions, but asserting something doesn't explain how it works. Many thanks for the help. 4.249.63.136 (talk) 21:45, 26 May 2011 (UTC)

"Sources this intense are not expected to last long so is merely a matter of luck" changed to- "Sources this intense are not expected to last long so it is merely a matter of luck" Pawprintoz (talk) 00:25, 2 February 2012 (UTC)

## Corrections

The article says: "in the Newtonian theory of gravitation physical interactions propagate at infinite speed." Someone could try to find a source for this claim. I don't know if Newton believed in infinite speed, but I'm sceptical about that. Also, it should be mentioned clearly in the lead that not gravitational waves nor gravitational radiation have been observed (proven) and that they are just something a widely accepted but unproven "theory" predicts. --Hartz (talk) 00:50, 6 November 2012 (UTC)

To your first point: Newton believed that gravity was an action at a distance, that acted instantaneously. So, yes Newton thought that gravitational interactions propagated at an infinite speed. (Or maybe more accurately, he did not believe that there was anything that needed to propagate, it just was.)
To your second point, this mentioned very clearly in the lede.TR 06:18, 6 November 2012 (UTC)
You assume that gravitional interaction is something that travels (like a particle or wave). Einstein thinks that gravitation would be waves. What if Newton was right (although he had no way to be sure): that gravitional interaction is not something that travels, it just is. Gravitational waves have not been observed and we cannot measure gravity as it is too weak a force to measure. --Hartz (talk) 08:29, 6 November 2012 (UTC)
I assume nothing. Something travelling at infinite speed is equivalent with it "just being", i.e. it being everywhere at the same time. The gist of the statement is that changes are felt instantaneously by distant observers (according to Newtonian gravity).TR 08:51, 6 November 2012 (UTC)
Gravity too weak to measure? You are kidding right? A force of 9.81 N per kg is fairly easy to measure.
As for gravitational waves not having been observed. Not directly, however the indirect evidence from binary pulsars is very strong. (Direct observation is likely to happen in the next 5 years (if gravitational waves exist).TR 08:51, 6 November 2012 (UTC)
The article reflects a certain assumption, but of course Einstein had his assumptions (everything is ok if we say that this is what Einstein thought). Please see gravitational constant and "the gravitational force is extremely weak compared with other fundamental forces" in that article. --Hartz (talk) 09:10, 6 November 2012 (UTC)
Regarding "gravity isn't weak", consider this, with just a battery, a length of coiled wire and a nail you can easily pull metal things away from the whole planet Earth's gravity even from as close as the Earth surface itself. And gravitational waves are much weaker than that since not only the source is literally lightyears away but amplitude of the wave itself at these distances is just about negligible. If gravitational waves are real, we are bobbing on a sea of them all the time and feel nothing. --TiagoTiago (talk) 18:00, 24 November 2012 (UTC)
Read again. I never said gravity wasn't weak. I just laughed at the notion that gravity is "too weak to measure". (Eventhough the coupling constant is very small, this is hugely compensated by the fact that there is just one type of gravitation charge (attractive) leading to very noticeble gravitational fields for large masses.)TR 07:12, 26 November 2012 (UTC)

## Don't we need two alternating fields for a wave?

At least for EM waves there are two fields... 108.200.53.58 (talk) 05:27, 9 November 2012 (UTC)

The answer is no. It is perfectly possible to have a wave in a scalar field. (Also EM waves, are waves in the EM field, which is a single (tensor) field.)TR 10:12, 9 November 2012 (UTC)