Do you mean gravitational radiation which fits a black body spectrum? Black body radiation normally is electromagnetic radiation so has nothing to do with gravitation per say.

The second reference you give above tries to replace GR with an ad hoc spin orbit term added to Newtonian gravitation. Why would anyone abandon GR in favor of such a limited and poorly motivated hypothesis?

Reference 1 and 3 are just the standard weak field discussions of GW. Reference 2 is a speculative discussion of gravitation as "information." How are these related to the either the original question or the one I posed?

Depends on what the terms are taken to mean. Gravitational waves are radiation, therefore we can talk meaningfully of their thermodynamics, which means the density of energy at given wavenumber. Since they are described by bosons, the distribution will be very similar to that of electromagnetic radiation. The difference will show up in the polarization, since electromagnetic waves describe vector propagation whereas gravitational waves describe tensor propagation. In fact that is what the BICEP2 telescope just announced some days ago.

Paul,

What I mean is that the so called gravitational waves as ripples of curvature of space-time may not exist in reality. If GR could be replaced by those proposals, then the counterpart of gravitational waves could be electromagnetic radiations with black body spectrum.

We have already spent almost hundred years trying to find the so called gravitational waves, instead we found all kinds of electromagnetic radiations without proper explanations. So I don't think the second proposal is a limited and poorly motivated hypothesis comparing to GR.

Gravitational waves, as ``ripples of curvature of space-time'' do exist. What the sentence *means* implies certain consequences. *One* such consequence is the energy loss of a partner of a binary pulsar, that leads to a variation of its period. General relativity, in which framework this loss is described by waves of spin 2, gives a result in extraordinary agreement with measurements. (cf. Nobel Prize in Physics 1993).

Such an agreement is not possible if the waves were of spin 1.

More recently the BICEP2 telescope measured cosmological perturbations that, also, can only be described by tensor waves not vector waves.

Stam,

"Such an agreement is not possible if the waves were of spin 1."

Can you cite some references to support this statement?

Feynman's lectures on gravitation and Hulse and Taylor's papers would be a good start.

It's already clear that gravitation, as an attractive force, is mediated by excitations of *even* spin. Spin 0 doesn't work, since light does get bent by gravitation and since light, whether described as photons, masless spin-1 particles, or electromagnetic waves, has traceless energy-momentum tensor, it can't couple to a scalar field. That's, incidentally, why there's no bending of light in Newton's theory, the non-relativistic limit of Einstein's theory.

(And all this, once more, doesn't have anything to do with Verlinde's proposal.)

What I asked for is the references to prove the energy loss of the partner of a binary pulsar can only be explained by waves of spin 2.

It might be even easier to explain this by using black body radiations.

Once more: the answer is in Hulse and Taylor's papers. Look at the Nobel Prize site:

http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/

Gravity is *not* described by spin 1 excitations, because it is always attractive.

Hulse and Taylor's paper cannot rule out the possibility of having alternative solutions.

We are still not quite sure that gravity is always attractive or not, hopefully the ALPHA experiment will provide an answer soon.

http://alpha.web.cern.ch/

Gravitational waves as ripples of curvature of space-time can be ruled out by Verline's proposal, which suggests gravity as an entropic force. Some kinds of black body radiations should be associated with an entropic force seems to be an inevitable conclusion. Detailed discussion is on section 4.4 of my paper.

Article A Cosmological Model with Variable Constants (Functions of t...

The failure to detect GW with earth bound experiments is hardly proof of non-existence of GWs. These experiments are hard, very hard. I expect even space born experiments will not be a cakewalk given the technical challenges.

When I first encountered the gravity as "entropy" argument I felt it was interesting but was not surprised when the papers on it died down. I would expect any "first-cause" explanation of gravity that didn't include GWs will likely be rejected as incomplete. The reason for this is the principle of equivalence combined with general covariance is difficult (perhaps impossible) to circumvent. It could be that almost any sufficiently complete argument leads to Einstein-like field equations and GWs.

Even though it is very hard, there might be an end in sight.

http://phys.org/news/2014-02-sight-gravity.html

Actually the alternative solution to the precession of binary pulsars was found by professor Arbab in 2010.

Function (21) in this paper should be the formula for gravitational radiations in form of black body radiations.

http://link.springer.com/article/10.1007%2Fs10509-010-0353-7

Guoliang,

This is precisely the conclusion I have arrived at by deriving per particle solutions to general relativity. Any energy lost from a system must be kinematic or thermodynamic in nature (which is also kinematic). With respect to classical electrodynamics, this can only be achieved by braking radiation. However, Einstein’s field equations instead transform the energy to metric waves without any explanation as to how this occurs on a per particle basis. The latest GW experiments were proposed on the claim that they would be able to detect gravitational waves. Yet the theoretical detection rates have recently varied by 1000x to account for the lack of positive events, i.e. enhanced LIGO alone expected a maximum of 1700 events over its run time (http://www.ligo.caltech.edu/LIGO_web/9904news/sources85.pdf).

A serious problem with the recent claims of an indirect detection of primordial gravitational waves is that B-polarization can also occur due to gravitational lensing. In an earlier draft of my “Theory of Everything” I was going to include a discussion on large-scale B-polarization and how it insists upon a global gravitational potential (now added to my most recent article, which is nearly finished). If the cosmic background radiation originates from within such global potential, then the CMBR dipole can be used to determine the center of the universe. Next I determined the alignment of B-polarization with the location determined from the CMBR dipole center and found a 3.2 sigma signal (this is without even considering additional affects due to large-scale structure). The black line is relative to a null result while a positive result depicts a peak at 0 degrees (observed). Since there are no free variables in this conclusion, it is a very significant result.

Michael,

Thank you for your comments.

Could you share more opinions on the BICEP2 results?

http://bicepkeck.org/b2_respap_arxiv_v1.pdf

The CMB itself could be cosmic background gravitational waves in form of black body radiations, Big Bang should be ruled out if this is confirmed.

Guoliang,

BICEP2 surveyed a relatively small region of the sky with the results pertaining to the 50 < l < 120 multipoles. The predictions resulting from a global gravitational potential could also be broken down into multipoles, although this component would dominate lower multipoles; i.e. over large angular scales (image below). Higher multipoles would be due to large-scale structure, with smaller deviations resulting from clusters and such. I’m also unsure of what they mean by lensed-LCDM for their model, as I couldn’t find anything with a quick search. I’ve heard quite a bit of skepticism with these results however such as “On the other hand, a BICEP2 detection of r∼0.2 would also strongly contradict appear to be at odds with the results from the Planck and WMAP satellites. Which probably goes to show that there is not much point believing every rumour” (http://blankonthemap.blogspot.com/2014/03/b-modes-rumours-and-inflation.html).

What I've been proposing is a global gravitational potential, which will logically require increased mass/energy density with decreasing radius from the center. Therefore, the existence of a global potential would also require a central object. All objects emit a black body spectrum, so the cosmic background radiation is naturally predicted in this model along with the observed B-mode at large scales.

Michael,

I just noticed that the blog posting you referenced was made prior to Monday's announcement, and that the words "strongly contradict" are stuck out - replaced by the words "appear to be at odds with" "... the results from the Planck and WMAP satellites."

As I understand, the quoted blog posting should conclude:

"On the other hand, a BICEP2 detection of r∼0.2 would also appear to be at odds with the results from the Planck and WMAP satellites. Which probably goes to show that there is not much point believing every rumour ...

"We will find out on Monday!"

The second of three articles was posted on Mon., Mar. 24, 2014 at http://blankonthemap.blogspot.com/2014/03/bicep2-reasons-to-be-sceptical-part-2.html. It addresses the question of whether the identified B-mode CMBR signal is (completely) caused by primordial gravitational waves. Most importantly, it simply points out that more complete dust data captured by Planck is now being analyzed (dust may also contribute to identified B-mode CMBR polarization):

"... Now one real test of these assumptions will come from Planck, because Planck will soon have the best map of dust in our Galaxy and therefore the best limits on the possible contamination. This is one of the reasons to look forward to Planck's own polarization results, due in about October or November."

It also suggests that phenomena other than primordial gravitational waves have contributed to the B-modes CMB polarization, concluding:

"The chances are much higher – I'd be tempted to say perhaps even as much as better than even money – that foregrounds contribute a part of the observed signal, and that therefore the actual value of the tensor-to-scalar ratio will come down from r=0.2, perhaps to as low as r=0.1, when Planck checks this result using their better dust mapping."

As of this writing, the third and final article has not yet been written. It will address whether the identified BICEP2 gravitational wave signal is actually associated with inflation...

Killing the Straw Man: Does BICEP Prove Inflation?

http://arxiv.org/abs/1403.5166v1

James,

The formatting was lost when I copied the quote, but it seemed like self-censorship with the two wordings. Although dust and local contamination are concerns, assumptions based upon the chosen cosmological model also play a large role in interpreting observations. Foreground contributions besides dust (large-scale structure, clusters, ect.) can substantially alter the CMBR regardless of it being radiation from a surface of last scattering or central object in a global gravitational potential. For example, gravitational lensing alone mixes E and B type polarizations (see http://cds.cern.ch/record/348954/files/9803150.pdf) and it should therefore be possible to reproduce the signal without invoking gravitational waves or other perturbations. LCDM however limits the possibilities and requires a mixture of several contributions due to its interpretation of the CMBR.

If LCDM were ruled out by other observations, then BICEP2 and other experiments would be based upon the wrong assumptions; i.e. the conclusions would have to be discarded. This is perhaps the central reason for being skeptical, as there are serious issues with big bang cosmology that have not been properly addressed. For example, it has recently been proposed that a “local hole” exists because the slope of galaxy counts rises much quicker than predicted in an expanding universe (in fact it fits a static, Euclidean metric). I have confirmed this with cluster counts from 0 to 0.2z, demonstrating that observations strongly contradict an expanding metric even locally. In terms of how much of a problem this is for LCDM, the required local hole is inconsistent with the big bang theory to the 4 – 5 sigma level (published values). The volume element isn’t the only issue, because angular diameter distance also follows the predictions of a static metric (I now have 4 unrelated and well constrained objects in agreement with each other). Combined with countless anomalies in nearly all aspects (CMBR, galaxy formation, large-scale structure, ect.), LCDM has a long way to go before any of these theoretical studies truly indicate something.