How Accurate Are Recent Tests of General Relativity Using the Double Pulsar?

[ZapperZ]

Published in ScienceExpress this week (the full citation when it appears in Science will be in our Noteworthy Physics Papers thread in the General Physics forum):

M. Kramer et al. Tests of General Relativity from Timing the Double Pulsar, ScienceExpress 14 Sept. 2006

Abstract: The double pulsar system, PSR J0737-3039A/B, is unique in that both neutron stars are detectable as radio pulsars. This, combined with significantly higher mean orbital velocities and accelerations when compared to other binary pulsars, suggested that the system would become the best available testbed for general relativity and alternative theories of gravity in the strong-field regime. Here we report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. Use of the theory-independent mass ratio of the two stars makes these tests uniquely different from earlier studies. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the "post-Keplerian" parameter s agrees with the value predicted by Einstein's theory of general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current Solar-system tests. It also implies that the second-born pulsar may have formed differently to the usually assumed core-collapse of a helium star.

Zz.

 

[clj4]

Published in ScienceExpress this week (the full citation when it appears in Science will be in our Noteworthy Physics Papers thread in the General Physics forum):

M. Kramer et al. Tests of General Relativity from Timing the Double Pulsar, ScienceExpress 14 Sept. 2006

Abstract: The double pulsar system, PSR J0737-3039A/B, is unique in that both neutron stars are detectable as radio pulsars. This, combined with significantly higher mean orbital velocities and accelerations when compared to other binary pulsars, suggested that the system would become the best available testbed for general relativity and alternative theories of gravity in the strong-field regime. Here we report on precision timing observations taken over the 2.5 years since its discovery and present four independent strong-field tests of general relativity. Use of the theory-independent mass ratio of the two stars makes these tests uniquely different from earlier studies. By measuring relativistic corrections to the Keplerian description of the orbital motion, we find that the "post-Keplerian" parameter s agrees with the value predicted by Einstein's theory of general relativity within an uncertainty of 0.05%, the most precise test yet obtained. We also show that the transverse velocity of the system's center of mass is extremely small. Combined with the system's location near the Sun, this result suggests that future tests of gravitational theories with the double pulsar will supersede the best current Solar-system tests. It also implies that the second-born pulsar may have formed differently to the usually assumed core-collapse of a helium star.

Zz.

Here is a very good synopsis of the GR - oriented experiments:

http://www.citebase.org/fulltext?format=application/pdf&identifier=oai:arXiv.org:gr-qc/9811036

And here is a very good synopsis of the SR-oriented experiments:

http://arxiv.org/abs/gr-qc/0504085

Good readings for all potential "challengers"...

 

[ZapperZ]

A review of this result can be found here for a limited time only.

http://www.nature.com/news/2006/060911/full/060911-9.html

Read it while you can.

Zz.

 

[Garth]

But still there is a degeneracy between different theories that pass this test.

These two neutron stars are orbiting each other and the data confirms to a high level that they are following GR geodesics.

In any theory which is conformally equivalent to GR in vacuo (i.e. those in which the Langrangian density reduces to that of canonical GR in vacuo) the geodesics/null geodesics of freely falling test particles/photons will be the same as those of GR.

One example of such a theory is given in this chapter Self Creation Cosmology - An Alternative Gravitational Theory in 'Horizons in World Physics, Volume 247: New Developments in Quantum Cosmology Research', Nova Science Publishers, Inc. New York. (See equations 16 - 23)

This degeneracy will shortly be resolved: Resolving the Degeneracy: Experimental tests of the New Self Creation Cosmology and a heterodox prediction for Gravity Probe B which can also be downloaded free here.

Garth

 

[ZapperZ]

Y'know, Garth, have you ever attempted to write a COMMENT to all these results that clearly and openly support GR while neglecting your theory? I mean, I am sure you KNOW that writing about it here on PF, as much as I love PF, really does not mean a hill of beans in the physics community. Why aren't you directing your energy to where it matters?

Zz.

 

[Garth]

Because I value your criticism Zz - you and others here do mean 'a hill of beans' to me!

These peer reviewed papers are directed at the physics/cosmology community - it is up to them to also likewise criticize in response.

Garth

 

[ZapperZ]

Because I value your criticism Zz - you and others here do mean 'a hill of beans' to me!

Well then, you're strange! I myself do not value my criticism/evaluation of any GR papers. Furthermore, since you ARE trying to gain recognition of your theory, this isn't the means to do it.

You still have not responded on why you never wrote even a single comment to all these papers. The GR/Astrophysics community do not read PF, nor use it as their source of info. If you think you have a valid alternative to also match these observations, and these papers are ignoring it, then it is YOUR responsibility to write a comment to them. I had to do it, and many other physicists had to do it one time or another.

Zz.

 

[Garth]

The general point that 'freely falling' test particles in SCC do follow the geodesics of GR has been made in peer reviewed papers.

I have one further paper ready to be submitted to A&SS, and another one in the pipeline to be submitted at a conference. I do not have time write in response to all the papers such as in the OP, but that may come yet.

And yes - I am strange!

Garth

 

[ZapperZ]

The general point that 'freely falling' test particles in SCC do follow the geodesics of GR has been made in peer reviewed papers.

However, every physicist know that often, due to the volumes of material that appear almost every week, the CONNECTION between one and another can sometime be lost, especially when it is an obscure point. I have had to point out either to the authors, or even when I'm refereeing papers, that either there is already supporting evidence, or contrary evidence, that they have neglected that were published in leading journals. One only needs to look at such journals to note that on occassion, other authors have to point out that they have published something that the authors have neglected to include or discuss that are relevant.

The fact that both the authors of the paper that I cited, AND the referees, didn't feel that they have neglected anything by not citing YOUR paper, clearly implies that you haven't made any impression yet to the community that requires that your idea be taken seriously. Unless you willing to at least write ONE comment to ONE paper as a start, then I don't see how by simply publishing more papers would change the situation. You are battling papers that appear in such high-impact and high-profile journals. Unless you can get your work published in a platform of similar caliber, I don't see how you can make any dent.

Zz.

 

[Garth]

I agree Zz, however, at the moment the watershed will be the publication of the GP-B results. (April 2007). If they do falsify SCC (as is most probable) then I, and the rest of the cosmology community, can lay it to rest, if not - well that will be a whole other ballgame.

Garth