GR Passes Double Pulsar Test

In a recent paper on testing GR with the 22.8ms double pulsar
J0737-3039 the authors assert that GR is consistent with the
observations to the 0.1% level. In fact they give the ratio
of the predicted and observed Shapiro delay parameter as:

prediction / observation = 1.0002 ( +0.0011 -0.0006 ).

Does anybody which, if any, of the competing hypotheses are
ruled out by this?

For your convenience here is the abstract:

====
astro-ph/0503386:

Title: Testing GR with the Double Pulsar: Recent Results
Authors: M.Kramer, D.R.Lorimer, et al
Comments: Contribution to The 22nd Texas Symposium on Relativistic
Astrophysics, Stanford University, December 2004, 7 pages, 2 figures

This first ever double pulsar system consists of two pulsars orbiting
the common center of mass in a slightly eccentric orbit of only 2.4-hr
duration. The pair of pulsars with pulse periods of 22ms and 2.8 sec,
respectively, confirms the long-proposed recycling theory for millisecond
pulsars and provides an exciting opportunity to study the works of pulsar
magnetospheres by a very fortunate geometrical alignment of the orbit
relative to our line-of-sight. In particular, this binary system represents
a truly unique laboratory for relativistic gravitational physics. This
contribution serves as an update on the currently obtained results and their
consequences for the test of general relativity in the strong-field regime.
A complete and more up-to-date report of the timing results will be presented
else where shortly.
====

Dark skies,

tom

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.

In sci.astro Tom Kirke wrote:
In a recent paper on testing GR with the 22.8ms double pulsar
J0737-3039 the authors assert that GR is consistent with the
observations to the 0.1% level. In fact they give the ratio
of the predicted and observed Shapiro delay parameter as:

prediction / observation = 1.0002 ( +0.0011 -0.0006 ).

Does anybody which, if any, of the competing hypotheses are
ruled out by this?

There are not many competing theories that are developed to
the point that they can give much beyond hand-waving for these
observations. The main competitors that are able to offer
actual quantitative predictions are a class of scalar-tensor
and multiscalar-tensor theories, theories in which gravity-like
interactions are mediated by a collection of added scalar fields
along with the metric of general relativity. The observations
of J0737-3039 don't rule these out -- one can always tune the
couplings to be small enough that they wouldn't yet be seen --
but they place new limits on the strengths of the extra scalar
interactions.

The lack of serious competitors is a bit of a handicap, since
it makes it hard to quantify tests of GR. (Just how good is
1.0002?) In the absence of real alternatives, what people in
this field have done is to write down a general set of possible
corrections to the equations of motion, either in the weak field
("post-Newtonian") or stronger field but few-body ("post-Keplerian")
limits. These are not so much competing hypotheses as frameworks
in which different hypotheses can be fit -- if you come up with a
new theory of gravity, you can quickly compare it to observation
by checking its predictions for a relatively few post-Newtonian
and post-Keplerian parameters. In this framework, the observed
limits are on particular parameters in the post-Keplerian framework,
which then provide constraints for future proposals.

You can find a good review of these issues in an article by Will,
http://relativity.livingreviews.org/...1-4/index.html.

Steve Carlip