From: metares@well.sf.ca.us (Tom Van Flandern)
Newsgroups: sci.astro,sci.physics
Subject: Re: Size of Second-Order GR Effects in Binary Pulsars
Date: 20 Dec 92 17:46:21 GMT
Organization: Whole Earth 'Lectronic Link


lip@s1.gov (Loren I. Petrich) writes:

> total energy, momentum, angular momentum, and center-of-mass location (the
> familiar 10 integrals) are well-defined quantities.

     There is apparently some argument about the system of equations being
over-determined because of an extra identity that has been found.  I can't
say for certain that Yu's paper is correct, but the matter isn't trivial
either.

> even if the total energy was not a well-defined quantity, one could always
> calculate the effect of the radiation reaction. I have to wonder how Yu's
> paper made it past the referees.

     It would help if you read it and gave us an informed opinion about the
actual line of reasoning.  Blind shots are not helpful.

> So Yu claims _zero_ G-wave flux?  That is contrary to all the GR literature
> I have ever read.  Any GR textbook will contain derivations in gory detail.
> Here's some books: ...

     Yu is familiar with these derivations, and opens his article by
repeating the derivation.  The issue is not with the derivation, but with the
assumptions on which it is based.  Yu reasons that the right-hand side of the
energy-change equation is vacuous.  He is not alone in thinking this.

> There is also the additional problem that GR works very well in the
> post-Newtonian limit in the Solar System, and it is post-Newtonian effects
> that allow the masses of the two Hulse-Taylor objects to be determined, as
> well as the orbit size. Plugging all these, with the eccentricity, into the
> GR G-wave orbit-decay rate formula gives essentially the right value.
> Alternate theories that differ from GR have to suffer some very fine tuning
> to get the right G-wave emission rate.

     It is important to read and understand the 1992 papers by Damour and
Taylor, as well as Yu.  Ordinary, classical GR with zero gravitational
radiation is just as consistent with the binary pulsar observations as is GR
with the Taylor radiation formula.  The other GR effects, the star masses,
and the orbital elements soak up the difference.  The radiation effects
cannot be separated out of the solutions, so one cannot say from the
observations whether they are zero or non-zero.

> If one takes the Newtonian orbit parameters: (a1 sin i), P, and e, and adds
> in the redshift effect and the precession rate (assuming the truth of GR's
> post-Newtonian approximation), one uniquely determines the masses, the
> semimajor axis, and the inclination.

     Sorry, that's not so.  You get different values for these parameters
from the observations depending on whether or not radiation is included in
the theoretical model.

> It just doesn't work out that way. The other elements don't "adjust". They
> are precisely fixed by post-Newtonian GR.

     The elements and masses are what is called "constants of integration."
They are completely free parameters.  No theory can predict their values.  If
observations are compared to a theory with radiation, one set of constants
gives the best fit.  If a theory without radiation is used, a different best
fit results.  In other problems one might be able to tell which fit was the
better.  But not so in this case: the fits are of equal quality.


and matt@physics2.berkeley.edu (Matt Austern) writes:

> The argument that Yu makes seems to apply only to the second assertion: he
> is trying to show that a time-dependent quadrupole doesn't radiate.

     That is not the main thrust of his argument.  See if you can get a copy
of the article and take a look at the math.  -|Tom|-

-- 
Tom Van Flandern / Washington, DC / metares@well.sf.ca.us
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.
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