NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/astro/13335

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Xref: sparky sci.astro:13335 sci.physics:21560
Newsgroups: sci.astro,sci.physics
Path: sparky!uunet!noc.near.net!lynx!mkagalen
From: [e-mail] (michael kagalenko)
Subject: Re: Size of Second-Order GR Effects in Binary Pulsars
Message-ID: <[e-mail]>
Organization: Northeastern University, Boston, MA. 02115, USA
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Tue, 22 Dec 1992 00:53:03 GMT
Lines: 101

In article <[e-mail]> [e-mail] (Loren I. Petrich) writes:
>In article <[e-mail]> [e-mail] (Tom Van Flandern) writes:
>>
>>[e-mail] (Loren I. Petrich) writes:
>>
>
>: 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.
>
>    That is just plain wrong. See Shapiro and Teukolsky's book,
>for example. Here are the parameters determined from observation:
>
>    [Newtonian]
>
>    Period: P = (2[pi])*sqrt(a^3/(M1+M2))
>
>    Rate of change: (dP/dt)
>
>    Projected semimajor axis: a*(M2/(M1+M2))*sin(i)
>
>    Eccentricity:
>
>    Periapsis position: [omega]
>
>    Rate of change: (d/dt)[omega]
>
>    GR prediction: (2[pi]/P)*(3*(M1+M2)/(a*(1-e^2)))
>
>    [Order (v/c) Post-Newtonian]
>
>    [beta] = (M1*M2*(M1+2*M2))/((M1+M2)^2/a)*e
>
>    From the period, the projected semimajor axis, the rate of
>periapsis advance, and [beta], one can find four quantities: a,
>sin(i), M1, and M2. If one assumes post-Newtonian GR, one has a
>_completely_ determined system.

The post of Ms. Petrich indicates the lack of understanding, how
phenomenology works. She uses the following scheme ;
1st  order of magnitude:  Newtonian
2nd  order of magnitude:  GR
Therefore, she divides parameters into "Newtonian" and "Non-Newtonian"
In fact, this  "perturbational" approach ought not to be used in
discussion of principal structure of GR.

>
>    Assuming GR for G-waves, one can calculate the value of
>(dP/dt) as a function of a, e, M1, and M2, determined from the rest of
>the observations, and compare it with the observed value. One finds 50
>sigmas of agreement so far.
>
>: 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
                  ^^^^^^^^^^^^^
This is the point. We aren't discussing perturbational method.

>: 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.
>
>    That is just plain wrong. See above.

Don't be so ignorant; you aren't the sole proprietor of truth.

>
>: 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 how is a "theory with no radiation" supposed to work out???
>
>    As I had explained above, whether or not (dP/dt) is due to
>G-waves has NOTHING to do with the determination of the rest of the
           ^^^^^^^^
Your mistake is here.

>orbit parameters.
>