Re: Question Concerning Gravity.

[Dennis Krause <kraused@WABASH.EDU>]

> Dear List Members:
>          In classical Newtonian gravity theory, the force of gravity falls
> off as the inverse square of distance. However in General relativity this is
> very slightly modified to an inverse 2+& where & is a very small value. Does
> anyone have any information on the value of &. Also does anyone believe that
> this small deviation can be related to the fact that the hypothetical
> exchange boson, the graviton, is also subject to the force it mediates. Any
> references on this would be helpful.
>
> Bob Zannelli

Dear Bob,

       The leading order correction to Newtonian gravity (1/r
potential energy) due to general relativity is a 1/r^3 potential
energy, not a 1/r^(2 + &). [See Marion and Thornton's "Classical
Dynamics" or most books on general relativity.] I believe the 1/r^(2
+ &) potential energy was introduced historically to explain the
discrepancy of Mercury's perihelion precession before general
relativity, but I am not aware of any theory which predicts such a
correction.  You are right that the correction requires that gravity
interacts with itself.  In Feynman's "Feynman Lectures on
Gravitation," he finds that if one tries to develop a theory of
gravity in which gravity doesn't gravitate (a linear theory), one
obtains the incorrect value of the perihelion precession.  Only when
one includes non-linear corrections (gravity gravitating) does the
theory match up with experiment.

                                       Dennis
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