🚀 go-pugleaf

In article <MATT.92Sep29114552@physics.berkeley.edu> matt@physics.berkeley.edu (Matt Austern) writes:

   In article <STEINLY.92Sep29105205@topaz.ucsc.edu> steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:

   > Figured I might as well interject at this point.
   > Tom? You lurking there waiting to pounce??? ;-)
   > The "gravity" from each component in a binary star does
   > not arrive delayed, see for example LPPT 12.4 and MTW 18.4 and 39.9,
   > especially eqn 39.64

   I know I've said this before, but I may as well say it again: I think
   we're begin confused over semantics; we have to be careful over what
   it means to talk about the speed of propagation of gravity.

   I contend that in a static situation (i.e., one where there is no
   gravitational radiation), it is meaningless to talk about the speed of
   propagation of gravity, since nothing is propagating.  I contend,
   then, that detecting a finite speed of gravitation is equivalent to
   detecting the effects of gravitational radiation.

I agree absolutely, there is however a point that - as Tom van
Flandern is happy to note - is often glossed over, namely that
if you do the calculation in a retarded potential formalism
the first two (1/2) order terms in (r - v/c) cancel - there is
no aberration, and hence the L-W formalism is not very useful.
You can look at it as either a very neat and not unexpected
feature of GR or as a Profound Mystery indicating something very
basic ;-)

   And, as is well known, this has been done in the case of binary
   neutron star systems.  The effects of radiation show up in (if I'm
   remembering right) the post-post-post-Newtonian approximation, and
   they have been observed.
 
Ooh! Yes indeed, both PSR1913+16 and 1534+12 show period derivatives
consistent with GR, depending on your religion either confirms GR
or is exactly consistent with GR...

*  Steinn Sigurdsson   			Lick Observatory      	*
*  steinly@lick.ucsc.edu		"standard disclaimer"  	*
*  The laws of gravity are very,very strict			*
*  And you're just bending them for your own benefit - B.B. 1988*