Re: Comparison of Gravitational waves with EM waves

tessel@um.bot

On Mon, 12 Dec 2005 ianparker2@gmail.com wrote:

> Maxwells Equations (spin = 1) state that the electric field is at right
> angles to the direction of motion. A gravitational field can be along
> the direction of motion. Moreover the tensor equations are quadrupolar.
> If they were dipolar (Maxwell) the Earth could only circle the Sun for
> 100 Million years. (30km/s = c/10,000).
>
> One year's Nobel prize for Physics was one by measuring the slowdown in
> pulsar transmissions. It fitted a quadupolar model to 10-15%.

I think you meant to say something like this:

Maxwell's theory of EM predicts the existence of electromagnetic
radiation which propagates as transverse waves at the speed of light,
with polarization properties loosely described as spin-1. The strongest
type of EM radiation in this theory is dipole radiation. Gtr predicts
the existence of gravitational radiation which propagates as transverse
waves at the speed of light, with polarization properties loosely
described as spin-2. The strongest type of radiation in this theory is
quadrupole radiation.

Russell Hulse and Joseph Taylor were awarded the 1993 Nobel Prize in
Physics for their observations of the remarkable binary pulsar PSR
B1913+16, which they discovered in 1974. Their observations are
consistent with the gtr prediction that gravitational radiation should
carry off energy at a certain rate from this system, leading to orbital
decay at a certain rate. This consistitutes an indirect confirmation of
the existence of gravitational radiation.

Other theories also predict such radiation. However, the LIGO/VIRGO/GEO
interferometric detectors are designed to directly verify the existence
of gravitational radiation, and they, with LISA (a proposed spaceborne
detector) should give much information about their properties. This
might confirm other gtr predictions while ruling out some alternatives
(which predict different properties for gravitational waves), but more
important, it might eventually lead to a new field of gravitational wave
astronomy which should neatly complement electromagnetic astronomy.

Your comment "a gravitational field can be along the direction of
motion" might be a garbled version of something D'Inverno mentions about
Petrov III versus Petrov N vacuum gravitational fields, but one should
probably focus first on the basics: the linearized gtr treatment of weak
gravitational waves in Minkowski vacuum background.

"T. Essel"