speed of gravity

Just a few corrections to Jack Dietz's comments on the exchange
particles for physical forces.

> All have zero rest mass and all have a set velocity of c,
> 2.998x10^8 m/s

Best estimates of particle masses, from the Particle Data Group
handbook are:
	PARTICLE	FORCE			MASS-ENERGY
	photon		Electromagnetic		< 3.0e-33 MeV
	W		Weak Nuclear		81 GeV
	pion		"Strong Nuclear"*	135 MeV (uncharged)

According to Yukawa, the strength of a force's potential as a function
of range is

	V = - K * exp(-u * r) / r

where K is a constant, r is the distance from the "charge", and u
is directly proportional to the exchange particle's mass (it's
mass times the speed of light divided by Plank's constant). For
zero mass, V = - K / r, which is the potential for the electric
field; so we can conclude that the Electric Force's exchange particle,
the photon, has zero mass (or close to it) and therefor travels at
the speed of light.

Since the gravitational force also has a potential proportional
to 1 / r, we can conclude that the gravitaional exchange particle,
dubbed the graviton, will also have a mass of zero, and will also
propagate at the speed of light.

				Rob Flammang

* The strong nuclear force is actually intermediated by the gluon,
but a long ranges (more than a few femtometers) the pion (which has
gluons in it) does most of the exchanging.