On the Interactions of Point Masses


The formula for the gravitational field (g) of a point mass (m1), whose motion up until time t < r/c is known, is(1)

g(r,t) = Gm1r/(r dot u)3 [u(c2-vret2) + r x (u x aret)].            (1)

In this equation

vret and aret are m1’s retarded velocity and acceleration respectively;

r points from the retarded position of m1 to point r;

u=c<r>vret is a utility vector;

<r> denotes the unit vector of r.

The formula for m1’s gravitomagnetic field is

O(r,t) = <r>/c x g(r,t).             (2)

The force experienced by a second mass, m2, at (r,t) and moving with velocity v2, is

F = m2(g + v2 x O).        (3)

m1, m2, g and O are mathematically imaginary. Thus the force, experienced by m2 in the field of m1, has a radial attractive component toward m1 and a transverse component found by application of the left-hand rule to v2 x O.

In order to calculate the motion of m2, Newton’s relativistically correct 2nd law must be applied.

F = d(m2v2)/dt.             (4)




1. See INTRODUCTION TO ELECTRDYNAMICS, Griffiths, Second Edition, Sect. 9.2