Abstract

A symmetrical spacetime model of relative motion is developed in relation to the hyperbola, t? − x? = 1. The model shows the Worldline of P (Inertial Frame coordinates xP, tP) moving symmetrically away from that of Q. If a ray of light leaves P at xP = 0, tP = a-b, is reflected from an event H on Q (xQ = 0, xP = b) and returns to P at xP = 0, tP = a+b, the value tP=a is an overestimate of the time on Ps clock as H occurs. The time overestimate results in an underestimate by P of the velocity of Q relative to P. There is therefore a velocity v = xP/tP = b/a , which is less than the velocity w = xP /(time on Ps clock as H occurs) = b/(<a) derived from a symmetrical model. The former, v, the usual definition, is limited by the equations to less than the speed of light; the latter, w, is not limited. The "twin paradox" is solved.