This paper shows the various parameters to be considered, duringelectron - positron annihilation. Many of the theories suggest that directionof gamma ray emission cannot be predicted. This is normally justifiedby using quantum mechanics. This paper gives an alternative explanation tounpredictability of gamma ray direction. This explanation does not require thelogic of quantum mechanics. It requires modification of classical mechanics toaccount of the forces between colliding particles.The logic of this paper is thatin case of pair production involving gamma ray and electron- positron pair, theclassical mechanics calculation itself shows perfect conservation of directionand magnitude of momentum. There, a little recoiling of the nucleus is observedfor conserving momentum. Hence it must be possible to use classicalmechanics for the process of electron- positron annihilation process also.