The fundamental forces of nature are mediated by the exchange of particles; photons mediate the electromagnetic force, gluons the strong force, W and Z particles the weak force. It is shown that the duration of the exchange of a force or messenger particle between two interacting particles is a function of the velocity through space of the two interacting particles and is also a function of the orientation of the two particles relative to their common velocity. The greater the velocity of the two particles the longer it takes for the particle exchange between them. The interaction between two particles is thus slowed by their motion through space. This slowing with velocity of the interaction between particles underlies the fundamental process occurring in any physical entity (proton, nucleus, atom, or macro object). It is the essence of time dilation. The dependence of time dilation on the orientation of two interacting particles relative to their common velocity is an important finding of this study and may appear to contradict the ‘known’ singular dependence of time dilation on velocity. The dependence of time dilation on the orientation of the interacting particles is overcome when a large number of particles are aggregated and their orientations relative to the velocity of the aggregate body or entity are randomized. Alternatively, the rapidly changing orientation of two particles in the turbulence of space will itself randomize the orientation of the particles and cause the value of time dilation of the particles to ‘average out’. We can look at time dilation in two ways; 1) time actually slows for the fast moving entity or 2) the basic process that governs the entity takes longer as the entity moves through space, but time itself does not slow down. This may be more a philosophical question than a scientific one. The momentum of current thought is clearly with time slowing down for the moving entity. The conclusion of this paper is that time dilation is a slowing of the fundamental process of an entity when the entity is moving through space, not a slowing of time itself.