Quantifying the concepts of rate and acceleration/deceleration of aging

In this paper, we shall attempt to quantify the rather abstractly and ambiguously used concepts of acceleration of aging and rate or velocity of aging. The use of the phrase "rate of aging", in the gerontological literature, requires that we formalize the concepts so that they may be discussed in a uniform manner. We shall perform this formalization by means of an analogy with various similar concepts from the discipline of physics. This set of analogies leads, quite naturally, to some practical ways in which we may discuss the acceleration of aging. Additionally, these analogies allow us to introduce two forms of acceleration of aging; uniform and non-uniform acceleration. By uniform acceleration, we shall see that we mean an acceleration which is independent of the age of the individual in the population. That is, every individual in the population feels the same magnitude of acceleration, no matter what his age. Non-uniform acceleration is an acceleration which is age-dependent. We shall introduce the concepts of relative acceleration and fraction relative acceleration as a means of deciding whether a population is undergoing uniform or non-uniform acceleration. Finally, these new developments will be applied to C. elegans, to rat, and to C57BL/6J mouse experimental data.