In mathematics, a quantity that decays exponentially is one that decreases at a rate proportional to its value. For example, since a radioactive atom has the same probability to decay at any given time, regardless of how long it already lived, the number of disintegrations in an assembly of such atoms is proportional to their number. Such an exponentially decaying population decreases, in atom per unit of time, three times as fast when there are six million atoms, as it does when there are two millions.
If we call x this quantity, the rate of change dx/dt obeys by definition the differential equation:
Examples of Exponential Decays
See also