PHYSICAL time is customarily measured by counting the number of times a suitably chosen cyclic process (for example an oscillating pendulum) is repeated, and equal intervals are defined as those during which the process is repeated the same number of times. It would, in principle, be possible to choose, instead of a cyclic process, a purely random one and define equal intervals of time as those during which random events are equally likely. Most random processes vary too much with environment (for example, molecular bombardment of a surface varies with temperature) to be selected as standards for measuring time but radioactive decay is believed to be virtually independent of environment. Thus, if radioactive decay is truly random, the number ΔN of nuclei disintegrating in a time-interval t, t + Δt, out of N like nuclei existing at time t is given by: where λ is a constant characteristic of the particular nuclei chosen.
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CARROLL, J. An Absolute Scale of Time. Nature 184, 260–261 (1959). https://doi.org/10.1038/184260a0
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