Cycles may be defined as any phenomena repeating after fairly regular time intervals. Generally cycles are found in anything to which numerical measurements may be assigned at intervals in time. Edward Dewey of the Foundation for the Study of Cycles said that every field studied had been found to have cycles.
The cause of cycles is generally that some restorative force exists whenever any system is displaced from its equilibrium. This applies equally to the motion of a pendulum, the orbiting of planets and the state of the economy, because it doesn't matter whether the system and the restoring force is physical or not.
It may be confidently said that although cycles are found in everything, they are never perfectly regular, but the period of the cycles also varies in cycles. In the case of the planets, they have eliptical orbits causing small variations in motion, but the disturbance of other bodies also causes other variations over varied time scales.
Because everything in the universe affects everything else, all vibrations, oscillations and disturbances reverberate about forever, continuously interacting. The wave nature of the universe is attested to by all modern scientific theories and the study of cycles is a wonderful way to study how influences move from one place to another, one time to another and one field of study to another. This can be done because cycles have many specific periods present that can be recognised, like fingerprints, when they appear somewhere else.