UNLABELLED: DISCOVERY: A periodicity of 500 years has been discovered in the political history of ancient Egypt and documented by means of inferential statistics. Periods of chaos and waning of central power (some of them called "intermediate periods") recurred every 500 years.
DATA & METHODS: Input for the computation is the mean duration of ruling dynasties calculated per each half century. Fisher's periodogram analysis and Halberg's cosinor regression have been used. A highly significant (p < 0.00002) periodicity of approximately 500 years has been found. Data are taken from two different historians and results for low and middle chronology are being compared. FURTHER RESULTS: Lability of dynastic power in ancient Egypt as well as China between 3000 and 500 B. C. culminated each 500 years synchronously. No local events, confined to Egypt or China alone, can serve as an explanation. The rhythm of "dark ages" seems to continue beyond Egyptian and ancient Chinese history into the modern era and seems to be world-wide.
HISTORICAL BACKGROUND: It is a surprising fact, that this periodicity has been known already to the priests of Babylon, who ascribed this to the maleficient influence of god Nergal. The same periodicity has been described by the Chinese philosopher Mencius in the 3rd century B.C. and attributed to the will of tian (heaven). Egyptians elevated their war god Seth every 500 years and European kings assumed masculine nicknames.
CONCLUSION: This recurring cultural pattern of aggressiveness and strife resembles overall traits of male psyche or mid-life crisis. We suggest to look for an unknown cosmophysical factor impacting the neuroendocrine system of man by raising the levels of androgens periodically. EXPLANATION HYPOTHESES: Sun impacts global weather on Earth, but there is no known significant periodicity of 500 years in solar activity. The Wheeler weather cycle almost fits the cycle of Egyptian political history. But his cold-dry periods seem to lag behind the periods of social destabilization and hence can not cause them. An alternative view (based on idealistic rather than materialistic presuppositions) is, that periodic long-term shifts of archetypes take place within the collective unconscious of mankind independently of external environment.