" Sri Yukteswar discovered the mathematical application of a 24,000-year equinoctial cycle to our present age. 4 The cycle is divided into an Ascending Arc and a Descending Arc, each of 12,000 years. Within each Arc fall four Yugas or Ages, called Kali, Dwapara, Treta, and Satya, corresponding to the Greek ideas of Iron, Bronze, Silver, and Golden Ages. My guru determined by various calculations that the last Kali Yuga or Iron Age, of the Ascending Arc, started about a.d. 500. The Iron Age, 1200 years in duration, is a span of materialism; it ended about a.d. 1700. That year ushered in Dwapara Yuga, a 2400-year period of electrical and atomic-energy developments: the age of telegraphy, radio, airplanes, and other space-annihilators. The 3600-year period of Treta Yuga will start in a.d. 4100; the age will be marked by common knowledge of telepathic communications and other time-annihilators. During the 4800 years of Satya Yuga, final age in an Ascending Arc, the intelligence of man will be highly developed; he will work in harmony with the divine plan. A Descending Arc of 12,000 years, starting with a Descending Golden Age of 4800 years, then begins for the world (in a.d. 12,500); man gradually sinks into ignorance. These cycles are the eternal rounds of maya, the contrasts and relativities of the phenomenal universe. 5 Men, one by one, escape from creation’s prison of duality as they awaken to consciousness of their inseverable divine unity with the Creator. Master "

― Paramahansa Yogananda , Autobiography of a Yogi