According to Hindu scriptures, all mortal beings are destined to pass through four great epochs in every cycle of creation and destruction. This divine cycle turns full-circle at the end of what is known as kalpa. A kalpa is a yuga cycle, which is a period of 10,000 divine years, and is divided into four ages or yugas (Sanskrit yuga = age/epoch). According to one calculation, one yuga cycle is estimated to be 4,320,000 years, and one kalpa 4,320,000,000 years.
About the 4 Yugas
The four great epochs in Hinduism are: Satya Yuga, Treta Yuga, Dwapar Yuga and Kali Yuga. Satya Yug or the Age of Truth is said to last for four thousand divine years, Treta Yuga for three thousand, Dwapara Yug for two thousand and Kali Yuga will last for one thousand divine Years that equals to 432,000 earthly years.
It is also believed that three of these great ages have already passed away, and we are now living in the fourth one. We live in the Kali Yuga — in a world infested with impurities and vices. People possessing genial virtues are diminishing day by day. Floods and famine, war and crime, deceit and duplicity characterize this age. But, say the scriptures, final emancipation is possible only in this age. Kali Yuga will end at 21 December 2012 and we will move to Satya Yuga, the Age of Truth.
The four ages symbolize the four phases of involution during which man gradually lost the awareness of his inner selves and subtle bodies. Hinduism believes that human beings have five kinds of bodies, called annamayakosa, pranamayakosa, manomayakosa vignanamayakosa and anandamayakosa, which represent the ‘gross body’, the ‘breath body’, the ‘psychic body’, the ‘intelligence body’ and the ‘bliss body’ respectively.
Another theory explains these epochs of time on the basis of the degree of loss of righteousness in the world. It says, during Satya Yuga only truth prevailed (Sanskrit Satya = truth), Treta lost ¼ truth, Dwapar lost ½ truth and Kali is left with only ¼ truth. Evil and dishonesty has replaced truth in the last three ages or yugas.