The Vedas measure cosmic time on a large scale. Four great ages, yugas—Satya, Treta, Dwapara, and Kali—rotate in cycles lasting millions of years. Kali-yuga is the last and worst of the four, characterized by an overall rise in vice and a degradation of virtue. The current Kali-yuga began around five thousand years ago.
The one advantage of Kali-yuga is the simplicity and straightforwardness of its recommended means of self-realization. In previous yugas, those seeking spiritual perfection had to perform long austerities, grand sacrifices, and costly Deity worship, none of which are possible today. The prescribed method for attaining the Supreme in Kali-yuga is simply kirtan, chanting the names of the Supreme Person.