According to Hindu cosmology, the universe is cyclical, passing through four world ages. Each yuga, as they are called, is shorter and less pleasant than the previous epoch due to the degeneration of morality.
Currently we are in the last, the Kali Yuga, in which dharma (correct behavior), is only one-fourth of its beginning quality. The Kali Yuga is only 4,320,000 years long. At its end, religion will disintegrate and society will become more secular. When the world becomes hopelessly degenerate, it will end in catastrophe and a new mahayuga ("great yuga") will begin.
One thousand yugas is one day in the life of Brahma, the godhead of Hinduism. At the end of each day, the universe comes to an end and is resorbed into the Brahma for an equally long night, during which time it exists only potentially. He reappears at dawn, and creation begins anew. The present age is the first day of the 51st year of Brahma’s life. He lives 100 years, each of which comprises 360 days and nights. Then he dies, and the universe is dissolved into nothingness that lasts for another cosmic century. Then he is reborn to live another 311,040 billion years.
The Kali Yuga allegedly began in 3012 BC, so apparently we have many cosmic hours to wait for it to end; nevertheless, many people believe that the end is nigh. At that time, the Kalki (White Horse) Avatar, the tenth and final incarnation of Vishnu, will arrive. The heavens will open and he will appear on his white horse with his sword "blazing like a comet". He will destroy the wicked and restore purity. Entire continents will sink and rise in the process.
The eschatological Hindu text Divya Maha Kala Jnana ("The Divine Knowledge of Time") allegedly was composed circa 1000 AD by Jagas Guru Srimad Virat Potaluru Veera Brahmendra Maha Swami. The book describes social conditions before the arrival of Kali Purusha, the Kalki Avatar, by the Kali year 5101 (~ 1999 AD). That being is the incarnation of Kali, the destructive and procreative female aspect of Brahma. At that time, Kali Purusha will be called Sree Sree Sree ("Thrice Great") Veera Bhoga Vasataraya Maha Swami. The text Kala Jnana also describes the current world conditions of sexual perversion and horrid disasters that precede the end of this era of errors.
The Vishnu Purana (4: 24) advises us as follows about the conditions at the end of this civilization:
"The leaders who will rule over the earth will be violent and will seize the goods of their subjects. The caste of servants will prevail and the outcasts will rule. Short will be their lives, insatiable their appetites; they will hardly understand the meaning of piety. Those with possessions will abandon agriculture and commerce and will live as servants or following various possessions. The leaders, with excuses of fiscal need, will rob and despoil their subjects and take away private property. Moral values and the rule of law will lessen from day to day until the world will be completely perverted and agnosticism will gain the day among men.
"The causes of devotion will be confined to physical well-being; the only bond between the sexes will be passion; the only road to success will be the lie. The earth will be honored for its material treasure only. The priestly vestments will be a substitute for the quality of the priest. A simple ablution will mean purification, the race will be incapable of producing divine birth. Men will ask: what authority have the traditional tests? Marriage will cease being a rite. Acts of devotion, however scanty, will not produce any result. Every way of life will be equally promiscuous for all. Those who own and spend more money will be the bosses of men who will have only one aim, the gaining of wealth however dishonestly. Every man will consider himself as good as a Brahmin. Men will be terrified of death and fear scarcity; by this alone they will keep up an outward appearance of religious feeling. Women will not obey the orders of their husbands or their parents. They will be selfish, abject, liars, fallen and given to evil ways. Their aims in life will be sensual satisfaction only.
"When the practices taught by the Vedas and the institutes of law shall nearly have ceased, and the close of the Kali age shall be nigh, a portion of that divine being who exists of his own spiritual nature in the character of Brahma, and who is the beginning and the end, and who comprehends all things, shall descend upon the earth. He will be born as Kalki in the family of an eminent Brahmin of Sambhala village, endowed with the eight superhuman faculties. By his irresistible might he will destroy all the barbarians and thieves, and all whose minds are devoted to iniquity. He will then re-establish righteousness upon earth; and the minds of those who live at the end of the Kali age shall be awakened, and shall be as pellucid as crystal.
The men who are thus changed by virtue of that peculiar time shall be as the seeds of human beings, and shall give birth to a race who shall follow the laws of the Krita age, the Age of Purity."