What is "time?"
Although one might assume that time is a fundamental aspect of reality, it is in fact a feature only of the material world. Time as we know it does not exist in the spiritual world. As difficult as it is to comprehend, in the spiritual world things take place even though there is no past or future.
Without time, nothing happens in the material world. As the most powerful force in the world, time is considered Krishna (as He says in the Bhagavad-gita). Time controls everything, and Krishna controls time. With the rising and setting of the sun, everyone’s life is diminished by the influence of time.
Time is relative. A year in higher planetary systems is much longer than a year on earth, and beings on higher planets live for extremely long periods of time by our estimation.
Time on earth moves in cycles of four eras, each era lasting hundreds of thousands of years. In the first era, known as Satya, human civilization is enlightened, but things begin to degrade in the next two eras, Treta and Dwapara. When we reach the Kali era (which we are currently in), civilization sinks more and more into chaos and ignorance. At the end of the Kali era, a partial universal destruction occurs, and a new cycle begins again with Satya. The cycle repeats itself one thousand times in each day of Brahma, the engineer of the universe.
The Vedic conception of time and history is thus much more expansive than that of the West, giving us a startling image of just how fleeting is our life in the human form. The Vedas stress that we should use every precious moment of human life for self-realization.