Now yuga means these four yugas: Satya-yuga, Tretā-yuga, Dvāpara-yuga and Kali-yuga. So these four yugas . . . satya-yuga means eighteen lakhs of years. Means eighteen hundred thousands of years. And Tretā-yuga means twelve hundred thousands of years. And Dvāpara-yuga means eight hundred thousands of years.
And Kali-yuga means four hundred thousands of years. This is the rough calculation. Eighteen, then twelve, then eight, plus four. How many years? Eighteen plus twelve becomes thirty, and thirty plus eight, thirty-eight, and four. That means forty-three hundred thousands of years makes one yuga, divya-yuga. So such one thousand. Sahasra-yuga-paryantam (BG 8.17). That means forty-three hundred thousands of years multiplied by one thousand, ahar yat. That calculation is one day of the inhabitants of the Brahmaloka.
So we cannot imagine, you see, that how long year. Such hundred years they live. That is their twelve hours. Similarly, twelve hours night. Similarly, thirty days, one month. Similarly, twelve months equal to one year. Such hundred years they live. So we cannot imagine even, even in the material world, how long a living entity can live even in this material world. So these are acintya. Acintya means beyond our conception. And what to speak of the spiritual world? We cannot calculate even anything of the material world perfectly.
Therefore the best thing is our process, Vedic process, is to receive knowledge by the ascending (descending) process. Kṛṣṇa has come from His kingdom, kingdom of God, the Kṛṣṇaloka. And it will be explained in the next verses:
- yadā yadā hi dharmasya
- glānir bhavati bhārata
- abhyutthānam adharmasya
- tadātmānaṁ sṛjāmy aham
- (BG 4.7)
He comes and He sends His own, I mean to say, confidential sons or servants to give us information of the spiritual world of God, or everything, both material and spiritual. This knowledge is perfect knowledge. We have to receive from the authority. In the material world also.
Now some students, they come here to learn scientific knowledge because it is understood Western countries, they're advanced in scientific knowledge. So why they come? Because they think that Western scientists are authorities. The process is there: to receive knowledge from authority. Similarly, some serious students, they go to India, they try to search out some saintly persons to receive knowledge about the spiritual world.
Actually, it is a fact that if you want to know about spiritual knowledge then you have to know it from India. That is recommended by one Chinese gentleman; I forget his name. His book is recommended as study book in the New York University. He has plainly written that if you have to understand the science of religion, then you have to go to India. He has clearly said that.