Now you try to understand what is the age of Brahmā by calculating one day. Your sahasra-yuga, we have got four yugas, Satya, Tretā, Dvāpara, Kali—these are called four... This calculation is forty-three hundred thousands of years. That is the sum total of the four yugas. Eighteen, twelve, eight, and four. How many it comes? Eighteen and twelve? Thirty, and then eight, thirty-eight, then four. This is rough calculation. Forty-two, forty-three. Sahasra-yuga-paryantam. So so many years, sahasra-yuga-paryantam ahaḥ. Ahaḥ means day. Sahasra-yuga-paryantam ahar yad brahmaṇo viduḥ (BG 8.17). This is the one day of Brahmā. One day means morning to evening. Forty-three hundred thousands of years your calculation. Therefore these things are to be understood through the śāstra. Otherwise, you have no knowledge. You cannot calculate. You cannot go to Brahmā, you cannot go even to the moon planet. And what to speak of Brahmaloka is the ultimate, the remotest part of this universe. So by your direct experience, you cannot calculate, and neither you can go. They estimate, the modern aeronautics, they estimate, that in order to go to the topmost planet will require forty thousands of years by going in the light year. Just like light year, we have got calculation.
So we cannot estimate by direct perception, even in this material world, and what to speak of the spiritual world. Not (possible.) Panthās tu koṭi-śata-vatsara-sampragamyo vāyor athāpi manaso muni-puṅgavānām (Bs. 5.34). By mental, muni-puṅga means mental speculation. You can go on mental speculating, but if you do even for many hundreds and thousand of years, it is not possible to calculate. You have to accept this truth through the śāstra; otherwise, it is not possible. Therefore Kṛṣṇa said, nityasyoktāḥ śarīr-ukta. Ukta means it is said. Not that "I am presenting some dogma," although He can do so. He's Supreme Personality of Godhead. This is the method. Unless there is ukta, said by authorities, previous authorities, ācāryas, you cannot say anything. This is called paramparā. You try to understand with your intelligence, but you cannot make any addition or alteration. That is not possible. Therefore it is called nityasyoktāḥ. It is said, it is already settled. You cannot argue. Nityasyoktāḥ śarīriṇaḥ anāśino 'prameyasya (BG 2.18), immeasurable.