We have discussed about brahmāstra. It is almost similar to the modern nuclear weapon or bomb, but it is made with chemicals, but this brahmāstra is made of mantra. That is the subtle way. Modern science has not reached to that point of subtle existence. Therefore they cannot understand how transmigration of the soul takes place. The modern science has no knowledge. Imperfect knowledge. They see the gross body, but they have no knowledge about the subtle body. But the subtle body is there. Just like we do not see your mind, but I know that you have got mind. You do not see my mind, but you know that I have got mind. Mind, intelligence and ego. My conception, identity, "I am," that conception is there. That is ego. And my intelligence and my mind, you cannot see, neither I can see. Therefore how the mind, intelligence and personal identity, or egotism, carries the soul to other body, they do not see it. They cannot see it. They see the gross body is stopped, everything is stopped. The gross body is burned into ashes; therefore they think everything is finished. Bhasmī-bhūtasya dehasya kutaḥ punar āgamano bhaved (Cārvāka Muni). The atheist class, they'll think like that. With poor fund of knowledge, they think that "I see the body is now burnt into ashes. Then where is the soul?" So "There is no soul, there is no God, it is all imagination." But that is not the fact; not that is the fact. The fact is that the gross body is finished, but the subtle body is there. Mano buddhir ahaṅkāraḥ. Bhūmir āpo 'nalo vāyuḥ khaṁ mano buddhir eva ca (BG 7.4). Apareyam itas tu viddhi me prakṛtiṁ parām (BG 7.5). So the action and reaction of the subtle thing, subtle matter... Mind is also matter, but subtle matter, very fine. Just like sky, ether. Ether is also matter, but it is very subtle, fine. And finer than the ether is the mind, and the finer than the mind is the intelligence. And finer than the intelligence is my egotism: "I am," this conception.
So they have no knowledge. Therefore they can manufacture weapon or bomb with the gross things. Bhūmir āpo 'nalo—the chemicals, that is gross. But this brahmāstra is not gross. This is also material, but it is made of subtle things: mind, intelligence and ego. Therefore Arjuna is asking Kṛṣṇa, "I do not know wherefrom it is coming, wherefrom this such high temperature is coming." It is stated here, tejaḥ parama-dāruṇam (SB 1.7.26). The temperature is so high, intolerable. So we should ask the authority. Kṛṣṇa is the best authority. So Arjuna is asking from Him, kim idaṁ svit kuto veti: "My dear Kṛṣṇa, wherefrom this temperature is coming?" Kim idam. Deva-deva. Why he's asking to Kṛṣṇa? Because Kṛṣṇa is the deva-deva.