The brahmastra is similar to the modern nuclear weapon manipulated by atomic energy. The atomic energy works wholly on total combustibility, and so the brahmastra also acts. It creates an intolerable heat similar to atomic radiation, but the difference is that the atomic bomb is a gross type of nuclear weapon, whereas the brahmastra is a subtle type of weapon produced by chanting hymns.
It is a different science, and in the days gone by such science was cultivated in the land of Bharatavarsa. The subtle science of chanting hymns is also material, but it has yet to be known by the modern material scientists. Subtle material science is not spiritual, but it has a direct relationship with the spiritual method, which is still subtler. A chanter of hymns knew how to apply the weapon as well as how to retract it. That was perfect knowledge. SB 1.7.27
It is a different science, and in the days gone by such science was cultivated in the land of Bharatavarsa. The subtle science of chanting hymns is also material, but it has yet to be known by the modern material scientists. Subtle material science is not spiritual, but it has a direct relationship with the spiritual method, which is still subtler. A chanter of hymns knew how to apply the weapon as well as how to retract it. That was perfect knowledge. SB 1.7.27