The expansion and contraction of world-systems
According to Buddhist cosmological systems the universe is constituted by innumerable “world-systems” or “world-spheres.” (loka-dḥātu, cakkavāḷa) comprising just thirty-one levels of existence (36). Much as the mind is not static or stable, neither, on a grander scale, are world-systems; they themselves go through vast cycles of expansion and contraction. According to the exegetical traditions of both the Theravādins and Sarvāstivādins, the formula I quoted from the Aggañña-sutta, referring as it does to the rebirth of beings in the realm of Radiance (ābhassara/ābhāsvara) (37) at the time of world contraction, describes this contraction as the result of destruction by fire. Both Buddhaghoṣa and Vasubandhu provide some further details about how the destruction proceeds (38). According to Buddhaghoṣa, world-systems contract in great clusters - he speaks of a billion (koṭi-sata-sahassa) world-systems contracting at a time (39). Both writers describe how, when they contract, world-systems contract from the bottom upward. Thus in the case of destruction by fire, the fire starts in the lower realms of the sense sphere and having burned up there, it invades the form realms; but having burned up the realms corresponding to the first jhāna/dhyāna, it stops. The realms corresponding to the second, third, and fourth jhānas, and the four realms, are thus spared the destruction. But destruction by fire is not the only kind of destruction, merely the most frequent - water and wind also wreak their havoc. When the destruction is by water, the three realms corresponding to the second jhāna are also included in the general destruction, while destruction by wind invades and destroys even the realms corresponding to the third jhāna. Overall, only the seven realms corresponding to the fourth jhāna and the four formless realms are never subject to this universal destructions (40).
So what becomes of the beings that occupy the lower realms when fire, water, and wind wreak their destruction? They cannot disappear from saṃsāra; they must go somewhere. Here we touch upon a question which passed something of a problem in the Buddhist tradition and to which its answers are not entirely consistent. The simply answer is that Buddhaghoṣa gives in the Visuddhimagga is that at the time of the destruction of a world-system by fire, all the beings that occupy the lower realms - including hell beings (nerayika) - are reborn in the Ābhassara Brahma realm (corresponding to the second jhāna) or above it. But since rebirth in the Brahma realm can only occur as a result of the practice of the jhānas Buddhaghoṣa has a problem. The chaos and hardships that are a prelude to the destruction of the world are hardly conducive to the practice of jhāna. Moreover, certain beings simply do not have the capacity to attain jhāna even if they try. [quote]There is no rebirth in the Brahma world without jhāna, and some beings are oppressed by the scarcity of food, and some are incapable of attaining jhāna. How are they reborn there? By virtue of jhāna acquired in the Deva world. For at that time, knowing that in a hundred thousand years the aeon will come to an end, the sense-sphere gods, called ‘Marshals of the World,’ loosen their head-dresses and , with dishevelled hair and pitiful faces, wiping their tears with their hands, clothed in red and wearing their garments in great disarray, come and frequent the haunts of men saying, “Good sirs, a hundred thousand years from now the aeon will come to an end: this world will be destroyed, the great ocean will dry up, and Sineru, king of mountains, will be burnt up and destroyed. The destruction of the world will reach the Brahma world. Develop loving kindness, good sirs. Develop compassion, sympathetic joy, and equanimity. Take Take care of your mothers and fathers; honour the elders of the family.” Hearing their words, both men and the deities of the earth are for the most part moved; they become kind to one another, and making merit by loving kindness and so on, they are reborn in the Deva world. There they enjoy the food of the gods and having completed the initial world on the air kasiṇa, they attain jhāna.
However there are others who are reborn in the Deva world by virtue of their kamma “that is to be experienced at an unspecific time.” for there is certainly no being wandering in saṃsāra devoid of kamma that is to be experienced at an unspecified time. They also similarly acquire jhāna there [in the Deva world]. So all beings are reborn in the Brahma world by virtue of their attainment of jhāna.