The next topic to be discussed is the plane of existence where kamma produces rebirth. This requires a short survey of Buddhist Cosmology, the Buddhist picture of the universe.
Buddhism divides the whole of sentient existence into three basic realms:
I. The sense sphere realm
II The realm of fine materiality
III The immaterial or formless realm
The Buddha points out that of all the planes of existence, the most fortunate for one seeking liberation is the human world, for it has a good balance between opposing factors of life. On the one hand, human life is not filled with unbearable suffering. It allows enough leisure, ease and comfort for us to reflect on the nature of existence so that we can develop our understanding. On the other hand, the human world is not so intensely pleasant and enjoyable that we become deceived by pleasures and enjoyment. The lifespan is not so long that it deceives us into thinking that our lives are eternal. It is short enough for us to become aware of the truth of impermanence.
II Realm of Fine Materiality
This is a realm of subtle matter. These states of existence are much purer than even the heavens of the sense-sphere realm. There the mind becomes bright and luminous. The lifespan is incredibly long, lasting for many aeons. And the gross forms of matter are absent. These realms, however, are also impermanent. Life there eventually comes to an end and the person will be reborn elsewhere as determined by his kamma.
III Immaterial or Formless Realm
These states of existence are entirely mental. The mind subsides without any material base, absorbed in pure peace, pure equanimity, for thousands of aeons. In these spheres too life finally comes to an end and the stream of consciousness takes rebirth elsewhere as determined by kamma.
Now the question might be raised whether a person with an education in science can really believe a cosmology like this, which seems to be ancient, outdated and superstitious. Hence I have to give a personal answer. To me the general form of this cosmology seems quite tenable. If we can see the logic behind the law of kamma, and then consider the different kinds of actions people are capable of performing, it becomes clear that there must be different planes of existence appropriate for the maturation of the different types of kamma.
In the case of such evil kamma as killing thousands of people cruelly and heartlessly, for such kamma to meet its fruits the person performing such kamma has to be born in a realm of intense suffering, the hells. On the other hand, if someone has performed very noble deeds such as giving up his limbs, his life or his wealth for the sake of others, if one has a loving and compassionate mind, there must also be a corresponding realm for such kamma to produce its due results. That is the heavenly realms. Also, when we understand the different meditative attainments, the jhanas and the formless attainments, and see how those higher levels of consciousness, are so vastly different from the usual familiar consciousness, it becomes clear that they correspond to other planes of existence. Thus the whole picture fits together quite logically.