Generally speaking, the last –life Bodhisattvas would stay in the Tusita before they descend to the human realm and obtain enlightenment (Buddha-hood). The births of the Buddhas can be observed through the aspects of space and time. From the aspect of space, the doctrine of the tri-sahasra-mahā-sahasra-loka-dhātu (trichiliocosm)” can be found in the early Buddhist texts. The Yogacarabhumi-sastra and other texts further state that the world systems within trichiliocosm shall be renovated and destructed altogether. The highest realm of the trichiliocosm is said to be “brahmaloka”, however, this word can be referred to as the first dhyāna realm, or it can also go as broad as to include the whole Form Realms and even the Formless Realm. Therefore, the concept of trichiliocosm contains the diversity of Buddhist cosmology, including the world structure, the process of renovation, destruction and duration of both, the increase and decrease of human life-span etc. A trichiliocosm is a Buddha-field, domain of one Buddha’s teaching career. This is in compliance with saying of the sutras; yet, Buddha’s activity can extend beyond his field. This can also lead to the reflection on the meaning of this world being finite or infinite. The concept of Buddha-field suggests that there are Buddhas in ten directions. The doctrine of “one-Buddha-only” emphasizes that there is only one Buddha throughout the world, who can give teachings to countless sentient beings according to their own potentials. Yet merely from the concept of “Buddhas in ten directions” still is not enough to express what said the Mahayanasajgraha: Innumerable sentient beings accomplish their practices simultaneously, and births of Buddha should not be only in a sequential order. the plurality of Buddha is affirmed. The significance of bodhisattva doctrine in Mahayana should be understood as emphasis on bodhisattva practice and there are innumerable bodhisattvas simultaneously accomplished their practices in different Buddha-field. From the aspect of time, Early Buddhist texts confirms the possibility of many Buddhas in the future. There are different understandings on what the term “bhadrakalpa(auspicious eon)” actually means. The concepts of Thousand Buddha of the Bhadrakalpa” , and “Five hundred Buddha of Bhadrakalpa” appeared in later times. Moreover, some opined that these Buddhas of Bhadrakalpa can be seen as the at-the-same-time Buddhas. According to the unanimous traditions of all the schools of Buddhism, Maitreya is the Buddha next to Gautama Buddha. There are three contexts to know the time Bodhisattva Maitreya, now living in Tusita, will descend to the human realm: 1. cycle of renovation, destruction of the world. 2. life-span of Tusita beings. 3. decline of Gautama Buddha’s dispensation. Life-span of Tusita beings is equivalent to 576,000,000 of human years according to early Buddhist texts, Chinese Buddhist texts, however, saw a variety of traditions as to when Buddha Maitreya will appear. We may see it same as what Chih-pan put: “Discourse of Buddha is consistent, the seeming discrepanc
