Hello! I have been reading up on Buddhism here and there, and have some doubts regarding some stuff I have read. Here are some of the questions I have been having.
1. In a lot of places, I see references to living beings and references to sentient beings. How exactly are these terms defined? Are they refering to the same thing or are these terms different? Is it possible to be reborn as a non-sentient being? Like say an amoeba or a bacteria? I see this as a problem because it isn't really agreed upon as to which beings are sentient, I have seen non-vegetarians argue that no beings apart from humans are sentient, while vegetarian groups often state that it is very likely that the animals we normally eat probably have some degree of sentience, although they probably don't have any doubts regarding single celled organisms.
2. Bodhisattvas are supposed to work for the complete enlightenment of all sentient beings right? (again the issue with sentience) However, I remember reading somewhere that there are infinite worlds and universes, and thus infinite sentient beings. Doesn't it logically follow that the work of a Bodhisattva will never be complete? If a Bodhisattva delays Buddhahood till the complete enlightenment of all sentient beings, then this means that he or she would never attain Buddhahood right?
3. When reading the Jewel Ornament Of Liberation, specifically the chapter about the suffering of samsara, which contains stuff about hells, it is mentioned that there are hells some distance below the ground. Although we really haven't excavated very far into the Earth's crust, wouldn't it be safe to conclude that this really isn't true? Metaphysical concepts such as deities are easy to swallow, however it is very jarring when something about the world is mentioned which we can confirm to be not true. If enlightened beings are omniscient, how is it possible for them to be wrong about the world?
4. I have read about Rebirth in Buddhism, and it sort of makes sense to me, but when people talk about for example a Lama being reincarnated, how is it possible without the existence of an unchanging self? Are they still talking about rebirth, or something different? I thought reincarnation was an idea from other religions which posit the existence of an unchanging, permanent self.