I’m back, after a hiatus. At long last, since I’ve had a lot of time to think about it in the meantime, I’m dealing with the subjects of death and rebirth.
Among other concepts, the traditional Buddhist six realms of rebirth seem to be inherited from Hinduism, which is to be expected given Buddhism’s roots. As for how rebirth is supposed to work under these circumstances, look at the literal description: being reborn as a different life form, but retaining the knowledge of the previous life forms. According to this view, any knowledge from previous lives has to be stored independently of the form, and in a format compatible with all possible forms, which is a problem. Also, this view assumes that what you are is stored entirely in your knowledge, which is another problem, as your form also affects you: what you do, how you react, and the like. Furthermore, someone else who gains your memories won’t become you; at best, they may interpret some of those memories the same way you do. Your memories may influence them, but influence is not the same as identity. (The technological goal some people have of achieving immortality by copying their consciousness into a computerized form not subject to ordinary human limits has this same discrepancy. Running the same software on two different kinds of hardware, so to speak, will not give the exact same results for both.) The alternative to it all is to just look at what’s there with regard to rebirth. Both your knowledge and your associated form change from moment to moment. Who and what you were five minutes ago, or even a split second ago, is not who and what you are now. Rebirth is therefore a continual process, just another form of change and, hence, impermanence. You cannot be reborn as another life form in the literal sense because of anatman: there is no permanent you. As such, the six realms would be metaphorical states of mind, rather than literal places.
(As an aside, with regard to forms, I’ve always found the pretas to be the most fascinating in terms of imagery. They’re the embodiment of a self-imposed addiction, an inability to appreciate what fills the void for more than a moment, if they can appreciate it at all. “I’ll never be happy until I have this bright shiny thing! Okay, I have it. Now I’ll never be happy until I have this even newer bright shiny thing!” There’s also another interesting form mentioned in the Brahmajala Sutta of the Digha Nikaya: the unconscious devas. These seem to be the embodiment of quietism, of the idea that blocking out all thoughts is the solution to the problem of duhkha. Eventually, of course, they’re supposed to have conscious thoughts in spite of this, and these thoughts kill them and lead them to be reborn elsewhere. In a similar vein, ordinary humans who try to stop all thinking the same way will eventually fail the same way, although their thoughts will, of course, be non-lethal.)
Compared to the above framework, rebirth in Sukhavati according to the Pure Land viewpoint is much simplified. The goal is simply to be reborn under the optimal conditions there, and the only other realms accessible for rebirth after that are the human and deva realms. The latter is apparently an extension of Sukhavati’s egalitarianism, as humans and devas are supposed to be practically indistinguishable there. Additionally, per the Larger Sukhavativyuha Sutra, a practitioner is supposed to see a vision at death, either of Amitabha and his entourage personally, or a facsimile practically indistinguishable from it (presumably unless the practitioner isn’t one with Amitabha already). This is a recurring metaphorical theme: all distinctions between human and deva, supposed reality and vision, and Sukhavati and the myriad other Pure Lands it encompasses, become blurred, and the false concept of duality is effectively broken.
For the sake of argument, I’ll also take a materialist tack. The idea of having your existence cease upon death is dubious, as you have to properly determine exactly what ceases to exist for that to make sense. It can’t just be consciousness, since you can be unconscious without being dead. It also can’t just be the matter and energy of the body and mind, since both do begin to decay but do not disappear immediately upon death. Additionally, living things can be revived under limited circumstances after being dead for a short time. Also, all cells in the living body continually die and are replaced until, given enough time, the body as a whole has been replaced. Furthermore, having things cease to exist, as opposed to having them merely change into other things (as parts of them do throughout existence anyway), violates the law of conservation of mass. In short, everything gets further muddled. There seems to be the same kind of flawed connective logic here as in Descartes’ axiom: “I think, therefore I am.” It sounds good until you look at the implications in enough detail, at which point the two qualities show themselves as correlating in some instances, but effectively separate. “The chair I’m sitting in must think, because it is.”
In the end, focusing on any metaphysical issues of death and/or rebirth will lead to speculation due to lack of evidence. The aforementioned Brahmajala Sutta goes into much detail about avoiding this (also with other forms of speculation not related to death and rebirth). While it does assume that memories attributed to past lives are actually from said lives, it cautions against extrapolating anything from them; for example, if you remember only so many eons of past lives, you can’t draw the conclusion that you’ve existed for eternity based on that, since you don’t remember eternity.
On the scientific side, science can provide more than enough details of the decay of the physical form upon death; that isn’t in question. What is in question is whether there’s more to it than the physical form. Regardless of belief, the only way to know for certain what happens after death is to either wait until science advances to the point where it can tell us, or, failing that, to die and see for oneself. The character of Lazarus Long in Robert Heinlein’s Time Enough For Love covered this succinctly: “Soon enough you will know. So why fret about it?”