There are those of us whose feet are firmly cemented in the empirical, objective truths of science, whose hearts a dedicated to the Buddha's teachings, and whose head negotiates an understanding that makes sense and gives direction to their lives.
Unfortunately approaching the Buddha's teaching from a belief that the scientific method of observation, hypothesis and repeatable experimentation is the only way that truth can be determined means that some teachings must be simply discredited as ‘unprovable', with added subtext that it is all deluded imagination. (see below Bertrand Russell definition of scientism)
It is also possible to ‘prove’ something false by approaching the teachings from a particular point of view (hermeneutics). Because the Discourses are not the exact words of the Buddha (which is true), or at least, that only a minute amount might be verbatim, then there must have been a lot of additions and interpretations. This allows us to form our own interpretation.
We might, therefore, decide that some teachings like rebirth were introduced to align Buddhadhamma with prevailing ideas of reincarnation and so make the Buddhadhamma more palatable. Presuming the Buddha did not teach rebirth or any form of afterlife, puts the Buddha in the annihilationist camp. And this means that Nibbana can only be either momentary or if attainable as a constant state by an occasional person, comes to an end at death. It cannot be a transcendent state beyond space and time, mind and matter,
It is one of our cultural biases that the scientific method is the only way to determine what is true. This is an extreme for it denies that for every individual an inner, personal, private, non-repeatable experience is an event as real as an eclipse of the moon.
The Buddha did not conduct objective experiments to prove his teachings. For instance, there is no instance of control groups where one set is given the Four Noble Truths with the practice of vipassana, another a set of Ignoble Truths and vipassana and a third, no Truths at all with vipassana in order to see which is the quickest way to awakening.
The Buddha's approach is what we would call phenomenological. It is about our personal experience of life. When he talks about the world, he sometimes calls it the All. He is referring not to the objective worlds out there which science investigates, but how we actually sense and feel and react to the inner world that appears in consciousness – the world out there as perceived by the individual, plus all the sensations, emotions and thoughts. The two can be very different. Take time for instance. Scientifically we can measure a minute. But as a personal experience a minute can flash by as we watch a film or crawl by as we wait for the kettle to boil.
When someone who has an out of body experience or a past life recall, such experiences are real for them and often life changing. For them their experiences are as true as gravity. And Nibbana by definition is unprovable to the sciences. The Buddha tells us there is nothing of the material world or the mental world in that experience and yet insists it is never changing and the greatest happiness of all.
If you are one of those who are not entirely convinced of Scientism, the secular belief that that there is only matter and that everything is ‘an emergent property’ out of matter and yet can’t quite get your head around rebirth and a transcendent Nibbana, surely the better position to take is one of ‘don’t know’ or ‘not sure’. We need not feel compelled to come to a conclusion, for so long as honest doubt guides our investigation, we will come to know for ourselves through our own direct experience.
If you don’t know, hang loose. You never know!
Bertrand Russell: Religion and Science p 242: Whatever knowledge is attainable, must be attained by scientific methods; and what science cannot discover, mankind cannot know.
Here are two books, downloadable and donation only, that collect a lot of the sayings from the Discourses around Nibbana and the process of awakening and a book that tackles rebirth. Don’t be put off by the title. It is quite readable.
Rebirth and the Stream of Life: A Philosophical Study of Reincarnation by Mikel Burley