In many Suttas the Buddha presents kamma and vipaka as the idea that certain types of intentional action have certain experiential outcomes. For example, in AN IV 232 we have:
""And what is kamma that is dark with dark result? There is the case where a certain person performs a harmful act of body, speech, or mind. He rearises in a harmful world where he is touched by harmful contacts...he experiences feelings that are exclusively painful, like those of the beings in hell..."
There are lots of other versions. My specific question is about the mechanism that brings this about. I would like to know people's thoughts on how this occurs. I don't think it is a stupid question, as normally we think of intentions as bringing about an immediate mental change (as when I intend to think about an elephant, or recollect things that make me happy); or bringing about an immediate physical change (as when I intend to raise my arm, etc.). The rest of the universe seems immune and indifferent to my intentions. I cannot cause a change in the weather by means of an unmediated intention. Nor can I alter your thoughts by merely intending to.
But the Buddha talks often of contact and feeling arising as a result of kamma made a while before. Intention acts, as it were, at a distance.
"Wherever one's selfhood turns up, there that kamma will ripen. Where that kamma ripens, there one will experience its fruit, either in this very life that has arisen or further along in the sequence". (AN III 33)
This does not seem to be one of those questions that the Buddha said should not be asked. The "exploding head" questions about kamma seem to be about predicting vipaka from kamma, not this simple point of the exact constant relation between kamma as a class of phenomena, and vipaka as another class.
(Lots of contemporary Buddhists try to solve this one in purely psychological terms. They talk in terms of intentions and actions conditioning the mind which thereafter experiences contacts differently as a result. But the Buddha's formulations seem to go way beyond these, referring as they do to contact being vipaka, and the vipaka cropping up after the demise of this body. Contact obviously has a willed aspect in that we select objects for attention, but I am less interested in why I notice being run over by the bus, and more interested in what brings the bus as the other component of contact...)
If the answer is that this must be taken on faith, I am happy with this. I would in fact prefer it to sophistry intended to demonstrate that someone knows more than me. All vague ideas and admissions of bafflement are welcome, as they would reassure me!
My thanks and best wishes.