A supplementary remark on a footnote in my forthcoming (but already submitted) dissertation:
The fact that there is no intuitive endpoint in the past – perhaps other than the Big Bang – does not mean there is no floor/asymptote to our epistemic modality regarding the past. The lack of an intuitive end to the infinitely projecting past doesn’t prevent an asymptote at 0% in subjective certainty, similar to the infinitely projecting future.
There does remain asymmetry in the structure of our subjective certainty about the past and the future, due to three factors that do not similarly complicate the future:
(1) autobiographical memory: Before this develops, everything would fall into the domain of evidentiality. A point near one’s birth (‘near’ here means ‘a few years after’) would thus be a major transition point for the epistemic modality of the past.
(2) history/records: At least we have written or oral records for periods of recorded history, but we can only theorize about “prehistoric” times. Fossils and experimental physics may help us a bit.
(3) The Big Bang: The precise impact of this on our folk knowledge of the past is unclear. (Many people may not even have heard of the Big Bang.)
In sum, the ‘unevenness’ of the “past modality” reveals itself in terms of sources of knowledge – being more restricted, first from a wide variety including one’s direct perception, to historians and archeologists, then to physicists (plus, there’s always one’s own speculation). The “future modality” isn’t uneven in the same manner, and it therefore isn’t exactly symmetric to the “past modality,” although both may be roughly monotonically decreasing with greater distances from the present.