Ben: we can know what influenced chazal, because there are many historians running around with thousands of artifacts, and lots of data from different periods/areas that chazal lived in. And regarding the earth debate, it is a machlokes in a gemara, there are different opinions. But the fact is there are Amoraim who hold it wae flat.
Sam2: all I know is be teaches at YU (in Jewish studies I believe). That aside, certain dinim are objective and should be in place forever- like Shabbos, kashrus, Talmud Torah, tznius, taharas hamishpachah, etc. however, there are other areas that are more flexible. Such as being maikil on cholov yisroel, shaking a woman’s hand, leaening secular studies, etc.
These are all areas where obviously innovation has occurred within the halachic system. L’olam va’ed certainly doesn’t apply to say, cholov yisroel! So explain that to me Sam. What’s the big heker? I’m ssking this seriously, since I respect you as someone that cares about Halacha and knowing mekoros well.