When I asked my teacher about why some physical descriptions in the bible or medical practices in the talmud seem impossible/wrong today he told me that the physical nature of the world changed, which he called meshane hateva. As a source he cited a mishna at the end of Sotah which talks about various curses to the physical world after the temple was destroyed. I'd like to know more about this idea. Are there any other, more explicit sources for it? Did things change all at once or gradually? Why do we still abide by certain health-related ideas from the talmud like not mixing fish and meat while not following others like turning a mill to relieve fever? Thank you.