Just reading the cosmology chapters in an introductory astronomy text would suffice. PEM was careful to describe the limits of scientific knowledge of the universe to those regions of the universe that were observable. Although he clearly allowed for non-observable regions as well, he excluded them from science because they could not be tested. Scientific theories are valuable only if they are testable. He was careful to point out that understanding does not require testing.
Knowledge springs only from empiricism.
Latitude and longitude lines lack physical substance, but have a substantial effect on our concepts of physics. Their effects as models are very real. PEM expressed the opinion that language might be too culturally constrained to suffice as descriptor of the scientific universe. Even mathematics is insufficient because mathematical theories are also incapable of explaining their own foundations. Towards the end of the class the matter of time was briefly introduced.