Actually I did imply that "we have known" when I claimed that Ptolemaic cosmology was the functioning scientific model of the universe, which shaped the Middle Age and Medieval worldview. You see Ptolemy used this thing called math when determining the size of the universe and the Earth in relation to it, which, as a field, has held fairly static over the past 1800 years or so relative to the fields of physics and biology. The fact is that "we" refers to the experts on a given field of knowledge because, in truth, we (the rest of us) are reliant upon them for information. The fact is that few, if any, lack the means (by way of education and/or technology) to know any of these things first-hand; therefore, we rely upon the experts to give us guidance.