The young specialist in English Lit, having quoted me, went on to lecture me severely on the fact that in every century people have thought they understood the Universe at last, and in every century they were proven to be wrong. It follows that the one thing we can say about out modern "knowledge" is that it is wrong.
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In the early days of civilization, the general feeling was that the Earth was flat. This was not because people were stupid, or because they were intent on believing silly things. They felt it was flat on the basis of sound evidence.
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Another way of looking at it is to ask what is the "curvature" of Earth's surface. Over a considerable length, how much does the surface deviate (on the average) from perfect flatness. The flat-Earth theory would make it seem that the surface doesn't deviate from flatness at all, that its curvature is 0 to the mile.
Nowadays, of course, we are taught that the flat-Earth theory is wrong; that it is all wrong, terribly wrong, absolutely. But it isn't. The curvature of the Earth is nearly 0 per mile, so that although the flat-Earth theory is wrong, it happens to be nearly right. That's why the theory lasted so long.
There were reasons, to be sure, to find the flat-Earth theory unsatisfactory and, about 350 B.C., the Greek philosopher Aristotle summarized them. First, certain stars disappeared beyond the Southern Hemisphere as one traveled north, and beyond the Northern Hemisphere as one traveled south. Second, the Earth's shadow on the Moon during a lunar eclipse was always the arc of a circle. Third, here on Earth itself, ships disappeared beyond the horizon hull-first in whatever direction they were traveling.
All three observations could not be reasonably explained if the Earth's surface were flat, but could be explained by assuming the Earth to be a sphere.
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In short, my English Lit friend, living in a mental world of absolute rights and wrongs, may be imagining that because all theories are wrong, the Earth may be thought spherical now, but cubical next century, and a hollow icosahedron the next, and a doughnut shape the one after.
What actually happens is that once scientists get hold of a good concept they gradually refine and extend if with a greater and greater subtlety as their instruments of measurement improve. Theories are not so much wrong as incomplete.