A *very* generous 3, instead of 2.5, and only because of the last chapter and the discussion on gravity waves. This was not a book about gravity, but rather, a book on philosophical and religious thought in ancient times up through the Renaissance. I ended up skipping many pages in the earlier chapters; I don't need to know nor do I care what religious thinkers thought about up and down and heaven and Earth 1500 years ago. It took me so long to read such a short book because I would rad a few pages, realize I was bored, and just put it down again. I kept at it instead of DNF just in case there was actual discussion of the physics of gravity, and there was, at the end, just a bit. I'll have to look for a different book, once that focuses on modern physics and gravity.