I would like to know the basic experimental observations or the logic which prove that the 3-d space which we inhabit is a close approximation of Euclidean Geometry. is it because parallel lines don't appear to converge or diverge? But how is this established, as we can't draw perfect straight lines. Do we observe behavior of parallel rays of light in vacuum or something similar. I am not concerned about the 4-d space-time . Just the good ol' 3-d space . . I am a beginner so it would be good if you direct me to websites where related info is given .