Question

Why did Feynman tell “we cannot locate earth's angular position, but we can tell that it is changing”?

Answer 1

IT meant that physics is invariant under a global rotation of co-ordinates, but even a uniform rotation would be detectable - e.g. through Newton's bucket and its GTR equivalents (accelerometers on a frame of nonzero extent that will tell us whether the frame is being Lie-dragged as it moves through time, Lense Thirring effect and so forth). We can of course make observations of different objects and check whether we have rotated relative to them. I'm guessing he means that we can't really rule out that these distant objects hadn't decided to up and shift together to produce an apparent .