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Published online by Cambridge University Press: 17 May 2016
1. In the late 18th century, portable clocks came into use in maritime navigation. This elementary advance was based on the then-untheorized relationship between time and space: if you knew what time it was and had a good fix on a star, you could know where you were. Some years ago two very precise atomic clocks were put aboard separate airplanes that went around the world in opposite directions. When they got back to the point where they started, they read differently and predictably in light of Einsteinian theory. The objective relativity of time and space was confirmed.Google Scholar