Today I got to drive by the Gap town clock. This cool clock tower is in a town not far from Lancaster, Pennsylvania that I have passed many times in my travels. I wish I knew its story, but that will need to wait for a later installment. Regardless it looks very interesting and has shingles on the side in different patterns that add to its appeal and completely fit with the kitchy country designs prevalent in Lancaster.
The clock is at a height above the ground and will always run faster than a clock at ground level due to the theory of relativity. The difference would be unmeasureable but mentioning it allows me to point out that today is the 100th year anniversary of Einstein publishing his seminal paper on relativity. A paper that changed the world.
Go find the paper and read it or find someone's exposition of the theory. In short - time and space are relative, it is the speed of light that is constant for all observers in all reference frames. That insight makes the theory.