# Relativity and earth's rotation

I read recently an old piece of Cecil’s about the effect of the rotation of the earth on aging at the poles vs. at the equator. (For the piece, go to http://www.straightdope.com/classics/a4_183.html)..) The main point is that clocks at sea level at the poles run in perfect synchronization with the poles at the equator. The effects of Special Relativity, which slow the clocks at the equator, exactly cancel the effects of general relativity which speed them up. The reasoning was not given however. The bulge of the sea at the equator results in an equal net force on any object at sea level around the world. (This is basically the principle that water seeks a constant level.) Thus, there is a symmetry in the problem, which leads to a cancellation of the effects. What is interesting is that if you are to change the altitude of one of the clocks, or have it run on a track around the globe at sea level, then it will go out of synchronization. Thus, clocks on sattelites are out of synch, as are clocks in Colorado.
A discussion of the studies of this effect on GPS sattelites is at http://www.metaresearch.org/mrb/gps-relativity.htm .

Since this is about Cecil’s column and not about a Mailbag Answer, I am closing the topic here and moving it to the forum called “COMMENTS ON CECIL’S COLUMNS.”

proulx

I’m not sure I would characterize it as there being an equal net force on any object at sea level around the world. Rather, sea level is an equipotential surface–everything at sea level has the same potential, around the world.

Oh, the link gets mangled with the parenthesis and period at the end. Here is another link: Do you age more quickly at the pole than than equator due to relativity?

rocks

Hey, I cut and paste the title of that link. The “than than” is sic!