Do GPS signals really travel slower eastward, and does that support geocentrism?
A viewer says he has read that GPS signals travel slower eastward, from San Francisco to New York, than westward, and asks whether, since the universe moves around the earth from east to west, the light should travel differently.
Answer
You have it almost right. In the geocentric model the earth is fixed and the universe rotates around it from east to west. So a light beam sent westward, with the rotating universe as its medium, travels faster, while a beam sent eastward, against that motion, meets resistance and travels slower. The difference between the eastward and westward light is about fifty nanoseconds, which sounds tiny but is very significant for GPS; it can be the difference between landing you in New York City or in a ditch. This is the problem: an electromagnetic signal sent east to west arrives at a different time than one sent west to east, which means the speed of light is not truly constant. Einstein faced two choices, a fixed earth at the center or a constant speed of light, and he chose the constant speed of light, and modern science has defended that for a hundred years because relativity and all of cosmology rest on it. So rather than admit the variance, the GPS computers are simply programmed to treat the speed of light as constant, because to admit otherwise would point to a fixed earth at the center, and therefore to a God who put it there.