I have been reading a lot of relativity-related material and clearing up a few gaps in my general knowledge. I read something that struck me as off. Perhaps I am missing something. Usenet Physics FAQ -> The Relativistic Rocket http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html [Broken] In the set-up: "If a rocket accelerates at 1g (9.81 m/s2) the crew will experience the equivalent of a gravitational field with the same strength as that on Earth." Presumably this means the entire crew will experience the same acceleration - at the leading and trailing ends of the ship, for instance. Later, we are told that: "inside the rocket, a clock attached to the rocket's ceiling (i.e. furthest from the motor) ages faster than a clock attached to its floor." Then in the next paragraph: "it tells us something fundamental about gravity, via Einstein's Equivalence Principle. Einstein postulated that any experiment done in a real gravitational field, provided that experiment has a fairly small spatial extent and doesn't take very long, will give a result indistinguishable from the same experiment done in an accelerating rocket. So the idea that the rocket's ceiling ages faster than its floor (and that includes the ageing of any bugs sitting on these) transfers to gravity: the ceiling of the room in which you now sit is ageing faster than its floor; and your head is ageing faster than your feet. ... This difference in ageings on Earth has been verified experimentally. In fact, it was absolutely necessary to take into account when the GPS satellite system was assembled." Now, I had been under the impression that differences in clock speeds at different altitudes were due to the gravitational field being weaker at higher altitudes. I understand that once we start expanding the width or height of our accelerating laboratory, we can make measurements to tell whether we are in acceleration vs gravitational field. Does the clock at the "top" of this accelerating frame indeed tick faster than one at the floor? Is the reason for this indeed analogous to clocks ticking *faster* at higher altitudes above the Earth's surface? Is the reason for gravitational time dilation closer to a massive body related or unrelated to the *greater* strength of the gravitational field there? Does a local measurement of acceleration/g-forces at the top of the accelerating frame differ from a measurement at the bottom? I would not have thought so. Even if it is true, I would have taken the gravitational difference in clock speeds near Earth to be something that could NOT be noticed or simulated for an observer in an accelerating box, such as by measuring clock speed at the leading vs trailing end. Thank you.