While gravitational redshift refers to what is seen, gravitational time dilation refers to what is deduced to be "really" happening once observational effects are taken into account. When using special relativity's relativistic Doppler relationships to calculate the change in energy and frequency (assuming no complicating route-dependent effects such as those caused by the frame-dragging of rotating black holes), then the Gravitational redshift and blueshift frequency ratios are the inverse of each other, suggesting that the "seen" frequency-change corresponds to the actual difference in underlying clockrate. Route-dependence due to frame-dragging may come into play, which would invalidate this idea and complicate the process of determining globally agreed differences in underlying clock rate. [/b] http://en.wikipedia.org/wiki/Gravit...l_redshift_versus_gravitational_time_dilation == So is *all* the perceived gravitational time dilation due to the gravitational redshifts?? Because when a clock is traveling away from you, and its light is redshifted, part of the reason why you perceive the clock to have slowed down is because the light (which contains the information of the clock ticks) takes longer and longer to get to you, but the tick rate doesn't change* It's easy to visualize if you imagine the clock is moving away at relativistic speeds. Of course there is also the "innate" time dilation due to the speed of the clock. The twin paradox wikipedia article goes into all of that in amazing detail. But I guess this is not the case for gravitational time dilation (?) *well it actually does get shorter. but even if it did not, this would still be a source of perceived time dilation (the fact that the light from it is redshifted because it's moving away from you). and I'm wondering if this is the sole source of gravitational time dilation or not.