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In another related question: How to connect Einstein's Special Relativity (SR) with General Relativity (GR)? , John Rennie stated that SR is a subset (or rather can be derived from) GR, but not vice versa.

I've also sifted through other related questions on the stack, but it's still not clear to me that if a physicist is trying to calculate time dilation if both SR and GR have to be considered.

In other words do speed and gravitation independently have effects on time dilation?

Or in all conceivable situations can one just apply the field equations of GR and be done with it?

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  • Oops, I keep forgetting I have god-like powers in the [general-relativity] tag these days. docscience, if you're unhappy with your question being closed shout and I'll withdraw my close vote. – John Rennie Jan 21 '15 at 16:10
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    The field equations give you the relation between the "matter field" and the curvature of spacetime, defined by the metric. The metric gives you the infinitesimal "line element" at each point in your chosen coordinate system (see this answer), so if you also know the coordinate path of the object whose time dilation you want to calculate, you then use the line element to do a line integral over that path, which gives the proper time along the path (assuming it's a timelike path). This works just as well for the SR line element as for a GR one. – Hypnosifl Jan 21 '15 at 16:34
  • @JohnRennie no problem - answers to the other post do help answer my own as does Hypnosifl's comment here. Thanks. The only thing that's still unclear is why acceleration and gravity are discussed rather than velocity and gravity. SR doesn't deal with accelerations or curved space, right? My (and I concede maybe wrong) understanding is that it's the relative constant velocities in SR that leads to the time dilation. But I have this nagging feeling it's the acceleration because of equivalence. – docscience Jan 21 '15 at 21:17

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