Thanks Michael. One can also add the problem of spacetime curvature, which makes the calculations you alluded to even more problematic, because the gravitational effects of curvature can only propagate at the speed of light; therefore one has to calculate relative curvature for any object at any point in spacetime. As the Einstein field equations are essentially unsolvable to the required degree of precision for any system comprising multiple bodies, the problem of “where was I” is therefore unsolvable.

Fortunately as we haven’t a clue what time is, nor why it appears to break symmetry, nor whether there is any way to traverse the timeline, there’s zero chance of us having to worry about the problem of coordinates!