Buzsaw,
How about the following model? Take a piece of paper and draw a straight line on it. Then bend the paper such that you bring one end of the line near the other end. Then imagine that you are a two-dimensional being living on the surface of the paper. Space as you know it has only two dimensions, you cannot directly observe a third dimension. (Just like the real-world Buzsaw is stuck in three dimensions, the paper-world Buzsaw is stuck in two-dimensions.)
Now look at a two-dimensional photon that takes the path of the line on the paper. What does it look like to you as a two-dimensional being? It looks like the photon takes a straight path, because you cannot see the curvature of the paper. All you see is a straight line. And, in fact, it
is a straight line, in two dimensions.
If I may suggest a definition of "straight", a definition Rrhain is so desperately awaiting from you, it would be "the shortest possible path between two points in space". If your space is the paper you live on (i.e. you can only move in the two dimensions your world consists of) then the shortest possible path from one end of the line to the other is the line itself, following, unbeknownst to you, the 3D-curvature of the paper.
Hope this helps.
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