Black Holes, Singularities, Confusion

Thanks for posting the diagrams, but can you explain something for me... why is "diagonal" (at 45 degrees) the fastest one can travel through space? Could we not (in theory) have someone traveling so fast that they travel purely through space (and hence, not through time) such that they'd be moving "horizontally" across the diagram?Greg P.

Thanks for your response. My question is why is the 45 degree angle the speed of light and not the horizontal? I was under the impression that light traveled purely through space and not at all through time (meaning a photon doesn't age)? At a 45 degree angle, where the vertical is time and the horizontal is space, it would suggest that light does in fact travel through time - and I didn't think that was possible.Greg P.