It's a book by Elizabeth Moon.

Isn't dark the absence of light, thus not qualifiably measurable? Dark exists where there is no light, so I gues one could define it's "speed" as being inversely proportional to the speed at which light arrives.

__________________
Though I am different from you,
We were born involved in one another.

For it was not into my ear you whispered, but into my heart. It was not my lips you kissed, but my soul.

Complete surrender should not just come at moments in which one faces overwhelming odds, but in the calm when it seems one is personally in complete control of one's life.