Tonight there were as many as grains of sand, a boundless cosmic beach, with a black ocean stretching infinitely behind (it).
Why and why not?
I get both instances on Google:
... it is a likeable geometry that covers up a mystery stretching infinitely behind it (but science hates a mystery). [Source]
It's right on an unknown, barely visited beach with the estuary lapping within yards of the door and meadows stretching infinitely behind. [Source]