That Arthur C. Clarke story is “Wall of Darkness.”
Here once again is the opening sentence: “Many and strange are the universes that drift like bubbles in the foam upon the River of Time.”
Note that (1) this was written at least a decade before anyone thought of the “Many Worlds Interpretation” of quantum theory, and (2) it’s elegantly and memorably said. Sir Arthur can write. And no, I’m not biased. Not at all. No way.