In the Star Trek episode "The Alternative Factor", 30 March 1967, A highly unscientific threat to destroy our entire universe plus an alternate one was revealed, destruction on a scale that makes mere galaxy-wide destruction seem infinitesimal:
KIRK: What's going on? This leaping from universe to universe. This wild talk about a murdering creature who destroys civilisations What's the purpose?
SPOCK: Jim, madness has no purpose or reason, but it may have a goal. He must be stopped, held. Destroyed if necessary.
KIRK: I don't follow you.
SPOCK: Two parallel universes project this. One positive, the other negative. Or, more specifically, one matter, the other antimatter.
KIRK: Do you know what you're saying? Matter and antimatter have a tendency to cancel each other out. violently.
SPOCK: Precisely. Under certain conditions, when two identical particles of matter and antimatter meet.
KIRK: Like Lazarus. Identical. Like both Lazarus', only one is matter and the other antimatter. If they meet.
SPOCK: Annihilation, Jim. Total, complete, absolute annihilation.
KIRK: Of everything that exists, everywhere.
And when Kirk meets the sane Lazarus:
LAZARUS: Here, yes.
KIRK: And if identical particles meet
LAZARUS: The end of everything. Civilisation, existence, all gone. I tried to stop him, Captain. That's why I took your dilithium crystals.
Of course "The Alternative Factor" was aired in 1967, after Skylark DuQuesne (1965) and The Star Kings (1947) were published.