Let me try again. Two possibilites:
Universe is eternal. Problem : How did it arise in the first place?
Universe arose out of nothing. Many-worlds interpretation (Universes are created every moment (and perhaps destroyed) but since they are in different planes of existence, so we cannot interact with them).
"In layman's terms, the hypothesis states there is a very large - perhaps infinite - number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes.
It is currently considered a mainstream interpretation along with the other decoherence interpretations, collapse theories (including the historical Copenhagen interpretation), and hidden variable theories such as the Bohmian mechanics.
Before many-worlds, reality had always been viewed as a single unfolding history. Many-worlds, however, views reality as a many-branched tree, wherein every possible quantum outcome is realised."
https://en.wikipedia.org/wiki/Many-worlds_interpretation
That is why Luis said that 'must' is a strong word to use. Science is not as straight-forward as it was in Newton's time. Who knows what will crop up next. Hope you understand our position.