If we don't define our terms, we'll just end up chasing our tails in circles; especially when everyone's opinions start pouring in.
Universe: a concept that embodies matter (atoms) and space (nothing).
It's capitalized because there is only one. We are referring to 'THE' Universe.
Although 'the Universe' is a noun for the purposes of ordinary speech, it cannot be treated as a noun in the course of a scientific discussion. The Universe is not an object as it embodies a relation. Of course, atoms move with respect to others, but when space or 'the' Universe starts moving, watch out!....you've had too much to drink!
To posit that there is another Universe, is to posit that space has a physical border separating Universes. Does space have a border which you can cross, like you can cut through a fence to escape a prison? If so, what is the border made from....steel, bricks, carbon, glass? And what is on the other side?
Nature has no ontological contradictions. Only humans do!