"The universe" is not a theory. It's basically just defined to be "everything," whether we can see it or not. It's not a hypothetical thing. It's a postulate thing. We don't know what exists or if anything exists outside our light horizon. Whether there is something or suddenly nothing beyond our light horizon, that doesn't mean the universe is "hypothetical". It still "is".

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Everyone is entitled to his own opinion, but not his own facts.