ELi5: Is the entire Universe (unobservable + observable) 13.8 billion years old or just the observable Universe 13.8 billion years old?

Question

ELi5: Is the entire Universe (unobservable + observable) 13.8 billion years old or just the observable Universe 13.8 billion years old?

In: Physics

Answer 1

Well the theory is that we can’t see further away because that means looking further back in time and when we try to do that no matter which way we look the universe becomes opaic, we can’t see through the gas of the early universe.

So if we are right about the whole big bang and why we can’t see any further then the entire universe is 13.8 billion years old.

But maybe we are wrong. Or we are just one of many universes, each with their own big bang origins and ages. We can’t really say what’s going on in the unobservable universe because it’s unobserved. We can spout theories all day but how would we ever test them to see if they are true?