ELi5: Is the entire Universe (unobservable + observable) 13.8 billion years old or just the observable Universe 13.8 billion years old?
In: Physics
Well, the non-observable universe is not observable, so by definition there is no way to know for sure.
There is a limit to how old it can be the closer it is to our observable universe, otherwise it would be observable as well. But far away the universe could technically be older.
That said, it is very difficult to imagine that the observable universe as it existed in its first microsecond could coexist in a wider universe already formed (more than a couple minutes old). So it is very likely that the whole universe expanded at the same time and is as old.
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