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

We have literally no way of knowing. We know how old the observable universe is due to measuring the radiation bombarding the Earth. None of the radiation from the unobservable universe has reached Earth yet, so we can’t measure it.

This is why it’s the unobservable universe. We cannot observe it.