ELi5: Is the entire Universe (unobservable + observable) 13.8 billion years old or just the observable Universe 13.8 billion years old?
In: Physics
There’s not any way to answer this since by definition we don’t have any idea what’s going on outside the observable universe. I will say that as far as I’m aware there’s no reason to assume it behaves any differently.
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?
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.
Can’t answer because no one knows. It’s like asking if there is an after life. No one knows that either.
I would say literally anything is possible, because we just do not know.
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.
If we can’t observe the unobservable universe, then we can’t really answer that question. Can we?
So, we know the universe is expanding, right? And we know a lot about what is causing that expansion and how it has unfolded over time, and we have some clues such as the cosmic microwave background that tell us what was going on at specific points in time. Well, if you put all of this information together and trace the expansion backwards, you get to a point around 13.8 billion years ago at which the universe very rapidly expanded and cooled, going through various stages in which it was dominated by different forms of matter. e.g. at one point it was too hot for atoms to stay together so the entire universe was made up of a plasma of free protons, electrons, etc., like you get in stars today. Well, the further back in time you go, the more unclear things get, as the increasingly hot and dense matter becomes increasingly unlike anything we can see today.
So we don’t know for sure that nothing happened prior to 13.8 billion years ago, we just know that our universe went through a lot of extreme changes at that point and that it’s impossible to probe any earlier in time with current knowledge and technology. And the big sticking point isn’t the speed of light or the edge of the observable universe or anything to do with that, it’s our lack of knowledge about how extremely extremely hot matter behaves.
The entire universe is 13.8 byo. We can also only see 13.8 bly as a consequence.
It is believed the universe is bigger than we can see, but not older.
[This Kurzgesagt video](https://youtu.be/uzkD5SeuwzM) explains the concept of the observable/unobservable universe very well.
The universe is believed to be 13.8b y.o. observable and unobservabke.
The reason that there is universe beyond 13.8 light years away is that, it is believed The universe itself is expanding faster than the speed of light.
The stuff we cannot see is still only 13.8b y.o. it’s just expanding away from us very, very quickly.
Latest Answers