[ELI5] If the beginning of the universe was 13B+ years ago, how is the boundry of the universe 46.5B ly away?
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Question: Are you asking, more specifically, how it isn’t further away or are you asking how it isn’t closer?
It’s important to know what we mean by “the boundary of the universe”. There’s a few boundaries, this one is the farthest parts of the universe we can see. This comes from a combination of light moving 13 billion light years, and the fact that space itself is expanding. So the things that were already very far away when they emitted that light have moved even further in the time since.
The most useful analogy for space expanding is to imagine two dots on the surface of a balloon. If you inflate the balloon more, the dots get farther apart, even though they haven’t moved on the balloon itself. This effect is particularly noticeable for far objects because the farther apart two things are, the more space there is in between to expand.
So to clarify: the things we are seeing are 45 B light years away *now* but we’re much closer when they gave off their light 13 B years ago.
>how is the boundry of the universe 46.5B ly away?
To the best of our knowledge there is no boundary of the universe. The models are that is like the surface of a sphere so if you go far enough you end up where you start or it is infinitely large.
What has a radius of 46.6 billion light-years is the Observable universe. That is just the part of the universe where emitted light has had enough time to reach earth from the beginning of the universe.
It is larger than you might expect for a 13.8 billion lightyears universe. The explanation is that the universe is expanding. So a point that is today 46.6 billion light-years away was closer in the past. so the light emitted at the beginning of the universe has table 13.8 lightyears through space to reach us but because the space in between has expanded what emitted it is today a lot farther away,
The observable universe is only creative to our position, in another galaxy you have the same area but centered around. You can compare it to that you can only see to the horizon on earth but the horizon is in a different locations for different observers. So just like your horizons on earth is not special our observable universe is not special.
This is a tough concept to explain in an ELIF… But here we go.
Think of a Balloon. If you blow it up a little and put two marker dots on it and measure the distance between those dots it; s one distance. If you put more air into the balloon the dots are further apart… More even more distance.
The universe is kind of like this. It is doing something we call expanding. Much like the surface of a Balloon expands.
The why to that is the complicated part.
Just know that what was a million miles 10 billion years ago is more than A million miles today. We exist on the surface of an expanding universe balloon.
Thank you all for the explanations
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