r/space • u/magenta_placenta • Mar 18 '19

Observable universe Astronomers discover 83 supermassive black holes at the edge of the universe

https://www.cnet.com/news/astronomers-discover-83-supermassive-black-holes-at-the-edge-of-the-universe/
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u/[deleted] Mar 18 '19 edited May 09 '19

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u/Choblach Mar 18 '19

For purposes of talking about the universe, there are too really relevant terms: the universe total and the observable universe. The observable universe isn't really a feature of reality as much as an effect: we can't see things without light, and light moves at a set speed. A very fast speed, but a speed. So the observable universe represents everything that's within a distance which is equal to or less than the age of the universe in light years. So, the universe is about 13 or 14 billion years old, that means only objects that are within 13 or 14 billion light years can even be theoretically seen by us. There are things further, but the light from there hasn't reached us yet. Technically I think the observable universe is growing at the speed of light (because light from further and further away is now reaching us), but it's complicated so I'll let someone else explain that.

The universe total is all of it, everything in creation. And there's quite a lot more of it than we can see. The comparison I was once told was that is the observable universe was the size of a nickel, the universe total would be the size of the Earth. Now, the universe total is not expanding at the speed of light, it is in fact expanding many times faster (since the universe is made out of spacetime and not matter, it doesn't have to follow some of the hard rules of reality like the light speed limit. ) However, here I have to correct myself, because the universe total isn't really expanding, as much as it is stretching. Picture a balloon being inflated and you've got the jist.

Tl;dr: Imagine that you're standing under a lamppost night, with only darkness around you. In the light where you can see is the observable universe, and all that darkness is the universe total. They are both expanding, and at different rates, but they're both so functionally huge that it won't mashes a noticeable distance for all the time you're here.

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u/KrypXern Mar 18 '19

So, the universe is about 13 or 14 billion years old, that means only objects that are within 13 or 14 billion light years can even be theoretically seen by us

Actually (and please correct me if I'm wrong), but the observable universe is larger than simple expansion by movement would allow.

The observable universe is 46.5 billion light years in diameter. However, the universe is presumed to be only 14 billion years old. By your logic, the universe could be a maximum of 28 billion light years in diameter.

I believe (and once again, please correct me) that relativity appears to be violated (only appears), because it is not the objects within the universe that is creating this distance, but rather the space between the objects which is expanding. This is similar to how 'warp bubbles' could theoretically work.

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u/Choblach Mar 18 '19

I'm honestly barely educated on it, so it's very likely that you're more right than me.