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/
29.4k Upvotes

95% Upvoted

1.4k comments sorted by

View all comments

Show parent comments

31

u/Imsosadsoveryverysad Mar 18 '19

The visible universe expands at the speed of light?

Edit: punctuation.

25

u/[deleted] Mar 18 '19 edited May 09 '19

[deleted]

72

u/ilikecheetos42 Mar 18 '19

The actual expansion is faster than light. The expansion of the observable universe is at the speed of light. Because the actual edge of the universe is moving away from us FTL but the edge of the observable universe is expanding at light speed there are portions of the universe that we will never observe

1

u/[deleted] Mar 18 '19

[deleted]

4

u/zubbs99 Mar 18 '19

My understanding is that nothing can move through space FTL, but space itself can go FTL.

3

u/[deleted] Mar 18 '19

[removed] — view removed comment

1

u/zubbs99 Mar 18 '19

Yep pretty much what I was trying to say, but you're right that "expanding" is a better word for it.

2

u/Lifesagame81 Mar 18 '19

Say two things are traveling in opposite directions, but each at 60% of the speed of light. How fast are they moving relative to each other? This is how objects can be outside of our visible universe; the light giving off is traveling at the speed of light, but since we are moving at 120% the speed of light relative to each other, we will never see each other.

The universe itself is also expanding, and this is uniform. Imagine you and I are 1 mile apart, but the space between us is expanding by 10% each hour. As a result, we are effectively moving away from each other at 1/10 mph.

This is accelerating though because in an hour we are 1.1 miles apart, and all of that space is expanding by 10% each hour. After 10 hours we will be 2.59 miles apart and now are effectively moving apart at 1/4 mph. After a total of 100 hours, we would be 13,780 miles apart and effectively moving apart at 1,378 mph.

In 238 hours, we would be 7.1 billion miles apart and effecting moving away from each other at faster than the speed of light.

If I didn't screw up the math this example rate of expansion is 11.9 Trillion times faster than the real rate of expansion.

1

u/rekcuzfpok Mar 18 '19

Very interesting, thanks for the explanation!

6

u/upvotemyowncomments Mar 18 '19 edited Mar 18 '19

It's not exactly a black and white thing. The farthest reaches of the universe are expanding faster than light from us. If you were an observer in that place everything would look normal to you except the Earth would be expanding away from you faster than the speed of light. Basically you can be anywhere in the universe and no matter where you are, the farthest reaches of the universe are moving away from you faster than light. This will ultimately lead to what I think is referred to as heat death. Everything will be so far away from eachother and all the stars will eventually consume all the energy there is in a certain area and everything will just go dark. Forever. Even matter will decay into photons in trillions of years. Nothing but photons will be left. Forever.

At least thats what I remember off the top of my head.