I've been having a really hard time reconciling the idea that we're not in the center of the universe with the idea that it looks the same in every direction, and that the Cosmic Microwave Background is the same distance everywhere. The other day, I think I finally got it, but I want to see if this is really the case.
First the things I think I know:
- The universe is 13.7 billion years old.
- Because of expansion, the actual diameter is much bigger than 13.7 billion light-years.
- Because of the speed of light, we can only see back 13.7 billion light-years (max). Anything further than that and the light will not have had time to reach us.
- The CMB is is the border between the clear universe we now have and the opaque one we had until 400,000 years ago.
If I have those right, then is this correct?
Since we can only see 13.7 BLY from where we are, the CMB does not represent the edge of the universe (or 400 KLY short of it), but rather it's like a small bubble suspended in a larger bubble. The reason the CMB will look the same to everyone no matter where they are is that their smaller bubble of visibility is centered on them wherever they happen to be.
Did the light really go on for me?