The Universe was always the same size?

[Banshii]

If something 11 billion light years away blew up such as a supernova, and we are only seeing it now... doesn't that mean the universe was already as big then as it is now? If not, the only way it would make sense is if the universe is expanding twice the speed of light, or us and the "event" have been traveling in direct opposite directions.

[Iggy]

If something 11 billion light years away blew up such as a supernova, and we are only seeing it now... doesn't that mean the universe was already as big then as it is now? If not, the only way it would make sense is if the universe is expanding twice the speed of light, or us and the "event" have been traveling in direct opposite directions.

 

The star that went supernova was, and the supernova remnant is, moving directly away from us.

 

"11 billion lightyears" can actually mean more than one thing. Let's assume that you mean that the supernova happened 11 billion years ago. That makes 11 billion lightyears a "light travel time distance" (this gets very complicated very quick)

 

The redshift that we would observe is z = 2.5 This makes the scale factor 1/3.5 and the current distance to the supernova remnant 19.293 billion lightyears. When the supernova happened the distance was 1/3.5 of that. In other words:

 

The distance was 5.512 billion lightyears when the supernova happened 11 billion years ago and the distance is currently 19.293 billion lightyears.

 

The universe has expanded 3.5 times over in those 11 billion years. All cosmic distances have increased by a factor of 3.5 in that time.

 

Does that work?

Edited April 7, 2013 by Iggy