[ExI] Observable Universe contains ten times more galaxies than previously thought

[Anders]

On 2016-10-20 09:31, Ben wrote:
> Anders <anders at aleph.se> Observed:
> > Yes, this news is based on a very odd use of the present tense.
> > Astronomers may be fine with considering the "present" as the 
> surface of  our past light cone, but most of us prefer to consider the
> > unreachable volumes with the same cosmological time as us as being 
> "now".
>
> Ah, but doesn't that contradict Relativity? I thought one consequence 
> of that was that there is no such thing as 'simultaneity', over large 
> enough scales. Surely anyone who wants to think about cosmology needs 
> to get used to that idea?

Cosmologists are totally fine with a lot of temporal coordinate systems. 
Cosmological time and co-moving time are pretty common ones, and they 
make it possible to talk about "now" in regions outside our light cone:
https://arxiv.org/pdf/1304.3823v1.pdf
Moving observers would see a different simultaneity, but since matter in 
the universe are roughly static relative to co-moving space coordinates 
this kind of simultaneity makes sense.




-- 
Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University