...... if we look at a spot in space > a billion light years away

we will only see the masses having radiated a billion years ago !
what ever did not radiate then .... we will not see ....

the same at 10 billion light years ....

so we will not be seeing a lot of materia in the universe
that is shurely there ..... but invisable for us !

so .... we can only speculate on the amount being there .....

is this the dark mass ... science is looking for ?

and ..... the stars shinning today .... are much more numerous
as the war at the beginning of this universe 10 billion years ago !

so we will have a lot more radiation going out from those stars today >
meaning they are pushing each other away from .....

and this is causing the universe to expand ever faster !

is this the dark energy science is looking for ?

being in fact the light energy .... going dark .... when all the stars are out >
for the gravitational effects to prevail again !

letting all the materia fall together ... for a new big bang to come up again

galactic central information