That is, the matter that makes up galaxies, etc. Doing that, plus using a different set of
observations, scientists are actually able to tell how old the universe is
--
that is
--
how long it has
been expanding. T
he current answer is that the universe has been expanding for 13.8 billion
years,
that is, the time since the origin of the universe, the event we call the Big Bang. Our cosmic
horizon is then the bubble of information where we live, the distance light ha
s traveled since the
Big Bang, a sphere with a radius of about 46 billion light years. There may be more universe out
there, like there is more ocean beyond the horizon, but we can't see it.
Circling back to the nature of reality, we see that cosmology te
lls us that there are aspects of the
world that are unknowable to us.
