I am quite a stranger to cosmology, so please go easy on me if what I say below is actually very stupid/ignorant! From the little exposure I've had to cosmology, it seems to me that in cosmology, a lot of approximations are taken, as well as a lot of huge assumptions made. For example, I've also read due to how crude the approximations are, sometimes the estimated age of a star seem to be even older than the estimated age of the universe. Also, the assumption of isotropy and homogeneity, seem to be argued in a hand-wavingly by the statement "when viewed on large scale". From what little I am exposed to so far, it seems that cosmology is not a very precise, and often times arguments are made in hand-waving ways and huge approximations are taken. The whole field just seems really crude。 Is that really so? Or am I dead wrong?