Modern cosmology is a field of speculative thoughts interspersed with points of evidence. These evidences act like tent poles holding up the fabric of cosmological theories. Theories such as steady state, big bang, M-theory, grand unified theory etc all give different explanations to the origins and the functioning of the universe. Personally, I found it more of science fiction than science.
Regardless, there are some fundamental axioms that physicists accept. Although, I am not a scientist, it seems hard to accept this lofty assumptions without critically questioning them. Below is a principle that always piqued my doubts related to modern cosmology.
The cosmological principle derives from the Copernican Principle but has no foundation in any particular physical model or theory, i.e. it can not be `proved' in a mathematical sense. However, it has been supported by numerous observations of our Universe and has great weight from purely empirical grounds. The greatest consequence of the cosmological principle is that it implies that all parts of space are causally connected at some time in the past (although they may no longer be connected today). Thus, a homogeneous Universe leads to the conclusion that the whole Universe appeared at a single moment of time, a Creation.
A corollary to the cosmological principle is that the laws of physics are universal. The same physical laws and models that applies here on the Earth also works in distant stars, galaxies, and all parts of the Universe - this of course simplifies our investigations immensely. Note also that it is assumed that physical constants (such as the gravitational constant, mass of the electron, speed of light) are also the unchanging from place to place within the Universe, and over time.
source - University of Oregon
In actuality, we have experience just on earth that gravity is not entirely constant across the globe. The same is said about time. At different altitudes, time and gravity although mathematically minuscule behaves differently. If we expand distance to light years, this small difference can add up. Regardless, we cannot know what we cannot know. So unless we travel long distances in outer space to see for ourselves, to assume speed of light, gravity etc to be universal constants across light years is based on huge leap of faith and faith is something science looks down upon. I think there is a sense of hypocrisy built in this assumption.