That's absolutely not true. Science is not certain at all about the origins of the universe. We don't understand the big bang, we don't understand how time and space can seemingly spring from nothing, and I think you'd be hard pressed to find a physicist who would claim to know very much at all about the big bang.
>That's absolutely not true.
It absolutely is true, I was specifically talking about the steady state theory: "While the steady-state model enjoyed some minority support in the scientific mainstream until the mid-20th century, it is now rejected by the vast majority of cosmologists, astrophysicists and astronomers, as the observational evidence points to a hot Big Bang cosmology with a finite age of the universe, which the steady-state model does not predict" [0]
And the observational evidence is interpreted as pointing to a Big Bang. There are other interpretations which don't require a finite age or an initial singularity.
Ex nihilo nihil fit.
it's the steady state model that science knows not to be true, but not the fact that the universe has no beginning and no end, and not the fact that there was no first cause. Science doesn't know anything of the sort.