Yes, we do know that space and time had a beginning.You don't know if space and time existed before the BB. I think it could have and nobody has proven it either way.Genesis describes the beginning of creation which is space and time.Genesis tells us that an invisible alien started the universe by saying "let there be light". Not proven at all by anyone, let alone science.News flash, Taz, Genesis tells us that the universe had a beginning.
Science confirms it.
Btw, science says that light didn't come into being until around 400 million years after the Big Bang.
Not too shabby all things considered.