Quiet. Of course we know the Emperor is not a god, the perpetual themselves knew of it before, but for the strength of the imperium and the need for morale we do not talk about it.
I know, the theory the Emperor never wanted to be seen as a god is there. 40k lore though is massive and convoluted, feels like you need a phd to understand all of it.
How do we know we are the original earth? What if we are taught that we are in the beginning of civilization and all our religion today is just a bastardized version of emperor worship?