Problems with Radiometric Dating?

I have a question (and it may not sound to scientific since I am not a scientist, but this does bother me). How do scientists know how much radioactive materials that decay was present at the creation (by big bang, by God, by whatever) of the universe next to their byproducts? (That is not to say that the byproducts present came from radioactive decay, just that they match up and an ignorant observer (someone not present at the creation of the universe) could mistake for something that came from radioactive decay.)NOTE: I do not speak about the present, I speak only about the creation of the universe. In the same way, what about the creation (by whatever means) of the planet earth? Do scientists know exactly what the dispersal of radioactive materials to their counterparts were when the earth came into being? (Once again I do not speak of the creation of rocks and the dispersion of radioactive materials and their decayed counterparts.)