In 1963, when I completed my PhD, it was mostly on the steady-state theory using mathematical formulations to describe creation of matter. People always argued that you cannot have matter coming out of nothing, what would happen to the law of conservation of matter. It is a normal criticism of the steady-state theory. One could answer it either in one sentence by saying what is the big-bang theory where the entire universe came out of nothing, so you are violating the law of conservation of matter and energy in a big way. But that would be to point out the weakness of the other theories and not answering your own theory.