A Pantheist believes that everything around us, i.e. the universe, is God. Therefore if it can be conceived that the universe might not, in certain conditions, exist e.g. 'before' the Big Bang, then God would not exist. So "what breathed fire into the equations?" If Einstein could say, "What really interests me is whether God had any choice in the creation of the world.” then surely he could not have been a Pantheist?