damian 1727, you ask, "Is space/time a "thing?" The indefiniteness of the meaning of the word "thing" makes your question hard to understand. Everything is a "thing" in one sense or another. That the Universe is made up of all matter and energy is about the most that one can say in answer to the question of what the Universe is. As for a ratio between mass and energy, it's not clear to me that there is any answer to that question since special relativity reveals that both are forms of the same thing. I really don't believe that anything more can be said in answer to your question.