I just read Carlo Rovelli new book "Reality is Not What It Seems: The Journey to Quantum Gravity" in one sitting. I'd like to know about the following: "Fields that live on themselves, without the need of a spacetime to serve as a substratum, as a support, and which are capable by themselves of generating spacetime, are called "covariant quantum fields." The substance of which the world is made has been radically simplified in recent years. The world, particles, light, energy, space, and time - all of this is nothing but the manifestation of a single type of entity: covariant quantum fields." Are all quantum gravity theories based on covariant quantum fields where the fields don't live on spacetime but created space and time?