John R. Cox,
re:quantum gravity
The concept of spacetime is a bridge between the universe and our reality. Space in our reality is time in the universe out there. The concept is necessary for us in order to be able to keep doing physics. The universe does not have this requirement and therefore it has no use for 'space'. I other words, 'space' plays no part in the working of the universe.
Gravity is time evolving at a diferent rate from place to place. Now, let's go quantum.
1) Time and probabilities:
The cloud of probability of a single free particle in a gravitational field does spans over different rates of time. The cloud is therefore skewed vertically because the particle does spend relatively more time at the bottom than at the top of the cloud. Easy for the mind to grasp. Probability is time dependent and time is running at a different rate in gravity which brings different probability of existence a.k.a. motion. The universality of the effect of gravity commes from its effect on anything that 'exists', irrespective of size, mass etc.
O.K, where do I get 'existence' from?
2) From "finding' to 'being' or 'existence':
The probability of finding a particle in A, as successfully described by shroedinger equation, is equal to the probability of existence of that particle in A. Once the equation is proven exact, we may replace the 'finding' by the 'being' or existence of the particle. The particle MUST BE there with the same (relative) probability as that of being found!!
This conversion from a physical to a metaphysical perspective is necessary in order to understand the universe without us being in the way. Very useful if we are careful.
In conclusion, quantum gravity is simple if we assume this metaphysical perspective, and Shroedinger's equation actually tells us what determines the probability of existence of a particle in a place. Look it up, knowing that the rate of time is 1 on T.