Christian,
I know gravity is described as the curvature of spacetime, but does that explain it, or just model it?
One problem I have with spacetime is that it is based on treating time simply as a measure of duration, which is based on the perception of time as a vector from past to future, along which this point of the present moves/exists, depending on your interpretation. Yet it seems much more rational to consider time as an effect of action, so it is the changing configuration of what is, that turns future potential into past circumstance. For example, rather than the earth traveling/existing along some dimension from yesterday to tomorrow, it is that tomorrow becomes yesterday because the earth rotates. This makes time an effect of action, similar to temperature. In essence, time is to temperature what frequency is to amplitude.
Duration does not transcend the state of the present, but is what is presently occurring between events, like the wave cycling between peaks.
Therefore there is no metaphysical "fabric of spacetime" and so no conceptual basis for an expanding universe, or blocktime, or wormholes, or multiverses, or any of the other speculative fantasizing arising from this conjecture.
Spacetime is simply correlation of measures of duration and distance and is mathematically accurate for the same reason epicycles are mathematically accurate; Perspective is inherently relative. There is no such thing as objective perspective. One could, with sufficient complexity, create a self-centric cosmology, for the quite logical reason we are the center of our view of the universe, but that wouldn't mean there are Titans pushing the entire universe in the other direction, every time one walks across the room, just as there is no giant cosmic gear wheels, or fabric of spacetime, pushing and pulling.
If time were a vector from past to future, logically the faster clock would move into the future more rapidly, but the opposite is true. Since it thermodynamically ages/burns quicker, it recedes into the past more rapidly.
Now the temporal vector is the basis of both narrative and linear logic, which are the basis of civilization, so it isn't an easy idea to put in context and I understand why it would be incorporated into foundational theories, but then we still see the sun as moving across the sky and it was only five hundred years ago we began to understand it is the earth spinning the opposite direction.
According to measurements of background radiation, overall space appears flat. This was proposed decades ago and measured by COBE and WMAP. The explanation given is that Inflation initially blew the universe up so much larger than is visible, it only appears flat on local scales, much as a local area of the earth's surface appears flat.
I could speculate as to the various relations between radiation and mass, but I will stop with the above observations as to why current theories may have to be reconsidered, not just continually patched.
Looking at the literature appearing in the popular press, Smolin et al, it might be worth your while to consider thinking about alternatives. I'm just offering some suggestions.
Again, pardon the rant.
Regards,
John