Sorry in advance for a potentially nonsensical question. But I’ve been thinking of this and couldn’t get a decent answer.

Assume spacetime is a quantum field with the propagation speed greater than c (let’s call it c1). All other fields we know of are at c (we’re assuming gravity is quantum too).

Coordinates on the spacetime field and standard model fields correlate. However, information travels faster on the spacetime field than the SM fields.

Assume the spacetime field expands. When it does so, due to c1 being higher than c, SM fields feel a lag for this expansion. Thus, they act as if spacetime is smaller than it actually is.

This means, SM fields seem uncharacteristically stronger than they’re supposed to be. This effect becomes more apparent as speed of expansion of spacetime grows (lag increases, SM fields operate as if spacetime is its actual size minus lag).

Let’s look at the Chandrasekhar limit. With this effect, it changes over time. When gravity becomes stronger temporarily, it lowers. Because it lowers, we need less mass to trigger a type la supernova. This reduces brightness than expected.

Thus, a standard candle isn’t as bright as we thought it to be. Also, its brightness changes with this changing “lag” between spacetime and the SM fields.

In our models, we incorrectly believe that standard candles are further away than they actually are (because we think that they are brighter than they actually are). This results in us calculating a higher expansion rate of spacetime.

While this effect would apply to the CMB, it would be less apparent as the universe was expanding at much lower speeds. This is the “real-er” value.

The above effect also means that galaxy formation would occur earlier than predicted (stronger SM fields).

Note: To clarify, the assumption is that gravity is a quantum field and that it is separate from this spacetime field. The propagation speed of gravity is the speed of light. It is NOT the speed of propagation of the spacetime field.