First assume there is an ND uniform matrix (like a crystal) cellular automata quantum computer (UCAQC) where each of its cells are Planck length size and made of M qubits (like a register (set)).
Assume our universe is a bubble/ball of information (energy) expanding in that matrix.
Assume time step of UCAQC is Planck time (which leads to speed of light being the ultimate speed).
Assume each particle of Standard Model is a ball/cluster/packet of information moving around.
Assume when two (or more) particles collide, they temporarily create a combined information (energy) ball that is unstable because (for some reason) only the particles of Standard Model is allowed, so the newly created unstable particle is forced to decay/divide into a set of particles allowed by Standard Model.
Naturally existence of a Newtonian spacetime is easy to explain for such a universe.
(Also realize it is naturally compatible with quantum mechanics.)
But how about Relativity?
I think Special Relativity is because flow of information about events is limited by speed of light for all observers.
A thought experiment:
Imagine we have a spaceship in Earth's orbit that sends blue laser to a receiver on the ground.
Imagine the spaceship starts moving away from Earth with its speed keep increasing towards speed of light.
Imagine it reaches a speed so that its laser light looks red to us and to our measurement instruments.
(Because of Special Relativity.)
Realize that an observer on the spaceship would still see blue laser photons leaving the device.
But an observer on the ground sees and measures red laser photons.
The question is, are the laser photons actually lost energy?
Are they really blue (higher energy) or red (lower energy) photons?
Cannot we say they are actually blue photons, same as when they were created, but we see/detect them as red photons because of our relative (observer) motion.
What is really happening is same as how Doppler Effect changes frequency of sounds.
Different observers see photons with different energies because density of information flow is different for each observer,
even though speed of information flow is the same (speed of light) for all observers.
That is why I do not think expansion of the universe actually cause photons to lose energy.
I think all photons stay the same as when they were created, but they can be perceived with different energies by different observers.
(So when we measure energy of a photon, we actually measure its information density; not its total information (which is constant and equal for all photons).)
Similarly, I think (positive) spacetime curvature around objects with mass, compresses Compton wavelength of all particles present.
In case of Black Holes, Compton wavelength of a particle gets compressed as it approaches the event horizon.
Upon reaching the event horizon, the wavelength drops to Planck length and you get Planck particles (which is I think what Black Holes are made of).