David,
I have the sense you are exploring how physics is getting sucked down the same rabbit hole as philosophy. May I offer an answer to the question of reality?
Reality is the extant. Nothing more, nothing less.
Well, then how do we decide what is extant and what is not?
A bit like carving a statue of Zeus. Chip away all that is not and leave all that is.
Yes, but what is real and what is not? Are the past and future real?
No.
Then how do you describe and explain what is real, if you don't have past and future?
You didn't ask how to explain reality, only what is reality. Big difference.
I thought relativity shows past and future are just different parts of the time vector?
What is time? The problem is that individuals experience it as a sequence of events and treat it as a vector from past to future, but that is just an effect, much like the sun moving across the sky and we remember how much confusion that caused. The reality is much simpler. Change causes future to become past. The earth is not traveling some dimension from yesterday to tomorrow. Tomorrow becomes yesterday because the earth rotates.
But what about spacetime?
We could use ideal gas laws and correlate temperature to volume and call it temperaturespace, but thermodynamics is not the basis of cause and effect logic and narrative, like time, so people have more perspective of it.
But what about the expanding universe? Isn't causal spacetime the basis for the cosmology?
One of the problems with complex arguments is that you loose sight of the big picture in all the details and look silly. According to Einstein, space is what you measure with a ruler. Since all those other galaxies are redshifted proportional to distance(which would be explainable as an optical effect), so the theory argues it's an expansion OF space, not IN space and so every point appears to be at the center. The problem is it still assumes a constant speed of light; That all those galaxies are moving away and the light will take longer to reach us, thus implying a stable speed of light. Now if you were to hand this in as homework; 1)That space is what you measure with a ruler. 2)That intergalactic space expands. 3) We know this because our ruler, the distance light travels in a year, remains constant and it requires more of them to cover the distance between galaxies. You would get a big fat F, but since the logical trail is so long and convoluted, no one looks at all of it and cosmology gets a pass. Keep in mind Einstein also argues gravity collapses space and these galaxies populating the universe are not just inert points of reference, but gravity wells, so it would make mathematical sense to say the space expanding between galaxies is also falling into them.
Now Einstein makes this argument because the ruler, mass points, are contracting. Yet radiation is expanding away from them. The argument for recession causing redshift is that photons travel as point particles, yet what is the proof of that? They have no internal structure to hold them together, exhibit wavelike properties in transit and the point characteristic seems largely a function of being absorbed by atoms. So if light expands out when released and the absorbed photon is only a sample of the wave front, why wouldn't it show redshift across quadrillions of miles, since the absorbed photon is likely multispectrum? Otherwise we assume point particles will follow in a line across these distances, exhibiting the clarity we measure of other galaxies?
So, mass contracts and radiation expands in a cosmic convection cycle and space has no physical features to bend, bound, stretch, etc. Therefore it is both infinite and absolute, ie. inert. We can measure this inertia as the centrifugal force of a spinning object, since assuming it is due to an outside reference would be problematic. Call it an unbound field, if you prefer
Time is to temperature, what frequency is to amplitude.
Information defines energy and energy manifests information. Since the energy is conserved, creating new information requires erasing old. Which goes a long way to explaining death, disease, wars, earthquakes and all the other falls off the edge of reality into the abyss that people are really curious about.