Francesco,
What if Nothing is fundamental? 1 is relative to -1, so they cancel out to zero. Wouldn't that mean zero is the fundament? This might seem a silly question, but consider physics, rather than math. Isn't space the physical equivalent of the mathematical zero?
What is the speed of light relative to, but the vacuum? According to GR, time and distance, the clock and the ruler, dilate equally, so that light is always measured at C, but wouldn't the frame with he least dilated time and distance, the longest ruler and fastest clock, be the closest to the equilibrium of this universal vacuum of space?
As measures of distance and duration can be correlated, time and space are presumably the same relative substance, but we could correlate volume and temperature, using ideal gas laws, why wouldn't they be the same? Time and temperature are both measures of action. One is individual frequency and the other is mass frequency and amplitude.
The problem of time is because our consciousness functions as flashes of cognition, so we think of time as the present "flowing" past to future, which physics codifies as measures of duration, but it is really change turning future to past. As in tomorrow becomes yesterday because the earth turns. Duration is the present, as events form and dissolve.
We are mobile organisms and so we equate events with moving through space. Neither the past or future physically exist, because the energy only exists in the present. It is "conserved." It is our ability to live outside the present, unlike plants and most animals, that gives us the power we have, but like understanding the universe is not geocentric, it does take some objectivity to understand the basis of this effect.
As for the idea the universe is expanding away from some event 13.8 billion years ago, one of the first patches to that idea was when Hubble and the other early theorists discovered that all those distant galaxies are redshifted directly proportional to distance, which made us appear as the center of the universe, so it was argued space itself must be expanding, because Spacetime! So every point must appear as the center. The fallacy is this totally overlooks the original premise of GR, that light is always measured as a Constant in the frame. That both clock and ruler are dilated equally. If it is taking light longer to cross this frame, in order to be redshifted, obviously it is not Constant to it.
So two metrics of space are being derived from the same intergalactic light, so which is the real space?
As for the idea that space is three dimensional and is an effect of geometry, rather than geometry a mapping of space; Nonsense. Three dimensions are the xyz coordinate system and require an 0,0,0 center point, which is a subjective location in space and any number can define the same space. Much as each of us is the center of our own coordinates. Consider how much political conflict is about applying different coordinates to the same space. Are longitude, latitude and altitude foundational to the surface of this planet, or just an effective mapping device?
So I would argue, that for physics, space is the fundament.
Regards,
John B. Merryman