fixed exterior coordinates is relative ruler of this universe and space unit is virtual metric unit of the ruler

1. fixed exterior coordinates is just a relative ruler of this universe

I imagine that this universe is like a bubble, dough or water ball which is made of dynamic mass and energy without absolute center, so we cant know this universe’s whole movement or absolute position and speed of mass or energy inside this universe.

But there is something fixed:

a) light speed in vacuum is always constant c in all directions for any local observer at any gravity,

b) the relative position and speed between mass and energy are fixed at least for 3D space of NOW intersection of static time field at a point of dynamic time.

So we can somehow use light speed constant measured locally to calculate a metric unit to calculate fixed relative position and speed of mass and energy in a fixed exterior coordinates at least for present NOW, right?

So we can calculate the interaction within a fixed static time field at a point of dynamic time to predict future change of the static time at future points of dynamic time.

2. space unit is virtual metric unit for the ruler – fixed exterior coordinates

There is no shape which can fill 3D space with isotropic, so space unit is just a virtual metric unit for the ruler of fixed exterior coordinates, which is like that the architect of this universe use a ruler with metric unit of d_p which incurs the virtual sphere like isotropic space unit.

So space unit does exist as metric unit in this universe but doesnt exist as real brick/voxel/pixel/grid of this universe.