Mach's Principle is gernerally ignored in modern physics. Many have tried to include it. But data indicates it is needed. So, in addition to uniting GR and QM, Mach's principle should be necessary.
I agree with Emmanouil. The frame of space is a medium, and it is the reaction of displacements in that medium which cause the properties of particles, including charge, momentum, inertia, gravity, magnetic fields, etc. A specific type of velocity limitation on the transverse motion of these displacements in space is what creates relativity. It is what causes Lorentz transformation of moving particles.
Using such an approach we are able to create a complete and unified theory. I have found no other solution which provides such an elegant and simple theory.
Mach's principle is an observation which points out that we have no way of measuring the linear inertia of a body except by referencing it to another body. There are at least 21 different interpretations of Mach's principle.
Some interpret Mach's principle by assuming that the mass of all the bodies of the universe somehow causes local inertia. I feel this is an error. In this I agree with Emmanouil.
The clues that space is a medium are many. 1. Energy resembling transverse waves propagates at a fixed speed through space. (This fixed velocity propagation of light is a compelling clue that space is comprised of something, and behaves like a medium.) 2. If the spinning fields of particles are velocity limited by this medium, it gives clear cause for Lorentz transformation of particles moving through this medium.
We know that the photon exhibits forward momentum P=E/C. It has been shown also that the total (forward and spin) momentum of the photon is Pt=Sqrt(2) E/C. If the spinning fields of all particles create this momentum then we have a clear description of the cause of mass for the electron, as an example...
(For a more complete discussion please refer to Space, Light, and Matter The Logical Universe).
So it seems space is a medium which consists of two components, and the energy of a particle pulls on space to displace space toward the particle. These longitudinal displacements spin about the particle (seeking a least-force region) and creating momentum in the process. And 3D confined circulating momentum creates mass.
For a more complete discussion please refer to the article mentioned above.
So, while looking for cause and effect solutions to the behavior of particles and relativity, it seems there is a fairly simple and elegant solution.
I agree with most (not the momentum part) of what you mentioned. I favor the interpretation of Mach as saying the whole universe contributes to the motion of bodies (particles).
What I thought I was addressing is the one argument against the medium - it has no identified source for matter to depress. So, the issue becomes whether the space-time, aether, my plenum, quantum vacuum, etc. is ontologically real. (see J.R. Croca, et al. ``Proposed experiments to clarify the real nature of the quantum wave'')
My answer is the experiment:
Interference Experiment with a Transparent Mask Rejects Wave Models of Light
Optics and photonics journal vol. 9, No. 6 jun 2019
I suggest in the question that any paradigm shift model to address the many problems of current physics MUST have an origin story for both matter AND the medium. This is done by satisfying Mach's Principle which many have tried and failed including GR, Sciema (inertia), etc.
I understand. Early in Einstein's career he suggested that there was no medium of space, but later, and for good reason, he changed his perspective.
What we see is... 1. Velocity limited propagation of "particles" of light.(Which suggests a medium.) 2. Curvature of light as it passes massive bodies. (Which suggests a warping of the medium of space.) 3. Lorentz transformation of moving bodies (Which suggests a medium of space. A velocity limitation of the spinning fields of particles. The result of a medium imposing limitations.) I feel it is no coincidence that Maxwell's equations mimic the equations of transverse waves in a medium of space. I do not feel that light is simply transverse waves, but rather that what we most often measure are the transverse motions of longitudinal displacements of space. This approach allow us to understand how gravity is created as well. The longitudinal displacement of space toward particles causes gravity.
It is my opinion that SR is not completely accurate (Some things are much faster than light), GR is more accurate in most ways. And Mach's principle is a observation of the principles imposed on our universe by the properties of space and it's interaction with the fundamental energy of particles.
light is a particle with a structure (not a point or a wave)
Plenum (aether, spacetime, etc.) waves are longitudinal with only a very small and very limited transverse component.
matter warps plenum to emerge to gravity.
hods are magnets with N & S poles (hence no monopoles).
Only 1 field and 1 force (plenum gradient).
There once was a time where nothing existed, means that both plenum and hods are created and are the only 2 components of the universe. So, when models suggest the gradient produces a force such as Newton & GR, they ignore the origin of the plenum.
What is your origin story?
Scalar Theory of Everything (STOE) unites the big, the small, and the four forces (GUT) by extending Newton's model