Buridan held that planets turned around the sun from inertia, pulled in by what would become gravity (circa 1350 CE). No doubt studying canon balls’ trajectory helped in the following centuries. By 1600 CE Kepler knew that masses attracted each other, and exactly reciprocally so… and inversely to the distance between them (it’s actually the square of the inverse). Gravity was theorized to be described by: Mm/dd… M and m being the masses of the object, and d the distance. Boulliaut aka Bullialdus, a French priest cum physicist suggested this.
Bulliadus had a neat little reasoning still valid nowadays, in strict analogy with light. Bullialdius hypothesized that gravity was carried by particles emitted by the mass and was proportional to the density of said particles. That’s called the “inverse square law” as the force it depicts is inversely proportional to the square of the distance. Bullialdus reasoning may look naive… But we have not progressed much since!
Bulliadus was made one of the initial members of the Royal Society, and has a crater on the Moon. Newton testified to the priority of Bullialdus during his quarrel with Hooke about who invented what). Newton more or less proved the equivalence of that law, plus the basic laws of mechanics…. with Kepler’s three laws.
Newton thought that instantaneous gravitation as he had it, made no sense whatsoever (he wrote in a letter).
The Turin born Simon de Laplace corrected this a century later, making gravity progressive, inventing in the process field theory and gravitational waves.
In June 1905 Henri Poincaré published relativistic gravitational waves. They have to propagate at c, the speed of light.
In the following decade, Einstein, with the help of his friends, including Besso and Hilbert, wrote down a relativistic version of Newton’s theory. One main ingredient is that time slows down next to masses, so star light deflection next to the sun is doubled, as light spends more time next to the sun, giving it more time to be deflected, etc. Another is that light follows geodesics of 4 dimensional space whose (Ricci) curvature K = T. Where T is the energy-momentum tensor.
The first order approximation of Einstein’s gravity is the classical Laplacian-Poincaré version.
But what “causes” Mm/dd? We don’t know yet. QED doesn’t really help.
Quantum ElectroDynamics (QED) reproduces the classical Coulomb potential (1/d) (giving the 1/dd force) with exchanges of virtual photons. The same is to be expected for gravity with virtual gravitons. Does that mean that virtual photons exchange “create” the 1/dd force? Not really: a critical examination of what happens says otherwise: QED starts with installing the “Proca Lagrangian” in the path integral. That Proca Lagrangian contains the Maxwell equations which contain in turn the Coulomb potential. So QED demonstrates its own hypothesis as far as (1/dd is concerned)…(That doesn’t mean QED is useless: it’s a perturbative theory which predicts some perturbations with great precision, and those are extremely technologically relevant!)
Nevertheless it seems that we are progressing spectacularly from what is, for common high energy physicists, an unexpected direction .
I hold that the true architecture of the world is given by Quantum Entanglement… And the progress there is spectacular: particles of different nature have been entangled.
SQPR hypothesizes that Quantum Entanglement has a finite range: if true it gives immediately Dark Matter and Dark Energy. Moreover, SQPR changes the nature of the vacuum. However the relationship with the 1/dd factor stays mysterious… So far, then, one can’t produce an explanation really deeper than Bullialdus offered…
Patrice Ayme.
Patrice Ayme's Thoughts 
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