Motivation
Too many people seem to think that Push Gravity, or indeed any mechanical explanation, is a valid model for gravitation. This is erroneous, as these models are either not internally consistent, or require physically impossible assumptions.
Basic premise of Push Gravity
The model assumes that gravity is caused by particles impacting massive bodies from all directions, thereby providing a push force wish causes a tendency for massive bodies to move towards each other, also because the bodies themselves cause a shielding effect, leading to pressure differentials due to the collisions not being fully elastic. This is also posited as the reason for the inverse square law – the incoming momentum flux is greater than the outgoing one. Further assumptions must be made to account for the fact that the gravitational force is primarily caused by total mass rather then surface area, namely that only a small number of particles actually interact with a massive body.
Reasons why Push Gravity does not work
1. The gravity particles are thought of classical particles with classical interactions. This notion is inconsistent with current understanding of particle physics – there is no particle which could have all the characteristics required by PG without violating one or more physical laws
2. The particle flux filling all space must be perfectly isotropic and of very high density. No known form of radiation of particle flux has these characteristics to the degree required by the theory
3. The neutrino. Modern proponents of PG often posit the neutrino as the mediating particle of the theory. This has been conclusively disproved by Richard Feynman in 1995 [1].
4. Transparency of matter. With increasing mass the change in gravitational shielding becomes mathematically less then the sum of the shieldings of the two bodies. To overcome this one has to place an extremely high lower bound on the flux density of these particles. This is inconsistent with experiments conducted to detect such flux energies [2]
5. Drag. Any mechanical model of PG necessarily creates a drag force, or else there would be no interaction between the particles and a massive body. In order to reduce the amount of drag to levels consistent with observation, the speed at which these particles move must be in the region of 10^17 m/s, which is many orders of magnitude higher than the speed of light.
6. Heat energy. If the particles of PG really move at superluminal speeds, which is in violation of basic physical principles, they would impart a heat energy onto any massive body sufficiently high to instantly incinerate any form of normal matter.
7. Aberration. In any mechanical model of gravity, the gravitational force can only act with finite speed, creating an aberration effect. Such an effect has not been observed.
8. Sources of gravity. As we know today, and as is experimentally well verified [3], all forms of energy are a source of the gravitational field, not just mass. This is not explainable by PG.
9. Time dilation. PG has no consistent mechanism to explain the well verified phenomenon of time dilation.
10. Deflection of light. PG cannot explain deflection of light rays while at the same time avoiding aforementioned problems with drag.
11. Thermodynamics. The flux of particles in PG would be many orders of magnitude more energetic then mass at rest. However, not transmission of energy is observed, even though there must be a form of interaction with ordinary matter. This leads to a violation of the laws of thermodynamics.
12. Perpetual motion. Due to shielding effects the existence of PG would make it possible to construct a perpetual motion machine. Again, this is in violation of the laws of thermodynamics.
13. Binding energy. Binding energy of elementary particles contributes to their gravitational energy, which is not explainable by PG.
14. Origin. There is no consistent explanation as to where those particles come from, why their flux never varies, why the field is perfectly isotropic, or why the total energy never decreases even if the universe is expanding.
15. Mathematics. The mathematics of PG are not self-consistent, and do not produce the correct results. [4]
16. Frame of reference. PG would create an absolute frame of reference, which means that the Theory of Relativity must be false. This is in contradiction to experiment and observation.
17. Large scale structure. Due to the necessary isotropy of the PG medium, over very large distances the net forces would cancel out. This does not explain the large scale structure of the universe.
18. Non-existence. No flux field or particle stream as needed by PG has ever been observed by experiment or observation.
Conclusion
PG was abandoned around 1900 due to some of the very serious problems listed above. It is not a viable model of gravitation, and even in its hey day ( around the time when LeSage was alive ) it had very few proponents, since even then it was recognized that there were serious problems with this model. It is in many ways in direct contradiction to empirical evidence, and would, in order to work, violate several fundamental laws of physics.
In short – push gravity is complete nonsense.
References
[1] ^ Feynman, R. P. (1995), Feynman Lectures on Gravitation, Addison-Wesley, pp. 23–28
[2] Bertolami, O. & Paramos, J. & Turyshev, S. G. (2006), General Theory of Relativity: Will it survive the next decade?, in H. Dittus, C. Laemmerzahl, S. Turyshev, , Lasers, Clocks, and Drag-Free: Technologies for Future Exploration in Space and Tests of Gravity: 27–67, arXiv:gr-qc/0602016
[3] Carlip, S. (1997), "Kinetic Energy and the Equivalence Principle", Am. J. Phys. 65: 409–413, arXiv:gr-qc/9909014, Bibcode 1998AmJPh..66..409C, doi:10.1119/1.18885
[4] Lesage's Shadows