Gravity mechanism: explosion analogy
Air based explosions
First consider a sphere of 1-m radius at sea level. The normal air pressure acting outward at the 1- radius is 101,000 Pascals, and the spherical surface area is 4Pi or 12.6 square metres. The outward force is therefore F = PA = 101,000 x 12.6 = 1,270,000 Newtons. Now this sphere of compressed air doesn’t explode outward at sea level, because the air beyond it is at the same pressure. The inward force cancels this outward force.
Second, consider an explosion. In an explosion in the air, the pressure at the boundary or ‘shock front’ is greater than normal atmospheric pressure. The excess pressure is normally called ‘overpressure’. Thus the outward force in an explosion is greater than the inward force from the surrounding ambient pressure air! This is why an explosion occurs.
But consider the original problem again: Newton’s 3rd law says that every action has an equal and opposite reaction. What is the reaction to the outward force due to the excess pressure in an explosion? Initially, before a vacuum develops, the reaction is simply the fact that the shock wave going north has an equal and opposite reaction by virtue of the part of the shock wave going south.
However, within seconds of an air burst, the out rushing air creates a nearly perfect vacuum at ground zero. This vacuum is a barrier preventing the force reaction from being carried by the opposite-directed outward shock wave. What happens then is that the reaction force occurs behind the shock front, as a long ‘under pressure’ phase develops, with wind blowing towards ground zero. This has in inward directed pressure and force, and is the reaction to the outward force of the blast wave.
The big bang: an explosion in the gauge-boson filled vacuum of space
Now look again at the big picture: the big bang. We know space is flooded with gauge bosons going at light speed and causing forces, because quantum field theory works well and is based on the concept that a force is caused by the exchange of gauge bosons, such as virtual photons between charges for electromagnetic forces. There are high-energy Higgs bosons in electroweak unification that cause inertial mass, and since Einstein’s equivalence principle of general relativity says inertial and gravitational masses are identical, the Higgs bosons may provide the physical mechanism of gravity.
In the big bang we also we see speeds increasing with distances, but really they are varying with time past. This is because when we see galaxies we don’t see them at a fixed distance (they are receding from us all the time), but at a fixed time in the chronology of the big bang! Actually there is a variation with both distance and time past, and we see recession velocities at bigger distances but also further back in time. (We cannot see to distance x without looking back in time by the amount t = x/c.) However, since the gravity force is carried at light speed, just like the visible light that carries the information on red shift, what matters regarding gravity is what we see. The linear variation of speed with time implies a fixed acceleration outward, equal to the speed of light divided by the age of the universe, which comes to 6 x 10^-10 m/s^2.
This tiny acceleration, when multiplied by the mass of the receding matter in the big bang, gives a massive outward force of F=ma = ~ 7 x 10^43 Newtons. This can’t be right, you think, because where is the reaction, the equal inward force implied by Newton’s 3rd law? GRAVITY! The gauge bosons form a perfect fluid, physically causing a drag-type directional-compression (the contraction term of general relativity and special relativity for gravity and for inertial motion, respectively) without any viscosity, since the gauge bosons or Higgs field only resist accelerations! The bosons flow around moving subatomic particles, filling in the volume they vacate. If the subatomic particles appear to accelerate in outward in the big bang from our perspective, the spacetime fabric bosons appear to accelerate the other way, predicting gravity by pushing things together: http://nigelcook0.tripod.com/