General relativity explains gravity as space-time curvature due to presence of matter. How the presence of matter curves space-time as gravitational effect is here explained in more causal detail.
This more detailed explanation of gravity is with regard to how matter radiates energy to produce vacuum effect. It considers gravity as a vacuum effect occurring in the wake of emitted radiation created by, say, converting composites of matter and antimatter contained within the space-time medium. The escaping radiation is invisible except that it results in gravitational effect.
How can radiation be invisible?
Radiation can be invisible because it is able to occupy the same space whereas matter cannot. Such invisibility is typical of wave action. Waves can superimpose to produce visible effect only if the medium of the wave action changes in a way it becomes observable. If the total action within a space large enough to be measured is counterbalanced, then no change of the medium need be seen.
Although light is invisible to other light, as having no momentum of mass onto other light, it still has momentum with regard to the presence of mass, and sometimes it even converts to mass by interacting with it. According to special relativity theory, mass in relative motion is relatively greater than mass relatively at rest. If the relative motion is caused by the reflection of light, then light loses energy in increasing the mass it reflects, as in compliance with conservation of energy. There is also the Higgs Mechanism to consider whereby particles similar to light become mass by moving slower through the Higgs Field. Light also moves slower through a gravitational field, but an increased mass effect, as observed by a local observer in the field, is relatively nullified by matter also moving slower in the field and by the observer and measuring devices also having an increased amount of mass-energy.
As for a non-detection of radiation by matter, there is a virtual field of energy in quantum physics that is detectable according to a Born rule of quantum probability. A quantum wave function is interpreted as a probability amplitude, as a measure of change, for detecting a particle within a given time and/or a particular location. The probability of detection can be extremely slight. Billions of neutrinos, for instance, move through our bodies every second, but Earth detects only a few of them. Neutrinos are thus virtually invisible to us for the most part.
As for the difference between light and mass, suppose mass is an equilibrium state of light waves moving at light speed and crossing paths from every direction. It is contained by not allowing other waves to pass through it. It allows some of the waves to pass through while it reflects others in maintaining its form. The form itself is also capable of moving through space at different speeds, as does mass. How this free motion is possible is according to its particular state of equilibrium. If in motion, then it reflects less energetic waves counter to the direction of relative motion in allowing the more energetic ones to pass through, and it reflects more energetic waves arriving in the direction of relative motion in allowing less energetic ones to pass through. In effect, mass itself is wavelike motion moving through quasi-vacuum space as its medium of propagation.
Suppose this new wave form of energy acquires additional properties, such as further converting energy of the space-time medium into gravitational energy, as constantly in proportion to the amount of mass according to the principle of equivalence, which Einstein proposed in equating relativistic effects of gravity to those of relative motion. Further consider there is an extremely slim probability of detecting this gravitational energy in providing a vacuum effect in the wake of its emission. It thus converts into a new form of energy that is only detectable as gravitational effect. Moreover, since it does not directly change the motion of other matter, it does not violate conservation of momentum. Moreover, the extremely slim probability of its detection renders it as a long range effect consistent with the force of gravity being relatively weak compared to an electrostatic force of such atomic masses as the electron and proton.
If our observable universe is a finite anomaly of an infinite source of virtual energy, then the supply of energy converted into gravitational radiation could be indefinite, such that there could be no observable effect of its recycling back into its original form after escaping from the universe. However, there could be an observable effect if it recycles back before leaving the universe. Perhaps it recycles back as dark energy to cause the universe to expand at a greater rate than it had expanded at in the past, as consistent with a cosmological constant that Einstein had proposed as a repulsive force counter to gravity.
On the other hand, if our universe is infinite in extent, then the radiant energy recycling back into its original form is merely an equilibrium state of existence. It would then be consistent with a tired light theory for various observations separated by the life span of the tiring light.
About Author / Additional Info:
I retired in 1999 and self educated myself by writing and research. In my book on physics I explain how light creates matter and gravity. I am now writing a book on economics.