Beginning students of the Reciprocal System often have difficulty understanding scalar motion, confusing it with vectorial motion. I will attempt here to clarify matters.
Assume as a thought experiment, a spherical light source in gravitational equilibrium with us, the observers. In our ordinary 3-D spatial reference system, the source is stationary, and photons are streaming away from it at the speed of light in all directions. Without the knowledge of the Reciprocal System, you might conclude that the photons have independent motion and are moving vectorially through coordinate space away from the source. However, the theory says that this is not the case from the standpoint of the true, natural reference system. The photons actually have no independent motion and thus are stuck in the same space-time units in which they originate. It is the atoms of the source that have independent motion and are moving against the space-time progression. This resulting motion is termed gravitation and is always inward. Most importantly, this motion is scalar: it is inward in all directions, with no one direction favored. It is because the source is moving inward in all directions that makes it appear that the photons are moving outward in all directions. Since the inward gravitational motion is taking place in space, the motion imputed to the photons is outward in space.
Likewise for the cosmic sector: the cosmic atoms are moving inward in time, and so cosmic observers would conclude that the photons from their light are moving outward in coordinate time. In actuality, of course, the photons remain in the same absolute space-time locations and are not moving either in coordinate space or coordinate time!
Now suppose, as in the Einstein-Podolsk-Rosen experiment, that two photons originate at the same event and move in opposite directions. In the material sector, the motion appears to be outward in space; in the cosmic sector, the motion appears to be outward in time. In actuality, we are moving inward in space away from the photons, and cosmic observers are moving inward in time away from photons. We have no independent motion in coordinate time (at low vectorial speeds), and since the photons do not either, we are able to effect a change in both photons by means of a change in one of them. Likewise, the cosmic observers have no independent motion in coordinate space (at low vectorial inverse speeds), and since the photons do not either, the cosmic observers are able to effect a change in both photons by means of a change in one of them. (Existents which are contiguous in either space or time may both be affected by application of a suitable single force).
Because photons are stationary in the natural reference system, they are not “lost” from either sector and are not “disappearing over the time or space horizon”; the universe is not “running down” toward a slow “heat death”.