Time and energy
The hypothesis of Planck being unsettled by the continuous interaction between mass and time, does not necessarily mean that particles do not exist. It means that particles need not exist, that there might be waves only.
The energy of light is equivalent to a certain quantity of mass. Light approaching earth gets more energy and therefore more mass due to earth’s gravitation. Light leaving earth looses energy and mass.
According to present-day understanding photons get the speed of light at the same moment they are emitted, regardless of the lightsource’s speed. In vacuum photons travel at a constant (maximum) speed, having a certain quantity of energy and an equivalent quantity of mass. In another medium than vacuum photons have a lower speed. (Virtual) photons do not possess rest mass, needing the speed of light to get a certain quantity of energy and become a real photon. Photons emitted by a lightsource do get the speed of light at the same moment of their emittance, apparently because of an acceleration from 0 km/s to the speed of light in 0 seconds.
Here we come upon the essential difference between covering longer/shorter distances per unit of time by acceleration/slowing-down (speed increase/decrease per unit of time) and by time-acceleration /time-delay (shorter/longer duration of the course of time). More/less energy is needed in cases of speed increase/decrease. Less/more time is needed in cases of time-acceleration/time-delay. The momentum of a body subjected to acceleration, increases. The momentum of a body which is slowing-down, decreases. On the other hand, the mass of a body subjected to time-acceleration, decreases (no change of momentum), whereas the mass of a body subjected to time-delay, increases (no change of momentum); see also post 2.
This also explains why, in contradiction with the general theory of relativity, forces felt by objects undergoing constant proper acceleration are distinguishable from those caused by gravitation.
To be continued.