In a Quora discussion involving Special Relativity, the following comment about the speed of photons in space led to this explanation”
“Even when the signal speed is kept at c in both approaching and stationary observer, the former receives the signal sooner. The word ‘sooner’ also means ‘faster’…”
The Case of a Stationery Observer
If the observer is stationery (as you just stated), then the observer will measure photons arriving at speed c.
The Case of an Observer Moving toward Photons
If the observer is moving toward the oncoming photon, the observer will still see the photons arriving at speed c. However, the observer will have shortened the distance the photon was earlier expected to travel. When the observer is moving toward the photon, the word “sooner” means “closer” and not “faster.” When you approach anything moving toward you, you are removing space that the photon otherwise would have traveled, and you reduce the time the thing needs to travel to get to you. “Faster” in this case is an illusion.
No matter where you are or how fast you are going, space will only transfer a photon from one quantum unit of space to the next at the speed c.
The Case of an Observer Moving Away from Photons
You might almost outrun a photon by moving away from the photon at near the speed of photons. However, when that photon finally is received by your eyes, it will move from the last quantum unit of empty space to your eye at the speed c. This is because when you are moving away from a given photon, you are adding space between you and the photon. In the case of outrunning photons, the arrival of the subsequent photons will be spaced out. Although each photon will still arrive at speed c, they will arrive less frequently, which causes a “red” Doppler type shift in the frequency of the light.
Photons always travel at c in the local space.
The Math of Special Relativity Works, but…
It is easy to understand why Special Relativity theory might seem valid when photons will always arrive at their destination traveling at c. The second postulate of Special Relativity theory states that photons travel at c in all reference frames; however, “reference frames” are mental constructs (see Time Dilation Theories are Smoke and Mirrors).
There is no such physical thing in the physical Universe as a reference frame. One can imagine that since the photon arrives at speed c, then it might have traveled as though from its source in a unique reference frame at speed c all along, but this is an illusion. The photon is moving at speed c in the local space (where space can be added or subtracted by relative motion), and the photon is not moving in an imagined reference frame.
Although the math of Special Relativity theory will work out, the first postulate assumes that space is not absolute. The absolute drift in space is instead thought in Special Relativity to be a drift in a physical, linear timeline. In Special Relativity theory, it is assumed that physical matter exists in Minkowski time frames, and that physical matter can move not only in space. but physical matter can also move through time. There is no physical evidence for a physical timeline. All physical matter is always fully accounted for in the present moment. No physical matter has ever dilated out of the present moment, and no historical record has ever recorded relativistic objects suddenly appearing from the future.
The simple explanation that agrees with all the facts is that space is absolute (and space includes time), and that photons always travel at c in the local space.