Why is the speed of light the same for everyone?
The speed of light is the same for everyone because it is a conversion between two counts every observer keeps, and motion has nothing in it that could change the conversion. Each observer measures distance as how long its own clock runs before a disturbance somewhere else can be answered, so the speed of the answer comes out as one, by construction. Motion does change how an observer sees the sky. Stars crowd toward the direction of travel, as James Bradley found in starlight in the 1720s. Every such shift keeps the angles at which lines cross, and the maps that keep those angles are exactly the transformations of special relativity. They leave the light cone where it was. Since 1983 the meter has been defined by light, so the number itself is a choice of units.
Also in Chapter 22: Why Do All the Clocks Agree?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 17: Why Is There a Speed Limit?watch a universe make its own particles