The speed of light is measured to have the same value of c = 3x108 m/s no matter who measures it, where they measure it or how fast they are moving through spacetime when they do so.
Reality is a break from stillness. 1 → Many
Speed, as we measure it in our locale, is a metric contingent on comparison. If you are moving at 10 meters per second, you are doing so in comparison to something that is at rest relative to you. However, that something is also moving with earth at approximately 460 m/s. Earth additionally, is moving with our solar system at 230 km/s and so on. The more we zoom out, the more we regress to the mean, the constant state of our ‘being’:
“Time is a flat circle” — Matthew Mcconaughey as Rustin Cohle in True Detective.
Everything is happening all at once and has happened in every fashion possible from infinity to epsilon. The speed of light is a constant perhaps because in our building blocks, we too follow the same wave-particle duality. We are only constant fixtures in our perception of reality in the flat circle that is our brief segment of time.
The way to break the stillness was, is and always has been for the 1 to become the many, introducing duality and subsequently the myriad. This therein opens the door for metrics of comparison, hierarchy in experience, and everything that makes our segment of the circle an exciting journey and not the emptiness it is by default.
Speed with no point of reference might as well be still.