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Though this site is skeptical of Einstein’s theory of relativity, it does make the theory more understandable.

In Newton’s world previous to Einstein, to explain for variations in the universe, time slowed down and other events had variability however tiny.

The theory of relativity says that universals like time and speed of light remain the same, but you and I as perceivers distort universals relative to where we are located. As an example, given on this web, a train is passing a station. The train appears to go at different speeds to the conductor-driver, the guard, a person walking train station and another standing stationary at the station. Both the conductor-driver and the caboose guard have flashlights that are already on. The speed of the light from their flashlights appears to vary. However, the speed of light appears to be constant and various measures over the years support this.

Thus, the location of the 4 described above sees light varying because of their location. In reality, the light and time are the same. It is the party of 4 given their varying locations that distort time and speed of light.