Velocity of light changes depending on the Aether it's in. There is no vacuum of space as that's just a made up fairy-tale just the same as the big bang or billions of years of Earth. There is an Aether, it's real and testable and gives off a certain amount of Ohms (300 something). Change the Ohms and you change the speed of light. Increase the Ohms increase light-speed, decrease Ohms and you decrease light-speed. To say lightspeed is a universal constant would mean that you would have to have the same amount of energy spread equally everywhere. Earth's magnetic field is probably producing the Ohms and because we live inside of the Earth the known universe is the Earth and the farther you get to center the more Ohms you lose. thus you lose lightspeed and you also shrink in size. This is very rare information though. Very few people know this as most are brainwashes into thinking Earth is a sphere that we live on the outside of and that it orbits the Sun. That simply is a fairy-tale. However the weaker Earth's magnetic field get's the more energy it outputs so the smaller it gets the hotter it burns. Earth has lost 10% of it's energy in just the last 100 years alone, there is not much time left for Earth or the Universe, only at most 115 years remain until the Universe will have lost it's energy and then it will simply melt into nothingness.
But I repeat the more condensed the Earth get's the hotter the field it spreads out which is why speed of light is actively increasing.