What factors can affect the speed of light?

As far as I know, the speed of light is constant only when it travels through a vacuum. This means the speed of light will remain constant as far it is moving through a vacuum, and it will always be 300,000 km/s. Although, the speed of light is believed to be constant in a sense, however, the fact still remains that it can be slowed down, especially when it travels through a medium like glass or air. When light travels through a vacuum, the refractive index is always 1.0, but the refractive index tends to change as light passes through a medium.

Most times, the refractive index of the new medium tends to increase, and this is exactly what is causing the reduction to the speed of light. What happens when light passes through a medium is that the electrons in the medium absorb light energy and they get excited, although this may not affect the speed of light.

The way that universe is expanding is determined, so scientists say, on the Big Bang Theory. When the universe “exploded,” it set everything into motion. New theories are being put forward all the time on how the speed of light will be determined. When Olaus Roemer first calculated the speed of light in the 1600s, the universe was determined to be stable.

What this means is that nothing was really “moving” or changing. Since they knew that planets and moons moved, there was no consideration of stars burning out or different variables taking place within the universe. It was seen as something that was and would remain as such. Now, we know today that the universe is continually changing and expanding. New areas and objects are being discovered all the time.

Black holes are changing the landscape of the universe. Each of the above-mentioned factors and more is determining the rate of acceleration or deceleration to the speed of light.