What happens if the speed of light is not constant?

Answer 1

We'll get consequences if the speed of light is not constant. GPS won't work, for just one off the top. GPS has clocks that are "tweaked" to account for the relative velocity of the satellites (which are called "birds") because they're moving around us. A consequence of c not being a constant might be that time is a constant. And GPS wouldn't work because the clocks of the birds are biased to account for their differential velocity. It's not much, but it's real and it's included in the system. And if c was not constant and time was, then the time base on which GPS functions would be "off" and the system would present gross inaccuracies with its readings. Which it doesn't, even with the clocks of the birds keeping different time than what we use here on earth. We always thought of time being a constant, and it took Einstein and his revelations to shake us out of that thinking. We now know that time is not constant, but light speed is. And that means that something else must be not constant. And it is time that is not constant. There is a bit more to this, but what is posted is a sufficient response to answer the question.

Answer 2

Refraction of light is associated with a change of speed of light.

The way in which light can change speed is by entering a different material with a different refractive index, or by exiting material.

Specifically, the index of refraction of a material is the speed of light in a vacuum divided by the speed of light in the material, n=c/v.

If the light enters the material at some angle other than straight into it, then it will be refracted. Refraction means that the light turns, this is the effect you can see when you have a straw in a glass of water.

The connection between speed and index of refraction is a general wave phenomena and not just related to light. Sound waves and water waves and others do the same thing but the name "index of refraction" is most commonly associated with light.

Answer 3

If the speed of light is not constant, it would challenge the principles of Einstein's theory of relativity, which is fundamental in modern physics. This would have significant implications for our understanding of the universe, including how we perceive time, distance, and the behavior of matter and energy. It would require a reevaluation of many scientific concepts and theories.