Why is the speed of light a constant?
We don’t know why the speed of light is a universal speed limit for information, energy and matter in our universe. This question is of the same nature as why are the physical laws the way we find them and not something else. Some astronomers and physicists believe that it is just pure luck. If any of the’ constants of nature’ or physical laws were different that the way we have found them so far, our universe would be so utterly transformed that it would not contain sentient organic life at all. Our existence is balanced on the razor’s edge between reality and nothingness. We are so tuned to nature as we find it that even the slightest change would have made our existence unlikely. So, we find the speed of light to have the velocity it has, and obeying the rules of special relativity, because by some perverse process, had it been otherwise we would not be here to wonder about it!
