That's what the researchers are after. It's hard to accept things as singular in themselves so they continuously challenge this "constant" status. The speed of

That's what the researchers are after. It's hard to accept things as singular in themselves so they continuously challenge this "constant" status. The speed of light is given by the nature of the light, which is (presumably) ultimately based on other constants, so in this case the light speed is constant only thanks to being a relation of other constants. If one of the relying constants proves to be at its turn only mostly constant that changes the status of all the upstream constants. That's why that rabbit hole of universe's constants' study is so important! That being said, there are constants out there (e.g. π, which is a constant relation instead of relation of constants) for which "challenge" would probably mean assuming another kind universe entirely.