> redefinition of the speed of light as the speed of causality Since when this is redefinition? As far as I understand, this was always the definition. In fact

> redefinition of the speed of light as the speed of causality Since when this is redefinition? As far as I understand, this was always the definition. In fact, calling it the speed of light was always a bit misleading, since, first off, actual speed of light depends on environment, and second, there is nothing really special about light. It's just under ideal circumstances it can propagate with the maximum possible speed, i.e. the speed of causality. Light isn't fundamental for the laws of physics, causality is.