Damned interesting.
The notion that "C" is variable has been around for a long time but this is the first time I remember physicists claiming that they can test to confirm it with astronomical data.
Of course, if they do get a discrepancy, what next? They will have to come up with a correlate method to CONFIRM that discrepancy so they know it's not an anomaly of some other principles at work. So I doubt anything conclusive will result from this specific measurement.
Every time C has been measured through interferometry or other means, it always works out to the limits of technology.
A lot depends on it remaining consistent - values of most of the basic features of the universe - total age of the universe and everything in it, total mass, total energy even the parameters of fundamental forces are at stake. If it can be variable, much of that goes out the window and they have to consider starting over. They'd have to throw out all calculated values about distance of objects using Cepheid variable stars, because they are too far away (old) to be sure that C was consistent in the time the light started toward us (more than 12 billion years ago).
Just to forestall any misconceptions about "C" - it refers to the speed of light IN A VACUUM. The speed of light can slow considerably depending on the medium in which it travels. Photons can be slowed to immobility by artificial means such a super-cold laser-beam interference chambers. When a particle like an electron exceeds the speed of light in a dielectric medium (heavy water for instance) it generates a blue glow (as seen in nuclear piles), but the actual speed of light is defined as never MORE than 186K miles per second.
