User blog comment:Interdimensional403/FTL possible sort of I guess.../@comment-2001921-20130508071611

If you mean the speed of light in certain media, we've known this for a long time. If you mean c, the speed of light in a vacuum, then no. Seeing as the speed of light is linked directly to things such as the electronic charge, proton and neutron mass, and such, we'd be able to recognise places where the speed of light was different because they would be completely inimical to life.