In a world of constant change, the speed of light is refreshingly constant, loyal and true. At precisely 299,792,458 meters per second, creation's speed limit is actually a critical part of how we understand the cosmos. So long as the speed of light is constant, Albert Einstein taught us, then space and time can be the flexible parts of the existential equation and the theory of Special Relativity works.
That said, it's possible that the speed of light used to be faster than it is. At least, that's the enduring theory of some upstart theoretical physicists over at the Imperial College of London. The theory holds that, in the very first instants of the Big Bang, the speed of light must have been faster than it is now, or else the universe would not look like it does today. It gets complicated, but Julian Huguet breaks it down nicely in today's DNews report.
Phys.org: Theory that challenges Einstein's physics could soon be put to the test
Smithsonian: Putting the Brakes on Light
NASA: What is the Inflation Theory?