C may be the fastest light travels but workarounds may exist. However, that particular theory has been proven to be a fact, so a workaround will not change it as a constant - it will only open a new area of physics.
Actually, according to physicists Günter Nimtz and Alfons Stahlhofen(engaged in research at the University of Koblenz, Germany), C is starting to look like "not" a constant. then again, much of what we assume is based on the Theory of Relativity(ToR). Which, while it is a great work on how the universe appears to work when sensed by Humans, is starting to look less like how the universe actually works. Indeed, many of our issues stem fro us refusing to recognize that the Universe does not care how we perceive it.
One example would be the inclusion of time as a real "thing" in our science.
Yes, every event has an event horizon. It elapses over the extent of that event horizon.
BUT... That elapsed occurrence is no different if you measure it in the currently recognized 24 hour Terran clock, the little remembered French Metric time system or the time system enforced by any of the other races that exist beyond our knowledge.
The fact is that time itself is nothing more than a system _we_devised_ to help understand the events we perceived. Admittedly, we can expect to perceive them in line with those predictions in the ToR, ..BUT.. how we perceive the occurrences does not mean that is what really happens at all. We may sense ourselves and our craft stretching out to infinity as we approach "C", but that sensation has nothing to do with the state of the ship in reality. So while we perceive it stretching to infinity, it is...in fact...not changing state at all. Given propulsion and control systems which can operate beyond "C"
(including sensors that can reach beyond reaction limits), it is easy to predict we will find so call Hyper-C as possible as violating the so called speed limit of light speed.
I am just saddened that research on such systems is dependent on overcoming our belief in the fairy tales that our perception molds the universe.
Marc