Relativity: Ten minutes to Alpha Centauri?
It is almost frightening how well special relativity works, and how internally consistent it is. The simple arguments presented here don’t do full justice to how smoothly the concepts of space and time are intertwined in the theory, and how much sense this link makes on close inspection. We can note, however, that the constancy of the speed of light is well-established experimentally (starting with the aforementioned Michelson-Morley experiment), and in fact time dilation has been confirmed experimentally almost countless times!
http://cc3d.free.fr/Relativity/Relat1.html
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html
Experimental constraints on Special Relativity
http://backreaction.blogspot.com/2012/08/how-to-beat-cosmic-speeding-ticket.html
Mathematics is not empirical. Experiment separates the wheat from the elegance.
http://www.npl.washington.edu/AV/altvw43.html
Scharnhorst effect. Lightspeed arises from vacuum permittivity and permeabilty.
http://arxiv.org/abs/1110.1919
Huge Casimir effect at finite temperature in electromagnetic Rindler space. Local lightspeed exceeds c=1 when Casimir energy is negative. Finite temperature Casimir energy appears to be positive here.
A loophole must be consistent with special relativity and empirically testable. GR is rich with testable loopholes, e.g., ECKS gravitation with chiral vacuum symmetries only acting upon fermionic matter, from spacetime torsion (operating like Lorentz force) rather than curvature (Green’s function remove chirality). Violating SR requires vacuum engineering – rich with theory but lacking reduction to practice.