Here is the problem with the belief c can not be crossed. Accelerate to half c, stop all thrust. How fast are you moving? How fast is light? Accelerate to half c again, stop all thrust. How fast are you moving? How fast is light?
Are you not now traveling at c and light magically twice c?
So if light would be constant in a complete vacuum, and I have no reason to doubt that claim, then the only reason c can always stay c regardless of your velocity is because your clock, i.e. your measuring device, has changed in relation to your velocity and the speed of c.
We have measured light on high speed trains, to the best calculations it travels at c in all cases.
Clocks at the equator tick differently than clocks at the poles.
Clocks in orbit tick differently than clocks on the equator or poles.
Car A = light and travels at 100 mph. Car B is stationary. Car C is traveling at half of A.
How does car C see car A traveling away from it at 100 mph the same as B? The only logical answer is that B and its measuring device has changed due to its velocity and energy input. Light is not 2 velocities for 2 different observers, the moving observer has changed as well as his clock in relation to velocity (increased energy). For all anyone knows we could be traveling at c through space this very moment. Since nothing has ever been observed at rest, with no motion, there is no way to judge velocity except that of relative velocity between two or more MOVING objects. So when a spacecraft begins acceleration, it is already moving through space, its only reference for velocity the Earth, which it counts as stationary, when it is not.
So one can never exceed c by using ones own measuring device, as it changes proportionally to velocity and the constant c. But to B C is already traveling at half c, but how fast is b already moving as the Earth spins, and orbits the Sun, and the Sun the galactic center, and the galaxy through space? So why does B say A is traveling at 100 mph? If observed from space both car B and C are moving, not just C. [link to www.thunderbolts.info