I see in you the makings of a great scientist. That is the kind of question Einstein asked. Maxwell's equations, which are very useful in describing electromagnetics, predict, or at least account for, the speed of light in terms of two independently measurable quantities, the permittivity and permeability of space.
Before Special Relativity, scientists recognized that this speed (as you perceived) must be referred to some medium in which the light waves travel. Effort was expended to find out what this medium was. The most famous and best experiment was the Michelson-Morley attempt to measure the speed of the earth through the "luminescent ether". The earth moves around the sun at 18 km/sec. Attempts to detect a difference of 36 km/sec in the speed of light, or any difference in speed, depending on direction, failed completely.
What was going on?
Einstein showed that one could get consistent results by abandoning an absolute frame of reference and the notion of absolute time, if all [inertial] reference frames were treaty equally. This required adopting some counter-intuitive ideas, but lead to a consistent laws of physics. One counter intuitive result was the lengths of objects in relative motion changed along the direction of motion. May I recommend A.P. French's very readable Special Relativity, for a more complete answer to your question?
Thank you for your reply. I have always had a deep interest in these larger questions.
Unfortunately, my advanced calculus skills ended up being a C-grade capability, so I’m afraid that the math really does often escape me.
I will definately put my hands on your recommended reading and give it a shot.
Given the issues with C that I mentioned, I wonder if perhaps space actually is a medium, packed with subatomic particles so small or different that we have yet to identify them. Perhaps if they had gravity, but were electromagnetically repulsed by atoms (with a force greater than gravity), this would also solve the dark matter issue. Such particles would be rare close to visible objects, but denser in the space between galaxies. Obviously this medium would have to allow the passage of light generally undisturbed. In this scenario, C might be more analogous to Mach 1 than an absolute limit.
Assuming this medium to exist, this might also affect light wavelengths over extremely long distances, and thus throw off what we think we know about progressive expansion of the universe.
If that is unbelievably stupid, forget it. If it is the hypothesis of the millenium, please cite me. ;-)