To make you SEE much better the reason I believe GENERAL RELATIVITY has been seen as "almost unattainable to most people to understand" all these years -since its proposal- I prepared a short work brought here from wikipedia... follow me on its details:
"One consequence of the laws of
electromagnetism (such as
Maxwell's equations) is that the speed
c of
electromagnetic radiation does not depend on the velocity of the object emitting the radiation; thus for instance the light emitted from a rapidly moving light source would travel at the same speed as the light coming from a stationary light source
(although the color, frequency, energy, and momentum of the light will be shifted, which is called the relativistic Doppler effect). If one combines this observation with the
principle of relativity, one concludes that all observers will measure the speed of light in vacuum as being the same, regardless of the
reference frame of the observer or the velocity of the object emitting the light. Because of this fact, one can view
c as a fundamental physical constant. This logic is the basis of the theory of
special relativity.
[3]
Observers traveling at large velocities will find that distances and times are distorted in accordance with the
Lorentz transforms; however, the transformations distort times and distances in such a way that the speed of light remains constant. A light sensor traveling near the speed of light would also find that colours of lights ahead were
shifted toward the violet end of the spectrum and of those behind were
redshifted, so that the Lorentz transformations and classical explanations of frequency shifting are in harmony..." [wikipedia 2008].
Don't worry! I didn't change the text a bit... I only change the appearance of the parts I'm interesting you to see and interpret.
First they say that no matter the "relativistic speed" (they love to use complicated words to make it hard to understand it... anyway!) ...of the light source, "c" will not change (!)
Ohhh! But later on they affirm that certain conditions [like gravitational pulls, etc] may introduce changes in the color of the light-wave... bla,bla,bla...etc.
They even gave it the name of "RELATIVISTIC DOPPLER EFFECT". I can imagine that such unexplainable contradiction in terms is what brought to physics so much troubles until today.
Think about it as an intelligent being:
IF we haven't (ever) observed "a priori" the color change effect in our experiments with light... who could have PREDICTED that this... "Doppler Effect" WOULD HAVE HAPPENED... AS IT DID? The concept of a CONSTANT SPEED OF CHANGE was logical and obvious from the time of Maxwell, no credits to Einstein about this (read history if you have any doubts) so... we had to explain -or at least find an explanation- to bring both contradicting observation together... Can you see it? I'm giving you the tool to understand why both obviously opposing "TRUTHS" can be one TRUTH... If was not "c" what's CONSTANT in the universe, but the "SHIFT between the electrical and magnetic field of the wave" JUST AS MAXWELL PROPOSED IN HIS DAYS! MAXWELL WAS RIGHT FROM THE VERY BEGININGS! The ONLY CONSTANT IN THIS UNIVERSE WAS THE "SHIFT" not the human-made-measurement of "c". (!) Allow me to illustrate this idea in a little bit more simplistic manner: Imagine that light was a bunch of horses ready to start the race. The fastest horse (the longer wavelength of the components of the given light) will brake from the rest and will go ahead in the race. Obviously the larger wavelength of all [component of what we know as light] will be the INFRARED. If we placed light sensors at a certain distance from the light-source... ISN'T IT LOGICAL TO THINK (AND PREDICT TOO) THAT IT WOULD BE THE INFRARED LIGHT [LOWEST FREQUENCY COMPONENT] THE FIRST HITTING THE SENSOR? YOU TELL ME...! I don't blame those who from the very beginings found Einstein's ideas incomprehensibles from the human stand point... I have and I don't feel ashame about it either. Since the actual dimensions between the different wavelength of the component of lights are so tiny... scientist will find themselves in a very difficult position trying to determine which wavelength of light must "dictate" the exact number defining "c." Since the INFRARED will be the "winner" of the "race" -as it should be always- I can imagine that all this time we have been considering that component when it comes to define the speed of light between large distances... We have been wrong the very moment we FIXED "c" with a final set of numbers. I believe that if we used special sensors for each and every wavelength of the components of light the answer will be different for every frequency. What do you think about all this? Let me know even if you disagree totally with my thoughts... especially so. HUMANBYDEFAULT