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Okay, I think you are getting on track. Maybe a bit ahead of yourself in some areas. I can try to give you my understanding of where this weirdness we call relativity comes from.
First of all, you had Maxwell who developed a theory of electromagnetism that was uniform (did I say uniform? Yep, uniform!) in all frames of reference. This was a big problem because the consequence of this was that light had to be uniform in all frames. Whether you were travelling at 99.9999999% the speed of light or were sitting still, if you sent off a light beam ahead of you, necessarily you would measure it to be going exactly 3 times 10^5 kilometers every second. Moreoever, ANY lightbeam that happens to cross your path will be measured to be going at that speed regardless of where it was originated from.
This is extremely counterintuitive. When I am going nearly the speed of sound and sitting on the nose of the aircraft, I will likely not hear a sound because it is too hard for any compression wave to reach my ears (I also won’t be able to breathe, but that’s the joys of doing these thought experiments, you don’t actually have to do them to figure out what’s going on). However, if I’m going nearly the speed of light, I can still see photons just fine.
So, Special Relativity was developed to deal with this strange phenomenon. It basically introduces mathematical factors that allow us to modify one of our tried and true beliefs about the universe… namely that an inch is an inch no matter who measures and how everywhere in the universe and a second is a second no matter who measures it and how anywhere in the universe. However, we don’t throw the idea of spatial and temporal absolute away completely. No! We just listen to Mr. Einstein when he tells us that we need to listen to Mr. Newton and Mr. Galileo and interpret a little farther: namely that inertial frames of reference (me sitting on a magic carpet going a particular speed) are indistinguishable. If you build your rulers and clocks on earth, then go sit on the carpet, your rulers and clocks will be fine. And if you land back on earth, your rulers and clocks will be running fine. However, you may notice a difference in the absolute TIME that is on two different clocks that were calibrated simultaneously when we built them.
Why is that? Because relativity says, “Goodbye!” to our concept of simultaneity. We think that if two runners start at a starting block and one runner is faster than the other, they will still measure the same time when they both meet at the finish line. This ain’t true, though. The faster runner’s clock will actually be a bit behind the slower runner’s clock. Likewise, if someone is sitting in the stands and sees the slower runner pass by with a ruler it will look like the ruler is a bit shorter than it should be… and the faster runner’s ruler will be even shorter. However, when they both stop at the end of the race for drinks, all three rulers will be the same size!
Okay, this probably all sounds contrived and made up, but it is exactly what must occur in order for the speed of light to be the speed limit of the universe. And why must the speed of light be the speed limit of the universe? Well, shhh!! I’ll tell you the reason that doesn’t get spoken very often (and I’m not quite sure why this is the case)… it’s because light is a wave that travels through a vacuum.
WHAT? Is JS Princeton off his rocker? What does light travelling through a vacuum have to do with relativity? Well, you may remember Michelson and Morley? They proved once and for all that the speed of light didn’t change no matter what your relative speed was to the background. This trounced the theory of ether. In effect, the nature of light is such that it travels through nothing just like it was travelling through SOMETHING. Maxwell was convinced that the ether existed because he though the electric and magnetic fields were real things. He didn’t figure out that while they were real things they didn’t need a medium through which to travel.
Einstein thought, while on his bicycle to his patent clerk’s job, what it would be like if he could travel the speed of light on this bicycle. Why then, as he was speeding up he’d see all the light ahead of him blueshifted and all the light behind him redshifted. However, once he REACHED the speed of light, there he would be travelling along with these light beams. He could see their crests and their troughs as stationary backdrops alongside of him. Light would be stationary! But that is a contradiction, because the solving of Maxwell’s Field Equations for the vacuum solution (that is LIGHT!) DEMANDS that the light waves travel at the speed of light. They AREN’T ALLOWED TO BE STATIONARY! The math doesn’t allow it.
This is a monumental insight. It’s what prompts the development of Special Relativity by considering the equivalence of reference frames (after all, if light must travel at the speed of light, then in all reference frames light must travel at the speed of light) and E=mc^2 because you can actually see that the energy endemic to matter as it accelerates towards the maximum is equal to that quantity if you carefully look at how much total energy it takes to accelerate a given object. And ulitmately, it leads Einstein to consider how, if space and time are not ultimately absolute, they must look. In effect, this is what leads Einstein to develop General Relativity which incorporates the conservation of energy together with the force of gravity in a thing of mathematical beauty.
If you want to read more about the “practical” effects of relativity, I suggest reading the following two books:
Gott’s Time Travel in Einstein’s Universe
and
Gamow’s
The New World of Mr Tompkins
Hope this helps!