I know the answer is many, some of them I already understand very well, time dilation etc, some other I might be able to grasp the idea (like light cone) and I will not be able to understand some others (i can't name it because i dont know what i dont know) I am a 2nd year physics major, just scratch the surface of SR and given a little peek hole by my lecturer about GR. I think before I go to my 3rd year, it is a good idea to be able to think in relativistic term intuitively before I jump into all the formula and equation and calculation that will be thrown at me at my later years. 1. lorent'z transformation are defined in term of speed of light and speed if light itself is determined in terms of epsilon and mu. In the case of non-vacum, light travel slower, and thus the slower version of speed of light is then subtituted for the lorentz's transformation? does the permiability and permifity of free space changes the space-time nature of the space it self? 2. a number of things travel at the speed of light, one of them is, of course, light. other things are the composition of lights, such as magnetic and electric field, and also gravitational field. (or changes in those field I should say). Is asking why these things travel in the speed of light is a valid question? is it because these information carry no mass (does not bend spacetime) or it is just the nature of these things? or is it because the nature of space time? 3. if something move faster, it gets heavier, i know the precise definition is not exactly that. my question is: does this relativistic mass (not the rest mass) bend space time? and if they don't, why does the rest mass does but the relativistic mass does not? 4. I think no body knows yet but I am not sure, why does the gravitational mass and the inertial mass the same? 5. in simple geometrical/topological term, what does it exactly meant for space time to be bent? I have seen a lot of picture and I do have an idea of it but not much enough that I can intuitively built up the formalism from scratch. Thank you.