Im in high school, and i live in mexico, here the science isnt very advance and in high school we dont learn this things, but i investigate myself, as far as i know E=mc2 means that any mass going to the square of the speed of light then it would transform into enrgy. about the black hole thingy, well if you go to speed of lght, nothing will actually happens to you, because the light itself travels at speed of light and nothing happens to it. now i think that einstein didnt knew the actual speed of light and he was just supposing that the speed of light is the quickest thing in the world. maybe as far as we know is the quickest thing but what about all the types of light that exist beside the visible light? also why would exactly the speed of light would make something to change, the speed is just the mesurement to know how much distance you travel in certain time. and as far as i know the black holes are formed when suns explode and die. nothing to do with speed of light. and for the spacetime, as far as i know it is like another dimension intead of having time and distance separeeted they are in just 1 dimension. and thats why einstein said that gravity isnt actually a force like newton said, it is a curve spacetime that the planet creates and also the sun and that makes the gravity. i saw that picture with spacetime grid too. but all of this is just an opinion of a 17 year old guy in mexico, i might be, very very wrong or very very right.