Einsteins Theory of Relativity

Without getting too complex, Einstein essentially came forward with the revolutionary idea that not only is motion relative, but time is too. In fact, they are linked together. The faster you move, the slower others will perceive that time has passed for you. Why? Well imagine this. As you are sitting in the bus you shine a beam of light at the opposite wall. Lets say in 1 second it covers 2 meters before hitting the other side of the bus. Now, lets think of this from the perspective of the person on the street. To them the bus is also moving so the beam of light actually covers 15 meters in that same second. Why is this weird? Think about it. Here we have an object that just traveled 12 meters farther in the same amount of time