| Just as a car passes a bystander, a light signal is generated at the exact midpoint of the car, which in turn travels to the ends of the car and triggers two events (the changing of the color of a lamp from green to red, one at each end of the car). The events are viewed from two different frames of reference, the CAR'S FRAME (attached to the car) and the BYSTANDER'S FRAME. The observer in the CAR'S FRAME says these two particular events were simultaneous, but the observer in the BYSTANDER'S FRAME disagrees. Who is right? Click here to see an animation of this situation). (WARNING: A fairly fast computer is required for best viewing. You can do the exercise without viewing the animation, but it will require you to imagine carefully what is happening.) |