Physics
Reference Frame in Special Relativity
Quick fact
In special relativity, there is no 'correct' reference frame; all inertial frames are equally valid, and the speed of light is the same in every one of them.
Why this is interesting
Imagine you're on a smoothly moving train playing catch with a friend. To you, the ball goes straight up and down. But to someone on the platform, it follows a curved path. Who is right?