## It Takes Two to Tango: The Decline of Observer-Physics

The velocity $v$ seems innocuous enough. But, it has been the seat of many a misunderstanding. In fact, Einstein introduced his theory of special relativity to emphasize the fact that the ultimate velocity is the speed of light, $c$. The position of a body moving from point $x=0$ at $t=0$ along the $x$-axis is simply $x=vt$. That is, we measure $x$ and $t$ and obtain the velocity as $v=x/t$.