What is Light clock?
The '''light clock''' is a simple way of showing a basic feature of [[Special relativity]]. A clock is designed to work by bouncing a flash of light off a distant mirror and using its return to trigger another flash of light, meanwhile counting how many flashes have occurred along the way. It is easy to show that people on Earth watching a spaceship fly overhead with such a clock would see it ticking relatively slowly. This effect is called [[time dilation]]. Before we study the light clock, consider another kind of relativity. Imagine that someone is dribbling a basketball in the hold of a large cargo jet. The basketball player is moving in the same direction as the jet airplane. The other people in the plane see him moving a meter or two as he makes one dribble. Between the time the ball bounces the first time and the ball bounces the second time, about one second has passed. But when the first bounce occurred the basketball was over Gibraltar, and when the second bounce occurred the basketball was over the water nearer to Spain. So the basketball has moved 280 meters with respect to Earth. [[File:Dribble over Strait.svg|500px]] Now consider a somewhat similar question of relative motion. This time we are going to consider what people looking at stars from the North Pole see when a very fast spaceship flies over them. We can use [[algebra]] and the [[Pythagorean theorem]] to calculate how much time slows on the spaceship. The only other thing we need is the equation that relates distance, '''d''', rate or speed of travel, '''r''', and time, '''t'''. The equation is: '''d = rt''' The [[speed of light]] is constant, so we will apply this value to two problems. We will call the speed of light '''c''', as this is the letter scientists usually use to name it. [[File:Light-clock schematic.svg|500px]] A clock is made by putting a light output at the bottom of a long pole, a mirror on top of the pole, and an electronic light detector down at the bottom of the pole. The clock is started by briefly closing a s