For special relativity, Einstein provided a thought experiment about how time slowed. This is when as a space traveler would increase his/her speed in space. Explained, as the rocket ship moved away from Earth, time slowed for its occupant.
The popular example is to imagine flying in a space ship where when moving fast enough it will alter its space and time.
Now Imagine in the spaceship a light clock which stands vertically or perpendicular to the direction of the ship. Consider the duration of the light clock as X ; and Z as the direction of the ship. For example, X is 90C to Z which is at 180o.
A full cycle of the light clock X occurs when it bounces a beam vertically from its top point AC to its bottom BD and back: i.e., marking a period of time.
Consider for a second in time, the interval for the light clock takes 1/2 second between points AC, or its top and BD or its base.
If velocity of the space craft in direction Z is at 0, then the beam bounces vertically at 90o with respect to Z:i.e.,marking time. This applies for both an occupant of the ship and a separate observer. It would further appear at 90o if both observers were in a parallel constant momentum.
If velocity of Z, the rocket ship, is increased, then the beam of light is considered proportionally delayed between its points.
Depending on velocity, X can appear as a sign wave where points AC and BDrepresent half the wave length in amplitude. When the beam returns round trip fromAC to AC, it is considered a unit of its frequency: hence Fq = Amp/Vel.
Given an amplitude amp and a velocity Z we have frequency Fq: amp/Vz = Fq. This is where Fq * Vel Z = amp.
About the Theory of Relative Gravity 