Third Model Unity Hypotenuse Model Given an angle of incidence, the path of the ray in free space can be used as the hypotenuse and set to 1. A right angle triangle can then be constructed in free space. This triangle in free space can then be transformed into a triangle in a refractive medium keeping the hypotenuse of 1 invariant. Knowing the refractive index of the material, then the value of x is X/R.I. The value of t is determined by x^2 + t^2 = 1 This model or template is not about length contraction or time dilation. For a given unit of time, a photon in free space will have a greater displacement in space than in a refractive medium. For a given distance, it will take a photon in a refractive medium a longer time than in free space. As a worldline. http://imageshack.us/photo/my-images/832/29j2.jpg/ Pythagorean treatment http://imageshack.us/photo/my-images/827/8ggf.jpg/