Does Light Always Travel the Path That Takes the Least Time?

We all are aware of the fact that light travels faster than sound. But, are you aware of the fact that the light always travels through the path that takes the least time? It is the Fermat’s principle, or the principle of least time named after a French mathematician Pierre de Fermat.

How do we know if light travels through shortest path?

When a ray of light passes through different mediums or different materials, it travels at different speeds and it bends in such a way that the path which is taken by the light to travel from one medium to another is the least possible time. The particles in the light simply can’t choose the shortest path, but the waves in the light somehow accidentally find out.

If you are looking into deep digging on how light travels through shortest path, this general mathematic equation can be of use to you. Let’s suppose D is the length of the path, and V is the speed of the light. T here denotes the time needed to travel from one medium to another. The time ‘T’ takes a traverse path which is D/V. In general,

, where D1 is the length of a path of first medium and V1 is the length of a path of the first medium, and D2 is the length of path of second medium and V2 is the length of a path of the second medium.

So, Fermat’s theory and the equation related to theory makes it clear that light always travels the path that takes the least time.

Alfred Boyd