Why does the light needs time to travel through vacuum?Is there something makes it needs time? How did we prove that there is nothing in vacuum?
When there is no medium, there is nothing to oppose the propagation of light and therefore it moves with a constant velocity. All electromagnetic waves including light travel in vacuum with the same velocity (3 x 10^8 m/s). Since the energy is to travel from one point to another, a finite time is also required.
The velocity of light is experimentally determined by many different methods. (Romer’s methos, Fizau’s method, Foucault’s method, Michelson’s method etc.)
When light travels in a medium, whenever light interacts with the matter, the atoms absorb light and are re – emitted and the average speed in a medium will be less than in vacuum. In vacuum, there is no matter t interact and that’s why there light travels with maximum velocity.
(If you remember the structure of atom, most of the space inside an atom is vacuum. The speed of light decreases only when it encounters matter. So, when we consider a particular medium, the speed of light is a constant in it)