The nature of light is described by the theory of quantum mechanics, which combines wave-like and particle-like properties. This duality is known as the wave-particle duality.
Light can behave as both a wave and a particle depending on the experimental setup and the observation being made. When light is observed as particles, they are called photons. Photons are discrete packets of energy that exhibit particle-like behavior. When light is observed as waves, it exhibits characteristics such as interference and diffraction, similar to other types of waves.
The wave-particle duality of light arises from the fundamental nature of quantum mechanics, where particles and waves are not separate entities but rather different aspects of the same underlying phenomenon. It is a fundamental property of all quantum objects, not just light.
As for why light chooses the quickest path, this can be explained by Fermat's principle of least time. According to this principle, light takes the path that minimizes the travel time between two points. This principle is a consequence of the wave nature of light.
When light travels from one point to another, it takes all possible paths between those points. However, the path that minimizes the time taken is the one that constructively interferes with itself, allowing the waves to reinforce each other and create a bright spot at the destination. This principle can be understood using the concept of optical path length, where light takes the path that minimizes the total distance traveled in a medium.
In summary, light exhibits both wave-like and particle-like properties due to the wave-particle duality of quantum mechanics. The quickest path taken by light is a consequence of Fermat's principle of least time, which is based on the wave nature of light and the constructive interference of waves.