Light has been one of the most interesting and challenging phenomenon to understand for a long time. Earlier theories on light were two fold, on one side were the Newtonian theory of light which said that light was composed of particles or corpuscles and travelled in straight lines and explained the entire phenomenon around the particle theory. Even complex nature of light called polarization was successfully explained by Newton using his particle theory. In the seventeenth century, Christian Huygens a Dutch mathematician and scientist proposed that light is a wave and constructed a mathematical model to explain phenomenon such as diffraction and polarization around the wave theory of light. Both these theories could partially explain light but in the face of modern findings such as the photoelectric effect by Einstein in 1905 and the De-Broglie theory that “all mater exhibits wave like behavior” which was confirmed by experiments conducted by Clinton Davisson and Lester Germer in 1927 at Bell Labs, America. The wave theory and the particle theory of light failed to independently explain this phenomenon but together they seemed to have something to say. The only logical conclusion that seemed possible was that light simultaneously behaved as both particles and waves. This was regarded as the “duality paradox”
Some fundamental and contradictory differences between waves and particles are – while waves can split into smaller and smaller wave fronts, particles are not infinitely divisible. Secondly, while particles transfer energy and momentum in discrete manner (particle after particle), waves can continuously transfer both energy and momentum. Thirdly, in simple terms, diffraction is the bending of light at a corner. While waves can bend around corners, it is difficult to imagine a particle bending around a corner. Fourthly, during interference while waves that overlap each other can either add up or cancel out each other or can be found in any intensity between these two extremes it is very difficult to imagine particles adding up or cancelling out each other and vanishing at once. Issues such as these, put scientists in a great amount of confusion as to whether light is a particle or a wave or whether this paradox can be settled at all.
It was at this junction that our understanding of physics was revolutionized with the advent of quantum mechanics, which is one of the most interesting topics taught during our Physics tuition classes. Quantum mechanics looked at the phenomenon of light not as a paradox but as coexistence where light just like all matter simultaneously exhibited both wave and particle like behavior. The wave particle duality found extreme applications like electron microscopy and neutron diffraction which gave us a glimpse of the mysterious ways of the nature and let us visually observe structures that are of the order of the Nano scale. A privilege visible light cannot offer. The wave-particle duality still stands as the foundation of the beautiful world of quantum mechanics.