What is quantum physics? Quantum Physics describes how light and matter behave at a atomic and sub-atomic level. Believe it or not, quantum physics has been around for over a century. One of the biggest questions that is asked in this field of study is the question of if light is a wave or a particle. The issue for trying to decide this is the fact that it behaves in both ways depending on what evironment it is in. This led to the idea of wave-particle duality, which is a temporary fix for explaining what happens.
This issue first arrised in the 1600s when Christiaan Huygens and Isaac Newton came up with two conflicting theories about light. Huygens proposed a theory that light was a wave, while Newton proposed a theory that said light was a particle. At the time, due to Newton's fame and issues with Huygens experiment, the idea that light was a particle prevailed. Then, around the 19th century, new issues were discovered that again challenged whether light was a wave or particle. For one, diffraction was discovered. This was shown in Thomas Young's double slit experiment, which showed light behaving as a wave. The solution was eventually proposed by de Broglie, in which he related Einstein's work and his Photon theory with the momentum of an atom. It was eventually agreed upon that light could behave as either a wave or a particle depending on the specific circumstances.