Once the previous chapter leaves us at the modern quantum world, we ask how we can recognize when quantum is really crucial? Where does that photon idea come from? And what is the revolutionary new element in quantum theory that on a deeper level did not exist with previous theories?
This chapter attempts to establish that a classical wave packet, using a specific shape in time and space, can bring the conceptual continuity between the divergent quantum-photon and classical-photon wave packet, while maintaining logical congruence between observed facts without asking nature to be non-causal, albeit statistical. It proposes a structure of the photon as a superexponential pulse that propagates by diffractively spreading, modeled precisely by the Huygens–resnel integral. Isaac Newton and Huygens gave birth to the concept of wave–corpuscular or modern wave–particle duality. The spell of wave–particle duality reemerged exactly a century after Young’s experiment, with the revolutionary success of Max Planck. While modeling the “thermalized” spontaneously emitted radiation inside a blackbody, S. N. Bose in 1924 was the first to recognize the need for a completely new statistical methodology of counting the states of photons if they are really indivisible quanta.