This paper analyzes the history and impact of the double-slit experiment on the world of physics. The experiment was initially created by Thomas Young in the early nineteenth century to prove that light behaved as a wave, and the experiment’s findings ended up being foundational to the classical wave theory of light. Decades later, the experiment was replicated once more with electrons instead of light and shockingly demonstrated that electrons possessed a dual nature of behavior in that they acted in some instances as particles and in others as waves. Despite numerous modifications and replications, the dual behavior of electrons has never been definitively explained. Numerous interpretations of quantum mechanics all offer their own explanations of the double-slit experiment’s results. Notably, the Copenhagen Interpretation states that an observer measuring a quantum system, such as the double-slit experiment, causes the electrons to behave classically (i.e. as a particle.) The Many Worlds Interpretation offers that multiple branching worlds come into existence to represent the physical occurrence of all probable outcomes of the double-slit experiment. In these and other interpretations, explanations of the double-slit experiment are key to proving their respective dogmas. The double-slit experiment has historically been very important to the worlds of both classical and quantum physics and is still being modified and replicated to this day. It is clear that it will continue to remain relevant even in the future of physics.