In this article we outline a history of the transition from Classical to Quantum Theory. It is the introduction to three linked articles which discuss (respectively) three experiments that marked pivotal moments in the history of modern physics, and built the stage for many of the other ground-breaking discoveries that prompted the jump from classical to quantum theory.
For most of human history, our scientific practices and pursuits rested on the belief that the physical world was made up of determinate and well-defined puzzle pieces. More importantly, we believed that these puzzle pieces were physically like the larger objects they constituted when pieced together. As early as 400 BCE, the Greek natural philosophers Leucippus of Miletus and Democritus of Abdera proposed that the universe was made of infinite tiny atoms in a vast void.
These atoms, the fundamental building blocks of the universe, were believed to be solid, indivisible,and unchanging. All visible changes in the physical world were attributed to the movement of these atoms, which created new objects and new physical states simply by rearranging themselves. Over time, our understanding of the atom evolved into a more nuanced and sophisticated model. But even as our scientific models developed, there remained an assumption that the physical universe could be reduced down to fundamental pieces with clear, determinate characteristics.
You can access each of the articles on the three experiments mentioned in this article, by click the appropriate link below: