It is difficult to discuss quantum physics without getting lost in philosophy. All of science is based on the principle of causality. We use models to better predict future outcomes based on observations of cause and effect. Electrons are a relatively new creation, which most people believe exist in a universe that obeys cause and effect. The photovoltaic effect was one of four of Albert Einstein's famous [1905 papers](https://en.wikipedia.org/wiki/Annus_Mirabilis_papers) and was the foundation of quantum theory. The idea that energy was quantized was the most instantly impactful work Einstein produced. During this era the electron was determined to be a point particle: it has no axis to rotate on, it is not a physical thing with dimensions that matter. Every year scientists devized more radical experiments and extended the implications of quantum physics. Einstein and others were unhappy with the results that were amassing, notoriously saying "God does not play dice[!]".
Einstein loathed the results the way that quantum theory was evolving. He was famously an atheist, in the previous quote its safe to assume that "Nature" is an effective substitute for God. The idea that observable pairs like position and momentum can't be observed without uncertainty in the counterpart does not coincide with the idea of a deterministic universe. In an effort to disprove the logical outcomes of the theories that were evolving Einstein and his colleagues Boris Podolsky and Nathan Rosen devised an elaborate thought experiment. The three scientists, in a desire to show the incomplete nature of Quantum Mechanics created the most inexplicable phenomena in nature - quantum entanglement.