The 1920s were an era of intense discovery and progress in the world of physics. Concepts such as matrix mechanics, the Schrödinger model of the atom, the Heisenberg uncertainty principle, and more dominated this era of progress. All of these concepts had a particular trait in common with one another: they showed that probability was the driving force behind reality. Many physicists, most notably among them, Albert Einstein, were not so willing to accept this idea to its fullest. Einstein brought his concerns with him, along with his challenging thought experiments, to the 5th Solvay Conference in 1927, where he and his colleague, Niels Bohr, would start a decades long debate over probability and the true nature of reality.