The Wykehamist
100 Years of Quantum Physics
V ery rarely are hundreds of scientists forced to confront the very foundation of the field they study. This happened, however, in 1925 when Werner Heisenberg released his revolutionary paper Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen, or, On the Quantum-Theoretical Reinterpretation of Kinematic and Mechanical Relations. The paper in question was a phenomenal breakthrough that acted as catalyst for the development of quantum physics; shortly after, several more seminal papers were published. These included, but were not limited to, Heisenberg’ s uncertainty principle, the development by Erwin Schrödinger of a wave-mechanical formulation inspired by de Broglie’ s hypothesis, and Paul Dirac’ s unification of special relativity and quantum physics in the Dirac equation( which also predicted the existence of antimatter and gave a theoretical justification for the elusive spin— though Dirac was unaware of his equation’ s significance).
I should make it clear that quantum physics didn’ t appear out of nowhere. At the start of the 1900s, physicists thought they had already figured out the fundamentals of the universe. That was, at least, until a few people noticed phenomena that could not be explained by classical mechanics. Max Planck is well-known for his work on the fact that black-body radiation( the light emitted by a hot object) did not follow the behaviour predicted by classical physics, in a situation known as the“ ultraviolet catastrophe”( the classical prediction being that the radiated energy would diverge at high frequencies). The photoelectric effect * too seemed to defy the laws of physics, with electrons only being released if light was above a certain frequency threshold, regardless of intensity. These anomalies revealed cracks in a foundation previously thought to be solid. New ideas emerged to explain these phenomena, for instance, de-Broglie’ s wave-particle duality, but it wasn’ t until the events of 1925 and the following years that a single unifying quantum theory began to be formulated.
These radical new ideas were not accepted by the scientific community with open arms; Einstein disagreed with the probabilistic Copenhagen interpretation of quantum theory, famously saying that“ God does not play dice”. Championed by young, up-andcoming scientists, this new theory being shot down so thoroughly by the most famous of the older generation was a very real threat to its existence in the early days.
There was even disagreement within those creating quantum theory; Schrödinger too disagreed with Bohr and Heisenberg, and the Copenhagen interpretation. The Copenhagen interpretation involves the idea that a particle has no definite properties until it is measured, i. e. when the wave function of that quantum system is collapsed, suggesting instead that a particle is described by a superposition of states and that we can only know the relative probabilities of each outcome. This goes against common sense in a way that Einstein, Schrödinger, and many others simply could not agree with. The famous thought experiment that has become the defining image of quantum physics, Schrödinger’ s cat, was actually created with the intent to disprove a theory that we now accept. The thought experiment was actually created as a reductio ad absurdum— attempting to prove that accepting the Copenhagen interpretation would lead to ridiculous assumptions, showing that it was not a complete quantum theory.
Schrödinger and Heisenberg also disagreed on the appropriate mathematical formulation; Schrödinger preferred to model the quality of‘ being somewhere’ or‘ having some energy’ as constant and the underlying state of the system as changing, whereas Heisenberg had them reversed.( In introductory quantum physics, Schrödinger’ s formulation
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