Werner Heisenberg and the History of Quantum Science and Technology: I. The First 100 Years of the Improvement of the Standard Model and the Modern-day Evolution of the Quantum World
A physicist from Germany submitted a paper to the journal in July 1925 on quantum-theoretical reinterpretation of mechanical relationships. The publication of Werner Heisenberg’s article was arguably the moment that ushered in the modern age of quantum mechanics, thus setting in train an astonishing revolution in our basic understanding of physics that has repercussions to this day. The United Nations has proclaimed 2025 to be the International Year of Quantum Science and Technology, in no small measure because of the events that began to unfold at breathtaking speed 100 years ago.
The standard model has been incredibly successful, culminating in the 2012 discovery of its linchpin elementary particle, the Higgs boson. But these extensions lie on less-solid theoretical ground than quantum mechanics does — and leave several phenomena unexplained, such as the nature of the ‘dark matter’ that seems to greatly outweigh conventional, visible matter in the wider cosmos. Moreover, one important phenomenon, gravity, still resists being quantized.
The quantum revolution has brought many things, but still has unfinished business. The years in which the foundation of quantum mechanics was laid paved the way for other branches of physics, such as the study of electromagnetism and states of matter. The original quantum theory does not cover objects that move at close to light speed. The work done by these people led to the creation of a model of particles and fields, which came together in the 1970s.
Some of the first applications of Heisenberg’s quantum-mechanical theory were worked on by Lucy Mensing, a member of his group, according to a historian at York University. One of the most notable events of the year will be the publication of a biographical volume of essays on 16 of them, Women in the History of Quantum Physics.
Heisenberg was not alone in expressing this doubt. He told Sommerfeld in December 1924 that the idea of electrons moving from one part of the quantum world to another was not feasible. Without the models, it was not clear what to do. As late as April 1925, Heisenberg wrote that in “the present state of quantum theory, one must rely on symbolic, model-like pictures that are more or less built on the mechanical behaviour of electrons in classical theory”3.
A century ago, there was a change in perspective for the physical sciences as consequential as the theory of evolution by natural selection was for biology.
This was a strategy born more out of desperation than from any philosophical conviction. In light of the complexity involved in handling several electrons, Heisenberg thought it was sensible to discard all hope of observing hitherto unobservable quantities.
By supposing that electrons move in elliptical orbits around an atomic nucleus, subject to certain quantization conditions, the Bohr–Sommerfeld model provided a set of rules for selecting certain ‘allowable’ orbits of a classical system (in the case of the hydrogen atom, an electron orbiting a proton), delivering calculated values in agreement with the observed energy spectrum. The spectrum of the hydrogen atom consisted of just one protons and one electrons and was explained by a model. But it had run into a host of problems in dealing with hydrogen molecules, and with atoms with more than one electron.
