The Hidden Figures of Quantum Physics: Stories of Lucy Mensing and the Science of Gravity, Photoelectricity, and the Star-Gerlach
Others will know how quantum ideas gave rise to the lasers that beam information through the cables of the Internet, and the transistors that provide the processing power of electronic chips. But quantum ideas also shape our understanding of nature, at all levels, explaining why solid objects don’t fall apart and how stars shine and, ultimately, die.
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 some things, but still has some work to do. In the years where quantum mechanics was laid down, other branches of physics such as the study of electromagnetism and states of matter were also rebuilt from quantum foundations. They also looked to extend their theories to encompass objects that move at close to light speed, something that the original quantum theory did not. These efforts drastically expanded the scope of quantum science and led researchers to develop the standard model of particles and fields, a process that finally came together in the 1970s.
These “hidden figures” include Lucy Mensing, who was a member of the same group as Heisenberg and worked out some of the first applications of his quantum-mechanical theory, says Daniela Monaldi, a historian at York University in Toronto, Canada. 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 wasn’t having it. After attending a colloquium in Munich, Germany, at which Schrödinger presented his theory, Heisenberg complained to Pauli that the wave theory could not account for a host of quantum phenomena, including the photoelectric effect — the emission of electrons from a metallic surface when it is illuminated — and the Stern–Gerlach effect, in which a beam of atoms was found to deflect in one of two ways when passing through a spatially varying magnetic field. Moreover, describing a many-particle system required a wavefunction in an abstract multidimensional space. The wavefunction was a useful tool, but it did not really describe a real wave. Heisenberg wrote that a wave theory of matter in the usual three-dimensional space would not yield an extensive description of atomic processes.
It was a fundamental change in perspective that was as consequential for the physical sciences as it was for the theory of evolution by natural selection.
This was a strategy born more out of desperation than from any philosophical conviction. As Heisenberg explained in the paper’s introduction, in light of the complexities involved in dealing with atoms with several electrons, “it seems sensible to discard all hope of observing hitherto unobservable quantities such as the position and period of the electron”.
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 model was able to explain the spectrum of the hydrogen atom, consisting of just one electron and a single protons, in the presence of an applied magnetic field or Stark effect. But it had run into a host of problems in dealing with hydrogen molecules, and with atoms with more than one electron.