The battle between quantum theory and relativity to be the most definitive discovery of the 20th century seemed to have ended with the Time magazine naming Albert Einstein the man of the century. Yet, doubts persist. In the real world, the quantum continues to have greater applicability than relativity. Most modern appliances employ quantum principles. Some, such as the electron microscope, operate at a scale where quantum effects score over classical phenomena.
Such was the extraordinariness of its precepts that when quantum theory first gained prominence at the beginning of the 20th century, Niels Bohr, one of its chief architects, proclaimed: “Those who are not shocked when they come across quantum theory cannot possibly have understood it.”
Manjit Kumar’s Quantum revisits an era where cutting-edge research (at the time) yielded new ideas about the nature of reality. 1905, Einstein’s annus mirabilis, brought forth the first stirrings of what would become his Special Theory of Relativity, forever changing man’s views on space and time.
However, around the same time, an arguably more earth-shaking theory was about to take root, and it busied itself not with the motion of large objects but with the spin of the tiniest particle known to man—the humble electron. Experiments at the sub-atomic level conducted by the holy trinity of Bohr, Max Planck and Werner Heisenberg showed that electrons do not follow the same rules of behaviour that had come to be gospel truth since Newton first propounded his laws in the seventeenth century. Rather, they seemed to show dual characteristics of wave and particle, depending on the mode of observation.
The need for quantum theory stemmed from black body radiation. A black body is a hypothetical object that absorbs all electromagnetic radiation that falls on it. According to Wikipedia, “No electromagnetic radiation passes through it and none is reflected. Because no light (visible electromagnetic radiation) is reflected or transmitted, the object appears black when it is cold. However, a black body emits a temperature-dependent spectrum of light. This thermal radiation from a black body is termed black-body radiation.”
In 1862, Gustav Kirchhoff, while studying the spectrum of a laboratory black body emitting radiation, observed the presence of discrete spectral lines that could not be accounted for. The question remained unanswered until 1900, when Planck postulated that electromagnetic radiation was not a uniform wave but a collection of discrete energy particles called quanta. In 1905, Einstein appropriated Planck’s theory to explain the photoelectric effect — the emission of electrons from metals when electromagnetic radiation falls on their surface. Einstein attributed this to the presence of discrete energy particles called photons in light.
But the real strangeness of the quantum theory, which at its basic postulates a wave-particle duality to all matter, was the discovery made by the young Heisenberg in 1927: “It is impossible to measure simultaneously both the position and velocity of a microscopic particle with any degree of accuracy or certainty.” That is, the measurement of one quantity plays havoc with the measurement of another and vice-versa. What this essentially entailed was a realisation, too shocking to be readily grasped, that reality is not a fixed entity but dependent on its observation.
The discovery of uncertainty caused an uproar in the scientific community, since it shook to the core the deterministic principles on which the entire edifice of physics—and by extension, the patterns of thinking—was based. Einstein famously quipped, “God does not play dice with the universe” and hoped that a still-undiscovered quantity would arrive in due course to resolve the inherent contradictions of the quantum. Bohr and Heisenberg, on the other hand, fashioned the Copenhagen Interpretation that gave credence to the central improbability of quantum mechanics. In their view, quantum mechanics was the best approximation of all motion, since for larger bodies, it approximated the laws of classical physics.
Kumar’s Quantum builds on the many discoveries that launched the world of the quantum and the fraught relationships among the dramatis personae, many of who moved in a rarified circle where talk of force fields and particle physics was common over tea and biscuits. Indeed, Kumar’s real achievement is not in throwing light on quantum mechanics per se, which descriptions are often mired in thick scientific jargon, but on a time when the thrill of discovery was so palpable it could slice through butter like a hot knife.
As for the quantum, the debate continues and Kumar ends his book on the hope that a “Theory of Everything” to resolve the deterministic outlook of Einstein with the thrilling uncertainty of Bohr, will come around in our lifetimes. Except, every new discovery is fraught with opening new vistas and shifting the ever-changing contours of not just science, but epistemology.