“About sixty years ago, the renowned American physicist Richard Feynman gave a series of lectures at Cornell University aimed at a general audience. In them, he remarked that there was a time when, according to newspaper reports, no more than twelve people worldwide understood the theory of relativity. Feynman doubted that this was actually the case, but asserted: Nobody understands quantum theory. (Loud laughter can be heard at this point in the film recording.) This sentence has since been frequently and readily quoted to demonstrate the supposed incomprehensibility of this theory. The title of the present volume also plays on this idea.
Of course, it's hard to imagine that scientists have been successfully applying this theory for a hundred years without understanding it. And that's not the case. As Feynman explains, his statement merely expresses the impossibility of grasping the theory within a preconceived framework and using images from classical physics. For this reason, he describes the theory in clear terms, without attempting to resort to analogies with familiar concepts.
Our authors seem to follow this approach as well. Contrary to the title of their book, they claim in the preface: Quantum physics is by no means incomprehensible. These authors, who are also a couple in private life, are Frank Verstraete, a professor at Ghent University, and Céline Broeckaert, a Belgian actress, author, and artist. The second author's task was probably primarily to translate the perhaps rather dry discussion of the male author into a more vivid and simplified language. However, it remains to be seen whether sentences like the following are truly helpful: "On a starry night, somewhere among the cypress trees of idyllic Pisa, Galileo was reinforced in his suspicion that only mathematics could help him." "Sitting next to a leaning tower, he gazed dreamily through his equally revolutionary invention, the telescope." Quite apart from that, Galileo did not invent the telescope, but was the first to consistently use it for astronomical observations – and he did so in the Republic of Venice.
In general, the two authors are not very precise with their historical remarks. For example, they claim that Werner Heisenberg, after his stay on Helgoland a hundred years ago, completed an article in which he arrived at exactly the same result as Erwin Schrödinger in his work – only Schrödinger hadn't even written his work at that time. We also read with astonishment that radios were already being built in Maxwell's time (1873).
The authors begin their discussion with a description of the achievements of their Flemish compatriot Simon Stevin, who unjustly stands in Galileo's shadow. As early as 1586, Stevin was able to demonstrate, through experiments involving objects dropped from the tower of the Nieuwe Kerk in Bruges, that objects of different weights fall at the same speed. However, whether this truly enlightened reason and shaped it in such a way that it led directly to the birth of quantum theory, as claimed, is not entirely convincing.
The main obstacle to understanding quantum theory is the quantum mechanical states that describe every system in the microworld and presumably beyond. These are wave functions, which have the property that any superposition of these functions can also describe the system. The well-known thought experiment of Schrödinger's cat, which exists in a strange intermediate state of being both dead and alive, illustrates the consequences that arise when this superposition principle is extended from the micro- to the macroworld. [1]
Such examples still ignite a sometimes heated debate among experts about the correct interpretation of quantum theory – in contrast to the purely descriptive approach favored by Feynman. The authors follow a perspective here that was particularly prevalent in the early years of the theory, championed by Heisenberg and Niels Bohr. It was then that the wave function ceased to describe a real state, but rather the information obtained after a measurement. But why shouldn't a formalism that successfully describes, for example, the experimentally observed superposition of states of a macromolecule, reflect reality? In fact, such a realistic interpretation is now gaining considerable popularity—although it is clear that it must be a nonlocal reality with (in Einstein's words) "spooky action at a distance." The interaction of quantum systems leads to an entanglement of the systems, which can persist even over arbitrary distances, for example, over several hundred kilometers in quantum cryptography experiments. Even the non-observation of strange superpositions, as in Schrödinger's cat experiment, can be explained by entanglement – specifically, by entanglement with the unobserved degrees of freedom of an interacting environment (misleadingly referred to as "noise" in the book).
The book's strengths lie in the areas related to the research field of the Ghent professor. Readers learn what holds solid bodies together, how quantum theory underpins fundamental laws of chemistry, and the significant role the theory plays in everyday life – from the chips in smartphones to MRI scans in medicine. Of course, the ubiquitous quantum computers, whose operation is based on entanglement, are also discussed. On the mathematical side, the book reveals the profound importance of symmetry (and its breaking) in physics.
So, will you understand quantum theory after reading this book? Probably not. But you might be infected by the enthusiasm that drives the authors and become curious to read more. Why not start with Feynman's filmed lectures? As the physicist emphasizes there, no prior knowledge is required – except for English.
Frank Verstraete and Céline Broeckaert: "Why Nobody Understands Quantum Theory." But everyone should know something about it.
C.H. Beck Verlag, Munich 2025. 351 pages, illustrations, hardcover, €28.00.” [2]
1. The understanding of quantum mechanics is primarily obstructed by the nature of quantum states, represented by wave functions (Ψcap psi), and the principle of superposition.
Key reasons this poses a challenge to understanding include:
- Superposition of Incompatible States: Wave functions allow a system to exist in a superposition of multiple, apparently distinct, and even contradictory, physical states simultaneously.
- The Measurement Problem: While the theory mathematically describes systems as being in superpositions (e.g., a particle in two places at once), measurements always yield a single, definite outcome. This contradiction—that the theory predicts a superposition, but we observe a single state—is central to the "measurement problem".
- Non-Intuitive Nature: Unlike classical physics, quantum mechanics deals with probabilities rather than certainties. A wave function represents a probability amplitude, not a direct, tangible, or "localizable" physical object until it is measured.
- The Wave Function is Not Observable: The wave function itself is a complex-valued mathematical entity that cannot be directly observed or drawn, which makes it hard to relate to daily, physical experience.
- Failure of Analogy: Standard, everyday intuitions about, say, a particle being at a specific spot at a specific time are completely challenged, as the wave function does not exist in ordinary physical space but in a more abstract, high-dimensional space.
In essence, while the mathematical formalism of superposed wave functions provides incredibly accurate predictions (like the interference pattern in a double-slit experiment), it fails to conform to our experience of a singular, definite reality.
2. Zustände, die die Welt bedeuten: Frank Verstraete und Céline Broeckaert wagen eine einfache Erklärung der Quantenmechanik. Frankfurter Allgemeine Zeitung; Frankfurt. 12 Nov 2025: 10. CLAUS KIEFER
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