Contrary to popular belief, the pioneering quantum physicists Niels Bohr and John von Neumann may have had more in common than previously thought regarding the interpretation of quantum measurements. A new analysis sheds light on the potential alignment of their views, challenging the long-held notion of a fundamental conflict between their approaches.
The Quantum Measurement Issue
During the early years of quantum mechanics, Bohr and von Neumann came up with two radically different conceptions for how measurements on quantum systems should be understood. Bohr would be of the opinion that those measurements need an unambiguous separation between the quantum system under consideration and the classical measuring apparatus. In contrast, von Neumann stated that quantum mechanics should apply universally, to the measurement apparatus as well.
This was famously believed for a couple of decades–these interpretations were mutually incompatible. The idea of measurement was critical for Bohr in his account of quantum mechanics, with a special emphasis that he placed on the fundamental role of classical concepts to explain quantum experiments. In contrast, the formal measurement model of von Neumann required that quantum mechanics must apply to the properties of both, the quantum system and the measuring apparatus, which appeared to contradict Bohr.
On Close Examination — These 2 Pairs Do Look Damn Alike
But a new analysis by Federico Laudisa at the University of Trento questions that stark opposition between Bohr and von Neumann. As Laudisa describes in detail, the role of these classical concepts in Bohr’s thinking might resemble von Neumann’s method more so than most historians have allowed by unpacking their ideas further.
The latter conclusion of Laudisa’s paper, published in The European Physical Journal H, is that Bohr may have not disputed von Neumann’s interpretation afterall. He adds that their conflicting perspectives could have been partly due to early textbooks not clearly stating we should quantify the objects of the classical world also by quantum laws during measurements.
Laudisa points out that rethinking how Bohr and von Neumann saw the quantum measurement process as similar could provide new insights into the history of one of quantum mechanics’ cornerstone processes. Laudisa’s book challenges the conventional wisdom that a deep difference persists between these two founders, and mines this comparison for the new kinds of insights it offers into what remains one of the major debates in quantum mechanics.
Conclusion
It is interesting to consider that Bohr and von Neumann might come closer regarding quantum measurements, as it seems Laudisa shows us, even if our standard picture of a fundamental clash between the two has been dramatically different. These findings should shed light on the long-standing questions at the root of how quantum mechanics was born and evolved, notoriously on whether classical or quantum notions play a role in measurement. As more information is amassed in the field of quantum physics, it may also be beneficial to return to these thinkers and explore how they helped build a foundation for contemporary explorations in the quantum.
