In the summer of 1925, Werner Heisenberg outlined the theory of quantum mechanics on the tiny German island of Helgoland. In his newest book, Carlo Rovelli poetically intertwines the story of the origin of quantum theory with its interpretation and philosophical consequences. It is his best work yet and includes a very lucid presentation of relational quantum mechanics. In this post, I want to go over some of the most interesting things the author touches upon. However, I highly recommend picking up this short and sweet work to grasp all the details for yourself.
In the first few parts of the book, the author outlines the initial debate between the boys’ physics of Jordan, Heisenberg, Pauli, and the wave theory of Schrodinger. The inspiration behind Heisenberg’s insight was attempting to figure out equations that predict the intensity of the light emitted when an electron becomes deexcited in an atom and falls down an energy level. Guided by Max Born and Niels Bohr, he decided to focus on only what is observable without mudding up his theory with previous ideas. In this way, he came up with the idea that if physical variables representing the electron get replaced with matrices, the equations predict exactly what experimental evidence shows. Paul Dirac also came up with a similar idea at that time, called non-commutative algebra. The idea was that order of physical variables matters, and position multiplied by momentum is not the same as momentum multiplied by position.
In 1926, Schrodinger managed to come up with his famous equation when spending some time in the mountains with his lover. There is a common theme of isolation and solitude that allows one to access the depths of nature here, which is quite poetic and reminds one of the famous Caspar David Friedrich’s painting Wanderer above the Sea of Fog. The key distinction of Schrodinger was that the ‘invisible’ wave function determines the probability of a particle’s position and pilots it through a hidden deterministic mechanism. On the other hand, Heisenberg and Bohr thought that quantum physics was strictly indeterministic and “God does not play dice”. This clash of ideas launched a century-long debate on the interpretations of fundamental quantum mechanics, which crosses the boundaries of philosophy, physics, literature, and art.
Then Rovelli outlines the main interpretations that have emerged since the 1920s. He critiques the many-worlds, hidden variable, and physical collapse theory on the basis of not being observable. He then discusses QBism or quantum Beyanism, which states that a human observer feels like quantum mechanics is not deterministic because she cannot see the whole picture. Rovelli is quite biased against these theories, especially with quickly dismissing physical collapse. This serves as the ground for presenting his relational interpretation, which he came up with in the 90s to explain entanglement.
Relational quantum mechanics builds upon special relativity in that each quantum state is observer dependent and two different observes can give two accurate descriptions of a quantum system. For instance, he states that entanglement is a dance for three and not a dance for two, meaning that the observer has a clear role in impacting quantum phenomena. However, he clearly solves some of the problems of the Copenhagen interpretation, which vaguely states that wave function collapse occurs when a macroscopic object is used to measure microscopic phenomena. Rovelli argues that particles that are in relation with other particles impact quantum mechanics and the wave function and that the universe is an interconnected web of relations. This is a very elegant theory that draws from logical positivism and the ideas of Ernst Mach, who inspired both Einstein and Heisenberg. It focuses only on what is observed, without trying to explain these phenomena with metaphysical invisible phenomena.
The author then transitions to connecting his theory with the Buddhist ideas of Nagarjuna who wrote that things do not exist, but only relations make up the world we know. This very beautiful connection between physics, literature and art is later continued when Rovelli discusses the easy and hard problems of consciousness, stating that there is no distinction between the mind and the body other than a different set of relations.
Overall, this book is a great introduction to interpretations of quantum mechanics. Even though, it does not offer textbook explanations and categorizations of each opposing viewpoint, Rovelli goes through the thinking process of physicists and philosophers who grapple with these ideas. The connections made with Shakespeare, Greek philosophers, Nagarjuna and personal anegdotes from Rovelli’s life make up a particularily entertaining read. It’s my favourite book of his yet and I am very excited for more. On a side note, it might seem that a few recent posts are slightly tangential to astrophysics. Personally, I am attempting to explore multiple areas of physics before I get to university, so that I am more well versed with terminology and interdisciplinary research. However, I think soon we will return to pure astrophysics. I especially want to make a few posts about the succesful (so far!) launch of James Webb and what it means for science.
References
Laudisa, F., & Rovelli, C. (2019, October 8). Relational Quantum Mechanics. Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/qm-relational/
Lopez, D. S. (2017). Nagarjuna | Biography, Philosophy, & Works. Encyclopedia Britannica. https://www.britannica.com/biography/Nagarjuna
Rovelli, C., Segre, E., & Carnell, S. (2021). Helgoland: Making Sense of the Quantum Revolution. Riverhead Books.