History of the Quantum Revolution – Review of “Helgoland: Making Sense of the Quantum Revolution” by Carlo Rovelli

This book functions as an introduction to quantum theory for beginners, and is quite lay-friendly. Quantum theory is that part of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level, where a different and eerie set of rules apply.

The Helgoland of the title is the name of the island on which physicist Werner Heisenberg spent the summer of 1925 figuring out details of how the quantum level of nature might operate, expanding on the ideas of his fellow physicist Neils Bohr. Bohr had come up with a theory about the arrangement of particles in an atom. He used concepts from classical physics, like that of angular momentum, but proposed tweaks that would better explain what scientists knew about an atom’s behavior. Bohr suggested that the electron’s angular momentum around the nucleus was quantized, that is, it could only have certain discrete values. Furthermore, he made the revolutionary proposal that while electrons revolve in stable orbits around the atomic nucleus, they can jump from one energy level (or orbit) to another, a phenomenon we now refer to as a “quantum leap.” When an electron makes this leap, it either emits or absorbs a chunk of light called a photon, a concept contributed by Einstein.

Heisenberg fleshed out Bohr’s ideas, leading to other refinements by physicists including Max Born, Wolfgang Pauli, Paul Dirac, and Erwin Schrödinger. The quantum theory detailed by these scientists, while still not totally understood, has led to all manner of technological advances. We don’t know exactly how it works, just that it does. Indeed, as the brilliant physicist Richard Feynmann once said, “I think I can safely say that nobody really understands quantum mechanics,” and yet, scientists have used the theory successfully to develop nuclear energy (and bombs), transistors and semiconductors, GPS navigation, and so much more.

1925 – Werner Heisenberg, a German theoretical physicist, proposed in 1925 in his famous Uncertainty Principle

Rovelli, a theoretical physicist, divides this short but lucid book into two sections. First he explains the development of quantum theory the best he can. He delineates the ways in which quantum theory does not at all conform to the dictates of classical physics, the discovery of which caused a revolution in science.

In the realm of subatomic particles, as the online magazine Space.com puts it, things behave in a way that can seem totally contradictory to what we experience in the macroscopic world.

For example, in classical Newtonian physics, particles making up matter can be defined precisely and follow predictable trajectories. In the universe defined by quantum theory, particles are better understood using the mathematics of wave functions, by which one can only calculate probabilities, not certainties, of particular positions and momenta for particles. One reason probability works better: quantum objects behave differently when they are being observed. As a New York Times article explains:

When we’re not looking, they exist in ‘superpositions’ of different possibilities, such as being at any one of various locations in space. But when we look, they suddenly snap into just a single location, and that’s where we see them. We can’t predict exactly what that location will be; the best we can do is calculate the probability of different outcomes.”

[I thought Rovelli a bit squeamish when he insisted on talking about the famous thought experiment of Erwin Schrödinger as involving a cat asleep or awake instead of dead or alive. It was, after all, just a thought experiment. I get that he likes cats, but the concept of “Schrödinger’s cat” is too well known for refashioning, in my view.]

That isn’t all, in terms of quantum-level weirdness. You may have heard the phrase “spooky action at a distance.” Coined by Einstein in 1947, this phrase describes another aspect of particles as revealed by quantum physics – they can become entangled with one another such that one particle can exchange information with another particle instantaneously, even if those two particles are separated by a great distance. Experiments have shown this to be true. You can see an explanatory infographic here.

Albert Einstein, Boris Podolsky and Nathan Rosen pointed out an apparent problem with quantum entanglement in 1935 that prompted Einstein to describe quantum entanglement as ‘spooky action at a distance.’ Wikimedia Commons

In the latter part of the book, Rovelli examines different schools of thought about how to explain scientific discoveries about quantum theory.

One of them, that I found rather appealing, was “QBism,” short for Quantum Bayesianism. This particular approach holds that what we discern as reality reflects a concatenation of probabilities and beliefs about phenomena given our incomplete knowledge of the world. It takes its punny name from the early 20th century Cubism art movement, in which objects were analyzed, broken up and reassembled in an abstracted form to represent multiple viewpoints about the “truth” of the subject.

Rovelli’s own preferred interpretation is also rooted in the recognition that quantum experiments show that matter is not well-defined. He proposes that everything can be understood as relational. That is, nothing exists outside of the context of its interactions. Indeed, one of the earliest findings of quantum physicists, as indicated above, was that the very act of observation affects the properties of electrons. For Rovelli, this seems to lead inexorably to an adoption of the teaching of the 3rd century Buddhist philosopher Nagarjuna, who wrote that “there is nothing that exists in itself, independently from something else.”

Evaluation: I wasn’t so convinced by Rovelli’s philosophical conclusions, but I appreciated the way in which he makes quantum theory so understandable. And his anecdotes from the history of quantum physics were quite enjoyable. He is one of the most successful “popularizers” of physics for good reason.

Strong: 4/5

Published in the U.S. by Riverhead Books, 2021