In Quantum Physics, Everything Is Relative

The conceptual breakthrough initiated by Heisenberg (who was mentored by Niels Bohr), and firmed up with contributions from Max Born, Wolfgang Pauli, Paul Dirac, Erwin Schrödinger and others, makes it clear that the world of the very small — that of photons, electrons, atoms and molecules — obeys rules that go against the grain of our everyday physical reality.

Take an electron that is emitted at Point A and is detected at Point B. One would assume that the electron follows a trajectory, the way a baseball does from a pitcher’s hand to a catcher’s mitt. To explain experimental observations, Heisenberg rejected the notion of a trajectory for the electron. The resulting quantum theory deals in probabilities. It lets you calculate the probability of finding the electron at Point B. It says nothing of the path the electron takes. In its most austere form, quantum theory even denies any reality to the electron until it is detected (leading some to posit that a conscious observer somehow creates reality).

Since the 1950s, scientists have tried to make quantum theory conform to the dictates of classical physics, including arguing for a hidden reality in which the electron does have a trajectory, or suggesting that the electron takes every possible path, but these paths are manifest in different worlds. Rovelli dismisses these attempts. “The cost of these approaches is to postulate a world full of invisible things.”

Instead, in “Helgoland” Rovelli explains his “relational” interpretation, in which an electron, say, has properties only when it interacts with something else. When it’s not interacting, the electron is devoid of physical properties: no position, no velocity, no trajectory. Even more radical is Rovelli’s claim that the electron’s properties are real only for the object it’s interacting with and not for other objects. “The world fractures into a play of points of view that do not admit of a univocal, global vision,” Rovelli writes. Or, as he puts it, “Facts are relative.” It’s a dramatic denunciation of physics as a discipline that provides an objective, third-person description of reality.

Rovelli’s writing, translated from Italian by Erica Segre and Simon Carnell, is simultaneously assured and humble. His erudition is evident, especially in his delightfully long segues into the kindred philosophies of Ernst Mach, Alexander Bogdanov (an early Bolshevik) and Nagarjuna, a second-century Buddhist thinker, whom Rovelli invokes when saying that “every perspective exists only in interdependence with something else, there is never an ultimate reality.”

“Helgoland” is poetic and spare. Readers unfamiliar with quantum physics may struggle to get its full import. To use his theory as a metaphor, Rovelli’s lyricism may depend on how many other, possibly plodding, nitty-gritty accounts of quantum physics one may have read: The more that number, the more “Helgoland” will seem a poem.