Helgoland

Book Review

deutschlandfunkkultur – Schrödinger's cat, entangled particles, observations that seem to create reality in the first place: quantum paradoxes that follow from the formulas of the most successful theory in physics.

All this has to do with Helgoland only insofar as the island offered Werner Heisenberg, who was plagued by hay fever, a pollen-free refuge for his calculations.

"At first I was deeply frightened," Carlo Rovelli quotes him, "I had the feeling of looking through the surface of atomic phenomena to a deep underlying ground of strange inner beauty."

# Farewell to Existence This is the subject of physics professor Rovelli's new book. For although quantum theory is very practically incorporated in many objects of modern everyday life, it is still disputed which reality it actually describes.

Carlo Rovelli argues for saying goodbye to the existence of objects. Only their interactions should be real. "If the electron does not interact with anything, it has no physical properties. It has no position, no velocity," Rovelli writes. And, "This is a radical mental step."

True enough! But Rovelli makes it palatable with poetic formulations: "The world of quanta is consequently more airy than the one conceived by the old physics. It is a world made of a fabric as airy as a Burano lace."

His approach enables the resolution of various paradoxes. From the point of view of Schrödinger's cat, for example, it is clear whether it is asleep or awake. But the observer from outside experiences other interactions and therefore reality presents itself differently to him or her.

# The Common Reality Averages Out (Die gemeinsame Realität mittelt sich heraus)

"This is the solution of the riddle, but its price is high: there is no clear factual account." On the quantum level, therefore, the facts of two persons do not have to agree. Fortunately, when it comes to larger matters, a common reality usually emerges after all. The whole book is delightfully short and yet contains a history of quantum theory and various illuminating digressions on, say, consciousness or the Russian Revolution. But its core is the exposition of the "Relational Interpretation of Quantum Mechanics". And there Carlo Rovelli is very convincing.

# A Country That Most Do Not Enter

But do not forget: We are talking about quantum phenomena - and they are by their very nature ambiguous. Other physicists offer alternative interpretations - the "many worlds theory" or the concept of "pilot waves", for example - and these also sound convincing to the lay audience.

They are, after all, travelogues from a land that most people will never set foot in. What really goes on there is perhaps less important than that the stories about it inspire. Measured against this, Carlo Rovelli's "Heligoland" is way ahead. -- Volkart Wildermuth