The windswept German island that inspired quantum physics

Helgoland is a craggy German island in the North Sea. Barely bigger than a few fields, it reaches high above the water on precipitous cliffs and is famous for its sweet air. It has a town and a harbour, and the 1,000-odd inhabitants speak a distinct dialect. In the summer of 1925, the 23-year-old physicist Werner Heisenberg went there to sort out his hay fever and solve the problem of reality.

Helgoland is a slightly misleading title for Carlo Rovelli’s inspiring, chaotic, delightfully unsatisfactory book of popular quantum physics. It isn’t about Heisenberg’s months there or his mathematical insights; ‘Helgoland’ is Rovelli’s shorthand for Heisenberg’s pellucid state of mind. On Helgoland, says Rovelli, Heisenberg almost got the philosophical approach to quantum theory right. Ever since, we’ve been getting it wrong.

The discovery of a quantum world began with experimental results. Certain things were taking place in German physics labs that should not be. Atoms were misbehaving. When scientists in Göttingen and Berlin crouched in front of the latest clever electronic instruments and peered, Alice-like, into the wonderland of the very small, what they saw shocked them bolt upright. Wonderland was ridiculous. There, logic was (and still is) fundamentally different.

Translated up to our size, the following nonsense was apparently perfectly possible: throw a full tankard across the hall in a Bierstube, let somebody notice (as it passes overhead) that this tankard has, say, a picture of a stag on it, and the beer inside turns green. That simple observation — ‘hey, look, there’s a stag on the tankard’ — and ping! the contents of the mug changes colour. But if nobody notices the decoration, the beer stays brown. In the quantum world, two defining qualities that have nothing to do with each other (tankard decoration and beer colour) can influence one another just because somebody’s looked at them.