PQ-QP = h/2πi – Uncertainty as a Fate


Ernst Peter Fischer: Werner Heisenberg – ein Wanderer zwischen zwei Welten. ISBN 978-3-662-43441-3 ⭐️⭐️⭐️ Writing a biography of a physicist presents a challenge: Should the book focus on the person or the science? Should it try to describe a human being’s life or should it explain that person’s scientific idea? At best it tries to reconcile both, but this effort quite often fails since most recent scientific discoveries are quite complicated to explain to a layman who might have a stronger interest in the person than in his ideas. Retracing the life of Werner Heisenberg (1901-1976), one of the founders of quantum mechanics, is a mission that seems right from the beginning doomed to fail.

The first chapters of the book are bound to discourage the reader. The language is clumsy at times, pompous at others. Bits of philosophical ideas about science, literature and music mix with leaps back and fro in Heisenberg’s life – a complete mess. The author tries to show off with his knowledge of German Romanticism and connects Heisenberg’s scientific ideas to Heisenberg’s Romantic outlook on the world wherever he sees fit which is confusing and totally unnecessary. However after some 80 pages, the author finds a straightforward way to explain the thinking of Heisenberg as it evolved with time and one of the rather interesting aspects of Heisenberg’s scientific studies.

Heisenberg discards the idea that there is something like an “objective reality” in natural sciences that one can observe, measure and describe. He suggests that man should try to explain natural phenomena with a theoretical model and warns at the same time that man is tempted to be guided by past experiences when building models instead of being creative and coming up with radically new models. Thinking out of the box, transcending traditional paradigms – this seems to be the supreme effort for a scientist, but also for man generally. We don’t like to change our basic assumptions of life, do we? Once you start asking questions, life can become quite messy, uncomfortable, even life-threatening.

Given that Heisenberg’s expertise was quantum mechanics and the mathematical models necessary to understand them, I cannot ignore the formula in the headline: PQ-QP=h/2πi. You do not need to understand it, but you need to understand its meaning for physics and philosophy. Basically the formula asserts a fundamental limit to the precision with which certain pairs of physical properties of a particle (a part of an atom, e. g. an electron), such as position and momentum can be known.

Taking a step back it means that the scientists changes the object of his study as he studies it, for example by trying to measure its momentum or determine its position, and thus falsifies his measurement by doing it. When talking of atoms, there are things we cannot know with precision – this was Heisenberg’s revolutionary idea. It introduced an element of uncertainty and threw over board another basic paradigm of classical physics: the law of cause and effect, which does not apply necessarily to subatomic particles. Things within the atom can happen randomly. A frightening thought? Don’t worry. Your coffee-machine is not going to break apart spontaneously, at least not because of quantum physics. However Heisenberg’s scientific breakthrough makes your iPhone and computer work, as it led after many more years to the invention of the semi-conductor. Intel inside – crystals and hopping electrons!

The book explains all this reasonably well, and at the same time gives an idea of what Heisenberg’s thoughts and feelings were when the Nazis rose to power, when the SS abused him as a “white Jew” promoting Jewish physics (Albert Einstein’s relativity theory) and how Heisenberg did not build a Nazi atomic bomb. If it weren’t for the botched introduction, I’d give the book four stars. I am glad that the author got around to solid story-telling and quantum theory for dummies. I am also glad I did not give up too soon.

Heisenberg was a keen amateur pianist and cellist. “One cannot live without music. But when I listen to music, I sometimes get the absurd idea that life could have a meaning”, he wrote in 1924. In his leisure time, when he was not crunching numbers or developing models, he liked to study challenging music written by Robert Schumann, for instance his piano cycle “Kreisleriana” (Op. 16), or Ludwig van Beethoven’s Cello Sonatas.

Satire and passion for the benefit of mankind

Two cello sonatas to please the king