The best books on physics and physicists

Richard Feynman, who I was lucky enough to be taught by at Caltech, was the most important American physicist of the post-war era. His greatest achievement – for which he shared the 1965 Nobel Prize for Physics – was “quantum electrodynamics”, the theory of how light interacts with matter. After winning the prize, a friend challenged him to explain QED to ordinary people. At first, Feynman thought it impossible. But then he found a way.

Feynman’s genius was to come with pictures, little “arrows” that depict how particles of light – photons – interact with particles of matter – principally electrons. In QED you will discover delightful explanations of things you thought you understood such as the reflection of light by a mirror. Perhaps you did not realise that photons striking a mirror bounce off in every possible direction but that in only one direction do they reinforce each other, all their little arrows adding up.

QED is one of the high points of the 20th-century – the most successful theory of physics ever devised, which predicts what we observe to an obscene number of decimal places. It is remarkable that Feynman found a way to explain it in such a slight and unthreatening popular book.

Paul Dirac was the only Englishman among the founders of “quantum theory”, the revolutionary description of the submicroscopic realm of atoms and their constituents created in the mid-1920s. He concocted an equation to describe an electron traveling close to the speed of light, which predicted an unsuspected world of “antimatter”, and which is inscribed on a flagstone in Westminster Abbey (the only other equation in the Abbey is Stephen Hawking’s expression for the temperature of a black hole). But Dirac was a very strange man. When asked how he found the “Dirac equation”, he replied: “I found it beautiful”. And, when a student in one of his lectures at Cambridge put their hand up and said “Professor Dirac, I don’t understand”, Dirac replied “That’s an observation not a question” and continued with the lecture. All this and more is recounted in Graham Farmelo’s charming and authoritative biography of the man who was the Mr. Spock of Physics.

The most striking thing about the night sky is that it is mostly black. But if your eyes, instead of seeing visible light, could see a type of invisible light known as microwaves, it would be white. The entire Universe is glowing with the “afterglow” of the big bang fireball. Greatly cooled by the expansion of the universe in the past 13.82 billion years, the “cosmic background radiation” now consists of low-energy radio waves, principally microwaves.

Imprinted on this radiation is a “baby photo” of the universe when it was a mere 400,000 years old and matter was beginning the long process of clumping under gravity that would culminate in galaxies such as our own Milky Way. From that photo can be extracted the numbers that define our Universe, from its age of 13.82 billion years to the fact that 70 percent of cosmic mass-energy is in the form of mysterious “dark energy”.

Lyman Page is a professor of astronomy at the Princeton University in New Jersey and his area of research has for decades been the heat afterglow of the big bang. My first thought, on picking up his book, was: “This will be just another academic jumping on the popular science bandwagon and short-changing the public with a pretty ordinary book.” Nothing could be further from the truth. This ranks alongside Steven Weinberg’s The First Three Minutes as the best book on cosmology I have ever read. A compact treasure-trove of cosmic insights to be read, mulled over, and read again.

The two towering figures of 20th-century physics were the German physicist Albert Einstein and the Danish physicist Niels Bohr. Both revolutionized our view of ultimate reality, with Einstein changing our picture of space, time and gravity, and Bohr changing our view of the submicroscopic world of atoms and their constituents. It is on this latter subject – “quantum theory” – that the two great friends clashed most fiercely. And it is the twists and turns of their titanic debate that Manjit Kumar recounts in such engaging detail in this page-turning account.

The Einstein-Bohr debate could not have been more important: it was about the nature of ultimate reality itself. Quantum theory contended that we can never know with certainty the outcome of atomic events, only the “probability” that they might happen, and that, furthermore, there is no objective reality “out there”, as Einstein believed, but that atoms and their like gain their properties only in their interaction with our observing instruments. Einstein lost the debate but his relentless assault on quantum theory proved invaluable, spurring its founders, including Bohr, to shore up and sharpen their ideas.

Helgoland refers to the barren, windswept island off the North Sea coast of Germany, where the 23-year-old Werner Heisenberg, physicist, and chronic hay-fever sufferer, retreated in June 1925 to try and make sense of the Alice in Wonderland world which atomic experiments had revealed beneath the skin of reality. The mind-bending submicroscopic realm was a place where a single item could be in two places at once; where events happened for no reason at all; and where atoms could influence each other instantaneously even if on opposite sides of the Universe.

Heisenberg’s lightbulb moment on Helgoland is only a minor part of this book. However, Rovelli is a very interesting man, who came into physics by an unusual route: political activism. It was only after he and his friends failed to instigate the revolution that would change the world to a more compassionate place that he discovered the magic of physics – and later became a best-selling author. Rovelli is a master at interweaving science and history and politics with engaging personal anecdotes. He has a unique ability to communicate the wonder of the universe to those who know nothing about it while providing new insights for those who know a lot. All this he does emphatically in Helgoland.