‘It’s as if reality didn’t exist’

For a century quantum physics has been essential to medicine, engineering, computers, nuclear power and even our knowledge of deep space. But what is quantum?

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The word “quantum” has different associations for many people. To lovers of 1970s rock it evokes memoriesof Quantum Jump, a band whose main claim to fame is singing the Guinness Book of Records’ longest word – the 57-letter name of a New Zealand hill – on their only top 10 single, The Lone Ranger.

‘A hundred years ago it was discovered that the equations do not work for small things and they were replaced with quantum.’

To others, the word may contain a mere seven letters but it’s just as indecipherable as the name of that hill. This is despite Brian Cox, Salford University professor and TV personality, seeming to mention quantum almost every time he’s on the box. Professor Cox also wrote a book titled The Quantum Universe and once boiled the word’s meaning down to “everything that can happen, does happen”.

Still, that fails to explain why boffins around the globe get excited by the expression quantum jump, or quantum leap as it is now more commonly known. Yet even they often struggle to define it. For example, one sought to illustrate the magnetic resistance of spinning “quantum mechanically entangled electrons” by comparing it to the fight between John Cleese’s Black Knight and King Arthur in the film Monty Python and the Holy Grail. About half of the electrons won’t magnetise, he observed, and thus displayed the same against-the-odds tenacity as Cleese did while being hacked down to a limbless and insult-spouting torso by King Arthur’s sword.

So here comes another attempt at nailing the meaning and significance of the word quantum. Only this time it might just be possible to understand, even by those of us who failed our school physics exams. It is a book by Italian theoretical physicist Carlo Rovelli, whose fans include David Hockney, Lily Cole and Benedict Cumberbatch, but rather than writing a bloated tome comprehensible only to science graduates, Rovelli’s book reads almost like a thriller.

The action begins on the Hong Kong island of Lama. Two men are picking their way along a path through the coastal jungle that fringes the beach. One is Rovelli, the other a Serbian-Austrian expert on quantum physics, Caslav Brukner. They are taking an afternoon break from attending an international conference on scientific theory and find themselves discussing a complex thought experiment. By the time they sit down on the sand just a few steps from the sea they are reduced to silent contemplation of their unexpected agreement on the subject. Then Caslav whispers: “Can this be believed? It’s as if reality…didn’t exist…”

Rovelli knew just how challenging the quantum theory remained. After a century of scientists studying it – even with modern technology, he writes in his book – “the theory that is one of the greatest ever achievements of science fills us with astonishment, confusion and disbelief”.

So what is this theory?

For Big Issue North, from his home in Canada, Rovelli explains that physics provide a scientific description of how things move and interact with one another, and three centuries ago this was turned into mathematical formulae by Isaac Newton.

“For 200 years,” says Rovelli, “the equations of Newton worked very well and were used by engineers and scientists to build all sorts of things, from bridges to airplanes. But then a hundred years ago it was discovered the equations do not work for small things and they were replaced by the new scheme of quantum theory, the basis of modern physics.”

A hundred years ago, in fact, like one of those Agatha Christie mysteries awash with so many red herrings that readers inevitably point the finger at the wrong villain, something wasn’t quite right about the quantum theory. “Many facts didn’t fit,” according to Rovelli.

And so for his book he turned to the person who finally made them fit, Werner Heisenberg, the sort of Hercule Poirot of quantum. In May 1925, after leaving a research fellowship at Copenhagen University, Heisenberg had found himself suffering a severe attack of hay fever. He retreated to a treeless German island in the North Sea archipelago of Helgoland (Heligoland in English), where there was almost no pollen to trigger his allergy and he could find blessed relief. While there he conceived the basis of the quantum theory, and worked out if not whodunnit then certainly whatdunnit and whydunnit.

Rovelli says of Heisenberg’s stay on the island that, like Einstein and his theory of relativity, the young physicist was prepared to believe that even our most rooted convictions can be wrong, and that abandoning common assumptions could lead to greater understanding. Knowledge had to be based solely on observations and be freed from theory, he decided while on Helgoland. And so whilst there, according to Rovelli, Heisenberg had an idea about physics that would transform the science in its entirety. It is an idea, Rovelli believes, that even a century later humanity has not yet fully resolved.

For several weeks Heisenberg breathed big healthy lungfuls of the virtually pollen-free North Sea air and dared to think what was then considered to be the scientifically unthinkable. Once upon a time in the scientific world, at the root of everything were just particles of matter guided by a few forces. If no one had been able to find the mysterious force capable of causing bizarre behaviour in electrons – something which impacted everything – then maybe scientists should simply stop trying to identify this apparently new force. Maybe, reasoned Heisenberg, they should stick with the laws of motion they were familiar with. From now on, they should base their understanding only on what they could observe, such as the light emitted by electrons.

Into the early hours of 7 June, he was engaged in a marathon session of recalculating the frequency and amplitude of light emitted by electrons moving in orbits. He made one failed mathematical calculation after another based on Newton’s tables, until he decides to abandon orbital movement entirely. Instead, he applied the behaviour of a pendulum.

“As a consequence,” Heisenberg wrote, “it was around three o’clock in the morning when the result of my calculations lay before me. It was correct in all terms. Suddenly I no longer had any doubts about the consistency of the new ‘quantum’ mechanics that my calculation described.”

Two days later he returned to the German mainland and continued his research at the Georg-August University of Göttingen. He had sent an advance copy of the Helgoland findings to his professor, admitting in a covering note: “I have written a crazy paper and I do not have the courage to submit it anywhere for publication.”

But his professor did have the courage, and sent it to a respected German scientific journal.

The great Einstein himself was then moved to comment: “The ideas… have everyone in suspense, and are preoccupying everyone with the slightest interest in theory.” Einstein added that it was “a calculation of real witchery”.

The theory made Heisenberg famous and in 1932 he was awarded the Nobel Prize for Physics. But fame caused his life to take a dark turn. As one of the generation of young physicists who had learned how to use the new quantum theory to manipulate atoms, in September 1939, shortly after the outbreak of the Second World War, he was invited to join a team assembled by Adolf Hitler to develop an atomic bomb.

He travelled to Copenhagen to meet his former teacher, Niels Bohr, and “discuss the moral problem entailed by the prospect of a terrifying weapon”. A short time later Bohr was willingly kidnapped by British commandos, taken to meet Churchill in London and then to the United States where, writes Rovelli, he was “put to work with the generation of young physicists who have learned how to use the new quantum theory to manipulate atoms” and build the bombs that annihilated Hiroshima and Nagasaki.

Heisenberg continued his atomic weapons research in Germany until he was captured by Allied forces in May 1945 and eventually flown to England. He said later that he had never contemplated building a bomb, only producing atomic energy. Rovelli writes that there is so much more to quantum theory than weapons. The theory has advanced our knowledge of everything from medicines that have saved millions of lives to computers and the entire field of astronomy, including the formation of galaxies.

He tells Big Issue North: “Computers are based on electronic components that are designed using quantum theory. Nuclear power plants are designed using quantum theory. The MRI widely used in hospitals and clinics for medical diagnosis is a direct application of quantum theory. The laser found in many modern technologies, from CD players to doors that automatically open, is an application of quantum theory.”

But, he says, a century after Heisenberg’s theory we still don’t fully understand it. “New discoveries lead to new questions. It is always so in life.”

Helgoland by Carlo Rovelli is published by Allen Lane

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