Ťhere are two kinds of geniuses, argued the celebrated mathematician Mark Kac. There is the “ordinary” kind, whom we could emulate if only we were a lot smarter than we actually are because there is no mystery as to how their minds work. After we have understood what they have done, we believe (perhaps foolishly) that we could have done it too. When it comes to the second kind of genius, the “magician”, even after we have understood what has been done, the process by which it was done remains forever a mystery.
Werner Heisenberg was definitely a magician, who conjured up some of the most remarkable insights into the nature of reality. Carlo Rovelli recounts the first act of magic performed by Heisenberg in the opening of Helgoland, his remarkably wide-ranging new meditation on quantum theory.
Rovelli has taken the title from the name of the rocky, barren, windswept island in the North Sea to where the 23-year-old German physicist fled in June 1925 to recover from a severe bout of hay fever and in need of solitude to think. It was during these few days on the island (also called Heligoland) 那, on completing calculation after calculation, Heisenberg made a discovery that left him dizzy, shaken and unable to sleep.
With the light touch of a skilled storyteller, Rovelli reveals that Heisenberg had been wrestling with the inner workings of the quantum atom in which electrons travel around the nucleus only in certain orbits, 在 certain distances, 和 certain precise energies before magically “leaping” from one orbit to another. Among the unsolved questions he was grappling with on Helgoland were: why only these orbits? Why only certain orbital leaps? As he tried to overcome the failure of existing formulas to replicate the intensity of the light emitted as an electron leapt between orbits, Heisenberg made an astonishing leap of his own. He decided to focus only on those quantities that are observable – the light an atom emits when an electron jumps. It was a strange idea but one that, as Rovelli points out, made it possible to account for all the recalcitrant facts and to develop a mathematically coherent theory of the atomic world.
For all its strangeness, quantum theory explains the functioning of atoms, the evolution of stars, the formation of galaxies, the primordial universe and the whole of chemistry. It makes our computers, washing machines and mobile phones possible. Although it has never been found wanting by any experiment, quantum theory remains more than a little disturbing for challenging ideas that we have long taken for granted.
One of the most well-known counterintuitive discoveries was arguably Heisenberg’s greatest act of quantum conjuring. The uncertainty principle forbids, at any given moment, the precise determination of both the position and the momentum of a particle. It is possible to measure exactly either where a particle is or how fast it is moving, but not both simultaneously. In a quantum dance of give-and-take, the more accurately one is measured the less precisely the other can be known or predicted. Heisenberg’s uncertainty principle is not due to any technological shortcomings of the equipment, but a deep underlying truth about the nature of things.
According to some, including Heisenberg, there is no quantum reality beyond what is revealed by an experiment, by an act of observation. Take Erwin Schrödinger’s famous mythical cat trapped in a box with a vial of poison. It is argued that the cat is neither dead nor alive but in a ghostly mixture, or superposition, of states that range from being totally dead to completely alive and every conceivable combination in between until the box is opened. It is this act of observation, opening the box, which decides the fate of the cat. Some would argue that the cat was dead or alive, and to find out one just had to look in the box. Yet in the “many worlds” interpretation of quantum theory, which is popular among physicists, each and every possible outcome of a quantum experiment actually exists. Schrödinger’s cat is alive in one universe and dead in another.
With the fate of Schrödinger’s cat in the balance and Heisenberg’s idea that quantum theory only describes observations, Rovelli inevitably asks the tricky questions: what is an observation? What is an observer?
He admits he is not an innocent bystander; he has skin in the game when it comes to trying to understand the quantum nature of reality. He is the champion of the “relational” interpretation that maintains quantum theory does not describe the way in which quantum objects manifest themselves to “observers”, but describes how every physical object manifests itself to any other physical object. The world that we observe is continuously interacting; it is better understood as a web of interactions 和 relations rather than objects.
Individual objects 是 summed up by the way in which they interact. If there were an object that had no interactions, no effect on anything, it would be as good as non-existent. When the electron does not interact with anything, Rovelli argues, it has no physical properties. It has no position; it has no velocity.
If all wasn’t challenging enough, Rovelli reveals that he is not afraid to mix quantum physics and eastern philosophy, something that others have done in the past with little success and some derision. It says much about him and his argument that he is not so easily dismissed. He has help in the form of one of the most important texts of Buddhism, Mūlamadhyamakakārikā, 或者 The Fundamental Verses of the Middle Way. Written in the second century by the Indian philosopher Nāgārjuna, its central argument is simply that there is nothing that exists in itself, independently from something else. It’s a perspective that Rovelli believes makes it easier to think about the quantum world. He may be right, but the words of Niels Bohr still come to mind: “Those who are not shocked when they first come across quantum theory cannot possibly have understood it.”