Helgoland: Making Sense of the Quantum Revolution

by Carlo Rovelli

Einstein had shown that even our most rooted convictions can be wrong. What seems most obvious to us now might turn out not to be correct.

Abandoning assumptions that seem self-evident can lead to greater understanding. Einstein had taught that everything should be based on what we see, not on what we assume to exist.

They had been following the discussions on the relation between reality and experience that ran through Austrian and German philosophy at the beginning of the century. Ernst Mach, who had exerted a decisive influence on Einstein, insisted that knowledge had to be based solely on observations,

Heisenberg attempts to recalculate the behavior of the electron using quantities we observe: the frequency and amplitude of emitted light.

It is the only fundamental theory about the world that until now has never been found wrong—and whose limits we still do not know.

But why is it that we are not able to describe where the electron is and what it is doing when we are not observing it? Why must we speak only of its “observables”? Why is it that we can speak of its effect when it leaps from one orbit to another, and yet we cannot say where it is at any given moment? What does it mean to replace numbers with tables of numbers?

“The objective of this work is to lay the foundations for a theory of quantum mechanics based exclusively on relations between quantities that are in principle observable.”

On the basis of some in fact rather vague theoretical analogies, de Broglie suggests it is possible to think of an electron as being like a small wave in motion.

Schrödinger’s ψ is therefore not a representation of a real entity: it is an instrument of calculation that gives the probability that something real will occur. It is like the weather forecasts telling us what could happen tomorrow.

Quantum theory, just as much in Heisenberg’s version as in Schrödinger’s, predicts probability, and not certainty.

Or is it that Nature actually leaps about here and there by chance? Einstein put the question in colorful language: Does God play dice?

It evolves in time according to the equation written by Schrödinger, as long as we do not look at it. When we look at it, pffft!, it disappears, concentrated into a point, and we see the particle there.26 As if the mere fact of observing it was enough to modify reality.

the theory predicts only the probability of observing one thing or another. The mystery deepens.

Remaining faithful to Werner Heisenberg’s seminal insight on Helgoland, the theory doesn’t tell us where to find any one particle of matter when we are not looking at it. It only speaks about the probability of finding it at one point if we observe it.

But what does a particle care if we are observing it or not? The most effective and powerful scientific theory is an enigma.

By the 1960s, interest in the conceptual problems was on the rise again, curiously added to by the fascination within hippie culture for the alternative otherness of quanta.41

In one way or another, they all require the acceptance of extreme possibilities: multiple universes, invisible variables, phenomena that have never been observed, and other such strange beasts. This is nobody’s fault: it is the fundamental strangeness of the

That is why ψ changes when we observe: not because something happens in the external world, but just because the information that we have changes. Our forecast of the weather changes if we look at a barometer: not because the weather promptly changes the moment that we consult the barometer, but because we have suddenly learned something that we did not know before.

Cubism and quantum theory both moved away from the idea that the world is representable from a single perspective. In the first decades of the twentieth century, it is the whole of European culture that no longer thinks we can represent the world in a simple and complete way.

The anthropologist Claude Lévi-Strauss understands that to study a culture is to change it; Sigmund Freud understands that doctors cannot evaluate patients’ minds without affecting them. In Italy, between the years 1909 and 1925, the years during which quantum theory is born, Luigi Pirandello writes One, No One and One Hundred Thousand (1926), which speaks of the splintering of reality into the points of view of countless observers . .

The theory gives us the probability that we will see something, and this is all that it is legitimate to say. It is not legitimate to say anything about the cat or the photon when we are not actually observing them.

Reality is a luxuriant stratification: snow-covered mountains and forests, the smiles of friends, the rumble of the subway on dirty winter mornings, our insatiable thirst, the dance of our fingers across a laptop keyboard, the taste of bread, the sorrow of the world, the night sky, the immensity of the stars, Venus shining alone in the ultramarine blue of twilight

At the heart of the “relational” interpretation of quantum theory is the idea that the theory does not describe the way in which quantum objects manifest themselves to us (or to special entities that do something special denoted “observing”). It describes how every physical object manifests itself to any other physical object. How any physical entity acts on any other physical entity.

Individual objects are the way in which they interact. If there was an object that had no interactions, no effect upon anything, emitted no light, attracted nothing and repelled nothing, was not touched and had no smell . . . it would be as good as nonexistent.

The world that we know, that relates to us, that interests us, what we call “reality,” is the vast web of interacting entities, of which we are a part, that manifest themselves by interacting with each other. It is with this web that we are dealing.

But quantum mechanics does not describe only these: it describes the elementary and universal grammar of physical reality underlying not just laboratory observations but every type and instance of interaction.

The discovery of quantum theory, I believe, is the discovery that the properties of any entity are nothing other than the way in which that entity influences others. It exists only through its interactions. Quantum theory is the theory of how things influence each other. And this is the best description of nature that we have.

This is a radical leap. It is equivalent to saying that everything consists solely of the way in which it affects something else. When the electron does not interact with anything, it has no physical properties. It has no position; it has no velocity.

Is it possible that a fact might be real with respect to you and not real with respect to me? Quantum theory, I believe, is the discovery that the answer is yes. Facts that are real with respect to an object are not necessarily so with respect to another.* A property may be real with respect to a stone, and not real with respect to another stone.55

The world is the network of relative facts: relations realized when physical entities interact. A stone collides with another stone. The light from the sun reaches my skin. You read these lines.

The life of an electron is not a line in space: it is a dotted manifestation of events, one here and another there. Events are punctiform, discontinuous, probabilistic, relative.

In Cosmological Koans, Anthony Aguirre describes this disconcerting conclusion in the following way: An electron is a particular type of regularity that appears among measurements and observations that we make. It is more pattern than a substance. It is order . . . Thus we arrive at a strange place. We break things down into smaller and smaller pieces, but then the pieces, when examined, are not there. Just the arrangements of them are. What then, are things, like the boat, or its sails, or your fingernails? What are they? If things are forms of forms of forms of forms, and if forms are order, and order is defined by us . . . they exist, it would appear, only as created by, and in relation to, us and the Universe. They are, the Buddha might say, emptiness.58 The

The world fractures into a play of points of view that do not admit of a univocal, global vision. It is a world of perspectives, of manifestations, not of entities with definite properties or unique facts. Properties do not reside in objects, they are bridges between objects.

Objects are such only with respect to other objects, they are nodes where bridges meet. The world is a perspectival game, a play of mirrors that exist only as reflections of and in each other. This phantasmal world of quanta is our world.

Entanglement shows that reality is definitely other than how we had conceived of it. Even if we know all that can be predicted about one object and another object, we still cannot predict everything about the two objects together.

Only God can see the two places at the same moment—but God, if She exists, does not tell us what She sees. What She sees is irrelevant to reality. We cannot rely upon the existence of something that only God can see.

The certainties of classical physics are just probabilities. The well-defined and solid picture of the world given by the old physics is an illusion.

short, Mach stands at a remarkable crossroads of science, politics, philosophy and literature. And some people still view the natural sciences, humanities and literature as unconnected!

Heisenberg’s article begins thus: “It is the aim of this work to lay the foundation for a theory of quantum mechanics based solely on relations between quantities that are in principle observable.” Almost a quotation from Mach.

Lenin accuses Bogdanov and Mach of being “idealists.” An idealist, for Lenin, negates the existence of a real world beyond the spirit and reduces reality to the content of the mind.

Against idealism, Lenin poses a materialism that sees the human being—human consciousness, human spirit—as an aspect of a concrete world that is objective, knowable, and comprising solely matter in motion in space.

Reality may be much more complex than the naive materialism of eighteenth-century physics. Prophetic words, for just a few years later Werner Heisenberg would open the door to the quantum level of reality.

Lenin speaks of absolute certainties. He presents the historical materialism of Marx and Engels as if it were timelessly valid. Bogdanov points out that this ideological dogmatism not only fails to accord with the dynamic of scientific thought, it also leads to calcified political dogmatism.

If, as Marx suggested, culture is influenced by economic structure, then postrevolutionary society would be able to produce a new culture that could no longer be the orthodox Marxism conceived before the revolution. Brilliant.

Bogdanov predicts that Lenin’s dogmatism would seal the Russian Revolution into a block of ice; prevent it from evolving further; suffocate the life out of all that had been gained through it; render it sclerotic. These, too, were prophetic words.

The novel describes a utopian, libertarian society on Mars that has overcome all distinctions between men and women and that uses an efficient statistical apparatus for processing economic data that can indicate to industries exactly what needs to be produced, and to the unemployed precisely in which factories to seek work, and so on, leaving everyone the freedom to choose how they should live.

A doctor, an economist, a philosopher, a natural scientist, a science-fiction novelist, a poet, teacher, politician, progenitor of cybernetics and of the science of organization, a pioneer of blood transfusion and a lifelong revolutionary, Aleksandr Bogdanov, prodigiously talented,97 is one of the most complex and fascinating figures of the intellectual world at the beginning of the twentieth century.

Aleksandr Bogdanov dies an incredible death, in a scientific experiment in which he exchanges his blood with a young man suffering from tuberculosis and malaria in an attempt to cure him. Right up until the end, the courage to experiment, the courage to exchange and share, the dream—and the practice—of brotherhood.

When Einstein objected to quantum mechanics by remarking that “God does not play dice,” Bohr responded by admonishing him, “Stop telling God what to do.” Which means: Nature is richer than our metaphysical prejudices. It has more imagination than we

David Albert, once asked me: “Carlo, how can you think that experiments in a laboratory made with little bits of metal and glass can have such significance as to put into question our most rooted metaphysical convictions about how the world works?”