DEEP READING · READ 18b
Helgoland · Carlo Rovelli · 2020
Quantum mechanics is the most precise theory humans have ever built — a century old and never once wrong — and yet after a hundred years no one can say what kind of world it is describing. Rovelli's answer: stop asking what a thing "is in itself" — in itself it is nothing. Position, speed, spin are never properties an object holds on its own; they are always properties of that object relative to another, and they become definite only in the instant the two interact. Outside of interactions, there are no facts. The world is not a heap of things each holding its own properties, sitting there quietly — it is a web of mutual manifestation and interaction, in which nothing exists with an intrinsic nature of its own. And this startling conclusion was stated eighteen centuries ago by Nāgārjuna: all things are empty, without self-nature, existing only in their dependence on one another.
Rovelli is an Italian theoretical physicist, a co-founder of loop quantum gravity — one of the main attempts to stitch gravity together with quantum mechanics — and the author of the global bestsellers Seven Brief Lessons on Physics and The Order of Time (the latter is Read 18 on this site). This 2020 book takes its name from a barren little island in the North Sea, Helgoland: in June 1925, the 23-year-old Werner Heisenberg fled his hay fever to this nearly plantless rock, and it was here that he thought through the crucial step from which quantum mechanics was born. The book braids three strands: part history (how quantum theory was built, and why it is so strange), part philosophy (Rovelli's own reading — the "relational interpretation"), and a third strand no one sees coming — a cross-cultural echo (Nāgārjuna's Madhyamaka, Ernst Mach's positivism). It is not a textbook; it is a front-line physicist's meditation on what kind of reality the quantum revolution actually implies.
Three claims, each building on the last:
The story begins with that step on the island. In the early 1920s physics was stuck on one question: how does an electron actually move inside an atom? Picture it as a little planet orbiting the nucleus, and the spectral lines you compute (the colors atoms emit) simply refuse to match. On Helgoland, Heisenberg made a radical decision: stop talking about the electron's invisible orbit altogether — talk only about what we can actually observe. What we can measure is the light an atom emits when it "jumps" from one energy level to another: its frequency, its brightness. So he arranged these jumps into a table, its rows and columns labeled by energy levels (a jump from state i to state j). His colleague Max Born recognized it at once: this is a matrix.
Matrices have a strange habit: the order of multiplication matters — A×B need not equal B×A. Cashed out in physics, this became the famous line: position X times momentum P does not equal P times X (XP − PX = iℏ). "Measure position then momentum" and "measure momentum then position" give different results. This is the mathematical seed of what later became the uncertainty principle. But the deeper layer Rovelli wants you to see is this: from its very first day, quantum mechanics was never about "what the electron is doing on its own" but about "how the electron manifests across a series of jumps" — it is about relations between events, not a little ball tracing a path. Between two observations the electron has no trajectory — not because we fail to know which way it went, but because there is none. Heisenberg wrote that he was too excited to sleep that night; he climbed a rock on the island to watch the sunrise, feeling he was looking into a strange, beautiful interior of nature. That gesture — keeping only mutual manifestation and throwing out the thing-in-itself — is the seed of everything in the book.
The sharpest thorn in the quantum world is called superposition. An electron can be in a superposition of "here" and "there" — and note, this is not "it is in one place and we don't know which," but that it genuinely occupies both, and interferes with itself. The cleanest evidence is the double-slit experiment: fire electrons one at a time, and each one behaves as if it passed through both slits at once, building up light-and-dark interference fringes on the screen; but the moment you place a detector at the slits to see which one it really took, the fringes vanish and it dutifully turns back into a single particle going through a single slit.
Here is the knot: the equation (Schrödinger's) evolves smoothly and predicts superposition; yet every time we actually look, we see one and only one definite outcome — never a ghostly "half here, half there." This is the century-old measurement problem: when, and by what, does a superposition become a single fact? Schrödinger's famous cat pushes it to the absurd — lock a cat in a box with an atom that may or may not decay, put the atom into a superposition of "decayed + not decayed," and the cat becomes a superposition of "alive + dead." For a hundred years, every school of interpretation has been racing to answer this. Rovelli's answer is the next two ideas.
This is the heart of the book. Rovelli's claim is crisp: the properties of a system are not absolute — they exist only relative to another system, and become actual only when the two interact. There is no such thing as "the state of the electron" full stop; there is only "the state of the electron relative to the thing that just struck it."
The analogy with speed makes it click. Asking "what is my true speed right now" is a meaningless question — relative to the ground I am at rest, relative to the sun I am racing along at thirty kilometers a second. Speed was never a property I hold alone; it is a relation between me and some reference body. Galileo relativized "speed" four hundred years ago; what Rovelli does is relativize every property — position, momentum, spin, even "alive or dead." And so the terrifying moment of "collapse" stops being mysterious: collapse is nothing but an interaction, seen from the standpoint of one of its participants. Here the "observer" need not be a person, need not be conscious, need not even be alive — a photon, a speck of dust, any physical system at all qualifies as an "observer" for whatever it interacts with. Measurement has nothing special about it; it is just interaction — and conversely, every interaction is a "measurement" for the parties involved. Between interactions, an object simply has no definite properties relative to a given other object — not hidden, just absent. This overturns how you see the world: reality is not a stack of objects each clutching its own properties, but a web of "mutual manifestation" — a thing just is the way it shows up to others, and beyond that there is no "it in itself."
If properties are relative to interactions, then one step further, facts themselves are relative — the book's most radical bite. Back to Schrödinger's cat: inside the box the cat (or the poison, or the atom) has already interacted, so relative to the cat, whether the decay happened is a definite fact — the cat is either alive or dead. But for the physicist outside, who has not yet opened the box and has not interacted with anything inside, relative to her, the cat-plus-atom is in superposition, and that fact has not yet "come true" for her. Both descriptions are complete and correct — they simply belong to different systems. There is no God's-eye "true state of the cat" forcing the two sides to agree.
Dizzying as it sounds, physics has pulled the same trick once before. Einstein's special relativity taught us that "which two events are simultaneous" has no absolute answer, only an answer relative to some observer — simultaneity is relative. Rovelli extends that line one notch: not only is "simultaneity" relative, but "what counts as a fact, what has really happened" becomes relative to a system. (Physicists call this kind of thought experiment "Wigner's friend": the friend inside the lab has already seen a definite outcome, while Wigner outside must still describe the whole lab — his friend included — with a superposition.) This forces you to surrender a deeply rooted belief: there is no single ledger recording all the objective facts of the universe; there are only "facts relative to each system," sewn together by further interactions. And it is precisely here that the sharpest criticism lies in wait (see below).
Gather up the steps above and you have Rovelli's whole worldview. Since nothing holds its properties "on its own," there is, underneath all these interactions, no set of self-standing "things" each carrying an "intrinsic essence." What truly exists are interactions, events; and an "object" is just a relatively stable knot in this web of interactions — defined entirely by "how it affects other things and how it is affected by them." An object is the sum of the ways it manifests to everything else; strip those manifestations away and no "it in itself" remains.
Rovelli also gives an information-theoretic gloss: quantum mechanics is a theory about how much information physical systems hold about one another. (Here "information" is not knowledge in a mind, but purely physical correlation — one system's state being hooked to another's.) He compresses the whole theory into two plain principles: first, any system carries only a finite amount of relevant information (this is the "quantum" itself — the origin of that minimal action ℏ; the world comes in grains, not infinitely divisible); second, you can always acquire new information (it is inexhaustible; no measurement ever "says all there is to say" about a system). Reality is just this ceaseless exchange of relative information. It invites you to change the question you ask: instead of "what is the world ultimately made of" (a substance question), ask "how does the world interact with itself" — relations are the bottom layer, and underneath the relations there is no harder bedrock.
At this point Rovelli found himself stuck: how can something exist only in relation, with no ground beneath it at all? A friend handed him Nāgārjuna (c. 2nd century CE) — founder of the Madhyamaka ("Middle Way") school of Mahāyāna Buddhism. Nāgārjuna's core can be put in a phrase: dependent origination is emptiness. "Dependent origination" (Sanskrit pratītyasamutpāda) means that all things arise in dependence on other conditions; "emptiness" (śūnyatā) means that, precisely because of this, all things are empty of self-nature (svabhāva — an independent, self-standing essence). A cart is not a "cart-in-itself"; it is just wheels, axle, and frame in a particular relation, plus the name we pin on it — dig under that bundle of relations and you find no kernel called "cart-ness." Nothing owns an independent essence; a thing is what it is entirely through its relations to other things.
What clinches it — and suits Rovelli exactly — is Nāgārjuna's next move: emptiness itself is empty ("the emptiness of emptiness"). "Relation," "emptiness," is not yet another ultimate ground. This is the very cure for Rovelli's vertigo: you do not need to lay some solid bedrock beneath the web of relations; the absence of bedrock is the whole point. To be clear: Rovelli does not say "quantum mechanics proves Buddhism," nor "Buddhism predicted quantum mechanics" (both are misreadings he takes pains to avoid — see below). He merely notices that the conclusion Western physics reached only when cornered — that nothing exists with a self-nature, that things exist only in dependence — is one the East thought all the way through two thousand years ago, and learned to live with in peace. The way this idea changes how you see the world: the deepest layer is not "stuff"; and you do not even need a "deepest layer" — quantum physics and Madhyamaka, coming from two opposite directions, arrive before the same "groundless" insight.
Read only this one book and you will take Rovelli for "the guy who interprets quantum mechanics" — and miss the picture. His day job, and his larger project, is loop quantum gravity — and "relation" is the thread that runs through all of his work. In that theory, even space itself is granular: there is a smallest "quantum of space" (area and volume come in minimal portions), and space is not a ready-made box that holds everything, but is woven out of a relational graph called a spin network — space is a relation between fields, not a stage. As for time, he already took it apart in The Order of Time (Read 18 here): in the most fundamental equations, the variable "time" simply drops out. Stack the three books together and Rovelli is really telling one story: matter, space, and time — the three things we take to be most solid and most "self-standing" — all lose their absolute, self-sufficient status and dissolve into relations. The quantum "no-self-nature" of Helgoland is just one face of this relational physics.
Distill a book that keeps circling back into a single line:
Where does it actually win? Line it up against the other big interpretations and it becomes clear. Many-Worlds (Everett) keeps the wavefunction forever real and never collapsing — at the price of infinitely many parallel universes, endlessly splitting, that you can never see. Hidden variables (Bohm's pilot wave) hands the electron's definite trajectory back to you — at the price of a guiding field spread instantaneously across the whole universe and a layer of hidden reality. Physical collapse (GRW) posits a genuine, random physical collapse — at the price of new physics never observed, with constants that must be hand-tuned. Rovelli's relational interpretation adds none of this — the same predictions, no extra universes, no hidden variables, no new physics — its one "price" is metaphysical: giving up "facts independent of any observer." Choosing among them is choosing which price you are willing to pay.
① Quantum mechanics is humanity's most precise theory, a century without error — yet in the world it describes, objects do not own definite properties of their own; the whole hundred-year impasse comes from our refusal to let that go.
② The first step Heisenberg took on that barren island set the key: speak only of the observable jumps, not of the electron's invisible orbit. Between two observations the electron has no trajectory — not unknown, but nonexistent.
③ Superposition is not "it's somewhere and we don't know where," but two states genuinely coexisting and interfering with each other; yet each time we look, we see one and only one outcome — this is the unsolved "measurement problem."
④ The heart of the relational interpretation: a property is definite only relative to another object, and only in the moment of interaction. Just as "speed" is nothing without a reference body, every property is nothing without the thing it is relative to.
⑤ "Collapse" is not mysterious; it is simply an interaction, seen from the standpoint of one of its participants — and the "observer" need not be a person or be conscious; a speck of dust will do.
⑥ Push further and even facts are relative: to itself the cat is dead, to the person outside the box it is in superposition, and both are correct. No God's-eye view forces the two to agree — just as relativity gives "simultaneity" no absolute answer either.
⑦ So the world is not a heap of property-clutching "things" but a web of mutual manifestation: a thing is the sum of the ways it shows up to everything else; strip those away and no "it in itself" is left.
⑧ Quantum mechanics is really a theory about how much information systems hold about one another: information is finite (hence the quantum) and inexhaustible (you can always measure again); relation is the bottom, and beneath relation there is no ground.
⑨ This is just what Nāgārjuna said long ago: all things are without self-nature, existing only in dependence; even "emptiness" is empty — no need to seek a ground. The echo is not a proof but a solace.
⑩ Don't misread it: the observer is not consciousness, and the quantum does not prove Buddhism. And whether "relative facts" are even self-consistent (the Frauchiger–Renner question) is still disputed — it is elegant, but not settled.