Quantum

Ever since the birth of quantum mechanics, the science community has lived with an ongoing paradox. The scientific results of the new tools — quantum mechanics and the special and general relativity theories — are overwhelming. Yet the resulting worldview discourse in science has conceptually and in vocabulary remained strongly on the classical and deterministic side tainted by ‘the outside reality’ view and the ‘privileged observer’.

This tension is most acute in the existing QM worldviews, especially around the place of the participant observer in the picture of reality. In special and general relativity, where the relational gets translated into the fabric of spacetime, the tension is less acute.

For most of last century, three established worldviews have dominated the landscape. The Copenhagen interpretation, born with quantum mechanics itself, simply declined the question: don’t ask what happens between measurements. The formalism works — use it. “Shut up and calculate,” as Mermin put it. Bohm (1952) restored determinism through hidden variables — particles always have definite positions, guided by a pilot wave. The price: non-locality, faster-than-light influence on trajectories. Many-Worlds (Everett, 1957) proposed that all outcomes are real, in branching universes — a bold move that removes collapse entirely, but is difficult to test and quietly lets the outside observer back in through the back door.

Each worldview gives up something different. None achieved consensus. And for decades, the dominant culture said: don’t ask. Working on interpretation was like entering a minefield, a professional risk. Bell never got a Nobel (he died in 1990, before the experimental confirmation was complete). Clauser was told he was ruining his career. The questions were real, but asking them was actively discouraged.

The early interpretations shared a common approach: here is a worldview, see how it fits the physics. From the 1980s, the question got turned around: what does the physics itself tell us about reality, about a potential worldview?

The decoherent histories approach (Griffiths, Gell-Mann & Hartle) was an important step in this direction. Decoherence is the physical process by which quantum systems, through constant interaction with their environment, produce stable, shared facts. The classical world we experience — definite objects, definite properties, reproducible measurements — is not a given. It is produced, through an enormous amount of interaction.

But the insight stopped before the relational reading. Decoherent histories focused on the shared, stable side — how the classical emerges. The other side of the coin, entanglement, remained a separate topic, a quantum puzzle rather than part of the same picture. Entanglement is what you have before decoherence has anchored the properties. If decoherence produces the anchored and shared, then entanglement is simply what is not yet anchored — properties coupled but floating outside the decohered context.

RQM took the same approach — what does the physics tell us? — but from the other side. Where decoherent histories focused on the shared and stable, RQM started from the coherent, the entangled. Its move was simple: drop the artificial observer status. The observer is not special. The observer is any physical system. A perspective, not a privilege.

Properties are not things systems have in themselves — they are facts established through interaction. Drop the assumption of observer-independent facts, and the paradoxes of quantum mechanics dissolve. No new constraints introduced, no hidden variables, no branching universes, no irreducible agents.

This approach was published in 1996 by Carlo Rovelli, alongside his main research interest of loop quantum gravity where spacetime itself is quantised and relational. The connection is natural: if spacetime is relational, quantum states should be too.

RQM was initially ignored, largely the case with all reality views on quantum mechanics. But it persisted and slowly built momentum. A small community formed: Laudisa in Milan, Smerlak, Bitbol in Paris. The SEP entry in 2002 gave it institutional recognition. Then in 2010, Bas van Fraassen — one of the world’s leading philosophers of science — published “Rovelli’s World,” a 27-page engagement that identified the central challenge: if facts are relative to observers, what connects different observers’ accounts? That question would drive RQM’s development for the next fifteen years.

While RQM was slowly building momentum, the ground within quantum mechanics started to shift. Quantum information changed the landscape. Shor’s algorithm (1994) showed that a quantum computer could break encryption that classical computers couldn’t touch. Quantum teleportation (1997) demonstrated that quantum states could be transferred using entanglement. Entanglement — once a philosophical curiosity that Einstein had dismissed as “spooky action at a distance” — became a practical engineering resource. The field that had been an esoteric backwater became a strategic priority.

And Bell’s work found its vindication. In 1964, John Bell had shown mathematically that if quantum mechanics is right, then nature must violate certain statistical limits — limits that any classical, locally deterministic picture of reality would obey. For decades, experiments confirmed the violations but always with potential loopholes — maybe the detectors were biased, maybe the measurements weren’t truly random. In 2015, three independent teams closed the loopholes definitively. In 2022, the Nobel Prize followed. The correlations are real. Nature does not behave classically. The questions Bell insisted on asking turned out to be the right ones.

In 2018, Frauchiger and Renner published a thought experiment that sharpened everything. It showed that three seemingly reasonable assumptions about quantum mechanics cannot all hold: that QM applies universally, that measurements produce single outcomes, and that reasoning transfers consistently between agents. Any interpretation must give up at least one.

The established views each reveal their compromise. Copenhagen limits where QM applies — there must be a classical domain. Many-Worlds gives up single outcomes — all results happen, in branching universes. Bohm holds all three but pays with non-locality. Each modifies the physics or the ontology to preserve the transferability of facts between observers.

RQM takes a different path. It keeps the physics universal and outcomes single for each system — but denies that facts transfer between systems without interaction. Then the role of decoherence entered the picture and provided a physical mechanism. Facts transfer when decoherence anchors them into a shared context. Where decoherence is absent — as in the Frauchiger-Renner setup, where agents are treated as quantum systems — there is no shared anchoring, and facts stay local.

And RQM’s own understanding kept evolving. In 2021, Di Biagio and Rovelli introduced the concept of stable facts. The classical world is the world of stable facts. But the crucial insight: decoherence is itself relational. The mechanism that produces shared, stable reality is relational all the way through — not a bridge between a quantum world and a classical one, but a single relational process operating at different degrees of anchoring. This is where RQM’s own development sits in affinity with SPLectrum’s reading: the shared and the stable are not given, they are produced relationally. In 2022, they clarified further: RQM is about events, not quantum states.

The picture that emerges is this: reality is relational — properties exist through interaction, not in isolation. Knowledge about that reality becomes shareable through decoherence anchoring — the physical process that produces stable, shared facts from relational ones. Where decoherence is present, we have the classical world we recognise — definite, shared, reproducible. Where it is absent, we have the quantum world — entangled, local, floating. Both are relational. The difference is in the anchoring.

This post is part of the positioning series. See also The Turn in Science.

Photo: Whispering Shiba / Unsplash