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Carlo Rovelli (1956–)

Rovelli built relational quantum mechanics — properties exist only through interaction, there is no observer-independent state, what is real is constituted through encounter rather than sitting behind it. His anti-foundationalism — “the foundation of science is not certainty but radical uncertainty about our own knowledge” — refused the final vocabulary from within physics. And his engagement with philosophy, from Nagarjuna to Heidegger to the pre-Socratics, makes him a rare working physicist who takes the relational turn seriously across disciplines. Where Kant asked how the mind structures experience, Rovelli asks how interaction structures reality — and the answer drops the privileged observer entirely.

Carlo Rovelli (1956–). Theoretical physicist and philosopher of science. Born in Verona, he was politically active in the Italian student movements of the 1970s — founding free radio stations, co-authoring a book on the Bologna protests, briefly detained for refusing military service. He studied physics at Bologna and Padova, held a joint appointment in physics and the history and philosophy of science at Pittsburgh, and has been based at Aix-Marseille University since 2000. Also affiliated with the Perimeter Institute, the Rotman Institute of Philosophy, and the Santa Fe Institute. One of the few working physicists with a sustained, serious engagement with philosophy — he has argued publicly that physics needs philosophy and philosophy needs physics (“Einstein would have never done relativity without having read all the philosophers”). The anti-authoritarian political stance and the anti-foundationalist physics are not unrelated — a consistent suspicion of fixed structures, whether political or physical.

Key concepts

Loop quantum gravity. Co-founded with Lee Smolin, building on Abhay Ashtekar’s reformulation of general relativity. Space is not continuous but composed of discrete quanta, woven into spin networks. Area and volume are quantised — space has a granular structure at the Planck scale. The theory is background-independent: it does not presuppose a fixed spacetime. With Reisenberger (1997) and later with Engle, Pereira, and Livine (2008), Rovelli developed the spinfoam approach — a sum-over-histories formulation for quantum gravity.

Relational quantum mechanics (RQM). Published in International Journal of Theoretical Physics (1996). The quantum state of a system is always relative to another physical system. There is no observer-independent state, just as there is no observer-independent velocity in classical mechanics. Properties exist only through interactions. This dissolves the measurement problem by rejecting the notion of a single, absolute quantum state. The interpretation has been further developed by van Fraassen and Bitbol.

Time. A sustained programme across multiple works. With Alain Connes, Rovelli developed the thermal time hypothesis (1994): in a generally covariant quantum theory, there is no fundamental time variable. Time emerges from the thermodynamic state of the system — specifically, from incomplete knowledge. The mathematical framework derives a time-flow from a thermal state using the Tomita-Takesaki theorem. “Time is ignorance.” In The Order of Time (2018), he dismantles our intuitions systematically: there is no universal “now,” time runs at different speeds at different altitudes, at the fundamental level the equations contain no time variable. The direction of time appears only through entropy — “the distinction between past and future is not present in the basic grammar of the world.” In “Memory and Entropy” (Entropy 24(8):1022, 2022), he formalised the connection between irreversibility and traces: three conditions for memory (systems separation, temperature differences, long thermalisation times), and a central mechanism — trace formation transforms low entropy into available information. All macroscopic information ultimately traces back to the universe’s past low-entropy state.

Entropy relative to a coupling. A distinct position, set out in “Is Time’s Arrow Perspectival?” (2015; in The Philosophy of Cosmology, Cambridge, 2017) and developed in “Where Was Past Low-Entropy?” (Entropy 21(5):466, 2019). Entropy depends on a coarse-graining — on which variables count as macroscopic — and Rovelli argues that this choice is neither a convention nor a state of anyone’s knowledge but is fixed by which variables physically couple one system to another: “A cup of hot tea does not cool down because of what I know or do not know about its molecules.” The resulting quantity he describes as objective but relative to the system it is relative to — the ignorance reading, in his phrase, stripped of its anthropocentric and subjectivist aspects. He works in the Gibbs rather than the Boltzmann formulation deliberately, since Boltzmann’s construction presupposes a system decomposable into many identical subsystems, which fails for field theory and general relativity. He then extends the proposal to the arrow of time itself, and marks the change in confidence as he does — the 2019 paper calls its second part “speculative and open ended” — the conjecture being that low past entropy may be fully perspectival. The proposal has had limited published uptake, and the objections he discusses (from Robert Wald, David Albert and James Hartle) are ones raised, he says, at an earlier presentation of the idea, which he answers himself in the 2015 paper rather than published replies.

Meaning from information and evolution. In “Meaning = Information + Evolution” (arXiv:1611.02420, 2016; published as “Meaning and Intentionality = Information + Evolution” in Wandering Towards a Goal, 2018), Rovelli gives a physical definition of meaningful information. Relative information in Shannon’s sense — correlation — is everywhere — the world, as he puts it, teems with correlated quantities — so on its own it cannot account for meaning. What singles out the meaningful correlations is survival: “surviving mechanisms survive by using correlations.” His example is a bacterium with an internal variable whose values, L and R, are correlated with food on its left or right and coupled to how it swims: R means “food is on the right”, and when the variable and the food disagree the information is “not true”. Intentionality, he writes, “is built into the definition”, and the definition “does not directly refer to anything mental”; truth is “based on the effectiveness of the consequence of holding something for true”, the sense in which a scientific theory is true when its predictions succeed. Meaningful information can grow recursively, up to contexts with a brain, language, society and norms. The argument rests on two moves. The first is Darwin’s: “we can legitimately reverse the causal relation between the existence of the mechanism and its function” — an idea he traces to Empedocles, quoting Aristotle’s Physics II.8. The second is that the definition is modal, as physics is: “Physics is not a science about how the world is: it is a science of how the world can be.” He closes with a caveat on his own argument: “we do not actually know the extent to which this structure is superimposed over the elementary texture of reality by ourselves … We are undoubtably limited parts of nature, and we are so even as understanders of this same nature.” The essay was taken up in Kolchinsky and Wolpert’s semantic-information paper (2018), which credits it for the idea of meaningful information as survival-relevant correlation.

Nagarjuna and relational ontology. In Helgoland (2021), Rovelli devotes a chapter to the second-century Buddhist philosopher Nagarjuna, whose Mulamadhyamakakarika argues that nothing exists independently — things are “empty” of intrinsic existence and exist only through relations. Rovelli reads this as a resonance with RQM — suggestive rather than systematic, an exploratory connection rather than a developed philosophical position. “Nagarjuna has given us a formidable conceptual tool for thinking about the relationality of quanta.” Rovelli’s broader position has affinities with ontic structural realism — relations are primary, not things — though he frames it through interactions rather than formal structures.

The equality of all things. His most recent book, from an invitation to Princeton’s philosophy department in November and December 2024; the seminar notes are public as “Princeton seminars on physics and philosophy” (arXiv:2407.01989, 2024). The title is taken from the second chapter of the Zhuangzi (齊物論), which Rovelli’s preface says points to the antifoundationalism he takes modern science to lead to: that electrons and minds, stones and laws, judgements and galaxies are not different in kind but notions that illuminate one another. Six lectures and an appendix run from the relational structure of reality, through the circularity of knowing the world from inside it, quantum spacetime, the arrow of time and free will, what exists, to a closing lecture without certainty or foundations that turns on the Zhuangzi’s exchange about the happiness of fish. Three figures anchor the argument — Wittgenstein, Nagarjuna and Zhuangzi — each questioning an absolute, externally observable reality. The moral claim is that values are relative but not arbitrary, arising through human relations and evolving toward a universalism held as a shared goal rather than assumed as a single perspective. The appendix, which several reviewers single out, is on how science actually works, and says he is not convinced by how it is generally presented. The preface credits Bas van Fraassen as among the first to take up the relational interpretation, citing his “Rovelli’s World” (1). Reception in English is early: Adam Frank’s review takes the book as an explicit rejection of any path to a God’s-eye view, with the objection that Rovelli dismisses the primacy of lived experience too quickly, Bergson on time in particular.

Anaximander and the nature of science. In Anaximander (2011/2023), Rovelli argues that the sixth-century BCE thinker inaugurated scientific thinking — not by finding the right answer but by introducing a mode of rational, naturalistic inquiry that rejected supernatural explanation. The essence of science is “learned rebellion”: building on predecessors while questioning them. “The foundation of science is not certainty but the very opposite, a radical uncertainty about our own knowledge.”

Where Rovelli stops

Rovelli’s relational quantum mechanics drops the privileged observer within physics: interaction in RQM is physical, one system relative to another. In the meaning essay he carries physical vocabulary as far as meaning and intentionality, and marks his own limit there — the modal structure the definition relies on may be laid over reality by ourselves, and he leaves that open rather than settling it.

Key works

See also: Relational quantum mechanics · Leibniz · Heraclitus