Carlo Rovelli's 1996 relational interpretation of quantum mechanics (RQM) seems to solve many of the quandaries of traditional theories, including the Copenhagen interpretation (what privileges the observer? Why does he/she instigate wavefunction collapse); the many-worlds interpretation (an infinity of unobservable universes); and spontaneous collapse theories such as that of GRW.

However, there seems to have been limited academic discussion of the theory. Is this due to a shortcoming of the theory, or has there simply not been enough time for it to disseminate?


2 Answers 2


I personally consider RQM to be an attempt at the "best of both worlds" between Copenhagen and MWI. By making measurements observer-dependent, it essentially accomplishes the same thing as entanglement of the system and observer in MWI. By refusing to speculate on other worlds, it has the veneer of realism of Copenhagen. (Full disclosure: I am an MWI supporter but am open to all ideas.)

The problem with RQM as far as I can tell is the "sparse ontology" or "flash ontology" problem. It is discussed briefly here. All measurable quantities in RQM are only defined in the exact instant that they are measured; for most instants in time, the state of the system is essentially undefined. The fundamental reason for this is that RQM postulates that the only thing you can talk about in physics is how systems interact rather than how they are.

According to your taste, this may be a positive or negative aspect of the theory. For me it definitely seems unphysical at best and like borderline solipsism at worst. But I can see obvious counterarguments:

  1. All interpretations of quantum mechanics have something unphysical about them.
  2. Pretty much all advances in physics since Copernicus have required us to get used to a new counterintuitive idea about reality, and this is probably no greater or worse than the previous ones.
  • $\begingroup$ I am absolutely inexpert in this field, but your " ... this is probably no greater or worse than the previous ones. ..." seems to be completely at odds with those far enough up the QM Dunning Kruger knowledge continuum to say that they only don't understand but can't understand. I understand this to not just an expression of the Copenhagen interpretation but a broader and more general claim. Feynman famously made such a claim but he is far from alone. $\endgroup$ Dec 8, 2021 at 4:23
  • $\begingroup$ @RusselMcMahon I understand what you're saying. I do think that QM is legitimately harder for a human being to understand intuitively or imagine visually than past revolutions such as the Copernican model (CM). On the other hand, it's difficult for us, with a modern worldview, to judge how strange and shocking the CM was in its day, precisely because we have grown up with it since childhood. So I would say that, in terms of worldview shift, QM should not be viewed as any more shocking than CM. But in terms of the theory itself being counterintuitive and difficult to imagine, then it is worse. $\endgroup$
    – sasquires
    Dec 9, 2021 at 3:55
  • $\begingroup$ OK. I was probably commenting on the wrong aspect of "ideas about reality". ALL other concepts tend to bend our brains, and some immensely so. Relativity far more than Copernicus I feel, BUT in both such cases the numerical solutions provide an explanation that can be tied to what we sensibly can understand. Even the General Theory of Relativity is "hard maths" that makes physical sense - even if we have to be dragged kicking and screaming to the table. Whereas QM perfectly describes what we see in relatively simple terms BUT it makes no sense at all in any way we can grasp. ... $\endgroup$ Dec 10, 2021 at 0:42
  • $\begingroup$ And 'Copenhagen' demands that it make no sense in any sensible terms. And Many Worlds "makes sense" but rolls its dice where it insists we can never see them. And anything else appears to be a compromise that tries to pretend to bypass these and make sense, even though nothing ever has. Most people are isolated enough from this that its not the super-Copernican shock that it should be. $\endgroup$ Dec 10, 2021 at 0:44

It's fair to say that the discussion about RQM has begun to gain momentum in recent years. I have the impression that it has increased in popularity among physicists and philosophers of physics.

But to make contact with the title of your question, there certainly are substantial open problems. Inter alia, some critics say that it leads to solipsism, and that it suffers from a sort of preferred-basis problem. It's also slightly unclear how the story extends to more general interaction settings (say, continous interactions). If you're interested in diving a littler deeper into some of these issues: here and here are some recent critiques, which Rovelli has replied to here and here, respectively.


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