It from Bit, Bit from It

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tldr; If we view the limit where measurement efficiency \(\eta\) approaches 1 as a boundary condition, then what the Quantum Zeno Effect seems to show is that a quantum-to-classical transition requires an irreversible step that dissipates at least the Landauer bound.

If you have ever felt uneasy reading about quantum mechanics, you are in good company. For nearly a century, the idea that a cat can be both alive and dead — or that an electron exists in a cloud of probability until "looked at" — has struck even world-class physicists as unreasonable. We often try to fix this unease by imagining a "real" hidden state behind the scenes, or by proposing that consciousness somehow collapses the wave function.

But what if quantum mechanics isn't the problem? What if we've been carrying around a mistaken assumption about reality itself?

In 1996, physicist Carlo Rovelli proposed a radical shift called Relational Quantum Mechanics (RQM). His argument parallels Einstein's breakthrough with Special Relativity. Before Einstein, physicists struggled to explain Maxwell's equations because they assumed time was absolute. Einstein solved the problem by accepting that time is relative to the observer. Rovelli suggests we must do the same for quantum states: no "absolute state" of a system exists. A system's state is always relative to another system.

Any System Can Observe

The first step toward clearing up quantum confusion is abandoning the idea that an "observer" must be human, conscious, or even complex. In Rovelli's framework, any physical system can observe another. An electron interacting with a photon observes it. A table lamp interacting with a hand observes it.

Rovelli's "Hypothesis 1" is simple: all systems are equivalent. The laws that describe a single atom also describe you, me, and the entire laboratory. This removes the need for "special systems" — consciousness, gravity, or anything else — to explain wave function collapse. Collapse isn't magical. It's just what happens when two systems exchange information.

"It from Bit" and "Bit from It" are not competing philosophies but two faces of a single principle: information is physical correlation, and physical correlation costs relative entropy — the divergence between two systems' descriptions that must be reconciled for them to share a fact. The lossless limit, in which correlation would be free, is unreachable. That unreachability is not a limitation of our technology. It may be what generates the physical world.

Two Observers, Two Truths

To see how this works, consider what Rovelli calls the "Third Person Problem."

Observer \(O\) measures a system \(S\) — say, an electron. \(O\) interacts with \(S\) and finds the electron is "Spin Up." For \(O\), the wave function has collapsed. Reality is definite: Spin Up.

Now imagine a second observer, \(P\), standing outside the room. \(P\) does not interact with the electron. Instead, she treats \(O\) and \(S\) together as a single quantum system. According to the Schrödinger equation, \(P\) describes them not as "Spin Up," but as an entangled superposition:

$$(\text{Electron Up} + \text{Observer seeing Up}) \text{AND} (\text{Electron Down} + \text{Observer seeing Down})$$

Who is right? Is the electron "really" Up, as \(O\) sees it? Or is it "really" in superposition, as \(P\) describes?

Standard quantum mechanics calls this a paradox. RQM calls it a feature. Both accounts are correct. The divergence between these two accounts — \(O\)'s definite outcome and \(P\)'s entangled superposition — is precisely the relative entropy between the descriptions maintained by two systems that have not yet interacted. That divergence vanishes only when \(P\) enters the room and correlates with \(O\), paying the thermodynamic cost of synchronization.

"Spin Up" is true relative to \(O\). "Superposition" is true relative to \(P\). No contradiction exists because \(O\) and \(P\) describe the system from different frames of reference — just as a moving train looks different to a passenger inside than to a bystander on the platform.

Correlation Keeps Reality Consistent

This might sound like solipsism — each of us living in a private dream world — but Rovelli anchors his framework in physical reality through consistency.

If \(P\) enters the room and asks \(O\) what he saw, a physical interaction takes place. Rovelli proves that quantum mechanics guarantees \(P\) will always find a result consistent with \(O\)'s measurement. If \(O\) saw "Up," \(P\) will measure that \(O\) recorded "Up."

This brings us to RQM's core mechanism: correlation.

For \(P\), the "measurement" that \(O\) performed is not a collapse; it establishes a correlation — an entanglement — between \(O\) and \(S\). The fact that \(O\) has "information" about \(S\) is physically identical to saying \(O\) and \(S\) are correlated. Information is correlation. And correlation is never free — establishing it requires...