Is Quantum Mechanics Universal? EWF Experiments and Non Absoluteness of Events

This paper argues that Convivial Solipsism provides a precise conceptual framework for the non-absoluteness of events revealed by Extended Wigner-type experiments, thereby resolving the tension between the universality of quantum mechanics and scientific intersubjectivity without relying on observer-independent facts.

The Gist

The Big Problem: The "Wigner's Friend" Paradox

Imagine a game of hide-and-seek, but with a twist involving quantum physics.

The Setup:

• Alice is inside a sealed, soundproof room. She is looking at a quantum coin that is spinning (it's both heads and tails at the same time).
• Bob is outside the room. He cannot see inside.

The Conflict:

1. Alice's View: She looks at the coin, and it lands on Heads. For her, the game is over. The coin is definitely Heads. She writes it down in her notebook.
2. Bob's View: Bob knows the laws of quantum mechanics say that if no one looks at the coin, it stays spinning (a mix of heads and tails). Since Bob hasn't looked inside, he treats the entire room (Alice + the coin) as one giant spinning system. To him, Alice is in a "superposition" of having seen Heads and having seen Tails simultaneously.

The Question:
Who is right? Is the coin definitely Heads (Alice's view), or is it still spinning (Bob's view)?

In standard physics, we usually assume there is one single reality: the coin is Heads, and Bob just doesn't know it yet. But recent experiments (called "Extended Wigner's Friend" scenarios) suggest that if we take quantum mechanics seriously for everyone (including people inside rooms), these two views can't both be true at the same time.

The Paper's Main Argument

The author, Hervé Zwirn, argues that we have been trying to solve this puzzle by assuming there is a "God's Eye View"—a single, absolute truth that everyone shares. He says this assumption is the problem.

Instead, he proposes a solution called Convivial Solipsism (ConSol).

The Core Idea: "My Reality vs. Your Reality"

Zwirn suggests that events are not absolute. They are relative to the person experiencing them.

• The Analogy of the Movie: Imagine you and a friend are watching a movie, but you are in different theaters with different screens.
  • In your theater, the hero survives.
  • In your friend's theater, the hero dies.
  • In a normal world, this would be impossible. But in this quantum world, both outcomes are "real" for the person watching them, but they don't have to match.

The paper claims that Alice's reality (where she saw Heads) and Bob's reality (where he sees a spinning mix) are both valid, but they exist in separate "perspectives." There is no single "Master Reality" that contains both.

How "Convivial Solipsism" Solves the Puzzle

The name sounds scary ("Solipsism" usually means "only I exist"), but the author adds "Convivial" (friendly) to make it work for science. Here is how it works:

1. The "Hanging-On" Mechanism
When Alice looks at the coin, her brain "hangs on" to one specific outcome (Heads). She locks into that reality. She doesn't physically change the universe; she just selects one path from the many possibilities.

• Bob is still outside. He hasn't "hung on" to anything yet. To him, the whole room is still a mix of possibilities.
• Crucial Point: Alice's selection of "Heads" doesn't force Bob to see "Heads." Bob's reality is independent until he interacts with her.

2. The "Tracking" Problem (The Communication Trap)
Usually, we assume that if Alice sees Heads and tells Bob, Bob will hear "Heads." This is called the Tracking Assumption.

• Zwirn's Twist: In this theory, when Bob asks Alice what she saw, he isn't accessing her internal memory. He is interacting with her as a physical object.
• The Analogy: Imagine Alice is a robot programmed to say "Heads" or "Tails." When Bob asks the robot, the robot's answer is determined by Bob's interaction with the robot, not necessarily by what the robot "thought" earlier.
• The Result: Bob might hear "Heads" even if, in Alice's private world, she saw "Tails."
• Wait, isn't that a lie? No. In this theory, there is no "lie" because there is no single truth to lie about. Alice's "Tails" and Bob's "Heads" are just different perspectives. They are both true for the person experiencing them.

3. Why Science Still Works (The "Convivial" Part)
You might ask: "If everyone has their own reality, how can we do science? How do we agree on facts?"

Zwirn argues that science doesn't need a "God's Eye View." It only needs internal consistency.

• The Analogy: Imagine you are playing a video game. You see a dragon. Your friend, playing on a different server, sees a unicorn.
  • You can talk to your friend.
  • If you ask, "Did you see a dragon?" your friend might say, "Yes, I saw a dragon!"
  • Why? Because the game is designed so that when you ask, the system makes the answer match your expectation.
• In ConSol: When Alice and Bob talk, the laws of physics ensure that their conversation is consistent within their shared interaction. They will agree on what they heard, even if their private memories of the event were different. Science works because every observer's personal timeline is consistent, not because everyone shares the same "absolute" timeline.

The "No-Go" Theorems Explained Simply

Scientists recently proved a "No-Go" theorem. It's like a math proof that says: "You cannot have all of these things at once:

1. Quantum mechanics applies to everyone (Universality).
2. There is one absolute truth for everyone (Absoluteness).
3. People can undo measurements (Super-observers).
4. Local cause and effect (Locality)."

Most physicists have to give up one of these.

• Some say: "Okay, quantum mechanics stops working for big people." (Giving up Universality).
• Some say: "Okay, there is no single truth." (Giving up Absoluteness).

Zwirn's Choice: He says we must give up Absoluteness. We must accept that "facts" are like opinions: they are real to the person holding them, but they don't have to be the same for everyone else.

The Conclusion: A New Way to See the World

The paper concludes that we don't need to be confused by these paradoxes. We just need to change how we think about "reality."

• Old View: The universe is a single stage, and everyone is watching the same play.
• New View (ConSol): The universe is a collection of individual screens. Everyone is watching their own version of the play.
• The Good News: Even though the screens are different, the movies are programmed to sync up perfectly whenever the characters talk to each other. So, we can still do science, share data, and agree on results, even if our private experiences of "what happened" are fundamentally different.

In short: The universe isn't a single, solid fact waiting to be discovered. It's a network of personal perspectives that are perfectly consistent with each other, even if they don't match. And that is enough to keep science running.

Technical Summary

Technical Summary: Is Quantum Mechanics Universal? Extended Wigner's Friend Experiments and Non-Absoluteness of Events

Problem Statement
The paper addresses the fundamental tension revealed by Extended Wigner's Friend (EWF) experiments between three core assumptions: the universality of quantum mechanics (U), the absoluteness of observed events (AOE), and the structure of physical reality. Recent no-go theorems (e.g., Bong et al., Brukner) demonstrate that these assumptions cannot be jointly maintained. However, the author argues that the prevailing conclusion—that "events are not absolute"—remains an under-specified interpretive slogan. Without a rigorous conceptual formulation of non-absoluteness, existing approaches risk ambiguity or the implicit reintroduction of observer-independent facts. The central problem is to provide a precise structural account of non-absolute events that preserves the universality of quantum mechanics while resolving the apparent conflict between perspectival outcomes and scientific intersubjectivity.

Methodology
The paper employs a conceptual analysis of the measurement problem and the logical structure of no-go theorems.

1. Taxonomy of Interpretations: The author constructs a taxonomy based on the status of reality (realist vs. non-realist) and the role of the state vector (ontic vs. epistemic), drawing on classifications by Harrigan & Spekkens and Schmid et al. This framework categorizes interpretations (Everett, QBism, RQM, Pragmatism, CSM, ConSol) regarding their answers to questions about reality, systems, state vectors, and measurement.
2. Analysis of Disaccords: The paper distinguishes between Type I, II, and III disaccords (inconsistencies between observer perspectives) and analyzes the conditions under which they arise.
3. Meta-Level vs. Perspective: A crucial methodological distinction is drawn between the "perspective" (the first-person experience of an observer) and the "meta-level" (a theoretical construct used to compare different perspectives). The author argues that many paradoxes arise from conflating these levels or assuming a "view from nowhere."
4. Evaluation of Assumptions: The paper scrutinizes the assumptions of EWF theorems, particularly the Tracking assumption (that an observer hears the actual result obtained by another) and the Absoluteness of Observed Events (AOE).

Key Contributions

• Refinement of Non-Absoluteness: The paper argues that denying AOE is insufficient without a precise formulation. It proposes that non-absoluteness requires a framework where events are relative to a perspective, and the "Tracking assumption" (Cross-Perspective Link) is not a necessary feature of reality but a specific hypothesis that can be violated.
• Convivial Solipsism (ConSol) as a Solution: The author presents Convivial Solipsism as a coherent framework that fully articulates non-absolute events. Key features of ConSol include:
  • Perspectival Selection: A measurement is defined not as a physical collapse but as the "hanging-on" of an observer's perception to one branch of a superposition. This selection is non-physical and does not alter the global quantum state.
  • Violation of Tracking: ConSol explicitly rejects the Tracking assumption. When Observer A asks Observer B for their result, A perceives a macroscopic quantity (e.g., speech) correlated with B's system, but this perceived result in A's perspective need not match the result B obtained in B's own perspective.
  • Conviviality: Despite the violation of Tracking, ConSol ensures "local consistency." If an observer asks another about a measurement they both performed, the answer heard will always be consistent with the asker's own result, preserving the appearance of intersubjective agreement within a single perspective.
• Formal Logic for Perspectival Interpretations: The author introduces a formal axiomatic logic (Section 9) to rigorously handle perspectival statements. This logic distinguishes between well-formed formulas within a perspective (Type-1) and meta-level comparisons (Type-2), preventing logical errors that arise from treating perspectival results as absolute facts.

Results

• Resolution of No-Go Theorems: By rejecting both the Absoluteness of Observed Events (AOE) and the Tracking assumption, ConSol escapes the contradictions derived in Extended Wigner's Friend no-go theorems. The contradiction relies on the ability to form joint probabilities of outcomes across different observers; ConSol argues that such joint probabilities are not meaningful within a single perspective and that the meta-level comparison required to derive the contradiction does not correspond to an accessible physical reality.
• Reinterpretation of Universality: The paper maintains the universality of quantum mechanics (unitary evolution applies to all systems, including observers) but restricts its application to the description of interactions from an external perspective. From the internal perspective of the observer performing the measurement, the process is non-unitary (resulting in a definite outcome).
• Intersubjectivity and Scientific Confirmation: The paper addresses the concern that non-absolute events undermine scientific intersubjectivity. It argues that scientific confirmation is intrinsically perspective-indexed. Observers confirm quantum mechanics within their own perspective, where communication appears reliable and consistent (due to "conviviality"). The goal of empirically confirming what happens in other inaccessible perspectives is shown to be illusory and unnecessary for the practice of science.

Significance
The paper claims that Extended Wigner's Friend experiments are not merely technical paradoxes but structural indicators of a necessary conceptual shift. The significance lies in demonstrating that scientific objectivity does not rely on observer-independent facts (absolute events) but on the internal coherence of perspectival structures. By providing a precise formulation of non-absoluteness through Convivial Solipsism, the paper resolves the tension between the universality of quantum mechanics and the uniqueness of measurement outcomes without resorting to hidden variables, retrocausality, or a breakdown of unitary evolution. It suggests that the "feral" nature of perspectival interpretations (where results are relative and tracking is violated) is a consistent and viable ontological framework that avoids the ambiguities of other "Copenhagenish" interpretations.