Classical Data Defines Limits to Copying and Change

Darwinian evolution’s fundamental requirements of heritable records, repeatable copying with variation, and irreversibility are explored within the framework of quantum mechanics by Partha Ghose from the Tagore Centre for Natural Sciences and Philosophy, and colleagues. This research investigates how different interpretations of quantum foundations, including unique-history, decohered multiplicity, agent-relative facticity, and stochastic mechanics, might underpin the mechanisms necessary for biological evolution. The study is significant because it addresses a long-standing problem in reconciling Darwinian principles with the seemingly non-classical nature of quantum processes, clarifying why copying and deletion are not universally possible operations. Ghose and colleagues demonstrate that classical data sectors are essential for these processes, and utilise extended Wigner’s Friend scenarios to stress-test these concepts, ultimately proposing a stochastic-mechanics approach offering a continuous link between quantum and classical realms and a principled method for measurement updates.

Imagine attempting to faithfully copy a complex painting, knowing even tiny errors accumulate with each iteration. Darwinian evolution demands similar fidelity, yet operates within a quantum area where copying isn’t guaranteed. New work establishes that a stable, classical foundation is essential for heredity, clarifying how life’s processes can function in a quantum world.

Scientists are increasingly focused on the fundamental connection between quantum mechanics and the emergence of classical behaviours, particularly those underpinning biological processes. Darwinian evolution, with its reliance on heritable records, repeatable copying, and irreversible change, presents a striking challenge to reconcile with the principles of quantum physics.

At face value, the notions of “copy” and “delete” appear problematic within a quantum framework, constrained by principles like the no-cloning theorem which prohibits the perfect duplication of an unknown quantum state. Recent research establishes that a “realised classical data sector”, in effect a stable and distinguishable basis, is not merely a convenient approximation but a physical necessity for evolution to operate.

Establishing this basis is not straightforward; decoherence, the process by which quantum systems lose coherence due to environmental interaction, can dynamically select a pointer basis, but does not guarantee a single, unique outcome. This prompts consideration of different ontological options, including unique-history interpretations, decohered multiplicity, and agent-relative perspectives, each offering a distinct way to locate facts and histories within a quantum world.

Investigations into extended Wigner’s Friend scenarios, thought experiments involving multiple observers, serve as critical tests for any theory attempting to reconcile coherent quantum systems with agents possessing stable records. A central finding highlights the impossibility of universally deleting an unknown quantum state through reversible operations, mirroring the no-cloning obstruction and revealing a fundamental limit to information manipulation.

By employing categorical quantum mechanics, researchers demonstrate that copying and deleting are not generic quantum operations, but rather emerge only when a preferred observable or basis is realised. Since evolution demands a copyable record sector and an arrow of irreversibility, this work clarifies the minimal structural ingredients required for heredity and variation to be well-defined within a quantum mechanical world.

A stochastic-mechanics foundation with variable diffusion offers a potential bridge between quantum and classical regimes, suggesting a principled way to implement measurement updates as conditioning combined with a time-symmetric minimal-change rule. Unlike previous approaches, this research doesn’t simply address how macroscopic records become stable, but rather focuses on the underlying physical requirements for the very existence of heritable information. Beyond theoretical implications, understanding these requirements could inform future investigations into the origins of life and the limits of information processing in biological systems.

Emergence of classicality via extended Wigner’s Friend scenarios and categorical mechanics

This work was underpinned by investigations into the foundations of quantum mechanics, specifically examining how classical behaviours emerge from quantum substrates. Categorical mechanics, a mathematical framework describing systems with inherent structural properties, provided a starting point for understanding copying and deletion processes, clarifying that these operations require a “classical data sector”, a preferred, commutative structure, for their realization.

As a result, the research team focused on establishing the precise conditions under which such a classical sector could arise within a quantum system. To explore this emergence, extended Wigner’s Friend scenarios were constructed, involving multiple observers each possessing a stable record of a quantum system’s state, and used as a stress test for different interpretations of quantum mechanics.

By simultaneously treating these “friends” as both coherent quantum systems and agents with stable records, researchers aimed to identify the minimal requirements for consistent record-keeping. Inside these complex scenarios, the team carefully tracked the flow of information and the potential for inconsistencies arising from differing observer perspectives.

Acknowledging that decoherence alone does not uniquely select a basis, the study considered several ontological options: unique-history, decohered multiplicity, agent-relative facticity, and stochastic mechanics with variable diffusion. Each option was evaluated for its ability to account for the emergence of a stable classical data sector. By systematically comparing these alternatives, the work sought to pinpoint the physical principles that govern the selection of a preferred basis.

Stochastic mechanics, incorporating variable diffusion, offered a continuous pathway between quantum and classical regimes, allowing for a principled implementation of measurement updates. At the core of the methodology lay an analysis of agency, the capacity of a system to act and record information. Unlike purely quantum systems, where the no-cloning theorem and linearity prevent perfect copying and deletion, the presence of classical resources was shown to be essential for record-based processes.

By examining the “agency constraint”, researchers demonstrated that minimal agency fails in a strictly coherent regime, highlighting the role of classicality in enabling heredity and variation. The team employed a stochastic-mechanics approach to model measurement updates as conditioning combined with a time-symmetric minimal-change rule.

Darwinian evolution requires a physically defined classical data sector for heritable information

The research firmly establishes that Darwinian evolution necessitates a “realised classical data sector”, a stable, distinguishable basis, for copying and deleting information. Categorical quantum mechanics reveals that copying and deleting are not generic quantum operations, existing only when referenced to a preferred basis or observable. Proposition 1, central to this work, demonstrates that heredity and repeatable symbol replication are ill-defined without a physically selected classical data sector at relevant scales.

The study highlights the impossibility of universal deletion of an unknown quantum state via reversible operation, mirroring the no-cloning obstruction. Understanding the implications of this no-cloning obstruction is key; it demonstrates a fundamental limit to information manipulation within quantum systems, and a core requirement for the physical basis of heredity.

Once records exist, the agency analysis can be interpreted as a sharpened “no-copy/no-record” obstruction, suggesting that any stable information-processing architecture, and thus the preconditions for heredity, are threatened in the absence of a preferred copyable record basis. Decoherence explains how a pointer basis can emerge dynamically and stabilise macroscopic records, but doesn’t, by itself, select a single history.

Instead, the global state remains entangled, requiring reversal of system-environment correlations for genuine recoherence. For a superposition, copying exists only relative to a distinguished classical sector, a preferred basis or record structure. This work recognizes that Darwinian evolution demands not just heritable records and variation, but also routine irreversibility.

By framing these requirements structurally within categorical quantum mechanics, the research clarifies the physical conditions under which heredity and effective copying become possible. Also, the agency constraint reinforces the idea that minimal agency, and by extension, stable information processing, fails in a strictly coherent regime lacking a preferred basis.

Life’s fidelity necessitates a distinct classical domain within quantum mechanics

Scientists have long grappled with reconciling the deterministic logic of Darwinian evolution with the probabilistic nature of quantum mechanics. Recent work suggests a fundamental requirement for life’s processes: a clearly defined, classical data sector within the quantum world. This isn’t merely a technical point about information storage; it addresses a deep inconsistency between how we understand heredity and variation, and the underlying physics governing reality.

For decades, the challenge lay in explaining how reliable copying, essential for inheritance, could emerge from the fuzziness of quantum states, where identical replication is forbidden by the no-cloning theorem. Establishing the need for a classical data sector is more than just identifying a missing piece; it reframes the problem, shifting attention from seeking quantum mechanisms for copying to understanding how a classical-like structure can arise and be maintained within a quantum system.

Classicality isn’t a fundamental property of the universe, this work implies that life’s processes actively create a degree of order, selecting a preferred basis for information storage and manipulation. Numbers detailed in the research demonstrate the limits of manipulating quantum information, mirroring restrictions already known from quantum theory.

The precise mechanisms by which this classical sector emerges and remains stable remain open to debate. While decoherence offers one explanation, it doesn’t fully account for the selection of a unique basis, leaving room for alternative interpretations. Unlike previous approaches that attempted to force quantum mechanics into a classical mold, this work accepts the quantum foundation and explores the necessary conditions for classical behaviour to emerge.

Further research clarifying the dynamics of this classical sector could inform the design of more effective quantum technologies, particularly in areas like quantum data storage and error correction. The implications extend beyond physics and biology. By highlighting the fundamental limits of information manipulation, this work touches upon the broader question of agency and the nature of reality itself.

The “agency constraint”, the idea that stable records are needed for even minimal agency, suggests a deep connection between information, consciousness, and the ability to act within the world. A continued exploration of the interaction between quantum mechanics and information theory promises to yield further insights into the foundations of both physics and life.