The No-Cloning Theorem Blocks Quantum Agency
The idea that consciousness might be a quantum phenomenon has long been a tantalizing possibility.
It suggests that our very awareness is tied to the strange, probabilistic world of atoms and particles. But a new mathematical analysis has thrown a wrench into this theory, identifying a single, fundamental parameter that makes it impossible: the “no-cloning theorem.” This law of quantum mechanics states that you cannot create an exact copy of an unknown quantum state. For a conscious agent to make decisions, it must be able to copy information about the world, evaluate different options, and then choose the best one. According to Emily Adlam at Chapman University, if the agent is purely quantum, this copying step is impossible “There will be a step in terms of taking information out of the environment that you’re going to respond to, and then some kind of [information] copying steps,” she explains “But if the agent is quantum — so must behave according to the laws of quantum mechanics — the copying step is impossible.” The agent could try to create imperfect copies, but this leads to another problem: extracting quantum information from the world changes it, so the agent’s world model reflects a slightly different world. These faults would compound, making accurate deliberation impossible. A purely quantum agent could only use quantum information processing, which makes available different processes than we are used to. “A realistic quantum operation is going to end up doing some kind of funny superposition of all of the possible options, weighted towards the better ones,” says Adlam. “You don’t actually implement the best option, you do this weird combination of all of them.” This finding challenges quantum theories of agency, free will, and consciousness itself.
A Minimal Definition of Agency Tests Quantum Theories.
In the 1990s, mathematician Roger Penrose and anesthesiologist Stuart Hameroff proposed that classical physics cannot explain consciousness alone and so it must arise in the quantum realm. Their idea was received with skepticism and remains controversial, but attempts to bring quantumness into explanations of consciousness have persisted since. The new study by Adlam and her colleagues examines the idea of purely quantum agency, which is a prerequisite for consciousness, and finds it does not work. Consciousness is notoriously hard to define, but the team formulated a minimal definition of agency using clear physical requirements. Quantum theories of consciousness, even if they focus on specific mechanisms in the brain like in Penrose and Hameroff’s proposal, ought to be compatible with this definition if they are to be plausible. Specifically, the researchers focused on a model of an agent that observes the world, creates a model of it, then uses that model to evaluate outcomes of different possible actions before deciding on performing one. The problems with a purely quantum agent that the researchers identified make it harder to justify an essentially quantum mechanism for both agency and consciousness. It is much more likely that these phenomena arise from, or are at least dominated by, classical mechanisms, says Adlam. “There could be some circumstances where perhaps doing a quantum calculation gives you a speed-up, but certainly it makes the whole process of agency look like it is basically founded in the classical regime,” she says. This represents a significant shift from the quantum consciousness theories that have been debated for decades.
Future Experiments with Quantum Computers May Provide Answers
Kelvin McQueen, also at Chapman University, presented these findings at the Foundations of Physics conference in Irvine, California, on 17 June “These results help us understand how agency and human-like perception can emerge in an otherwise quantum mechanical universe,” he said. The conclusions impose technological constraints on any agents that quantum computers may be able to simulate in the future. Sally Shrapnel at the University of Queensland in Australia offers a different perspective. In her view, the researchers’ model of agency is informed by a specific interpretation of what is essentially real in the quantum world. If quantum states are seen not as idealized building blocks of reality, but rather objects that reflect our knowledge of the world, then a quantum model of agency could be less constraining, she says. For example, an agent could be modeled as continuously interacting with an environment and dynamically converging on a decision instead of deliberating between world models, which would allow for a combination of classical and quantum information processing. Shrapnel says that all existing theories of quantum consciousness are not as strictly quantum as the model of agency in the new study, so they may not be fully off the table just yet. Both Adlam and Shrapnel say that future experiments with quantum computers may shed more light on the mixing of quantum and classical information processing that may pertain to this discussion. The work opens a new path for understanding how consciousness might emerge from the physical laws we already know, though Shrapnel cautions that existing quantum consciousness theories may not be as strictly quantum as the model tested here