Quantum Reality

1. Quantum Mechanics Reveals a Fundamentally Bizarre and Counter-Intuitive Reality

I can happily attest to the fact that, like charismatic physicist Richard Feynman, I still don’t understand quantum mechanics.

Lumpy nature. Quantum mechanics shattered classical notions of a smooth, continuous physical world, revealing that nature is inherently "lumpy." Max Planck's discovery of quanta and Einstein's light-quantum hypothesis (photons) showed that energy and light are absorbed and emitted in discrete packets, not continuously. This lumpiness extends to matter, with electrons occupying discrete energy levels in atoms, leading to "quantum jumps."

Wave-particle duality. One of the most profound revelations is that entities like light and electrons exhibit both wave-like and particle-like properties. Louis de Broglie proposed that particles like electrons could also be waves, a concept dramatically confirmed by electron diffraction experiments. These experiments show that individual electrons, when unobserved, behave as delocalized waves, passing through multiple slits simultaneously and interfering with themselves, only to be detected as localized particles.

Probabilistic nature. Erwin Schrödinger's wave equation describes quantum systems using wavefunctions, but Max Born interpreted the square of the wavefunction as representing only the probability of finding an associated particle. This means quantum mechanics can only predict what might happen, not what will happen, introducing an inherent randomness that deeply troubled Einstein. Werner Heisenberg's uncertainty principle further solidified this, stating a fundamental limit on what can be simultaneously known about pairs of properties like position and momentum, not due to measurement clumsiness, but as an intrinsic feature of nature.

2. Defining "Reality" is a Philosophical Precondition for Scientific Understanding

Our reality is made up of shadows, of things-as-they-appear, and we have no real way of knowing to what extent the representation shaped by our perceptions reflects reality as it really is, a reality of things-in-themselves.

Perception as shadows. Our sensory experiences provide a "representation" of reality, akin to Plato's allegory of the cave where prisoners perceive only shadows. We cannot directly access "things-in-themselves" (noumena, in Kant's terms), only "things-as-they-appear" (phenomena). This fundamental limitation means we can never be sure our perceptions perfectly reflect objective reality.

Scientific realism. Despite this, science operates on foundational assumptions, or "metaphysical preconceptions." Two key realist propositions are:

• Proposition #1: Objective reality exists independently of our observation or thought (e.g., "The Moon is still there when nobody looks at it").
• Proposition #2: Invisible entities like electrons are real if we can interact with them (e.g., "If you can spray them then they are real").
  These assumptions, though unprovable, are essential for meaningful scientific inquiry, demonstrating that metaphysics is an unavoidable part of science.

Empirical vs. metaphysical. Scientists primarily study an "empirical reality" derived from observations and measurements, which are always "theory-laden." However, to move beyond mere data collection and seek deeper understanding ("why?" and "how?"), scientists must engage with "metaphysical reality"—a realm of abstract imaginings, values, and beliefs about how reality should be. This interplay between abstract preconceptions and concrete data is where scientific theories are forged.

3. Scientific Theories Bridge Metaphysical Preconceptions and Empirical Data

The positive argument for realism is that it is the only philosophy that doesn’t make the success of science a miracle.

Hypothetico-deductive method. Science doesn't simply collect data and induce laws; it often begins with creative hypotheses, born from metaphysical preconceptions, from which empirical consequences are deduced. These theories are then tested against "hard facts." If a theory's predictions are upheld, it gains credibility; if falsified, it's either revised or replaced. This process, championed by Karl Popper, highlights the dynamic interplay between abstract ideas and empirical evidence.

Testability as demarcation. To distinguish science from pseudoscience, a "testability" criterion is crucial. A scientific theory must, in principle, be capable of making contact with empirical evidence. Theories that are purely metaphysical, offering no testable predictions or being endlessly adjustable, fall outside the realm of science. This ensures that scientific progress is grounded in observable phenomena, even if the underlying concepts are abstract.

Theory's dual purpose. A successful scientific theory serves two main functions:

• Instrumental: It allows for calculations and predictions, acting as a "black box" to produce useful outputs.
• Interpretational: It provides understanding by assigning meaning to its concepts, representing the properties and behaviors of physical things.
  This leads to Proposition #3: "The base concepts appearing in scientific theories represent the real properties and behaviours of real physical things." Furthermore, Proposition #4 states that "Scientific theories provide insight and understanding, enabling us to do some things that we might otherwise not have considered or thought possible," emphasizing the "active" nature of realist interpretations in driving new discoveries.

4. The Copenhagen Interpretation: Embrace the Mystery and "Shut Up and Calculate"

There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.

Complementarity and limits. Niels Bohr, a key architect of the Copenhagen interpretation, argued that classical language is inadequate to describe quantum phenomena. He proposed "complementarity," where wave-like and particle-like behaviors are mutually exclusive but equally valid descriptions, depending on the experimental setup. This implies a fundamental limit to our knowledge of the quantum world, which remains inaccessible beyond its empirical manifestations.

Anti-realist stance. Copenhagen is fundamentally anti-realist regarding the wavefunction (rejecting Proposition #3). It asserts that the quantum state is not a description of an objective, independently existing reality, but rather a summary of what we can say or know about nature through our measurements. This perspective avoids the paradoxes of quantum mechanics by declaring questions about "what is actually happening" at the quantum level to be meaningless.

"Nothing to see here." The interpretation, solidified by Bohr, Heisenberg, and Pauli, became the orthodoxy, embedded in the mathematical axioms of quantum mechanics. It dismisses concerns about wavefunction collapse or "spooky action at a distance" as artifacts of trying to apply classical intuition to an inherently quantum realm. The prevailing advice became to "shut up and calculate," focusing on the theory's predictive power rather than its elusive meaning, effectively sailing towards the "rock shoal of Scylla" – an empty instrumentalism.

5. Einstein's Challenge: Quantum Mechanics is Incomplete and Non-Local

If, without in any way disturbing a system, we can predict with certainty (i.e. with a probability equal to unity) the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity.

EPR paradox. Einstein, Podolsky, and Rosen (EPR) challenged the completeness of quantum mechanics in 1935 with a thought experiment involving entangled particles. They argued that if particles A and B are entangled and then separated, measuring particle A instantly reveals the state of particle B without disturbing it. If local realism holds (particles are independent and no faster-than-light influence), then particle B's state must have been predetermined, implying quantum mechanics is incomplete as it doesn't describe this pre-existing reality.

Bell's inequality. John Bell, in 1964, transformed the EPR paradox into a testable hypothesis. He derived an inequality that any "local hidden variable" theory (where particles have predetermined properties and no faster-than-light communication) must satisfy. Quantum mechanics, however, predicted a violation of this inequality, suggesting a deeper, non-local connection between entangled particles.

Experimental confirmation. Decades of experiments, notably by Alain Aspect in the 1980s and subsequent studies over increasing distances and with "cosmic" randomness, consistently confirmed quantum mechanics' predictions, violating Bell's inequality. This ruled out all local hidden variable theories. Later, Leggett's inequality further ruled out "crypto non-local" hidden variables, which allowed for pre-existing properties but permitted non-local influences on measurement settings. The conclusion is stark: if we insist on a realist interpretation (Proposition #3), then reality must be non-local, meaning distant entangled particles can instantaneously influence each other.

6. Realist Interpretations Demand Non-Locality or Ad Hoc Physical Mechanisms

The act of measurement on [A] polarizes [B] (in the direction of the analyzing field acting on [A]) and in any subsequent measurement on [B], the results will come out in the way predicted by quantum mechanics.

De Broglie–Bohm theory. David Bohm revived de Broglie's pilot-wave theory, proposing a "guidance condition" where a real wavefunction (quantum potential) steers real particles along definite paths. This interpretation restores causality and determinism, eliminating the need for wavefunction collapse. However, it explicitly embraces non-locality: measuring one entangled particle instantaneously influences the quantum potential of its distant partner, guiding its future behavior. This "spooky action at a distance" is a core feature, though it cannot be used for faster-than-light communication.

Physical collapse mechanisms. To avoid non-locality or the "shifty split" between quantum and classical realms, other realist interpretations propose new physical mechanisms for wavefunction collapse:

• Decoherence: While often used in anti-realist contexts, decoherence can be interpreted as a real physical process where a quantum system's coherence is rapidly lost due to interaction with its environment. This explains the emergence of classical behavior but doesn't resolve the problem of which outcome is chosen.
• GRW theory: Ghirardi, Rimini, and Weber proposed adding a new term to the Schrödinger equation, causing spontaneous, random "hits" that localize the wavefunction. This mechanism, with two new physical constants, ensures individual particles rarely collapse but macroscopic objects collapse almost instantly, resolving Schrödinger's cat paradox.
• Diósi–Penrose theory: This theory links wavefunction collapse to gravity, suggesting that superpositions break down when they encounter significant spacetime curvature. It proposes that mass-energy density, rather than particle count, triggers collapse, offering a potential bridge between quantum mechanics and general relativity.

Active realism. These realist interpretations, despite their "ad hoc" nature or counter-intuitive consequences, are "active" (Proposition #4). They provide concrete, testable predictions that motivate experimentalists to design sophisticated experiments, such as the MAQRO mission, to probe the boundaries of quantum coherence and search for evidence of spontaneous collapse. This pursuit of deeper understanding, even at a high cost, drives scientific innovation.

7. Consciousness as the Catalyst for Quantum Reality: A Mind-Bending Proposal

It follows that the being with a consciousness must have a different role in quantum mechanics than the inanimate measuring device…. It is not necessary to see a contradiction here from the point of view of orthodox quantum mechanics, and there is none if we believe that the alternative is meaningless, whether my friend’s consciousness contains either the impression of having seen a flash or of not having seen a flash. However, to deny the existence of the consciousness of a friend to this extent is surely an unnatural attitude, approaching solipsism, and few people, in their hearts, will go along with it.

Von Neumann's ego. John von Neumann's formalization of quantum mechanics highlighted the "collapse of the wavefunction" (Process 1) as distinct from its continuous evolution (Process 2). He argued that Process 2 applies to all physical systems, including measuring devices and even the observer's brain. To explain why we only experience one outcome, he suggested that the collapse occurs when the measurement is registered in the observer's "abstract ego" or conscious mind, placing consciousness outside the realm of physical calculation.

Wigner's Friend paradox. Eugene Wigner extended this, posing a scenario where a friend (Alice) makes a measurement in a lab, but an external observer (Wigner) doesn't know the outcome. For Wigner, Alice and her observation remain in a superposition until he interacts with her. This implies that consciousness itself triggers the collapse, leading to the unsettling conclusion that denying a friend's conscious experience before one's own observation is "unnatural" and "approaching solipsism."

Orchestrated Objective Reduction (Orch-OR). Roger Penrose and Stuart Hameroff proposed a quantum basis for consciousness, suggesting that consciousness arises from non-computable wavefunction collapses within the brain. Their Orch-OR theory posits that protein structures called microtubules in neurons form coherent quantum superpositions of different conformational states. When these superpositions reach a critical mass density, they undergo a gravitationally induced objective reduction (Diósi–Penrose collapse), and this non-computable event is identified with a moment of conscious experience.

Critique and implications. This interpretation, while attempting to solve two intractable problems (collapse and consciousness) by linking them, faces significant challenges. The primary criticism is that maintaining quantum coherence in the "warm, wet, and noisy" environment of the brain for the necessary timescales seems highly improbable due to rapid environmental decoherence. Furthermore, even if a quantum mechanism for consciousness were found, it wouldn't necessarily solve the "hard problem" of explaining why these physical processes give rise to subjective experience.

8. The Many-Worlds Interpretation: A Multiverse of Splitting Realities

Whereas before the observation we had a single observer state afterwards there were a number of different states for the observer, all occurring in a superposition. Each of these separate states is a state for an observer, so that we can speak of the different observers described by the different states.

Abandoning collapse. Hugh Everett III, under John Wheeler's supervision, proposed a radical solution: simply abandon the collapse postulate (Process 1). He argued that the Schrödinger equation (Process 2) universally governs all physical systems, including observers. Instead of a single outcome being realized, all possible outcomes of a quantum measurement are realized, but in different, branching "worlds."

Relative states and splitting observers. In Everett's "relative state" formulation, when a quantum system in superposition interacts with a measuring device and an observer, the entire system (quantum system + device + observer) evolves into a superposition where each component corresponds to a distinct outcome and a distinct "observer state." The observer doesn't experience a superposition; instead, they "split" into multiple versions, each experiencing one specific outcome in their own, separate world. This means there are multiple versions of "you," each with different memories and experiences.

Many-worlds and its appeal. Bryce DeWitt popularized Everett's ideas as the "many-worlds interpretation," describing a universe "continuously splitting into a multiplicity of mutually unobservable but equally real worlds." This interpretation offers a deterministic, local, and complete quantum theory, as the wavefunction never truly collapses, and all possibilities are realized. It avoids the "shifty split" and the randomness of collapse, making it appealing to those seeking a more elegant and unified description of reality.

9. The Multiverse: A Leap into Untestable Metaphysics, Not Science

It’s my opinion that the state of the arguments, and evidence, about other universes closely parallels that about dinosaurs. Namely: they’re real—get over it.

Proliferation of worlds. The many-worlds interpretation implies an astronomical number of parallel universes, each branching off with every quantum superposition. This "schizophrenia with a vengeance" raises questions about the reality and observability of these worlds. While some proponents argue these worlds are "effective" for practical purposes, others, like David Deutsch, insist they are physically real, even suggesting they explain the power of quantum computing by leveraging computational resources across multiple universes.

Untestability and the demarcation problem. A major criticism is the lack of empirical evidence for these parallel universes. The "quantum suicide" thought experiment, where an observer repeatedly faces a quantum-triggered gun, suggests that in a many-worlds scenario, the observer would only ever experience survival. However, this subjective "proof" cannot convince others, highlighting the untestable nature of the claim. This raises the "demarcation problem": if a theory makes no testable predictions, is it still science, or has it become pure metaphysics?

Metaphysical baggage. The multiverse, particularly in its more literal interpretations, is seen by critics as "magical realism" that carries "too much metaphysical baggage." It offers no practical insights or new avenues for experimental investigation (violating Proposition #4). When a theory's metaphysical content overwhelms its empirical grounding, it risks slipping into the "whirlpool of Charybdis," losing its scientific integrity and becoming indistinguishable from untestable speculation.

10. The Enduring Dilemma: No Easy Answers for Quantum Reality

I’m pretty confident that quantum mechanics is not the end. Despite its unparalleled success, we know it doesn’t incorporate space and time in the right way.

The interpretational impasse. Quantum mechanics forces a profound choice: either accept an anti-realist interpretation where conceptual problems vanish but deeper truths about reality remain inaccessible, or embrace a realist interpretation that comes with a high price. The anti-realist path (Copenhagen, relational QM, information-theoretic views) offers predictive power but no "how" or "why." The realist path (de Broglie–Bohm, spontaneous collapse, consciousness-causes-collapse, many worlds) attempts to provide deeper meaning but introduces non-locality, ad hoc mechanisms, or an untestable proliferation of universes.

Author's "bad feeling." The author, despite a long-standing preference for Einstein's realism, expresses growing doubts about Proposition #3—that the base concepts of a theory, like the wavefunction, necessarily represent real physical states. The flexibility of the wavefunction (its ability to be expressed in different bases) suggests it might be more akin to a "coding of our experience" rather than a description of an objective physical state. The enormous, often untestable, metaphysical costs of current realist interpretations further fuel this skepticism.

The unfinished revolution. Ultimately, quantum mechanics is likely not the final theory. Its incompatibility with general relativity regarding space and time suggests a deeper, unifying theory is needed. However, current attempts at quantum gravity do not yet offer clear solutions to these interpretational dilemmas. The quest for a complete and coherent understanding of quantum reality remains an "unfinished revolution," leaving physicists and philosophers to grapple with profound questions about the nature of existence, knowledge, and the very limits of scientific inquiry.

Last updated: October 3, 2025