# [[Philosophy of Science]] # Chapter 3: What is Real? The Challenge of Scientific Realism in Modern Physics ## 3.1 The Realist Imperative and the No-Miracles Argument Having defined the core philosophical positions in Chapter 2, we now turn to the first major question: What epistemic attitude should we adopt towards our best scientific theories? Should we believe they offer a fundamentally true picture of the world? **Scientific Realism**, as defined, asserts precisely this: science aims for and achieves approximately true descriptions of objective reality, including its unobservable aspects. The driving force behind this conviction is the powerful intuition captured by the **No-Miracles Argument (NMA)**. The argument insists that the stunning predictive accuracy, explanatory scope, and technological fecundity of mature scientific theories would be utterly inexplicable—a miracle of cosmic proportions—if these theories were not genuinely latching onto the real structures, entities, and causal processes of the universe. How could theories postulating unobservable electrons, curved spacetime, or specific quantum fields lead to working lasers, accurate GPS systems, and precise predictions about particle collisions unless these posits corresponded, at least approximately, to reality? Realism presents itself as the only philosophy that renders the success of science intelligible. This chapter critically examines this realist imperative, arguing that while intuitively appealing, the NMA faces severe challenges when confronted with the history of science and, most acutely, the conceptual landscape of modern fundamental physics, particularly quantum mechanics. The evidence suggests that empirical success, however impressive, may be a poor guide to ontological truth, thereby undermining standard scientific realism. ## 3.2 History’s Verdict: The Pessimistic Meta-Induction The historical record of science provides a potent counterargument to the No-Miracles Argument, known as the **Pessimistic Meta-Induction (PMI)**. As Larry Laudan and others have documented, the history of even highly successful science is replete with theories whose central theoretical terms are now believed not to refer to anything real and whose fundamental theoretical claims are considered false. Examples include the caloric theory of heat (postulating an indestructible heat fluid), the phlogiston theory of combustion (postulating a substance released during burning), the luminiferous ether (the medium thought to carry light waves), various biological theories based on vital forces, and even aspects of Newtonian mechanics (absolute space and time, universal applicability). These theories were often empirically successful by the standards of their day, made novel predictions, guided research, and were widely accepted by the scientific community. Yet, they were eventually overthrown and their core ontologies discarded. The PMI argues inductively from this historical pattern: if numerous past successful theories turned out to be fundamentally false regarding their unobservable posits, then we have strong reason to believe that our current successful theories, despite their greater empirical scope and precision, are likely also false in their fundamental claims and will eventually be replaced. This historical evidence directly challenges the realist inference from success to approximate truth. It suggests that empirical success might be achievable by theories that are significantly wrong about the underlying reality, perhaps because they capture certain relational structures or empirical regularities correctly while being mistaken about the fundamental ontology. While realists attempt to counter the PMI by refining criteria for “maturity” or arguing for referential continuity across theory change, the historical argument remains a powerful reason for epistemic caution regarding the ontological claims of current science. It suggests that the “miracle” argument might be based on an insufficiently critical reading of scientific history. ## 3.3 Underdetermination: The Quantum Challenge to Uniqueness The logical problem of **Underdetermination of Theory by Evidence (UTE)** provides another strong challenge to realism, and finds its most compelling real-world illustration in the interpretation of quantum mechanics. The UTE points out that empirical evidence can never logically entail the truth of a unique theory, as multiple incompatible theories can always, in principle, be constructed to fit the same finite data. While finding genuinely distinct, powerful, empirically equivalent rivals might be difficult in some areas, quantum mechanics presents exactly this situation at the heart of fundamental physics. As discussed previously, the major interpretations of quantum mechanics—Copenhagen variants, Many-Worlds (MWI), Bohmian Mechanics (BM), Objective Collapse Models (OCMs, in regimes where predictions overlap), QBism, Relational Quantum Mechanics (RQM)—all reproduce the same statistical predictions derived from the core quantum formalism (Schrödinger equation, Born rule) for standard experiments. Yet, they offer radically different and mutually exclusive ontological pictures. MWI posits countless parallel universes. BM posits particles guided by a non-local wave. OCMs posit stochastic physical collapses. QBism posits subjective agent beliefs. RQM posits relational facts. This situation poses an insurmountable problem for standard scientific realism. If QM is our best, most successful fundamental theory, realism demands we believe in the ontology it describes. But *which* ontology? The empirical evidence, the very success realism appeals to, provides no basis for choosing between these fundamentally different realities. The theory is empirically adequate across multiple, incompatible ontological interpretations. This strongly suggests that the quantum formalism, while predictively powerful, **fails to provide a unique or adequate representation of fundamental reality** in a way that supports a standard realist commitment. The underdetermination is not merely a philosopher’s logical possibility; it is a concrete reality within our most fundamental science, severely weakening the claim that empirical success licenses belief in the specific unobservable reality postulated by *the* theory. ## 3.4 Quantum Mechanics: Realism’s Interpretive Quagmire Beyond the general problem of underdetermination, the specific conceptual features and paradoxes of quantum mechanics create further deep difficulties for realist interpretations, suggesting the theory actively resists a straightforward realist reading. The **Measurement Problem** lies at the core. As detailed in later chapters, the standard formulation requires an unexplained “collapse” to reconcile the theory’s deterministic evolution with probabilistic outcomes. Realist interpretations struggle to resolve this coherently. MWI avoids collapse but invokes an unobservable, extravagant multiverse. BM introduces non-locality and a problematic configuration-space wave. OCMs modify the fundamental dynamics in an ad hoc manner. The lack of a compelling realist solution to this internal inconsistency within the standard framework (or its mainstream interpretations) suggests a deep representational failure. The **Ontology of the Wavefunction (|ψ⟩)** is another major hurdle for realism. Is this central mathematical object a real physical field? If so, how does it exist and act in the high-dimensional configuration space required for multi-particle systems? How does this abstract entity connect to the 3D world? The conceptual difficulties of configuration space realism are so severe that they undermine any simple ontic interpretation of |ψ⟩. This forces realists towards complex alternatives (like Bohm’s dual ontology or MWI’s universal wavefunction) or suggests that |ψ⟩ might represent something other than a direct physical state (potentiality, information, structure), pushing away from standard realism. Furthermore, **Quantum Contextuality** and **Non-locality** fundamentally contradict the classical realist picture of a world composed of separable objects possessing definite, intrinsic properties that interact locally. Quantum reality appears holistic, relational, and context-dependent in ways that defy description in terms of classical objects and local causality. A realist interpretation must somehow accommodate these deeply non-classical features, forcing a radical departure from intuitive or classical realism. Faced with these cumulative difficulties—underdetermination, the measurement problem, wavefunction ontology issues, contextuality, non-locality—many researchers adopt explicitly **anti-realist** (instrumentalist, QBist) or **relational** (RQM) stances towards quantum mechanics. These positions gain traction precisely because they dissolve the paradoxes by *abandoning* the attempt to provide a literal, observer-independent, classically-intuitive description of quantum reality. While they face the reciprocal challenge of explaining QM’s objective success, their viability underscores the profound failure of standard scientific realism to provide a coherent interpretation of our most fundamental theory of matter. ## 3.5 The Shifting Ontologies of Physics: Entities Under Erasure The challenge to realism is reinforced by the ambiguous or non-fundamental status of entities postulated even outside the quantum realm. As scientific understanding progresses, entities once considered fundamental often reveal themselves to be derivative, effective, or even illusory constructs, further supporting the historical caution urged by the PMI. Within **Quantum Field Theory (QFT)**, the notion of fundamental **particles** is undermined by issues of localization and interaction, suggesting they are emergent excitations of underlying fields. Yet, the **fields** themselves face mathematical difficulties (infinities, renormalization) and ontological ambiguity (operators vs. substance), with the Effective Field Theory perspective indicating they are likely scale-dependent approximations rather than ultimate realities. If neither particles nor fields provide a stable fundamental ontology, realism about the specific posits of QFT becomes problematic. Similarly, **spacetime** in General Relativity, while dynamic, is likely **emergent** from a deeper quantum gravity layer, not a fundamental entity. If the very stage of reality is not fundamental, realism about theories describing that stage as fundamental (like classical GR) is challenged. Realism seems perpetually pushed towards believing in the speculative, unconfirmed entities of the *next* proposed theory (strings, loops, etc.), rather than finding stable ground in current, well-confirmed ones. This pattern of **ontological instability**—where the fundamental constituents posited by successful theories are later revealed as non-fundamental or problematic—weakens the realist claim that science progressively reveals the true furniture of the world. It suggests, instead, that science progresses by developing increasingly powerful *representational tools* and *effective descriptions*, whose relationship to an ultimate, underlying reality remains complex and potentially indirect. ## 3.6 Structural Realism: A Possible Retreat for Realism? Confronted by the historical argument (PMI), underdetermination (UTE), and the ontological instability within modern physics, **Structural Realism** offers a potential retreat for the beleaguered realist. It proposes shifting the focus of realist commitment away from the *nature* of unobservable entities (which seems historically unstable) towards the *mathematical structures* and relations described by successful theories, which often exhibit continuity across theory change. **Epistemic Structural Realism (ESR)** claims we can only know the structural relations, remaining agnostic about the underlying objects or relata. **Ontic Structural Realism (OSR)** makes the bolder claim that structure *is* the fundamental reality; objects are derivative or non-existent. OSR resonates particularly well with the abstract, relational nature of modern physics (gauge theories, GR geometry, QM Hilbert space structure) and avoids commitment to problematic particle or field ontologies. It suggests that the success of science stems from correctly capturing the real relational structure of the world, even if our descriptions of the “things” related change. However, structural realism is not a panacea. ESR faces the Newman objection regarding its potential triviality. OSR confronts the metaphysical challenge of “relations without relata” and must provide a convincing account of how the world of apparent objects emerges from pure structure. While offering a sophisticated way to reconcile realism with theory change and ontological ambiguity, structural realism remains a developing philosophical position, itself highlighting the difficulties in formulating a straightforward realist interpretation of modern physics. It represents a significant modification, perhaps even a dilution, of traditional scientific realism’s ambitions. ## 3.7 Synthesis: Realism Tested, Representation Found Wanting The evidence marshaled from the history of science and, more pointedly, from the conceptual foundations of modern physics delivers a powerful critique of traditional scientific realism. The No-Miracles Argument, realism’s main pillar, appears significantly weakened when confronted with the historical frequency of successful-yet-false theories (PMI) and the stark reality of ontological underdetermination exemplified by quantum mechanics (UTE). Our most predictively successful theories, QM and GR/QFT, exhibit profound internal conceptual problems (measurement problem, ambiguous field/particle ontology, singularities) and mutual incompatibilities that resist coherent realist interpretation within standard frameworks. Core theoretical entities like particles, fields, and spacetime appear increasingly problematic, provisional, or non-fundamental. This confluence of evidence strongly suggests a **fundamental representational failure** at the heart of current physics. The mathematical formalisms are undeniably powerful tools for prediction, but their ability to provide a consistent, unified, and ontologically plausible *representation* of fundamental reality is severely challenged. The very success of the calculations might mask this deeper representational inadequacy. While anti-realist positions like constructive empiricism or instrumentalism avoid the ontological commitments that trouble realism, they face the reciprocal challenge of explaining science’s structural coherence and predictive power without appealing to correspondence with reality. Structural realism offers a potential middle path by focusing on mathematical relations, but it remains philosophically contested and requires significant development, particularly regarding emergence. The conclusion forced by the evidence is that **naive scientific realism is untenable** in light of modern physics. The burden of proof lies heavily on proponents of realism to either resolve the deep ontological and interpretational crises within existing theories or to provide compelling justification for realism about the speculative posits of future theories. Until then, the “reality question”—What is real, and do our theories truly describe it?—remains profoundly open. The state of fundamental physics itself provides strong reasons to adopt epistemic humility and question whether our current scientific frameworks, despite their power, offer a transparent window onto the ultimate nature of existence. This representational failure is a key indicator of the foundational crisis motivating this entire inquiry. [[4 What is the World Made Of]]