# [[Philosophy of Science]] # Chapter 2: How Do We Define Reality? Key Distinctions in Philosophy of Science ## 2.1 Introduction: The Need for Conceptual Tools Before embarking on a critical analysis of the foundations of modern physics, it is imperative to establish a clear conceptual toolkit. Physics, in its quest to understand the universe, inevitably grapples with profound questions that extend beyond empirical observation and mathematical calculation into the domain of philosophy. Questions about the nature of reality, the limits of knowledge, the structure of causation, and the validity of scientific methods require precise philosophical concepts for rigorous discussion. Just as physics relies on well-defined mathematical terms, a philosophical critique requires clarity regarding its fundamental distinctions. This chapter serves as that essential primer. It introduces and defines core concepts and dichotomies from metaphysics, epistemology, and the philosophy of science that are indispensable for dissecting the assumptions underlying physical theories and for evaluating the coherence and adequacy of the pictures of reality they present. Establishing this shared vocabulary—defining terms like realism, materialism, determinism, reductionism, objectivity, locality, continuity, explanation, and law—is the necessary prerequisite for the evidence-based critique and synthesis undertaken in the subsequent chapters. Understanding these distinctions allows us to precisely articulate *how* and *why* modern physics challenges classical assumptions and where the deepest foundational problems lie. ## 2.2 Reality and Representation: Realism vs. Anti-realism A central philosophical fault line running through the interpretation of science concerns the relationship between our scientific theories and the world itself. The core debate revolves around **Scientific Realism** versus **Scientific Anti-realism**. **Scientific Realism**, in its standard formulation, holds that our best and most mature scientific theories provide (at least approximately) true descriptions of an objective, mind-independent reality. This commitment entails believing not only in the existence of observable phenomena but also in the reality of the unobservable entities (like electrons, quarks, fields, curved spacetime) postulated by these theories to explain the observables. Realists argue, via the **No-Miracles Argument (NMA)**, that the stunning predictive and explanatory success of science would be inexplicable if these theories weren’t genuinely latching onto the real underlying structures and causal mechanisms of the world. **Scientific Anti-realism**, in contrast, challenges this epistemic optimism, particularly regarding the unobservable realm. It encompasses several distinct positions. **Instrumentalism** views theories simply as useful instruments or tools for prediction and control, denying that theoretical terms need refer to real entities or that theories possess truth values beyond their utility. **Constructive Empiricism**, articulated by Bas van Fraassen, argues that the aim of science is **empirical adequacy**—truth about observable phenomena—and that belief in claims about unobservables is epistemically unwarranted; we should accept theories as empirically adequate but remain agnostic about the reality of the unobservable entities they posit. Other anti-realist arguments draw on the **Pessimistic Meta-Induction (PMI)**, noting the historical frequency with which successful past theories employing now-discarded ontologies were overturned, and the **Underdetermination of Theory by Evidence (UTE)**, highlighting the logical possibility of empirically equivalent but ontologically incompatible theories. This realism/anti-realism dichotomy forces us to ask: Does the success of physics license belief in the reality of its theoretical posits, or only in its ability to predict what we can observe? ## 2.3 Fundamental Substance: Materialism, Physicalism, and Alternatives What is the universe ultimately made of? What is the fundamental “stuff” or substance? **Materialism** is the traditional ontological view that everything that exists is matter, or configurations of matter. **Physicalism** is its broader contemporary successor, asserting that everything is physical, or supervenes on the physical. This means that all facts, including facts about minds, biology, or chemistry, are ultimately grounded in and determined by the fundamental entities, properties, and laws described by physics. Physicalism is often closely associated with **Reductionism**, the methodological and metaphysical view that complex phenomena can be fully explained by reducing them to their simpler, underlying physical parts and interactions. The success of physics in explaining chemical and some biological phenomena lends support to this view. However, several alternative ontological frameworks challenge physicalism. **Substance Dualism** (famously associated with Descartes) posits two fundamentally distinct kinds of substance, typically mental and physical, that interact. **Property Dualism** suggests that while there may only be one kind of substance (physical), there are two distinct kinds of properties (physical and mental), with mental properties being irreducible to physical ones. **Idealism** reverses the physicalist priority, claiming that mind, consciousness, or mental phenomena are fundamental, and the physical world is derivative, perhaps an illusion or a construct of mind. More relevant to contemporary physics debates, **Ontic Structural Realism (OSR)** proposes that fundamental reality consists not of objects or substances with intrinsic properties, but of **relational structures**, often identified with the mathematical structures described by physics. In this view, relations are ontologically primary. These alternatives force us to question the assumption that reality is exhausted by “physical stuff” in the classical sense and consider whether structure, information, or even mind might play a more fundamental role. ## 2.4 Change and Causation: Determinism vs. Indeterminism How does the universe evolve? Is its future trajectory rigidly fixed, or does genuine chance play a role? **Determinism** is the metaphysical doctrine that the state of the universe at any given time, combined with the laws of nature, uniquely determines its state at all other times. Given the laws and initial conditions, only one possible future (and past) exists. This view often aligns with classical notions of **Causality** as a necessary connection where causes necessitate their effects according to deterministic laws. **Indeterminism**, conversely, denies that all events are uniquely determined by prior causes and laws. It allows for the existence of objective chance or fundamental randomness in the universe’s evolution. From a given state, multiple future states might be possible, each with a certain probability. This raises questions about the nature of **Probability**: Is it merely **epistemic**, reflecting our ignorance of underlying deterministic factors (as assumed in classical statistical mechanics)? Or is it **ontic**, representing objective chance, propensity, or inherent fuzziness in reality itself (as suggested by standard interpretations of quantum mechanics)? The interpretation of probability (e.g., as frequency, propensity, or subjective degree of belief) is deeply intertwined with the stance on determinism. Indeterminism also forces a reconsideration of causality, potentially allowing for probabilistic causation where causes merely influence the likelihood of effects. ## 2.5 Structure and Connection: Locality vs. Non-locality, Continuum vs. Discreteness What is the fundamental architecture of reality’s stage and the nature of connections within it? Classical physics assumed **Locality**, the principle that interactions are mediated through direct contact or fields propagating no faster than light, forbidding instantaneous action-at-a-distance. This principle is central to Einstein’s theory of relativity. **Non-locality**, conversely, posits the possibility of instantaneous correlations or influences between spatially separated systems, regardless of the distance between them. Quantum entanglement provides strong empirical evidence challenging local realism, forcing consideration of fundamental non-locality. Another crucial structural question concerns the texture of reality: Is spacetime, and perhaps other fundamental quantities like energy or action, **Continuous**? This means they are infinitely divisible, like the real number line, allowing for smooth change and underpinning the use of calculus and differential geometry in classical physics and GR. Alternatively, is reality fundamentally **Discrete** or granular at some smallest scale (perhaps the Planck scale)? This view suggests that spacetime might be composed of indivisible units or “atoms,” or that physical processes occur in discrete steps. Quantum mechanics introduces discreteness through quantization, and theories like Loop Quantum Gravity and Digital Physics explicitly explore fundamental discreteness. The choice between a continuous or discrete fundamental architecture has profound implications for the appropriate mathematical description of reality. ## 2.6 Knowledge and Understanding: Objectivity, Observation, and Explanation How do we acquire knowledge about reality, and what is the nature of that knowledge? The classical scientific ideal emphasizes **Objectivity**: knowledge should accurately reflect a mind-independent reality, free from the subjective biases or perspectives of the observer. **Observation** and experiment were traditionally seen as neutral ways to access objective facts about this reality. However, this ideal is challenged by several considerations. **Theory-Ladenness** is the idea from philosophy of science that observations are never pure data but are always interpreted through the lens of pre-existing theories, concepts, and expectations. What we “see” is shaped by what we know or believe. **Observer Dependence** is a more radical challenge, particularly prominent in interpretations of quantum mechanics, suggesting that the state or properties of a system might be fundamentally relative to the observer or the act of measurement itself, questioning the very possibility of an observer-independent reality at the quantum level. Furthermore, what constitutes a valid scientific **Explanation**? Is it simply showing how an event follows from laws (**Deductive-Nomological model**)? Is it identifying the underlying **Causal mechanisms**? Is it achieving **Unification** by showing how diverse phenomena fit under fewer general principles? Or can explanations sometimes be purely **Mathematical**, appealing to abstract structures or constraints? The lack of a single, universally agreed-upon model of explanation suggests that scientific understanding itself might be multifaceted and context-dependent, challenging a simplistic view of objective explanation. ## 2.7 Interplay: Reductionism vs. Emergence Finally, how do different levels of reality and description relate to each other? **Reductionism** is the view, often associated with physicalism, that complex systems and phenomena can ultimately be fully understood and explained by reducing them to their simpler, underlying components and the laws governing them. Higher-level sciences (like chemistry or biology) are, in principle, reducible to fundamental physics. **Emergence**, conversely, argues that novel properties, behaviors, or even entities can arise at higher levels of complexity that are irreducible to, or unpredictable from, the properties of the constituent parts alone. A distinction is often made between **Weak Emergence**, where novel properties are unexpected due to complexity but still ultimately determined by the micro-level, and **Strong Emergence**, which posits fundamentally new properties or causal powers at higher levels that are irreducible and potentially exert “downward causation” on the lower levels. The tension between successful reductionist explanations in science and phenomena that seem genuinely emergent (from phase transitions in physics to consciousness in neuroscience) is a key theme in understanding the hierarchical structure of reality and the limits of purely bottom-up explanations. These philosophical concepts and dichotomies—Realism/Anti-realism, Materialism/Alternatives, Determinism/Indeterminism, Locality/Non-locality, Continuum/Discreteness, Objectivity/Observer Dependence, Reductionism/Emergence, and models of Explanation and Law—provide the essential framework for the critical analysis that follows. By understanding these distinctions, we can better diagnose how modern physics challenges classical assumptions, identify the specific philosophical commitments underlying different theories and interpretations, and evaluate where the deepest foundational problems lie, paving the way for the subsequent chapters’ detailed examination of these issues as manifested in physics. [[3 What is Real]]