Reality

Not to be confused with Realty.

For other uses, see Reality (disambiguation).

Reality is the state of all objects as they exist, rather than how might they be imagined to be. Different cultures and academic disciplines conceptualize it in various ways.

Philosophical questions about the nature of reality, existence, or being are considered under the rubric of ontology, a major branch of metaphysics in the Western intellectual tradition. Ontological questions also feature in diverse branches of philosophy, including the philosophy of science, religion, mathematics, and logic. These include questions about whether only physical objects are real (e.g., physicalism), whether reality is fundamentally immaterial (e.g., idealism), whether hypothetical unobservable entities posited by scientific theories exist (e.g., scientific realism), whether God exists, whether numbers and other abstract objects exist, and whether possible worlds exist. Skeptics question whether any of those claims are true, and suggest more extreme postulates.

Definition

Reality is the totality of existing entities. It encompasses the whole cosmos and everything within it, including rocks, trees, humans, and stars. In a slightly different sense, reality is not the totality itself but an aspect shared by all its constituents. In this sense, it is the state of being real or what all real entities have in common, separating them from unreal or illusory ones. When used as a countable noun, the expression a reality denotes a specific domain or coherent, interconnected framework, such as the social reality of a particular culture or the virtual reality of a specific video game world.

Reality is often contrasted with appearance: appearance is how things seem to be, while reality is how they in fact are. It is controversial whether this contrast marks a genuine and fundamental difference between an experienced realm of appearances and an inaccessible realm of reality. Another outlook holds that appearance and reality are different ways of considering the same being, locating the difference in the conceptual framing rather than a division of worlds. This view is consistent with the idea that accurate appearances show things as they are, suggesting that appearance and reality can align and are not necessarily distinct. Both accurate and inaccurate appearances may themselves be part of reality, for instance as brain events, according to one suggestion. Real entities are typically taken to exist on their own, independent of what people think about them. When a person encounters them, their appearances may reveal only some features while leaving others hidden. Whereas appearances can be vague, as in a blurry vision, it is often suggested that reality is fully determinate or fixed in all details.

The word reality comes from the Latin term realitas, rooted in the word res, meaning 'thing', and from the French term réalité. Its earliest known use in English dates to the early 1500s. The concept of reality is relevant to many fields, including metaphysics, a branch of philosophy that studies the nature and fundamental structure of reality, and the empirical sciences, which examine the constituents and laws of the natural world through observation and experimentation.

Criteria

Criteria of reality are proposed features or standards that distinguish real entities from unreal ones. An often-cited criterion identifies causal powers as the mark of reality. Discussed in ancient Greek philosophy as the Eleatic principle, it states that to be real is to be able to produce changes and to be affected by them. For example, Mahatma Gandhi was real because he was able to mobilize millions and shape India's struggle for independence. Santa Claus, by contrast, is unreal because he cannot act upon the world. However, stories about Santa Claus, such as written texts in children's books, are part of reality since they can influence how people think. The Eleatic principle is controversial because it denies that abstract objects studied in fields like mathematics, such as numbers, are real.

Another influential proposal treats mind-independence as a criterion of reality, arguing that real entities do not depend on how people think about them. This view emphasizes that reality is encountered, rather than invented, and can resist or frustrate beliefs and desires, unlike malleable imaginary creations. For example, if a planet or a virus is real then it exists on its own and behaves according to its nature, even if people are unaware or hold false beliefs about it. Unreal entities, by contrast, depend for their existence on thoughts and ideas; they would not arise or would vanish without the mental activity creating or sustaining them. For instance, a fictional character like Gandalf would not be there if no one had ever thought about him. A difficulty for this criterion is to account for the reality of mental entities themselves, given that thoughts, memories, and emotions seem to be part of the world.

A closely related criterion holds that to be real is to be non-illusory. It focuses on how things seem to be, distinguishing real appearances, which are as they seem, from illusory ones, which are not as they seem. In a broad sense, appearances are not limited to what people perceive but can also include memories, beliefs, and thoughts. According to this criterion, veridical perceptions track reality by presenting it as it is, whereas entities found in hallucinations, dreams, and mirages count as unreal because they misrepresent the world.

A different criterion equates reality with being genuine. Proposed by J. L. Austin and grounded in ordinary language philosophy, it suggests that being real is always relative to a category or entity, such as a real diamond. This view contrasts being real with being fake, like the distinction between a real duck and a fake one used as a decoy. A challenge for approaches grounded in ordinary language is that the term real serves many linguistic purposes, not all of which are relevant to the metaphysical concept of reality. For example, it can express that something is excellent relative to its kind, as in the exclamation "Now this is real coffee!"

Other suggested criteria identify reality with what is observable, measurable, coherent, useful, objective, intersubjective, or fundamental.

Related concepts

The term reality overlaps with various related concepts, such as being, existence, world, actuality, and truth. Depending on the context, these terms may function as synonyms or play distinct theoretical roles. In the broadest sense, being is the most general category that applies to everything and contrasts only with nothingness. Some philosophers, such as Alexius Meinong, hold that being is a broader concept than reality, encompassing nonexistent objects, such as merely possible or incomplete objects, in addition to real or actual ones. In a narrow sense, being contrasts with becoming, and denotes stable or permanent aspects of reality. Becoming, by contrast, covers change, like when an entity shifts from one state of being to another. A central topic in ontology is the categories of being—fundamental classes that map out a comprehensive inventory of reality.

Existence is commonly understood as the bare fact that something is, indicating that an entity is part of the world without specifying its nature. It is often contrasted with essence, which denotes the nature or characteristic features of an entity. It is frequently possible to understand the essence of something without knowing whether it exists. Ontologists discuss whether existence can be understood as a property of individuals, analogous to ordinary features like being red, or whether it is instead a concept or quantificational device expressing that a property has instances.

A world is a totality of entities, conceived as a maximally large situation or a system encompassing everything in space and time as a whole: all that was, is, and will be. Some philosophers hold that reality consists of only one world: the actual universe. A different view suggests that reality is made up of many worlds that exist in parallel to one another, each representing a distinct way of how things could have been. For example, David Lewis's modal realism asserts that there exist countless spatiotemporally unified possible worlds, each just as real as the actual world. Similarly, the many-worlds interpretation of quantum physics suggests that in quantum measurements, not only one but all possible outcomes occur, interpreted as a branching of the universe into multiple worlds.

Actuality encompasses the states of entities that are realized or manifested. It contrasts with potentiality, which denotes dispositions an entity has but does not exercise. For example, an acorn has the potential to grow into an oak tree under the right conditions, but the oak tree is not yet actualized. In a slightly different sense, actuality is often discussed in relation to possibility and necessity as different modes of being. Actuality comprises what is the case, possibility denotes what could be the case, and necessity concerns what must be the case. The distinction is often framed in terms of possible worlds: a state is possible if it holds in at least one possible world; it is actual if it holds in the actual world; and it is necessary if it holds in all possible worlds. While actuality and necessity are often treated as aspects of reality, there are debates about the extent to which possibilities are part of it, for example, regarding the contrast between real or authentic possibilities and formal or inauthentic ones.

Truth is conformity to reality. It contrasts with falsehood, which encompasses misrepresentations that do not align with reality. Truth is often understood as a property of statements or beliefs that describe the world as it is. In this sense, truth is not the same as reality but a feature of accurate representations of it: truth depends on reality. In a different sense, the term truth is used as a synonym for reality, as in the statement "In truth, he was not qualified for the job." Various theories of the nature of truth have been proposed. According to correspondence theory, a statement is true if it corresponds to facts. The coherence theory suggests that truth consists in logical consistency and mutual support among beliefs. Pragmatic theories define truth relative to consequences, holding that truth is what works or what would withstand the test of unlimited inquiry. Deflationary theories hold that truth has no significant intrinsic nature beyond its minimal linguistic role in truth-related expressions.

Constituents

Various categories of being or constituents of reality are discussed in the academic discourse. There are disagreements about which exist at the most fundamental level and whether reality is ultimately composed of one or several types.

A central distinction is between particulars and universals. Particulars are unique, non-repeatable entities, such as Julius Caesar, the river Nile, and the Moon. As individual entities, they contrast with universals, which are general, repeatable entities that can have many instances, such as the color blue, the shape roundness, and the property of being a mammal. Particulars are often characterized as entities that instantiate universals but are not themselves instantiated by anything else. In this sense, they exist in themselves, while universals exist in something else.

Universals are often analyzed in terms of properties and relations. A property expresses a characteristic or quality of another entity. For example, roundness is a property of the particulars the Moon and the Sun. Relations are ways in which two or more entities stand to one another. For instance, being-smaller-than is a relation that holds between the Moon and the Sun. One approach analyzes the instantiation of universals in terms of facts or states of affairs. For example, the fact "Socrates is mortal" has two components: the particular Socrates and the universal mortality. Events are proposed constituents of reality that occur in time, such as the discovery of penicillin and the Second World War.

Another influential distinction is between concrete and abstract objects. According to a common view, concrete objects exist in space and time, such as a flower, a horse, and a ship. They can undergo changes, have causal powers, and influence each other, like when a horse eats a flower and destroys it in the process. Abstract objects lack spatiotemporal location, do not change, and have neither causes nor effects, such as mathematical numbers and geometrical shapes. It is disputed whether abstract objects are fundamental constituents of reality or merely conceptual constructions.

Philosophers have proposed various theories of categories. Aristotle developed a system of ten categories, which has substance as the central category while other categories, such as quantity, quality, and place, depend on substances or act as modifications. Immanuel Kant outlined a system of twelve categories, which he regarded as pure concepts of understanding, divided into the classes of quantity, quality, relation, and modality. Other theories in the Western tradition were proposed by Edmund Husserl, Samuel Alexander, Roderick Chisholm, and E. J. Lowe. In ancient Hindu philosophy, the school of Samkhya identified pure consciousness and matter as the two foundational principles of reality, while the school of Vaisheshika proposed a system of seven categories: substance, quality, motion, universal, particular, inherence, and non-being. In ancient Chinese thought, Taoism regarded the Tao as the omnipresent, self-existent, imperceptible, and incomprehensible source of all existence. The related yinyang school treated yin and yang as two correlated forces whose interaction underlies all natural processes.

Physicists use concepts such as elementary particle, force, field, and spacetime to analyze the fundamental constituents of the universe. In quantum mechanics, the Standard Model describes all known elementary particles, dividing them into two classes: fermions, such as electrons, and bosons, such as photons. It also describes their interactions through all fundamental forces except gravity, which is explained by the theory of general relativity. String theory is an attempt to unify quantum mechanics and general relativity, positing tiny vibrating strings as the basic constituents underlying elementary particles and their interactions.

Western philosophy

Philosophy addresses two different aspects of the topic of reality: the nature of reality itself, and the relationship between the mind (as well as language and culture) and reality.

On the one hand, ontology is the study of being, and the central topic of the field is couched, variously, in terms of being, existence, "what is", and reality. The task in ontology is to describe the most general categories of reality and how they are interrelated. If a philosopher wanted to proffer a positive definition of the concept "reality", it would be done under this heading. As explained above, some philosophers draw a distinction between reality and existence. In fact, many analytic philosophers today tend to avoid the term "real" and "reality" in discussing ontological issues. But for those who would treat "is real" the same way they treat "exists", one of the leading questions of analytic philosophy has been whether existence (or reality) is a property of objects. It has been widely held by analytic philosophers that it is not a property at all, though this view has lost some ground in recent decades.

On the other hand, particularly in discussions of objectivity that have grounding in both metaphysics and epistemology, philosophical discussions of reality often concern the ways in which reality is or is not in some way dependent upon (or, to use fashionable jargon, "constructed" out of) mental and cultural factors such as perceptions, beliefs, and other mental states, as well as cultural artifacts—such as religions and political movements—on up to the vague notion of a common cultural world view (or Weltanschauung).

Realism

The view that there is a reality independent of any beliefs, perceptions, etc., is called realism. More specifically, philosophers are given to speaking about "realism about" this and that, such as realism about universals or realism about the external world. Generally, where one can identify any class of object, the existence or essential characteristics of which is said not to depend on perceptions, beliefs, language, or any other human artifact, one can speak of "realism about" that object.

A correspondence theory of knowledge about what exists claims that "true" knowledge of reality represents accurate correspondence of statements about and images of reality with the actual reality that the statements or images are attempting to represent. For example, the scientific method can verify that a statement is true based on the observable evidence that a thing exists. Many humans can point to the Rocky Mountains and say that this mountain range exists, and continues to exist even if no one is observing it or making statements about it.

Anti-realism

One can also speak of anti-realism about the same objects. Anti-realism is the latest in a long series of terms for views opposed to realism. Perhaps the first was idealism, so called because reality was said to be in the mind, or a product of our ideas. Berkeleyan idealism is the view, propounded by the Irish empiricist George Berkeley, that the objects of perception are actually ideas in the mind. In this view, one might be tempted to say that reality is a "mental construct"; this is not quite accurate, however, since, in Berkeley's view, perceptual ideas are created and coordinated by God. By the 20th century, views similar to Berkeley's were called phenomenalism. Phenomenalism differs from Berkeleyan idealism primarily in that Berkeley believed that minds, or souls, are not merely ideas nor made up of ideas, whereas varieties of phenomenalism, such as that advocated by Russell, tended to go farther to say that the mind itself is merely a collection of perceptions, memories, etc., and that there is no mind or soul over and above such mental events. Finally, anti-realism became a fashionable term for any view which held that the existence of some object depends upon the mind or cultural artifacts. The view that the so-called external world is really merely a social, or cultural, artifact, called social constructionism, is one variety of anti-realism. Cultural relativism is the view that social issues such as morality are not absolute, but at least partially cultural artifact. Potentially the most extreme form of anti-realism is solipsism — the belief that oneself is the only thing in existence.

Perception

The question of direct or "naïve" realism, as opposed to indirect or "representational" realism, arises in the philosophy of perception and of mind out of the debate over the nature of conscious experience; the epistemological question of whether the world we see around us is the real world itself or merely an internal perceptual copy of that world generated by neural processes in our brain. Naïve realism is known as direct realism when developed to counter indirect or representative realism, also known as epistemological dualism, the philosophical position that our conscious experience is not of the real world itself but of an internal representation, a miniature virtual-reality replica of the world.

Timothy Leary coined the influential term Reality Tunnel, by which he means a kind of representative realism. The theory states that, with a subconscious set of mental filters formed from their beliefs and experiences, every individual interprets the same world differently, hence "Truth is in the eye of the beholder". His ideas influenced the work of his friend Robert Anton Wilson.

Abstract objects and mathematics

The status of abstract entities, particularly numbers, is a topic of discussion in mathematics.

In the philosophy of mathematics, the best known form of realism about numbers is Platonic realism, which grants them abstract, immaterial existence. Other forms of realism identify mathematics with the concrete physical universe.

Anti-realist stances include formalism and fictionalism.

Some approaches are selectively realistic about some mathematical objects but not others. Finitism rejects infinite quantities. Ultra-finitism accepts finite quantities up to a certain amount. Constructivism and intuitionism are realistic about objects that can be explicitly constructed, but reject the use of the principle of the excluded middle to prove existence by reductio ad absurdum.

The traditional debate has focused on whether an abstract (immaterial, intelligible) realm of numbers has existed in addition to the physical (sensible, concrete) world. A recent development is the mathematical universe hypothesis, the theory that only a mathematical world exists, with the finite, physical world being an illusion within it.

An extreme form of realism about mathematics is the mathematical multiverse hypothesis advanced by Max Tegmark. Tegmark's sole postulate is: All structures that exist mathematically also exist physically. That is, in the sense that "in those [worlds] complex enough to contain self-aware substructures [they] will subjectively perceive themselves as existing in a physically 'real' world". The hypothesis suggests that worlds corresponding to different sets of initial conditions, physical constants, or altogether different equations should be considered real. The theory can be considered a form of Platonism in that it posits the existence of mathematical entities, but can also be considered a mathematical monism in that it denies that anything exists except mathematical objects.

Properties

Main article: Problem of universals

The problem of universals is an ancient problem in metaphysics about whether universals exist. Universals are general or abstract qualities, characteristics, properties, kinds or relations, such as being male/female, solid/liquid/gas or a certain colour, that can be predicated of individuals or particulars or that individuals or particulars can be regarded as sharing or participating in. For example, Scott, Pat, and Chris have in common the universal quality of being human or humanity.

The realist school claims that universals are real – they exist and are distinct from the particulars that instantiate them. There are various forms of realism. Two major forms are Platonic realism and Aristotelian realism. Platonic realism is the view that universals are real entities and they exist independent of particulars. Aristotelian realism, on the other hand, is the view that universals are real entities, but their existence is dependent on the particulars that exemplify them.

Nominalism and conceptualism are the main forms of anti-realism about universals.

Time and space

Main article: Philosophy of space and time

Hubble Ultra-Deep Field image of distant galaxies illustrates a challenge to understanding reality at any given instant: the light from these stars was emitted billions of years ago and many of these stars have moved, merged, or evolved since then.

A traditional realist position in ontology is that time and space have existence apart from the human mind. Idealists deny or doubt the existence of objects independent of the mind. Some anti-realists whose ontological position is that objects outside the mind do exist, nevertheless doubt the independent existence of time and space.

Kant, in the Critique of Pure Reason, described time as an a priori notion that, together with other a priori notions such as space, allows us to comprehend sense experience. Kant denies that either space or time are substance, entities in themselves, or learned by experience; he holds rather that both are elements of a systematic framework we use to structure our experience. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantitatively compare the interval between (or duration of) events. Although space and time are held to be transcendentally ideal in this sense, they are also empirically real, i.e. not mere illusions.

Idealist writers such as J. M. E. McTaggart in The Unreality of Time have argued that time is an illusion.

As well as differing about the reality of time as a whole, metaphysical theories of time can differ in their ascriptions of reality to the past, present and future separately.

• Presentism holds that the past and future are unreal, and only an ever-changing present is real.
• The block universe theory, also known as Eternalism, holds that past, present and future are all real, but the passage of time is an illusion. It is often said to have a scientific basis in relativity.
• The growing block universe theory holds that past and present are real, but the future is not.

Time, and the related concepts of process and evolution are central to the system-building metaphysics of A. N. Whitehead and Charles Hartshorne.

Theories of everything (TOE) and philosophy

Main article: Theory of everything (philosophy)

The philosophical implications of a physical TOE are frequently debated. For example, if philosophical physicalism is true, a physical TOE will coincide with a philosophical theory of everything.

The "system building" style of metaphysics attempts to answer all the important questions in a coherent way, providing a complete picture of the world. Plato and Aristotle could be said to be early examples of comprehensive systems. In the early modern period (17th and 18th centuries), the system-building scope of philosophy is often linked to the rationalist method of philosophy, that is the technique of deducing the nature of the world by pure a priori reason. Examples from the early modern period include the Leibniz's Monadology, Descartes's Dualism, Spinoza's Monism. Hegel's Absolute idealism and Whitehead's Process philosophy were later systems.

Other philosophers do not believe its techniques can aim so high. Some scientists think a more mathematical approach than philosophy is needed for a TOE, for instance Stephen Hawking wrote in A Brief History of Time that even if we had a TOE, it would necessarily be a set of equations. He wrote, "What is it that breathes fire into the equations and makes a universe for them to describe?"

Phenomenology

On a much broader and more subjective level, private experiences, curiosity, inquiry, and the selectivity involved in personal interpretation of events shapes reality as seen by one and only one person and hence is called phenomenological. While this form of reality might be common to others as well, it could at times also be so unique to oneself as to never be experienced or agreed upon by anyone else. Much of the kind of experience deemed spiritual occurs on this level of reality.

Phenomenology is a philosophical method developed in the early years of the twentieth century by Edmund Husserl (1859–1938) and a circle of followers at the universities of Göttingen and Munich in Germany. Subsequently, phenomenological themes were taken up by philosophers in France, the United States, and elsewhere, often in contexts far removed from Husserl's work.

The word phenomenology comes from the Greek phainómenon, meaning "that which appears", and lógos, meaning "study". In Husserl's conception, phenomenology is primarily concerned with making the structures of consciousness, and the phenomena which appear in acts of consciousness, objects of systematic reflection and analysis. Such reflection was to take place from a highly modified "first person" viewpoint, studying phenomena not as they appear to "my" consciousness, but to any consciousness whatsoever. Husserl believed that phenomenology could thus provide a firm basis for all human knowledge, including scientific knowledge, and could establish philosophy as a "rigorous science".

Husserl's conception of phenomenology has been criticised and developed by his student and assistant Martin Heidegger (1889–1976), by existentialists like Maurice Merleau-Ponty (1908–1961) and Jean-Paul Sartre (1905–1980), and by other philosophers, such as Paul Ricoeur (1913–2005), Emmanuel Levinas (1906–1995), and Dietrich von Hildebrand (1889–1977).

Skeptical hypotheses

A brain in a vat that believes it is walking

Skeptical hypotheses in philosophy suggest that reality could be very different from what we think it is; or at least that we cannot prove it is not. Examples include:

• The "Brain in a vat" hypothesis is cast in scientific terms. It supposes that one might be a disembodied brain kept alive in a vat, and fed false sensory signals. This hypothesis is related to the Matrix hypothesis below.
• The "Dream argument" of Descartes and Zhuangzi supposes reality to be indistinguishable from a dream.
• Descartes' Evil demon is a being "as clever and deceitful as he is powerful, who has directed his entire effort to misleading me."
• The five minute hypothesis (or omphalos hypothesis or Last Thursdayism) suggests that the world was created recently together with records and traces indicating a greater age.
• Diminished reality refers to artificially diminished reality, not due to limitations of sensory systems but via artificial filters.
• The Matrix hypothesis or Simulated reality hypothesis suggest that we might be inside a computer simulation or virtual reality. Related hypotheses may also involve simulations with signals that allow the inhabitant species in virtual or simulated reality to perceive the external reality.

Non-western philosophy

Hindu philosophy

Main article: Vedanta

Hindu philosophy, particularly the Vedic tradition, includes a number of subtly different and nuanced perspectives about the nature of reality and unified consciousness They are as follows (order irrelevant):

1. Advaita – non-dualism
2. Tattvavada (Dvaita) – dualism
3. Dvaitadvaita – dualistic non-dualism
4. Bhedabheda – difference and non-difference
5. Vishishtadvaita – qualified non-dualism
6. Suddhadvaita – pure non-dualism
7. Achintya-Bheda-Abheda – inconceivable difference and non-difference
8. Dvaitadvaita Vedanta - natural identity-in-difference
9. Akshar Purushottam Darshan - multiple eternal realities

Jain philosophy

Main article: Tattva (Jainism)

Jain philosophy postulates that seven tattva (truths or fundamental principles) constitute reality. These seven tattva are:

1. Jīva – The soul which is characterized by consciousness.
2. Ajīva – The non-soul.
3. Asrava – Influx of karma.
4. Bandha – The bondage of karma.
5. Samvara – Obstruction of the inflow of karmic matter into the soul.
6. Nirjara – Shedding of karmas.
7. Moksha – Liberation or Salvation, i.e. the complete annihilation of all karmic matter (bound with any particular soul).

Science

Scientific method

Science is used to comprehend reality. The scientific method concerns three concepts: reality, observation, and understanding. To apply the method requires that reality be observable in some way, that the observations can be summarized in a comprehendible way, and that the resulting understanding can be compared to reality or falsified.

Scientific realism

Scientific realism is the view that reality exists externally to the mind, that this external world is what science describes, and that scientific theories constitute an understand of reality. By contrast, the scientific philosophy called instrumentalism rejects the reality of unobservable aspects of scientific theories. For example, in instrumentalism the electron is not an element of reality but the effect it creates in a cloud chamber is real.

Realism and locality in physics

Main article: Principle of locality

Realism in the sense used by physicists does not equate to realism in metaphysics. The latter is the claim that the world is mind-independent: that even if the results of a measurement do not pre-exist the act of measurement, that does not require that they are the creation of the observer. Furthermore, a mind-independent property does not have to be the value of some physical variable such as position or momentum. A property can be dispositional (or potential), i.e. it can be a tendency: in the way that glass objects tend to break, or are disposed to break, even if they do not actually break. Likewise, the mind-independent properties of quantum systems could consist of a tendency to respond to particular measurements with particular values with ascertainable probability. Such an ontology would be metaphysically realistic, without being realistic in the physicist's sense of "local realism" (which would require that a single value be produced with certainty).

A closely related term is counterfactual definiteness (CFD), used to refer to the claim that one can meaningfully speak of the definiteness of results of measurements that have not been performed (i.e. the ability to assume the existence of objects, and properties of objects, even when they have not been measured).

Local realism is a significant feature of classical mechanics, of general relativity, and of classical electrodynamics; but not quantum mechanics. In a work now called the EPR paradox, Einstein relied on local realism to suggest that hidden variables were missing in quantum mechanics. However, John S. Bell subsequently showed that the predictions of quantum mechanics are inconsistent with hidden variables, a result known as Bell's theorem. The predictions of quantum mechanics have been verified: Bell's inequalities are violated. This means either particles have no definite positions independent of observation (no realism) or distant measurements can affect each other (no locality) or both. Different interpretations of quantum mechanics violate different parts of local realism.

The transition from "possible" to "actual" is a major topic of quantum physics, with related theories including quantum darwinism.

Role of "observation" in quantum mechanics

See also: Quantum decoherence

The quantum mind–body problem refers to the philosophical discussions of the mind–body problem in the context of quantum mechanics. Since quantum mechanics involves quantum superpositions, which are not perceived by observers, some interpretations of quantum mechanics place conscious observers in a special position.

The founders of quantum mechanics debated the role of the observer, and of them, Wolfgang Pauli and Werner Heisenberg believed that quantum mechanics expressed the observers knowledge and when an experiment was completed the additional knowledge should be incorporated in the wave function, an effect that came to be called state reduction or collapse. This point of view, which was never fully endorsed by Niels Bohr, was denounced as mystical and anti-scientific by Albert Einstein. Pauli accepted the term, and described quantum mechanics as lucid mysticism.

Heisenberg and Bohr always described quantum mechanics in logical positivist terms. Bohr also took an active interest in the philosophical implications of quantum theories such as his complementarity, for example. He believed quantum theory offers a complete description of nature, albeit one that is simply ill-suited for everyday experiences – which are better described by classical mechanics and probability. Bohr famously avoided any characterization of "reality".

Eugene Wigner reformulated the "Schrödinger's cat" thought experiment as "Wigner's friend" and proposed that the consciousness of an observer is the demarcation line which precipitates collapse of the wave function, independent of any realist interpretation. Commonly known as "consciousness causes collapse", this controversial interpretation of quantum mechanics states that observation by a conscious observer is what makes the wave function collapse. However, this is a minority view among quantum philosophers, considering it a misunderstanding. There are other possible solutions to the "Wigner's friend" thought experiment, which do not require consciousness to be different from other physical processes. Moreover, Wigner shifted to those interpretations in his later years.

Multiverse

The multiverse is the hypothetical set of multiple possible universes (including the historical universe we consistently experience) that together comprise everything that exists: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them. The term was coined in 1895 by the American philosopher and psychologist William James. In the many-worlds interpretation (MWI), one of the mainstream interpretations of quantum mechanics, there are an infinite number of universes and every possible quantum outcome occurs in at least one universe, albeit there is a debate as to how real the (other) worlds are.

The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes, depend on the specific multiverse hypothesis considered. Multiverses have been hypothesized in cosmology, physics, astronomy, religion, philosophy, transpersonal psychology and fiction, particularly in science fiction and fantasy. In these contexts, parallel universes are also called "alternative universes", "quantum universes", "interpenetrating dimensions", "parallel dimensions", "parallel worlds", "alternative realities", "alternative timelines", and "dimensional planes", among others.

Cyclic theories

This section is an excerpt from Multiverse § Cyclic theories.[edit]

In several theories, there is a series of, in some cases infinite, self-sustaining cycles – typically a series of Big Crunches (or Big Bounces). However, the respective universes do not exist at once but are forming or following in a logical order or sequence, with key natural constituents potentially varying between universes (see § Anthropic principle).

Some cyclic theories postulate continuous expansion of the universe across cycles to ensure entropy growth, but they have been shown not be truly cyclic in time. In any case these types of scientific hypotheses do not fundamentally alter concepts of the ultimate origin of reality such as the cosmological argument. A theist can argue for perpetual divine creation or for an unmoved mover responsible for the first universe in the sequence.

Anthropic principle

This paragraph is an excerpt from Anthropic principle.[edit]

In philosophy of science and cosmology, the anthropic principle (also known as the observation selection effect) is the proposition that the range of possible observations that could be made about the universe is limited by the fact that observations are only possible in the type of universe that is capable of developing observers in the first place. Proponents of the anthropic principle argue that it explains why the universe has the age and the fundamental physical constants necessary to accommodate intelligent life. If either had been significantly different, no one would have been around to make observations. Anthropic reasoning has been used to address the question as to why certain measured physical constants take the values that they do, rather than some other arbitrary values, and to explain a perception that the universe appears to be finely tuned for the existence of life.

Personal and collective reality

White matter tracts within a human brain, as visualized by MRI tractography

Each individual has a different view of reality, with different memories and personal history, knowledge, personality traits and experience. This system, mostly referring to the human brain, affects cognition and behavior and into this complex new knowledge, memories, information, thoughts and experiences are continuously integrated. The connectome – neural networks/wirings in brains – is thought to be a key factor in human variability in terms of cognition or the way we perceive the world (as a context) and related features or processes. Sensemaking is the process by which people give meaning to their experiences and make sense of the world they live in. Personal identity is relating to questions like how a unique individual is persisting through time.

Sensemaking and determination of reality also occurs collectively, which is investigated in social epistemology and related approaches. From the collective intelligence perspective, the intelligence of the individual human (and potentially AI entities) is substantially limited and advanced intelligence emerges when multiple entities collaborate over time. Collective memory is an important component of the social construction of reality and communication and communication-related systems, such as media systems, may also be major components (see #Technology).

Philosophy of perception raises questions based on the evolutionary history of humans' perceptual apparatuses, particularly or especially individuals' physiological senses, described as "[w]e don't see reality—we only see what was useful to see in the past", partly suggesting that "[o]ur species has been so successful not in spite of our inability to see reality but because of it".

Scientific theories of everything

A theory of everything (TOE) is a putative theory of theoretical physics that fully explains and links together all known physical phenomena, and predicts the outcome of any experiment that could be carried out in principle. The theory of everything is also called the final theory. Many candidate theories of everything have been proposed by theoretical physicists during the twentieth century, but none have been confirmed experimentally. The primary problem in producing a TOE is that general relativity and quantum mechanics are hard to unify. This is one of the unsolved problems in physics.

Initially, the term "theory of everything" was used with an ironic connotation to refer to various overgeneralized theories. For example, a great-grandfather of Ijon Tichy, a character from a cycle of Stanisław Lem's science fiction stories of the 1960s, was known to work on the "General Theory of Everything". Physicist John Ellis claims to have introduced the term into the technical literature in an article in Nature in 1986. Over time, the term stuck in popularizations of quantum physics to describe a theory that would unify or explain through a single model the theories of all fundamental interactions and of all particles of nature: general relativity for gravitation, and the standard model of elementary particle physics – which includes quantum mechanics – for electromagnetism, the two nuclear interactions, and the known elementary particles.

Current candidates for a theory of everything include string theory, M theory, and loop quantum gravity.

Technology

Media

See also: § Personal and collective reality, and § Belief studies

Media – such as news media, social media, websites including Wikipedia, and fiction – shape individuals' and society's perception of reality (including as part of belief and attitude formation) and are partly used intentionally as means to learn about reality. Various technologies have changed society's relationship with reality such as the advent of radio and TV technologies.

Research investigates interrelations and effects, for example aspects in the social construction of reality. A major component of this shaping and representation of perceived reality is agenda, selection and prioritization – not only (or primarily) the quality, tone and types of content – which influences, for instance, the public agenda. Disproportional news attention for low-probability incidents – such as high-consequence accidents – can distort audiences' risk perceptions with harmful consequences. Various biases such as false balance, public attention dependence reactions like sensationalism and domination by "current events", as well as various interest-driven uses of media such as marketing can also have major impacts on the perception of reality. Time-use studies found that e.g. in 2018 the average U.S. American "spent around eleven hours every day looking at screens".

Virtual reality and cyberspace

Virtual reality (VR) is a computer-simulated environment that can simulate physical presence in places in the real world, as well as in imaginary worlds.

Reality-virtuality continuum

The virtuality continuum is a continuous scale ranging between the completely virtual, a virtuality, and the completely real: reality. The reality–virtuality continuum therefore encompasses all possible variations and compositions of real and virtual objects. It has been described as a concept in new media and computer science, but in fact it could be considered a matter of anthropology. The concept was first introduced by Paul Milgram.

The area between the two extremes, where both the real and the virtual are mixed, is the so-called mixed reality. This in turn is said to consist of both augmented reality, where the virtual augments the real, and augmented virtuality, where the real augments the virtual. Cyberspace, the world's computer systems considered as an interconnected whole, can be thought of as a virtual reality; for instance, it is portrayed as such in the cyberpunk fiction of William Gibson and others. Second Life and MMORPGs such as World of Warcraft are examples of artificial environments or virtual worlds (falling some way short of full virtual reality) in cyberspace.

"RL" in internet culture

On the Internet, "real life" refers to life in the real world. It generally references life or consensus reality, in contrast to an environment seen as fiction or fantasy, such as virtual reality, lifelike experience, dreams, novels, or movies. Online, the acronym "IRL" stands for "in real life", with the meaning "not on the Internet". Sociologists engaged in the study of the Internet have determined that someday, a distinction between online and real-life worlds may seem "quaint", noting that certain types of online activity, such as sexual intrigues, have already made a full transition to complete legitimacy and "reality". The abbreviation "RL" stands for "real life". For example, one can speak of "meeting in RL" someone whom one has met in a chat or on an Internet forum. It may also be used to express an inability to use the Internet for a time due to "RL problems". A related abbreviation is "AFK", which stands for "away from keyboard", signifying that one is (at least temporarily) choosing to disengage themselves from the virtual world so as to focus preferentially on the real one.

World views

Further information: World view

A common colloquial usage would have reality mean "perceptions, beliefs, and attitudes toward reality", as in "My reality is not your reality." This is often used just as a colloquialism indicating that the parties to a conversation agree, or should agree, not to quibble over deeply different conceptions of what is real. For example, in a religious discussion between friends, one might say (attempting humor), "You might disagree, but in my reality, everyone goes to heaven."

Reality can be defined in a way that links it to worldviews or parts of them (conceptual frameworks): Reality is the totality of all things, structures (actual and conceptual), events (past and present) and phenomena, whether observable or not. It is what a world view (whether it be based on individual or shared human experience) ultimately attempts to describe or map.

A worldview (also world-view or world view) or Weltanschauung is the fundamental cognitive orientation of an individual or society encompassing the whole of the individual's or society's knowledge, culture, and point of view. When two parties view the same real world phenomenon, if their world views differ, one may include elements that the other does not leading to differing conclusions, despite the shared reference point.

A worldview can include natural philosophy; fundamental, existential, and normative postulates; or themes, values, emotions, and ethics.

Certain ideas from physics, philosophy, sociology, literary criticism, and other fields shape various theories of reality. One such theory is that there simply and literally is no reality beyond the perceptions or beliefs we each have about reality. Such attitudes are summarized in popular statements, such as "Perception is reality" or "Life is how you perceive reality" or "reality is what you can get away with" (Robert Anton Wilson), and they indicate anti-realism – that is, the view that there is no objective reality, whether acknowledged explicitly or not.

Many of the concepts of science and philosophy are often defined culturally and socially. This idea was elaborated by Thomas Kuhn in his book The Structure of Scientific Revolutions (1962). The Social Construction of Reality, a book about the sociology of knowledge written by Peter L. Berger and Thomas Luckmann, was published in 1966. It explained how knowledge is acquired and used for the comprehension of reality. Out of all the realities, the reality of everyday life is the most important one since our consciousness requires us to be completely aware and attentive to the experience of everyday life.

See also

• Alternate history – Fictional genre where historical events occur differently
• Consciousness – Awareness of internal and external existence
• Extended modal realism – Version of modal realism
• Fact – Datum or structured component of reality
• Hyperreality – Term for cultural process of shifting ideas of reality
• Modal realism – Philosophical concept
• Potentiality and actuality – Principles in the philosophy of Aristotle
• Unphysicality

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External links

• Miller, Alexander. "Realism". In Zalta, Edward N. (ed.). Stanford Encyclopedia of Philosophy. ISSN 1095-5054. OCLC 429049174.
• C.D. Broad on Reality
• Phenomenology Online: Materials discussing and exemplifying phenomenological research
• The Matrix as Metaphysics by David Chalmers