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Reality is the sum or aggregate of all that is real or existent within a
system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment (systems), environment, is described by its boundaries, ...
, as opposed to that which is only imaginary, nonexistent or nonactual. The term is also used to refer to the ontological status of things, indicating their existence. In
physical Physical may refer to: *Physical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally co ...
terms, reality is the totality of a system, known and unknown. Philosophical questions about the nature of reality or existence or being are considered under the
rubric A rubric is a word or section of text that is traditionally written or printed in red ink for emphasis. The word derives from the la, rubrica, meaning red ochre or red chalk, and originates in Medieval illuminated manuscripts from the 13th cent ...
of
ontology In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality. Ontology addresses questions like how entities are grouped into categories and which of these entities exis ...
, which is a major branch of
metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
in the Western philosophical tradition. Ontological questions also feature in diverse branches of
philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. Some ...
, including the
philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methods, and implications of science. The central questions of this study concern what qualifies as science, the reliability of scientific theories, and the ultim ...
, of religion, of mathematics, and
philosophical logic Understood in a narrow sense, philosophical logic is the area of logic that studies the application of logical methods to philosophical problems, often in the form of extended logical systems like modal logic. Some theorists conceive philosophical ...
. These include questions about whether only physical objects are real (i.e.,
physicalism In philosophy, physicalism is the metaphysical thesis that "everything is physical", that there is "nothing over and above" the physical, or that everything supervenes on the physical. Physicalism is a form of ontological monism—a "one substanc ...
), whether reality is fundamentally immaterial (e.g.
idealism In philosophy, the term idealism identifies and describes metaphysical perspectives which assert that reality is indistinguishable and inseparable from perception and understanding; that reality is a mental construct closely connected to ide ...
), whether hypothetical unobservable entities posited by scientific theories exist, whether a ' God' exists, whether numbers and other abstract objects exist, and whether
possible world A possible world is a complete and consistent way the world is or could have been. Possible worlds are widely used as a formal device in logic, philosophy, and linguistics in order to provide a semantics for intensional logic, intensional and mod ...
s exist.
Epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Episte ...
is concerned with what can be
known Knowledge can be defined as awareness of facts or as practical skills, and may also refer to familiarity with objects or situations. Knowledge of facts, also called propositional knowledge, is often defined as true belief that is distinc ...
or inferred as likely and how, whereby in the modern world emphasis is put on
reason Reason is the capacity of consciously applying logic by drawing conclusions from new or existing information, with the aim of seeking the truth. It is closely associated with such characteristically human activities as philosophy, science, ...
,
empirical evidence Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
and
science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...
as sources and methods to determine or investigate reality.


World views


World views and theories

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 Colloquialism (), also called colloquial language, everyday language or general parlance, is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom norm ...
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. Certain ideas from physics, philosophy, sociology,
literary criticism Literary criticism (or literary studies) is the study, evaluation, and interpretation of literature. Modern literary criticism is often influenced by literary theory, which is the philosophical discussion of literature's goals and methods. Th ...
, 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 the popular statement, "Perception is reality" or "Life is how you perceive reality" or "reality is what you can get away with" (
Robert Anton Wilson Robert Anton Wilson (born Robert Edward Wilson; January 18, 1932 – January 11, 2007) was an American author, futurist, psychologist, and self-described agnostic mystic. Recognized within Discordianism as an Episkopos, pope and saint, 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 Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups.Tyl ...
and
socially Social organisms, including human(s), live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchange is voluntary or not. Etymology The word "social" derives from ...
. This idea was elaborated by
Thomas Kuhn Thomas Samuel Kuhn (; July 18, 1922 – June 17, 1996) was an American philosopher of science whose 1962 book ''The Structure of Scientific Revolutions'' was influential in both academic and popular circles, introducing the term '' paradigm ...
in his book '' The Structure of Scientific Revolutions'' (1962). ''
The Social Construction of Reality ''The Social Construction of Reality: A Treatise in the Sociology of Knowledge'' (1966), by Peter L. Berger and Thomas Luckmann, proposes that social groups and individual persons who interact with each other, within in a system of social classes, ...
'', 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.


Related concepts


A priori and a posteriori


Potentiality and actuality


Belief


Belief studies


Western philosophy

Philosophy addresses two different aspects of the topic of reality: the nature of reality itself, and the relationship between the
mind The mind is the set of faculties responsible for all mental phenomena. Often the term is also identified with the phenomena themselves. These faculties include thought, imagination, memory, will, and sensation. They are responsible for various m ...
(as well as
language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...
and culture) and reality. On the one hand,
ontology In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality. Ontology addresses questions like how entities are grouped into categories and which of these entities exis ...
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 Analytic philosophy is a branch and tradition of philosophy using analysis, popular in the Western world and particularly the Anglosphere, which began around the turn of the 20th century in the contemporary era in the United Kingdom, United Sta ...
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 Objectivity can refer to: * Objectivity (philosophy), the property of being independent from perception ** Objectivity (science), the goal of eliminating personal biases in the practice of science ** Journalistic objectivity, encompassing fairne ...
that have feet in both
metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
and
epistemology Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Episte ...
, 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 Jargon is the specialized terminology associated with a particular field or area of activity. Jargon is normally employed in a particular Context (language use), communicative context and may not be well understood outside that context. The conte ...
, "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 movement A political movement is a collective attempt by a group of people to change government policy or social values. Political movements are usually in opposition to an element of the status quo, and are often associated with a certain ideology. Some t ...
s, on up to the vague notion of a common cultural
world view A worldview 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. A worldview can include natural p ...
, or .


Realism

The view that there is a reality independent of any beliefs, perceptions, etc., is called
realism Realism, Realistic, or Realists may refer to: In the arts *Realism (arts), the general attempt to depict subjects truthfully in different forms of the arts Arts movements related to realism include: *Classical Realism *Literary realism, a move ...
. 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 In metaphysics and philosophy of language, the correspondence theory of truth states that the truth or falsity of a statement is determined only by how it relates to the world and whether it accurately describes (i.e., corresponds with) that world ...
of
knowledge Knowledge can be defined as awareness of facts or as practical skills, and may also refer to familiarity with objects or situations. Knowledge of facts, also called propositional knowledge, is often defined as true belief that is distinc ...
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 The scientific method is an empirical method for acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries; see the article history of scientific m ...
can
verify CONFIG.SYS is the primary configuration file for the DOS and OS/2 operating systems. It is a special ASCII text file that contains user-accessible setup or configuration directives evaluated by the operating system's DOS BIOS (typically residing ...
that a statement is true based on the observable evidence that a thing exists. Many humans can point to the
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
and say that this
mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...
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 In philosophy, the term idealism identifies and describes metaphysical perspectives which assert that reality is indistinguishable and inseparable from perception and understanding; that reality is a mental construct closely connected to ide ...
, so called because reality was said to be in the mind, or a product of our ''ideas''.
Berkeleyan idealism Subjective idealism, or empirical idealism, is a form of philosophical monism that holds that only minds and mental contents exist. It entails and is generally identified or associated with immaterialism, the doctrine that material things do no ...
is the view, propounded by the Irish
empiricist In philosophy, empiricism is an epistemological theory that holds that knowledge or justification comes only or primarily from sensory experience. It is one of several views within epistemology, along with rationalism and skepticism. Empir ...
George Berkeley George Berkeley (; 12 March 168514 January 1753) – known as Bishop Berkeley (Bishop of Cloyne of the Anglican Church of Ireland) – was an Anglo-Irish philosopher whose primary achievement was the advancement of a theory he called "immate ...
, 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 In metaphysics, phenomenalism is the view that physical objects cannot justifiably be said to exist in themselves, but only as perceptual phenomena or sensory stimuli (e.g. redness, hardness, softness, sweetness, etc.) situated in time and in sp ...
. 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 Russell may refer to: People * Russell (given name) * Russell (surname) * Lady Russell (disambiguation) * Lord Russell (disambiguation) Places Australia *Russell, Australian Capital Territory *Russell Island, Queensland (disambiguation) **Ru ...
, 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 Cultural relativism is the idea that a person's beliefs and practices should be understood based on that person's own culture. Proponents of cultural relativism also tend to argue that the norms and values of one culture should not be evaluated ...
is the view that
social issues A social issue is a problem that affects many people within a society. It is a group of common problems in present-day society and ones that many people strive to solve. It is often the consequence of factors extending beyond an individual's cont ...
such as morality are not absolute, but at least partially
cultural artifact A cultural artifact, or cultural artefact (see American and British English spelling differences), is a term used in the social sciences, particularly anthropology, ethnology and sociology for anything created by humans which gives information ...
.


Being

The nature of
being In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality. Ontology addresses questions like how entities are grouped into categories and which of these entities exis ...
is a perennial topic in metaphysics. For, instance
Parmenides Parmenides of Elea (; grc-gre, Παρμενίδης ὁ Ἐλεάτης; ) was a pre-Socratic Greek philosopher from Elea in Magna Graecia. Parmenides was born in the Greek colony of Elea, from a wealthy and illustrious family. His dates a ...
taught that reality was a single unchanging Being, whereas
Heraclitus Heraclitus of Ephesus (; grc-gre, Ἡράκλειτος , "Glory of Hera"; ) was an ancient Greek pre-Socratic philosopher from the city of Ephesus, which was then part of the Persian Empire. Little is known of Heraclitus's life. He wrote ...
wrote that all things flow. The 20th-century philosopher Heidegger thought previous philosophers have lost sight the question of Being (qua Being) in favour of the questions of beings (existing things), so that a return to the Parmenidean approach was needed. An
ontological catalogue In ontology, the theory of categories concerns itself with the ''categories of being'': the highest ''genera'' or ''kinds of entities'' according to Amie Thomasson. To investigate the categories of being, or simply categories, is to determine the mo ...
is an attempt to list the fundamental constituents of reality. The question of whether or not existence is a
predicate Predicate or predication may refer to: * Predicate (grammar), in linguistics * Predication (philosophy) * several closely related uses in mathematics and formal logic: **Predicate (mathematical logic) **Propositional function **Finitary relation, o ...
has been discussed since the Early Modern period, not least in relation to the
ontological argument for the existence of God An ontological argument is a philosophical argument, made from an ontological basis, that is advanced in support of the existence of God. Such arguments tend to refer to the state of being or existing. More specifically, ontological arguments a ...
. Existence, ''that'' something is, has been contrasted with '' essence'', the question of ''what'' something is. Since existence without essence seems blank, it associated with
nothingness Nothing, the complete absence of anything, has been a matter of philosophical debate since at least the 5th century BC. Early Greek philosophers argued that it was impossible for ''nothing'' to exist. The atomists allowed ''nothing'' but only i ...
by philosophers such as Hegel.
Nihilism Nihilism (; ) is a philosophy, or family of views within philosophy, that rejects generally accepted or fundamental aspects of human existence, such as objective truth, knowledge, morality, values, or meaning. The term was popularized by Ivan ...
represents an extremely negative view of being, the
absolute Absolute may refer to: Companies * Absolute Entertainment, a video game publisher * Absolute Radio, (formerly Virgin Radio), independent national radio station in the UK * Absolute Software Corporation, specializes in security and data risk manage ...
a positive one.


Explanations for the existence of something rather than nothing


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 Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
experience Experience refers to conscious events in general, more specifically to perceptions, or to the practical knowledge and familiarity that is produced by these conscious processes. Understood as a conscious event in the widest sense, experience involv ...
;Lehar, Steve. (2000)
The Function of Conscious Experience: An Analogical Paradigm of Perception and Behavior
, ''Consciousness and Cognition''.
Lehar, Steve. (2000)

, ''The Function of Conscious Experience''.
the
epistemological Epistemology (; ), or the theory of knowledge, is the branch of philosophy concerned with knowledge. Epistemology is considered a major subfield of philosophy, along with other major subfields such as ethics, logic, and metaphysics. Episte ...
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 In Biology, biology, the nervous system is the Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals to and from different parts of its ...
processes in our brain. Naïve realism is known as ''direct'' realism when developed to counter ''indirect'' or representative realism, also known as
epistemological dualism In the philosophy of perception and philosophy of mind, the question of direct or naïve realism, as opposed to indirect or representational realism, is the debate over the nature of Consciousness, conscious Qualia, experience;Lehar, Steve. (200 ...
, the philosophical position that our conscious experience is not of the real world itself but of an internal representation, a miniature
virtual-reality Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), ed ...
replica of the world. Timothy Leary coined the influential term
Reality Tunnel Reality tunnel is a theory that, with a subconscious set of mental filters formed from beliefs and experiences, every individual interprets the same world differently, hence "Truth is in the eye of the beholder". It is similar to the idea of repres ...
, by which he means a kind of
representative realism In the philosophy of perception and philosophy of mind, the question of direct or naïve realism, as opposed to indirect or representational realism, is the debate over the nature of conscious experience;Lehar, Steve. (2000)The Function of Consc ...
. 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 Robert Anton Wilson (born Robert Edward Wilson; January 18, 1932 – January 11, 2007) was an American author, futurist, psychologist, and self-described agnostic mystic. Recognized within Discordianism as an Episkopos, pope and saint, 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 philosophy of mathematics is the branch of philosophy that studies the assumptions, foundations, and implications of mathematics. It aims to understand the nature and methods of mathematics, and find out the place of mathematics in people's ...
, 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 Formalism may refer to: * Form (disambiguation) * Formal (disambiguation) * Legal formalism, legal positivist view that the substantive justice of a law is a question for the legislature rather than the judiciary * Formalism (linguistics) * Scient ...
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 Constructivism may refer to: Art and architecture * Constructivism (art), an early 20th-century artistic movement that extols art as a practice for social purposes * Constructivist architecture, an architectural movement in Russia in the 1920s a ...
and
intuitionism In the philosophy of mathematics, intuitionism, or neointuitionism (opposed to preintuitionism), is an approach where mathematics is considered to be purely the result of the constructive mental activity of humans rather than the discovery of fu ...
are realistic about objects that can be explicitly constructed, but reject the use of the
principle of the excluded middle In logic, the law of excluded middle (or the principle of excluded middle) states that for every proposition, either this proposition or its negation is true. It is one of the so-called three laws of thought, along with the law of noncontradi ...
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 In physics and cosmology, the mathematical universe hypothesis (MUH), also known as the ultimate ensemble theory and struogony (from mathematical structure, Latin: struō), is a speculative "theory of everything" (TOE) proposed by cosmologist Max T ...
, 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 orldscomplex enough to contain self-aware substructures
hey Hey or Hey! may refer to: Music * Hey (band), a Polish rock band Albums * ''Hey'' (Andreas Bourani album) or the title song (see below), 2014 * ''Hey!'' (Julio Iglesias album) or the title song, 1980 * ''Hey!'' (Jullie album) or the title s ...
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

The problem of universals is an ancient problem in
metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
about whether
universals In metaphysics, a universal is what particular things have in common, namely characteristics or qualities. In other words, universals are repeatable or recurrent entities that can be instantiated or exemplified by many particular things. For exa ...
exist. Universals are general or abstract qualities, characteristics, properties, kinds or
relations Relation or relations may refer to: General uses *International relations, the study of interconnection of politics, economics, and law on a global level *Interpersonal relationship, association or acquaintance between two or more people *Public ...
, 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 Aristotle's Theory of Universals is Aristotle's classical solution to the Problem of Universals, sometimes known as the hylomorphic theory of immanent realism. Universals are the characteristics or qualities that ordinary objects or things have ...
. ''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 In metaphysics, nominalism is the view that universals and abstract objects do not actually exist other than being merely names or labels. There are at least two main versions of nominalism. One version denies the existence of universalsthings t ...
and conceptualism are the main forms of anti-realism about universals.


Time and space

A traditional realist position in
ontology In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality. Ontology addresses questions like how entities are grouped into categories and which of these entities exis ...
is that time and space have existence apart from the human mind.
Idealists In philosophy, the term idealism identifies and describes metaphysical perspectives which assert that reality is indistinguishable and inseparable from perception and understanding; that reality is a mental construct closely connected to ide ...
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 ("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...
'' notion that, together with other ''a priori'' notions such as
space Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider ...
, allows us to comprehend
sense experience Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences an ...
. Kant denies that either space or time are
substance Substance may refer to: * Matter, anything that has mass and takes up space Chemistry * Chemical substance, a material with a definite chemical composition * Drug substance ** Substance abuse, drug-related healthcare and social policy diagnosis ...
, 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
measurement Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. In other words, measurement is a process of determining how large or small a physical quantity is as compared ...
s are used to quantify how far apart
objects Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...
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 John McTaggart Ellis McTaggart (3 September 1866 – 18 January 1925) was an English idealist metaphysician. For most of his life McTaggart was a fellow and lecturer in philosophy at Trinity College, Cambridge. He was an exponent of the philo ...
in ''
The Unreality of Time ''The Unreality of Time'' is the best-known philosophical work of the Cambridge idealist J. M. E. McTaggart (1866–1925). In the argument, first published as a journal article in '' Mind'' in 1908, McTaggart argues that time is unreal b ...
'' 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 The future is the time after the past and present. Its arrival is considered inevitable due to the existence of time and the laws of physics. Due to the apparent nature of reality and the unavoidability of the future, everything that currently ...
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 The growing block universe theory of time (or the growing block view), states that the past and present both exist, and the future as yet does not. The present is an objective property, to be compared with a moving spotlight. By the passage of tim ...
theory holds that past and present are real, but the future is not. Time, and the related concepts of process and
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
are central to the
system-building metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
of
A. N. Whitehead Alfred North Whitehead (15 February 1861 – 30 December 1947) was an English mathematician and philosopher. He is best known as the defining figure of the philosophical school known as process philosophy, which today has found applicat ...
and Charles Hartshorne.


Possible worlds

The term "
possible world A possible world is a complete and consistent way the world is or could have been. Possible worlds are widely used as a formal device in logic, philosophy, and linguistics in order to provide a semantics for intensional logic, intensional and mod ...
" goes back to Leibniz's theory of possible worlds, used to analyse necessity,
possibility Possibility is the condition or fact of being possible. Latin origins of the word hint at ability. Possibility may refer to: * Probability, the measure of the likelihood that an event will occur * Epistemic possibility, a topic in philosophy an ...
, and similar modal notions.
Modal realism Modal realism is the view propounded by philosopher David Lewis that all possible worlds are real in the same way as is the actual world: they are "of a kind with this world of ours." It is based on the following tenets: possible worlds exist; p ...
is the view, notably propounded by David Kellogg Lewis, that all possible worlds are as real as the actual world. In short: the actual world is regarded as merely one among an infinite
set Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements *Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electro ...
of
logically possible Logical possibility refers to a logical proposition that cannot be disproved, using the axioms and rules of a given system of logic. The logical possibility of a proposition will depend upon the system of logic being considered, rather than on the ...
worlds, some "nearer" to the actual world and some more remote. Other theorists may use the Possible World framework to express and explore problems without committing to it ontologically. Possible world theory is related to alethic logic: a proposition is ''necessary'' if it is true in all possible worlds, and ''possible'' if it is true in at least one. The many worlds interpretation of quantum mechanics is a similar idea in science.


Theories of everything (TOE) and philosophy

The philosophical implications of a physical TOE are frequently debated. For example, if philosophical
physicalism In philosophy, physicalism is the metaphysical thesis that "everything is physical", that there is "nothing over and above" the physical, or that everything supervenes on the physical. Physicalism is a form of ontological monism—a "one substanc ...
is true, a physical TOE will coincide with a philosophical theory of everything. The "system building" style of
metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
attempts to answer ''all'' the important questions in a coherent way, providing a complete picture of the world.
Plato Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...
and
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
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 Gottfried Wilhelm (von) Leibniz . ( – 14 November 1716) was a German polymath active as a mathematician, philosopher, scientist and diplomat. He is one of the most prominent figures in both the history of philosophy and the history of mathema ...
's Monadology, Descartes's
Dualism Dualism most commonly refers to: * Mind–body dualism, a philosophical view which holds that mental phenomena are, at least in certain respects, not physical phenomena, or that the mind and the body are distinct and separable from one another ** ...
, Spinoza's
Monism Monism attributes oneness or singleness (Greek: μόνος) to a concept e.g., existence. Various kinds of monism can be distinguished: * Priority monism states that all existing things go back to a source that is distinct from them; e.g., i ...
.
Hegel Georg Wilhelm Friedrich Hegel (; ; 27 August 1770 – 14 November 1831) was a German philosopher. He is one of the most important figures in German idealism and one of the founding figures of modern Western philosophy. His influence extends a ...
's
Absolute idealism Absolute idealism is an ontologically monistic philosophy chiefly associated with G. W. F. Hegel and Friedrich Schelling, both of whom were German idealist philosophers in the 19th century. The label has also been attached to others such as Josi ...
and Whitehead's
Process philosophy Process philosophy, also ontology of becoming, or processism, is an approach to philosophy that identifies processes, changes, or shifting relationships as the only true elements of the ordinary, everyday real world. In opposition to the classic ...
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 ''A Brief History of Time: From the Big Bang to Black Holes'' is a book on theoretical cosmology by English physicist Stephen Hawking. It was first published in 1988. Hawking wrote the book for readers who had no prior knowledge of physics. I ...
'' 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 Phenomenology may refer to: Art * Phenomenology (architecture), based on the experience of building materials and their sensory properties Philosophy * Phenomenology (philosophy), a branch of philosophy which studies subjective experiences and a ...
. 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 In its most common sense, philosophical methodology is the field of inquiry studying the methods used to do philosophy. But the term can also refer to the methods themselves. It may be understood in a wide sense as the general study of principles ...
developed in the early years of the twentieth century by
Edmund Husserl , thesis1_title = Beiträge zur Variationsrechnung (Contributions to the Calculus of Variations) , thesis1_url = https://fedora.phaidra.univie.ac.at/fedora/get/o:58535/bdef:Book/view , thesis1_year = 1883 , thesis2_title ...
and a circle of followers at the universities of
Göttingen Göttingen (, , ; nds, Chöttingen) is a college town, university city in Lower Saxony, central Germany, the Capital (political), capital of Göttingen (district), the eponymous district. The River Leine runs through it. At the end of 2019, t ...
and
Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the States of Germany, German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the List of cities in Germany by popu ...
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 Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
, and the
phenomena A phenomenon ( : phenomena) is an observable event. The term came into its modern philosophical usage through Immanuel Kant, who contrasted it with the noumenon, which ''cannot'' be directly observed. Kant was heavily influenced by Gottfried W ...
which appear in acts of consciousness, objects of systematic reflection and analysis. Such reflection was to take place from a highly modified "
first person First person or first-person may refer to: * First person (ethnic), indigenous peoples, usually used in the plural * First person, a grammatical person * First person, a gender-neutral, marital-neutral term for titles such as first lady and first ...
" 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 Knowledge can be defined as awareness of facts or as practical skills, and may also refer to familiarity with objects or situations. Knowledge of facts, also called propositional knowledge, is often defined as true belief that is distinc ...
, including scientific knowledge, and could establish philosophy as a "rigorous science". Husserl's conception of phenomenology has also been criticised and developed by his student and assistant
Martin Heidegger Martin Heidegger (; ; 26 September 188926 May 1976) was a German philosopher who is best known for contributions to phenomenology, hermeneutics, and existentialism. He is among the most important and influential philosophers of the 20th centur ...
, by
existentialists Existentialism ( ) is a form of philosophical inquiry that explores the problem of human existence and centers on human thinking, feeling, and acting. Existentialist thinkers frequently explore issues related to the meaning, purpose, and value ...
like Maurice Merleau-Ponty and
Jean-Paul Sartre Jean-Paul Charles Aymard Sartre (, ; ; 21 June 1905 – 15 April 1980) was one of the key figures in the philosophy of existentialism (and phenomenology), a French playwright, novelist, screenwriter, political activist, biographer, and litera ...
, and by other philosophers, such as
Paul Ricoeur Paul may refer to: *Paul (given name), a given name (includes a list of people with that name) *Paul (surname), a list of people People Christianity *Paul the Apostle (AD c.5–c.64/65), also known as Saul of Tarsus or Saint Paul, early Chris ...
,
Emmanuel Levinas Emmanuel Levinas (; ; 12 January 1906 – 25 December 1995) was a French philosopher of Lithuanian Jewish ancestry who is known for his work within Jewish philosophy, existentialism, and phenomenology, focusing on the relationship of ethics to me ...
, and Dietrich von Hildebrand.


Skeptical hypotheses

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 In philosophy, the brain in a vat (BIV) is a scenario used in a variety of thought experiments intended to draw out certain features of human conceptions of knowledge, reality, truth, mind, consciousness, and meaning. It is a modern incarnatio ...
" 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 Zhuangzi may refer to: * ''Zhuangzi'' (book) (莊子), an ancient Chinese collection of anecdotes and fables, one of the foundational texts of Daoism **Zhuang Zhou Zhuang Zhou (), commonly known as Zhuangzi (; ; literally "Master Zhuang"; als ...
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 The Omphalos hypothesis is one attempt to reconcile the scientific evidence that the Earth is billions of years old with a literal interpretation of the Genesis creation narrative, which implies that the Earth is only a few thousand years old. I ...
(or
omphalos hypothesis The Omphalos hypothesis is one attempt to reconcile the scientific evidence that the Earth is billions of years old with a literal interpretation of the Genesis creation narrative, which implies that the Earth is only a few thousand years old. ...
or
Last Thursdayism The Omphalos hypothesis is one attempt to reconcile the scientific evidence that the Earth is billions of years old with a literal interpretation of the Genesis creation narrative, which implies that the Earth is only a few thousand years old. ...
) 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 Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...
* The Matrix hypothesis or
Simulated reality hypothesis The simulation hypothesis proposes that all of our existence is a simulated reality, such as a computer simulation. The simulation hypothesis bears a close resemblance to various other skeptical scenarios from throughout the history of philosophy. ...
suggest that we might be inside a
computer simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be dete ...
or
virtual reality Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), educ ...
. 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 ancient philosophy and religion


Jain philosophy

Jain philosophy postulates that seven tattva (truths or fundamental principles) constitute reality. These seven ''tattva'' are: # '' Jīva'' – The
soul In many religious and philosophical traditions, there is a belief that a soul is "the immaterial aspect or essence of a human being". Etymology The Modern English noun ''soul'' is derived from Old English ''sāwol, sāwel''. The earliest attes ...
which is characterized by consciousness. # ''
Ajīva ''Ajiva'' (Sanskrit) is anything that has no soul or life, the polar opposite of " jīva" (soul). Because ''ajiva'' has no life, it does not accumulate ''karma'' and cannot die. Examples of ajiva include chairs, computers, paper, plastic, etc. ...
'' – The non-soul. # '' Asrava'' – Influx of
karma Karma (; sa, कर्म}, ; pi, kamma, italic=yes) in Sanskrit means an action, work, or deed, and its effect or consequences. In Indian religions, the term more specifically refers to a principle of cause and effect, often descriptivel ...
. # '' Bandha'' – The bondage of karma. # '' Samvara'' – Obstruction of the inflow of karmic matter into the soul. # '' Nirjara'' – Shedding of karmas. # ''
Moksha ''Moksha'' (; sa, मोक्ष, '), also called ''vimoksha'', ''vimukti'' and ''mukti'', is a term in Hinduism, Buddhism, Jainism and Sikhism for various forms of emancipation, enlightenment, liberation, and release. In its soteriology, ...
'' – Liberation or Salvation, i.e. the complete annihilation of all karmic matter (bound with any particular soul).


Physical sciences


Scientific realism

Scientific realism Scientific realism is the view that the universe described by science is real regardless of how it may be interpreted. Within philosophy of science, this view is often an answer to the question "how is the success of science to be explained?" Th ...
is, at the most general level, the view that the world (the
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...
) described by science (perhaps ideal science) is the real world, as it is, independent of what we might take it to be. Within
philosophy of science Philosophy of science is a branch of philosophy concerned with the foundations, methods, and implications of science. The central questions of this study concern what qualifies as science, the reliability of scientific theories, and the ultim ...
, it is often framed as an answer to the question "how is the success of science to be explained?" The debate over what the success of science involves centers primarily on the status of entities that are not directly observable discussed by scientific theories. Generally, those who are scientific realists state that one can make reliable claims about these entities (viz., that they have the same ontological status) as directly observable entities, as opposed to instrumentalism. The most used and studied scientific theories today state more or less the truth.


Realism and locality in physics

''Realism'' in the sense used by physicists does not equate to
realism Realism, Realistic, or Realists may refer to: In the arts *Realism (arts), the general attempt to depict subjects truthfully in different forms of the arts Arts movements related to realism include: *Classical Realism *Literary realism, a move ...
in
metaphysics Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
. 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 In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass an ...
. A property can be ''
disposition A disposition is a quality of character, a habit, a preparation, a state of readiness, or a tendency to act in a specified way. The terms dispositional belief and occurrent belief refer, in the former case, to a belief that is held in the mind bu ...
al'' (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 In physics, the principle of locality states that an object is influenced directly only by its immediate surroundings. A theory that includes the principle of locality is said to be a "local theory". This is an alternative to the concept of ins ...
is a significant feature of classical mechanics, of
general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
, and of electrodynamics; but
quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...
has shown that quantum entanglement is possible. This was rejected by Einstein, who proposed the
EPR paradox EPR may refer to: Science and technology * EPR (nuclear reactor), European Pressurised-Water Reactor * EPR paradox (Einstein–Podolsky–Rosen paradox), in physics * Earth potential rise, in electrical engineering * East Pacific Rise, a mid-ocea ...
, but it was subsequently quantified by Bell's inequalities. If Bell's inequalities are violated, either local realism ''or'' counterfactual definiteness must be incorrect; but some physicists dispute that experiments have demonstrated Bell's violations, on the grounds that the sub-class of inhomogeneous Bell inequalities has not been tested or due to experimental limitations in the tests. Different interpretations of quantum mechanics violate different parts of local realism and/or counterfactual definiteness. The transition from "possible" to "actual" is a major topic of
quantum physics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, qua ...
, with related theories including quantum darwinism.


Role of "observation" in quantum mechanics

The quantum mind–body problem refers to the philosophical discussions of the mind–body problem in the context of
quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...
. Since quantum mechanics involves
quantum superposition Quantum superposition is a fundamental principle of quantum mechanics. It states that, much like waves in classical physics, any two (or more) quantum states can be added together ("superposed") and the result will be another valid quantum ...
s, 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 Wolfgang Ernst Pauli (; ; 25 April 1900 – 15 December 1958) was an Austrian theoretical physicist and one of the pioneers of quantum physics. In 1945, after having been nominated by Albert Einstein, Pauli received the Nobel Prize in Physics fo ...
and
Werner Heisenberg Werner Karl Heisenberg () (5 December 1901 – 1 February 1976) was a German theoretical physicist and one of the main pioneers of the theory of quantum mechanics. He published his work in 1925 in a breakthrough paper. In the subsequent series ...
believed that it was the observer that produced
collapse Collapse or its variants may refer to: Concepts * Collapse (structural) * Collapse (topology), a mathematical concept * Collapsing manifold * Collapse, the action of collapsing or telescoping objects * Collapsing user interface elements ** ...
. This point of view, which was never fully endorsed by Niels Bohr, was denounced as mystical and anti-scientific by
Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...
. Pauli accepted the term, and described quantum mechanics as ''lucid mysticism''. Heisenberg and Bohr always described quantum mechanics in
logical positivist Logical positivism, later called logical empiricism, and both of which together are also known as neopositivism, is a movement in Western philosophy whose central thesis was the verification principle (also known as the verifiability criterion o ...
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 never specified a demarcation line above which objects cease to be quantum and become classical. He believed that it was not a question of physics, but one of philosophy. Eugene Wigner reformulated the " Schrödinger's cat"
thought experiment A thought experiment is a hypothetical situation in which a hypothesis, theory, or principle is laid out for the purpose of thinking through its consequences. History The ancient Greek ''deiknymi'' (), or thought experiment, "was the most anci ...
as " Wigner's friend" and proposed that the consciousness of an observer is the demarcation line which precipitates
collapse of the wave function In quantum mechanics, wave function collapse occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to interaction with the external world. This interaction is called an ''observat ...
, independent of any realist interpretation. Commonly known as "
consciousness causes collapse Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scient ...
", this controversial
interpretation of quantum mechanics An interpretation of quantum mechanics is an attempt to explain how the mathematical theory of quantum mechanics might correspond to experienced reality. Although quantum mechanics has held up to rigorous and extremely precise tests in an extraord ...
states that
observation Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The ...
by a
conscious Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
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.Michael Esfeld, (1999)
Essay Review: Wigner's View of Physical Reality
published in Studies in History and Philosophy of Modern Physics, 30B, pp. 145–154, Elsevier Science Ltd.


Multiverse

The
multiverse The multiverse is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, information, and the physical laws and constants that describe them. The di ...
is the
hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...
set of multiple possible
universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. Acc ...
s (including the historical universe we consistently experience) that together comprise everything that exists: the entirety of
space Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider ...
, time,
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic partic ...
, and energy as well as the
physical law Scientific laws or laws of science are statements, based on repeated experiments or observations, that describe or predict a range of natural phenomena. The term ''law'' has diverse usage in many cases (approximate, accurate, broad, or narrow) a ...
s and
constants Constant or The Constant may refer to: Mathematics * Constant (mathematics), a non-varying value * Mathematical constant, a special number that arises naturally in mathematics, such as or Other concepts * Control variable or scientific const ...
that describe them. The term was coined in 1895 by the American philosopher and psychologist
William James William James (January 11, 1842 – August 26, 1910) was an American philosopher, historian, and psychologist, and the first educator to offer a psychology course in the United States. James is considered to be a leading thinker of the lat ...
. 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 Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...
,
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
,
astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
, 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.


Anthropic principle


Personal and collective reality

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 The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the ...
, affects
cognition Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
and behavior and into this complex new
knowledge Knowledge can be defined as awareness of facts or as practical skills, and may also refer to familiarity with objects or situations. Knowledge of facts, also called propositional knowledge, is often defined as true belief that is distinc ...
, memories, information,
thought In their most common sense, the terms thought and thinking refer to conscious cognitive processes that can happen independently of sensory stimulation. Their most paradigmatic forms are judging, reasoning, concept formation, problem solving, a ...
s and experiences are continuously integrated. The connectomeneural 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 Meaning most commonly refers to: * Meaning (linguistics), meaning which is communicated through the use of language * Meaning (philosophy), definition, elements, and types of meaning discussed in philosophy * Meaning (non-linguistic), a general te ...
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 Collective intelligence (CI) is shared or group intelligence (GI) that emerges from the collaboration, collective efforts, and competition of many individuals and appears in consensus decision making. The term appears in sociobiology, politic ...
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 Collective memory refers to the shared pool of memories, knowledge and information of a social group that is significantly associated with the group's identity. The English phrase "collective memory" and the equivalent French phrase "la mémoire c ...
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 . Philosophy of perception raises questions based on the evolutionary history of humans' perceptual apparatuses, particularly or especially individuals' physiological senses, described as " don't see reality — we only see what was useful to see in the past", partly suggesting that " r 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 A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may be s ...
of
theoretical physics Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experim ...
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 General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
and
quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...
are hard to unify. This is one of the
unsolved problems in physics The following is a list of notable unsolved problems grouped into broad areas of physics. Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon ...
. 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 John Ellis may refer to: Academics *John Ellis (scrivener) (1698–1791), English political writer *John Ellis (naturalist) (1710–1776), English botanical illustrator *John Ellis (physicist, born 1946), British theoretical physicist at CERN * Jo ...
claims to have introduced the term into the technical literature in an article in ''
Nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
'' in 1986. Over time, the term stuck in popularizations of
quantum physics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, qua ...
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 General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...
for gravitation, and the
standard model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
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 In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. String theory describes how these strings propagate through space and interac ...
,
M theory M-theory is a theory in physics that unifies all consistent versions of superstring theory. Edward Witten first conjectured the existence of such a theory at a string theory conference at the University of Southern California in 1995. Witten's ...
, and
loop quantum gravity Loop quantum gravity (LQG) is a theory of quantum gravity, which aims to merge quantum mechanics and general relativity, incorporating matter of the Standard Model into the framework established for the pure quantum gravity case. It is an attem ...
.


Technology


Media

Media – such as
news media The news media or news industry are forms of mass media that focus on delivering news to the general public or a target public. These include news agencies, print media (newspapers, news magazines), broadcast news (radio and television), and th ...
,
social media Social media are interactive media technologies that facilitate the creation and sharing of information, ideas, interests, and other forms of expression through virtual communities and networks. While challenges to the definition of ''social medi ...
, websites including
Wikipedia Wikipedia is a multilingual free online encyclopedia written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and using a wiki-based editing system. Wikipedia is the largest and most-read refer ...
, and
fiction Fiction is any creative work, chiefly any narrative work, portraying individuals, events, or places that are imaginary, or in ways that are imaginary. Fictional portrayals are thus inconsistent with history, fact, or plausibility. In a traditi ...
– 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 Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of learnin ...
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 In journalism and mass media, sensationalism is a type of editorial tactic. Events and topics in news stories are selected and worded to excite the greatest number of readers and viewers. This style of news reporting encourages biased or emotion ...
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".


Filter bubbles and echo chambers


Virtual reality and cyberspace

Virtual reality Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), educ ...
(VR) is a computer-simulated environment that can simulate physical presence in places in the real world, as well as in imaginary worlds. The
virtuality continuum Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), ed ...
is a continuous scale ranging between the completely virtual, a
virtuality Virtual reality (VR) is a Simulation, simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video g ...
, 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 Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
, but in fact it could be considered a matter of
anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics, in both the present and past, including past human species. Social anthropology studies patterns of behavi ...
. 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 Augmented reality (AR) is an interactive experience that combines the real world and computer-generated content. The content can span multiple sensory modalities, including visual, auditory, haptic, somatosensory and olfactory. AR can be de ...
, where the virtual augments the real, and
augmented virtuality Mixed reality (MR) is a term used to describe the merging of a real-world environment and a computer-generated one. Physical and virtual objects may co-exist in mixed reality environments and interact in real time. Mixed reality is largely synony ...
, where the real augments the virtual.
Cyberspace Cyberspace is a concept describing a widespread interconnected digital technology. "The expression dates back from the first decade of the diffusion of the internet. It refers to the online world as a world 'apart', as distinct from everyday rea ...
, 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 Cyberpunk is a subgenre of science fiction in a dystopian futuristic setting that tends to focus on a "combination of lowlife and high tech", featuring futuristic technological and scientific achievements, such as artificial intelligence and cyber ...
fiction of
William Gibson William Ford Gibson (born March 17, 1948) is an American-Canadian speculative fiction writer and essayist widely credited with pioneering the science fiction subgenre known as ''cyberpunk''. Beginning his writing career in the late 1970s, his ...
and others. ''
Second Life ''Second Life'' is an online multimedia platform that allows people to create an avatar for themselves and then interact with other users and user created content within a multi player online virtual world. Developed and owned by the San Fra ...
'' and
MMORPG A massively multiplayer online role-playing game (MMORPG) is a video game that combines aspects of a role-playing video game and a massively multiplayer online game. As in role-playing games (RPGs), the player assumes the role of a Player charac ...
s such as ''
World of Warcraft ''World of Warcraft'' (''WoW'') is a massively multiplayer online role-playing game (MMORPG) released in 2004 by Blizzard Entertainment. Set in the ''Warcraft'' fantasy universe, ''World of Warcraft'' takes place within the world of Azeroth ...
'' are examples of artificial environments or
virtual world A virtual world (also called a virtual space) is a computer-simulated environment which may be populated by many users who can create a personal avatar, and simultaneously and independently explore the virtual world, participate in its activities ...
s (falling some way short of full virtual reality) in cyberspace.


"RL" in internet culture

On the Internet, "
real life Real life is a phrase used originally in literature to distinguish between the real world and fictional, virtual or idealized worlds, and in acting to distinguish between actors and the characters they portray. It has become a popular term on the ...
" refers to life in the real world. It generally references
life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
or
consensus reality Consensus reality is that which is generally agreed to be reality, based on a consensus view. The appeal to consensus arises from the idea that humans do not fully understand or agree upon the nature of knowledge or ontology, often making it unce ...
, in contrast to an environment seen as fiction or fantasy, such as
virtual reality Virtual reality (VR) is a simulated experience that employs pose tracking and 3D near-eye displays to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video games), educ ...
, lifelike experience, dreams, novels, or movies. Online, the
acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization''), but sometimes use syllables, as ...
"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 An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters or words taken from the full version of the word or phrase; for example, the word ''abbrevia ...
"RL" stands for "real life". For example, one can speak of "meeting in RL" someone whom one has met in a
chat Chat or chats may refer to: Communication * Conversation, particularly casual * Online chat, text message communication over the Internet in real-time * Synchronous conferencing, a formal term for online chat * SMS chat, a form of text messagin ...
or on an
Internet forum An Internet forum, or message board, is an online discussion site where people can hold conversations in the form of posted messages. They differ from chat rooms in that messages are often longer than one line of text, and are at least temporar ...
. It may also be used to express an inability to use the Internet for a time due to "RL problems".


See also

*
Alternate history Alternate history (also alternative history, althist, AH) is a genre of speculative fiction of stories in which one or more historical events occur and are resolved differently than in real life. As conjecture based upon historical fact, altern ...
* Counterfactual history * Derealization *
Extended modal realism Extended modal realism is a metaphysical theory developed by Takashi Yagisawa. It concerns the question of what it means that something is possible or necessary. Modal realism is the view that besides the actual world, there are many possible worl ...
*
Modal realism Modal realism is the view propounded by philosopher David Lewis that all possible worlds are real in the same way as is the actual world: they are "of a kind with this world of ours." It is based on the following tenets: possible worlds exist; p ...
* Hyperreality


Notes


References

* *
Alt URL


Further reading

*
George Musser George Musser (born 1965) is a contributing editor for ''Scientific American'' magazine in New York and the author of ''The Complete Idiot’s Guide to String Theory'' and of ''Spooky Action at a Distance''. Biography Musser did his undergraduate ...
, "Virtual Reality: How close can physics bring us to a truly fundamental understanding of the world?", ''
Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many famous scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it. In print since 1845, it i ...
'', vol. 321, no. 3 (September 2019), pp. 30–35. **"
Physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
is... the bedrock of the broader search for
truth Truth is the property of being in accord with fact or reality.Merriam-Webster's Online Dictionarytruth 2005 In everyday language, truth is typically ascribed to things that aim to represent reality or otherwise correspond to it, such as beliefs ...
.... Yet hysicistssometimes seem to be struck by a collective
impostor syndrome Impostor syndrome, also known as impostor phenomenon or impostorism, is a psychological occurrence in which an individual doubts their skills, talents, or accomplishments and has a persistent internalized fear of being exposed as a fraud. Despi ...
.... Truth can be elusive even in the best-established theories.
Quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...
is as well tested a theory as can be, yet its interpretation remains inscrutable. . 30.The deeper physicists dive into reality, the more reality seems to evaporate." . 34.


External links

*
C.D. Broad on Reality

Phenomenology Online: Materials discussing and exemplifying phenomenological research


{{Authority control Abstraction Concepts in aesthetics Concepts in metaphysics Philosophy of mind Concepts in epistemology Concepts in logic Concepts in metaphilosophy Concepts in the philosophy of language Concepts in the philosophy of science Consensus reality Emergence Empiricism Epistemological theories Metaphysical theories Metaphysics of mind Ontology Religion Philosophical logic Philosophy of logic Philosophy of mathematics Philosophy of religion Philosophy of technology Qualia Rationalism Thought Truth