Reality

Reality

Overview
In philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, reality is the state of things as they actually exist, rather than as they may appear or might be imagined. In a wider definition, reality includes everything that is and has been
Being
Being , is an English word used for conceptualizing subjective and objective aspects of reality, including those fundamental to the self —related to and somewhat interchangeable with terms like "existence" and "living".In its objective usage —as in "a being," or "[a] human being" —it...

, whether or not it is observable
Observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...

 or comprehensible
Comprehension (logic)
In logic, the comprehension of an object is the totality of intensions, that is, attributes, characters, marks, properties, or qualities, that the object possesses, or else the totality of intensions that are pertinent to the context of a given discussion...

. A still more broad definition includes everything that has existed, exists, or will exist.

Philosophers, mathematicians, and others ancient and modern such as Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

, Plato
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

, Frege, Wittgenstein, Russell
Bertrand Russell
Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS was a British philosopher, logician, mathematician, historian, and social critic. At various points in his life he considered himself a liberal, a socialist, and a pacifist, but he also admitted that he had never been any of these things...

 etc., have made a distinction between thought
Thought
"Thought" generally refers to any mental or intellectual activity involving an individual's subjective consciousness. It can refer either to the act of thinking or the resulting ideas or arrangements of ideas. Similar concepts include cognition, sentience, consciousness, and imagination...

 corresponding to reality, coherent abstractions, and that which cannot even be rationally
Reason
Reason is a term that refers to the capacity human beings have to make sense of things, to establish and verify facts, and to change or justify practices, institutions, and beliefs. It is closely associated with such characteristically human activities as philosophy, science, language, ...

 thought.
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Quotations

Reality is that which, when you stop believing in it, doesn't go away.

Philip K. Dick, in "How To Build A Universe That Doesn't Fall Apart Two Days Later" (1978)

Reality leaves a lot to the imagination.

John Lennon, quoted in Sunday Herald Sun (19 January 2003)

It is not the form of things that must be attended to but their spirit. The real is what matters, not the apparent. In politics, reality is that which is unseen. ~ José Martí

I'm not crazy about reality, but it's still the only place to get a decent meal.

Groucho Marx, quoted in Philosophy on the Go‎ (2007) by Joey Green, p. 78

The first thing necessary for a constructive dealing with time is to learn to live in the reality of the present moment. For psychologically speaking, this present moment is all we have.

Rollo May, in Man’s Search for Himself (1953)

Consciousness is unquantifiable, a ghost in the machine, barely considered real at all, though in a sense this flickering mosaic of awareness is the only true reality that we can ever know.

Alan Moore in What Is Reality?

Ideas, unlike solid structures, do not perish. They remain immortal, immaterial and everywhere, like all Divine things. Ideas are a golden, savage landscape that we wander unaware, without a map. Be careful: in the last analysis, reality may be exactly what we think it is.

Alan Moore in What Is Reality?

Reality is what you make of it.

Prot in "K-PAX" (1995)

There is no reality but God, says the completely surrendered sheik, who is an ocean for all beings.

Rumi|Jelaluddin Rumi, in The Essential Rumi (1995) translated by Coleman Barks with John Moyne, A. J. Arberry and Reynold Nicholson; "The Grasses" in Ch. 4 Spring Giddiness, p. 44

You knock at the door of Reality. You shake your thought wings, loosen your shoulders, and open.

Rumi|Jelaluddin Rumi, in The Essential Rumi (1995) translated by Coleman Barks with John Moyne, A. J. Arberry and Reynold Nicholson; "The Gift of Water" Ch. 18 The Three Fish, p. 200
Encyclopedia
In philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, reality is the state of things as they actually exist, rather than as they may appear or might be imagined. In a wider definition, reality includes everything that is and has been
Being
Being , is an English word used for conceptualizing subjective and objective aspects of reality, including those fundamental to the self —related to and somewhat interchangeable with terms like "existence" and "living".In its objective usage —as in "a being," or "[a] human being" —it...

, whether or not it is observable
Observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...

 or comprehensible
Comprehension (logic)
In logic, the comprehension of an object is the totality of intensions, that is, attributes, characters, marks, properties, or qualities, that the object possesses, or else the totality of intensions that are pertinent to the context of a given discussion...

. A still more broad definition includes everything that has existed, exists, or will exist.

Philosophers, mathematicians, and others ancient and modern such as Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

, Plato
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

, Frege, Wittgenstein, Russell
Bertrand Russell
Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS was a British philosopher, logician, mathematician, historian, and social critic. At various points in his life he considered himself a liberal, a socialist, and a pacifist, but he also admitted that he had never been any of these things...

 etc., have made a distinction between thought
Thought
"Thought" generally refers to any mental or intellectual activity involving an individual's subjective consciousness. It can refer either to the act of thinking or the resulting ideas or arrangements of ideas. Similar concepts include cognition, sentience, consciousness, and imagination...

 corresponding to reality, coherent abstractions, and that which cannot even be rationally
Reason
Reason is a term that refers to the capacity human beings have to make sense of things, to establish and verify facts, and to change or justify practices, institutions, and beliefs. It is closely associated with such characteristically human activities as philosophy, science, language, ...

 thought. By contrast existence
Existence
In common usage, existence is the world we are aware of through our senses, and that persists independently without them. In academic philosophy the word has a more specialized meaning, being contrasted with essence, which specifies different forms of existence as well as different identity...

is often restricted solely to that which has physical existence
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...

 or has a direct basis in it in the way that thoughts do in the brain.

Reality is often contrasted with what is imaginary, delusional, (only) in the mind
Mind
The concept of mind is understood in many different ways by many different traditions, ranging from panpsychism and animism to traditional and organized religious views, as well as secular and materialist philosophies. Most agree that minds are constituted by conscious experience and intelligent...

, dream
Dream
Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...

s, what is abstract
Abstraction
Abstraction is a process by which higher concepts are derived from the usage and classification of literal concepts, first principles, or other methods....

, what is false
Lie
For other uses, see Lie A lie is a type of deception in the form of an untruthful statement, especially with the intention to deceive others....

, or what is fictional. The truth
Truth
Truth has a variety of meanings, such as the state of being in accord with fact or reality. It can also mean having fidelity to an original or to a standard or ideal. In a common usage, it also means constancy or sincerity in action or character...

 refers to what is real, while falsity
Falsity
Falsity or falsehood is a perversion of truth originating in the deceitfulness of one party, and culminating in the damage of another party...

 refers to what is not. Fiction
Fiction
Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

s are not considered real.

Truth vs. Fact


The term "truth" has no single definition about which a majority of professional philosophers and scholars agree, and various theories of truth continue to be debated. Metaphysical objectivism holds that truths are independent of our beliefs; except for propositions that are actually about our beliefs or sensations, what is true or false is independent of what we think is true or false. According to some trends in philosophy, such as postmodernism
Postmodernism
Postmodernism is a philosophical movement evolved in reaction to modernism, the tendency in contemporary culture to accept only objective truth and to be inherently suspicious towards a global cultural narrative or meta-narrative. Postmodernist thought is an intentional departure from the...

/post-structuralism
Post-structuralism
Post-structuralism is a label formulated by American academics to denote the heterogeneous works of a series of French intellectuals who came to international prominence in the 1960s and '70s...

, truth is subjective. When two or more individuals agree upon the interpretation and experience of a particular event, a consensus about an event and its experience begins to be formed. This being common to a few individuals or a larger group, then becomes the "truth" as seen and agreed upon by a certain set of people – the consensus reality
Consensus reality
Consensus reality is an approach to answering the philosophical question "What is real?" It gives a practical answer: reality is either what exists, or what we can agree seems to exist....

. Thus one particular group
Group (sociology)
In the social sciences a social group can be defined as two or more humans who interact with one another, share similar characteristics and collectively have a sense of unity...

 may have a certain set of agreed-upon truths, while another group might have a different set. This allows different communities and societies to have very different notions
Notion (philosophy)
A notion in philosophy is a reflection in the mind of real objects and phenomena in their essential features and relations. Notions are usually described in terms of scope and content...

 of reality and truth about the external world. The religion
Religion
Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...

 and beliefs of people or communities are one example of this level of socially constructed reality. Truth cannot simply be considered truth if one speaks and another hears because individual bias and fallibility challenge the idea that certainty or objectivity are easily grasped. For anti-realists
Anti-realism
In analytic philosophy, the term anti-realism is used to describe any position involving either the denial of an objective reality of entities of a certain type or the denial that verification-transcendent statements about a type of entity are either true or false...

, the inaccessibility of any final, objective truth means that there is no truth beyond the socially accepted consensus. (Although this means there are many truths, not a single truth.)

For realists
Philosophical realism
Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....

, the world is a set of definite facts, which exist independently of human perceptions ("The world is all that is the case" – Tractatus Logico-Philosophicus
Tractatus Logico-Philosophicus
The Tractatus Logico-Philosophicus is the only book-length philosophical work published by the Austrian philosopher Ludwig Wittgenstein in his lifetime. It was an ambitious project: to identify the relationship between language and reality and to define the limits of science...

), and these facts are the final arbiter of truth. Michael Dummett
Michael Dummett
Sir Michael Anthony Eardley Dummett FBA D.Litt is a British philosopher. He was, until 1992, Wykeham Professor of Logic at the University of Oxford...

 expresses this in terms of the principle
of bivalence: Lady Macbeth
Lady Macbeth
Lady Macbeth may refer to:*Lady Macbeth, from William Shakespeare's play Macbeth**Queen Gruoch of Scotland, the real-life Queen on whom Shakespeare based the character...

 had three children or she did not; a tree falls or it does not. A statement will be true if it corresponds
Correspondence theory of truth
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 that world...

 to these facts – even if the correspondence cannot be established. Thus the dispute between the realist and anti-realist conception of truth hinges on reactions to the epistemic accessibility (knowability, graspability) of facts.

A "fact
Fact
A fact is something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability, that is whether it can be shown to correspond to experience. Standard reference works are often used to check facts...

" or factual entity, on the other hand, is a phenomenon
Phenomenon
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

 that is perceived as an elemental principle. It is rarely one that could be subject to personal interpretation. Instead, it is most often an observed phenomenon of the natural world. The proposition that "viewed from most places on Earth, the Sun rises in the east" is a fact. It is a fact for people belonging to any group or nationality, regardless of which language they speak or which part of the hemisphere they come from. The Galilean
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

 proposition in support of the Copernican theory
Theory
The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

, that the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 is the center of the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

, is one that states the fact of the natural world
Nature
Nature, in the broadest sense, is equivalent to the natural world, physical world, or material world. "Nature" refers to the phenomena of the physical world, and also to life in general...

. However, during his lifetime Galileo was ridiculed for that factual proposition, because far too few people had a consensus about it in order to accept it as a truth, and at the time the Ptolemaic model
Geocentric model
In astronomy, the geocentric model , is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece...

 was just as accurate a predictor. Fewer propositions are factual in content in the world, as compared to the many truths shared by various communities, which are also fewer than the innumerable individual world view
World view
A comprehensive world view is the fundamental cognitive orientation of an individual or society encompassing the entirety of the individual or society's knowledge and point-of-view, including natural philosophy; fundamental, existential, and normative postulates; or themes, values, emotions, and...

s. Much of scientific exploration
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

, experimentation, interpretation and analysis
Scientific method
Scientific method refers to a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering empirical and measurable evidence subject to specific principles of...

 is done on this level.

This view of reality is expressed in Philip K. Dick
Philip K. Dick
Philip Kindred Dick was an American novelist, short story writer and essayist whose published work is almost entirely in the science fiction genre. Dick explored sociological, political and metaphysical themes in novels dominated by monopolistic corporations, authoritarian governments and altered...

's statement that "Reality is that which, when you stop believing in it, doesn't go away."

Reality, world views, and theories of reality


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
A colloquialism is a word or phrase that is common in everyday, unconstrained conversation rather than in formal speech, academic writing, or paralinguistics. Dictionaries often display colloquial words and phrases with the abbreviation colloq. as an identifier...

 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 world views 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
Literary criticism is the study, evaluation, and interpretation of literature. Modern literary criticism is often informed by literary theory, which is the philosophical discussion of its methods and goals...

, and other fields shape various theories of reality. One such belief 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
Robert Anton Wilson , known to friends as "Bob", was an American author and polymath who became at various times a novelist, philosopher, psychologist, essayist, editor, playwright, poet, futurist, civil libertarian and self-described agnostic mystic...

), and they indicate anti-realism
Anti-realism
In analytic philosophy, the term anti-realism is used to describe any position involving either the denial of an objective reality of entities of a certain type or the denial that verification-transcendent statements about a type of entity are either true or false...

 – 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
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...

 and socially
Sociology
Sociology is the study of society. It is a social science—a term with which it is sometimes synonymous—which uses various methods of empirical investigation and critical analysis to develop a body of knowledge about human social activity...

. This idea was elaborated by Thomas Kuhn
Thomas Kuhn
Thomas Samuel Kuhn was an American historian and philosopher of science whose controversial 1962 book The Structure of Scientific Revolutions was deeply influential in both academic and popular circles, introducing the term "paradigm shift," which has since become an English-language staple.Kuhn...

 in his book The Structure of Scientific Revolutions
The Structure of Scientific Revolutions
The Structure of Scientific Revolutions , by Thomas Kuhn, is an analysis of the history of science. Its publication was a landmark event in the history, philosophy, and sociology of scientific knowledge and it triggered an ongoing worldwide assessment and reaction in — and beyond — those scholarly...

(1962). The Social Construction of Reality
The Social Construction of Reality
The Social Construction of Reality is a book about the sociology of knowledge written by Peter L. Berger and Thomas Luckmann and published in 1966....

 a book about the sociology of knowledge
Sociology of knowledge
The Sociology of knowledge is the study of the relationship between human thought and the social context within which it arises, and of the effects prevailing ideas have on societies...

 written by Peter L. Berger
Peter L. Berger
Peter Ludwig Berger is an Austrian-born American sociologist well known for his work, co-authored with Thomas Luckmann, The Social Construction of Reality: A Treatise in the Sociology of Knowledge .-Biography:...

 and Thomas Luckmann
Thomas Luckmann
Thomas Luckmann is a German sociologist of Slovene origin. His main areas of research are the sociology of communication, Sociology of knowledge, sociology of religion, and the philosophy of science.- Biography :...

 was published in 1966.

Western philosophy


Philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 addresses two different aspects of the topic of reality: the nature of reality itself, and the relationship between the mind
Mind
The concept of mind is understood in many different ways by many different traditions, ranging from panpsychism and animism to traditional and organized religious views, as well as secular and materialist philosophies. Most agree that minds are constituted by conscious experience and intelligent...

 (as well as language
Language
Language may refer either to the specifically human capacity for acquiring and using complex systems of communication, or to a specific instance of such a system of complex communication...

 and culture
Culture
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...

) and reality.

On the one hand, ontology
Ontology
Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...

 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
Category of being
In metaphysics , the different kinds or ways of being are called categories of being or simply categories. To investigate the categories of being is to determine the most fundamental and the broadest classes of entities...

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

On the other hand, particularly in discussions of objectivity
Objectivity (philosophy)
Objectivity is a central philosophical concept which has been variously defined by sources. A proposition is generally considered to be objectively true when its truth conditions are met and are "mind-independent"—that is, not met by the judgment of a conscious entity or subject.- Objectivism...

 that have feet in both metaphysics
Metaphysics
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

 and epistemology, philosophical discussions of "reality" often concern the ways in which reality is, or is not, in some way dependent upon (or, to use fashionable jargon
Jargon
Jargon is terminology which is especially defined in relationship to a specific activity, profession, group, or event. The philosophe Condillac observed in 1782 that "Every science requires a special language because every science has its own ideas." As a rationalist member of the Enlightenment he...

, "constructed" out of) mental and cultural factors such as perceptions, beliefs, and other mental states, as well as cultural artifacts, such as religion
Religion
Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...

s and political movement
Political movement
A political movement is a social movement in the area of politics. A political movement may be organized around a single issue or set of issues, or around a set of shared concerns of a social group...

s, on up to the vague notion of a common cultural world view
World view
A comprehensive world view is the fundamental cognitive orientation of an individual or society encompassing the entirety of the individual or society's knowledge and point-of-view, including natural philosophy; fundamental, existential, and normative postulates; or themes, values, emotions, and...

, or Weltanschauung.

The view that there is a reality independent of any beliefs, perceptions, etc., is called realism
Philosophical realism
Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....

. 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.

One can also speak of anti-realism about the same objects. Anti-realism
Anti-realism
In analytic philosophy, the term anti-realism is used to describe any position involving either the denial of an objective reality of entities of a certain type or the denial that verification-transcendent statements about a type of entity are either true or false...

is the latest in a long series of terms for views opposed to realism. Perhaps the first was idealism, so called because reality was said to be in the mind, or a product of our ideas. Berkeleyan idealism is the view, propounded by the Irish empiricist
Empiricism
Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

 George Berkeley
George Berkeley
George Berkeley , also known as Bishop Berkeley , was an Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism"...

, that the objects of perception are actually ideas in the mind. In this view, one might be tempted to say that reality is a "mental construct"; this is not quite accurate, however, since in Berkeley's view perceptual ideas are created and coordinated by God. By the 20th century, views similar to Berkeley's were called phenomenalism
Phenomenalism
Phenomenalism is the view that physical objects do not exist as things in themselves but only as perceptual phenomena or sensory stimuli situated in time and in space...

. 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
Bertrand Russell
Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS was a British philosopher, logician, mathematician, historian, and social critic. At various points in his life he considered himself a liberal, a socialist, and a pacifist, but he also admitted that he had never been any of these things...

, 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 event
Mental event
A mental event is a particular occurrence of something going on in the mind or mind substitute. It can be a thought, a dream, a feeling, a realization, or any other mental activity. Mental events are not limited to human thought but can be associated with animal and artificial intelligence as...

s. 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
Social constructionism
Social constructionism and social constructivism are sociological theories of knowledge that consider how social phenomena or objects of consciousness develop in social contexts. A social construction is a concept or practice that is the construct of a particular group...

, is one variety of anti-realism. Cultural relativism
Cultural relativism
Cultural relativism is the principle that an individual human's beliefs and activities should be understood by others in terms of that individual's own culture. This principle was established as axiomatic in anthropological research by Franz Boas in the first few decades of the 20th century and...

 is the view that social issues
Social issues
Social issues are controversial issues which relate to people's personal lives and interactions. Social issues are distinguished from economic issues...

 such as morality are not absolute, but at least partially cultural artifact
Cultural artifact
A cultural artifact is a term used in the social sciences, particularly anthropology, ethnology, and sociology for anything created by humans which gives information about the culture of its creator and users...

.

A correspondence theory of knowledge
Knowledge
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

 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
Scientific method
Scientific method refers to a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering empirical and measurable evidence subject to specific principles of...

 can verify
Empiricism
Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

 that a statement is true based on the observable evidence that a thing exists. Many humans can point to the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

 and say that this mountain range
Mountain range
A mountain range is a single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, formation, and age; a component part of a mountain system or of a mountain chain...

 exists, and continues to exist even if no one is observing it or making statements about it.

Being


The nature of being
Being
Being , is an English word used for conceptualizing subjective and objective aspects of reality, including those fundamental to the self —related to and somewhat interchangeable with terms like "existence" and "living".In its objective usage —as in "a being," or "[a] human being" —it...

 is a perennial topic in metaphysics. For, instance Parmenides
Parmenides
Parmenides of Elea was an ancient Greek philosopher born in Elea, a Greek city on the southern coast of Italy. He was the founder of the Eleatic school of philosophy. The single known work of Parmenides is a poem, On Nature, which has survived only in fragmentary form. In this poem, Parmenides...

 taught that reality was a single unchanging Being, whereas Heraclitus
Heraclitus
Heraclitus of Ephesus was a pre-Socratic Greek philosopher, a native of the Greek city Ephesus, Ionia, on the coast of Asia Minor. He was of distinguished parentage. Little is known about his early life and education, but he regarded himself as self-taught and a pioneer of wisdom...

 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 is an attempt to list the fundamental constituents of reality. The question of whether or not existence
Existence
In common usage, existence is the world we are aware of through our senses, and that persists independently without them. In academic philosophy the word has a more specialized meaning, being contrasted with essence, which specifies different forms of existence as well as different identity...

 is a predicate has been discussed since the Early Modern period, not least in relation to the ontological argument for the existence of God. Existence, that something is, has been contrasted with essence
Essence
In philosophy, essence is the attribute or set of attributes that make an object or substance what it fundamentally is, and which it has by necessity, and without which it loses its identity. Essence is contrasted with accident: a property that the object or substance has contingently, without...

, the question of what something is.
Since existence without essence seems blank, it associated with nothingness by philosophers such as Hegel. Nihilism
Nihilism
Nihilism is the philosophical doctrine suggesting the negation of one or more putatively meaningful aspects of life. Most commonly, nihilism is presented in the form of existential nihilism which argues that life is without objective meaning, purpose, or intrinsic value...

 represents an extremely negative view of being, the absolute a positive one.

Perception


The question of direct or "naïve" realism, as opposed to indirect or "representational" realism, arises in the philosophy of perception
Philosophy of perception
The philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledge of, the world. Any explicit account of perception requires a commitment to one of a variety of ontological or...

 and of mind
Philosophy of mind
Philosophy of mind is a branch of philosophy that studies the nature of the mind, mental events, mental functions, mental properties, consciousness and their relationship to the physical body, particularly the brain. The mind-body problem, i.e...

 out of the debate over the nature of conscious
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...

 experience
Qualia
Qualia , singular "quale" , from a Latin word meaning for "what sort" or "what kind," is a term used in philosophy to refer to subjective conscious experiences as 'raw feels'. Examples of qualia are the pain of a headache, the taste of wine, the experience of taking a recreational drug, or the...

; the epistemological question of whether the world we see around us is the real world itself or merely an internal perceptual copy of that world generated by neural processes in our brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

. Naïve realism
Naïve realism
Naïve realism, also known as direct realism or common sense realism, is a philosophy of mind rooted in a common sense theory of perception that claims that the senses provide us with direct awareness of the external world...

 is known as direct realism when developed to counter indirect or representative realism, also known as epistemological dualism
Dualism
Dualism denotes a state of two parts. The term 'dualism' was originally coined to denote co-eternal binary opposition, a meaning that is preserved in metaphysical and philosophical duality discourse but has been diluted in general or common usages. Dualism can refer to moral dualism, Dualism (from...

, the philosophical
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 position that our conscious experience is not of the real world itself but of an internal representation, a miniature virtual-reality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...

 replica of the world.

Abstract objects and mathematics


The status of abstract
Abstraction (mathematics)
Abstraction in mathematics is the process of extracting the underlying essence of a mathematical concept, removing any dependence on real world objects with which it might originally have been connected, and generalising it so that it has wider applications or matching among other abstract...

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

In the philosophy of mathematics
Philosophy of mathematics
The philosophy of mathematics is the branch of philosophy that studies the philosophical assumptions, foundations, and implications of mathematics. The aim of the philosophy of mathematics is to provide an account of the nature and methodology of mathematics and to understand the place of...

, the best known form of realism about numbers is Platonic realism
Platonic realism
Platonic realism is a philosophical term usually used to refer to the idea of realism regarding the existence of universals or abstract objects after the Greek philosopher Plato , a student of Socrates. As universals were considered by Plato to be ideal forms, this stance is confusingly also called...

, which grants them abstract, immaterial existence. Other forms of realism identify mathematics with the concrete physical universe.

Anti-realist stances include formalism
Formalism (mathematics)
In foundations of mathematics, philosophy of mathematics, and philosophy of logic, formalism is a theory that holds that statements of mathematics and logic can be thought of as statements about the consequences of certain string manipulation rules....

 and fictionalism.

Some approaches are selectively realistic about some mathematical objects but not others. Finitism
Finitism
In the philosophy of mathematics, one of the varieties of finitism is an extreme form of constructivism, according to which a mathematical object does not exist unless it can be constructed from natural numbers in a finite number of steps...

 rejects infinite quantities. ultra-finitism accepts finite quantities up to a certain amount. Constructivism
Constructivism (mathematics)
In the philosophy of mathematics, constructivism asserts that it is necessary to find a mathematical object to prove that it exists. When one assumes that an object does not exist and derives a contradiction from that assumption, one still has not found the object and therefore not proved its...

 and intuitionism
Intuitionism
In the philosophy of mathematics, intuitionism, or neointuitionism , is an approach to mathematics as the constructive mental activity of humans. That is, mathematics does not consist of analytic activities wherein deep properties of existence are revealed and applied...

 are realistic about objects that can be explicitly constructed, but reject the use of the principle of the excluded middle to prove existence by reductio ad absurdum
Reductio ad absurdum
In logic, proof by contradiction is a form of proof that establishes the truth or validity of a proposition by showing that the proposition's being false would imply a contradiction...

.

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

An extreme form of realism about mathematics is the mathematical multiverse hypothesis advanced by Max Tegmark
Max Tegmark
Max Tegmark is a Swedish-American cosmologist. Tegmark is a professor at the Massachusetts Institute of Technology and belongs to the scientific directorate of the Foundational Questions Institute.-Early life:...

. Tegmark's sole postulate is: All structures that exist mathematically also exist physically. That is, in the sense that "in those [worlds] complex enough to contain self-aware substructures [they] will subjectively perceive themselves as existing in a physically 'real' world". The hypothesis suggests that worlds corresponding to different sets of initial conditions, physical constants, or altogether different equations should be considered real. The theory can be considered a form of Platonism
Platonism
Platonism is the philosophy of Plato or the name of other philosophical systems considered closely derived from it. In a narrower sense the term might indicate the doctrine of Platonic realism...

 in that it posits the existence of mathematical entities, but can also be considered a mathematical monism
Philosophy of mathematics
The philosophy of mathematics is the branch of philosophy that studies the philosophical assumptions, foundations, and implications of mathematics. The aim of the philosophy of mathematics is to provide an account of the nature and methodology of mathematics and to understand the place of...

 in that it denies that anything exists except mathematical objects.

Properties


The problem of universals is an ancient problem in metaphysics
Metaphysics
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

 about whether universals
Universal (metaphysics)
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 example, suppose there are two chairs in a room, each of...

 exist. Universals are general or abstract qualities, characteristics, properties
Property (philosophy)
In modern philosophy, logic, and mathematics a property is an attribute of an object; a red object is said to have the property of redness. The property may be considered a form of object in its own right, able to possess other properties. A property however differs from individual objects in that...

, kinds or relations, such as being male/female, solid/liquid/gas or a certain colour, that can be predicated of individuals or particulars or that individuals or particulars can be regarded as sharing or participating in. For example, Scott, Pat, and Chris have in common the universal quality of being human or humanity.

The realist school claims that universals are real – they exist and are distinct from the particulars that instantiate them. There are various forms of realism. Two major forms are Platonic realism
Platonic realism
Platonic realism is a philosophical term usually used to refer to the idea of realism regarding the existence of universals or abstract objects after the Greek philosopher Plato , a student of Socrates. As universals were considered by Plato to be ideal forms, this stance is confusingly also called...

 and Aristotelian realism. Platonic realism is the view that universals are real entities and they exist independent of particulars. Aristotelian realism, on the other hand, is the view that universals are real entities, but their existence is dependent on the particulars that exemplify them.

Nominalism
Nominalism
Nominalism is a metaphysical view in philosophy according to which general or abstract terms and predicates exist, while universals or abstract objects, which are sometimes thought to correspond to these terms, do not exist. Thus, there are at least two main versions of nominalism...

 and conceptualism
Conceptualism
Conceptualism is a philosophical theory that explains universality of particulars as conceptualized frameworks situated within the thinking mind. Intermediate between Nominalism and Realism, the conceptualist view approaches the metaphysical concept of universals from a perspective that denies...

 are the main forms of anti-realism about universals.

Time and space



A traditional realist
Philosophical realism
Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....

 position in ontology
Ontology
Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...

 is that time and space have existence apart from the human mind. Idealists
Idealism
In philosophy, idealism is the family of views which assert that reality, or reality as we can know it, is fundamentally mental, mentally constructed, or otherwise immaterial. Epistemologically, idealism manifests as a skepticism about the possibility of knowing any mind-independent thing...

 deny or doubt the existence of objects independent of the mind. Some anti-realists
Anti-realism
In analytic philosophy, the term anti-realism is used to describe any position involving either the denial of an objective reality of entities of a certain type or the denial that verification-transcendent statements about a type of entity are either true or false...

 whose ontological position is that objects outside the mind do exist, nevertheless doubt the independent existence of time and space.

Kant
Immanuel Kant
Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....

, in the Critique of Pure Reason
Critique of Pure Reason
The Critique of Pure Reason by Immanuel Kant, first published in 1781, second edition 1787, is considered one of the most influential works in the history of philosophy. Also referred to as Kant's "first critique," it was followed by the Critique of Practical Reason and the Critique of Judgement...

, described time as an a priori
A priori and a posteriori (philosophy)
The terms a priori and a posteriori are used in philosophy to distinguish two types of knowledge, justifications or arguments...

notion that, together with other a priori notions such as space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...

, allows us to comprehend sense experience. Kant denies that either space or time are substance
Substance theory
Substance theory, or substance attribute theory, is an ontological theory about objecthood, positing that a substance is distinct from its properties. A thing-in-itself is a property-bearer that must be distinguished from the properties it bears....

, 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
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...

s are used to quantify
Quantity
Quantity is a property that can exist as a magnitude or multitude. Quantities can be compared in terms of "more" or "less" or "equal", or by assigning a numerical value in terms of a unit of measurement. Quantity is among the basic classes of things along with quality, substance, change, and relation...

 how far apart object
Physical body
In physics, a physical body or physical object is a collection of masses, taken to be one...

s are, and temporal measurements are used to quantitatively compare the interval between (or duration of) events. Although
space and time are held to be transcedentally ideal in this sense, they are also empirically real, i.e. not mere illusions.

Idealist writers such as J. M. E. McTaggart
J. M. E. McTaggart
John McTaggart was an 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 philosophy of Hegel and among the most notable of the British idealists.-Personal life:J. M. E. McTaggart was born in 1866...

 in The Unreality of Time
The Unreality of Time
The Unreality of Time is the best-known philosophical work of the Cambridge idealist J. M. E. McTaggart. In the paper, first published in 1908 in Mind 17: 457-73, McTaggart argues that time is unreal because our descriptions of time are either contradictory, circular, or insufficient...

have argued that time is an illusion.

As well as differing about the reality of time as a whole, metaphysical theories of time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

 can differ in their ascriptions of reality to the past
Past
Most generally, the past is a term used to indicate the totality of events which occurred before a given point in time. The past is contrasted with and defined by the present and the future. The concept of the past is derived from the linear fashion in which human observers experience time, and is...

, present
Present
Present is a time that is neither past nor future.Present may also refer to:- Time and timing :* Present tense, the grammatical tense of a verb* Before Present, radiocarbon dates relative to AD 1950* Presenting, a medical term* Presenteeism...

 and future
Future
The future is the indefinite time period after the present. Its arrival is considered inevitable due to the existence of time and the laws of physics. Due to the nature of the reality and the unavoidability of the future, everything that currently exists and will exist is temporary and will come...

 separately.
  • Presentism
    Presentism (philosophy of time)
    Saint Augustine proposed that the present is a knife edge between the past and the future and could not contain any extended period of time. This seems evident because, if the present is extended, it must have separate parts - but these must be simultaneous if they are truly part of the present...

     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
    Theory of relativity
    The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance....

    .
  • The growing block universe
    Growing block universe
    According to the Growing Block Universe or The Growing Block View theory of time, the past and present exist and the future does not exist. The present is an objective property, to be compared with a moving spotlight. By the passage of time more of the world comes into being, therefore the block...

     theory holds that past and present are real, but the future is not.


Time, and the related concepts of process
Process (philosophy)
In philosophy and systems theory, basic processes, or logical homologies as they were termed by Ludwig von Bertalanffy, are unifying principles which operate in many different systemic contexts. For example, feedback is a principle that figures prominently in the science of cybernetics...

 and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 are central to the system-building metaphysics of A. N. Whitehead and Charles Hartshorne
Charles Hartshorne
Charles Hartshorne was a prominent American philosopher who concentrated primarily on the philosophy of religion and metaphysics. He developed the neoclassical idea of God and produced a modal proof of the existence of God that was a development of St. Anselm's Ontological Argument...

.

Possible worlds


The term "possible world
Possible world
In philosophy and logic, the concept of a possible world is used to express modal claims. The concept of possible worlds is common in contemporary philosophical discourse and has also been disputed.- Possibility, necessity, and contingency :...

" goes back to Leibniz's theory of possible worlds, used to analyse necessity
Necessity
In U.S. criminal law, necessity may be either a possible justification or an exculpation for breaking the law. Defendants seeking to rely on this defense argue that they should not be held liable for their actions as a crime because their conduct was necessary to prevent some greater harm and when...

, possibility
Logical possibility
A logically possible proposition is one that can be asserted without implying a logical contradiction. This is to say that a proposition is logically possible if there is some coherent way for the world to be, under which the proposition would be true...

, and similar modal notions
Modal logic
Modal logic is a type of formal logic that extends classical propositional and predicate logic to include operators expressing modality. Modals — words that express modalities — qualify a statement. For example, the statement "John is happy" might be qualified by saying that John is...

. Modal realism
Modal realism
Modal realism is the view, notably propounded by David Kellogg Lewis, that all possible worlds are as real as the actual world. It is based on the following tenets: possible worlds exist; possible worlds are not different in kind from the actual world; possible worlds are irreducible entities; the...

 is the view, notably propounded by David Kellogg Lewis
David Kellogg Lewis
David Kellogg Lewis was an American philosopher. Lewis taught briefly at UCLA and then at Princeton from 1970 until his death. He is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years...

, that all possible worlds
Possible Worlds
Possible Worlds may refer to:* Possible worlds, a concept in philosophy* Possible Worlds , by John Mighton** Possible Worlds , by Robert Lepage, based on the Mighton play* Possible Worlds , by Peter Porter...

 are as real as the actual world. In short: the actual world is regarded as merely one among an infinite
Infinity
Infinity is a concept in many fields, most predominantly mathematics and physics, that refers to a quantity without bound or end. People have developed various ideas throughout history about the nature of infinity...

 set
Set theory
Set theory is the branch of mathematics that studies sets, which are collections of objects. Although any type of object can be collected into a set, set theory is applied most often to objects that are relevant to mathematics...

 of logically possible 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
Physicalism
Physicalism is a philosophical position holding that everything which exists is no more extensive than its physical properties; that is, that there are no kinds of things other than physical things...

 is true, a physical TOE will coincide with a philosophical theory of everything.

The "system building" style of metaphysics
Metaphysics
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

 attempts to answer all the important questions in a coherent way, providing a complete picture of the world. Plato
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

 and Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 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 ratioanlist method of philosophy,that is the technique of deducing the nature of the world by pure apriori reason. Examples from the early modern period include the Leibniz's Monadology
Monadology
The Monadology is one of Gottfried Leibniz’s best known works representing his later philosophy. It is a short text which sketches in some 90 paragraphs a metaphysics of simple substances, or monads.- Text :...

, Descarte's Dualism
Dualism
Dualism denotes a state of two parts. The term 'dualism' was originally coined to denote co-eternal binary opposition, a meaning that is preserved in metaphysical and philosophical duality discourse but has been diluted in general or common usages. Dualism can refer to moral dualism, Dualism (from...

, Spinoza's Monism
Monism
Monism is any philosophical view which holds that there is unity in a given field of inquiry. Accordingly, some philosophers may hold that the universe is one rather than dualistic or pluralistic...

. Hegel's Absolute idealism
Absolute idealism
Absolute idealism is an ontologically monistic philosophy attributed to G. W. F. Hegel. It is Hegel's account of how being is ultimately comprehensible as an all-inclusive whole. Hegel asserted that in order for the thinking subject to be able to know its object at all, there must be in some...

 and Whitehead
Whitehead
-With common given names on further disambiguation pages:*Alan Whitehead *George Whitehead *Henry Whitehead *James Whitehead *John Whitehead...

's Process philosophy
Process philosophy
Process philosophy identifies metaphysical reality with change and dynamism. Since the time of Plato and Aristotle, philosophers have posited true reality as "timeless", based on permanent substances, whilst processes are denied or subordinated to timeless substances...

 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
Stephen Hawking
Stephen William Hawking, CH, CBE, FRS, FRSA is an English theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity...

 wrote in A Brief History of Time
A Brief History of Time
A Brief History of Time is a popular science book written by renown physicist Stephen Hawking and first published by the Bantam Dell Publishing Group in 1988. It became a best-seller and has sold more than 10 million copies...

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?”.

Phenomenological reality


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 individual and hence is called phenomenological. While this
form of reality might be common to others as well, it could at times also be so unique to oneself as to never be experienced or agreed upon by anyone else. Much of the kind of experience deemed spiritual
Spirituality
Spirituality can refer to an ultimate or an alleged immaterial reality; an inner path enabling a person to discover the essence of his/her being; or the “deepest values and meanings by which people live.” Spiritual practices, including meditation, prayer and contemplation, are intended to develop...

 occurs on this level of reality.

Phenomenology is a philosophical method
Philosophical method
Philosophical method is the study of how to do philosophy. A common view among philosophers is that philosophy is distinguished by the methods that philosophers follow in addressing philosophical questions...

 developed in the early years of the twentieth century by Edmund Husserl
Edmund Husserl
Edmund Gustav Albrecht Husserl was a philosopher and mathematician and the founder of the 20th century philosophical school of phenomenology. He broke with the positivist orientation of the science and philosophy of his day, yet he elaborated critiques of historicism and of psychologism in logic...

 and a circle of followers at the universities of Göttingen
Göttingen
Göttingen is a university town in Lower Saxony, Germany. It is the capital of the district of Göttingen. The Leine river runs through the town. In 2006 the population was 129,686.-General information:...

 and Munich
Munich
Munich The city's motto is "" . Before 2006, it was "Weltstadt mit Herz" . Its native name, , is derived from the Old High German Munichen, meaning "by the monks' place". The city's name derives from the monks of the Benedictine order who founded the city; hence the monk depicted on the city's coat...

 in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

. 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
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 phainómenon, meaning "that which appears", and lógos, meaning "study". In Husserl's conception, phenomenology is primarily concerned with making the structures of consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...

, and the phenomena which appear in acts of consciousness, objects of systematic reflection and analysis. Such reflection was to take place from a highly modified "first person
First-person narrative
First-person point of view is a narrative mode where a story is narrated by one character at a time, speaking for and about themselves. First-person narrative may be singular, plural or multiple as well as being an authoritative, reliable or deceptive "voice" and represents point of view in the...

" 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
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

, including scientific knowledge, and could establish philosophy as a "rigorous science".

Husserl's conception of phenomenology has been criticised and developed not only by himself, but also by his student and assistant Martin Heidegger
Martin Heidegger
Martin Heidegger was a German philosopher known for his existential and phenomenological explorations of the "question of Being."...

, by existentialists, such as Maurice Merleau-Ponty
Maurice Merleau-Ponty
Maurice Merleau-Ponty was a French phenomenological philosopher, strongly influenced by Karl Marx, Edmund Husserl and Martin Heidegger in addition to being closely associated with Jean-Paul Sartre and Simone de Beauvoir...

, Jean-Paul Sartre
Jean-Paul Sartre
Jean-Paul Charles Aymard Sartre was a French existentialist philosopher, playwright, novelist, screenwriter, political activist, biographer, and literary critic. He was one of the leading figures in 20th century French philosophy, particularly Marxism, and was one of the key figures in literary...

, and by other philosophers, such as Paul Ricoeur
Paul Ricoeur
Paul Ricœur was a French philosopher best known for combining phenomenological description with hermeneutic interpretation...

, Emmanuel Levinas
Emmanuel Lévinas
Emmanuel Levinas was a Lithuanian-born French Jewish philosopher and Talmudic commentator.-Life:Emanuelis Levinas received a traditional Jewish education in Lithuania...

, and Dietrich von Hildebrand
Dietrich von Hildebrand
Dietrich von Hildebrand was a German Catholic philosopher and theologian who was called by Pope Pius XII "the 20th Century Doctor of the Church."...

.

Skeptical hypotheses


Skeptical hypotheses in philosophy suggest that reality is 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
    Brain in a vat
    In philosophy, the brain in a vat is an element used in a variety of thought experiments intended to draw out certain features of our ideas of knowledge, reality, truth, mind, and meaning...

    " 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, by a mad scientist
    Mad scientist
    A mad scientist is a stock character of popular fiction, specifically science fiction. The mad scientist may be villainous or antagonistic, benign or neutral, and whether insane, eccentric, or simply bumbling, mad scientists often work with fictional technology in order to forward their schemes, if...

    .
  • The "Dream argument
    Dream argument
    The dream argument is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and...

    " of Descartes and Zhuangzi
    Zhuangzi
    Zhuangzi was an influential Chinese philosopher who lived around the 4th century BCE during the Warring States Period, a period corresponding to the philosophical summit of Chinese thought — the Hundred Schools of Thought, and is credited with writing—in part or in whole—a work known by his name,...

     supposes reality to be indistinguishable from a dream.
  • Descarte's Evil demon is a being "as clever and deceitful as he is powerful, who has directed his entire effort to misleading me."
  • The five minute hypothesis (or omphalos hypothesis or Last Thursdayism) suggests that the world was created recently together with records and traces indicating a greater age.
  • The Matrix hypothesis or Simulated reality hypothesis suggest that we might be inside a computer simulation
    Computer simulation
    A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

     or virtual reality
    Virtual reality
    Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...


Scientific realism


Scientific realism
Scientific realism
Scientific realism is, at the most general level, the view that the world described by science is the real world, as it is, independent of what we might take it to be...

 is, at the most general level, the view that the world 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
The philosophy of science is concerned with the assumptions, foundations, methods and implications of science. It is also concerned with the use and merit of science and sometimes overlaps metaphysics and epistemology by exploring whether scientific results are actually a study of truth...

, 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 unobservable entities
Unobservables
An unobservable is an entity whose existence, nature, properties, qualities or relations are not directly observable by man. In philosophy of science typical examples of "unobservables" are atomic particles, the force of gravity, causation and beliefs or desires . However, some philosophers An...

 apparently talked about by scientific theories
Theory
The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

. Generally, those who are scientific realists assert that one can make reliable claims about unobservables (viz., that they have the same ontological
Ontology
Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...

 status) as observables, as opposed to instrumentalism
Instrumentalism
In the philosophy of science, instrumentalism is the view that a scientific theory is a useful instrument in understanding the world. A concept or theory should be evaluated by how effectively it explains and predicts phenomena, as opposed to how accurately it describes objective...

.

Realism and locality in physics


Realism in the sense used by physicists does not equate to realism
Philosophical realism
Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....

 in metaphysics
Metaphysics
Metaphysics is a branch of philosophy concerned with explaining the fundamental nature of being and the world, although the term is not easily defined. Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:...

.
The latter is the claim that the world is in some sense mind-independent: that even if the results of a possible measurement do not pre-exist the act of measurement, that does not require that they are the creation of the observer (contrary to the "consciousness causes collapse" interpretation of quantum mechanics). Furthermore, a mind-independent property does not have to be the value of some physical variable such as position or momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

. A property can be disposition
Disposition
A disposition is 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 but not currently being considered, and in the latter case, to a belief that is...

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
Counterfactual definiteness
In some interpretations of quantum mechanics, counterfactual definiteness is the ability to speak with meaning of the definiteness of the results of measurements that have not been performed...

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

Local realism is a significant feature of classical mechanics, of general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

, and of electrodynamics; but quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

 largely rejects this principle due to the theory of distant quantum entanglement
Quantum entanglement
Quantum entanglement occurs when electrons, molecules even as large as "buckyballs", photons, etc., interact physically and then become separated; the type of interaction is such that each resulting member of a pair is properly described by the same quantum mechanical description , which is...

s, an interpretation rejected by Einstein in the EPR paradox
EPR paradox
The EPR paradox is a topic in quantum physics and the philosophy of science concerning the measurement and description of microscopic systems by the methods of quantum physics...

 but subsequently apparently quantified by Bell's inequalities. Any theory, such as quantum mechanics, that violates Bell's inequalities must abandon either local realism or counterfactual definiteness
Counterfactual definiteness
In some interpretations of quantum mechanics, counterfactual definiteness is the ability to speak with meaning of the definiteness of the results of measurements that have not been performed...

; 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
Interpretation of quantum mechanics
An interpretation of quantum mechanics is a set of statements which attempt to explain how quantum mechanics informs our understanding of nature. Although quantum mechanics has held up to rigorous and thorough experimental testing, many of these experiments are open to different interpretations...

 violate different parts of local realism and/or counterfactual definiteness
Counterfactual definiteness
In some interpretations of quantum mechanics, counterfactual definiteness is the ability to speak with meaning of the definiteness of the results of measurements that have not been performed...

.

Role of the observer 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
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

. Since quantum mechanics involves quantum superposition
Quantum superposition
Quantum superposition is a fundamental principle of quantum mechanics. It holds that a physical system exists in all its particular, theoretically possible states simultaneously; but, when measured, it gives a result corresponding to only one of the possible configurations.Mathematically, it...

s, which are not perceived by observers
Measurement in quantum mechanics
The framework of quantum mechanics requires a careful definition of measurement. The issue of measurement lies at the heart of the problem of the interpretation of quantum mechanics, for which there is currently no consensus....

, 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 Pauli
Wolfgang Ernst Pauli was an Austrian theoretical physicist and one of the pioneers of quantum physics. In 1945, after being nominated by Albert Einstein, he received the Nobel Prize in Physics for his "decisive contribution through his discovery of a new law of Nature, the exclusion principle or...

 and Werner Heisenberg
Werner Heisenberg
Werner Karl Heisenberg was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory...

 believed that it was the observer that produced collapse. This point of view, which was never fully endorsed by Niels Bohr
Niels Bohr
Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in...

, was denounced as mystical and anti-scientific by Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

. Pauli accepted the term, and described quantum mechanics as lucid mysticism.

Heisenberg and Bohr always described quantum mechanics in logical positivist
Logical positivism
Logical positivism is a philosophy that combines empiricism—the idea that observational evidence is indispensable for knowledge—with a version of rationalism incorporating mathematical and logico-linguistic constructs and deductions of epistemology.It may be considered as a type of analytic...

 terms. Bohr also took an active interest in the philosophical implications of quantum theories such as his complementarity
Complementarity
-Mathematics:*Complementary angles, in geometry* Complementarity theory, a concept related to optimization -Physical sciences:* Complementarity , a property of nucleic acid molecules in molecular biology...

, 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
Schrödinger's cat
Schrödinger's cat is a thought experiment, usually described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The scenario presents a cat that might be...

" thought experiment
Thought experiment
A thought experiment or Gedankenexperiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences...

 as "Wigner's friend
Wigner's friend
Wigner's friend is a thought experiment proposed by the physicist Eugene Wigner; it is an extension of the Schrödinger's cat experiment designed as a point of departure for discussing the Quantum mind/body problem.- The thought experiment :...

" and proposed that the consciousness of an observer is the demarcation line which precipitates collapse of the wave function, independent of any realist interpretation. Commonly known as "consciousness causes collapse", this interpretation
Interpretation of quantum mechanics
An interpretation of quantum mechanics is a set of statements which attempt to explain how quantum mechanics informs our understanding of nature. Although quantum mechanics has held up to rigorous and thorough experimental testing, many of these experiments are open to different interpretations...

 of quantum mechanics states that observation
Observation
Observation is either an activity of a living being, such as a human, consisting of receiving knowledge of the outside world through the senses, or the recording of data using scientific instruments. The term may also refer to any data collected during this activity...

 by a conscious observer is what makes the wave function collapse.

The multiverse


The multiverse
Multiverse
The multiverse is the hypothetical set of multiple possible universes that together comprise all of reality.Multiverse may also refer to:-In fiction:* Multiverse , the fictional multiverse used by DC Comics...

 is the hypothetical set of multiple possible universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

s (including the historical universe we consistently experience) that together comprise everything that exists: the entirety of space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...

, time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

, matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

, and energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 as well as the physical law
Physical law
A physical law or scientific law is "a theoretical principle deduced from particular facts, applicable to a defined group or class of phenomena, and expressible by the statement that a particular phenomenon always occurs if certain conditions be present." Physical laws are typically conclusions...

s and constants
Physical constant
A physical constant is a physical quantity that is generally believed to be both universal in nature and constant in time. It can be contrasted with a mathematical constant, which is a fixed numerical value but does not directly involve any physical measurement.There are many physical constants in...

 that describe them. The term was coined in 1895 by the American philosopher and psychologist William James
William James
William James was a pioneering American psychologist and philosopher who was trained as a physician. He wrote influential books on the young science of psychology, educational psychology, psychology of religious experience and mysticism, and on the philosophy of pragmatism...

. The various universes within the multiverse are sometimes called parallel universe
Parallel universe (fiction)
A parallel universe or alternative reality is a hypothetical self-contained separate reality coexisting with one's own. A specific group of parallel universes is called a "multiverse", although this term can also be used to describe the possible parallel universes that constitute reality...

s.

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
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...

, physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

, astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

, religion
Religion
Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...

, philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, transpersonal psychology
Transpersonal psychology
Transpersonal psychology is a form of psychology that studies the transpersonal, self-transcendent or spiritual aspects of the human experience....

 and fiction
Fiction
Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

, particularly in science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 and fantasy
Fantasy
Fantasy is a genre of fiction that commonly uses magic and other supernatural phenomena as a primary element of plot, theme, or setting. Many works within the genre take place in imaginary worlds where magic is common...

. 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.

Scientific theories of everything


A theory of everything
Theory of everything
A theory of everything is a putative theory of theoretical physics that fully explains and links together all known physical phenomena, and predicts the outcome of any experiment that could be carried out in principle....

 (TOE) is a putative theory
Theory
The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

 of theoretical physics
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...

 that fully explains and links together all known physical phenomena, and predicts the outcome of any experiment that could be carried out in principle and is not related to math in anyway.

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
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

 and quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

 are hard to unify. This is one of the unsolved problems in physics
Unsolved problems in physics
This is a list of some of the major unsolved problems in physics. Some of these problems are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result...

.

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
Ijon Tichy
Ijon Tichy is a fictional character who appears in several works of Stanisław Lem, including The Futurological Congress, Peace on Earth, Observation on the Spot, The Star Diaries and Memoirs of a Space Traveller .-Character:Tichy is a space explorer whose interplanetary...

, a character from a cycle of Stanisław Lem's science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 stories of the 1960s, was known to work on the "General Theory of Everything". Physicist John Ellis
John Ellis (physicist)
Jonathan Richard Ellis FRS is a British theoretical physicist who is currently Clerk Maxwell Professor of Theoretical Physics at King's College London. After completing his secondary education at Highgate School, he attended Cambridge University, earning his Ph.D. in theoretical particle physics...

 claims to have introduced the term into the technical literature in an article in Nature in 1986. Over time, the term stuck in popularizations of quantum physics to describe a theory that would unify or explain through a single model the theories of all fundamental interaction
Fundamental interaction
In particle physics, fundamental interactions are the ways that elementary particles interact with one another...

s and of all particles of nature: general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

 for gravitation, and the standard model
Standard Model
The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...

 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
String theory
String theory is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything , a manner of describing the known fundamental forces and matter in a mathematically complete system...

, M theory, and loop quantum gravity
Loop quantum gravity
Loop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...

.

Virtual reality and cyberspace


Virtual reality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...

 (VR) is a term that applies to computer-simulated
Computer simulation
A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

 environments that can simulate physical presence in places in the real world, as well as in imaginary worlds.

The Virtuality Continuum
Virtuality Continuum
thumb|right|400px|Reality-Virtuality Continuum.The Virtuality Continuum is a phrase used to describe a concept that there is a continuous scale ranging between the completely virtual, a Virtuality, and the completely real: Reality. The reality-virtuality continuum therefore encompasses all possible...

 is a phrase used to describe a concept that there is a continuous scale ranging between the completely virtual, a Virtuality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...

, and the completely real: Reality. The reality-virtuality continuum therefore encompasses all possible variations and compositions of real and virtual
Virtual
The term virtual is a concept applied in many fields with somewhat differing connotations, and also, differing denotations.The term has been defined in philosophy as "that which is not real" but may display the salient qualities of the real....

 objects. It has been described as a concept in new media
New media
New media is a broad term in media studies that emerged in the latter part of the 20th century. For example, new media holds out a possibility of on-demand access to content any time, anywhere, on any digital device, as well as interactive user feedback, creative participation and community...

 and computer science
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, but in fact it could be considered a matter of anthropology
Anthropology
Anthropology is the study of humanity. It has origins in the humanities, the natural sciences, and the social sciences. The term "anthropology" is from the Greek anthrōpos , "man", understood to mean mankind or humanity, and -logia , "discourse" or "study", and was first used in 1501 by German...

. 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
Mixed reality
Mixed reality refers to the merging of real and virtual worlds to produce new environments and visualisations where physical and digital objects co-exist and interact in real time...

. This in turn is said to consist of both Augmented Reality
Augmented reality
Augmented reality is a live, direct or indirect, view of a physical, real-world environment whose elements are augmented by computer-generated sensory input such as sound, video, graphics or GPS data. It is related to a more general concept called mediated reality, in which a view of reality is...

, where the virtual augments the real, and Augmented virtuality
Augmented virtuality
Augmented virtuality refers to the merging of real world objects into virtual worlds.As an intermediate case in the Virtuality Continuum, it refers to predominantly virtual spaces, where physical elements, e.g. physical objects or people, are dynamically integrated into, and can interact with the...

, where the real augments the virtual.
Cyberspace
Cyberspace
Cyberspace is the electronic medium of computer networks, in which online communication takes place.The term "cyberspace" was first used by the cyberpunk science fiction author William Gibson, though the concept was described somewhat earlier, for example in the Vernor Vinge short story "True...

, 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
Cyberpunk is a postmodern and science fiction genre noted for its focus on "high tech and low life." The name is a portmanteau of cybernetics and punk, and was originally coined by Bruce Bethke as the title of his short story "Cyberpunk," published in 1983...

 fiction of William Gibson
William Gibson
William Gibson is an American-Canadian science fiction author.William Gibson may also refer to:-Association football:*Will Gibson , Scottish footballer...

 and others. Second life
Second Life
Second Life is an online virtual world developed by Linden Lab. It was launched on June 23, 2003. A number of free client programs, or Viewers, enable Second Life users, called Residents, to interact with each other through avatars...

 and MMORPG
MMORPG
Massively multiplayer online role-playing game is a genre of role-playing video games in which a very large number of players interact with one another within a virtual game world....

s such as World of Warcraft
World of Warcraft
World of Warcraft is a massively multiplayer online role-playing game by Blizzard Entertainment. It is the fourth released game set in the fantasy Warcraft universe, which was first introduced by Warcraft: Orcs & Humans in 1994...

are examples of artificial environments or virtual world
Virtual world
A virtual world is an online community that takes the form of a computer-based simulated environment through which users can interact with one another and use and create objects. The term has become largely synonymous with interactive 3D virtual environments, where the users take the form of...

s (falling some way short of full virtual reality) in cyberspace.

"RL" in internet culture


On the Internet, "real life
Real life
Real life is a term usually used to denote actual human life lived by real people in contrast with the lives of fictional or fantasy characters.-Usage online and in fiction:On the Internet, "real life" refers to life in the real world...

" refers to life in the real world. It generally references life
Personal life
Personal life is the course of an individual's life, especially when viewed as the sum of personal choices contributing to one's personal identity. It is a common notion in modern existence—although more so in more prosperous parts of the world such as Western Europe and North America...

 or consensus reality
Consensus reality
Consensus reality is an approach to answering the philosophical question "What is real?" It gives a practical answer: reality is either what exists, or what we can agree seems to exist....

, in contrast to an environment seen as fiction
Fiction
Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

 or fantasy
Fantasy
Fantasy is a genre of fiction that commonly uses magic and other supernatural phenomena as a primary element of plot, theme, or setting. Many works within the genre take place in imaginary worlds where magic is common...

, such as virtual reality
Virtual reality
Virtual reality , also known as virtuality, is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds...

, lifelike experience
Lifelike experience
Lifelike is an adjective that relates to anything that simulates real life, in accordance with its laws. Its goal is to immerse individuals into what is called a lifelike experience. It gets as close as possible to real life behavior, appearance, senses, etc. therefore enabling its subject to...

, dream
Dream
Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...

s, novel
Novel
A novel is a book of long narrative in literary prose. The genre has historical roots both in the fields of the medieval and early modern romance and in the tradition of the novella. The latter supplied the present generic term in the late 18th century....

s, or movie
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...

s. Online, the acronym "IRL" stands for "in real life", with the meaning "not on the Internet". Sociologists engaged in the study of the Internet have determined that someday, a distinction between online and real-life worlds may seem "quaint", noting that certain types of online activity, such as sexual intrigues, have already made a full transition to complete legitimacy and "reality". The abbreviation
Abbreviation
An abbreviation is a shortened form of a word or phrase. Usually, but not always, it consists of a letter or group of letters taken from the word or phrase...

 "RL" stands for "real life". For example, one can speak of "meeting in RL" someone whom one has met in a chat
Online chat
Online chat may refer to any kind of communication over the Internet, that offers an instantaneous transmission of text-based messages from sender to receiver, hence the delay for visual access to the sent message shall not hamper the flow of communications in any of the directions...

 or on an Internet forum
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 at least temporarily archived...

. It may also be used to express an inability to use the Internet for a time due to "RL problems".

See also


  • Absolute (philosophy)
    Absolute (philosophy)
    The Absolute is the concept of an unconditional reality which transcends limited, conditional, everyday existence. It is sometimes used as an alternate term for "God" or "the Divine", especially, but by no means exclusively, by those who feel that the term "God" lends itself too easily to...

  • Alternate history
  • Advaita
  • Allegory of the Cave
    Allegory of the cave
    The Allegory of the Cave—also known as the Analogy of the Cave, Plato's Cave, or the Parable of the Cave—is an allegory used by the Greek philosopher Plato in his work The Republic to illustrate "our nature in its education and want of education"...

  • Authenticity
    Authenticity
    Authenticity refers to the truthfulness of origins, attributions, commitments, sincerity, devotion, and intentions.Authenticity or Authentic may refer to:*Authentication, having passed the tests thereof...

  • Roland Barthes
    Roland Barthes
    Roland Gérard Barthes was a French literary theorist, philosopher, critic, and semiotician. Barthes' ideas explored a diverse range of fields and he influenced the development of schools of theory including structuralism, semiotics, existentialism, social theory, Marxism, anthropology and...

  • Capgras delusion
    Capgras delusion
    The Capgras delusion theory is a disorder in which a person holds a delusion that a friend, spouse, parent, or other close family member has been replaced by an identical-looking impostor...

  • Charles Fort
    Charles Fort
    Charles Hoy Fort was an American writer and researcher into anomalous phenomena. Today, the terms Fortean and Forteana are used to characterize various such phenomena. Fort's books sold well and are still in print today.-Biography:Charles Hoy Fort was born in 1874 in Albany, New York, of Dutch...

  • Consensus reality
    Consensus reality
    Consensus reality is an approach to answering the philosophical question "What is real?" It gives a practical answer: reality is either what exists, or what we can agree seems to exist....

  • Cotard delusion
    Cotard delusion
    The Cotard delusion or Cotard's syndrome or Walking Corpse Syndrome is a rare neuropsychiatric disorder in which people hold a delusional belief that they are dead , do not exist, are putrefying, or have lost their blood or internal organs...

  • Counterfactual history
  • Delusion
    Delusion
    A delusion is a false belief held with absolute conviction despite superior evidence. Unlike hallucinations, delusions are always pathological...

  • Determinism
    Determinism
    Determinism is the general philosophical thesis that states that for everything that happens there are conditions such that, given them, nothing else could happen. There are many versions of this thesis. Each of them rests upon various alleged connections, and interdependencies of things and...

  • Derealization
    Derealization
    Derealization is an alteration in the perception or experience of the external world so that it seems unreal. Other symptoms include feeling as though one's environment is lacking in spontaneity, emotional coloring and depth. It is a dissociative symptom of many conditions, such as psychiatric and...

  • Phillip K. Dick
  • Dissociation
    Dissociation
    Dissociation is an altered state of consciousness characterized by partial or complete disruption of the normal integration of a person’s normal conscious or psychological functioning. Dissociation is most commonly experienced as a subjective perception of one's consciousness being detached from...

  • Dream
    Dream
    Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep. The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, philosophical intrigue and religious...

  • Dreamtime
    Dreamtime
    In the animist framework of Australian Aboriginal mythology, The Dreaming is a sacred era in which ancestral Totemic Spirit Beings formed The Creation.-The Dreaming of the Aboriginal times:...

     (religion
    Religion
    Religion is a collection of cultural systems, belief systems, and worldviews that establishes symbols that relate humanity to spirituality and, sometimes, to moral values. Many religions have narratives, symbols, traditions and sacred histories that are intended to give meaning to life or to...

    )
  • Dreamworld
    Dreamworld
    Dreamworld is a large theme park situated on the Gold Coast in Queensland. It is currently Australia's largest theme park with over 27 rides including 4 roller coasters. The park is made up of several themed lands: Ocean Parade, Kid's World, Wiggles World, Gold Rush Country, Rocky Hollow, Tiger...

  • E-prime
    E-Prime
    E-Prime is a version of the English language that excludes all forms of the verb to be. E-Prime does not allow conjugations of to be , archaic forms E-Prime (short for English-Prime, sometimes denoted E′) is a version of the English language that excludes all forms of the verb to be. E-Prime does...


  • Emanationism
    Emanationism
    Emanationism is an idea in the cosmology or cosmogony of certain religious or philosophical systems. Emanation, from the Latin emanare meaning "to flow from" or "to pour forth or out of", is the mode by which all things are derived from the First Reality, or Principle...

  • Empiricism
    Empiricism
    Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

  • Existence
    Existence
    In common usage, existence is the world we are aware of through our senses, and that persists independently without them. In academic philosophy the word has a more specialized meaning, being contrasted with essence, which specifies different forms of existence as well as different identity...

  • Explanatory model
    Explanatory model
    An explanatory model is a useful description and explanation of why and how a thing works or an explanation of why a phenomenon is the way it is....

  • False awakening
    False awakening
    A false awakening is a vivid and convincing dream about awakening from sleep, while the dreamer in reality continues to sleep. After a false awakening, subjects often dream they are performing daily morning rituals such as cooking, cleaning and eating...

  • Fiction
    Fiction
    Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

  • Fictionalism
    Fictionalism
    Fictionalism is a methodological theory in philosophy that suggests that statements of a certain sort should not be taken to be literally true, but merely as a useful fiction...

  • Fregoli delusion
    Fregoli delusion
    The Fregoli delusion or the delusion of doubles is a rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise...

  • Imagination
    Imagination
    Imagination, also called the faculty of imagining, is the ability of forming mental images, sensations and concepts, in a moment when they are not perceived through sight, hearing or other senses...

  • Hallucination
    Hallucination
    A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid,...

  • Hyperreality
    Hyperreality
    Hyperreality is used in semiotics and postmodern philosophy to describe a hypothetical inability of consciousness to distinguish reality from fantasy, especially in technologically advanced postmodern societies...

  • Illusion
    Illusion
    An illusion is a distortion of the senses, revealing how the brain normally organizes and interprets sensory stimulation. While illusions distort reality, they are generally shared by most people....

  • Jorge Luis Borges
    Jorge Luis Borges
    Jorge Francisco Isidoro Luis Borges Acevedo , known as Jorge Luis Borges , was an Argentine writer, essayist, poet and translator born in Buenos Aires. In 1914 his family moved to Switzerland where he attended school, receiving his baccalauréat from the Collège de Genève in 1918. The family...

  • Language and thought
    Language and thought
    A variety of different authors, theories and fields purport influences between language and thought.Many point out the seemingly common-sense realization that upon introspection we seem to think in the language we speak...

  • Map and territory
  • Marshall McLuhan
    Marshall McLuhan
    Herbert Marshall McLuhan, CC was a Canadian educator, philosopher, and scholar—a professor of English literature, a literary critic, a rhetorician, and a communication theorist...

  • The Matrix
    The Matrix
    The Matrix is a 1999 science fiction-action film written and directed by Larry and Andy Wachowski, starring Keanu Reeves, Laurence Fishburne, Carrie-Anne Moss, Joe Pantoliano, and Hugo Weaving...


  • Maya (illusion)
    Maya (illusion)
    Maya , in Indian religions, has multiple meanings, usually quoted as "illusion", centered on the fact that we do not experience the environment itself but rather a projection of it, created by us. Maya is the principal deity that manifests, perpetuates and governs the illusion and dream of duality...

  • Mental representation
    Mental representation
    A representation, in philosophy of mind, cognitive psychology, neuroscience, and cognitive science, is a hypothetical internal cognitive symbol that represents external reality, or else a mental process that makes use of such a symbol; "a formal system for making explicit certain entities or types...

  • Nihilism
    Nihilism
    Nihilism is the philosophical doctrine suggesting the negation of one or more putatively meaningful aspects of life. Most commonly, nihilism is presented in the form of existential nihilism which argues that life is without objective meaning, purpose, or intrinsic value...

  • Noumenon
    Noumenon
    The noumenon is a posited object or event that is known without the use of the senses.The term is generally used in contrast with, or in relation to "phenomenon", which refers to anything that appears to, or is an object of, the senses...

  • Nagarjuna
    Nagarjuna
    Nāgārjuna was an important Buddhist teacher and philosopher. Along with his disciple Āryadeva, he is credited with founding the Mādhyamaka school of Mahāyāna Buddhism...

  • Ontology
    Ontology
    Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...

  • Paranormal
    Paranormal
    Paranormal is a general term that designates experiences that lie outside "the range of normal experience or scientific explanation" or that indicates phenomena understood to be outside of science's current ability to explain or measure...

  • Phenomenon
    Phenomenon
    A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

  • Principle of locality
    Principle of locality
    In physics, the principle of locality states that an object is influenced directly only by its immediate surroundings. Experiments have shown that quantum mechanically entangled particles must violate either the principle of locality or the form of philosophical realism known as counterfactual...

  • Psychosis
    Psychosis
    Psychosis means abnormal condition of the mind, and is a generic psychiatric term for a mental state often described as involving a "loss of contact with reality"...

  • Rashomon (film)
    Rashomon (film)
    The bandit's storyTajōmaru, a notorious brigand , claims that he tricked the samurai to step off the mountain trail with him and look at a cache of ancient swords he discovered. In the grove he tied the samurai to a tree, then brought the woman there. She initially tried to defend herself with a...

  • Real world
    Real World
    The real world is another term for reality. It may also refer to:-Television:* The Real World, a television show* "The Real World" , a television episode-Music:* "Real World" , an album by Kokia...

  • Reality in Buddhism
    Reality in Buddhism
    Buddhism evolved a variety of doctrinal/philosophical traditions, each with its distinct ideas of reality. The following are still regularly studied in some branches of the Buddhist tradition: Theravada, Vaibhashika, Sautrantika, Jojitsu, Madhyamika, Yogacara, tiantai, Huayan...

  • Reality shifts (mysticism
    Mysticism
    Mysticism is the knowledge of, and especially the personal experience of, states of consciousness, i.e. levels of being, beyond normal human perception, including experience and even communion with a supreme being.-Classical origins:...

    )
  • Reality-based community
    Reality-based community
    Reality-based community is an informal term in the United States. In the fall of 2004, the phrase "proud member of the reality-based community" was first used to suggest the commentator's opinions are based more on observation than on faith, assumption, or ideology...

     (politics
    Politics
    Politics is a process by which groups of people make collective decisions. The term is generally applied to the art or science of running governmental or state affairs, including behavior within civil governments, but also applies to institutions, fields, and special interest groups such as the...

    )
  • Reality TV
  • Red pill
  • Reification (disambiguation)

  • Sapir-Whorf hypothesis
  • Semiotics
    Semiotics
    Semiotics, also called semiotic studies or semiology, is the study of signs and sign processes , indication, designation, likeness, analogy, metaphor, symbolism, signification, and communication...

  • Simulacrum
    Simulacrum
    Simulacrum , from the Latin simulacrum which means "likeness, similarity", was first recorded in the English language in the late 16th century, used to describe a representation, such as a statue or a painting, especially of a god...

  • Simulated reality
    Simulated reality
    Simulated reality is the proposition that reality could be simulated—perhaps by computer simulation—to a degree indistinguishable from "true" reality. It could contain conscious minds which may or may not be fully aware that they are living inside a simulation....

  • Skepticism
    Skepticism
    Skepticism has many definitions, but generally refers to any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere...

  • Social constructionism
    Social constructionism
    Social constructionism and social constructivism are sociological theories of knowledge that consider how social phenomena or objects of consciousness develop in social contexts. A social construction is a concept or practice that is the construct of a particular group...

  • Solipsism
    Solipsism
    Solipsism is the philosophical idea that only one's own mind is sure to exist. The term comes from Latin solus and ipse . Solipsism as an epistemological position holds that knowledge of anything outside one's own mind is unsure. The external world and other minds cannot be known, and might not...

  • Sunyata
  • Surrealism
    Surrealism
    Surrealism is a cultural movement that began in the early 1920s, and is best known for the visual artworks and writings of the group members....

  • Vanilla Sky
    Vanilla Sky
    Vanilla Sky is a 2001 American psychological thriller film directed, co-produced and co-written by Cameron Crowe. The film is an English-language remake of the 1997 Spanish movie Abre los ojos , the screenplay for which was written by Alejandro Amenábar and Mateo Gil...

  • The Truman Show
    The Truman Show
    The Truman Show is a 1998 American satirical comedy-drama film directed by Peter Weir and written by Andrew Niccol. The cast includes Jim Carrey as Truman Burbank, as well as Laura Linney, Noah Emmerich, Ed Harris and Natascha McElhone...

  • Thoughtform
    Thoughtform
    A thoughtform is a manifestation of mental energy, also known as a tulpa in Tibetan mysticism. Its concept is related to the Western philosophy and practice of magic. links mantras and yantras to thoughtforms:...

  • The Usual Suspects
    The Usual Suspects
    The Usual Suspects is a 1995 American neo-noir film written by Christopher McQuarrie and directed by Bryan Singer. It stars Stephen Baldwin, Gabriel Byrne, Benicio del Toro, Chazz Palminteri, Kevin Pollak, Kevin Spacey and Pete Postlethwaite....

  • Waking Life
    Waking Life
    Waking Life is an American animated film , directed by Richard Linklater and released in 2001. The entire film was shot using digital video and then a team of artists using computers drew stylized lines and colors over each frame.The film focuses on the nature of dreams, consciousness, and...

     (film)
  • Zhuangzi
    Zhuangzi
    Zhuangzi was an influential Chinese philosopher who lived around the 4th century BCE during the Warring States Period, a period corresponding to the philosophical summit of Chinese thought — the Hundred Schools of Thought, and is credited with writing—in part or in whole—a work known by his name,...



External links