Philosophy of space and time is the branch of philosophy concerned with the issues surrounding the ontology, epistemology, and character of space and time. While such ideas have been central to philosophy from its inception, the philosophy of space and time was both an inspiration for and a central aspect of early analytic philosophy. The subject focuses on a number of basic issues, including—but not limited to—whether or not time and space exist independently of the mind, whether they exist independently of one another, what accounts for time's apparently unidirectional flow, whether times other than the present moment exist, and questions about the nature of identity (particularly the nature of identity over time). For other uses, see Philosophy (disambiguation). ... This article is about ontology in philosophy. ... Theory of knowledge redirects here: for other uses, see theory of knowledge (disambiguation) According to Plato, knowledge is a subset of that which is both true and believed Epistemology or theory of knowledge is the branch of philosophy that studies the nature, methods, limitations, and validity of knowledge and belief. ... This article is about the idea of space. ... Look up time in Wiktionary, the free dictionary. ... Analytic philosophy (sometimes, analytical philosophy) is a generic term for a style of philosophy that came to dominate English-speaking countries in the 20th century. ...

Realism and anti-realism

A traditional realist position in ontology is that time and space have existence apart from the human mind. Idealists deny or doubt the existence of objects independent of the mind. Some anti-realists whose ontological position is that objects outside the mind do exist, nevertheless doubt the independent existence of time and space. Contemporary philosophical realism, also referred to as metaphysical realism, is the belief in a reality that is completely ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc. ... This article is about ontology in philosophy. ... This section may require cleanup to meet Wikipedias quality standards. ... In philosophy, the term anti-realism is used to describe any position involving either the denial of the objective reality of entities of a certain type or the insistence that we should be agnostic about their real existence. ...

Kant, in the Critique of Pure Reason, described time as an a priori notion that, together with other a priori notions such as space, allows us to comprehend sense experience. For Kant, neither space nor time are conceived as substances, but rather both are elements of a systematic framework we use to structure our experience. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantitatively compare the interval between (or duration of) events. Kant redirects here. ... Title page of the 1781 edition. ... The terms a priori and a posteriori are used in philosophy to distinguish between two different types of propositional knowledge. ... This article is about the idea of space. ... Look up substance in Wiktionary, the free dictionary. ... Look up Framework in Wiktionary, the free dictionary. ... Measurement is the estimation of the magnitude of some attribute of an object, such as its length or weight, relative to a unit of measurement. ... Quantity is a kind of property which exists as magnitude or multitude. ... A physical body is an object which can be described by the theories of classical mechanics, or quantum mechanics, and experimented upon by physical instruments. ... For other uses of this term, see Spacetime (disambiguation). ...

Idealist writers such as J. M. E. McTaggart in The Unreality of Time have argued that time is an illusion (see also The flow of time below). John McTaggart Ellis McTaggart (1866-1925) was the leading Hegel scholar in England at the beginning of the 20th Century, and friend and teacher of Bertrand Russell and G. E. Moore. ... Wikisource has original text related to this article: The Unreality of Time To meet Wikipedias quality standards, this article or section may require cleanup. ... Philosophy of space and time is the branch of philosophy concerned with the issues surrounding the ontology, epistemology, and character of space and time. ...

The writers discussed here are for the most part realists in this regard; for instance, Gottfried Leibniz held that his monads existed, at least independently of the mind of the observer. Leibniz redirects here. ... Look up monad in Wiktionary, the free dictionary. ...

Absolutism and relationalism

Leibniz and Newton

The great debate between defining notions of space and time as real objects themselves (absolute), or whether they are merely orderings upon actual objects (relational), began between physicists Isaac Newton (via his spokesman, Samuel Clarke) and Gottfried Leibniz in the papers of the Leibniz-Clarke Correspondence. The term absolutism can mean: A belief in absolute truth moral absolutism, the belief that there is some absolute standard of right and wrong political absolutism, a political system where one person holds absolute power, also called apolytarchy from Gr. ... Relationism is a framework of social thought governing political, economic and social behaviour. ... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... Gottfried Leibniz Gottfried Wilhelm von Leibniz (July 1, 1646 in Leipzig - November 14, 1716 in Hannover) was a German philosopher, scientist, mathematician, diplomat, librarian, and lawyer of Sorb descent. ...

Arguing against the absolutist position, Leibniz offers a number of thought experiments with the purpose of showing that there is contradiction in assuming the existence of facts such as absolute location and velocity. These arguments trade heavily on two principles central to his philosophy: the principle of sufficient reason and the identity of indiscernibles. The principle of sufficient reason holds that for every fact there is a reason that is sufficient to explain what and why it is the way it is and not otherwise. The identity of indiscernibles states that if there is no way of telling two entities apart then they are one and the same thing. The principle of sufficient reason states that anything that happens does so for a definite reason. ... The identity of indiscernibles is an ontological principle; i. ...

The example Leibniz uses involves two proposed universes situated in absolute space. The only discernible difference between them is that the latter is positioned five feet to the left of the first. The possibility of the example is only available if such a thing as absolute space exists. Such a situation, however, is not possible according to Leibniz, for if it were, where a universe was positioned in absolute space would have no sufficient reason, as it might very well have been anywhere else. Therefore, it is contradicting the principle of sufficient reason, and there could exist two distinct universes that were in all ways indiscernible, thus contradicting the identity of indiscernibles.

Standing out in Clarke’s (and Newton’s) response to Leibniz arguments is the bucket argument: Water in a bucket, hung from a rope and set to spin, will start with a flat surface. As the water begins to spin in the bucket, the surface of the water will become concave. If the bucket is stopped, the water will continue to spin, and while the spin continues the surface will remain concave. The concave surface is apparently not the result of the interaction of the bucket and the water, since the water is flat when the bucket first starts to spin, becomes concave as the water starts to spin, and remains concave as the bucket stops. Isaac Newtons rotating bucket argument attempts to show that true rotational motion cannot be defined as the relative rotation of the body with respect to the immediately surrounding bodies. ...

In this response, Clarke argues for the necessity of the existence of absolute space to account for phenomena like rotation and acceleration that cannot be accounted for on a purely relationalist account. Clarke argues that since the curvature of the water occurs in the rotating bucket as well as in the stationary bucket containing spinning water, it can only be explained by stating that the water is rotating in relation to the presence of some third thing—absolute space. In physics, the notion of absolute space underlies the laws of classical physics of Isaac Newton. ... Relationism is a framework of social thought governing political, economic and social behaviour. ...

Leibniz describes a space that exists only as a relation between objects, and which has no existence apart from the existence of those objects. Motion exists only as a relation between those objects. Newtonian space provided the absolute frame of reference within which objects can have motion. In Newton’s system the frame of reference exists independently of the objects which are contained in it. These objects can be described as moving in relation to space itself. For many centuries, the evidence of a concave water surface held authority.

Mach

Another important figure in this debate is 19th century physicist, Ernst Mach. While he did not deny the existence of phenomena like that seen in the bucket argument, he still denied the absolutist conclusion by offering a different answer as to what the bucket was rotating in relation to: the fixed stars. Ernst Mach Ernst Mach (February 18, 1838 – February 19, 1916) was an Austrian-Czech physicist and philosopher and is the namesake for the Mach number and the optical illusion known as Mach bands. ... The fixed stars (from the Latin stellae fixae) are celestial objects that do not seem to move in relation to the other stars of the night sky. ...

Mach suggested that thought experiments like the bucket argument are problematic. If we were to imagine a universe that only contains a bucket, on Newton’s account, this bucket could be set to spin relative to absolute space, and the water it contained would form the characteristic concave surface. But, in the absence of anything else in the universe it would be difficult to confirm that the bucket was indeed spinning. It seems equally possible that the surface of the water in the bucket would remain flat.

Mach argued that, in effect, the water experiment in an otherwise empty universe would remain flat. But if another object was introduced into this universe, perhaps a distant star, there is now something relative to which the bucket could be seen as rotating. The water inside the bucket could possibly have a slight curve. To account for the curve that we observe, an increase in the number of objects in the universe also increases the curvature in the water. Mach argued that the momentum of an object, whether angular or linear, exists as a result of the sum of the effects of other objects in the universe (Mach's Principle). In theoretical physics, particularly in discussions of gravitation theories, Machs principle is the name given by Einstein to a vague hypothesis first supported by the physicist and philosopher Ernst Mach. ...

Einstein

Einstein, a prominent physicist in the 20th century, proposed that relativistics are based on the principle of relativity. This theory holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used. The greatest difficulty for this idea was Maxwell’s equations. These included the speed of light in a vacuum, and imply that the speed of light is only constant relative to the postulated luminiferous ether. “Einstein” redirects here. ... The luminiferous aether: it was hypothesised that the Earth moves through a medium of aether that carries light In the late 19th century the luminiferous aether (light-bearing aether), or ether, was a substance postulated to be the medium for the propagation of light. ...

Unfortunately for Einstein, all attempts to measure any speed relative to this ether failed. Special relativity is a formalization of the principle of relativity which does not contain a privileged inertial frame of reference such as the luminiferous ether or absolute space, from which Einstein inferred that no such frame exists. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ...

Einstein generalized relativity to frames of reference that were non-inertial. He achieved this by positing the Equivalence Principle, which states that the force felt by an observer in a given gravitational field and that felt by an observer in an accelerating frame of reference are indistinguishable. This led to the conclusion that the mass of an object warps the geometry of the space-time surrounding it, as described in Einstein’s field equations. In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... In physics, the Einstein field equation or Einstein equation is a differential equation in Einsteins theory of general relativity. ...

An inertial frame of reference is one that is following a geodesic of space-time. An object that moves against a geodesic experiences a force. An object in free fall does not experience a force, because it is following a geodesic. An object standing on the earth, however, will experience a force, as it is being held against the geodesic by the surface of the planet. In light of this, the bucket of water rotating in empty space will experience a force because it rotates with respect to the geodesic. The water will become concave, not because it is rotating with respect to the distant stars, but because it is rotating with respect to the geodesic. In physics, and specifically general relativity, geodesics are the world lines of a particle free from all external force. ... For other uses, see Free-fall (disambiguation). ...

Einstein partially advocates Mach’s principle in that distant stars explain inertia because they provide the gravitational field against which acceleration and inertia occur. But contrary to Leibniz’ account, this warped space-time is as integral a part of an object as are its other defining characteristics such as volume and mass. If one holds, contrary to idealist beliefs, that objects exist independently of the mind, it seems that Relativistics commits them to also hold that space and temporality have the exact same type of independent existence. In theoretical physics, particularly in discussions of gravitation theories, Machs principle is the name given by Einstein to a vague hypothesis first supported by the physicist and philosopher Ernst Mach. ...

Conventionalism

The position of conventionalism states that there is no fact of the matter as to the geometry of space and time, but that it is decided by convention. The first proponent of such a view, Henri Poincaré, reacting to the creation of the new non-euclidean geometry, argued that which geometry applied to a space was decided by convention, since different geometries will describe a set of objects equally well, based on considerations from his sphere-world. Jules Henri Poincaré (April 29, 1854 – July 17, 1912) (IPA: [1]) was one of Frances greatest mathematicians and theoretical physicists, and a philosopher of science. ... Behavior of lines with a common perpendicular in each of the three types of geometry The term non-Euclidean geometry describes hyperbolic, elliptic and absolute geometry, which are contrasted with Euclidean geometry. ... The idea of a sphere-world was constructed by Henri Poincaré while pursuing his argument for conventionalism (see philosophy of space and time), offered a thought experiment about a sphere with strange properties. ...

This view was developed and updated to include considerations from relativistic physics by Hans Reichenbach. Reichenbach's conventionalism, applying to space and time, focusses around the idea of coordinative definition. Hans Reichenbach (September 26, 1891, Hamburg, – April 9, 1953, Los Angeles) was a leading philosopher of science, educator and proponent of logical positivism. ...

Coordinative definition has two major features. The first has to do with coordinating units of length with certain physical objects. This is motivated by the fact that we can never directly apprehend length. Instead we must choose some physical object, say the Standard Metre at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures), or the wavelength of cadmium to stand in as our unit of length. The second feature deals with separated objects. Although we can, presumably, directly test the equality of length of two measuring rods when they are next to one another, we can not find out as much for two rods distant from one another. Even supposing that two rods, whenever brought near to one another are seen to be equal in length, we are not justified in stating that they are always equal in length. This impossibility undermines our ability to decide the equality of length of two distant objects. Sameness of length, to the contrary, must be set by definition. This article is about the unit of length. ... The Bureau International des Poids et Mesures (International Bureau of Weights and Measures, or BIPM) is a standards organization, one of the three organizations established to maintain the SI system under the terms of the Metre Convention. ... For other uses, see Wavelength (disambiguation). ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Standard atomic weight 112. ...

Such a use of coordinative definition is in effect, on Reichenbach's conventionalism, in the General Theory of Relativity where light is assumed, i.e. not discovered, to mark out equal distances in equal times. After this setting of coordinative definition, however, the geometry of spacetime is set.

As in the absolutism/relationalism debate, contemporary philosophy is still in disagreement as to the correctness of the conventionalist doctrine. While conventionalism still holds many proponents, cutting criticisms concerning the coherence of Reichenbach's doctrine of coordinative definition have led many to see the conventionalist view as untenable.

The structure of spacetime

Building from a mix of insights from the historical debates of absolutism and conventionalism as well as reflecting on the import of the technical apparatus of the General Theory of Relativity, details as to the structure of spacetime have made up a large proportion of discussion within the philosophy of space and time, as well as the philosophy of physics. The following is a short list of topics. For other uses of this term, see Spacetime (disambiguation). ... Philosophy of physics is the study of the fundamental, philosophical questions underlying modern physics, the study of matter and energy and how they interact. ...

The relativity of simultaneity

According to special relativity each point in the universe can have a different set of events that compose its present instant. This has been used in the Rietdijk-Putnam argument to demonstrate that relativity predicts a block universe in which events are fixed in four dimensions. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... If special relativity is true then each observer will have their own plane of simultaneity that contains a unique set of events that constitute the observers present moment. ... Eternalism is a philosophical approach to the ontological nature of time. ...

Invariance vs. covariance

Bringing to bear the lessons of the absolutism/relationalism debate with the powerful mathematical tools invented in the 19th and 20th century, Michael Friedman draws a distinction between invariance upon mathematical transformation and covariance upon transformation. Michael Jan Friedman is an author of nearly sixty books of fiction and nonfiction, more than half of which are in the Star Trek universe. ... In mathematics, a transformation in elementary terms is any of a variety of different functions from geometry, such as rotations, reflections and translations. ...

Invariance, or symmetry, applies to objects, i.e. the symmetry group of a space-time theory designates what features of objects are invariant, or absolute, and which are dynamical, or variable. The symmetry group of an object (e. ...

Covariance applies to formulations of theories, i.e. the covariance group designates in which range of coordinate systems the laws of physics hold. This picture illustrates how the hours on a clock form a group under modular addition. ... In mathematics as applied to geometry, physics or engineering, a coordinate system is a system for assigning a tuple of numbers to each point in an n-dimensional space. ...

This distinction can be illustrated by revisiting Leibniz's thought experiment, in which the universe is shifted over five feet. In this example the position of an object is seen not to be a property of that object, i.e. location is not invariant. Similarly, the covariance group for classical mechanics will be any coordinate systems that are obtained from one another by shifts in position as well as other translations allowed by a Galilean transformation. Classical mechanics (commonly confused with Newtonian mechanics, which is a subfield thereof) is used for describing the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies. ... The Galilean transformation is used to transform between the coordinates of two reference frames which differ only by constant relative motion within the constructs of Newtonian physics. ...

In the classical case, the invariance, or symmetry, group and the covariance group coincide, but, interestingly enough, they part ways in relativistic physics. The symmetry group of the GTR includes all differentiable transformations, i.e. all properties of an object are dynamical, in other words there are no absolute objects. The formulations of the GTR, unlike that of classical mechanics, do not share a standard, i.e. there is no single formulation paired with transformations. As such the covariance group of the GTR is just the covariance group of every theory.

Historical frameworks

A further application of the modern mathematical methods, in league with the idea of invariance and covariance groups, is to try to interpret historical views of space and time in modern, mathematical language.

In these translations, a theory of space and time is seen as a manifold paired with vector spaces, the more vector spaces the more facts there are about objects in that theory. The historical development of spacetime theories is generally seen to start from a position where many facts about objects or incorporated in that theory, and as history progresses, more and more structure is removed. On a sphere, the sum of the angles of a triangle is not equal to 180° (see spherical trigonometry). ... The fundamental concept in linear algebra is that of a vector space or linear space. ...

For example, Aristotle's theory of space and time holds that not only is there such a thing as absolute position, but that there are special places in space, such as a center to the universe, a sphere of fire, etc. Newtonian spacetime has absolute position, but not special positions. Galilean spacetime has absolute acceleration, but not absolute position or velocity. And so on. For other uses, see Aristotle (disambiguation). ...

Holes

With the GTR, the traditional debate between absolutism and relationalism has been shifted to whether or not spacetime is a substance, since the GTR largely rules out the existence of, e.g., absolute positions. One powerful argument against spacetime substantivalism, offered by John Earman is known as the "hole argument". John Earman is a philosopher of physics. ...

This is a technical mathematical argument but can be paraphrased as follows:

Define a function d as the identity function over all elements over the manifold M, excepting a small neighbourhood (topology) H belonging to M. Over H d comes to differ from identity by a smooth function. An identity function f is a function which doesnt have any effect: it always returns the same value that was used as its argument. ... This is a glossary of some terms used in the branch of mathematics known as topology. ... In mathematical analysis, a differentiability class is a classification of functions according to the properties of their derivatives. ...

With use of this function d we can construct two mathematical models, where the second is generated by applying d to proper elements of the first, such that the two models are identical prior to the time t=0, where t is a time function created by a foliation of spacetime, but differ after t=0. A mathematical model is an abstract model that uses mathematical language to describe the behaviour of a system. ... In mathematics, a foliation is a geometric device used to study manifolds. ...

These considerations show that, since substantivalism allows the construction of holes, that the universe must, on that view, be indeterministic. Which, Earman argues, is a case against substantivalism, as the case between determinism or indeterminism should be a question of physics, not of our commitment to substantivalism.

The direction of time

The problem of the direction of time arises directly from two contradictory facts. First, the fundamental physical laws are time-reversal invariant. In other words, anything that can happen moving forward through time is just as possible moving backwards in time. Or, put in another way, through the eyes of physics, there will be no distinction, in terms of possibility, between what happens in a movie if the film is run forward, or if the film is run backwards. Second, our experience of time, at the macroscopic level, is not time-reversal invariant. Glasses fall and break all the time, but shards of glass do not put themselves back together and fly up on tables. We have memories of the past, and none of the future. We feel we can't change the past but can affect the future. Invariant may have meanings invariant (computer science), such as a combination of variables not altered in a loop invariant (mathematics), something unaltered by a transformation invariant (music) invariant (physics) conserved by system symmetry This is a disambiguation page — a navigational aid which lists other pages that might otherwise share... Macroscopic is commonly used to describe physical objects that are measurable and observable by the naked eye. ...

The causation solution

One solution to this problem takes a metaphysical view, in which the direction of time follows from an asymmetry of causation. We know more about the past because the elements of the past are causes for the effect that is our perception. We feel we can't affect the past and can affect the future because we can't affect the past and can affect the future. Plato (Left) and Aristotle (right), by Raphael (Stanza della Segnatura, Rome) Metaphysics is the branch of philosophy concerned with explaining the ultimate nature of reality, being, and the world. ... Causality or causation denotes the relationship between one event (called cause) and another event (called effect) which is the consequence (result) of the first. ...

There are two major difficulties with this view. First is the problem of distinguishing the cause from the effect in a non-arbitrary way. The use of causation in constructing a temporal ordering could easily become circular. The second problem is with not the consistency of this view, but its explanatory power. While the causation account, if successful may account for some time-asymmetric phenomena like perception and action, it does not account for many others, like the breaking glass described above.

The thermodynamics solution

The second major family of solutions to this problem, and by far the one that has generated the most literature, finds the existence of the direction of time as relating to the nature of thermodynamics.

The answer from classical thermodynamics states that while our basic physical theory is, in fact, time-reversal symmetric, thermodynamics is not. In particular, the second law of thermodynamics states that the net entropy of a closed system never decreases, and this explains why we often see glass breaking, but not coming back together. Thermodynamics (from the Greek θερμη, therme, meaning heat and δυναμις, dynamis, meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ... For other uses, see: information entropy (in information theory) and entropy (disambiguation). ...

But in statistical mechanics things get more complicated. On one hand, statistical mechanics is far superior to classical thermodynamics, in that thermodynamic behavior, glass breaking, can be explained by the fundamental laws of physics paired with a statistical postulate. But statistical mechanics, unlike classical thermodynamics, is time-reversal symmetric. The second law of thermodynamics, as it arises in statistical mechanics, merely states that it is overwhelmingly likely that net entropy will increase, but it is not an absolute law. Statistical mechanics is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... For Wikipedia statistics, see m:Statistics Statistics is the science and practice of developing human knowledge through the use of empirical data expressed in quantitative form. ...

Current thermodynamic solutions to the problem of the direction of time aim to find some further fact, or feature of the laws of nature to account for this discrepancy.

The laws solution

A third type of solution to the problem of the direction of time, although much less represented, argues that the laws are not time-reversal symmetric. For example, certain processes in quantum mechanics, relating to the weak nuclear force, are not time-reversible, keeping in mind that when dealing with quantum mechanics time-reversibility comprises a more complex definition. For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ...

But this type of solution is insufficient because 1) the time-symmetric phenomena in QM are too few to account for the uniformity of macroscopic time-asymmetry and 2) it relies on the assumption that QM is the final or correct description of physical processes.

One recent proponent of the laws solution is Tim Maudlin who argues that, in addition to quantum mechanical phenomena, our basic spacetime physics (general relativity) is time-reversal asymmetric. He denies the definitions, often quite complicated, that underlie time-reversal symmetries, arguing that these definitions themselves cause the appearance of a problem of the direction of time. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ...

The flow of time

The problem of the flow of time, as it has been treated in analytic philosophy, owes its beginning to a paper written by J. M. E. McTaggart. In this paper McTaggart introduces two temporal series that are central to our understanding of time. The first series, which means to account for our intuitions about temporal becoming, or the moving Now, is called the A-series. The A-series orders events according to their being in the past, present or future, simpliciter and in comparison to each other. The B-series eliminates all reference to the present, and the associated temporal modalities of past and future, and orders all events by the temporal relations earlier than and later than. John McTaggart Ellis McTaggart (1866-1925) was the leading Hegel scholar in England at the beginning of the 20th Century, and friend and teacher of Bertrand Russell and G. E. Moore. ... The B-theory of time is a term, given to one a two positions taken by theorists, in the philosophy of time. ...

McTaggart, in his paper The Unreality of Time, argues that time is unreal since a) the A-series is inconsistent and b) the B-series alone cannot account for the nature of time as the A-series describes an essential feature of it. Wikisource has original text related to this article: The Unreality of Time To meet Wikipedias quality standards, this article or section may require cleanup. ...

Building from this framework, two camps of solution have been offered. The first, the A-theorist solution, takes becoming as the central feature of time, and tries to construct the B-series from the A-series by offering an account of how B-facts come to be out of A-facts. The second camp, the B-theorist solution, takes as decisive McTaggart's arguments against the A-series and tries to construct the A-series out of the B-series, for example, by temporal indexicals.

Dualities

Quantum field theory models have shown that it is possible for theories in two different spacetime backgrounds, like AdS/CFT or T-duality, to be equivalent. Quantum field theory (QFT) is the quantum theory of fields. ... In physics, the AdS/CFT correspondence is the equivalence between a string theory or supergravity defined on some sort of Anti de Sitter space and a conformal field theory defined on its boundary whose dimension is lower by one. ... T-duality is a symmetry of string theory, relating type IIA and type IIB string theory, and the two heterotic string theories. ...

Presentism and Eternalism

Main articles: Presentism (philosophy of time) and Eternalism (philosophy of time)

According to Presentism, time is an ordering of various realities. At a certain time some things exist and others do not. This is the only reality we can deal with and we cannot for example say that Homer exists because at the present time he does not. An Eternalist, on the other hand, holds that time is a dimension of reality on a par with the three spatial dimensions, and hence that all things—past present and future—can be said to be just as real as things in the present are. According to this theory, then, Homer really does exist, though we must still use special language when talking about somebody who exists at a distant time—just as we would use special language when talking about something a long way away (the very words near, far, above, below, over there, and such are directly comparable to phrases such as in the past, a minute ago, and so on). In the philosophy of time, presentism is the belief that neither the future nor the past exists. ... Eternalism is a philosophical approach to the ontological nature of time. ... In the philosophy of time, presentism is the belief that neither the future nor the past exists. ... For other uses, see Reality (disambiguation). ... For other uses, see Homer (disambiguation). ... Eternalism is a philosophical approach to the ontological nature of time. ...

Endurantism and perdurantism

Main articles: Endurantism and Perdurantism

The positions on the persistence of objects are somewhat similar. An endurantist holds that for an object to persist through time is for it to exist completely at different times (each instance of existence we can regard as somehow separate from previous and future instances, though still numerically identical with them). A perdurantist on the other hand holds that for a thing to exist through time is for it to exist as a continuous reality, and that when we consider the thing as a whole we must consider an aggregate of all its "temporal parts" or instances of existing. Endurantism is seen as the conventional view and flows out of our innate ideas (when I talk to somebody I think I am talking to that person as a complete object, and not just a part of a cross-temporal being), but perduranists have attacked this position. (An example of a perdurantist is David Lewis.) One argument perdurantists use to state the superiority of their view is that perdurantism is able to take account of change in objects. This article or section is in need of attention from an expert on the subject. ... Perdurantism or perdurance theory is a philosophical theory of persistence and identity. ... This article or section is in need of attention from an expert on the subject. ... Perdurantism or perdurance theory is a philosophical theory of persistence and identity. ... Temporal Parts are used in contemporary metaphysics in the debate over persistence of material objects. ... David K. Lewis David Kellogg Lewis (September 28, 1941 – October 14, 2001) is considered to have been one of the leading analytic philosophers of the latter half of the 20th century. ...

The relations between these two questions mean that on the whole Presentists are also endurantists and Eternalists are also perdurantists (and vice versa), but this is not a necessary connection and it is possible to claim, for instance, that time's passage indicates a series of ordered realities, but that objects within these realities somehow exist outside of the reality as a whole, even though the realities as wholes are not related. However, such positions are rarely adopted. In the philosophy of time, presentism is the belief that neither the future nor the past exists. ... Eternalism is a philosophical approach to the ontological nature of time. ...

References

John Randolph Lucas (born 18 June 1929) is a British philosopher. ... Hans Reichenbach (September 26, 1891, Hamburg, – April 9, 1953, Los Angeles) was a leading philosopher of science, educator and proponent of logical positivism. ... Hans Reichenbach (September 26, 1891, Hamburg, – April 9, 1953, Los Angeles) was a leading philosopher of science, educator and proponent of logical positivism. ... Bastiaan Cornelis van Fraassen (born Goes, the Netherlands, 5 April 1941) is a member of the Princeton University Philosophy department, currently entering phased retirement. ...

See also

• Arrow of time
• Endurantism
• Eternalism
• Metaphysics
• Perdurantism
• Presentism
• Spacetime
• Temporal Parts
• Time travel in science and Time travel in fiction
• Zeno's paradoxes

This article or section does not cite its references or sources. ... This article or section is in need of attention from an expert on the subject. ... Eternalism is a philosophical approach to the ontological nature of time. ... Plato (Left) and Aristotle (right), by Raphael (Stanza della Segnatura, Rome) Metaphysics is the branch of philosophy concerned with explaining the ultimate nature of reality, being, and the world. ... Perdurantism or perdurance theory is a philosophical theory of persistence and identity. ... In the philosophy of time, presentism is the belief that neither the future nor the past exists. ... For other uses of this term, see Spacetime (disambiguation). ... Temporal Parts are used in contemporary metaphysics in the debate over persistence of material objects. ... Time travel is a concept that has long fascinated humanity—whether it is Merlin experiencing time backwards, or religious traditions like Mohammeds trip to Jerusalem and ascent to heaven, returning before a glass knocked over had spilt its contents. ... Poster for Back to the Future (1985). ... “Arrow paradox” redirects here. ...

External links

• Brown, C.L., 2006, "What is Space?" A philosophical, largely Wittgensteinian, approach towards a dissolution of the question: "What is space?"
• Rea, M. C., "Four Dimensionalism" in The Oxford Handbook for Metaphysics. Oxford Univ. Press. Describes presentism and four dimensionalism.