FACTOID # 8: Bookworms: Vermont has the highest number of high school teachers per capita and third highest number of librarians per capita.
 
 Home   Encyclopedia   Statistics   States A-Z   Flags   Maps   FAQ   About 
   
 
WHAT'S NEW
 

SEARCH ALL

FACTS & STATISTICS    Advanced view

Search encyclopedia, statistics and forums:

 

 

(* = Graphable)

 

 


Encyclopedia > Causality (physics)

Causality describes the relationship between causes and effects, and is fundamental to all natural science, especially physics. It is also studied from the perspectives of philosophy, computer science, and statistics. Part of a scientific laboratory at the University of Cologne. ... Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and characterization of universal laws which govern matter, energy, space, and time. ... The philosopher Socrates about to take poison hemlock as ordered by the court. ... Computer scaence, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ... A graph of a Normal bell curve showing statistics used in educational assessment and comparing various grading methods. ...


In classical physics, it was assumed that all events are caused by earlier ones according to the known laws of nature, culminating in Pierre-Simon Laplace's claim that if the current state of the world were known with precision, it could be computed for any time in the future or the past. This is known as determinism. Classical physics is physics based on principles developed before the rise of quantum theory, usually including the special theory of relativity and general theory of relativity. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Determinism is the philosophical proposition that every event, including human cognition, decision and action, is causally determined by an unbroken chain of prior occurrences. ...


According to classical physics, the cause simply had to precede its effect. In modern physics, the notion of causality had to be clarified. Modern physics may refer to: Quantum mechanics Theory of relativity 20th-century physics in general See also History of physics This is a disambiguation page: a list of articles associated with the same title. ...


The insights of the theory of special relativity confirmed the assumption of causality, but they made the meaning of the word "precede" observer-dependent. Consequently, the relativistic principle of causality says that the cause must precede its effect according to all inertial observers. This is equivalent to the statement that the cause and its effect are separated by a timelike interval, and the effect belongs to the future light cone of its cause. Equivalently, special relativity has shown that it is not only impossible to influence the past; it is also impossible to influence distant objects by signals that travel faster than the speed of light. The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... In physics, an inertial frame of reference, or inertial frame for short (also descibed as absolute frame of reference), is a frame of reference in which the observers move without the influence of any accelerating or decelerating force. ... In physics and mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einsteins theory of special relativity is most conveniently formulated. ... In special relativity, a light cone is the pattern describing the temporal evolution of a flash of light in Minkowski spacetime. ... A line showing the speed of light on a scale model of Earth and the Moon The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation...


In the theory of general relativity, the concept of causality is generalized in the most straightforward way: the effect must belong to the future light cone of its cause, even if the spacetime is curved. New subtleties must be taken into account when we investigate causality in quantum mechanics and relativistic quantum field theory in particular. In quantum field theory, causality is closely related to the principle of locality. A careful analysis of the phenomena is needed, and the outcome slightly depends on the chosen interpretation of quantum mechanics: this is especially the case of the experiments involving quantum entanglement that require Bell's Theorem for their implications to be fully understood. General relativity (GR) [also called the general theory of relativity (GTR) and general relativity theory (GRT)] is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... In physics, spacetime is a mathematical model that combines space and time into a single construct called the space-time continuum. ... Fig. ... Quantum field theory (QFT) is the quantum theory of fields. ... In physics, the principle of locality is that distant objects cannot have direct influence on one another: an object is influenced directly only by its immediate surroundings. ... It has been suggested that Quantum mechanics, philosophy and controversy be merged into this article or section. ... It has been suggested that Quantum coherence be merged into this article or section. ... Bells theorem is the most famous legacy of the late Irish phyisicist John Bell. ...


Despite these subtleties, causality remains an important and valid concept in physical theories. For example, the notion that events can be ordered into causes and effects is necessary to prevent causality paradoxes such as the grandfather paradox, which asks what happens if a time-traveller kills his own grandfather before he ever meets the time-traveller's grandmother. See also Chronology protection conjecture. This article or section does not cite any references or sources. ... The grandfather paradox is a paradox of time travel, first conceived by the science fiction writer René Barjavel in his 1943 book Le Voyageur Imprudent (The Imprudent Traveller) [1]. The paradox, stated in the second person, is this: Suppose you traveled back in time and killed your biological grandfather before... The chronology protection conjecture is a conjecture by the physicist Professor Stephen Hawking that the laws of physics are such as to prevent time travel (closed timelike curves) on all but sub-microscopic scales. ...


Distributed causality


Theories in physics like the Butterfly effect from chaos theory open up the possibility of a type of Distributed parameter systems in causality. The butterfly effect theory proposes: Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and characterization of universal laws which govern matter, energy, space, and time. ... Point attractors in 2D phase space. ... A plot of the Lorenz attractor for values r = 28, σ = 10, b = 8/3 In mathematics and physics, chaos theory describes the behavior of certain nonlinear dynamical systems that under certain conditions exhibit dynamics that are sensitive to initial conditions (popularly referred to as the butterfly effect). ... Distributed parameter system (as opposed to a lumped parameter system) refers to system whose state-space is infinite-dimensional. ...

"Small variations of the initial condition of a nonlinear dynamical system may produce large variations in the long term behavior of the system."

This opens up the opportunity to understand a distributed causality.

Causal contact

In physics, two entities are said to be in causal contact if there may be an event that has affected both in a causal way. Every object of mass in space, for instance, exerts a field force on all other objects of mass, according to Newton's law of universal gravitation. Because this force exerted by one object affects the motion of the other, it can be said that these two objects are in causal contact. Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ... Space has been an interest for philosophers and scientists for much of human history. ... In physics, force is an influence that may cause a body to accelerate. ... Sir Isaac Newton, (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist, regarded by many as the greatest figure in the history of science. ... It has been suggested that this article or section be merged into Gravity. ...


The only objects that are not in causal contact (according to accepted physics) are those for which there is no event in the history of the universe that could have sent a beam of light to both. For example, if the universe were not expanding and had existed for 13 billion years, anything more than 26 billion light-years away from the earth would not be in causal contact with it. Anything less than 26 billion light-years away would because an event occurring 13 billion years in the past that was 13 billion light-years away from both the earth and the object under question could have affected both (the gravity in question).

A worldline through a light cone in 2D space plus a time dimension.

A good illustration of this principle is the Light cone: Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... A world line of an object or person is the sequence of events labeled with time and place, that marks the history of the object or person. ... In special relativity, a light cone is the pattern describing the temporal evolution of a flash of light in Minkowski spacetime. ...


The light cone is constructed as follows. Taking as event p a flash of light (light pulse) at time t0, all events that can be reached by this pulse from p form the future light cone of p, whilst those events that can send a light pulse to p form the past light cone of p.


Given an event E, the light cone classifies all events in spacetime into 5 distinct categories:

  • Events on the future light cone of E.
  • Events on the past light cone of E.
  • Events inside the future light cone of E are those which are affected by the beam of light emitted at E.
  • Events inside the past light cone of E are those which can emit a beam of light and affect what is happening at E.
  • All other events are in the (absolute) elsewhere of E and are those that will never affect and can never be affected by E.

See also

It has been suggested that this article be split into multiple articles accessible from a disambiguation page. ... The causal sets programme is an approach to quantum gravity. ... It has been suggested that this article or section be merged into Observable universe. ... Philosophy of physics is the study of the fundamental, philosophical questions underlying modern physics, the study of matter and energy and how they interact. ...

External links

  • Causal Processes, Stanford Encyclopedia of Philosophy
  • Caltech Tutorial on Relativity — A nice discussion of how observers moving relatively to each other see different slices of time.
  • Faster-than-c signals, special relativity, and causality. This article explains that faster than light signals do not necessarily lead to a violation of causality.

  Results from FactBites:
 
Consciousness, Causality, Quantum Physics (3596 words)
The standard interpretation of quantum physics assumes that the quantum world is characterized by absolute indeterminism and that quantum systems exist objectively only when they are being measured or observed.
According to the conventional interpretation of quantum physics, however, not only is it impossible for us to measure a particle's position and momentum simultaneously with equal precision, a particle does not possess well-defined properties when it is not interacting with a measuring instrument.
Bohm's ontological interpretation of quantum physics rejects the assumption that the wave function gives the most complete description of reality possible, and thereby avoids the need to introduce the ill-defined and unsatisfactory notion of wave-function collapse (and all the paradoxes that go with it).
Causality (physics) - Wikipedia, the free encyclopedia (600 words)
Causality describes the relationship between causes and effects, and is fundamental to all natural science, especially physics.
In classical physics, it was assumed that all events are caused by earlier ones according to the known laws of nature, culminating in Pierre-Simon Laplace's claim that if the current state of the world would be known with precision, it could be computed for any time in the future.
This is equivalent to the statement that the cause and its effect are separated by a timelike interval, and the effect belongs to the future light cone of its cause.
  More results at FactBites »

 
 

COMMENTARY     


Share your thoughts, questions and commentary here
Your name
Your comments

Want to know more?
Search encyclopedia, statistics and forums:

 


Press Releases |  Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m