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Encyclopedia > Action at a distance (physics)

In physics, action at a distance is the interaction of two objects which are separated in space with no known mediator of the interaction. This term was used most often with early theories of gravity and electromagnetism to describe how an object could "know" the mass (in the case of gravity) or charge (in electromagnetism) of another distant object. A black hole concept drawing by NASA. Physics (from the Greek, φυσικός (physikos), natural, and φύσις (physis), nature) is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. ... Interaction is a kind of action which occurs as two or more objects have an effect upon one another. ... Wikiquote has a collection of quotations related to: Space Attempting to understand the nature of space has always been a prime occupation for philosophers and scientists. ... It has been suggested that gravitation be merged into this article or section. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, which exerts a force on those particles that possess the property of electric charge, and is in turn affected by the presence and motion of such particles. ...


According to Albert Einstein's theory of special relativity, instantaneous action-at-a-distance was seen to violate the relativistic upper limit on speed of propagation of information. If one of the interacting objects were suddenly displaced from its position, the other object would feel its influence instantaneously, meaning information had been transmitted faster than the speed of light. To meet Wikipedias quality standards, this article may require cleanup. ... Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. It replaced Newtonian notions of space and time and incorporated electromagnetism as represented by Maxwells equations. ... Cherenkov effect in a swimming pool nuclear reactor. ...

Contents


Electricity

Coulomb's law in electrostatics appears to be a theory with action-at-a-distance - Coulomb's law deals with charges which have always been static. Efforts to develop a theory of interaction between moving charges, electrodynamics, led to the necessity to introduce the concept of a field with physical properties. In the theory of electrodynamics as formulated in Maxwell's equations, interactions between moving charges are mediated by propagating deformations of an electromagnetic field. These deformations propagate with the speed of light and therefore do not violate special relativity. The deformations of the field can carry momentum independently, thus facilitating conservation of angular momentum. In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ... Electrostatics is the branch of physics that deals with the forces exerted by a static (i. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ... Look up static in Wiktionary, the free dictionary. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... In physics, a field is an assignment of a quantity to every point in space (or more generally, spacetime). ... Maxwells equations (sometimes called the Maxwell equations) are the set of four equations, attributed to James Clerk Maxwell, that describe the behavior of both the electric and magnetic fields, as well as their interactions with matter. ...


Gravity

Newton

Newton's theory of gravity offered no prospect of identifying any mediator of gravitational interaction. His theory assumed that gravitation acts instantaneously, regardless of distance. Newton had shown mathematically that if the gravitational interaction is not instantaneous, angular momentum is not conserved, and Kepler's observations gave strong evidence that in planetary motion angular momentum is conserved. (The mathematical proof is only valid in the case of a Euclidean geometry) Sir Isaac Newton, PRS, (4 January [O.S. 25 December 1642] 1643 – 31 March [O.S. 20 March] 1727) was an English physicist, mathematician, astronomer, alchemist, inventor and natural philosopher who is regarded by many as the most influential scientist in history. ... In mathematics, Euclidean geometry is the familiar kind of geometry on the plane or in three dimensions. ...


A related question, raised by Ernst Mach, was how rotating bodies know how much to bulge at the equator. How do they know their rate of rotation? This, it seems, requires an action-at-a-distance from distant matter, informing the rotating object about the state of the universe. Einstein coined the term Mach's principle for this question. 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. ... This article is in need of attention from an expert on the subject. ...


Einstein

One of the conditions that a relativistic theory of gravitation must meet is to be mediated with a speed that does not exceed lightspeed. It could be seen from the previous success of electrodynamics that the relativistic theory of gravitation would have to use the concept of a field or something similar.


This problem has been resolved by Einstein's theory of general relativity in which gravitational interaction is mediated by deformation of space-time geometry. Matter warps the geometry of space-time and these effects are, as with electric and magnetic fields, propagated at the speed of light. Thus, in the presence of matter, space-time becomes non-Euclidean, resolving the apparent conflict between Newton's proof of the conservation of angular momentum and Einstein's theory of special relativity. Mach's question is resolved because local space-time geometry is informing a rotating body about the rest of the universe. In Newton's theory of motion, space acts on objects, but is not acted upon. In Einstein's theory of motion, matter acts upon space-time geometry, deforming it, and space-time geometry acts upon matter. General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ... Behavior of lines with a common perpendicular in each of the three types of geometry The term non-Euclidean geometry (also spelled: non-Euclidian geometry) describes both hyperbolic and elliptic geometry, which are contrasted with Euclidean geometry. ...


Quantum mechanics

Current physical theories incorporate the upper limit on propagation of interaction as one of their basic building blocks, hence ruling out instantaneous action-at-a-distance. Einstein coined the term "spooky action at a distance" to describe certain interpretations of quantum mechanics that appear to imply instantaneous action at a distance - particularly those which incorporate quantum entanglement. However, some advocates of these types of interpretations maintain such effects are not actually present. Relativistic quantum field theory requires interactions to propagate at less than the speed of light, so quantum entanglement cannot be used for faster than light-speed propagation of matter, energy, or information. A simple introduction to this subject is provided in Basics of quantum mechanics. ... Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ... Quantum field theory (QFT) is the application of quantum mechanics to fields. ... Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. ...


See also


  Results from FactBites:
 
Physics - Crystalinks (3771 words)
Physics is the science that deals with the structure of matter and the interactions between the fundamental constituents of the observable universe.
Physics plays an important role in all the natural sciences, however, and all such fields have branches in which physical laws and measurements receive special emphasis, bearing such names as astrophysics, geophysics, biophysics, and even psychophysics.
The ultimate aim of physics is to find a unified set of laws governing matter, motion, and energy at small (microscopic) subatomic distances, at the human (macroscopic) scale of everyday life, and out to the largest distances (e.g., those on the extragalactic scale).
Action at a distance (computer science) - Wikipedia, the free encyclopedia (638 words)
Action at a distance is an anti-pattern (a recognized common error) in which behavior in one part of a program varies wildly based on difficult or impossible to identify operations in another part of the program.
The way to avoid the problems associated with action at a distance are a proper design which avoids global variables and alters data in a controlled and local manner.
One of the advantages of functional programming is that action at a distance is de-emphasised, sometimes to the point of being impossible to express at all in the source language.
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