Difference between revisions of "Action at a distance"
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| − | '''Action at a distance''' | + | '''Action at a distance''' refers to at least two phenomena in the history of science, involving something affecting something else in a way that is beyond the common sense of the time. In each case the phenomenon was/is considered "spooky". |
| − | + | In [[Isaac Newton]]'s time, his theory of gravity was a case of this. The idea that an object could exert a force on another object without touching it was hard to accept. And yet the Sun reached across space and attracted the planets. Newton famously said "Hypotheses non fingo", or "I feign no hypotheses". He was saying that his theory was observed to be true, but he couldn't explain why. At that time scientists were just barely becoming aware that light travels at a finite speed, and no deeper ramifications of the [[speed of light]] were known, so whether the gravitational force propagates at the speed of light was not an issue. It is now known that it does propagate at the speed of light. | |
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| + | During the 17th and 18 centuries, research into [[Electrostatics|electric]] and magnetic fields showed that there was nothing particularly "spooky" going on, and that charged or magnetized objects can indeed reach across space and exert a force. The work of [[James Clerk Maxwell]], particularly his [[Maxwell's Equations]], put this on a sound theoretical footing, and showed that the speed of light has a profound significance in physics, and is the speed at which these forces propagate. | ||
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| + | In both of the above cases it is impossible for information to propagate, gravitationally or electromagnetically, faster than the speed of light. | ||
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| + | Starting in the early 20th century, with the advent of [[quantum mechanics]], a new form of action at a distance has appeared, and it is spooky. It takes the form of [[quantum entanglement]], in which multiple particles seem to share some quantum-mechanical state information across distances, that could in theory be considerable, and in which those particles "simultaneously" exhibit that information. | ||
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| + | At the atomic level, this is known as "non-locality". | ||
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Some scientists have long resisted the possibility of action at at distance (non-locality), and the [[theory of relativity]] assumes that information travelling instantaneously, or faster than the [[speed of light]], is impossible. Quantum entanglement therefore appears to violate relativity as one particle affects another instantaneously. However, no information can be encoded with the particles, so no information can be sent faster than the speed of light, in accordance with relativity. | Some scientists have long resisted the possibility of action at at distance (non-locality), and the [[theory of relativity]] assumes that information travelling instantaneously, or faster than the [[speed of light]], is impossible. Quantum entanglement therefore appears to violate relativity as one particle affects another instantaneously. However, no information can be encoded with the particles, so no information can be sent faster than the speed of light, in accordance with relativity. | ||
Revision as of 04:55, May 29, 2018
Action at a distance refers to at least two phenomena in the history of science, involving something affecting something else in a way that is beyond the common sense of the time. In each case the phenomenon was/is considered "spooky".
In Isaac Newton's time, his theory of gravity was a case of this. The idea that an object could exert a force on another object without touching it was hard to accept. And yet the Sun reached across space and attracted the planets. Newton famously said "Hypotheses non fingo", or "I feign no hypotheses". He was saying that his theory was observed to be true, but he couldn't explain why. At that time scientists were just barely becoming aware that light travels at a finite speed, and no deeper ramifications of the speed of light were known, so whether the gravitational force propagates at the speed of light was not an issue. It is now known that it does propagate at the speed of light.
During the 17th and 18 centuries, research into electric and magnetic fields showed that there was nothing particularly "spooky" going on, and that charged or magnetized objects can indeed reach across space and exert a force. The work of James Clerk Maxwell, particularly his Maxwell's Equations, put this on a sound theoretical footing, and showed that the speed of light has a profound significance in physics, and is the speed at which these forces propagate.
In both of the above cases it is impossible for information to propagate, gravitationally or electromagnetically, faster than the speed of light.
Starting in the early 20th century, with the advent of quantum mechanics, a new form of action at a distance has appeared, and it is spooky. It takes the form of quantum entanglement, in which multiple particles seem to share some quantum-mechanical state information across distances, that could in theory be considerable, and in which those particles "simultaneously" exhibit that information.
At the atomic level, this is known as "non-locality".
Some scientists have long resisted the possibility of action at at distance (non-locality), and the theory of relativity assumes that information travelling instantaneously, or faster than the speed of light, is impossible. Quantum entanglement therefore appears to violate relativity as one particle affects another instantaneously. However, no information can be encoded with the particles, so no information can be sent faster than the speed of light, in accordance with relativity.
Several theories have been developed as ways of denying action at a distance (non-locality). These include:
- theories positing the existence of gravitons
- string theory
- quantum field theory
