Gravity

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{{sci-outline}}
 
{{sci-outline}}
'''Gravity''' has been speculated about since at least 800 BCE in the Indian subcontinent when it was identified as the effect of weight. Every school of philosophers since that time had some explanation for gravity - some approaching or even equalling that of Sir Isaac Newton who in 1687 published ''Principia'' which laid down the inverse square law of attraction due to gravity.
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'''Gravity''', the opposite of Comedy, has been speculated about since at least 800 BCE, when in the Indian subcontinent it was identified as the effect of weight. Every school of philosophers since that time has had some explanation for gravity - some approaching or even equalling that of Sir Isaac Newton who in 1687 published ''Principia Mathematica'', which laid down the inverse square law of attraction due to gravity.
  
Since his day Newton's ''Law of Gravity'' was found to be sufficiently accurate as to enable the prediction of the location of the planet Neptune.  
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Since his day, Newton's ''Law of Gravity'' has proven sufficiently accurate to enable the prediction of the location of the planet Neptune. In was the late 19th century, small irregularities in the orbit of the innermost planet, Mercury, could not be explained through Newtonian Gravity Theory, and it began to be questioned. Einstein's General Theory of Relativity solved the problem.
It was the late 19th century when small irregularities in the orbit of the innermost planet, Mercury, could not be explained through Newtonian Gravity Theory that it began to be questioned. Einstein's General Theory of Relativity solved the problem.
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Everyone will be familiar with the visual and physical representation of Gravitation as described by the General Theory i.e. A stretched elastic membrane deflected by the weight of objects placed on it. This is a difficult visualisation of the mathematical idea of curvature in spacetime, requiring that the four dimensions of spacetime be visualised as a two dimensional elastic sheet which is distorting in some other dimension. Once this mental leap has been performed it is easy to see how varying masses have varying effects on the curvature of spacetime,; the larger the mass, the greater the distortion and the further reaching its effect. This is most often shown by placing a large, dense object (a bowling ball or cannonball) on the sheet and then rolling other balls past it at varying distances. As a thought experiment one can envisage fairly well the effects of the two objects on each other. The trouble with this demonstration is of course friction.
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Everyone will be familiar with the visual and physical representation of Gravitation as described by the General Theory, i.e., a stretched elastic membrane deflected by the weight of objects placed on it. This is a difficult visualisation of the mathematical idea of curvature in spacetime, requiring that the four dimensions of spacetime be visualised as a two dimensional elastic sheet which is distorting in some other dimension. Once this mental leap has been performed it is easy to see how varying masses have varying effects on the curvature of spacetime,; the larger the mass, the greater the distortion and the further reaching its effect.<ref>Although technically gravity reaches from every object in the universe to every other, its effects due to very distant ones become much less noticeable.</ref>  This is most often shown by placing a large, dense object (a bowling ball or cannonball) on the membrane and then rolling other balls past it at varying distances. As a thought experiment one can envisage fairly well the effects of the two objects on each other. The trouble with this demonstration is, of course, friction with the membrane.
  
In order to discuss Gravity and Quantum Field Theory in the same mathematical environment, gravitation is theorised to be facilitated by the exchange of virtual gravitons between masses. This is an extremely esoteric field and way beyond the scope of this article.  
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In order to discuss Gravity and Quantum Field Theory in the same mathematical environment, gravitation is theorised to be facilitated by the exchange of virtual particles called ''gravitons'' between masses. This is an extremely esoteric field and way beyond the scope of this article.  
  
There should be waves of gravity created (analogous to bursts of electromagnetic energy) when massive events, such as the collapse of a star into a neutron star or [[black hole]], occur. There are several devices in place and uder construction on the surface of the Earth which rely on the compression or expansion of physical objects at angles to each other. These are normally kilometer-plus tubes whose lengths are constantly monitored by laser reflection/interfernce. The anticipated difference in these length is of the order of 10<sup>-10</sup> cm or less.  
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There should be waves of gravity created (analogous to bursts of electromagnetic energy) when massive events, such as the collapse of a star into a neutron star or [[black hole]], occur. In an attempt to detect or measure these, there are several devices in place and under construction on the surface of the Earth which rely on the compression or expansion of physical objects at angles to each other. These are normally kilometer-plus tubes whose lengths are constantly monitored by laser reflection/interfernce. The anticipated difference in these lengths is of the order of 10<sup>-10</sup> cm or less.  
  
Gravity is one of the basic forces of the [[Universe]] and (the gravitational constant) is believed to have remained the same since a vanishingly small time ([[Planck's constant|the Planck time]]) following the  [[Big Bang|big bang]]. As with the other forces any variation, however small, would result in a very different universe.
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Gravity is one of the basic forces of the [[Universe]] and (the gravitational constant) is believed to have remained the same since a vanishingly small time ([[Planck's constant|the Planck time]]) following the  [[Big Bang|big bang]]. As with the other forces, any variation, however small, would result in a very different universe.
  
The above has been extracted loosely from  [http://en.wikipedia.org/wiki/Gravitation Wikipedia's "Gravitation" article] which is a good start for a more in depth view of the subject.
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The above has been extracted loosely from  [http://en.wikipedia.org/wiki/Gravitation Wikipedia's "Gravitation" article] which is a good start for a more in-depth view of the subject.
 
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[[Category:science]][[Category:astronomy]][[Category:physics]]
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There is no such thing as '''gravity''' : the earth sucks!
 
There is no such thing as '''gravity''' : the earth sucks!
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==References and notes==
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<references/>
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[[Category:science]][[Category:astronomy]][[Category:physics]]

Revision as of 19:50, 17 January 2008

— Outline Only —
This article is only a brief description of the subject, and is not intended to give a full explanation.
Check out the "see also" or "references" sections, or Wikipedia's article for more detail.

Gravity, the opposite of Comedy, has been speculated about since at least 800 BCE, when in the Indian subcontinent it was identified as the effect of weight. Every school of philosophers since that time has had some explanation for gravity - some approaching or even equalling that of Sir Isaac Newton who in 1687 published Principia Mathematica, which laid down the inverse square law of attraction due to gravity.

Since his day, Newton's Law of Gravity has proven sufficiently accurate to enable the prediction of the location of the planet Neptune. In was the late 19th century, small irregularities in the orbit of the innermost planet, Mercury, could not be explained through Newtonian Gravity Theory, and it began to be questioned. Einstein's General Theory of Relativity solved the problem.

Everyone will be familiar with the visual and physical representation of Gravitation as described by the General Theory, i.e., a stretched elastic membrane deflected by the weight of objects placed on it. This is a difficult visualisation of the mathematical idea of curvature in spacetime, requiring that the four dimensions of spacetime be visualised as a two dimensional elastic sheet which is distorting in some other dimension. Once this mental leap has been performed it is easy to see how varying masses have varying effects on the curvature of spacetime,; the larger the mass, the greater the distortion and the further reaching its effect.[1] This is most often shown by placing a large, dense object (a bowling ball or cannonball) on the membrane and then rolling other balls past it at varying distances. As a thought experiment one can envisage fairly well the effects of the two objects on each other. The trouble with this demonstration is, of course, friction with the membrane.

In order to discuss Gravity and Quantum Field Theory in the same mathematical environment, gravitation is theorised to be facilitated by the exchange of virtual particles called gravitons between masses. This is an extremely esoteric field and way beyond the scope of this article.

There should be waves of gravity created (analogous to bursts of electromagnetic energy) when massive events, such as the collapse of a star into a neutron star or black hole, occur. In an attempt to detect or measure these, there are several devices in place and under construction on the surface of the Earth which rely on the compression or expansion of physical objects at angles to each other. These are normally kilometer-plus tubes whose lengths are constantly monitored by laser reflection/interfernce. The anticipated difference in these lengths is of the order of 10-10 cm or less.

Gravity is one of the basic forces of the Universe and (the gravitational constant) is believed to have remained the same since a vanishingly small time (the Planck time) following the big bang. As with the other forces, any variation, however small, would result in a very different universe.

The above has been extracted loosely from Wikipedia's "Gravitation" article which is a good start for a more in-depth view of the subject.

There is no such thing as gravity : the earth sucks!

References and notes

  1. Although technically gravity reaches from every object in the universe to every other, its effects due to very distant ones become much less noticeable.
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