

Subject:
General Relativity and gravity
Category: Science > Physics Asked by: milesjordanga List Price: $2.00 
Posted:
18 Apr 2006 05:58 PDT
Expires: 18 May 2006 05:58 PDT Question ID: 720133 
If Einstein explained in the General Theory of Relativity that gravitation is caused by the curvature of spacetime rather than the force of gravity then why do scientists still count gravity as one of the 4 fundamental forces of the universe? 

Subject:
Re: General Relativity and gravity
Answered By: hedgiega on 19 Apr 2006 00:01 PDT Rated: 
miles it is not 'either or' one RATHER THAN the other, as in as in "curvature of spacetime rather than the force of gravity" Einstein pioneered 'geometrisation of physics'  he has shown that abstract geometries http://www.maths.gla.ac.uk/~wws/cabripages/klein/klein0.html can be used as a language for physical theories. So, his General Theory of Relativity (GTR) is still a theory of gravity, and his theory of gravity is reduced to Newton's theory when v/c <<1. advanced links: " Geometry and modern cuttingedge Science More than two thousand years ago, Plato, with a leap of the imagination had remarked: "The Gods ever geometrize." Physicists have now given rigorous proof that Plato was indeed right. We have now reached a stage where Physics and Biology have both been geometrized. Through explaining gravity as curvature of spacetime Einstein's General Relativity initiated the geometrization of Physics. More recently the work of Professor Myron Evans has advanced this to a new and sublime height and the work of Paul Pinter has shown the connection between the geometrization of Physics and the evolution of intelligent life and hence geometrized biology. The American theoretical physicist John Archibald Wheeler,.." http://www.mumfordbooks.co.uk/CAT.asp?CatID=38 abstract geometries: http://en.wikipedia.org/wiki/NonEuclidean_geometry http://en.wikipedia.org/wiki/Riemannian_geometry 
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Subject:
Re: General Relativity and gravity
From: qed100ga on 18 Apr 2006 17:03 PDT 
When they refer to "The Forces", they mean rather generally "The Interactions". In modern theory, everything has been *reduced*, supposedly, to a manageably small menu of redundant objects & their modes of interaction. One such mode is gravitation between regions of space filled with momentumenergy, i.e., "mass". A region containing mass induces curvature locally. The curvature of one locality determines the curvature of adjacent localities, extending outward radially from the concentration of mass. Actually, there's energy, mass, in each infinitesimal locality, thus its curvature, and thus that tiny region interacts with the neighboring regions, endowing them with potential energy: their curvatures. As you appear to understand, general relativity models gravity rather differently from the other thoroughly quantum mechanical interactions. But nevertheless, gravity is (so far) an irreducible player in the big chess game called The Universe, and so it is one of the "forces". 
Subject:
Re: General Relativity and gravity
From: qed100ga on 19 Apr 2006 11:22 PDT 
It should be noted that GR is effectively equivalent to Newton's law not just when v ~ 0. It's also necessary for the local curvature to be ~ 0, and, just as importantly, for the radius between gravitating objects to be ~ 0. The reason for the distance condition is that, in Newton's theory, there's a tacit assumption of interaction across arbitrarily large distance with zero delay time ("instantaneous action at a distance"). GR, on the other hand, is characteristically local in all interactions, there is no gravitational interaction between Earth & the Moon; there is only motion determined by curvature exactly where either body happens to be and disturbances in the field propagate at a finite speed. For Einstein's & Newton's laws to tend to generate precisely the same numbers out to the nth decimal place, they must deal with homogenous, empty space. 
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